[{"Name":"Cell Reproduction","TopicPlaylistFirstVideoID":0,"Duration":null,"Videos":[{"Watched":false,"Name":"Cell Reproduction","Duration":"2m 4s","ChapterTopicVideoID":25493,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":"https://www.proprep.uk/Images/Videos_Thumbnails/25493.jpeg","UploadDate":"2021-05-09T12:31:07.2930000","DurationForVideoObject":"PT2M4S","Description":null,"MetaTitle":"Cell Reproduction: Video + Workbook | Proprep","MetaDescription":"Cell Biology and Genetics - Cell Reproduction. Watch the video made by an expert in the field. Download the workbook and maximize your learning.","Canonical":"https://www.proprep.uk/general-modules/all/introduction-to-biology/cell-biology-and-genetics/cell-reproduction/vid26310","VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:06.795","Text":"Hi there. Welcome to this part of the course that deals with cell reproduction,"},{"Start":"00:06.795 ","End":"00:09.660","Text":"gene expression and genetics."},{"Start":"00:09.660 ","End":"00:14.055","Text":"We\u0027re going to start out by looking at cell reproduction."},{"Start":"00:14.055 ","End":"00:16.425","Text":"In this first little video,"},{"Start":"00:16.425 ","End":"00:22.365","Text":"we\u0027ll give it a little bit of an overview and see really what cell reproduction is for."},{"Start":"00:22.365 ","End":"00:28.910","Text":"First of all, you all know that the organisms that you\u0027re most familiar with,"},{"Start":"00:28.910 ","End":"00:30.200","Text":"that is us,"},{"Start":"00:30.200 ","End":"00:35.810","Text":"we reproduce sexually by having a male that produces a sperm,"},{"Start":"00:35.810 ","End":"00:37.885","Text":"a female that produces an egg,"},{"Start":"00:37.885 ","End":"00:40.175","Text":"and then they are fertilized,"},{"Start":"00:40.175 ","End":"00:46.390","Text":"and they then fuse into something called a zygote."},{"Start":"00:46.390 ","End":"00:48.500","Text":"We\u0027ll come back to that a lot later."},{"Start":"00:48.500 ","End":"00:53.435","Text":"The zygote is the ancestor cell of all cells in the body."},{"Start":"00:53.435 ","End":"00:57.170","Text":"That single cell then divides via a process called"},{"Start":"00:57.170 ","End":"01:02.295","Text":"mitosis into many cells, which then differentiate."},{"Start":"01:02.295 ","End":"01:09.290","Text":"They change their cell type into a whole organism right into the offspring."},{"Start":"01:09.290 ","End":"01:14.110","Text":"Actually, that differentiation occurs not only in the baby,"},{"Start":"01:14.110 ","End":"01:17.600","Text":"but it can occur later as well."},{"Start":"01:17.600 ","End":"01:22.805","Text":"All multicellular organisms use cell division for both growth"},{"Start":"01:22.805 ","End":"01:28.340","Text":"and the maintenance and repair of cells and tissues and of course,"},{"Start":"01:28.340 ","End":"01:29.990","Text":"in order for this to happen,"},{"Start":"01:29.990 ","End":"01:34.280","Text":"cell division must be very closely regulated."},{"Start":"01:34.280 ","End":"01:40.370","Text":"Regulation is going to be a cardinal point in the videos to come."},{"Start":"01:40.370 ","End":"01:45.650","Text":"But this is not good only for multicellular organisms."},{"Start":"01:45.650 ","End":"01:50.675","Text":"It\u0027s also good for single-celled organisms because single-celled organisms"},{"Start":"01:50.675 ","End":"01:57.220","Text":"use the same kind of cell division as their major method of reproduction."},{"Start":"01:57.220 ","End":"02:03.900","Text":"Single-celled organisms use cell division as their method of reproduction."}],"ID":26310},{"Watched":false,"Name":"Cell Division Part a","Duration":"6m 15s","ChapterTopicVideoID":25491,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.140 ","End":"00:04.530","Text":"Welcome back. Now that we\u0027ve had a little bit of"},{"Start":"00:04.530 ","End":"00:08.265","Text":"an introduction into what cell division is for,"},{"Start":"00:08.265 ","End":"00:13.650","Text":"let\u0027s look at it in much greater detail in different kinds of organisms."},{"Start":"00:13.650 ","End":"00:15.090","Text":"By the end of this section,"},{"Start":"00:15.090 ","End":"00:20.340","Text":"you should be able to describe the structure of prokaryotic that is"},{"Start":"00:20.340 ","End":"00:27.029","Text":"usually single cells that have no nucleus and eukaryotic genomes,"},{"Start":"00:27.029 ","End":"00:32.835","Text":"those are cells that have a nucleus and very often they will be multicellular,"},{"Start":"00:32.835 ","End":"00:34.170","Text":"although they don\u0027t have to be."},{"Start":"00:34.170 ","End":"00:38.645","Text":"You\u0027ll be able to describe the structure of prokaryotic and eukaryotic genomes."},{"Start":"00:38.645 ","End":"00:41.345","Text":"You should be able to distinguish between chromosomes,"},{"Start":"00:41.345 ","End":"00:42.970","Text":"genes, and traits,"},{"Start":"00:42.970 ","End":"00:48.110","Text":"and you should be able to describe the mechanisms of chromosome compaction."},{"Start":"00:48.110 ","End":"00:50.780","Text":"Because after all will see the DNA is very long,"},{"Start":"00:50.780 ","End":"00:54.265","Text":"but yet it\u0027s compacted into a small space."},{"Start":"00:54.265 ","End":"00:58.070","Text":"Let\u0027s start out looking at prokaryotes."},{"Start":"00:58.070 ","End":"01:00.920","Text":"Those are things like bacteria, for instance,"},{"Start":"01:00.920 ","End":"01:04.940","Text":"that have no nucleus in them and they serve as"},{"Start":"01:04.940 ","End":"01:09.970","Text":"very good examples for cell division at a basic level."},{"Start":"01:09.970 ","End":"01:12.940","Text":"We\u0027re looking at the reproduction of cells or cell division."},{"Start":"01:12.940 ","End":"01:16.970","Text":"We know that that is a key factor for continuity of life because after all,"},{"Start":"01:16.970 ","End":"01:18.290","Text":"when a cell divides,"},{"Start":"01:18.290 ","End":"01:24.080","Text":"then each cell has to have the characteristics of the parents."},{"Start":"01:24.080 ","End":"01:26.830","Text":"In order to get to cell division,"},{"Start":"01:26.830 ","End":"01:30.320","Text":"there has to be something called a cell cycle."},{"Start":"01:30.320 ","End":"01:33.875","Text":"There is a sequence of events that happens inside"},{"Start":"01:33.875 ","End":"01:38.120","Text":"the cell that describes the stages of a cell\u0027s life."},{"Start":"01:38.120 ","End":"01:42.395","Text":"We\u0027ll come back to that in much greater detail later."},{"Start":"01:42.395 ","End":"01:45.440","Text":"We talked about the genome."},{"Start":"01:45.440 ","End":"01:51.160","Text":"The genome is all the genetic material that\u0027s inside the cell."},{"Start":"01:51.160 ","End":"01:57.680","Text":"The genome is the cell\u0027s DNA and it\u0027s packed as a double-stranded molecule."},{"Start":"01:57.680 ","End":"02:04.124","Text":"In prokaryotes, that\u0027s the non-nucleated cells like bacteria,"},{"Start":"02:04.124 ","End":"02:10.580","Text":"a single looped or a circular double-stranded DNA is what we\u0027ll find in those cells."},{"Start":"02:10.580 ","End":"02:13.340","Text":"That is, the DNA is a circle."},{"Start":"02:13.340 ","End":"02:16.490","Text":"It\u0027s double-stranded, but it\u0027s connected at the ends."},{"Start":"02:16.490 ","End":"02:18.395","Text":"There really are no ends,"},{"Start":"02:18.395 ","End":"02:23.060","Text":"and the DNA is localized in an area called the nucleoid."},{"Start":"02:23.060 ","End":"02:25.410","Text":"It\u0027s not spread evenly all over the cell,"},{"Start":"02:25.410 ","End":"02:29.439","Text":"it\u0027s found in a particular region called the nucleoid."},{"Start":"02:29.439 ","End":"02:35.105","Text":"Some prokaryotes have additional pieces of DNA called plasmids."},{"Start":"02:35.105 ","End":"02:38.540","Text":"They are not essential for normal growth,"},{"Start":"02:38.540 ","End":"02:41.270","Text":"but they may contain within them genes that helps"},{"Start":"02:41.270 ","End":"02:44.225","Text":"the prokaryotes or help the bacteria grow."},{"Start":"02:44.225 ","End":"02:50.270","Text":"For instance, they may encode on their DNA resistance to antibiotics."},{"Start":"02:50.270 ","End":"02:52.640","Text":"That\u0027s just an example."},{"Start":"02:52.640 ","End":"02:55.100","Text":"In eukaryotes on the other hand,"},{"Start":"02:55.100 ","End":"02:58.055","Text":"remember we have a nucleus and in"},{"Start":"02:58.055 ","End":"03:03.335","Text":"those cells we have several double-stranded linear DNA molecules."},{"Start":"03:03.335 ","End":"03:06.020","Text":"In other words, not just 1 like we had in a prokaryote,"},{"Start":"03:06.020 ","End":"03:07.595","Text":"but we have several."},{"Start":"03:07.595 ","End":"03:10.580","Text":"The other difference is that they are linear."},{"Start":"03:10.580 ","End":"03:13.685","Text":"There are ends to the DNA."},{"Start":"03:13.685 ","End":"03:19.715","Text":"Each species has a characteristic number of these DNA molecules."},{"Start":"03:19.715 ","End":"03:24.125","Text":"Each DNA molecule is on 1 chromosome,"},{"Start":"03:24.125 ","End":"03:31.555","Text":"so each species has a characteristic number of chromosomes in the nuclei of its cells."},{"Start":"03:31.555 ","End":"03:36.575","Text":"Now there are 2 different cells that will find in many eukaryotes,"},{"Start":"03:36.575 ","End":"03:41.980","Text":"especially in multicellular organisms, but not only."},{"Start":"03:41.980 ","End":"03:46.570","Text":"There are somatic cells which are deployed."},{"Start":"03:46.570 ","End":"03:52.275","Text":"That means they\u0027ve got 2 copies of each chromosome and we\u0027ll see that in a minute,"},{"Start":"03:52.275 ","End":"03:54.620","Text":"and there are gametes."},{"Start":"03:54.620 ","End":"04:01.575","Text":"Gametes are either sperm or eggs in higher organisms."},{"Start":"04:01.575 ","End":"04:06.785","Text":"We have similar things in plants like pollen and the male,"},{"Start":"04:06.785 ","End":"04:11.040","Text":"like sperm and the eggs also in plants."},{"Start":"04:11.040 ","End":"04:13.430","Text":"Those are the sex cells and they are haploid."},{"Start":"04:13.430 ","End":"04:19.789","Text":"They have only one copy of each chromosome and they\u0027re denoted"},{"Start":"04:19.789 ","End":"04:26.435","Text":"as being n or 1n whereas somatic cells are 2n."},{"Start":"04:26.435 ","End":"04:31.715","Text":"I mean, they\u0027ve got 2 copies and we\u0027ll see that where do these copies come from?"},{"Start":"04:31.715 ","End":"04:37.160","Text":"Each chromosome of the homologous pair comes from a different parents."},{"Start":"04:37.160 ","End":"04:42.380","Text":"One will be a paternal copy and 1 will be a maternal copy."},{"Start":"04:42.380 ","End":"04:48.440","Text":"Each pair of these chromosomes,"},{"Start":"04:48.440 ","End":"04:51.890","Text":"we can say have homologous chromosomes within them."},{"Start":"04:51.890 ","End":"04:54.245","Text":"They\u0027re not identical to each other."},{"Start":"04:54.245 ","End":"05:00.635","Text":"They have the same length and they have the same genes in the same location on them."},{"Start":"05:00.635 ","End":"05:06.185","Text":"Each of these little stripes here is meant to denote a gene that will encode a protein."},{"Start":"05:06.185 ","End":"05:10.295","Text":"But they\u0027re not identical sequence, they\u0027re quite similar,"},{"Start":"05:10.295 ","End":"05:13.850","Text":"but not identical of the homologous chromosomes,"},{"Start":"05:13.850 ","End":"05:18.540","Text":"again, that we got each one of them from a different parent."},{"Start":"05:18.540 ","End":"05:21.890","Text":"The genes that are on them then we\u0027ll determine"},{"Start":"05:21.890 ","End":"05:25.420","Text":"the specific characteristics of the organism and how did they do that,"},{"Start":"05:25.420 ","End":"05:30.245","Text":"they do it because each gene encodes a protein."},{"Start":"05:30.245 ","End":"05:34.175","Text":"Actually, we\u0027ll see later that there are some genes that encode other things too."},{"Start":"05:34.175 ","End":"05:40.485","Text":"But the majority of the genes encode specific proteins."},{"Start":"05:40.485 ","End":"05:42.650","Text":"Then it\u0027s these proteins,"},{"Start":"05:42.650 ","End":"05:44.480","Text":"the specific proteins that are made in"},{"Start":"05:44.480 ","End":"05:47.420","Text":"the specific amounts that each of them that are made,"},{"Start":"05:47.420 ","End":"05:52.605","Text":"that will then determine the traits of the organisms,"},{"Start":"05:52.605 ","End":"05:55.830","Text":"and of course the traits can be a little bit different."},{"Start":"05:55.830 ","End":"05:58.845","Text":"Those are the variations of those characteristics."},{"Start":"05:58.845 ","End":"06:00.455","Text":"We could say, for instance,"},{"Start":"06:00.455 ","End":"06:05.250","Text":"that there are people with lighter skin and darker skin."},{"Start":"06:05.250 ","End":"06:08.390","Text":"They\u0027ve all got color in their skin,"},{"Start":"06:08.390 ","End":"06:11.210","Text":"but some have a little bit more and some have a little bit less,"},{"Start":"06:11.210 ","End":"06:15.270","Text":"and that is a difference in traits."}],"ID":26308},{"Watched":false,"Name":"Cell Division Part b","Duration":"9m 20s","ChapterTopicVideoID":25492,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:01.130 ","End":"00:06.089","Text":"Let\u0027s look a little bit more closely now at the differences"},{"Start":"00:06.089 ","End":"00:10.395","Text":"in the DNA that might encode these different traits."},{"Start":"00:10.395 ","End":"00:14.610","Text":"The variation of individuals within a species is due to"},{"Start":"00:14.610 ","End":"00:19.905","Text":"the specific combination of the genes that are inherited from both parents,"},{"Start":"00:19.905 ","End":"00:23.595","Text":"so here we might have a homologous set of chromosomes,"},{"Start":"00:23.595 ","End":"00:27.480","Text":"and if we\u0027re looking at flowers now or at plants in this case,"},{"Start":"00:27.480 ","End":"00:32.220","Text":"there may be a particular locus at which there is"},{"Start":"00:32.220 ","End":"00:36.090","Text":"a particular gene that"},{"Start":"00:36.090 ","End":"00:42.300","Text":"encodes for a protein that will be able to make flowers of that plant purple."},{"Start":"00:42.300 ","End":"00:47.210","Text":"Whereas at the same locus there could be some variation in that gene and"},{"Start":"00:47.210 ","End":"00:52.190","Text":"the flowers of that plant will be white, so again,"},{"Start":"00:52.190 ","End":"00:59.240","Text":"this is a gene at this particular place and that\u0027s the same place,"},{"Start":"00:59.240 ","End":"01:03.060","Text":"same locus of this homologous pair of chromosomes,"},{"Start":"01:03.060 ","End":"01:07.005","Text":"and there can be variations in the genes."},{"Start":"01:07.005 ","End":"01:10.755","Text":"Of course, even small changes in the DNA,"},{"Start":"01:10.755 ","End":"01:13.085","Text":"can result in alternative traits,"},{"Start":"01:13.085 ","End":"01:15.620","Text":"even a single point mutation,"},{"Start":"01:15.620 ","End":"01:18.995","Text":"a single difference in 1 nucleotide,"},{"Start":"01:18.995 ","End":"01:20.285","Text":"as we\u0027ll see later,"},{"Start":"01:20.285 ","End":"01:23.120","Text":"can make an alternative traits."},{"Start":"01:23.120 ","End":"01:27.590","Text":"Now within the species these variations tend to be rather minor."},{"Start":"01:27.590 ","End":"01:32.510","Text":"You don\u0027t have the different genes in different places and you don\u0027t have"},{"Start":"01:32.510 ","End":"01:34.910","Text":"genes that are turned around in different directions or"},{"Start":"01:34.910 ","End":"01:37.850","Text":"have insertions or deletions or things like that."},{"Start":"01:37.850 ","End":"01:38.960","Text":"They tend to be rather minor,"},{"Start":"01:38.960 ","End":"01:43.805","Text":"but there are these differences and that\u0027s what makes us all so interesting."},{"Start":"01:43.805 ","End":"01:48.485","Text":"Now, let\u0027s look at the DNA variation"},{"Start":"01:48.485 ","End":"01:53.720","Text":"that we may find between different homologous chromosomes."},{"Start":"01:53.720 ","End":"01:57.925","Text":"These differences that we find here,"},{"Start":"01:57.925 ","End":"02:04.810","Text":"maybe on genes actually that don\u0027t necessarily express themselves as,"},{"Start":"02:04.810 ","End":"02:05.890","Text":"let\u0027s say, a color,"},{"Start":"02:05.890 ","End":"02:09.280","Text":"but rather they may even regulate the expression of"},{"Start":"02:09.280 ","End":"02:14.060","Text":"other genes such that there are other traits that are formed,"},{"Start":"02:14.060 ","End":"02:22.075","Text":"so it could be a fairly complex situation even when there are small differences,"},{"Start":"02:22.075 ","End":"02:26.320","Text":"small single nucleotide polymorphisms"},{"Start":"02:26.320 ","End":"02:31.675","Text":"or SNPs between the different genes inside different individuals."},{"Start":"02:31.675 ","End":"02:38.385","Text":"Interestingly, the DNA differences between humans is less than 1 percent,"},{"Start":"02:38.385 ","End":"02:41.620","Text":"so we\u0027re all 99 percent the same."},{"Start":"02:41.620 ","End":"02:46.550","Text":"But it\u0027s the 1 percent really that makes us interesting, and furthermore,"},{"Start":"02:46.550 ","End":"02:50.690","Text":"were only 4 percent different than chimpanzees,"},{"Start":"02:50.690 ","End":"02:52.340","Text":"so we\u0027re quite similar,"},{"Start":"02:52.340 ","End":"02:56.255","Text":"but those small differences certainly do make a difference."},{"Start":"02:56.255 ","End":"02:58.915","Text":"Now, remember we talked about"},{"Start":"02:58.915 ","End":"03:05.270","Text":"the homologous chromosomes where we get 1 from each parent and we said they\u0027re the same."},{"Start":"03:05.270 ","End":"03:08.525","Text":"Well, that\u0027s true in almost all cases."},{"Start":"03:08.525 ","End":"03:10.639","Text":"There are the sex chromosomes,"},{"Start":"03:10.639 ","End":"03:13.205","Text":"there are the X and Y chromosomes,"},{"Start":"03:13.205 ","End":"03:17.870","Text":"which do not obey the rule of homologous chromosome uniformity,"},{"Start":"03:17.870 ","End":"03:21.800","Text":"so there\u0027s quite a difference actually between an X and"},{"Start":"03:21.800 ","End":"03:28.950","Text":"a Y chromosome and they are not homologous and they carry different genes."},{"Start":"03:29.050 ","End":"03:36.840","Text":"Well, the DNA actually is extremely, extremely long."},{"Start":"03:36.840 ","End":"03:38.430","Text":"Very long, in fact,"},{"Start":"03:38.430 ","End":"03:44.030","Text":"the length of the DNA in 1 cell of a human,"},{"Start":"03:44.030 ","End":"03:45.650","Text":"if you were to extend it all,"},{"Start":"03:45.650 ","End":"03:48.510","Text":"would be about 2 meters long,"},{"Start":"03:48.510 ","End":"03:54.275","Text":"2 meters long, and its diameter though is only about 2 nanometers."},{"Start":"03:54.275 ","End":"03:58.325","Text":"Nano means 10^minus 9 meters,"},{"Start":"03:58.325 ","End":"04:02.995","Text":"so it\u0027s extremely thin, but extremely long."},{"Start":"04:02.995 ","End":"04:09.530","Text":"How does that 2 meters worth of DNA get packed into a cell?"},{"Start":"04:09.530 ","End":"04:12.905","Text":"Well, that\u0027s something that we\u0027ll look at momentarily."},{"Start":"04:12.905 ","End":"04:17.990","Text":"In fact, just to give a feel for how long while that DNA is, in 1 cell,"},{"Start":"04:17.990 ","End":"04:20.330","Text":"we said it\u0027s about 2 meters and depending"},{"Start":"04:20.330 ","End":"04:23.420","Text":"upon how many cells you\u0027ve gotten your body at the moment,"},{"Start":"04:23.420 ","End":"04:27.890","Text":"it could be that you\u0027re a little human like a baby or a big human like an adult,"},{"Start":"04:27.890 ","End":"04:29.660","Text":"so there can be some differences."},{"Start":"04:29.660 ","End":"04:31.280","Text":"But just to give you a feel,"},{"Start":"04:31.280 ","End":"04:35.185","Text":"if all the DNA in your body were stretched out to the end,"},{"Start":"04:35.185 ","End":"04:41.465","Text":"it would stretch back to the moon and back again about 1,500 times,"},{"Start":"04:41.465 ","End":"04:46.930","Text":"so that\u0027s an extraordinary length of DNA and it\u0027s all packed very,"},{"Start":"04:46.930 ","End":"04:50.015","Text":"very tightly inside ourselves."},{"Start":"04:50.015 ","End":"04:52.550","Text":"It\u0027s got to be packaged very,"},{"Start":"04:52.550 ","End":"04:54.710","Text":"very tightly inside the cell nucleus,"},{"Start":"04:54.710 ","End":"04:56.705","Text":"but at the same time,"},{"Start":"04:56.705 ","End":"05:01.294","Text":"it\u0027s got to be readily accessible so that the genes can be expressed."},{"Start":"05:01.294 ","End":"05:06.410","Text":"If a particular gene needs to be expressed and made protein from it,"},{"Start":"05:06.410 ","End":"05:10.040","Text":"it has to be accessible to some huge machinery."},{"Start":"05:10.040 ","End":"05:12.915","Text":"The same thing goes for replication."},{"Start":"05:12.915 ","End":"05:19.250","Text":"When the DNA is replicated before a cell divides,"},{"Start":"05:19.250 ","End":"05:22.580","Text":"then again, there\u0027s this enormous machinery that has to"},{"Start":"05:22.580 ","End":"05:26.455","Text":"reach every little piece of DNA in the cell."},{"Start":"05:26.455 ","End":"05:29.405","Text":"For this reason the DNA is condensed,"},{"Start":"05:29.405 ","End":"05:33.485","Text":"extremely condensed during certain stages of the cell cycle,"},{"Start":"05:33.485 ","End":"05:41.270","Text":"but is then spread out at least to some extent during other stages of the cell cycle."},{"Start":"05:41.270 ","End":"05:45.005","Text":"Let\u0027s look a little bit how this condensation works."},{"Start":"05:45.005 ","End":"05:49.390","Text":"It turns out that there are several different levels of condensation."},{"Start":"05:49.390 ","End":"05:53.450","Text":"At the first most basic level of condensation,"},{"Start":"05:53.450 ","End":"05:56.780","Text":"the DNA, that\u0027s the blue in this figure,"},{"Start":"05:56.780 ","End":"06:03.840","Text":"wraps around a core of proteins that are called histone proteins,"},{"Start":"06:03.840 ","End":"06:08.035","Text":"and at a relatively regular interval."},{"Start":"06:08.035 ","End":"06:10.820","Text":"We talk about the core DNA,"},{"Start":"06:10.820 ","End":"06:12.920","Text":"that\u0027s the DNA that wraps around these histones,"},{"Start":"06:12.920 ","End":"06:16.040","Text":"and it\u0027s about 146 base pairs."},{"Start":"06:16.040 ","End":"06:18.660","Text":"Then there is a linker DNA."},{"Start":"06:18.660 ","End":"06:22.460","Text":"There\u0027s a linker that\u0027s between 2 different nucleosomes and it can vary,"},{"Start":"06:22.460 ","End":"06:24.710","Text":"let\u0027s say between 20 and 60 base pairs,"},{"Start":"06:24.710 ","End":"06:28.715","Text":"just to give you a feel for what that length might be."},{"Start":"06:28.715 ","End":"06:35.710","Text":"This complex of histones is called a nucleosome,"},{"Start":"06:35.710 ","End":"06:41.675","Text":"and it\u0027s a complex of both DNA and histone protein."},{"Start":"06:41.675 ","End":"06:46.685","Text":"Between the nucleosomes is the linker DNA as we mentioned before."},{"Start":"06:46.685 ","End":"06:53.045","Text":"The condensed DNA molecule is about 7 times shorter than without the histones,"},{"Start":"06:53.045 ","End":"06:56.690","Text":"so the degree of compaction that we\u0027ve achieved"},{"Start":"06:56.690 ","End":"07:02.180","Text":"with nucleosomes is only about a factor of 7."},{"Start":"07:02.180 ","End":"07:04.280","Text":"To look now at the dimensions,"},{"Start":"07:04.280 ","End":"07:06.935","Text":"the beads are about 10 nanometers in diameter."},{"Start":"07:06.935 ","End":"07:11.930","Text":"Remember the DNA is about 2 nanometers in diameter."},{"Start":"07:11.930 ","End":"07:15.950","Text":"Now we have an additional level of condensation,"},{"Start":"07:15.950 ","End":"07:21.110","Text":"so here are the nucleosomes right after they\u0027d have packed the DNA."},{"Start":"07:21.110 ","End":"07:22.985","Text":"Here\u0027s the double-stranded DNA,"},{"Start":"07:22.985 ","End":"07:29.900","Text":"and it will compact into something called the 30-nanometer chromatin fiber."},{"Start":"07:29.900 ","End":"07:32.630","Text":"This is something we can see in electron microscopes"},{"Start":"07:32.630 ","End":"07:35.450","Text":"and there\u0027s good evidence that something like this happens here."},{"Start":"07:35.450 ","End":"07:43.775","Text":"You can see that the nucleosomes are packaged in such a way that they make like a wheel,"},{"Start":"07:43.775 ","End":"07:49.445","Text":"some kind of a spiral actually that goes into a chromatin fiber,"},{"Start":"07:49.445 ","End":"07:52.025","Text":"then going to be compacted further."},{"Start":"07:52.025 ","End":"07:57.390","Text":"This condensation of the 30-nanometre fiber condenses the chromosome"},{"Start":"07:57.390 ","End":"08:03.270","Text":"about 50 fold shorter than the extended form."},{"Start":"08:03.270 ","End":"08:09.270","Text":"We had 7 and now we\u0027ve got about another 7 fold compaction,"},{"Start":"08:09.270 ","End":"08:11.870","Text":"so we\u0027re about at 50 fold shorter,"},{"Start":"08:11.870 ","End":"08:13.640","Text":"but that\u0027s not enough."},{"Start":"08:13.640 ","End":"08:16.520","Text":"We\u0027ve got another level of condensation,"},{"Start":"08:16.520 ","End":"08:19.010","Text":"a third level of condensation that"},{"Start":"08:19.010 ","End":"08:24.650","Text":"these fibers will condense further in a way that we don\u0027t understand very"},{"Start":"08:24.650 ","End":"08:28.550","Text":"well into a chromosome"},{"Start":"08:28.550 ","End":"08:33.235","Text":"which is so condensed that you can see it\u0027s in a light microscope,"},{"Start":"08:33.235 ","End":"08:37.080","Text":"and this condensation ensures that a chromosome will not"},{"Start":"08:37.080 ","End":"08:41.540","Text":"overlap with another chromosome because if the DNA is very extended,"},{"Start":"08:41.540 ","End":"08:43.190","Text":"it\u0027ll get all tangled up."},{"Start":"08:43.190 ","End":"08:48.305","Text":"But at certain stages of the cell cycle, as we\u0027ll see,"},{"Start":"08:48.305 ","End":"08:51.950","Text":"the DNA should not get tangled with other DNA and"},{"Start":"08:51.950 ","End":"08:56.575","Text":"this additional form of condensation and ensures that."},{"Start":"08:56.575 ","End":"09:01.040","Text":"In this video, we have learned to describe"},{"Start":"09:01.040 ","End":"09:05.255","Text":"the structure of prokaryotic and eukaryotic genomes."},{"Start":"09:05.255 ","End":"09:09.500","Text":"We\u0027ve now been able to distinguish between chromosomes,"},{"Start":"09:09.500 ","End":"09:10.940","Text":"genes and traits,"},{"Start":"09:10.940 ","End":"09:14.480","Text":"and we have described the mechanisms or"},{"Start":"09:14.480 ","End":"09:19.860","Text":"some very basic mechanisms at least of chromosome compaction."}],"ID":26309},{"Watched":false,"Name":"The Cell Cycle","Duration":"17m 12s","ChapterTopicVideoID":25498,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.140 ","End":"00:03.435","Text":"Hi, I\u0027m glad you\u0027re back."},{"Start":"00:03.435 ","End":"00:05.060","Text":"In the previous videos,"},{"Start":"00:05.060 ","End":"00:08.835","Text":"we talked a little bit about what happens when cells divide,"},{"Start":"00:08.835 ","End":"00:13.680","Text":"and I alluded to the cell cycle but didn\u0027t really explain it."},{"Start":"00:13.680 ","End":"00:15.720","Text":"Remember in the cell cycle,"},{"Start":"00:15.720 ","End":"00:17.610","Text":"I said that things, for instance,"},{"Start":"00:17.610 ","End":"00:21.195","Text":"have to occur such that the chromosomes don\u0027t get tangled with each other."},{"Start":"00:21.195 ","End":"00:23.850","Text":"Well, let\u0027s try to understand exactly what"},{"Start":"00:23.850 ","End":"00:28.140","Text":"happens during the period between the times that"},{"Start":"00:28.140 ","End":"00:35.040","Text":"the cell actually divides and see if we can understand better how the DNA is replicated,"},{"Start":"00:35.040 ","End":"00:38.730","Text":"and then how the cell actually divides."},{"Start":"00:38.730 ","End":"00:40.340","Text":"By the end of this section,"},{"Start":"00:40.340 ","End":"00:45.625","Text":"you should be able to describe the 3 stages of interphase,"},{"Start":"00:45.625 ","End":"00:51.355","Text":"those are the things that happen between the times that the cell divides,"},{"Start":"00:51.355 ","End":"00:57.710","Text":"and you should be able to discuss the behavior of the chromosomes during karyokinesis,"},{"Start":"00:57.710 ","End":"01:00.730","Text":"and you\u0027ll find out what that is, and mitosis."},{"Start":"01:00.730 ","End":"01:06.140","Text":"You\u0027ll be able to explain how the cytoplasmic content is divided during cytokinesis,"},{"Start":"01:06.140 ","End":"01:10.790","Text":"and you\u0027ll be able to define the quiescent G_0 phase."},{"Start":"01:10.790 ","End":"01:20.245","Text":"We\u0027ll see what that is. We know that when a cell divides we get 2 cells,"},{"Start":"01:20.245 ","End":"01:24.225","Text":"4 cells, 8 cells, 16 cells."},{"Start":"01:24.225 ","End":"01:25.380","Text":"There is cell division."},{"Start":"01:25.380 ","End":"01:27.605","Text":"Now, notice in this picture,"},{"Start":"01:27.605 ","End":"01:29.540","Text":"we started with a particular volume,"},{"Start":"01:29.540 ","End":"01:35.203","Text":"the cells divided, but they also became smaller,"},{"Start":"01:35.203 ","End":"01:37.295","Text":"each of them became smaller."},{"Start":"01:37.295 ","End":"01:42.395","Text":"The other thing that can happen during the cell cycle is there can be cell growth,"},{"Start":"01:42.395 ","End":"01:47.590","Text":"that is each cell can add volume to itself."},{"Start":"01:47.590 ","End":"01:52.850","Text":"There\u0027s a difference between cell division and cell growth."},{"Start":"01:52.850 ","End":"01:55.996","Text":"In cell proliferation,"},{"Start":"01:55.996 ","End":"02:00.800","Text":"really what we want in order for the cells to maintain identical copies of themselves,"},{"Start":"02:00.800 ","End":"02:04.675","Text":"they have to both divide and grow."},{"Start":"02:04.675 ","End":"02:07.170","Text":"We\u0027ve got cell growth and division,"},{"Start":"02:07.170 ","End":"02:10.185","Text":"and we\u0027ll see now how that happens."},{"Start":"02:10.185 ","End":"02:14.325","Text":"When 2 daughter cells are produced, that\u0027s what they\u0027re called."},{"Start":"02:14.325 ","End":"02:15.600","Text":"When a cell divides,"},{"Start":"02:15.600 ","End":"02:19.690","Text":"we\u0027ve got both growth and division."},{"Start":"02:19.700 ","End":"02:26.205","Text":"During 1 division cycle or 1 cell cycle,"},{"Start":"02:26.205 ","End":"02:28.720","Text":"there is something called interphase,"},{"Start":"02:28.720 ","End":"02:30.815","Text":"that\u0027s most of the time."},{"Start":"02:30.815 ","End":"02:35.780","Text":"What we\u0027re doing here is we\u0027re making a graphic representation of what\u0027s"},{"Start":"02:35.780 ","End":"02:41.060","Text":"happening inside the cell during 1 cycle."},{"Start":"02:41.060 ","End":"02:43.250","Text":"We can divide that cycle,"},{"Start":"02:43.250 ","End":"02:47.940","Text":"it turns out into 4 different major phases."},{"Start":"02:47.940 ","End":"02:54.590","Text":"We\u0027ll see that those 4 phases are defined primarily by this S phase,"},{"Start":"02:54.590 ","End":"02:56.546","Text":"that\u0027s the synthesis phase,"},{"Start":"02:56.546 ","End":"02:58.940","Text":"when the DNA is synthesized."},{"Start":"02:58.940 ","End":"03:02.930","Text":"Something happens before and something happens after,"},{"Start":"03:02.930 ","End":"03:10.315","Text":"and before the cells actually divide in the mitotic phase, the M phase."},{"Start":"03:10.315 ","End":"03:16.655","Text":"Moving into the mitotic phase demands unique internal and external conditions."},{"Start":"03:16.655 ","End":"03:19.880","Text":"For instance, we have to have cell growth"},{"Start":"03:19.880 ","End":"03:23.930","Text":"and there are various conditions that will apply,"},{"Start":"03:23.930 ","End":"03:30.440","Text":"also the chromosomes have to be untangled and other things of that sort."},{"Start":"03:30.440 ","End":"03:33.935","Text":"Then of course, we\u0027ve got this mitotic phase in which the cells actually"},{"Start":"03:33.935 ","End":"03:38.040","Text":"divide into 2 separate cells,"},{"Start":"03:38.040 ","End":"03:41.555","Text":"and that will be called cytokinesis."},{"Start":"03:41.555 ","End":"03:44.450","Text":"Cyto means cells, kinesis means movement."},{"Start":"03:44.450 ","End":"03:48.920","Text":"The cells will actually move apart one from the other."},{"Start":"03:48.920 ","End":"03:53.460","Text":"There\u0027ll be the nuclei in eukaryotic cells will divide into 2,"},{"Start":"03:53.460 ","End":"03:59.335","Text":"there\u0027s actually movement at this point of the cells one from the other."},{"Start":"03:59.335 ","End":"04:02.590","Text":"Let\u0027s look at this in more detail."},{"Start":"04:03.860 ","End":"04:08.150","Text":"Most of the cell cycle that we\u0027re talking about,"},{"Start":"04:08.150 ","End":"04:10.940","Text":"we said can be divided into 3 phases."},{"Start":"04:10.940 ","End":"04:17.360","Text":"The first phase after the cell divides is called G_1 or first gap,"},{"Start":"04:17.360 ","End":"04:19.580","Text":"but usually it\u0027s just called G_1."},{"Start":"04:19.580 ","End":"04:21.980","Text":"Then we have the DNA synthesis phase,"},{"Start":"04:21.980 ","End":"04:25.745","Text":"the S phase, and then the G_2 phase."},{"Start":"04:25.745 ","End":"04:29.540","Text":"Let\u0027s look more closely now at the G_1 phase."},{"Start":"04:29.540 ","End":"04:34.855","Text":"It\u0027s very hard to see much going on in a light microscope in this case,"},{"Start":"04:34.855 ","End":"04:39.170","Text":"but what\u0027s happening is that there is accumulation of DNA building blocks,"},{"Start":"04:39.170 ","End":"04:41.350","Text":"all sorts of other building blocks in the cell,"},{"Start":"04:41.350 ","End":"04:45.500","Text":"that are associated with proteins and energy reserves."},{"Start":"04:45.500 ","End":"04:48.160","Text":"There\u0027s a lot of business going on,"},{"Start":"04:48.160 ","End":"04:53.765","Text":"that\u0027s really where the cell is living for the most part during this G_1 phase."},{"Start":"04:53.765 ","End":"04:57.740","Text":"Then we have this S phase in which the DNA is replicated."},{"Start":"04:57.740 ","End":"04:59.630","Text":"We have DNA synthesis,"},{"Start":"04:59.630 ","End":"05:02.150","Text":"so we had 1 copy of the DNA,"},{"Start":"05:02.150 ","End":"05:04.275","Text":"by the end of the S phase,"},{"Start":"05:04.275 ","End":"05:08.945","Text":"we\u0027re going to have 2 copies of the DNA."},{"Start":"05:08.945 ","End":"05:12.920","Text":"Remember, they\u0027re going to be the homologous chromosomes,"},{"Start":"05:12.920 ","End":"05:15.900","Text":"as we mentioned a few videos earlier,"},{"Start":"05:15.900 ","End":"05:22.625","Text":"but each of the chromosomes when it divides makes sister chromatids."},{"Start":"05:22.625 ","End":"05:26.210","Text":"Don\u0027t confuse this with homologous chromosomes."},{"Start":"05:26.210 ","End":"05:31.340","Text":"The sister chromatids are identical because they are"},{"Start":"05:31.340 ","End":"05:37.250","Text":"simply copies of one another that\u0027s the result of DNA synthesis during this S phase,"},{"Start":"05:37.250 ","End":"05:44.225","Text":"and they become attached to each other primarily at the centromeric region."},{"Start":"05:44.225 ","End":"05:48.420","Text":"Each chromosome has 1 centromere at the middle of it,"},{"Start":"05:48.420 ","End":"05:51.620","Text":"that\u0027s a sequence of DNA that you will see will become"},{"Start":"05:51.620 ","End":"05:56.030","Text":"important for separation of the chromosomes later."},{"Start":"05:56.030 ","End":"05:58.790","Text":"Then there are other things that are happening at this point"},{"Start":"05:58.790 ","End":"06:01.520","Text":"that we\u0027ll discuss a little bit more in detail later."},{"Start":"06:01.520 ","End":"06:05.560","Text":"There\u0027s something called a mitotic spindle,"},{"Start":"06:05.560 ","End":"06:09.410","Text":"there\u0027s something called centrioles that"},{"Start":"06:09.410 ","End":"06:13.670","Text":"become important also for dividing the chromosomes,"},{"Start":"06:13.670 ","End":"06:16.230","Text":"and we\u0027ll see that in a minute."},{"Start":"06:16.430 ","End":"06:18.750","Text":"Centrioles we\u0027ll see,"},{"Start":"06:18.750 ","End":"06:21.350","Text":"will be important for helping cell division,"},{"Start":"06:21.350 ","End":"06:22.850","Text":"for organizing cell division,"},{"Start":"06:22.850 ","End":"06:26.990","Text":"but they\u0027re not present in plants or in most fungi."},{"Start":"06:26.990 ","End":"06:29.135","Text":"After the S phase,"},{"Start":"06:29.135 ","End":"06:34.430","Text":"we\u0027ve got the G2 phase or the second gap phase,"},{"Start":"06:34.430 ","End":"06:38.255","Text":"in which things are going to be prepared for mitosis."},{"Start":"06:38.255 ","End":"06:40.895","Text":"For one thing, energy stores are replenished,"},{"Start":"06:40.895 ","End":"06:45.560","Text":"and the necessary proteins for mitosis are synthesized."},{"Start":"06:45.560 ","End":"06:50.705","Text":"There is some dismantling of the cytoskeleton, that is,"},{"Start":"06:50.705 ","End":"06:54.289","Text":"there is some sort of a skeleton"},{"Start":"06:54.289 ","End":"06:59.330","Text":"of structural proteins that keep the cell shape before it divides."},{"Start":"06:59.330 ","End":"07:05.465","Text":"Some of these are dismantled and there are duplications of some of the cell organelles."},{"Start":"07:05.465 ","End":"07:11.420","Text":"Organelles are small membrane-defined like organs that are inside the cell."},{"Start":"07:11.420 ","End":"07:13.630","Text":"For instance, things called mitochondria,"},{"Start":"07:13.630 ","End":"07:17.385","Text":"you have learnt about that previously."},{"Start":"07:17.385 ","End":"07:22.580","Text":"In addition, there is additional cell growth so the cells can become large"},{"Start":"07:22.580 ","End":"07:28.385","Text":"enough before the cells actually divide in the mitotic phase."},{"Start":"07:28.385 ","End":"07:30.410","Text":"Now in this mitotic phase,"},{"Start":"07:30.410 ","End":"07:32.390","Text":"there is a dance that goes on."},{"Start":"07:32.390 ","End":"07:35.075","Text":"There\u0027s a dance really of the chromosomes,"},{"Start":"07:35.075 ","End":"07:38.670","Text":"and they\u0027re just like in a dance class,"},{"Start":"07:38.670 ","End":"07:42.264","Text":"you\u0027ll learn about different steps in classical dance in any case."},{"Start":"07:42.264 ","End":"07:44.750","Text":"There are all these steps,"},{"Start":"07:44.750 ","End":"07:50.090","Text":"a multi-step process where the duplicated chromosomes that duplicated themselves in"},{"Start":"07:50.090 ","End":"07:57.260","Text":"the S phase move like in a dance into new and the identical daughter cells in the end,"},{"Start":"07:57.260 ","End":"08:02.420","Text":"and how that happens is what we\u0027re going to see momentarily."},{"Start":"08:02.420 ","End":"08:04.040","Text":"There are several steps to it."},{"Start":"08:04.040 ","End":"08:07.790","Text":"The first step is called karyokinesis."},{"Start":"08:07.790 ","End":"08:13.865","Text":"Kinesis, remember I said was movement, karyo means nucleus."},{"Start":"08:13.865 ","End":"08:17.895","Text":"This is nuclear division, that\u0027s the karyokinesis."},{"Start":"08:17.895 ","End":"08:20.320","Text":"That is before cytokinesis,"},{"Start":"08:20.320 ","End":"08:24.055","Text":"as we mentioned before, that\u0027s the division of the cells."},{"Start":"08:24.055 ","End":"08:27.835","Text":"First, there\u0027s division of the nuclei,"},{"Start":"08:27.835 ","End":"08:31.720","Text":"although the nuclear membrane often disintegrates at this point,"},{"Start":"08:31.720 ","End":"08:34.870","Text":"and there then is cytokinesis,"},{"Start":"08:34.870 ","End":"08:40.205","Text":"the separation of the cytoplasmic components when the cell actually divides."},{"Start":"08:40.205 ","End":"08:44.850","Text":"Let\u0027s look at this dance in more detail."},{"Start":"08:44.850 ","End":"08:50.740","Text":"Karyokinesis, in the division of what\u0027s inside the nucleus,"},{"Start":"08:50.740 ","End":"08:53.145","Text":"occurs in multiple steps."},{"Start":"08:53.145 ","End":"08:59.615","Text":"We\u0027ve got something called prophase, and then prometaphase."},{"Start":"08:59.615 ","End":"09:04.315","Text":"Then there is something called metaphase,"},{"Start":"09:04.315 ","End":"09:07.180","Text":"and then anaphase,"},{"Start":"09:07.180 ","End":"09:10.435","Text":"and then finally telophase."},{"Start":"09:10.435 ","End":"09:13.930","Text":"There are these various steps in which"},{"Start":"09:13.930 ","End":"09:17.845","Text":"all sorts of things are happening in the difference stages."},{"Start":"09:17.845 ","End":"09:27.265","Text":"What we\u0027re going to do now is look at this dance and look in more detail at each step."},{"Start":"09:27.265 ","End":"09:30.660","Text":"Let\u0027s start first with prophase,"},{"Start":"09:30.660 ","End":"09:32.440","Text":"that\u0027s the first phase."},{"Start":"09:32.440 ","End":"09:35.140","Text":"Pro means first."},{"Start":"09:35.140 ","End":"09:38.995","Text":"The first thing that happens is the chromosomes that"},{"Start":"09:38.995 ","End":"09:42.625","Text":"had been extended earlier they condense."},{"Start":"09:42.625 ","End":"09:44.559","Text":"There\u0027s a very strong condensation."},{"Start":"09:44.559 ","End":"09:48.250","Text":"We had mentioned this in the previous video."},{"Start":"09:48.250 ","End":"09:56.260","Text":"The centrosomes, that is what is attached to the centromeres begin to"},{"Start":"09:56.260 ","End":"10:00.370","Text":"move and there is the formation at the same time of"},{"Start":"10:00.370 ","End":"10:05.545","Text":"a new protein complex that is called the mitotic spindle."},{"Start":"10:05.545 ","End":"10:11.095","Text":"These are tubes or tubes of proteins,"},{"Start":"10:11.095 ","End":"10:12.879","Text":"1 of which is called tubulin,"},{"Start":"10:12.879 ","End":"10:15.070","Text":"actually that are going to be,"},{"Start":"10:15.070 ","End":"10:20.920","Text":"as it were the muscles that are going to move the chromosomes to different poles,"},{"Start":"10:20.920 ","End":"10:26.200","Text":"to different sides of the cell before cell division."},{"Start":"10:26.200 ","End":"10:31.000","Text":"At the same time there is the breakdown of the nucleoli."},{"Start":"10:31.000 ","End":"10:36.745","Text":"Nucleoli are particular regions within the cell nucleus."},{"Start":"10:36.745 ","End":"10:40.630","Text":"Then we move into prometaphase,"},{"Start":"10:40.630 ","End":"10:43.930","Text":"which is the first change phase."},{"Start":"10:43.930 ","End":"10:45.280","Text":"What happens here?"},{"Start":"10:45.280 ","End":"10:51.190","Text":"There is condensation of the chromosomes to a even more condensed state."},{"Start":"10:51.190 ","End":"10:55.255","Text":"This can be seen now in the light microscope."},{"Start":"10:55.255 ","End":"11:00.580","Text":"These microtubules have moved and extended"},{"Start":"11:00.580 ","End":"11:06.700","Text":"themselves and each sister chromatid develops a kinetochore."},{"Start":"11:06.700 ","End":"11:09.445","Text":"Remember the DNA is divided."},{"Start":"11:09.445 ","End":"11:13.120","Text":"Each piece of DNA, there\u0027re 2 pieces of them,"},{"Start":"11:13.120 ","End":"11:17.440","Text":"and I said that they are connected right at the centromeric region,"},{"Start":"11:17.440 ","End":"11:19.570","Text":"at this kinetic core."},{"Start":"11:19.570 ","End":"11:23.320","Text":"The microtubules are going to attach to this kinetochore,"},{"Start":"11:23.320 ","End":"11:25.465","Text":"and that\u0027s what we see here."},{"Start":"11:25.465 ","End":"11:30.249","Text":"The mitotic spindle binds these kinetic cores and the chromosomes"},{"Start":"11:30.249 ","End":"11:35.605","Text":"note become oriented to the opposite poles."},{"Start":"11:35.605 ","End":"11:40.210","Text":"They\u0027re being pulled actually in both directions,"},{"Start":"11:40.210 ","End":"11:42.490","Text":"we will see in mitosis."},{"Start":"11:42.490 ","End":"11:46.285","Text":"Then we move into the next phase called metaphase,"},{"Start":"11:46.285 ","End":"11:48.655","Text":"or the change phase."},{"Start":"11:48.655 ","End":"11:53.110","Text":"During metaphase, the chromosomes move into"},{"Start":"11:53.110 ","End":"11:57.580","Text":"the middle of the cell along something called the metaphase plate."},{"Start":"11:57.580 ","End":"12:03.760","Text":"This metaphase plate, they all line up over here on the equatorial plane,"},{"Start":"12:03.760 ","End":"12:04.960","Text":"is if you look at this,"},{"Start":"12:04.960 ","End":"12:07.440","Text":"let\u0027s say you think of it as a globe of the cell,"},{"Start":"12:07.440 ","End":"12:11.575","Text":"as a globe there will be 2 poles and there\u0027s an equator."},{"Start":"12:11.575 ","End":"12:15.850","Text":"Some of this terminology is borrowed really from the globe."},{"Start":"12:15.850 ","End":"12:19.570","Text":"There\u0027s what we call the equatorial plane."},{"Start":"12:19.570 ","End":"12:24.550","Text":"Then the sister chromatids are being pulled in each direction,"},{"Start":"12:24.550 ","End":"12:27.640","Text":"but they\u0027re still tightly attached to each other by"},{"Start":"12:27.640 ","End":"12:31.600","Text":"a protein or by a series of proteins called cohesin."},{"Start":"12:31.600 ","End":"12:35.800","Text":"They are cohesive, they keep the chromosomes together,"},{"Start":"12:35.800 ","End":"12:37.270","Text":"the sister chromatids together,"},{"Start":"12:37.270 ","End":"12:41.545","Text":"despite the fact that they\u0027re being pulled in each direction."},{"Start":"12:41.545 ","End":"12:47.905","Text":"At this point the chromosomes are maximally condensed and in one go,"},{"Start":"12:47.905 ","End":"12:50.665","Text":"we suddenly have anaphase."},{"Start":"12:50.665 ","End":"12:55.240","Text":"Anaphase is this upward phase or it\u0027s the phase in which the sister chromatids"},{"Start":"12:55.240 ","End":"13:00.430","Text":"do come apart because the cohesin proteins are suddenly degraded,"},{"Start":"13:00.430 ","End":"13:03.850","Text":"enzymatically broken down, the cohesin is broken"},{"Start":"13:03.850 ","End":"13:07.225","Text":"down and all at once and this can be seen in the microscope."},{"Start":"13:07.225 ","End":"13:12.100","Text":"The sister chromatids move to the various poles of the cell,"},{"Start":"13:12.100 ","End":"13:18.220","Text":"and each chromatid is pulled individually and very rapidly to the opposite pole."},{"Start":"13:18.220 ","End":"13:21.565","Text":"The cells also at the same time become somewhat"},{"Start":"13:21.565 ","End":"13:26.710","Text":"elongated and the polar microtubules slide against each other."},{"Start":"13:26.710 ","End":"13:30.250","Text":"Again, it\u0027s somewhat like what goes on inside of a muscle."},{"Start":"13:30.250 ","End":"13:36.640","Text":"Then finally we reached the last phase called telophase or the distance phase."},{"Start":"13:36.640 ","End":"13:39.475","Text":"Each of these words,"},{"Start":"13:39.475 ","End":"13:43.885","Text":"before the word phase there is an abbreviation which comes from Latin."},{"Start":"13:43.885 ","End":"13:48.295","Text":"The Latin for telo distance phase."},{"Start":"13:48.295 ","End":"13:55.690","Text":"The chromosomes at this point reach the opposite poles and begin to decondense,"},{"Start":"13:55.690 ","End":"13:58.180","Text":"unravel in many of the cells,"},{"Start":"13:58.180 ","End":"14:01.135","Text":"although in some cases that doesn\u0027t happen, but usually it does."},{"Start":"14:01.135 ","End":"14:04.795","Text":"Then mitotic spindles are depolymerized."},{"Start":"14:04.795 ","End":"14:07.144","Text":"The mitotic spindles disappear."},{"Start":"14:07.144 ","End":"14:14.300","Text":"The tubulin and then becomes monomers instead of a polymer which is this long tube."},{"Start":"14:14.300 ","End":"14:19.899","Text":"The nuclear envelopes begin to reassemble around the chromosomes,"},{"Start":"14:19.899 ","End":"14:25.300","Text":"and we are now beginning to complete"},{"Start":"14:25.300 ","End":"14:29.155","Text":"our cell cycle because the next stage"},{"Start":"14:29.155 ","End":"14:33.475","Text":"is going to be separation of the cells or cytokinesis."},{"Start":"14:33.475 ","End":"14:37.840","Text":"Cyto remember cells, and kinesis is motion."},{"Start":"14:37.840 ","End":"14:40.525","Text":"They actually have movement of the cells."},{"Start":"14:40.525 ","End":"14:48.460","Text":"We have a cleavage furrow which gets made between the 2 cells."},{"Start":"14:48.460 ","End":"14:53.845","Text":"That\u0027s just really an elongation of the membranes of the cell,"},{"Start":"14:53.845 ","End":"14:56.500","Text":"which then will split from each other."},{"Start":"14:56.500 ","End":"14:59.170","Text":"You\u0027ll have a membrane going around each new cell."},{"Start":"14:59.170 ","End":"15:02.882","Text":"In plants we call this something a little bit different,"},{"Start":"15:02.882 ","End":"15:07.090","Text":"we call it a cell plate which forms between the 2 cells,"},{"Start":"15:07.090 ","End":"15:10.930","Text":"but it\u0027s basically the same thing."},{"Start":"15:10.930 ","End":"15:15.520","Text":"Finally, we want to consider another phase that we"},{"Start":"15:15.520 ","End":"15:20.470","Text":"hadn\u0027t talked about called G_0 or a gap 0."},{"Start":"15:20.470 ","End":"15:24.930","Text":"Now sometimes cells are not really going through the cell cycle,"},{"Start":"15:24.930 ","End":"15:27.970","Text":"they need a pause button as it were."},{"Start":"15:27.970 ","End":"15:35.335","Text":"The pause button is basically an elongated G_1 period where not much is happening,"},{"Start":"15:35.335 ","End":"15:39.100","Text":"and we give that term G_0."},{"Start":"15:39.100 ","End":"15:45.385","Text":"S phase is delayed and we have a G_0 phase."},{"Start":"15:45.385 ","End":"15:51.145","Text":"That is primarily dependent upon environmental conditions."},{"Start":"15:51.145 ","End":"15:54.325","Text":"It depends on what the environmental conflict conditions are,"},{"Start":"15:54.325 ","End":"15:57.145","Text":"so how long this G_0 phase may last."},{"Start":"15:57.145 ","End":"16:00.115","Text":"It could last a very, very long time."},{"Start":"16:00.115 ","End":"16:03.114","Text":"In humans for instance, in adults,"},{"Start":"16:03.114 ","End":"16:05.635","Text":"many of the cells are not really dividing,"},{"Start":"16:05.635 ","End":"16:08.860","Text":"but they\u0027re alive, they\u0027re in G_0."},{"Start":"16:08.860 ","End":"16:15.970","Text":"Then when conditions improve or when the conditions are right, let us say,"},{"Start":"16:15.970 ","End":"16:17.980","Text":"then there could be, let\u0027s say,"},{"Start":"16:17.980 ","End":"16:25.135","Text":"an external trigger which will send the cells into S phase and start them dividing."},{"Start":"16:25.135 ","End":"16:27.460","Text":"As I mentioned in some cells,"},{"Start":"16:27.460 ","End":"16:30.220","Text":"especially in higher organisms,"},{"Start":"16:30.220 ","End":"16:32.170","Text":"the G_0 can be very long."},{"Start":"16:32.170 ","End":"16:33.940","Text":"In cardiac muscle for instance,"},{"Start":"16:33.940 ","End":"16:38.260","Text":"the muscle that\u0027s in our heart and nerve cells,"},{"Start":"16:38.260 ","End":"16:42.685","Text":"they can remain in G_0 sometimes even for years."},{"Start":"16:42.685 ","End":"16:48.370","Text":"In this section, we learned how to describe the 3 stages of interface,"},{"Start":"16:48.370 ","End":"16:53.140","Text":"we discussed the behavior of the chromosomes during carryover kinesis."},{"Start":"16:53.140 ","End":"16:54.940","Text":"Now you know what carrier kinesis is."},{"Start":"16:54.940 ","End":"17:02.005","Text":"Remember it\u0027s the movement of the division of the nucleus and during mitosis,"},{"Start":"17:02.005 ","End":"17:07.240","Text":"and we explained how the cytoplasmic contact is divided during cytokinesis,"},{"Start":"17:07.240 ","End":"17:12.290","Text":"and we defined the quiescent G_0 phase."}],"ID":26315},{"Watched":false,"Name":"Control of the Cell Cycle Part a","Duration":"8m 33s","ChapterTopicVideoID":25494,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.140 ","End":"00:02.835","Text":"It\u0027s good to be back."},{"Start":"00:02.835 ","End":"00:06.405","Text":"We\u0027ve been talking about the cell cycle."},{"Start":"00:06.405 ","End":"00:09.345","Text":"As you\u0027ll remember in the previous video,"},{"Start":"00:09.345 ","End":"00:12.150","Text":"and we\u0027ve described what is necessary to get from"},{"Start":"00:12.150 ","End":"00:15.270","Text":"one stage of the cell cycle to the next stage of the cell cycle."},{"Start":"00:15.270 ","End":"00:17.355","Text":"But let\u0027s think about it for a minute."},{"Start":"00:17.355 ","End":"00:21.030","Text":"If the cell cycle were totally unregulated,"},{"Start":"00:21.030 ","End":"00:23.920","Text":"then cells would just divide."},{"Start":"00:24.020 ","End":"00:33.015","Text":"For instance, there\u0027d be no G_0 and all of us would be just one big huge ball of cells."},{"Start":"00:33.015 ","End":"00:37.050","Text":"It\u0027s extremely important that the cell cycle be regulated."},{"Start":"00:37.050 ","End":"00:40.445","Text":"In fact, if it\u0027s not regulated properly,"},{"Start":"00:40.445 ","End":"00:44.870","Text":"then often we\u0027ll get a disease called cancer."},{"Start":"00:44.870 ","End":"00:48.935","Text":"Tumors are usually unregulated cell division."},{"Start":"00:48.935 ","End":"00:54.500","Text":"Let\u0027s look at the regulation of the cell cycle the control of the cell cycle."},{"Start":"00:54.500 ","End":"00:56.060","Text":"By the end of this section,"},{"Start":"00:56.060 ","End":"00:59.870","Text":"you should be able to understand how the cell cycle is controlled by mechanisms"},{"Start":"00:59.870 ","End":"01:04.010","Text":"that are both internal and external to the cell."},{"Start":"01:04.010 ","End":"01:08.270","Text":"You should be able to explain how the 3 internal control checkpoints,"},{"Start":"01:08.270 ","End":"01:11.230","Text":"these will be checkpoints at which we have a go,"},{"Start":"01:11.230 ","End":"01:13.820","Text":"no go decision to be made."},{"Start":"01:13.820 ","End":"01:22.795","Text":"How these control checkpoints occur at the end of G_1 and in the G_2/M transition,"},{"Start":"01:22.795 ","End":"01:24.720","Text":"and then also during metaphase."},{"Start":"01:24.720 ","End":"01:27.770","Text":"There\u0027ll be 3 different control checkpoints that"},{"Start":"01:27.770 ","End":"01:30.590","Text":"we\u0027ll be looking at and you should be able to"},{"Start":"01:30.590 ","End":"01:33.260","Text":"describe the molecules that control the cell cycle"},{"Start":"01:33.260 ","End":"01:36.875","Text":"through both positive and negative regulation."},{"Start":"01:36.875 ","End":"01:42.860","Text":"Let\u0027s look at the cell cycle now expressed a little bit differently than before."},{"Start":"01:42.860 ","End":"01:44.090","Text":"It\u0027s not quite the same figure,"},{"Start":"01:44.090 ","End":"01:45.935","Text":"but it\u0027s very similar."},{"Start":"01:45.935 ","End":"01:48.950","Text":"The first point I want to make is that the length of"},{"Start":"01:48.950 ","End":"01:52.670","Text":"the cell cycle is quite different in different organisms."},{"Start":"01:52.670 ","End":"01:54.455","Text":"In humans, for instance,"},{"Start":"01:54.455 ","End":"02:00.255","Text":"it\u0027s somewhere on the order of 20 hours or 24 hours roughly."},{"Start":"02:00.255 ","End":"02:03.375","Text":"In fission yeast,"},{"Start":"02:03.375 ","End":"02:08.510","Text":"this is a certain kind of a yeast that divides exactly into 2,"},{"Start":"02:08.510 ","End":"02:09.980","Text":"it\u0027s about 2 hours."},{"Start":"02:09.980 ","End":"02:11.630","Text":"A different budding yeast,"},{"Start":"02:11.630 ","End":"02:16.865","Text":"which is what we use in bread and making beer and wine,"},{"Start":"02:16.865 ","End":"02:18.905","Text":"it has a shorter time."},{"Start":"02:18.905 ","End":"02:21.905","Text":"Notice that in this case, in the budding yeast,"},{"Start":"02:21.905 ","End":"02:28.140","Text":"there is essentially no G_2 between the S and the M almost no time passes."},{"Start":"02:28.140 ","End":"02:30.110","Text":"In Drosophila embryos, in fact,"},{"Start":"02:30.110 ","End":"02:33.255","Text":"they don\u0027t even have much of a G_1 they just divide."},{"Start":"02:33.255 ","End":"02:35.570","Text":"They go M-S, M-S,"},{"Start":"02:35.570 ","End":"02:37.675","Text":"M-S, and it\u0027s really fast."},{"Start":"02:37.675 ","End":"02:40.410","Text":"It\u0027s about 8 minutes, the cell cycle,"},{"Start":"02:40.410 ","End":"02:45.410","Text":"so it\u0027s very variable and sometimes even within a single organism,"},{"Start":"02:45.410 ","End":"02:48.200","Text":"it\u0027s variable so it needs to be controlled."},{"Start":"02:48.200 ","End":"02:51.770","Text":"Now in rapidly human dividing cells,"},{"Start":"02:51.770 ","End":"02:53.750","Text":"the 24-hour cycle roughly,"},{"Start":"02:53.750 ","End":"02:55.730","Text":"the G_1 will be about 9 hours,"},{"Start":"02:55.730 ","End":"02:57.605","Text":"the S will be about 10 hours."},{"Start":"02:57.605 ","End":"03:00.320","Text":"The G_2 phase will be about 4.5 hours,"},{"Start":"03:00.320 ","End":"03:02.810","Text":"and the M phase, only about half an hour."},{"Start":"03:02.810 ","End":"03:06.155","Text":"But these times it can be different, of course,"},{"Start":"03:06.155 ","End":"03:10.950","Text":"in different organisms, in different cell types."},{"Start":"03:11.470 ","End":"03:15.109","Text":"The regulation of the cell cycle"},{"Start":"03:15.109 ","End":"03:18.710","Text":"can be controlled not only genetically say in different organisms,"},{"Start":"03:18.710 ","End":"03:23.240","Text":"but it also can be regulated by external events,"},{"Start":"03:23.240 ","End":"03:25.760","Text":"events that are external to the cell."},{"Start":"03:25.760 ","End":"03:30.770","Text":"For instance, we can see that there are cases even in humans of"},{"Start":"03:30.770 ","End":"03:36.860","Text":"initiation and inhibition of cell division that are triggered by external events."},{"Start":"03:36.860 ","End":"03:38.930","Text":"Look at these 2 adults."},{"Start":"03:38.930 ","End":"03:41.585","Text":"One of them is very small, a dwarf,"},{"Start":"03:41.585 ","End":"03:46.545","Text":"and one is a giant, is very tall."},{"Start":"03:46.545 ","End":"03:51.365","Text":"These are big differences that are caused by"},{"Start":"03:51.365 ","End":"03:56.840","Text":"the lack of these external events or by too much of some external events."},{"Start":"03:56.840 ","End":"04:01.585","Text":"These external events actually are external hormones."},{"Start":"04:01.585 ","End":"04:04.640","Text":"You could have lack of human growth hormone;"},{"Start":"04:04.640 ","End":"04:07.040","Text":"human growth hormone, HGH,"},{"Start":"04:07.040 ","End":"04:11.300","Text":"or that can inhibit cell division because you\u0027ve got"},{"Start":"04:11.300 ","End":"04:15.530","Text":"not enough of this growth hormone and that will induce dwarfism."},{"Start":"04:15.530 ","End":"04:18.230","Text":"The cells won\u0027t divide fast enough."},{"Start":"04:18.230 ","End":"04:20.330","Text":"On the opposite end of the spectrum,"},{"Start":"04:20.330 ","End":"04:22.445","Text":"if you\u0027ve got too much of that HGH,"},{"Start":"04:22.445 ","End":"04:25.230","Text":"you can get gigantism."},{"Start":"04:25.230 ","End":"04:28.290","Text":"The creation of these giants."},{"Start":"04:28.290 ","End":"04:31.820","Text":"The crowding of the cells that turns out normally in"},{"Start":"04:31.820 ","End":"04:34.910","Text":"normal conditions, inhibit cell division."},{"Start":"04:34.910 ","End":"04:36.650","Text":"That\u0027s also an external event."},{"Start":"04:36.650 ","End":"04:39.040","Text":"It\u0027s an external stimulus,"},{"Start":"04:39.040 ","End":"04:41.845","Text":"an external signal that cells might see."},{"Start":"04:41.845 ","End":"04:45.815","Text":"Somehow crowding of cells inhibits cell division."},{"Start":"04:45.815 ","End":"04:53.855","Text":"The enlargement of a cell size when the cells grow that promotes cell division."},{"Start":"04:53.855 ","End":"04:57.545","Text":"Again, that is not really an external event,"},{"Start":"04:57.545 ","End":"05:05.735","Text":"but it\u0027s something that clearly will define when a cell divides and when it doesn\u0027t."},{"Start":"05:05.735 ","End":"05:08.060","Text":"How does this control work?"},{"Start":"05:08.060 ","End":"05:10.040","Text":"Well, there is regulation,"},{"Start":"05:10.040 ","End":"05:13.235","Text":"it turns out at various checkpoints."},{"Start":"05:13.235 ","End":"05:16.730","Text":"It\u0027s not that the cell cycle slows down or"},{"Start":"05:16.730 ","End":"05:20.570","Text":"speeds up in a very uniform way rather there are"},{"Start":"05:20.570 ","End":"05:25.130","Text":"3 principal checkpoints which the cell cycle has to get"},{"Start":"05:25.130 ","End":"05:30.950","Text":"through in order for the cell cycle to continue."},{"Start":"05:30.950 ","End":"05:32.630","Text":"Of course, in most cases,"},{"Start":"05:32.630 ","End":"05:36.920","Text":"daughter cells are going to be identical to the parent cell."},{"Start":"05:36.920 ","End":"05:39.975","Text":"What are these mechanisms?"},{"Start":"05:39.975 ","End":"05:43.150","Text":"Near the end of G_1,"},{"Start":"05:43.150 ","End":"05:48.530","Text":"there is a checkpoint in which basically what we want to"},{"Start":"05:48.530 ","End":"05:53.480","Text":"see is that the DNA is going to be complete,"},{"Start":"05:53.480 ","End":"05:55.535","Text":"is going to be without any mistakes in it."},{"Start":"05:55.535 ","End":"05:58.760","Text":"The integrity of the DNA is checked at"},{"Start":"05:58.760 ","End":"06:03.230","Text":"this checkpoint because we don\u0027t want to duplicate the effect of DNA."},{"Start":"06:03.230 ","End":"06:06.695","Text":"There are other things that happened at this G_1 checkpoint as well,"},{"Start":"06:06.695 ","End":"06:08.480","Text":"and we\u0027ll see them later."},{"Start":"06:08.480 ","End":"06:14.270","Text":"At the G_2/M transition between G_2 and M,"},{"Start":"06:14.270 ","End":"06:18.410","Text":"we want to be sure that the S phase has been completed"},{"Start":"06:18.410 ","End":"06:22.985","Text":"properly and that the DNA has duplicated completely."},{"Start":"06:22.985 ","End":"06:24.530","Text":"There\u0027s a check for that."},{"Start":"06:24.530 ","End":"06:28.940","Text":"Then thirdly, it\u0027s very important that during metaphase,"},{"Start":"06:28.940 ","End":"06:31.280","Text":"each kinetochore is attached to"},{"Start":"06:31.280 ","End":"06:34.960","Text":"a spindle fiber because if it\u0027s not, what\u0027s going to happen?"},{"Start":"06:34.960 ","End":"06:39.080","Text":"Remember, the spindle fibers are going to be pulling"},{"Start":"06:39.080 ","End":"06:41.270","Text":"the chromosomes to opposite poles of"},{"Start":"06:41.270 ","End":"06:44.000","Text":"the cell so if they\u0027re not attached to the kinetochore,"},{"Start":"06:44.000 ","End":"06:47.420","Text":"we might get a chromosome that\u0027s left behind,"},{"Start":"06:47.420 ","End":"06:51.935","Text":"and so one cell will have too many and another cell will not have enough."},{"Start":"06:51.935 ","End":"06:54.175","Text":"Well, that is a problem."},{"Start":"06:54.175 ","End":"06:55.490","Text":"There\u0027s a checkpoint there,"},{"Start":"06:55.490 ","End":"06:59.720","Text":"that checks that and doesn\u0027t allow the cohesion to break down"},{"Start":"06:59.720 ","End":"07:05.770","Text":"during anaphase until all the chromosomes are where they ought to be."},{"Start":"07:05.770 ","End":"07:09.930","Text":"Let\u0027s look at the first G_1 checkpoint."},{"Start":"07:09.930 ","End":"07:12.784","Text":"At the first G_1 checkpoint,"},{"Start":"07:12.784 ","End":"07:14.450","Text":"as we said before,"},{"Start":"07:14.450 ","End":"07:21.280","Text":"we look to see whether the DNA is defective or not defective and there is a go,"},{"Start":"07:21.280 ","End":"07:25.190","Text":"no go decision that\u0027s going to be made at that point."},{"Start":"07:25.190 ","End":"07:30.435","Text":"Without the go, the cells simply enter G_0 and"},{"Start":"07:30.435 ","End":"07:32.870","Text":"they will try to repair the DNA or if"},{"Start":"07:32.870 ","End":"07:35.930","Text":"there are other external forces that keep it in G_0,"},{"Start":"07:35.930 ","End":"07:38.670","Text":"it will stay in G_0."},{"Start":"07:38.840 ","End":"07:43.910","Text":"It turns out that there are regulator molecules that regulate the cell cycle."},{"Start":"07:43.910 ","End":"07:46.970","Text":"These are molecules that are within the cell,"},{"Start":"07:46.970 ","End":"07:49.455","Text":"not external they\u0027re internal."},{"Start":"07:49.455 ","End":"07:52.925","Text":"There are 2 groups of molecules that control the cell cycle."},{"Start":"07:52.925 ","End":"07:56.420","Text":"There are positive ones and negative ones,"},{"Start":"07:56.420 ","End":"07:58.070","Text":"as we\u0027ll see soon."},{"Start":"07:58.070 ","End":"08:01.670","Text":"They may act individually or they can"},{"Start":"08:01.670 ","End":"08:06.410","Text":"influence other regulatory proteins as we\u0027ll see as well."},{"Start":"08:06.410 ","End":"08:10.475","Text":"Fortunately, the failure of just one single regulator"},{"Start":"08:10.475 ","End":"08:14.885","Text":"usually has very little effect on the cell cycle because there\u0027s redundancy."},{"Start":"08:14.885 ","End":"08:21.110","Text":"It\u0027s very important as you understand that the cell cycle occur properly."},{"Start":"08:21.110 ","End":"08:24.250","Text":"There\u0027s redundancy that\u0027s built into the system."},{"Start":"08:24.250 ","End":"08:28.535","Text":"The effect of non-functioning regulators, however,"},{"Start":"08:28.535 ","End":"08:33.690","Text":"could be fatal if multiple processes are affected."}],"ID":26311},{"Watched":false,"Name":"Control of the Cell Cycle Part b","Duration":"8m 9s","ChapterTopicVideoID":25495,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:01.220 ","End":"00:07.410","Text":"Now let\u0027s look at how one of the positive regulators works."},{"Start":"00:07.410 ","End":"00:10.140","Text":"Positive regulation of the cell cycle as"},{"Start":"00:10.140 ","End":"00:13.605","Text":"opposed to negative that we\u0027ll see in a few minutes."},{"Start":"00:13.605 ","End":"00:20.189","Text":"One of the most important positive regulators is cyclins, or our cyclins."},{"Start":"00:20.189 ","End":"00:26.415","Text":"It\u0027s a group of proteins that interact with cyclin-dependent kinases."},{"Start":"00:26.415 ","End":"00:28.020","Text":"Now what are kinases?"},{"Start":"00:28.020 ","End":"00:31.800","Text":"Kinases are enzymes so for instance,"},{"Start":"00:31.800 ","End":"00:34.815","Text":"it says here\u0027s CDK, cyclin-dependent kinase,"},{"Start":"00:34.815 ","End":"00:38.700","Text":"which phosphorylates it puts a phosphate group on"},{"Start":"00:38.700 ","End":"00:42.635","Text":"a particular target protein that it knows to interact with."},{"Start":"00:42.635 ","End":"00:50.000","Text":"Now these CDKs are dependent on the interaction with cyclin."},{"Start":"00:50.000 ","End":"00:53.120","Text":"Cyclin is this regulatory molecule."},{"Start":"00:53.120 ","End":"00:57.020","Text":"We\u0027re going to see that the cyclin is going to cycle,"},{"Start":"00:57.020 ","End":"00:58.320","Text":"that\u0027s why it\u0027s got that name,"},{"Start":"00:58.320 ","End":"00:59.630","Text":"during the cell cycle."},{"Start":"00:59.630 ","End":"01:04.520","Text":"It\u0027s going to go up and down and they are positive regulators."},{"Start":"01:04.520 ","End":"01:09.260","Text":"When a cyclin interacts with a CDK,"},{"Start":"01:09.260 ","End":"01:12.920","Text":"it then activates the enzyme such that"},{"Start":"01:12.920 ","End":"01:19.595","Text":"the target protein will then be phosphorylated and if the cyclin then is degraded,"},{"Start":"01:19.595 ","End":"01:30.220","Text":"it will no longer be able to activate the protein and the CDK will not work anymore."},{"Start":"01:30.220 ","End":"01:33.410","Text":"Let\u0027s see. The concentrations of"},{"Start":"01:33.410 ","End":"01:38.240","Text":"the cyclin proteins change throughout the cell cycle and they determine,"},{"Start":"01:38.240 ","End":"01:43.430","Text":"as I said, when the CDK cyclin complex is form and be active."},{"Start":"01:43.430 ","End":"01:44.825","Text":"Now in this figure,"},{"Start":"01:44.825 ","End":"01:49.490","Text":"the cyclin is denoted as this purple half circle,"},{"Start":"01:49.490 ","End":"01:54.620","Text":"and the CDK is this yellow blob."},{"Start":"01:54.620 ","End":"01:56.810","Text":"You can notice that they interact."},{"Start":"01:56.810 ","End":"01:59.930","Text":"Now the cyclin itself through the cell cycle."},{"Start":"01:59.930 ","End":"02:02.330","Text":"Here we\u0027ve got M and then the next cycle,"},{"Start":"02:02.330 ","End":"02:05.510","Text":"G1, S, G2, M and so on, another cell cycle."},{"Start":"02:05.510 ","End":"02:08.090","Text":"You notice that the cyclins,"},{"Start":"02:08.090 ","End":"02:11.195","Text":"actually it\u0027s the green curve over here,"},{"Start":"02:11.195 ","End":"02:13.593","Text":"goes up and down."},{"Start":"02:13.593 ","End":"02:19.400","Text":"Then the activity of the cyclin-dependent kinase"},{"Start":"02:19.400 ","End":"02:20.540","Text":"here we\u0027ve got an example of"},{"Start":"02:20.540 ","End":"02:25.655","Text":"one called maturation promoting factor or mitosis promoting factor, MPF."},{"Start":"02:25.655 ","End":"02:31.340","Text":"You notice that the activity of the CDK also goes up and"},{"Start":"02:31.340 ","End":"02:37.550","Text":"down depending upon the interaction"},{"Start":"02:37.550 ","End":"02:41.945","Text":"between the cyclin and the cyclin-dependent kinase."},{"Start":"02:41.945 ","End":"02:45.700","Text":"We\u0027ve got a fluctuation of the activity."},{"Start":"02:46.040 ","End":"02:53.680","Text":"Let\u0027s look at this in the context of the entire cell cycle and watch what\u0027s happening."},{"Start":"02:53.680 ","End":"02:57.365","Text":"If here we have the cell cycle and I\u0027ve left"},{"Start":"02:57.365 ","End":"03:01.580","Text":"the piece of the previous figure over here on the right."},{"Start":"03:01.580 ","End":"03:04.385","Text":"As the cyclin accumulates,"},{"Start":"03:04.385 ","End":"03:10.725","Text":"it then can bind the cyclin-dependent kinase."},{"Start":"03:10.725 ","End":"03:12.995","Text":"After it has done that,"},{"Start":"03:12.995 ","End":"03:17.390","Text":"then there\u0027s phosphorylation which occurs and allows the cell to"},{"Start":"03:17.390 ","End":"03:23.500","Text":"progress through the G2, M checkpoint."},{"Start":"03:23.500 ","End":"03:28.760","Text":"Following mitosis, what happens is that the cyclin is"},{"Start":"03:28.760 ","End":"03:34.714","Text":"degraded and the CDK is no longer active."},{"Start":"03:34.714 ","End":"03:37.820","Text":"Now in addition to positive regulators,"},{"Start":"03:37.820 ","End":"03:40.460","Text":"there are negative regulators. As we said before."},{"Start":"03:40.460 ","End":"03:45.815","Text":"An example of negative regulator would be the retinoblastoma protein,"},{"Start":"03:45.815 ","End":"03:50.125","Text":"which is sometimes called Rb for short."},{"Start":"03:50.125 ","End":"03:53.295","Text":"Here it is in this figure Rb."},{"Start":"03:53.295 ","End":"03:58.400","Text":"It can be either phosphorylated as you see over here,"},{"Start":"03:58.400 ","End":"04:02.720","Text":"in which case it does not interact with another factor called"},{"Start":"04:02.720 ","End":"04:08.670","Text":"E2F and if it\u0027s not phosphorylated and then it can interact with E2F."},{"Start":"04:08.670 ","End":"04:15.935","Text":"Now what does it do? It prevents the transcription of RNA,"},{"Start":"04:15.935 ","End":"04:22.170","Text":"for our proteins which are required for S phase."},{"Start":"04:22.170 ","End":"04:26.810","Text":"If Rb is connected to E2F and is sitting on"},{"Start":"04:26.810 ","End":"04:32.145","Text":"the appropriate genes, it stops transcription."},{"Start":"04:32.145 ","End":"04:34.730","Text":"It\u0027s a negative regulator."},{"Start":"04:34.730 ","End":"04:39.470","Text":"If it\u0027s sitting there, it won\u0027t allow progression through the cell cycle."},{"Start":"04:39.470 ","End":"04:45.030","Text":"Remember the CDK cyclin was a positive regulator."},{"Start":"04:45.030 ","End":"04:51.035","Text":"It turns out that the transcription of these genes are required"},{"Start":"04:51.035 ","End":"04:58.445","Text":"for the CDK cyclin to progress and what do they do?"},{"Start":"04:58.445 ","End":"05:07.580","Text":"They then are important for the phosphorylation of Rb and therefore"},{"Start":"05:07.580 ","End":"05:11.990","Text":"it detaches from E2F and then you can get gene transcription and"},{"Start":"05:11.990 ","End":"05:17.202","Text":"then translation of the enzymes that are required to go through the S phase."},{"Start":"05:17.202 ","End":"05:22.205","Text":"Again, if the Rb is attached to the E2F,"},{"Start":"05:22.205 ","End":"05:27.610","Text":"it is this negative regulator which will then be removed"},{"Start":"05:27.610 ","End":"05:36.045","Text":"by the CDK cyclin acting right to phosphorylate the Rb."},{"Start":"05:36.045 ","End":"05:39.790","Text":"The Rb here is the target protein that we talked about in"},{"Start":"05:39.790 ","End":"05:46.315","Text":"the previous slide and then we get movement through the S phase."},{"Start":"05:46.315 ","End":"05:52.165","Text":"This will act primarily at the G1 checkpoint,"},{"Start":"05:52.165 ","End":"05:56.950","Text":"not allowing the cells into S phase."},{"Start":"05:56.950 ","End":"06:03.115","Text":"But it\u0027s actually a little bit more complicated than that because the control remember,"},{"Start":"06:03.115 ","End":"06:08.200","Text":"was at the G1 checkpoint that if the DNA is damaged,"},{"Start":"06:08.200 ","End":"06:14.825","Text":"we don\u0027t want to go into S. It turns out that if the DNA is damaged,"},{"Start":"06:14.825 ","End":"06:21.275","Text":"another protein called p53 is activated,"},{"Start":"06:21.275 ","End":"06:27.385","Text":"which then activates p21,"},{"Start":"06:27.385 ","End":"06:36.760","Text":"which then prevents CDK cyclins from phosphorylating the Rb."},{"Start":"06:36.760 ","End":"06:43.625","Text":"If the Rb is phosphorylated,"},{"Start":"06:43.625 ","End":"06:52.650","Text":"then we can go into S. All of this will be dependent on DNA damage."},{"Start":"06:52.670 ","End":"06:59.095","Text":"As the levels of p53 rise when the DNA is damaged,"},{"Start":"06:59.095 ","End":"07:01.690","Text":"then as I said, p21 is triggered,"},{"Start":"07:01.690 ","End":"07:06.640","Text":"which then enforces the halt in the cell cycle by p53"},{"Start":"07:06.640 ","End":"07:11.560","Text":"by binding to an inhibiting the activity of the CDK cyclins."},{"Start":"07:11.560 ","End":"07:13.614","Text":"I\u0027m just repeating what I just said,"},{"Start":"07:13.614 ","End":"07:15.485","Text":"and in that case,"},{"Start":"07:15.485 ","End":"07:20.020","Text":"if the Rb is not phosphorylated,"},{"Start":"07:20.020 ","End":"07:24.235","Text":"then the cells can not go into S. Now,"},{"Start":"07:24.235 ","End":"07:28.915","Text":"stress of all sorts can promote higher levels of p53,"},{"Start":"07:28.915 ","End":"07:30.205","Text":"not only DNA damage,"},{"Start":"07:30.205 ","End":"07:33.610","Text":"other stress and those stresses then"},{"Start":"07:33.610 ","End":"07:38.400","Text":"reduce the likelihood of cell movement into the S phase."},{"Start":"07:38.400 ","End":"07:42.620","Text":"In this section, we learned how to understand how"},{"Start":"07:42.620 ","End":"07:45.440","Text":"the cell cycle is controlled by mechanisms that are"},{"Start":"07:45.440 ","End":"07:49.225","Text":"both internal and external to the cell."},{"Start":"07:49.225 ","End":"07:58.055","Text":"We explained how 3 internal control checkpoints occur at the end of G1, at the G2,"},{"Start":"07:58.055 ","End":"08:01.080","Text":"M transition and during metaphase,"},{"Start":"08:01.080 ","End":"08:03.830","Text":"and we described the molecules that control"},{"Start":"08:03.830 ","End":"08:08.610","Text":"the cell cycle through positive and negative regulation."}],"ID":26312},{"Watched":false,"Name":"Cancer and the Cell Cycle Part a","Duration":"6m 26s","ChapterTopicVideoID":25489,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.485","Text":"Hi, so welcome back."},{"Start":"00:04.485 ","End":"00:07.605","Text":"We\u0027re discussing cell reproduction."},{"Start":"00:07.605 ","End":"00:12.060","Text":"In this video, we\u0027ll talk about cancer and the cell cycle."},{"Start":"00:12.060 ","End":"00:15.060","Text":"Remember, we talked about the cell cycle in the last video."},{"Start":"00:15.060 ","End":"00:18.885","Text":"Here we\u0027re going to apply it to understanding cancer."},{"Start":"00:18.885 ","End":"00:20.610","Text":"By the end of this section,"},{"Start":"00:20.610 ","End":"00:25.560","Text":"you will be able to describe how cancer is caused by uncontrolled cell growth."},{"Start":"00:25.560 ","End":"00:28.170","Text":"You\u0027ll understand how proto-oncogenes are"},{"Start":"00:28.170 ","End":"00:31.995","Text":"normal cell genes that when mutated become oncogene."},{"Start":"00:31.995 ","End":"00:35.900","Text":"We talked before about proto-oncogenes."},{"Start":"00:35.900 ","End":"00:38.285","Text":"We\u0027ll talk about how they become oncogenes here."},{"Start":"00:38.285 ","End":"00:42.755","Text":"We\u0027ll describe how tumor suppressors function and we\u0027ll explain"},{"Start":"00:42.755 ","End":"00:48.630","Text":"how mutants tumor suppressors also can cause cancer."},{"Start":"00:48.650 ","End":"00:51.735","Text":"What is cancer?"},{"Start":"00:51.735 ","End":"00:57.980","Text":"I think you probably know that if you look at breast cancer,"},{"Start":"00:57.980 ","End":"01:02.630","Text":"you probably know that there is initially tumor which a woman might be able to"},{"Start":"01:02.630 ","End":"01:08.630","Text":"feel in her breast that at first is very small,"},{"Start":"01:08.630 ","End":"01:13.970","Text":"it grows and then at some point it may,"},{"Start":"01:13.970 ","End":"01:16.180","Text":"if she\u0027s very unlucky,"},{"Start":"01:16.180 ","End":"01:19.864","Text":"leave the tissue of the breasts,"},{"Start":"01:19.864 ","End":"01:24.575","Text":"go into either the lymphatic system,"},{"Start":"01:24.575 ","End":"01:29.780","Text":"which is denoted by this green figure here,"},{"Start":"01:29.780 ","End":"01:31.820","Text":"or possibly go into the blood system."},{"Start":"01:31.820 ","End":"01:36.710","Text":"But in any case, it may take some of these cancer cells out of"},{"Start":"01:36.710 ","End":"01:39.290","Text":"this initial tumor and deliver them"},{"Start":"01:39.290 ","End":"01:43.220","Text":"someplace else in the body and that\u0027s called metastasis."},{"Start":"01:43.220 ","End":"01:48.170","Text":"You\u0027ll have a metastatic tumor which originated in"},{"Start":"01:48.170 ","End":"01:53.855","Text":"the breast and really be breast tumor but found someplace else."},{"Start":"01:53.855 ","End":"01:59.930","Text":"That\u0027s bad news as you all know when there is metastasis."},{"Start":"01:59.930 ","End":"02:08.540","Text":"Now all cancers starts when a particular gene is mutated or changed to give rise to"},{"Start":"02:08.540 ","End":"02:13.205","Text":"a faulty protein that then is very important"},{"Start":"02:13.205 ","End":"02:18.455","Text":"in cell reproduction in the cell cycle as we\u0027ve seen before,"},{"Start":"02:18.455 ","End":"02:23.645","Text":"even minor mistakes may allow subsequent mistakes to occur more readily."},{"Start":"02:23.645 ","End":"02:29.540","Text":"In other words, it can be downstream effects of an initial mistake in"},{"Start":"02:29.540 ","End":"02:36.770","Text":"a gene and the cell cycle of these genes will increase its speed."},{"Start":"02:36.770 ","End":"02:41.335","Text":"In other words, the cell cycle will take less time overall."},{"Start":"02:41.335 ","End":"02:49.000","Text":"As the effectiveness of the control and repair mechanisms in these cells decreases"},{"Start":"02:49.000 ","End":"02:57.490","Text":"so that the cells become more and more numerous in the tumor."},{"Start":"02:58.350 ","End":"03:04.630","Text":"Again, the growth of mutated cells outpaces the growth of normal cells,"},{"Start":"03:04.630 ","End":"03:07.885","Text":"and therefore, there is a tumor."},{"Start":"03:07.885 ","End":"03:10.375","Text":"Now there are 2 different tumors."},{"Start":"03:10.375 ","End":"03:12.625","Text":"There are benign tumors."},{"Start":"03:12.625 ","End":"03:15.040","Text":"That\u0027s the better tumor if you\u0027d like."},{"Start":"03:15.040 ","End":"03:18.895","Text":"In other words, it stays put where it originally formed."},{"Start":"03:18.895 ","End":"03:24.225","Text":"Often there is some an encasement around the cells that are reproducing"},{"Start":"03:24.225 ","End":"03:30.290","Text":"quickly here shown are red and these cells are not cancerous."},{"Start":"03:30.290 ","End":"03:33.020","Text":"They won\u0027t spread to other places."},{"Start":"03:33.020 ","End":"03:37.280","Text":"But still, you could have a loss of control."},{"Start":"03:37.280 ","End":"03:45.065","Text":"But that\u0027s not cancer because they will always remain only at the original sites."},{"Start":"03:45.065 ","End":"03:47.960","Text":"On the other hand, there are malignant tumors."},{"Start":"03:47.960 ","End":"03:53.420","Text":"Those are cancer cells that do spread to other organs."},{"Start":"03:53.420 ","End":"04:00.980","Text":"In this case, the capsule or the capsid in which the original cells were,"},{"Start":"04:00.980 ","End":"04:04.400","Text":"can break open and as we discussed in the previous slide,"},{"Start":"04:04.400 ","End":"04:10.435","Text":"may enter the blood or lymph system and then deposits someplace else."},{"Start":"04:10.435 ","End":"04:14.315","Text":"What causes these changes initially?"},{"Start":"04:14.315 ","End":"04:16.565","Text":"Well, there are 2 possibilities."},{"Start":"04:16.565 ","End":"04:20.450","Text":"Remember when we discussed the cell cycle in the previous video,"},{"Start":"04:20.450 ","End":"04:26.585","Text":"we discussed both positive and negative cell cycle regulators."},{"Start":"04:26.585 ","End":"04:32.240","Text":"It turns out that errors in these cell cycle regulators or"},{"Start":"04:32.240 ","End":"04:37.820","Text":"the genes that encode the cell cycle regulators can cause cancer."},{"Start":"04:37.820 ","End":"04:43.640","Text":"Let\u0027s first start by looking at positive cell cycle regulators."},{"Start":"04:43.640 ","End":"04:48.700","Text":"Well, those would be oncogenes or proto-oncogenes."},{"Start":"04:48.700 ","End":"04:56.975","Text":"Proto-oncogenes are the genes that encode these positive cell cycle regulators."},{"Start":"04:56.975 ","End":"04:59.385","Text":"Once they become mutated,"},{"Start":"04:59.385 ","End":"05:04.820","Text":"these proto-oncogenes now are called oncogenes and they are"},{"Start":"05:04.820 ","End":"05:11.210","Text":"the ones that will cause a cell to become cancerous if they are mutated."},{"Start":"05:11.210 ","End":"05:13.130","Text":"Now in most instances,"},{"Start":"05:13.130 ","End":"05:16.280","Text":"the alteration of the DNA sequence will result in"},{"Start":"05:16.280 ","End":"05:21.560","Text":"a less functional or possibly even a non-functional protein."},{"Start":"05:21.560 ","End":"05:27.635","Text":"In those cases, if the result of that is that the cell cannot reproduce,"},{"Start":"05:27.635 ","End":"05:32.060","Text":"then the mutation is not propagated and the damage is minimal."},{"Start":"05:32.060 ","End":"05:39.155","Text":"In fact, cells like this may actually die and go into apoptosis."},{"Start":"05:39.155 ","End":"05:45.155","Text":"However, sometimes the gene mutation may cause a change that"},{"Start":"05:45.155 ","End":"05:53.105","Text":"increases the activity of a cell or increases the activity of a positive regulator,"},{"Start":"05:53.105 ","End":"06:00.970","Text":"making the cell cycle less controlled and move faster."},{"Start":"06:00.970 ","End":"06:04.925","Text":"Here we will have a normal cell in which there is"},{"Start":"06:04.925 ","End":"06:09.890","Text":"some mutation caused by cancer-causing agents that will make"},{"Start":"06:09.890 ","End":"06:15.980","Text":"a proto-oncogene turn into an oncogene or an active oncogene and that will"},{"Start":"06:15.980 ","End":"06:23.600","Text":"result in the cell reproducing more quickly and in an uncontrolled fashion,"},{"Start":"06:23.600 ","End":"06:26.130","Text":"become a cancer cell."}],"ID":26306},{"Watched":false,"Name":"Cancer and the Cell Cycle Part b","Duration":"5m 18s","ChapterTopicVideoID":25490,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.080 ","End":"00:05.595","Text":"If the resulting daughter cells are too damaged to undergo further cell division,"},{"Start":"00:05.595 ","End":"00:09.150","Text":"then the mutation would not be propagated as we said before,"},{"Start":"00:09.150 ","End":"00:11.685","Text":"and no harm would be done to the organism."},{"Start":"00:11.685 ","End":"00:18.330","Text":"However, if the atypical daughter cells do undergo further cell divisions,"},{"Start":"00:18.330 ","End":"00:24.945","Text":"subsequent generations of the cells may accumulate even more mutations."},{"Start":"00:24.945 ","End":"00:28.170","Text":"Look here at the normal cell division."},{"Start":"00:28.170 ","End":"00:31.230","Text":"Everything\u0027s under control and we have"},{"Start":"00:31.230 ","End":"00:36.170","Text":"the normal proto-oncogene in the case of these green cells,"},{"Start":"00:36.170 ","End":"00:37.805","Text":"or this green gene here,"},{"Start":"00:37.805 ","End":"00:43.714","Text":"which is active in controlling a normal cell cycle."},{"Start":"00:43.714 ","End":"00:44.870","Text":"If, on the other hand,"},{"Start":"00:44.870 ","End":"00:47.720","Text":"this proto-oncogene becomes mutated,"},{"Start":"00:47.720 ","End":"00:53.330","Text":"then there\u0027ll be some gain of function and abnormal cell cycle."},{"Start":"00:53.330 ","End":"00:57.320","Text":"It will go through checkpoints in the cell cycle when it shouldn\u0027t,"},{"Start":"00:57.320 ","End":"01:01.175","Text":"and we may get cancer cells."},{"Start":"01:01.175 ","End":"01:04.310","Text":"Any protein that influences the cell cycle can"},{"Start":"01:04.310 ","End":"01:07.550","Text":"be altered to override cell cycle checkpoints."},{"Start":"01:07.550 ","End":"01:11.300","Text":"They could be positive ones like we just mentioned here,"},{"Start":"01:11.300 ","End":"01:18.345","Text":"these proto-oncogenes, or they could be negative genes, tumor suppressor genes."},{"Start":"01:18.345 ","End":"01:21.000","Text":"They have the opposite effect, of course."},{"Start":"01:21.000 ","End":"01:24.020","Text":"Remember the tumor suppressor gene,"},{"Start":"01:24.020 ","End":"01:26.240","Text":"when it is activated,"},{"Start":"01:26.240 ","End":"01:29.210","Text":"keeps the cell from going through the cell cycle."},{"Start":"01:29.210 ","End":"01:33.275","Text":"They behave in a negative way and we\u0027ll look at them in a minute."},{"Start":"01:33.275 ","End":"01:37.220","Text":"In any case, an oncogene is any gene that when altered,"},{"Start":"01:37.220 ","End":"01:41.675","Text":"leads to an increase in the rate of the cell cycle progression."},{"Start":"01:41.675 ","End":"01:45.755","Text":"Let\u0027s look again at the tumor suppressor genes."},{"Start":"01:45.755 ","End":"01:49.385","Text":"Tumor suppressor genes are segments of DNA that encode"},{"Start":"01:49.385 ","End":"01:53.840","Text":"negative regulator proteins that can prevent uncontrolled division."},{"Start":"01:53.840 ","End":"01:59.825","Text":"Remember we discussed p53 for instance in the previous video."},{"Start":"01:59.825 ","End":"02:06.265","Text":"The normal p53 prevents cell cycle progression,"},{"Start":"02:06.265 ","End":"02:10.535","Text":"but the mutated p53 may"},{"Start":"02:10.535 ","End":"02:15.785","Text":"allow the cell cycle to continue and those cells become cancerous."},{"Start":"02:15.785 ","End":"02:20.750","Text":"How? Well, remember there were proteins, for instance,"},{"Start":"02:20.750 ","End":"02:25.265","Text":"tumor suppressor genes such as Rb retinoblastoma,"},{"Start":"02:25.265 ","End":"02:29.090","Text":"there\u0027s P53, there\u0027s the p21 that interacts,"},{"Start":"02:29.090 ","End":"02:31.010","Text":"if you remember with the retinoblastoma."},{"Start":"02:31.010 ","End":"02:34.075","Text":"Let\u0027s look back at that again in a minute."},{"Start":"02:34.075 ","End":"02:39.560","Text":"They all block cell cycle progression until certain events are completed."},{"Start":"02:39.560 ","End":"02:44.210","Text":"In other words, at checkpoints."},{"Start":"02:44.210 ","End":"02:46.610","Text":"Particularly, let\u0027s look at p53."},{"Start":"02:46.610 ","End":"02:49.730","Text":"Remember, the p53 protein operates at"},{"Start":"02:49.730 ","End":"02:55.280","Text":"the G_1 checkpoint and keeps cells from moving through the G_1."},{"Start":"02:55.280 ","End":"02:57.170","Text":"Importantly,"},{"Start":"02:57.170 ","End":"03:06.290","Text":"p53 is a cardinal protein because in more than 50 percent of all human cancers,"},{"Start":"03:06.290 ","End":"03:08.620","Text":"all human tumor cells,"},{"Start":"03:08.620 ","End":"03:11.820","Text":"in more than 50 percent of them,"},{"Start":"03:11.820 ","End":"03:14.970","Text":"the p53 genes have been altered."},{"Start":"03:14.970 ","End":"03:19.040","Text":"That\u0027s something that really needs to be looked at very carefully."},{"Start":"03:19.040 ","End":"03:21.590","Text":"Functional p53, in other words,"},{"Start":"03:21.590 ","End":"03:22.850","Text":"if it hasn\u0027t been mutated,"},{"Start":"03:22.850 ","End":"03:27.740","Text":"will deem the cell unsalvageable and trigger apoptosis."},{"Start":"03:27.740 ","End":"03:31.745","Text":"If something goes wrong and p53 is functional,"},{"Start":"03:31.745 ","End":"03:39.170","Text":"cells like that will die and not trigger cancer."},{"Start":"03:39.170 ","End":"03:45.230","Text":"Remember this diagram that we saw in the previous video?"},{"Start":"03:45.230 ","End":"03:50.615","Text":"Remember, DNA damage can activate p53,"},{"Start":"03:50.615 ","End":"03:53.930","Text":"which then activates p21,"},{"Start":"03:53.930 ","End":"03:59.915","Text":"which prevents the CDK cyclin complexes from activating"},{"Start":"03:59.915 ","End":"04:07.370","Text":"Rb that is important in the checkpoint at G_1."},{"Start":"04:07.370 ","End":"04:12.530","Text":"If p53 then is mutated, yes,"},{"Start":"04:12.530 ","End":"04:18.305","Text":"then we won\u0027t get adequate levels of p21,"},{"Start":"04:18.305 ","End":"04:24.595","Text":"and so there\u0027s not going to be an effective block of the CDK activation."},{"Start":"04:24.595 ","End":"04:29.030","Text":"The cell will then proceed directly from G_1 to"},{"Start":"04:29.030 ","End":"04:33.695","Text":"S regardless of internal and external conditions."},{"Start":"04:33.695 ","End":"04:37.390","Text":"That is, the cell will become cancerous."},{"Start":"04:37.390 ","End":"04:42.365","Text":"Very importantly, when the cell divides,"},{"Start":"04:42.365 ","End":"04:46.655","Text":"the mutation that let\u0027s say it was in the p53,"},{"Start":"04:46.655 ","End":"04:50.610","Text":"will be inherited in both the cells."},{"Start":"04:50.610 ","End":"04:53.015","Text":"Both daughter cells will inherit"},{"Start":"04:53.015 ","End":"04:59.840","Text":"the mutated p53 gene and therefore they too will continue to divide very quickly,"},{"Start":"04:59.840 ","End":"05:05.120","Text":"and we\u0027ll have an exponential increase in the number of cells"},{"Start":"05:05.120 ","End":"05:11.780","Text":"that accumulate oncogenes and non-functional tumor suppressor genes."},{"Start":"05:11.780 ","End":"05:17.800","Text":"That\u0027s a very bad situation, that\u0027s cancer."}],"ID":26307},{"Watched":false,"Name":"Prokaryotic Cell Division Part a","Duration":"7m 19s","ChapterTopicVideoID":25496,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:01.070 ","End":"00:07.110","Text":"Welcome back. In the last few videos we\u0027ve been discussing"},{"Start":"00:07.110 ","End":"00:13.635","Text":"cell reproduction of higher organisms of eukaryotic cells."},{"Start":"00:13.635 ","End":"00:16.770","Text":"We discussed the cell cycle and we"},{"Start":"00:16.770 ","End":"00:20.940","Text":"discussed the cancer when the cell cycle goes a bit of right."},{"Start":"00:20.940 ","End":"00:27.270","Text":"Now let\u0027s look at bacteria or prokaryotic cell division."},{"Start":"00:27.270 ","End":"00:29.610","Text":"By the end of this section,"},{"Start":"00:29.610 ","End":"00:33.470","Text":"you\u0027ll be able to describe the process of binary fission in"},{"Start":"00:33.470 ","End":"00:39.520","Text":"prokaryotes and you should be able to explain how FtsZ and tubulin,"},{"Start":"00:39.520 ","End":"00:41.265","Text":"these are 2 different proteins,"},{"Start":"00:41.265 ","End":"00:46.115","Text":"FtsZ in bacteria and tubulin in eukaryotes,"},{"Start":"00:46.115 ","End":"00:51.815","Text":"how these proteins are examples of homologous proteins of homology."},{"Start":"00:51.815 ","End":"00:57.420","Text":"We\u0027ll discuss a little bit the evolution of these proteins."},{"Start":"00:57.820 ","End":"01:03.785","Text":"Prokaryotic cells are somewhat different than eukaryotic cells."},{"Start":"01:03.785 ","End":"01:07.265","Text":"For one thing, they\u0027re much simpler."},{"Start":"01:07.265 ","End":"01:12.095","Text":"They don\u0027t have internal membranes in them like eukaryotes do."},{"Start":"01:12.095 ","End":"01:17.540","Text":"Basically, a prokaryotic cell bacterium is like"},{"Start":"01:17.540 ","End":"01:22.820","Text":"a sack of enzymes and other materials like DNA inside,"},{"Start":"01:22.820 ","End":"01:25.370","Text":"but we don\u0027t have a nucleus."},{"Start":"01:25.370 ","End":"01:29.360","Text":"Therefore, cell separation or"},{"Start":"01:29.360 ","End":"01:34.639","Text":"cell division will be simpler because we don\u0027t have to divide a nucleus."},{"Start":"01:34.639 ","End":"01:35.960","Text":"We do, however,"},{"Start":"01:35.960 ","End":"01:38.480","Text":"have to divide the DNA."},{"Start":"01:38.480 ","End":"01:43.055","Text":"Replicated DNA has to be separated equally between the 2 cells."},{"Start":"01:43.055 ","End":"01:50.720","Text":"Let\u0027s look first at this in a general way and then we\u0027ll look a little bit more closely."},{"Start":"01:50.720 ","End":"01:55.200","Text":"Bacteria, of course, are unicellular organisms Each of"},{"Start":"01:55.200 ","End":"02:00.200","Text":"the 2 cells after division will be identical to the original one."},{"Start":"02:00.200 ","End":"02:06.305","Text":"The genomic DNA must be replicated and then equally allocated to the 2 different cells."},{"Start":"02:06.305 ","End":"02:07.790","Text":"At the same time,"},{"Start":"02:07.790 ","End":"02:10.685","Text":"other cytoplasmic contents like, let\u0027s say,"},{"Start":"02:10.685 ","End":"02:14.975","Text":"ribosomes and other materials which are"},{"Start":"02:14.975 ","End":"02:21.305","Text":"dissolved inside the cell will have to be divided reasonably equally as well."},{"Start":"02:21.305 ","End":"02:24.215","Text":"Of course, in order to do that,"},{"Start":"02:24.215 ","End":"02:29.900","Text":"there is going to have to be a cell membrane which is going to close upon itself."},{"Start":"02:29.900 ","End":"02:33.830","Text":"We started out with 1 cell which is going to divide into two."},{"Start":"02:33.830 ","End":"02:36.620","Text":"So we\u0027re going to have to have some movement of"},{"Start":"02:36.620 ","End":"02:40.520","Text":"the plasma membrane and as well the cell wall,"},{"Start":"02:40.520 ","End":"02:42.845","Text":"which many bacteria have around them,"},{"Start":"02:42.845 ","End":"02:45.880","Text":"which will divide the cell into 2."},{"Start":"02:45.880 ","End":"02:51.950","Text":"Actually this division is quite simple because usually in prokaryotes,"},{"Start":"02:51.950 ","End":"02:54.695","Text":"the DNA is circular."},{"Start":"02:54.695 ","End":"02:57.980","Text":"There are no ends to this DNA,"},{"Start":"02:57.980 ","End":"03:01.265","Text":"as we\u0027ll see in the coming slides."},{"Start":"03:01.265 ","End":"03:05.795","Text":"We\u0027ll have a single circular DNA chromosome,"},{"Start":"03:05.795 ","End":"03:08.400","Text":"which is going to divide into 2."},{"Start":"03:08.420 ","End":"03:12.680","Text":"Let\u0027s look now at another figure that\u0027s a little bit more detailed."},{"Start":"03:12.680 ","End":"03:20.930","Text":"First start out by looking at the DNA during replication inside of a bacterial cell."},{"Start":"03:20.930 ","End":"03:25.615","Text":"Notice first of all that there are these red areas."},{"Start":"03:25.615 ","End":"03:29.400","Text":"If we look at one of the pieces of RNA,"},{"Start":"03:29.400 ","End":"03:30.875","Text":"one of the chromosomes,"},{"Start":"03:30.875 ","End":"03:32.060","Text":"there is a red area."},{"Start":"03:32.060 ","End":"03:34.655","Text":"This is the origin of replication."},{"Start":"03:34.655 ","End":"03:40.895","Text":"At this position, the replication begins and it moves by directionally."},{"Start":"03:40.895 ","End":"03:46.400","Text":"It moves into the right and to the left at the same time."},{"Start":"03:46.400 ","End":"03:50.480","Text":"If you look at how DNA is replicated in other videos,"},{"Start":"03:50.480 ","End":"03:53.615","Text":"you\u0027ll see that there are replication forks."},{"Start":"03:53.615 ","End":"03:56.750","Text":"In this case there are 2 replication forks,"},{"Start":"03:56.750 ","End":"04:01.055","Text":"one going to the right and one going to the left."},{"Start":"04:01.055 ","End":"04:10.125","Text":"Replication starts at the origin of replication and then is bidirectional."},{"Start":"04:10.125 ","End":"04:12.770","Text":"It\u0027s not shown in this figure,"},{"Start":"04:12.770 ","End":"04:17.525","Text":"but actually this origin replication is very near,"},{"Start":"04:17.525 ","End":"04:21.650","Text":"becomes attached to actually to the plasma membrane."},{"Start":"04:21.650 ","End":"04:30.750","Text":"That will be important for pulling the 2 pieces of DNA apart when the cell divides."},{"Start":"04:30.750 ","End":"04:36.430","Text":"The cell elongates, it grows during this process as well."},{"Start":"04:36.430 ","End":"04:41.705","Text":"Since the membrane is growing and is moving apart,"},{"Start":"04:41.705 ","End":"04:47.770","Text":"these 2 origins, 1 in 1 piece of DNA and the other in the other piece of DNA."},{"Start":"04:47.770 ","End":"04:51.380","Text":"Yes, so we have one on top here and on 1 of the bottom and so these are"},{"Start":"04:51.380 ","End":"04:55.535","Text":"the same too as you see in this second figure."},{"Start":"04:55.535 ","End":"04:59.215","Text":"Each of them are pulled in opposite directions,"},{"Start":"04:59.215 ","End":"05:05.605","Text":"one to the left and one to the right as the chromosome grows."},{"Start":"05:05.605 ","End":"05:12.320","Text":"Then after the chromosomes have been pulled completely separate from one another,"},{"Start":"05:12.320 ","End":"05:15.530","Text":"notice in order to do that there has to be a resolution of"},{"Start":"05:15.530 ","End":"05:19.580","Text":"the replication which is occurring in the 2 different directions."},{"Start":"05:19.580 ","End":"05:24.920","Text":"When the replication forks will meet each other at the opposite end,"},{"Start":"05:24.920 ","End":"05:25.950","Text":"that\u0027s what we see here,"},{"Start":"05:25.950 ","End":"05:27.725","Text":"the replication forks have met,"},{"Start":"05:27.725 ","End":"05:33.755","Text":"then the 2 pieces of DNA can separate and move into separate poles."},{"Start":"05:33.755 ","End":"05:38.090","Text":"At this point, something new starts to happen and that"},{"Start":"05:38.090 ","End":"05:43.715","Text":"is the cytoplasmic separation begins. How does that happen?"},{"Start":"05:43.715 ","End":"05:47.960","Text":"Notice these little green circles."},{"Start":"05:47.960 ","End":"05:57.095","Text":"Yes, these little green dots or circles represent the FtsZ protein or FtsZ protein,"},{"Start":"05:57.095 ","End":"05:59.675","Text":"if you come from the British world."},{"Start":"05:59.675 ","End":"06:05.060","Text":"The FtsZ protein is a protein which can be"},{"Start":"06:05.060 ","End":"06:10.220","Text":"both a monomer that is individual single units,"},{"Start":"06:10.220 ","End":"06:14.060","Text":"as you can see here, but it can also polymerize,"},{"Start":"06:14.060 ","End":"06:15.410","Text":"as you can see here."},{"Start":"06:15.410 ","End":"06:19.940","Text":"You can form a larger polymer and"},{"Start":"06:19.940 ","End":"06:25.220","Text":"that polymerization becomes important in the separation of the cells."},{"Start":"06:25.220 ","End":"06:26.975","Text":"How does that happen?"},{"Start":"06:26.975 ","End":"06:34.925","Text":"These little FtsZ proteins polymerize and forms a ring."},{"Start":"06:34.925 ","End":"06:39.740","Text":"This ring then recruits the new membrane,"},{"Start":"06:39.740 ","End":"06:43.160","Text":"which is being created in the middle here and"},{"Start":"06:43.160 ","End":"06:48.020","Text":"the cell wall materials that are on the outside."},{"Start":"06:48.020 ","End":"06:56.135","Text":"This new piece which begins to form between the cells is called a septum,"},{"Start":"06:56.135 ","End":"07:01.160","Text":"which forms between the 2 daughter nucleoids."},{"Start":"07:01.160 ","End":"07:04.400","Text":"The nucleoids are the protein and DNA,"},{"Start":"07:04.400 ","End":"07:09.245","Text":"so it\u0027s the DNA of the 2 different chromosomes and the proteins are associated with them."},{"Start":"07:09.245 ","End":"07:16.175","Text":"This septum grows and grows and grows until eventually the 2 cells separate,"},{"Start":"07:16.175 ","End":"07:19.260","Text":"the daughter cells separate."}],"ID":26313},{"Watched":false,"Name":"Prokaryotic Cell Division Part b","Duration":"3m 39s","ChapterTopicVideoID":25497,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.050 ","End":"00:04.125","Text":"Now you\u0027ll remember in eukaryotic cells,"},{"Start":"00:04.125 ","End":"00:09.240","Text":"we had chromosomes which condensed and there was"},{"Start":"00:09.240 ","End":"00:12.705","Text":"a centromeric region and the centromeric region"},{"Start":"00:12.705 ","End":"00:16.830","Text":"then became attached to a mitotic spindle,"},{"Start":"00:16.830 ","End":"00:22.230","Text":"which included in it the protein tubulin."},{"Start":"00:22.230 ","End":"00:29.565","Text":"Tubulin is also a polymer of subunits of monomers."},{"Start":"00:29.565 ","End":"00:39.525","Text":"What we\u0027re going to see here is that the FtsZ protein is similar to the tubulin."},{"Start":"00:39.525 ","End":"00:44.780","Text":"In fact, the tubulin is probably hereditary or it\u0027s"},{"Start":"00:44.780 ","End":"00:52.870","Text":"an evolutionary product of the FtsZ protein or something like it."},{"Start":"00:53.420 ","End":"01:00.935","Text":"Again, the mitotic spindles that we saw are in eukaryotic cells."},{"Start":"01:00.935 ","End":"01:02.630","Text":"In prokaryotic cells,"},{"Start":"01:02.630 ","End":"01:08.240","Text":"we don\u0027t have mitotic spindles like this because there is no karyokinesis."},{"Start":"01:08.240 ","End":"01:12.320","Text":"Karyokinesis remember is the division of the nucleus and here we"},{"Start":"01:12.320 ","End":"01:17.105","Text":"don\u0027t have a nucleus and so there\u0027s no karyokinesis."},{"Start":"01:17.105 ","End":"01:22.280","Text":"But what we do have is we have the FtsZ protein,"},{"Start":"01:22.280 ","End":"01:25.475","Text":"which causes the creation of the septum,"},{"Start":"01:25.475 ","End":"01:28.370","Text":"as we saw earlier."},{"Start":"01:28.370 ","End":"01:36.079","Text":"As I said, the FtsZ protein is similar to the tubulin."},{"Start":"01:36.079 ","End":"01:39.825","Text":"The FtsZ when it polymerizes,"},{"Start":"01:39.825 ","End":"01:45.995","Text":"forms 3-dimensional structures that very much actually resemble tubulin."},{"Start":"01:45.995 ","End":"01:49.220","Text":"Let\u0027s look at that a little bit more closely."},{"Start":"01:49.220 ","End":"01:52.750","Text":"The mitotic spindle apparatus,"},{"Start":"01:52.750 ","End":"01:56.355","Text":"as we said, contains tubulin."},{"Start":"01:56.355 ","End":"01:59.940","Text":"FtsZ and tubulin,"},{"Start":"01:59.940 ","End":"02:07.295","Text":"in order for them to polymerize from monomers to polymers, require energy."},{"Start":"02:07.295 ","End":"02:11.060","Text":"The energy source for these things,"},{"Start":"02:11.060 ","End":"02:12.845","Text":"for these polymerization,"},{"Start":"02:12.845 ","End":"02:16.130","Text":"is GTP, not ATP."},{"Start":"02:16.130 ","End":"02:23.375","Text":"Usually, you\u0027ll remember that ATP is usually the source for most cellular functions."},{"Start":"02:23.375 ","End":"02:25.205","Text":"However, in this case,"},{"Start":"02:25.205 ","End":"02:30.930","Text":"GTP is used as the source of energy for"},{"Start":"02:30.930 ","End":"02:36.930","Text":"polymerization of both FtsZ and tubulin."},{"Start":"02:36.930 ","End":"02:41.855","Text":"There\u0027s another similarity there between FtsZ and tubulin."},{"Start":"02:41.855 ","End":"02:45.505","Text":"They are homologous structures."},{"Start":"02:45.505 ","End":"02:50.770","Text":"In other words, these bundles that are created by FtsZ in the case of"},{"Start":"02:50.770 ","End":"02:57.190","Text":"prokaryotes and tubulin fibers are homologous,"},{"Start":"02:57.190 ","End":"02:58.900","Text":"they look much the same."},{"Start":"02:58.900 ","End":"03:05.050","Text":"It turns out that if we look at the genes that encode these 2 different proteins,"},{"Start":"03:05.050 ","End":"03:06.835","Text":"the FtsZ and the tubulin,"},{"Start":"03:06.835 ","End":"03:11.405","Text":"we see that they have an evolutionary similarity."},{"Start":"03:11.405 ","End":"03:19.020","Text":"Evidently, tubulin evolved from an early form of FtsZ."},{"Start":"03:19.630 ","End":"03:28.180","Text":"However, it has diversified tremendously since this prokaryotic origin of FtsZ."},{"Start":"03:28.180 ","End":"03:31.835","Text":"The tubulin, the current day tubulin,"},{"Start":"03:31.835 ","End":"03:36.420","Text":"is different but homologous to the FtsZ."}],"ID":26314},{"Watched":false,"Name":"Exercise 1","Duration":"1m 4s","ChapterTopicVideoID":27199,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.620","Text":"Welcome back. We\u0027ve been studying cell reproduction and it\u0027s"},{"Start":"00:04.620 ","End":"00:10.170","Text":"time to do some exercises and see if you remember what you\u0027ve learned."},{"Start":"00:10.170 ","End":"00:14.865","Text":"Let\u0027s start out by looking at the first exercise."},{"Start":"00:14.865 ","End":"00:19.665","Text":"A diploid cell has how many chromosomes?"},{"Start":"00:19.665 ","End":"00:22.290","Text":"A diploid cell has x,"},{"Start":"00:22.290 ","End":"00:24.735","Text":"the number of chromosomes as a haploid cell."},{"Start":"00:24.735 ","End":"00:26.565","Text":"Is it 1/4,"},{"Start":"00:26.565 ","End":"00:28.170","Text":"is it 1/2,"},{"Start":"00:28.170 ","End":"00:29.640","Text":"is it twice,"},{"Start":"00:29.640 ","End":"00:31.275","Text":"or is it 4 times?"},{"Start":"00:31.275 ","End":"00:33.120","Text":"I\u0027m sure you know the answer."},{"Start":"00:33.120 ","End":"00:34.770","Text":"It\u0027s not 1/4,"},{"Start":"00:34.770 ","End":"00:37.365","Text":"that\u0027s for sure, it\u0027s not 1/2,"},{"Start":"00:37.365 ","End":"00:39.465","Text":"it\u0027s not 4 times,"},{"Start":"00:39.465 ","End":"00:42.935","Text":"it is twice. Now why is that?"},{"Start":"00:42.935 ","End":"00:53.340","Text":"Of course, each zygote that is fertilized egg is going to have 2 chromosomes in it,"},{"Start":"00:55.760 ","End":"00:58.500","Text":"1 from each parent."},{"Start":"00:58.500 ","End":"01:04.050","Text":"A diploid cell has twice the number of chromosomes as a haploid cell."}],"ID":28281},{"Watched":false,"Name":"Exercise 2","Duration":"43s","ChapterTopicVideoID":27178,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:05.307","Text":"An organism\u0027s traits are determined by the specific combination of inherited,"},{"Start":"00:05.307 ","End":"00:07.300","Text":"cells, well, maybe,"},{"Start":"00:07.300 ","End":"00:09.400","Text":"genes, that sounds good."},{"Start":"00:09.400 ","End":"00:10.780","Text":"How about proteins?"},{"Start":"00:10.780 ","End":"00:12.415","Text":"Well, are they inherited?"},{"Start":"00:12.415 ","End":"00:15.635","Text":"Chromatids? Well, that doesn\u0027t make a lot of sense, does it?"},{"Start":"00:15.635 ","End":"00:18.835","Text":"It\u0027s not cells, it\u0027s not proteins,"},{"Start":"00:18.835 ","End":"00:23.560","Text":"it\u0027s not chromatids, it is genes, of course."},{"Start":"00:23.560 ","End":"00:28.630","Text":"As you remember, the genes are spread along"},{"Start":"00:28.630 ","End":"00:33.370","Text":"the chromosomes and we have 1 parental copy and 1 maternal copy."},{"Start":"00:33.370 ","End":"00:37.884","Text":"Each of them has quite a number of genes"},{"Start":"00:37.884 ","End":"00:43.700","Text":"on each chromosome and that\u0027s what we inherit from our parents."}],"ID":28282},{"Watched":false,"Name":"Exercise 3","Duration":"48s","ChapterTopicVideoID":27179,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:06.310","Text":"The first level of DNA organization in a eukaryotic cell is maintained by which molecule?"},{"Start":"00:08.450 ","End":"00:14.055","Text":"Cells, well, genes,"},{"Start":"00:14.055 ","End":"00:17.295","Text":"proteins, I don\u0027t know."},{"Start":"00:17.295 ","End":"00:20.055","Text":"Well, chromatids is the right answer."},{"Start":"00:20.055 ","End":"00:21.480","Text":"Remember, we"},{"Start":"00:21.480 ","End":"00:31.560","Text":"have homologous chromatids"},{"Start":"00:31.560 ","End":"00:36.120","Text":"that arise after a chromosome duplicates its DNA,"},{"Start":"00:36.120 ","End":"00:40.596","Text":"and they can consider is the first level of DNA organization,"},{"Start":"00:40.596 ","End":"00:42.630","Text":"each of these is a chromatid,"},{"Start":"00:42.630 ","End":"00:45.219","Text":"first level of DNA organization,"},{"Start":"00:45.219 ","End":"00:48.420","Text":"because it\u0027s the most packed."}],"ID":28283},{"Watched":false,"Name":"Exercise 4","Duration":"25s","ChapterTopicVideoID":27180,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.140 ","End":"00:06.390","Text":"Identical copies of chromatin held together by cohesin at the centromere are called."},{"Start":"00:06.390 ","End":"00:08.265","Text":"Well, we just talked about that."},{"Start":"00:08.265 ","End":"00:10.040","Text":"It\u0027s not histones, it\u0027s not nucleosomes,"},{"Start":"00:10.040 ","End":"00:13.695","Text":"it\u0027s not chromatin, it is sister chromatids."},{"Start":"00:13.695 ","End":"00:18.930","Text":"We have 2 chromatids and they are identical"},{"Start":"00:18.930 ","End":"00:25.300","Text":"to each other because they\u0027re the result of DNA replication in S phase."}],"ID":28284},{"Watched":false,"Name":"Exercise 5","Duration":"51s","ChapterTopicVideoID":27181,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.725","Text":"Chromosomes are duplicated during what stage of the cell cycle?"},{"Start":"00:04.725 ","End":"00:07.425","Text":"Is it G_1? Is it S?"},{"Start":"00:07.425 ","End":"00:08.790","Text":"Is it prophase?"},{"Start":"00:08.790 ","End":"00:11.430","Text":"Or is it prometaphase?"},{"Start":"00:11.430 ","End":"00:13.430","Text":"Well, it\u0027s not G_1,"},{"Start":"00:13.430 ","End":"00:16.065","Text":"it\u0027s not prophase,"},{"Start":"00:16.065 ","End":"00:19.365","Text":"it\u0027s not prometaphase, it\u0027s S phase."},{"Start":"00:19.365 ","End":"00:26.579","Text":"Remember during interphase, which is most of the cell cycle,"},{"Start":"00:26.579 ","End":"00:28.320","Text":"all of this is interphase,"},{"Start":"00:28.320 ","End":"00:36.210","Text":"the DNA is synthesized during the S phase."},{"Start":"00:36.210 ","End":"00:42.215","Text":"Of course, the G_1 phase is not where the DNA is duplicated."},{"Start":"00:42.215 ","End":"00:44.270","Text":"It\u0027s not during the G_2 phase."},{"Start":"00:44.270 ","End":"00:50.850","Text":"Prophase and prometaphase are simply not part of interphase."}],"ID":28285},{"Watched":false,"Name":"Exercise 6","Duration":"56s","ChapterTopicVideoID":27182,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:06.015","Text":"Which of the following events does not occur during some stage of interface,"},{"Start":"00:06.015 ","End":"00:08.415","Text":"or some of the stages of interface?"},{"Start":"00:08.415 ","End":"00:10.545","Text":"Is it DNA duplication?"},{"Start":"00:10.545 ","End":"00:12.510","Text":"Is it organelle duplication?"},{"Start":"00:12.510 ","End":"00:14.730","Text":"Is it increase in cell size?"},{"Start":"00:14.730 ","End":"00:17.925","Text":"Or is it separation of sister chromatids?"},{"Start":"00:17.925 ","End":"00:21.510","Text":"Now, remember, we are looking at which of the following events"},{"Start":"00:21.510 ","End":"00:25.500","Text":"does not occur during some stage of interface,"},{"Start":"00:25.500 ","End":"00:31.519","Text":"and that\u0027s not DNA duplication because it does happen during the S-phase."},{"Start":"00:31.519 ","End":"00:35.795","Text":"It\u0027s not organelle duplication because that also"},{"Start":"00:35.795 ","End":"00:41.255","Text":"occurs mostly during G2 of the cell cycle."},{"Start":"00:41.255 ","End":"00:43.730","Text":"What about increase in cell size?"},{"Start":"00:43.730 ","End":"00:45.965","Text":"Well, yes, the cell does grow."},{"Start":"00:45.965 ","End":"00:48.709","Text":"It is the separation of sister chromatids."},{"Start":"00:48.709 ","End":"00:52.880","Text":"The separation of sister chromatids during anaphase,"},{"Start":"00:52.880 ","End":"00:56.340","Text":"as you can see in this diagram."}],"ID":28286},{"Watched":false,"Name":"Exercise 7","Duration":"55s","ChapterTopicVideoID":27183,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.170 ","End":"00:05.175","Text":"The mitotic spindles arise from which cell structure?"},{"Start":"00:05.175 ","End":"00:08.700","Text":"Is it the centromere, the centrosome,"},{"Start":"00:08.700 ","End":"00:13.125","Text":"the kinetochore, or the cleavage furrow?"},{"Start":"00:13.125 ","End":"00:16.035","Text":"Well, it\u0027s not the centromere."},{"Start":"00:16.035 ","End":"00:18.270","Text":"It\u0027s not the kinetochore,"},{"Start":"00:18.270 ","End":"00:20.490","Text":"and it\u0027s not the cleavage furrow."},{"Start":"00:20.490 ","End":"00:22.710","Text":"It is the centrosome."},{"Start":"00:22.710 ","End":"00:25.245","Text":"Remember, during prophase,"},{"Start":"00:25.245 ","End":"00:33.960","Text":"we have the early mitotic spindle which emanates from the centrosomes."},{"Start":"00:33.960 ","End":"00:37.450","Text":"From the centrosomes, we have the mitotic spindle."},{"Start":"00:37.450 ","End":"00:41.950","Text":"The centrosomes are outside of the nucleus."},{"Start":"00:41.950 ","End":"00:46.430","Text":"The early mitotic spindle is going to be formed from them,"},{"Start":"00:46.430 ","End":"00:55.110","Text":"which will then later attach to the kinetochores."}],"ID":28287},{"Watched":false,"Name":"Exercise 8","Duration":"57s","ChapterTopicVideoID":27184,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:03.150","Text":"The attachment of the mitotic spindle fibers to"},{"Start":"00:03.150 ","End":"00:07.625","Text":"the kinetochores is a characteristics of which stage of mitosis?"},{"Start":"00:07.625 ","End":"00:09.640","Text":"That should be easy at this point."},{"Start":"00:09.640 ","End":"00:11.985","Text":"Is it prophase, prometaphase,"},{"Start":"00:11.985 ","End":"00:14.069","Text":"metaphase, or anaphase?"},{"Start":"00:14.069 ","End":"00:16.380","Text":"Well, not prophase as we know,"},{"Start":"00:16.380 ","End":"00:18.450","Text":"not metaphase as we know,"},{"Start":"00:18.450 ","End":"00:24.270","Text":"not anaphase, it is prometaphase."},{"Start":"00:25.460 ","End":"00:29.240","Text":"That is just before."},{"Start":"00:29.240 ","End":"00:31.805","Text":"Pro means before."},{"Start":"00:31.805 ","End":"00:35.569","Text":"Just at the very beginning of metaphase, just before metaphase,"},{"Start":"00:35.569 ","End":"00:39.056","Text":"when the chromosomes are going to align,"},{"Start":"00:39.056 ","End":"00:45.530","Text":"then that is when the mitotic fibers will connect to the kinetochores."},{"Start":"00:45.530 ","End":"00:47.390","Text":"The kinetochore, if you remember,"},{"Start":"00:47.390 ","End":"00:52.985","Text":"is the area that is between the 2 sister chromatids."},{"Start":"00:52.985 ","End":"00:57.180","Text":"It\u0027s what holds them together at the centromere."}],"ID":28288},{"Watched":false,"Name":"Exercise 9","Duration":"51s","ChapterTopicVideoID":27185,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:03.750","Text":"Unpacking of chromosomes and the formation of"},{"Start":"00:03.750 ","End":"00:08.385","Text":"a new nuclear envelope is characteristic of which stage of mitosis?"},{"Start":"00:08.385 ","End":"00:10.695","Text":"Is it prometaphase,"},{"Start":"00:10.695 ","End":"00:13.110","Text":"is it metaphase,"},{"Start":"00:13.110 ","End":"00:18.195","Text":"is it anaphase or is it telophase?"},{"Start":"00:18.195 ","End":"00:21.165","Text":"Well, it\u0027s not prometaphase,"},{"Start":"00:21.165 ","End":"00:24.945","Text":"it is not metaphase,"},{"Start":"00:24.945 ","End":"00:27.945","Text":"it is not anaphase,"},{"Start":"00:27.945 ","End":"00:29.880","Text":"well, it\u0027s telophase."},{"Start":"00:29.880 ","End":"00:35.400","Text":"Remember in telophase, we have the unpacking of the chromosomes."},{"Start":"00:35.400 ","End":"00:37.665","Text":"Remember, they were very tightly packed here,"},{"Start":"00:37.665 ","End":"00:42.105","Text":"so now they are very dispersed during telophase,"},{"Start":"00:42.105 ","End":"00:50.550","Text":"and we have a new nuclear envelope which forms around each new nucleus."}],"ID":28289},{"Watched":false,"Name":"Exercise 10","Duration":"1m 14s","ChapterTopicVideoID":27186,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:05.595","Text":"The separation of the sister chromatids is characteristic of which stage of mitosis,"},{"Start":"00:05.595 ","End":"00:09.615","Text":"prometaphase, metaphase, anaphase or telophase?"},{"Start":"00:09.615 ","End":"00:11.850","Text":"Well, we know now it\u0027s not prometaphase."},{"Start":"00:11.850 ","End":"00:13.095","Text":"We just spoke about that."},{"Start":"00:13.095 ","End":"00:16.710","Text":"It\u0027s not metaphase, it is not telophase."},{"Start":"00:16.710 ","End":"00:20.355","Text":"It is anaphase, as we have described before,"},{"Start":"00:20.355 ","End":"00:25.365","Text":"when each of the sets of chromatids is pulled in"},{"Start":"00:25.365 ","End":"00:31.065","Text":"opposite directions to the opposing poles of the cells during mitosis."},{"Start":"00:31.065 ","End":"00:33.750","Text":"The chromosomes become visible under"},{"Start":"00:33.750 ","End":"00:36.300","Text":"a light microscope during which stage of the mitosis?"},{"Start":"00:36.300 ","End":"00:39.525","Text":"Well, that should be light microscope."},{"Start":"00:39.525 ","End":"00:42.200","Text":"That should be when they\u0027re most packed."},{"Start":"00:42.200 ","End":"00:45.190","Text":"Is it prophase?"},{"Start":"00:45.190 ","End":"00:47.475","Text":"Is it prometaphase,"},{"Start":"00:47.475 ","End":"00:49.355","Text":"metaphase, or anaphase?"},{"Start":"00:49.355 ","End":"00:51.005","Text":"It\u0027s not prometaphase."},{"Start":"00:51.005 ","End":"00:52.355","Text":"We just spoke about that."},{"Start":"00:52.355 ","End":"00:58.505","Text":"It\u0027s not metaphase itself when the chromosomes are lined up in the middle of the poles."},{"Start":"00:58.505 ","End":"01:00.830","Text":"It\u0027s not anaphase when they\u0027re separated."},{"Start":"01:00.830 ","End":"01:07.430","Text":"It certainly is prophase when they become very tightly packed,"},{"Start":"01:07.430 ","End":"01:10.085","Text":"when before they were dispersed."},{"Start":"01:10.085 ","End":"01:14.220","Text":"That is during prophase."}],"ID":28290},{"Watched":false,"Name":"Exercise 11","Duration":"1m 9s","ChapterTopicVideoID":27187,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.080 ","End":"00:03.870","Text":"The fusing of Golgi vesicles at"},{"Start":"00:03.870 ","End":"00:08.145","Text":"the metaphase plate of dividing plant cells forms what structure?"},{"Start":"00:08.145 ","End":"00:10.293","Text":"Is it the cell plates,"},{"Start":"00:10.293 ","End":"00:11.820","Text":"is it the actin ring,"},{"Start":"00:11.820 ","End":"00:13.530","Text":"is it a cleavage furrow,"},{"Start":"00:13.530 ","End":"00:16.605","Text":"or is it a mitotic spindle?"},{"Start":"00:16.605 ","End":"00:21.015","Text":"Well, an acting ring is something a little bit different."},{"Start":"00:21.015 ","End":"00:22.905","Text":"We didn\u0027t learn a lot about that."},{"Start":"00:22.905 ","End":"00:26.070","Text":"Cleavage furrow, well, not really."},{"Start":"00:26.070 ","End":"00:27.270","Text":"We\u0027ll explain in a minute why,"},{"Start":"00:27.270 ","End":"00:31.110","Text":"and it\u0027s certainly not the mitotic spindle. Look at the figure."},{"Start":"00:31.110 ","End":"00:35.534","Text":"Remember in plant cells what happens,"},{"Start":"00:35.534 ","End":"00:41.730","Text":"we get a new cell plate which is formed,"},{"Start":"00:41.730 ","End":"00:51.485","Text":"and it arises by fusing of vesicles that are called Golgi vesicles."},{"Start":"00:51.485 ","End":"00:55.865","Text":"It\u0027s these vesicles which were in the cells"},{"Start":"00:55.865 ","End":"01:03.110","Text":"beforehand that fuse to cause the formation of the cell plates,"},{"Start":"01:03.110 ","End":"01:09.900","Text":"and that eventually will form a new cell wall between plant cells."}],"ID":28291},{"Watched":false,"Name":"Exercise 12","Duration":"1m 9s","ChapterTopicVideoID":27188,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:08.775","Text":"At which of the cell cycle checkpoints do external forces have the greatest influence?"},{"Start":"00:08.775 ","End":"00:10.290","Text":"Is it G_1,"},{"Start":"00:10.290 ","End":"00:13.275","Text":"G_2, M, or G_0?"},{"Start":"00:13.275 ","End":"00:15.435","Text":"Well, it\u0027s not G_2,"},{"Start":"00:15.435 ","End":"00:18.090","Text":"it\u0027s not M, it\u0027s not G_0."},{"Start":"00:18.090 ","End":"00:21.000","Text":"Let\u0027s remember what the checkpoints are."},{"Start":"00:21.000 ","End":"00:26.220","Text":"Remember, we have a G_2 checkpoint that is just before M,"},{"Start":"00:26.220 ","End":"00:29.235","Text":"we have one that\u0027s inside M,"},{"Start":"00:29.235 ","End":"00:32.505","Text":"and we\u0027ll see another exercise about that,"},{"Start":"00:32.505 ","End":"00:36.090","Text":"and then we have the G_1 checkpoint."},{"Start":"00:36.090 ","End":"00:38.345","Text":"What is the G_1 checkpoint?"},{"Start":"00:38.345 ","End":"00:46.565","Text":"Well, the G_1 checkpoint is going to keep the cells from going into the S phase."},{"Start":"00:46.565 ","End":"00:50.330","Text":"What will happen if there is that G_1 checkpoint?"},{"Start":"00:50.330 ","End":"00:53.245","Text":"The cells, if they stop,"},{"Start":"00:53.245 ","End":"00:58.780","Text":"here\u0027s the checkpoint, will stay in G_0."},{"Start":"00:59.060 ","End":"01:02.715","Text":"That\u0027s the checkpoint."},{"Start":"01:02.715 ","End":"01:06.195","Text":"There is no such thing as a G_0 checkpoint,"},{"Start":"01:06.195 ","End":"01:10.060","Text":"it is the G_1 checkpoint."}],"ID":28292},{"Watched":false,"Name":"Exercise 13","Duration":"1m 6s","ChapterTopicVideoID":27189,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:05.610","Text":"What is the main prerequisite for clearance at the G2 checkpoint?"},{"Start":"00:05.610 ","End":"00:08.880","Text":"Is it that a cell has reached a sufficient size?"},{"Start":"00:08.880 ","End":"00:13.155","Text":"Is it that an adequate stockpile of nucleotides has been formed?"},{"Start":"00:13.155 ","End":"00:16.140","Text":"Is it accurate and complete DNA replication,"},{"Start":"00:16.140 ","End":"00:21.210","Text":"or is it proper attachment of the mitotic spindle fibers to kinetochores?"},{"Start":"00:21.210 ","End":"00:25.305","Text":"Now, we\u0027re looking here at the G2 checkpoint."},{"Start":"00:25.305 ","End":"00:27.900","Text":"It\u0027s not that the cell has reached sufficient size."},{"Start":"00:27.900 ","End":"00:31.515","Text":"It\u0027s not that an adequate stockpile of nucleotides have been made."},{"Start":"00:31.515 ","End":"00:35.795","Text":"It\u0027s not that proper attachment of mitotic spindles to the kinetochores happens."},{"Start":"00:35.795 ","End":"00:41.750","Text":"It is accurate and complete DNA replication."},{"Start":"00:41.750 ","End":"00:44.720","Text":"We\u0027re looking now at the G2 checkpoint."},{"Start":"00:44.720 ","End":"00:48.830","Text":"In other words, the entrance into M. If there was"},{"Start":"00:48.830 ","End":"00:53.630","Text":"not sufficient replication or the replication was not complete in S,"},{"Start":"00:53.630 ","End":"00:57.890","Text":"then we certainly don\u0027t want to go into M. We don\u0027t want to divide the cell."},{"Start":"00:57.890 ","End":"01:00.080","Text":"Therefore, at this checkpoint,"},{"Start":"01:00.080 ","End":"01:06.180","Text":"there is checking to see that all of the DNA has been replicated."}],"ID":28293},{"Watched":false,"Name":"Exercise 14","Duration":"1m 4s","ChapterTopicVideoID":27190,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:02.895","Text":"If the M checkpoint is not cleared,"},{"Start":"00:02.895 ","End":"00:05.475","Text":"what stage of mitosis will be blocked?"},{"Start":"00:05.475 ","End":"00:08.940","Text":"Will it be prophase, will be prometaphase,"},{"Start":"00:08.940 ","End":"00:10.290","Text":"will be metaphase,"},{"Start":"00:10.290 ","End":"00:12.570","Text":"or will it be anaphase?"},{"Start":"00:12.570 ","End":"00:15.465","Text":"Well, it\u0027s the M checkpoint."},{"Start":"00:15.465 ","End":"00:18.750","Text":"The M checkpoint, so it\u0027s not prophase,"},{"Start":"00:18.750 ","End":"00:21.345","Text":"it\u0027s not prometaphase,"},{"Start":"00:21.345 ","End":"00:24.660","Text":"it\u0027s not metaphase itself."},{"Start":"00:24.660 ","End":"00:26.940","Text":"It is anaphase, of course."},{"Start":"00:26.940 ","End":"00:28.935","Text":"Remember, anaphase."},{"Start":"00:28.935 ","End":"00:33.780","Text":"Anaphase is the separation of the chromatids."},{"Start":"00:33.780 ","End":"00:36.180","Text":"That\u0027s anaphase."},{"Start":"00:36.180 ","End":"00:45.815","Text":"If at the M checkpoint does not see that there is good separation of all the chromatids,"},{"Start":"00:45.815 ","End":"00:48.140","Text":"that checkpoint will not be passed."},{"Start":"00:48.140 ","End":"00:55.789","Text":"Only if the chromatids have been separated completely and all of them being separated,"},{"Start":"00:55.789 ","End":"01:00.500","Text":"will the cell be able to complete mitosis and enter G1."},{"Start":"01:00.500 ","End":"01:03.690","Text":"The answer is anaphase."}],"ID":28294},{"Watched":false,"Name":"Exercise 15","Duration":"59s","ChapterTopicVideoID":27191,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:06.195","Text":"Which protein is a positive regulator that phosphorylates other proteins when activated?"},{"Start":"00:06.195 ","End":"00:07.800","Text":"Is it P53?"},{"Start":"00:07.800 ","End":"00:10.035","Text":"Is it retinoblastoma protein?"},{"Start":"00:10.035 ","End":"00:15.195","Text":"Is its cyclin or is it cyclin-dependent kinase or CDK?"},{"Start":"00:15.195 ","End":"00:18.120","Text":"Well, it\u0027s not P53."},{"Start":"00:18.120 ","End":"00:22.530","Text":"That\u0027s not a kinase, it doesn\u0027t phosphorylate."},{"Start":"00:22.530 ","End":"00:26.385","Text":"Retinoblastoma, you\u0027re going to remember is itself"},{"Start":"00:26.385 ","End":"00:30.590","Text":"phosphorylated so it\u0027s not a positive regulator that phosphorylates."},{"Start":"00:30.590 ","End":"00:32.180","Text":"Cyclin is a regulator,"},{"Start":"00:32.180 ","End":"00:33.335","Text":"so it\u0027s not going to be that."},{"Start":"00:33.335 ","End":"00:36.365","Text":"Well, it is the cyclin-dependent kinase."},{"Start":"00:36.365 ","End":"00:43.890","Text":"Remember, the cyclin-dependent kinases phosphorylates in this case,"},{"Start":"00:43.890 ","End":"00:47.600","Text":"RB, so here\u0027s the phosphorylated RB,"},{"Start":"00:47.600 ","End":"00:50.450","Text":"and we see this in the other diagram that we learned about"},{"Start":"00:50.450 ","End":"00:53.675","Text":"this cyclin-dependent kinase, the CDK."},{"Start":"00:53.675 ","End":"01:00.090","Text":"Cyclin is what does the phosphorylation of the RB."}],"ID":28295},{"Watched":false,"Name":"Exercise 16","Duration":"1m 34s","ChapterTopicVideoID":27192,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:03.450","Text":"Many of the negative regulator protein of the cell cycle,"},{"Start":"00:03.450 ","End":"00:06.180","Text":"were discovered in what type of cells?"},{"Start":"00:06.180 ","End":"00:08.415","Text":"Was it gametes,"},{"Start":"00:08.415 ","End":"00:10.320","Text":"cells in G_0,"},{"Start":"00:10.320 ","End":"00:11.670","Text":"in cancer cells,"},{"Start":"00:11.670 ","End":"00:14.115","Text":"or in stem cells?"},{"Start":"00:14.115 ","End":"00:18.840","Text":"Well, not gametes, not cells in G_0,"},{"Start":"00:18.840 ","End":"00:20.535","Text":"and not in stem cells."},{"Start":"00:20.535 ","End":"00:22.883","Text":"Of course, it was cancer cells,"},{"Start":"00:22.883 ","End":"00:25.990","Text":"because the negative regulators,"},{"Start":"00:26.270 ","End":"00:28.755","Text":"if they go awry,"},{"Start":"00:28.755 ","End":"00:33.758","Text":"will allow the cells to grow uncontrollably,"},{"Start":"00:33.758 ","End":"00:36.945","Text":"and those, of course, are cancer cells."},{"Start":"00:36.945 ","End":"00:43.580","Text":"It is negative regulators that were discovered in cancer cells."},{"Start":"00:43.580 ","End":"00:50.405","Text":"Which negative regulatory molecule can trigger cell suicide called apoptosis,"},{"Start":"00:50.405 ","End":"00:53.660","Text":"apoptosis is cell suicide,"},{"Start":"00:53.660 ","End":"00:56.285","Text":"if vital cell cycle events did not occur?"},{"Start":"00:56.285 ","End":"00:59.296","Text":"Is it p53, p21,"},{"Start":"00:59.296 ","End":"01:04.152","Text":"retinoblastoma protein, or CDK, cyclin-dependent kinase."},{"Start":"01:04.152 ","End":"01:07.455","Text":"Not p21, not RB,"},{"Start":"01:07.455 ","End":"01:09.985","Text":"and not CDK. It\u0027s p53."},{"Start":"01:09.985 ","End":"01:12.997","Text":"Remember, normal p53,"},{"Start":"01:12.997 ","End":"01:14.330","Text":"that\u0027s not mutated,"},{"Start":"01:14.330 ","End":"01:17.823","Text":"not the one that\u0027s going to cause cancer."},{"Start":"01:17.823 ","End":"01:23.710","Text":"But in a normal p53 cell damage that occurs to the cell during the cell cycle,"},{"Start":"01:23.710 ","End":"01:26.785","Text":"causes, among other things,"},{"Start":"01:26.785 ","End":"01:32.170","Text":"apoptosis programmed cell death."}],"ID":28296},{"Watched":false,"Name":"Exercise 17","Duration":"52s","ChapterTopicVideoID":27193,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:03.570","Text":"What are changes to the order of"},{"Start":"00:03.570 ","End":"00:06.870","Text":"the nucleotides in a segment of DNA that codes for a protein?"},{"Start":"00:06.870 ","End":"00:11.325","Text":"Are they proto-oncogenes that are changes to the order?"},{"Start":"00:11.325 ","End":"00:13.650","Text":"Are they tumor suppressor genes?"},{"Start":"00:13.650 ","End":"00:14.790","Text":"Are they gene mutations?"},{"Start":"00:14.790 ","End":"00:17.310","Text":"Or are they negative regulators?"},{"Start":"00:17.310 ","End":"00:20.175","Text":"Well, not proto-oncogenes, we know what those are."},{"Start":"00:20.175 ","End":"00:22.275","Text":"They\u0027re not tumor suppressor genes."},{"Start":"00:22.275 ","End":"00:24.540","Text":"They are not negative regulars, of course."},{"Start":"00:24.540 ","End":"00:26.640","Text":"They are gene mutations."},{"Start":"00:26.640 ","End":"00:31.320","Text":"Mutations are changes to"},{"Start":"00:31.320 ","End":"00:35.445","Text":"the order of nucleotides in a segment of DNA that codes for a protein."},{"Start":"00:35.445 ","End":"00:38.250","Text":"Actually, mutations could also be in a segment"},{"Start":"00:38.250 ","End":"00:41.057","Text":"of DNA that does not necessarily code for a protein,"},{"Start":"00:41.057 ","End":"00:44.560","Text":"it could also be some other kind of a regulator."},{"Start":"00:44.560 ","End":"00:47.900","Text":"At this point, we\u0027re talking mostly about mutations that"},{"Start":"00:47.900 ","End":"00:52.319","Text":"occur in DNA that encodes proteins."}],"ID":28297},{"Watched":false,"Name":"Exercise 18","Duration":"1m 6s","ChapterTopicVideoID":27194,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:05.565","Text":"A gene that codes for a positive cell-cycle regulator is called,"},{"Start":"00:05.565 ","End":"00:07.500","Text":"a kinase inhibitor,"},{"Start":"00:07.500 ","End":"00:09.705","Text":"a tumor suppressor gene,"},{"Start":"00:09.705 ","End":"00:13.305","Text":"a proto-oncogene, or an oncogene?"},{"Start":"00:13.305 ","End":"00:20.265","Text":"This is now a positive cell-cycle regulator and it\u0027s not a kinase inhibitor,"},{"Start":"00:20.265 ","End":"00:22.380","Text":"it\u0027s not a tumor suppressor gene,"},{"Start":"00:22.380 ","End":"00:24.405","Text":"and it\u0027s not an oncogene."},{"Start":"00:24.405 ","End":"00:28.560","Text":"Of course, it\u0027s a proto-oncogene."},{"Start":"00:28.560 ","End":"00:34.984","Text":"A proto-oncogene is going to be a positive cell cycle regulator."},{"Start":"00:34.984 ","End":"00:40.085","Text":"It will become an oncogene once it\u0027s mutated."},{"Start":"00:40.085 ","End":"00:44.540","Text":"It\u0027s before it becomes an oncogene and just a"},{"Start":"00:44.540 ","End":"00:50.180","Text":"normal piece of DNA that is a positive cell regulator."},{"Start":"00:50.180 ","End":"00:55.745","Text":"Of course, when there are cancer causing agents that might cause mutations,"},{"Start":"00:55.745 ","End":"01:00.320","Text":"then it may become an oncogene,"},{"Start":"01:00.320 ","End":"01:03.455","Text":"yes, which will cause cancer."},{"Start":"01:03.455 ","End":"01:06.030","Text":"That is the notation."}],"ID":28298},{"Watched":false,"Name":"Exercise 19","Duration":"43s","ChapterTopicVideoID":27195,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:03.750","Text":"Now a mutated gene that codes for"},{"Start":"00:03.750 ","End":"00:08.550","Text":"an altered version of a Cdk that is active in the absence of cyclin is a,"},{"Start":"00:08.550 ","End":"00:11.250","Text":"and this is simple because we just discussed it before."},{"Start":"00:11.250 ","End":"00:12.810","Text":"It\u0027s an altered version,"},{"Start":"00:12.810 ","End":"00:14.370","Text":"so it must be mutated."},{"Start":"00:14.370 ","End":"00:16.020","Text":"Would it be a kinase inhibitor?"},{"Start":"00:16.020 ","End":"00:18.390","Text":"No. Is it a tumor-suppressor gene?"},{"Start":"00:18.390 ","End":"00:21.060","Text":"No. Is it an oncogene?"},{"Start":"00:21.060 ","End":"00:25.260","Text":"Well, we\u0027ll see, or is it a proto-oncogene?"},{"Start":"00:25.260 ","End":"00:27.780","Text":"Well, of course, it\u0027s going to be the oncogene"},{"Start":"00:27.780 ","End":"00:30.930","Text":"for the same reason that we just discussed before."},{"Start":"00:30.930 ","End":"00:34.510","Text":"It\u0027s the proto-oncogene,"},{"Start":"00:35.030 ","End":"00:40.035","Text":"which becomes an oncogene."},{"Start":"00:40.035 ","End":"00:43.120","Text":"Yes, so it\u0027s this."}],"ID":28299},{"Watched":false,"Name":"Exercise 20","Duration":"51s","ChapterTopicVideoID":27196,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:05.055","Text":"Which molecule is CDK inhibitor that is controlled by p53?"},{"Start":"00:05.055 ","End":"00:07.560","Text":"A CDK inhibitor."},{"Start":"00:07.560 ","End":"00:12.330","Text":"Always look for the keyword being asked in the question. Is it cyclin?"},{"Start":"00:12.330 ","End":"00:14.025","Text":"Is it anti-kinase?"},{"Start":"00:14.025 ","End":"00:17.535","Text":"Is it Rb retinoblastoma or is it p21?"},{"Start":"00:17.535 ","End":"00:19.110","Text":"Well, it\u0027s not cyclin,"},{"Start":"00:19.110 ","End":"00:20.715","Text":"not an anti-kinase,"},{"Start":"00:20.715 ","End":"00:23.850","Text":"not retinoblastoma, it is p21."},{"Start":"00:23.850 ","End":"00:25.860","Text":"Remember this figure."},{"Start":"00:25.860 ","End":"00:35.070","Text":"P21 is the inhibitor of the CDK cyclin complexes."},{"Start":"00:35.070 ","End":"00:39.600","Text":"Therefore, Rb, if p21 is active, yes,"},{"Start":"00:39.600 ","End":"00:44.705","Text":"then the CDK cyclins will not be able to phosphorylate Rb."},{"Start":"00:44.705 ","End":"00:47.945","Text":"So it\u0027s a CDK inhibitor."},{"Start":"00:47.945 ","End":"00:51.690","Text":"Yes, it\u0027s a CDK inhibitor, p21."}],"ID":28300},{"Watched":false,"Name":"Exercise 21","Duration":"1m 4s","ChapterTopicVideoID":27197,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.860","Text":"Which eukaryotic cell cycle event is missing in binary fission?"},{"Start":"00:04.860 ","End":"00:08.069","Text":"Well, binary fission is bacteria."},{"Start":"00:08.069 ","End":"00:10.995","Text":"We\u0027re talking about division of bacteria."},{"Start":"00:10.995 ","End":"00:13.050","Text":"Is it cell growth?"},{"Start":"00:13.050 ","End":"00:16.065","Text":"No. Is it DNA duplication?"},{"Start":"00:16.065 ","End":"00:18.974","Text":"No. Is it karyokinesis?"},{"Start":"00:18.974 ","End":"00:23.055","Text":"Karyo, remember nucleus, kinesis."},{"Start":"00:23.055 ","End":"00:26.385","Text":"Well, karyo means nucleus,"},{"Start":"00:26.385 ","End":"00:30.525","Text":"remember, and we\u0027re talking about bacteria here. Well, let\u0027s see."},{"Start":"00:30.525 ","End":"00:33.770","Text":"Let\u0027s skip that one and go on to cytokinesis."},{"Start":"00:33.770 ","End":"00:37.730","Text":"Cytokinesis is separation of the cells it\u0027s not that either."},{"Start":"00:37.730 ","End":"00:39.140","Text":"It is karyokinesis."},{"Start":"00:39.140 ","End":"00:45.575","Text":"Remember, when we have binary fission of prokaryotes of bacteria,"},{"Start":"00:45.575 ","End":"00:47.555","Text":"there is no nucleus."},{"Start":"00:47.555 ","End":"00:50.960","Text":"That is certainly something which is"},{"Start":"00:50.960 ","End":"00:55.070","Text":"missing in binary fission because if there\u0027s no nucleus,"},{"Start":"00:55.070 ","End":"00:57.200","Text":"we can\u0027t have karyokinesis."},{"Start":"00:57.200 ","End":"01:04.230","Text":"The movement kinesis is movement of nuclei because it\u0027s not there."}],"ID":28301},{"Watched":false,"Name":"Exercise 22","Duration":"57s","ChapterTopicVideoID":27198,"CourseChapterTopicPlaylistID":237417,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.140","Text":"FtsZ proteins direct the formation of"},{"Start":"00:04.140 ","End":"00:09.555","Text":"what that will eventually form the new cell walls of the daughter cells."},{"Start":"00:09.555 ","End":"00:13.815","Text":"We\u0027re talking now about FtsZ proteins."},{"Start":"00:13.815 ","End":"00:16.725","Text":"Remember those are in bacteria."},{"Start":"00:16.725 ","End":"00:20.780","Text":"It\u0027s not going to be the contractile ring or is it"},{"Start":"00:20.780 ","End":"00:24.860","Text":"the cell plate or is it cytoskeleton or is it the septum?"},{"Start":"00:24.860 ","End":"00:26.690","Text":"Well, not the cytoskeleton."},{"Start":"00:26.690 ","End":"00:28.715","Text":"We\u0027re talking about bacteria here."},{"Start":"00:28.715 ","End":"00:30.170","Text":"It\u0027s not the septum,"},{"Start":"00:30.170 ","End":"00:31.895","Text":"it\u0027s the cell plate."},{"Start":"00:31.895 ","End":"00:36.320","Text":"Remember the FtsZ protein or the FtsZ protein"},{"Start":"00:36.320 ","End":"00:42.065","Text":"forms a ring of repeating units that directs the partition between the nucleotides."},{"Start":"00:42.065 ","End":"00:45.815","Text":"Nucleotides are where the DNA is"},{"Start":"00:45.815 ","End":"00:50.900","Text":"inside the bacteria and when the bacterium begins to divide,"},{"Start":"00:50.900 ","End":"00:57.300","Text":"this FtsZ ring begins to form separating the bacteria."}],"ID":28302}],"Thumbnail":null,"ID":237417},{"Name":"Meiosis and Sexual Reproduction","TopicPlaylistFirstVideoID":0,"Duration":null,"Videos":[{"Watched":false,"Name":"Meiosis and Sexual Reproduction","Duration":"2m 12s","ChapterTopicVideoID":25501,"CourseChapterTopicPlaylistID":237418,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:08.250","Text":"Welcome back. Now that you know something about mitosis and the division of cells,"},{"Start":"00:08.250 ","End":"00:14.999","Text":"let\u0027s continue on to sexual reproduction and what is required for sexual reproduction,"},{"Start":"00:14.999 ","End":"00:18.070","Text":"and that is meiosis."},{"Start":"00:18.620 ","End":"00:24.665","Text":"First of all, the ability to reproduce is a basic characteristic of all organisms."},{"Start":"00:24.665 ","End":"00:26.825","Text":"If something is alive,"},{"Start":"00:26.825 ","End":"00:28.549","Text":"it\u0027s got to reproduce."},{"Start":"00:28.549 ","End":"00:31.265","Text":"It\u0027s got to be able to make more copies,"},{"Start":"00:31.265 ","End":"00:35.540","Text":"either of itself or something very much like itself."},{"Start":"00:35.540 ","End":"00:39.920","Text":"Now you all know that a man and"},{"Start":"00:39.920 ","End":"00:46.495","Text":"a woman can get together and reproduce in the form of a child,"},{"Start":"00:46.495 ","End":"00:52.565","Text":"but the child is not exactly the same as either the mother or the father."},{"Start":"00:52.565 ","End":"00:57.125","Text":"This coming together is really sexual reproduction."},{"Start":"00:57.125 ","End":"01:00.270","Text":"Let\u0027s look at how that happens."},{"Start":"01:00.350 ","End":"01:03.560","Text":"First of all, the heredity is"},{"Start":"01:03.560 ","End":"01:07.594","Text":"the transmission of those traits from generation to generation."},{"Start":"01:07.594 ","End":"01:10.958","Text":"Now, some of the traits may clearly come from 1 parent,"},{"Start":"01:10.958 ","End":"01:15.050","Text":"and other traits really can\u0027t tell where they come from."},{"Start":"01:15.050 ","End":"01:19.505","Text":"There is some sort of a combination of the 2 parents."},{"Start":"01:19.505 ","End":"01:24.290","Text":"There is variation that is demonstrated by the differences between parents,"},{"Start":"01:24.290 ","End":"01:27.760","Text":"the offspring, and the siblings."},{"Start":"01:27.760 ","End":"01:35.300","Text":"Interestingly, the heredity and the variation together are what we call genetics."},{"Start":"01:35.300 ","End":"01:38.705","Text":"The genetics will explain to us,"},{"Start":"01:38.705 ","End":"01:43.400","Text":"if we can understand that exactly how it is that the characteristics,"},{"Start":"01:43.400 ","End":"01:53.000","Text":"the newborn are a combination of both parents and why it\u0027s variance between,"},{"Start":"01:53.000 ","End":"01:56.720","Text":"say, different siblings from the same 2 parents."},{"Start":"01:56.720 ","End":"01:58.805","Text":"In order to understand all that,"},{"Start":"01:58.805 ","End":"02:03.065","Text":"we need to understand meiosis to begin with."},{"Start":"02:03.065 ","End":"02:06.529","Text":"In the next 2 videos,"},{"Start":"02:06.529 ","End":"02:11.550","Text":"we\u0027re going to learn about the basics of meiosis."}],"ID":26318},{"Watched":false,"Name":"The Process of Meiosis Part a1","Duration":"5m 29s","ChapterTopicVideoID":25504,"CourseChapterTopicPlaylistID":237418,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.290 ","End":"00:05.235","Text":"Welcome back to our discussion of sexual reproduction."},{"Start":"00:05.235 ","End":"00:10.035","Text":"Sexual reproduction requires the formation of gametes,"},{"Start":"00:10.035 ","End":"00:13.080","Text":"which are 1n as opposed 2n,"},{"Start":"00:13.080 ","End":"00:17.445","Text":"and this occurs through a process called meiosis."},{"Start":"00:17.445 ","End":"00:21.510","Text":"This process of meiosis is fairly complex, fairly long."},{"Start":"00:21.510 ","End":"00:22.785","Text":"There are 2 parts to it."},{"Start":"00:22.785 ","End":"00:25.470","Text":"There\u0027s meiosis I and meiosis II,"},{"Start":"00:25.470 ","End":"00:28.530","Text":"and so we\u0027ve divided this video into 2 parts."},{"Start":"00:28.530 ","End":"00:31.560","Text":"The part 1 we\u0027ll discuss meiosis I,"},{"Start":"00:31.560 ","End":"00:35.025","Text":"and part 2 we\u0027ll discuss meiosis II."},{"Start":"00:35.025 ","End":"00:37.970","Text":"By the end of this entire section,"},{"Start":"00:37.970 ","End":"00:41.750","Text":"you should be able to describe the behavior of the chromosomes during meiosis"},{"Start":"00:41.750 ","End":"00:45.515","Text":"and the differences between the first and second meiotic divisions;"},{"Start":"00:45.515 ","End":"00:48.020","Text":"that\u0027s the meiosis I and meiosis II."},{"Start":"00:48.020 ","End":"00:53.415","Text":"You should be able to describe the cellular events that take place during meiosis."},{"Start":"00:53.415 ","End":"00:57.559","Text":"You should be able to explain the differences between meiosis and mitosis,"},{"Start":"00:57.559 ","End":"01:00.080","Text":"and we\u0027ll concentrate a bit on that,"},{"Start":"01:00.080 ","End":"01:03.830","Text":"showing you where they\u0027re the same and where there are different."},{"Start":"01:03.830 ","End":"01:08.630","Text":"You should be able to explain the mechanisms within the meiotic process that"},{"Start":"01:08.630 ","End":"01:13.315","Text":"produce genetic variation among the haploid gametes."},{"Start":"01:13.315 ","End":"01:16.110","Text":"There is tremendous genetic variation."},{"Start":"01:16.110 ","End":"01:21.230","Text":"We all know that 2 children that are born from the same parents,"},{"Start":"01:21.230 ","End":"01:22.610","Text":"if they\u0027re not identical twins,"},{"Start":"01:22.610 ","End":"01:24.290","Text":"are quite different from one another,"},{"Start":"01:24.290 ","End":"01:26.615","Text":"so how does that work?"},{"Start":"01:26.615 ","End":"01:31.690","Text":"First, let\u0027s look at the process of meiosis in detail."},{"Start":"01:31.690 ","End":"01:34.460","Text":"As we all know, during the cell cycle there is"},{"Start":"01:34.460 ","End":"01:40.205","Text":"an S phase during which time DNA is replicated."},{"Start":"01:40.205 ","End":"01:43.970","Text":"In this picture you can see that we have"},{"Start":"01:43.970 ","End":"01:48.530","Text":"a blue chromosome that may have come from the father,"},{"Start":"01:48.530 ","End":"01:53.305","Text":"and a red chromosome that may have come from the mother."},{"Start":"01:53.305 ","End":"01:58.875","Text":"These 2 chromosomes are homologous chromosomes."},{"Start":"01:58.875 ","End":"02:00.674","Text":"They\u0027re not the same,"},{"Start":"02:00.674 ","End":"02:04.220","Text":"but they\u0027re very, very similar."},{"Start":"02:04.220 ","End":"02:07.655","Text":"They\u0027re at least about 95 percent the same,"},{"Start":"02:07.655 ","End":"02:08.840","Text":"so they\u0027re quite similar."},{"Start":"02:08.840 ","End":"02:10.580","Text":"These are homologous chromosomes."},{"Start":"02:10.580 ","End":"02:15.470","Text":"All the chromosomes in the cell during the S phase of course duplicate,"},{"Start":"02:15.470 ","End":"02:19.999","Text":"and the DNA in this case is going to remain attached."},{"Start":"02:19.999 ","End":"02:21.925","Text":"The 2 different strands of DNA,"},{"Start":"02:21.925 ","End":"02:24.560","Text":"the 2 different copies of the chromosome,"},{"Start":"02:24.560 ","End":"02:28.010","Text":"will stay attached and will become what are called"},{"Start":"02:28.010 ","End":"02:33.685","Text":"sister chromatids into 1 duplicated chromosome."},{"Start":"02:33.685 ","End":"02:39.485","Text":"Now, the entire process of meiosis is going to generate"},{"Start":"02:39.485 ","End":"02:46.015","Text":"these gametes and each of which will have only 1 set of chromosomes."},{"Start":"02:46.015 ","End":"02:49.250","Text":"When the gametes unite during fertilization,"},{"Start":"02:49.250 ","End":"02:54.490","Text":"they\u0027ll form the zygote that contains the 2 sets of chromosomes."},{"Start":"02:54.490 ","End":"02:58.400","Text":"Sexual reproduction requires a nuclear division"},{"Start":"02:58.400 ","End":"03:01.250","Text":"that splits the number of chromosomes because we\u0027re starting"},{"Start":"03:01.250 ","End":"03:08.690","Text":"out with a 2n organism and each of the gametes is going to be only 1n,"},{"Start":"03:08.690 ","End":"03:15.235","Text":"so there has to be a reduction in chromosome number, half of them."},{"Start":"03:15.235 ","End":"03:25.205","Text":"Each of the parental chromosomes ends up in a separate cell at the end of meiosis II."},{"Start":"03:25.205 ","End":"03:31.080","Text":"Each somatic cell contains 2 copies of each chromosome as you know,"},{"Start":"03:31.080 ","End":"03:34.250","Text":"and those are the homologous chromosomes."},{"Start":"03:34.250 ","End":"03:36.905","Text":"Here we see again these homologous chromosomes."},{"Start":"03:36.905 ","End":"03:43.145","Text":"Diploid organisms inherit 1 copy of each homologous chromosome from each parent,"},{"Start":"03:43.145 ","End":"03:51.725","Text":"therefore the gametes must have in them only 1 of each homologous chromosome."},{"Start":"03:51.725 ","End":"03:55.415","Text":"Let\u0027s look at a bit more detail about meiosis."},{"Start":"03:55.415 ","End":"04:00.635","Text":"Nuclear division that forms 4 haploid cells from 1 diploid cell."},{"Start":"04:00.635 ","End":"04:06.138","Text":"In mitosis you\u0027ll remember that there\u0027s simply division of the cell in 2."},{"Start":"04:06.138 ","End":"04:09.635","Text":"There were 46 chromosomes in human cells,"},{"Start":"04:09.635 ","End":"04:14.090","Text":"and each of the cells after division also contains"},{"Start":"04:14.090 ","End":"04:19.925","Text":"46 chromosomes through a mechanism of mitosis that we learned about."},{"Start":"04:19.925 ","End":"04:22.685","Text":"Meiosis is actually quite similar,"},{"Start":"04:22.685 ","End":"04:27.220","Text":"except that there are 2 steps in this process that"},{"Start":"04:27.220 ","End":"04:32.105","Text":"yield 4 different gametes, 4 different cells."},{"Start":"04:32.105 ","End":"04:36.199","Text":"Each of them is not deployed, it is haploid."},{"Start":"04:36.199 ","End":"04:40.100","Text":"It has only 1 of each homologous chromosome."},{"Start":"04:40.100 ","End":"04:42.725","Text":"There\u0027s a first division."},{"Start":"04:42.725 ","End":"04:47.830","Text":"It\u0027s called the reduction division or first meiotic division,"},{"Start":"04:47.830 ","End":"04:52.020","Text":"and that will produce the 23 chromosomes,"},{"Start":"04:52.020 ","End":"04:56.270","Text":"and then we\u0027ll see how through a process that\u0027s quite similar to"},{"Start":"04:56.270 ","End":"05:01.325","Text":"mitosis we end up with 4 different gametes."},{"Start":"05:01.325 ","End":"05:04.910","Text":"This entire process of meiosis actually"},{"Start":"05:04.910 ","End":"05:08.250","Text":"employs many of the same cellular mechanisms as mitosis,"},{"Start":"05:08.250 ","End":"05:11.120","Text":"so you\u0027re quite familiar with a lot of it already,"},{"Start":"05:11.120 ","End":"05:14.045","Text":"except that there are these 2 rounds of division,"},{"Start":"05:14.045 ","End":"05:15.260","Text":"as I mentioned earlier,"},{"Start":"05:15.260 ","End":"05:20.505","Text":"that are called meiosis I and meiosis II."},{"Start":"05:20.505 ","End":"05:24.045","Text":"The 2 rounds result in the 4 daughter cells,"},{"Start":"05:24.045 ","End":"05:29.680","Text":"the 4 gametes, rather than the 2 cells that are found in mitosis."}],"ID":26321},{"Watched":false,"Name":"The Process of Meiosis Part a2","Duration":"6m 51s","ChapterTopicVideoID":25505,"CourseChapterTopicPlaylistID":237418,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.050 ","End":"00:05.190","Text":"Let\u0027s look in greater detail at what\u0027s going on and focus"},{"Start":"00:05.190 ","End":"00:10.275","Text":"on just 1 set of homologous chromosomes."},{"Start":"00:10.275 ","End":"00:12.330","Text":"At S phase, as we said,"},{"Start":"00:12.330 ","End":"00:16.980","Text":"there is duplication of the DNA forming for each"},{"Start":"00:16.980 ","End":"00:21.915","Text":"of the chromosomes in a 2-inch cell an additional copy of the DNA,"},{"Start":"00:21.915 ","End":"00:26.655","Text":"this replication, this is no different than anything that we\u0027ve learned earlier."},{"Start":"00:26.655 ","End":"00:31.170","Text":"However, from here things begin to change a little bit because"},{"Start":"00:31.170 ","End":"00:36.600","Text":"the resulting sister chromatids are closely associated along their lengths."},{"Start":"00:36.600 ","End":"00:39.540","Text":"There\u0027s cohesion. Whereas in normal mitosis,"},{"Start":"00:39.540 ","End":"00:41.875","Text":"what\u0027s going to happen is that they\u0027re going to separate,"},{"Start":"00:41.875 ","End":"00:44.960","Text":"and 1 copy is going to go into each cell."},{"Start":"00:44.960 ","End":"00:47.090","Text":"But in meiosis, to begin with,"},{"Start":"00:47.090 ","End":"00:52.250","Text":"they stay closely associated and they\u0027re stuck together"},{"Start":"00:52.250 ","End":"01:00.170","Text":"by various molecules that keep them together in the process of cohesion."},{"Start":"01:00.170 ","End":"01:08.090","Text":"The chromatids then are sorted into 4 haploid daughter cells at the end of the day."},{"Start":"01:08.090 ","End":"01:11.075","Text":"Before we looked at these cells,"},{"Start":"01:11.075 ","End":"01:16.379","Text":"there were 2 copies of each chromosome,"},{"Start":"01:16.379 ","End":"01:18.480","Text":"making 4 altogether,"},{"Start":"01:18.480 ","End":"01:23.340","Text":"2 originated in the father and 2 originated in the mother."},{"Start":"01:23.340 ","End":"01:26.700","Text":"At the end of the mitotic process,"},{"Start":"01:26.700 ","End":"01:31.985","Text":"1 copy from the father will be in 1 gamete,"},{"Start":"01:31.985 ","End":"01:34.175","Text":"1 copy will be in another gamete,"},{"Start":"01:34.175 ","End":"01:38.630","Text":"1 copy from the mother for the maternal DNA will be in 1 gamete,"},{"Start":"01:38.630 ","End":"01:42.755","Text":"and finally, the last 1 in the last gamete."},{"Start":"01:42.755 ","End":"01:45.755","Text":"So there are 4 haploid cells."},{"Start":"01:45.755 ","End":"01:49.165","Text":"However, it\u0027s actually a bit more complicated than that."},{"Start":"01:49.165 ","End":"01:52.815","Text":"Let\u0027s look at a little bit more detail."},{"Start":"01:52.815 ","End":"01:58.985","Text":"Meiosis is actually not too different from mitosis in the sense that it has a prophase,"},{"Start":"01:58.985 ","End":"02:01.100","Text":"a metaphase, anaphase,"},{"Start":"02:01.100 ","End":"02:04.070","Text":"and a telophase that results in cytokinesis,"},{"Start":"02:04.070 ","End":"02:06.100","Text":"just as we learned earlier."},{"Start":"02:06.100 ","End":"02:08.270","Text":"In the first phase,"},{"Start":"02:08.270 ","End":"02:12.601","Text":"in the prophase, prophase 1 because it\u0027s the first mitotic division,"},{"Start":"02:12.601 ","End":"02:15.305","Text":"the nuclear envelope begins to break down,"},{"Start":"02:15.305 ","End":"02:19.440","Text":"as is the case in mitosis."},{"Start":"02:19.440 ","End":"02:23.630","Text":"Here are the 4 stages and in each case,"},{"Start":"02:23.630 ","End":"02:31.055","Text":"the figure that is highlighted will be enlarged on the right in our diagrams."},{"Start":"02:31.055 ","End":"02:33.485","Text":"The nuclear envelope begins to break down."},{"Start":"02:33.485 ","End":"02:36.575","Text":"The proteins that are associated with homologous chromosomes,"},{"Start":"02:36.575 ","End":"02:41.280","Text":"bring the pair closer together."},{"Start":"02:41.280 ","End":"02:43.370","Text":"Here what you see is that you had"},{"Start":"02:43.370 ","End":"02:50.490","Text":"a duplicated maternal chromosome and the homologous paternal chromosome."},{"Start":"02:50.490 ","End":"02:51.810","Text":"Each of them is duplicated,"},{"Start":"02:51.810 ","End":"02:56.645","Text":"so they\u0027re actually 4 strands of DNA there. We\u0027ll see that in a minute."},{"Start":"02:56.645 ","End":"03:03.275","Text":"They are held together at various points by these chiasmata in"},{"Start":"03:03.275 ","End":"03:08.180","Text":"a formation that is called synapsis is"},{"Start":"03:08.180 ","End":"03:14.270","Text":"this pairing of the 2 homologous chromosomes."},{"Start":"03:14.270 ","End":"03:20.135","Text":"Now, notice that there are these chiasmata that hold them together"},{"Start":"03:20.135 ","End":"03:26.730","Text":"and there is the start of the forming of the spindle microtubules."},{"Start":"03:27.260 ","End":"03:31.565","Text":"Let\u0027s look a little bit more at the chiasmata."},{"Start":"03:31.565 ","End":"03:33.485","Text":"The chiasmata,"},{"Start":"03:33.485 ","End":"03:36.515","Text":"in these enlarged figures"},{"Start":"03:36.515 ","End":"03:41.360","Text":"are at locations that in which is particularly close association."},{"Start":"03:41.360 ","End":"03:44.915","Text":"Maybe you can see a little bit of enlargement of this area."},{"Start":"03:44.915 ","End":"03:49.715","Text":"The proteins that hold the 2 strands of DNA together forms"},{"Start":"03:49.715 ","End":"03:53.030","Text":"a protein structure between the homologous chromosomes"},{"Start":"03:53.030 ","End":"03:56.780","Text":"and that\u0027s called a synaptonemal complex."},{"Start":"03:56.780 ","End":"04:01.355","Text":"That\u0027s the complex of the 2 chromosomes that are being held together."},{"Start":"04:01.355 ","End":"04:07.220","Text":"Now it\u0027s really interesting and special about this is that at these chiasma,"},{"Start":"04:07.220 ","End":"04:10.240","Text":"there is a process of crossing over."},{"Start":"04:10.240 ","End":"04:15.575","Text":"A very special process in which the DNA is cut in both strands,"},{"Start":"04:15.575 ","End":"04:20.630","Text":"in the same position on both the maternal and paternal chromosomes and then they"},{"Start":"04:20.630 ","End":"04:26.585","Text":"crossover so that after an annealing or a connection,"},{"Start":"04:26.585 ","End":"04:31.310","Text":"a ligation of the DNA,"},{"Start":"04:31.310 ","End":"04:34.400","Text":"say the paternal with the maternal strands,"},{"Start":"04:34.400 ","End":"04:36.065","Text":"will get a chromosome,"},{"Start":"04:36.065 ","End":"04:42.920","Text":"which is at first all paternal and then continues on as maternal."},{"Start":"04:42.920 ","End":"04:46.025","Text":"Conversely, we\u0027ll have another one which started out"},{"Start":"04:46.025 ","End":"04:49.940","Text":"as all maternal and continuous as paternal."},{"Start":"04:49.940 ","End":"04:53.000","Text":"There\u0027s this process of crossing over."},{"Start":"04:53.000 ","End":"04:54.980","Text":"It happens as I said,"},{"Start":"04:54.980 ","End":"04:57.220","Text":"usually at these chiasmata."},{"Start":"04:57.220 ","End":"05:02.615","Text":"It can be observed visually in the microscope because all this happens"},{"Start":"05:02.615 ","End":"05:09.005","Text":"after the chromosomes have condensed and are therefore visible in the light microscope,"},{"Start":"05:09.005 ","End":"05:14.690","Text":"is crossing over events occur at recombination nodules at"},{"Start":"05:14.690 ","End":"05:22.720","Text":"particular places because they contain within them specific large protein assemblies."},{"Start":"05:22.720 ","End":"05:27.175","Text":"If we mark the points of these chiasmata,"},{"Start":"05:27.175 ","End":"05:32.300","Text":"then we can tell maybe where the crossover will be."},{"Start":"05:32.300 ","End":"05:36.050","Text":"Not at every chiasma is there a crossover,"},{"Start":"05:36.050 ","End":"05:38.935","Text":"but in many cases there is."},{"Start":"05:38.935 ","End":"05:42.890","Text":"They\u0027ll be near the recombination nodule and at"},{"Start":"05:42.890 ","End":"05:46.610","Text":"that point the double-stranded DNA of each chromatid is cleaved."},{"Start":"05:46.610 ","End":"05:50.480","Text":"The cut ends are modified so that they\u0027ll rely gate,"},{"Start":"05:50.480 ","End":"05:55.635","Text":"and then a new connection is made between the non-sister chromatids."},{"Start":"05:55.635 ","End":"06:03.395","Text":"Non-sister because 1 is from the paternal side and 1 is from the maternal side."},{"Start":"06:03.395 ","End":"06:07.204","Text":"Now we\u0027ll see the figure a little bit differently."},{"Start":"06:07.204 ","End":"06:11.750","Text":"Here we have the maternal and paternal chromosomes."},{"Start":"06:11.750 ","End":"06:17.015","Text":"Each of these is actually doubled, as we know,"},{"Start":"06:17.015 ","End":"06:21.950","Text":"and the synaptonemal complex begins to break down and the chromosomes"},{"Start":"06:21.950 ","End":"06:28.325","Text":"begin to condense at the same time as this crossing over occurs."},{"Start":"06:28.325 ","End":"06:31.070","Text":"Homologous chromosomes remain attached to each other"},{"Start":"06:31.070 ","End":"06:34.400","Text":"at the centromere and at the chiasmata, as we said."},{"Start":"06:34.400 ","End":"06:37.820","Text":"The number of chiasmata interestingly varies according"},{"Start":"06:37.820 ","End":"06:41.555","Text":"to the species and also the length of the chromosome."},{"Start":"06:41.555 ","End":"06:51.490","Text":"The numbers can vary very much between just 1 or 2 on each chromosome to as many as 25."}],"ID":26322},{"Watched":false,"Name":"The Process of Meiosis Part a3","Duration":"7m 58s","ChapterTopicVideoID":25499,"CourseChapterTopicPlaylistID":237418,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.410 ","End":"00:05.610","Text":"Here you can see a crossed over chromosome."},{"Start":"00:05.610 ","End":"00:10.080","Text":"It starts out as being blue and ends up as being red."},{"Start":"00:10.080 ","End":"00:14.610","Text":"Here\u0027s 1 that starts out being red and ends up being blue."},{"Start":"00:14.610 ","End":"00:25.215","Text":"What you have here actually are 4 different strands of DNA called a tetrad."},{"Start":"00:25.215 ","End":"00:29.470","Text":"These are called tetrads because tet means 4."},{"Start":"00:31.190 ","End":"00:36.915","Text":"Inside the tetrad, we get this crossing over at the chiasmata,"},{"Start":"00:36.915 ","End":"00:38.520","Text":"as we mentioned earlier."},{"Start":"00:38.520 ","End":"00:42.005","Text":"Here it\u0027s displayed even more clearly."},{"Start":"00:42.005 ","End":"00:44.480","Text":"Then after there is a resolution of this picture,"},{"Start":"00:44.480 ","End":"00:48.335","Text":"we get continuous blue to red,"},{"Start":"00:48.335 ","End":"00:50.930","Text":"red to blue chromosomes."},{"Start":"00:50.930 ","End":"00:57.080","Text":"That is the first source of genetic variation in the nuclei provided or"},{"Start":"00:57.080 ","End":"01:03.830","Text":"produced by meiosis because these crossing overs can occur anywhere along the chromosome."},{"Start":"01:03.830 ","End":"01:07.115","Text":"There may be reasons that are hotter than others,"},{"Start":"01:07.115 ","End":"01:09.725","Text":"might call them hotspots, but in general,"},{"Start":"01:09.725 ","End":"01:12.605","Text":"you can have this crossing over occur anywhere,"},{"Start":"01:12.605 ","End":"01:17.630","Text":"leading to almost infinite numbers of variations."},{"Start":"01:17.630 ","End":"01:23.225","Text":"Now notice that this reciprocal exchange of DNA between maternal and paternal chromosomes"},{"Start":"01:23.225 ","End":"01:30.020","Text":"leads to mixed DNA from both parents that did not exist before."},{"Start":"01:30.020 ","End":"01:32.060","Text":"It did not exist before,"},{"Start":"01:32.060 ","End":"01:37.780","Text":"because we\u0027ve got a new combination on 1 chromosome."},{"Start":"01:37.780 ","End":"01:40.190","Text":"The crossover events, as I said,"},{"Start":"01:40.190 ","End":"01:45.440","Text":"can occur almost anywhere along the length of the synapsed chromosomes."},{"Start":"01:45.440 ","End":"01:48.145","Text":"Let\u0027s see what happens next."},{"Start":"01:48.145 ","End":"01:54.110","Text":"In a different figure we will see that there is the attachment of"},{"Start":"01:54.110 ","End":"01:59.435","Text":"the spindle fiber microtubules to the kinetochore proteins of the centrosomes."},{"Start":"01:59.435 ","End":"02:02.940","Text":"This is very much like in mitosis."},{"Start":"02:02.940 ","End":"02:08.540","Text":"These microtubules will have grown from the microtubule organizing centers that are"},{"Start":"02:08.540 ","End":"02:14.300","Text":"at the edges of the cell at 2 different sides of it."},{"Start":"02:14.300 ","End":"02:17.060","Text":"Here\u0027s the microtubule organizing center."},{"Start":"02:17.060 ","End":"02:22.100","Text":"These microtubules will polymerize and grow and they will attach to"},{"Start":"02:22.100 ","End":"02:28.065","Text":"the centrosomes that are on the chromosomes and they attach,"},{"Start":"02:28.065 ","End":"02:30.120","Text":"as I said, to the centrosomes there at"},{"Start":"02:30.120 ","End":"02:33.800","Text":"the kinetochores of the 2 fused homologous chromosomes,"},{"Start":"02:33.800 ","End":"02:37.580","Text":"leading to a kinetochore microtubule."},{"Start":"02:37.580 ","End":"02:41.035","Text":"This is the kinetochore microtubule."},{"Start":"02:41.035 ","End":"02:48.950","Text":"That is what\u0027s going to pull the chromosomes apart once we reach anaphase."},{"Start":"02:48.950 ","End":"02:50.990","Text":"But at this stage,"},{"Start":"02:50.990 ","End":"02:54.410","Text":"the homologous chromosomes are still held together at"},{"Start":"02:54.410 ","End":"03:01.915","Text":"the chiasmata and the nuclear membrane is broken down entirely."},{"Start":"03:01.915 ","End":"03:10.040","Text":"Let\u0027s go back to the previous figure in which you can see that at"},{"Start":"03:10.040 ","End":"03:13.100","Text":"this point the homologous chromosomes are arranged at"},{"Start":"03:13.100 ","End":"03:18.710","Text":"the metaphase plate with the kinetochores facing opposite poles,"},{"Start":"03:18.710 ","End":"03:21.665","Text":"very much like in mitosis."},{"Start":"03:21.665 ","End":"03:24.440","Text":"Except there\u0027s 1 big difference here."},{"Start":"03:24.440 ","End":"03:26.855","Text":"This is extremely important."},{"Start":"03:26.855 ","End":"03:28.775","Text":"Have a look at this picture."},{"Start":"03:28.775 ","End":"03:36.620","Text":"You see that in this figure we have the red maternal chromosomes facing down."},{"Start":"03:36.620 ","End":"03:40.010","Text":"They\u0027re going to end up in the cell that\u0027s going to end up at the bottom."},{"Start":"03:40.010 ","End":"03:41.300","Text":"On the other hand,"},{"Start":"03:41.300 ","End":"03:43.444","Text":"the same homologous chromosome,"},{"Start":"03:43.444 ","End":"03:46.715","Text":"paternal 1 is going to end up in the top 1."},{"Start":"03:46.715 ","End":"03:52.225","Text":"However, another chromosome, a different chromosome, in that 1,"},{"Start":"03:52.225 ","End":"03:56.170","Text":"the paternal 1 is going to end up at the bottom and the"},{"Start":"03:56.170 ","End":"04:00.760","Text":"maternal 1 will end up at the top."},{"Start":"04:00.760 ","End":"04:03.595","Text":"This alignment is random."},{"Start":"04:03.595 ","End":"04:06.249","Text":"Every cell will do it differently."},{"Start":"04:06.249 ","End":"04:10.525","Text":"Homologous pairs orient themselves randomly at the equator,"},{"Start":"04:10.525 ","End":"04:13.180","Text":"and that is very important in determining"},{"Start":"04:13.180 ","End":"04:17.410","Text":"the genes that are going to be carried by a particular cell,"},{"Start":"04:17.410 ","End":"04:19.180","Text":"by a particular gamete."},{"Start":"04:19.180 ","End":"04:21.580","Text":"Now the number of combinations is enormous."},{"Start":"04:21.580 ","End":"04:31.925","Text":"The number of combinations is 23 chromosomes and so the number of combinations is 2^23,"},{"Start":"04:31.925 ","End":"04:38.930","Text":"which is over 8 million possible combinations of paternal and maternal chromosomes."},{"Start":"04:38.930 ","End":"04:41.030","Text":"If you add that to"},{"Start":"04:41.030 ","End":"04:45.920","Text":"the different combinations that arise because of crossing over as we just saw,"},{"Start":"04:45.920 ","End":"04:50.255","Text":"then you can appreciate that the number of"},{"Start":"04:50.255 ","End":"04:54.650","Text":"differences in combinations that can arise in the gametes is enormous."},{"Start":"04:54.650 ","End":"04:57.920","Text":"Therefore, it\u0027s not surprising that"},{"Start":"04:57.920 ","End":"05:02.460","Text":"the children of parents are different from 1 another,"},{"Start":"05:02.460 ","End":"05:04.805","Text":"the siblings are different from 1 another,"},{"Start":"05:04.805 ","End":"05:07.475","Text":"unless, of course, they\u0027re identical twins."},{"Start":"05:07.475 ","End":"05:13.280","Text":"The randomness coupled with the crossing over events are responsible for pretty"},{"Start":"05:13.280 ","End":"05:19.410","Text":"much all of the genetic variation in the offspring of a couple."},{"Start":"05:19.420 ","End":"05:21.860","Text":"We just discussed metaphase."},{"Start":"05:21.860 ","End":"05:23.060","Text":"Let\u0027s move on to anaphase."},{"Start":"05:23.060 ","End":"05:27.395","Text":"In anaphase, remember that the chromosomes are separated."},{"Start":"05:27.395 ","End":"05:32.345","Text":"At this point, the microtubules pull the linked chromosomes apart."},{"Start":"05:32.345 ","End":"05:34.060","Text":"Remember they\u0027re still linked,"},{"Start":"05:34.060 ","End":"05:37.099","Text":"so they are tightly bound at the centromere."},{"Start":"05:37.099 ","End":"05:40.550","Text":"But at the same time the chiasmata begin to break"},{"Start":"05:40.550 ","End":"05:44.990","Text":"apart as the microtubules pull the homologous chromosomes,"},{"Start":"05:44.990 ","End":"05:47.220","Text":"so they\u0027re being pulled in this direction,"},{"Start":"05:47.220 ","End":"05:55.550","Text":"but the connections at the chiasmata between the homologous chromosomes begins to fray."},{"Start":"05:55.550 ","End":"05:59.855","Text":"Finally we reach telophase and cytokinesis,"},{"Start":"05:59.855 ","End":"06:05.585","Text":"in which the chromosomes find themselves in separated cells."},{"Start":"06:05.585 ","End":"06:08.685","Text":"There\u0027s a cleavage furrow which occurs"},{"Start":"06:08.685 ","End":"06:13.910","Text":"and the chromosomes are separated into 2 separate cells."},{"Start":"06:13.910 ","End":"06:17.840","Text":"Now further events may or may not occur depending on the species."},{"Start":"06:17.840 ","End":"06:19.285","Text":"What events?"},{"Start":"06:19.285 ","End":"06:23.760","Text":"Well, the DNA might decondense into something which is more like"},{"Start":"06:23.760 ","End":"06:29.115","Text":"interface chromatin that we have in mitosis,"},{"Start":"06:29.115 ","End":"06:37.605","Text":"and envelopes may form around these chromosomes to form nuclei in these separated cells."},{"Start":"06:37.605 ","End":"06:40.160","Text":"This may happen or may not."},{"Start":"06:40.160 ","End":"06:42.110","Text":"It depends on the species,"},{"Start":"06:42.110 ","End":"06:43.520","Text":"it depends on the organisms."},{"Start":"06:43.520 ","End":"06:48.540","Text":"Cytokinesis sometimes can occur even without the reformation nuclei."},{"Start":"06:48.540 ","End":"06:54.290","Text":"At this stage, it very much depends upon which organisms we\u0027re talking about."},{"Start":"06:54.290 ","End":"07:02.360","Text":"In humans, we do have this separation and they can last for a long time with nuclei."},{"Start":"07:02.360 ","End":"07:05.630","Text":"2 haploid cells are formed,"},{"Start":"07:05.630 ","End":"07:12.125","Text":"though each chromosome notice still consists of 2 sister chromatids."},{"Start":"07:12.125 ","End":"07:18.630","Text":"We\u0027ve got these 2 sister chromatids that are on 1 chromosome."},{"Start":"07:18.740 ","End":"07:21.770","Text":"Let\u0027s summarize up to here."},{"Start":"07:21.770 ","End":"07:23.240","Text":"In Meiosis 1,"},{"Start":"07:23.240 ","End":"07:29.400","Text":"creates a huge genetically diverse collection of gametes."},{"Start":"07:29.400 ","End":"07:30.950","Text":"This happens in 2 ways."},{"Start":"07:30.950 ","End":"07:34.130","Text":"First, there\u0027s the crossover between"},{"Start":"07:34.130 ","End":"07:38.215","Text":"non-sister chromatids of each homologous pair of chromosomes,"},{"Start":"07:38.215 ","End":"07:43.850","Text":"and there is random assortment then of these chromosomes afterwards into"},{"Start":"07:43.850 ","End":"07:46.580","Text":"the different gametes and there\u0027s a sorting of"},{"Start":"07:46.580 ","End":"07:52.060","Text":"the maternal and paternal chromosomes at the metaphase plate."},{"Start":"07:52.060 ","End":"07:54.000","Text":"In the next video,"},{"Start":"07:54.000 ","End":"07:57.760","Text":"we\u0027ll look at Meiosis 2."}],"ID":26316},{"Watched":false,"Name":"The Process of Meiosis Part b","Duration":"7m 25s","ChapterTopicVideoID":25500,"CourseChapterTopicPlaylistID":237418,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.620 ","End":"00:04.380","Text":"Now in our discussion of sexual reproduction,"},{"Start":"00:04.380 ","End":"00:06.420","Text":"until now we\u0027ve concentrated on"},{"Start":"00:06.420 ","End":"00:11.430","Text":"meiosis I that you should all be experts at, at this point."},{"Start":"00:11.430 ","End":"00:17.920","Text":"Now we\u0027re going to be discussing meiosis II in this Part 2 of the video."},{"Start":"00:18.140 ","End":"00:20.820","Text":"Right after meiosis I,"},{"Start":"00:20.820 ","End":"00:24.735","Text":"there is a phase called interkinesis,"},{"Start":"00:24.735 ","End":"00:28.595","Text":"which is right after cytokinesis."},{"Start":"00:28.595 ","End":"00:30.200","Text":"It\u0027s like interface,"},{"Start":"00:30.200 ","End":"00:33.950","Text":"it\u0027s a period during which not a lot happens and it"},{"Start":"00:33.950 ","End":"00:37.970","Text":"may be shorter and it may be longer depending on the organism."},{"Start":"00:37.970 ","End":"00:40.330","Text":"In some species, cells enter"},{"Start":"00:40.330 ","End":"00:43.640","Text":"this brief interkinesis or sometimes it\u0027s called"},{"Start":"00:43.640 ","End":"00:47.615","Text":"interphase II before entering meiosis II."},{"Start":"00:47.615 ","End":"00:50.840","Text":"But unlike interface I,"},{"Start":"00:50.840 ","End":"00:54.050","Text":"interkinesis lacks an S phase."},{"Start":"00:54.050 ","End":"00:56.030","Text":"Now, usually during interphase,"},{"Start":"00:56.030 ","End":"00:57.695","Text":"remember there is an S phase."},{"Start":"00:57.695 ","End":"01:03.875","Text":"The chromosomes are duplicated in this interkinesis there is no S phase,"},{"Start":"01:03.875 ","End":"01:08.565","Text":"therefore there is no duplication of the chromosomes."},{"Start":"01:08.565 ","End":"01:11.915","Text":"However, the microtubules do reassemble"},{"Start":"01:11.915 ","End":"01:15.320","Text":"into 2 new spindles for the second meiotic division,"},{"Start":"01:15.320 ","End":"01:20.810","Text":"and in many plants will find that they will actually skip"},{"Start":"01:20.810 ","End":"01:23.705","Text":"this telophase I and interkinesis and they\u0027ll go"},{"Start":"01:23.705 ","End":"01:28.625","Text":"directly into prophase II when they produce their gametes,"},{"Start":"01:28.625 ","End":"01:35.300","Text":"which could be pollen or the eggs that are formed in flowers."},{"Start":"01:35.300 ","End":"01:38.555","Text":"Let\u0027s now look at meiosis II."},{"Start":"01:38.555 ","End":"01:41.330","Text":"Meiosis II has a prophase,"},{"Start":"01:41.330 ","End":"01:43.445","Text":"a metaphase, an anaphase, and a telophase,"},{"Start":"01:43.445 ","End":"01:48.785","Text":"just like we\u0027re used to and they are synchronous,"},{"Start":"01:48.785 ","End":"01:51.395","Text":"went during in the different cells."},{"Start":"01:51.395 ","End":"01:58.220","Text":"The 2 cells produced in meiosis I go through meiosis II synchronously."},{"Start":"01:58.220 ","End":"02:03.830","Text":"Each cell has half the number of sister chromatids to separate out as a diploid cell."},{"Start":"02:03.830 ","End":"02:08.075","Text":"Remember, we started out in the case of humans with 46 chromosomes,"},{"Start":"02:08.075 ","End":"02:10.970","Text":"and after meiosis I,"},{"Start":"02:10.970 ","End":"02:15.005","Text":"the reduction division, we have only 23."},{"Start":"02:15.005 ","End":"02:19.880","Text":"The sister chromatids, in this case in meiosis II weak become"},{"Start":"02:19.880 ","End":"02:25.580","Text":"separated and ultimately for new haploid gametes are formed."},{"Start":"02:25.580 ","End":"02:27.940","Text":"Let\u0027s, as we did before,"},{"Start":"02:27.940 ","End":"02:30.000","Text":"look at the details."},{"Start":"02:30.000 ","End":"02:31.855","Text":"In prophase II,"},{"Start":"02:31.855 ","End":"02:35.720","Text":"if the chromosomes were decondensed in telophase I,"},{"Start":"02:35.720 ","End":"02:38.270","Text":"they have to re-condense."},{"Start":"02:38.270 ","End":"02:40.865","Text":"If the nuclear envelopes were formed,"},{"Start":"02:40.865 ","End":"02:44.210","Text":"they during this interkinesis period,"},{"Start":"02:44.210 ","End":"02:50.780","Text":"they have to fragment into vesicles so that we can get division as we did before."},{"Start":"02:50.780 ","End":"02:53.930","Text":"The chromosomes and the microtubule organizing centers,"},{"Start":"02:53.930 ","End":"02:57.350","Text":"the MTOCs that were associated with them are"},{"Start":"02:57.350 ","End":"03:02.015","Text":"duplicated during interkinesis and they move away from each other."},{"Start":"03:02.015 ","End":"03:06.980","Text":"You can see them here moving to each other and to opposite poles of the cell,"},{"Start":"03:06.980 ","End":"03:09.760","Text":"and new spindles are formed."},{"Start":"03:09.760 ","End":"03:16.250","Text":"Then we get into metaphase and it starts with a prometaphase."},{"Start":"03:16.250 ","End":"03:20.665","Text":"Of course everything is 2 because we\u0027re in the second meiotic division."},{"Start":"03:20.665 ","End":"03:24.455","Text":"So nuclear envelopes in this phase are completely broken down."},{"Start":"03:24.455 ","End":"03:27.080","Text":"The spindle is completely formed,"},{"Start":"03:27.080 ","End":"03:31.280","Text":"and then just as we are familiar with before,"},{"Start":"03:31.280 ","End":"03:36.130","Text":"the chromosomes line up on the plates,"},{"Start":"03:36.130 ","End":"03:39.755","Text":"the metaphase plate that\u0027s between the 2 cells,"},{"Start":"03:39.755 ","End":"03:48.010","Text":"and they are connected to the microtubules that are emanating from the opposite poles."},{"Start":"03:48.010 ","End":"03:51.110","Text":"Metaphase itself, the sister chromatids are maximally"},{"Start":"03:51.110 ","End":"03:54.140","Text":"condensed and they\u0027re aligned at the equator."},{"Start":"03:54.140 ","End":"03:57.020","Text":"Then finally we move into anaphase."},{"Start":"03:57.020 ","End":"04:01.275","Text":"Anaphase you\u0027ll remember is the separation of the chromosomes,"},{"Start":"04:01.275 ","End":"04:03.470","Text":"and in this case, just like before,"},{"Start":"04:03.470 ","End":"04:07.790","Text":"the sister chromatids are pulled apart and they move towards the opposite poles,"},{"Start":"04:07.790 ","End":"04:13.030","Text":"and the cell becomes elongated by the non-kinetochore microtubules,"},{"Start":"04:13.030 ","End":"04:22.250","Text":"and ultimately we\u0027re going to get separation of the chromosomes into 2 separate cells."},{"Start":"04:22.250 ","End":"04:25.960","Text":"At this point, let\u0027s look at the differences in"},{"Start":"04:25.960 ","End":"04:30.760","Text":"chromosome alignment between meiosis I and meiosis II."},{"Start":"04:30.760 ","End":"04:35.140","Text":"In prometaphase I, the microtubules attach to"},{"Start":"04:35.140 ","End":"04:41.785","Text":"the fused kinetochores of homologous chromosomes in prometaphase II."},{"Start":"04:41.785 ","End":"04:43.600","Text":"In meiosis II,"},{"Start":"04:43.600 ","End":"04:48.969","Text":"the microtubules attach to the individual kinetochore of the sister chromatids."},{"Start":"04:48.969 ","End":"04:55.090","Text":"Because here we had 2 chromatids that were connected in meiosis I whereas in meiosis II,"},{"Start":"04:55.090 ","End":"04:59.795","Text":"we\u0027ve only got 1 copy of each chromosome."},{"Start":"04:59.795 ","End":"05:02.840","Text":"In metaphase I,"},{"Start":"05:02.840 ","End":"05:09.020","Text":"now homologous chromosomes are arranged at the midline of the cell and in metaphase II,"},{"Start":"05:09.020 ","End":"05:13.460","Text":"the sister chromatids are also arranged at the midpoints of the cells,"},{"Start":"05:13.460 ","End":"05:16.605","Text":"but they are in metaphase II, of course."},{"Start":"05:16.605 ","End":"05:18.385","Text":"In anaphase I,"},{"Start":"05:18.385 ","End":"05:20.326","Text":"the separation of the chromatids,"},{"Start":"05:20.326 ","End":"05:28.470","Text":"the homologous chromatids separate both in anaphase I and in anaphase II."},{"Start":"05:28.610 ","End":"05:37.555","Text":"Let\u0027s now continue and look at telophase and cytokinesis in meiosis II."},{"Start":"05:37.555 ","End":"05:41.840","Text":"The chromosomes arrive at opposite poles and begin"},{"Start":"05:41.840 ","End":"05:46.310","Text":"to decondense to go into something that\u0027s more like interface,"},{"Start":"05:46.310 ","End":"05:49.850","Text":"nuclear envelopes form and they form around the chromosomes."},{"Start":"05:49.850 ","End":"05:54.650","Text":"Cytokinesis separates the cells as they do,"},{"Start":"05:54.650 ","End":"06:02.540","Text":"this cleavage furrow is created just as is done in other cell divisions,"},{"Start":"06:02.540 ","End":"06:08.270","Text":"both meiosis I and mitosis and the cells that are produced,"},{"Start":"06:08.270 ","End":"06:12.890","Text":"the 4 cells that are produced are going to be genetically unique."},{"Start":"06:12.890 ","End":"06:15.705","Text":"Why? Well, remember,"},{"Start":"06:15.705 ","End":"06:23.090","Text":"because of both crossing over and the random distribution of the chromosomes."},{"Start":"06:23.090 ","End":"06:27.110","Text":"Finally, let\u0027s compare meiosis and mitosis."},{"Start":"06:27.110 ","End":"06:30.560","Text":"Mitosis keeps the number of chromosomes sets."},{"Start":"06:30.560 ","End":"06:32.630","Text":"we have the same number of chromosomes."},{"Start":"06:32.630 ","End":"06:33.845","Text":"We started with 2n,"},{"Start":"06:33.845 ","End":"06:40.280","Text":"and we end up with 2n creating cells that are genetically identical to the parent cell."},{"Start":"06:40.280 ","End":"06:46.025","Text":"Whereas in meiosis, the products are each going to be different"},{"Start":"06:46.025 ","End":"06:53.015","Text":"genetically from their parents because of those 2 things I mentioned,"},{"Start":"06:53.015 ","End":"06:59.905","Text":"because of crossing over and random distribution of the chromosomes."},{"Start":"06:59.905 ","End":"07:05.195","Text":"The main differences between mitosis and meiosis occur in meiosis I."},{"Start":"07:05.195 ","End":"07:10.135","Text":"There you have synapsis and crossing over in prophase I,"},{"Start":"07:10.135 ","End":"07:16.990","Text":"you have homologous pairs at the metaphase plates that will distribute randomly,"},{"Start":"07:16.990 ","End":"07:23.170","Text":"and you have separation of homologs during anaphase I."}],"ID":26317},{"Watched":false,"Name":"Sexual Reproduction Part a1","Duration":"6m 48s","ChapterTopicVideoID":25502,"CourseChapterTopicPlaylistID":237418,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.270 ","End":"00:05.800","Text":"Until now, we\u0027ve discussed meiosis to a considerable degree and of course,"},{"Start":"00:05.800 ","End":"00:09.400","Text":"the purpose of meiosis is to produce gametes."},{"Start":"00:09.400 ","End":"00:14.320","Text":"That is to produce sperm and eggs in higher organisms."},{"Start":"00:14.320 ","End":"00:19.600","Text":"The next thing that happens as you all know is fertilization."},{"Start":"00:19.600 ","End":"00:22.360","Text":"That\u0027s what sexual reproduction is all about."},{"Start":"00:22.360 ","End":"00:27.505","Text":"It\u0027s about bringing these gametes together and as you all know,"},{"Start":"00:27.505 ","End":"00:30.460","Text":"there is a tremendous drive for this to happen."},{"Start":"00:30.460 ","End":"00:34.540","Text":"Therefore, there must be a biological reason for it."},{"Start":"00:34.540 ","End":"00:38.710","Text":"The question is, why is sex fun?"},{"Start":"00:38.710 ","End":"00:45.500","Text":"Let\u0027s see if we can figure out a little bit of that from a biological perspective."},{"Start":"00:45.500 ","End":"00:47.739","Text":"By the end of this section,"},{"Start":"00:47.739 ","End":"00:50.390","Text":"you should be able to explain that meiosis"},{"Start":"00:50.390 ","End":"00:54.035","Text":"and sexual reproduction are highly evolved traits,"},{"Start":"00:54.035 ","End":"00:57.379","Text":"you should be able to identify variation among offspring"},{"Start":"00:57.379 ","End":"01:01.025","Text":"as a potential evolutionary advantage."},{"Start":"01:01.025 ","End":"01:03.590","Text":"Evolutionary advantage, that\u0027s going to be the answer really to"},{"Start":"01:03.590 ","End":"01:08.060","Text":"our question of sexual reproduction and you should"},{"Start":"01:08.060 ","End":"01:11.465","Text":"be able to describe the 3 different life-cycle types"},{"Start":"01:11.465 ","End":"01:15.975","Text":"among sexually reproducing multi-cellular organisms."},{"Start":"01:15.975 ","End":"01:21.895","Text":"You\u0027ll see there are different life-cycles not everybody does the same thing as we do."},{"Start":"01:21.895 ","End":"01:25.220","Text":"They may do it in different ways. Let\u0027s have a look."},{"Start":"01:25.220 ","End":"01:31.330","Text":"First of all, you all know that there\u0027s a father and a mother and when"},{"Start":"01:31.330 ","End":"01:37.420","Text":"they come together to fertilize the egg with the sperm,"},{"Start":"01:37.420 ","End":"01:40.480","Text":"then you can get a child."},{"Start":"01:40.480 ","End":"01:45.310","Text":"You get a new organism that comes out and this new organism"},{"Start":"01:45.310 ","End":"01:50.245","Text":"has a unique combination of genes that is inherited from both parents."},{"Start":"01:50.245 ","End":"01:52.675","Text":"We\u0027ve discussed that a bit earlier."},{"Start":"01:52.675 ","End":"01:57.460","Text":"It turns out that most eukaryotes can and do reproduce"},{"Start":"01:57.460 ","End":"02:03.565","Text":"sexually and often it is the only mode of reproduction, but not always."},{"Start":"02:03.565 ","End":"02:07.085","Text":"We\u0027ll see that a little bit later."},{"Start":"02:07.085 ","End":"02:11.900","Text":"Now, I don\u0027t know if it\u0027s easy for you or hard for you to think about disadvantages,"},{"Start":"02:11.900 ","End":"02:13.715","Text":"maybe you think there are only advantages,"},{"Start":"02:13.715 ","End":"02:15.740","Text":"but actually, from a biological perspective,"},{"Start":"02:15.740 ","End":"02:20.089","Text":"we can think of disadvantages of sexual reproduction."},{"Start":"02:20.089 ","End":"02:23.570","Text":"First of all, you might think that"},{"Start":"02:23.570 ","End":"02:28.100","Text":"there is an advantage of creating more of something that is perfect."},{"Start":"02:28.100 ","End":"02:30.785","Text":"You\u0027ve got a well-adapted organism,"},{"Start":"02:30.785 ","End":"02:33.035","Text":"why not make more of it?"},{"Start":"02:33.035 ","End":"02:36.980","Text":"Those would be genetic clones and at the face of it,"},{"Start":"02:36.980 ","End":"02:44.250","Text":"this might appear to be a better system than continually mixing up the genome."},{"Start":"02:44.300 ","End":"02:50.480","Text":"Another thing is that sexual reproduction requires another organism of the opposite sex."},{"Start":"02:50.480 ","End":"02:55.715","Text":"Let\u0027s say you\u0027re a well-adapted organism leaving out in the middle of nowhere"},{"Start":"02:55.715 ","End":"03:02.300","Text":"and there are very few organisms that are of the same species as you,"},{"Start":"03:02.300 ","End":"03:05.599","Text":"you may not be able to find a mate and therefore,"},{"Start":"03:05.599 ","End":"03:09.855","Text":"the genes that are so well adapted in you could die out."},{"Start":"03:09.855 ","End":"03:12.390","Text":"Maybe that\u0027s a disadvantage."},{"Start":"03:12.390 ","End":"03:16.025","Text":"Furthermore of course there\u0027s a slow growth rate of a population like this."},{"Start":"03:16.025 ","End":"03:17.600","Text":"It doesn\u0027t happen very quickly."},{"Start":"03:17.600 ","End":"03:20.030","Text":"If all you have to do is just double"},{"Start":"03:20.030 ","End":"03:24.125","Text":"yourself through mitosis or something like that just to clone yourself,"},{"Start":"03:24.125 ","End":"03:26.000","Text":"that could maybe happen very quickly,"},{"Start":"03:26.000 ","End":"03:31.025","Text":"but if you have to find a mate each time it can happen very slowly."},{"Start":"03:31.025 ","End":"03:36.290","Text":"We all know about that when it comes to sometimes people getting"},{"Start":"03:36.290 ","End":"03:42.600","Text":"older in life and never finding a mate and they then don\u0027t have children."},{"Start":"03:42.830 ","End":"03:47.085","Text":"Sexual reproduction and why it\u0027s so good,"},{"Start":"03:47.085 ","End":"03:56.035","Text":"why it\u0027s so important as a reproductive strategy is a central question in Biology."},{"Start":"03:56.035 ","End":"03:59.665","Text":"Let\u0027s see if we can answer this central question in Biology."},{"Start":"03:59.665 ","End":"04:01.145","Text":"Let\u0027s look, for instance,"},{"Start":"04:01.145 ","End":"04:06.620","Text":"let\u0027s say at a bug that has some mutation that occurs in it,"},{"Start":"04:06.620 ","End":"04:09.680","Text":"and now it becomes resistant to a pesticide."},{"Start":"04:09.680 ","End":"04:12.740","Text":"Well, clearly that\u0027s an advantage for it."},{"Start":"04:12.740 ","End":"04:19.445","Text":"A different bug may have some mutation in it that causes it to be better camouflaged."},{"Start":"04:19.445 ","End":"04:25.835","Text":"Well, that gives an advantage but if there is sexual reproduction between these 2 bugs,"},{"Start":"04:25.835 ","End":"04:30.980","Text":"and they can make a new bug that\u0027s got both camouflage and"},{"Start":"04:30.980 ","End":"04:36.410","Text":"pesticide resistance then this bug is doing much better than any of its parents."},{"Start":"04:36.410 ","End":"04:42.845","Text":"It\u0027s this combination really of new traits that arise by mutation,"},{"Start":"04:42.845 ","End":"04:49.430","Text":"which can give this new bug advantage because of sexual reproduction."},{"Start":"04:49.430 ","End":"04:52.970","Text":"The variation among offspring is"},{"Start":"04:52.970 ","End":"04:56.715","Text":"very important to the survival and reproduction of population."},{"Start":"04:56.715 ","End":"05:00.320","Text":"There could be variation of, let\u0027s say,"},{"Start":"05:00.320 ","End":"05:04.685","Text":"this new mutation such that it is not present in a new bug,"},{"Start":"05:04.685 ","End":"05:08.115","Text":"in the babies of this bug but it could be present,"},{"Start":"05:08.115 ","End":"05:09.335","Text":"same thing could be here."},{"Start":"05:09.335 ","End":"05:11.135","Text":"There\u0027s tremendous variation."},{"Start":"05:11.135 ","End":"05:12.395","Text":"As we mentioned earlier,"},{"Start":"05:12.395 ","End":"05:16.880","Text":"meiosis causes huge variation and therefore it can"},{"Start":"05:16.880 ","End":"05:21.440","Text":"test the environment basically many different ways."},{"Start":"05:21.440 ","End":"05:25.700","Text":"There are all combinations of traits that may give an"},{"Start":"05:25.700 ","End":"05:30.755","Text":"organism an advantage in the surrounding environment,"},{"Start":"05:30.755 ","End":"05:34.660","Text":"and therefore it might survive better."},{"Start":"05:34.660 ","End":"05:41.750","Text":"This sexual reproduction allows a tremendous variation among offspring"},{"Start":"05:41.750 ","End":"05:48.864","Text":"that is not possible in simple clonal reproduction or simple divisions."},{"Start":"05:48.864 ","End":"05:54.855","Text":"In fact, in asexual organisms that is those that just divide,"},{"Start":"05:54.855 ","End":"06:01.730","Text":"the only source of variation it\u0027s a mutation and not this variation in the offspring."},{"Start":"06:01.730 ","End":"06:07.205","Text":"Of course, in sexually reproducing organisms like this bug,"},{"Start":"06:07.205 ","End":"06:09.124","Text":"there are also mutations."},{"Start":"06:09.124 ","End":"06:13.370","Text":"I just showed you an example of how these mutations can come together"},{"Start":"06:13.370 ","End":"06:18.700","Text":"to produce more of a super-bug if you like, a super-bug."},{"Start":"06:18.700 ","End":"06:22.595","Text":"In contrast to mutations during asexual reproduction,"},{"Start":"06:22.595 ","End":"06:26.000","Text":"that is non-sexual asexual reproduction,"},{"Start":"06:26.000 ","End":"06:28.910","Text":"mutations during sexual reproduction can be"},{"Start":"06:28.910 ","End":"06:32.360","Text":"continually reshuffled as it\u0027s being done with"},{"Start":"06:32.360 ","End":"06:35.000","Text":"this bug from 1 generation to the next when"},{"Start":"06:35.000 ","End":"06:39.770","Text":"different parents combine their genomes and therefore,"},{"Start":"06:39.770 ","End":"06:43.820","Text":"new environmental conditions that arise may be able to be dealt"},{"Start":"06:43.820 ","End":"06:49.080","Text":"with more efficiently than with an asexual reproduction."}],"ID":26319},{"Watched":false,"Name":"Sexual Reproduction Part a2","Duration":"16m 35s","ChapterTopicVideoID":25503,"CourseChapterTopicPlaylistID":237418,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.270 ","End":"00:05.050","Text":"Until now, we\u0027ve discussed meiosis to a considerable degree,"},{"Start":"00:05.050 ","End":"00:09.400","Text":"and of course, the purpose of meiosis is to produce gametes."},{"Start":"00:09.400 ","End":"00:14.320","Text":"That is to produce sperm and eggs in higher organisms."},{"Start":"00:14.320 ","End":"00:16.240","Text":"The next thing that happens,"},{"Start":"00:16.240 ","End":"00:19.600","Text":"as you all know, is fertilization."},{"Start":"00:19.600 ","End":"00:22.390","Text":"That\u0027s what sexual reproduction is all about,"},{"Start":"00:22.390 ","End":"00:25.360","Text":"it\u0027s about bringing these gametes together."},{"Start":"00:25.360 ","End":"00:27.505","Text":"As you all know,"},{"Start":"00:27.505 ","End":"00:30.370","Text":"there is a tremendous drive for this to happen,"},{"Start":"00:30.370 ","End":"00:34.540","Text":"and therefore, there must be a biological reason for it."},{"Start":"00:34.540 ","End":"00:38.725","Text":"The question is, why is sex fun?"},{"Start":"00:38.725 ","End":"00:45.500","Text":"Let\u0027s see if we can figure out a little bit of that from a biological perspective."},{"Start":"00:45.500 ","End":"00:47.755","Text":"By the end of this section,"},{"Start":"00:47.755 ","End":"00:50.720","Text":"you should be able to explain that meiosis and"},{"Start":"00:50.720 ","End":"00:54.070","Text":"sexual reproduction are highly evolved traits."},{"Start":"00:54.070 ","End":"00:57.379","Text":"You should be able to identify variation among offspring"},{"Start":"00:57.379 ","End":"01:01.025","Text":"as a potential evolutionary advantage."},{"Start":"01:01.025 ","End":"01:03.590","Text":"Evolutionary advantage, that\u0027s going to be the answer really to"},{"Start":"01:03.590 ","End":"01:07.015","Text":"our question of sexual reproduction."},{"Start":"01:07.015 ","End":"01:09.000","Text":"You should be able to describe"},{"Start":"01:09.000 ","End":"01:15.890","Text":"the 3 different life cycle types among sexually reproducing multicellular organisms."},{"Start":"01:15.890 ","End":"01:18.755","Text":"You\u0027ll see there are different life cycles,"},{"Start":"01:18.755 ","End":"01:21.895","Text":"not everybody does the same thing as we do,"},{"Start":"01:21.895 ","End":"01:25.220","Text":"they may do it in different ways. Let\u0027s have a look."},{"Start":"01:25.220 ","End":"01:31.330","Text":"First of all, you all know that there\u0027s a father and a mother and when"},{"Start":"01:31.330 ","End":"01:37.420","Text":"they come together to fertilize the egg with the sperm,"},{"Start":"01:37.420 ","End":"01:40.480","Text":"then you can get a child,"},{"Start":"01:40.480 ","End":"01:45.310","Text":"you get a new organism that comes out and this new organism"},{"Start":"01:45.310 ","End":"01:50.230","Text":"has a unique combination of genes that is inherited from both parents."},{"Start":"01:50.230 ","End":"01:52.675","Text":"We\u0027ve discussed that a bit earlier."},{"Start":"01:52.675 ","End":"01:56.950","Text":"It turns out that most eukaryotes can and do"},{"Start":"01:56.950 ","End":"02:01.240","Text":"reproduce sexually and often it is the only mode of reproduction,"},{"Start":"02:01.240 ","End":"02:07.085","Text":"but not always and we\u0027ll see that a little bit later."},{"Start":"02:07.085 ","End":"02:11.900","Text":"Now I don\u0027t know if it\u0027s easy for you or hard for you to think about disadvantages,"},{"Start":"02:11.900 ","End":"02:13.715","Text":"maybe you think there are only advantages,"},{"Start":"02:13.715 ","End":"02:15.740","Text":"but actually from a biological perspective,"},{"Start":"02:15.740 ","End":"02:20.089","Text":"we can think of disadvantages of sexual reproduction."},{"Start":"02:20.089 ","End":"02:23.570","Text":"First of all, you might think that"},{"Start":"02:23.570 ","End":"02:28.234","Text":"there is an advantage of creating more of something that is perfect."},{"Start":"02:28.234 ","End":"02:30.785","Text":"You\u0027ve got a well-adapted organism,"},{"Start":"02:30.785 ","End":"02:33.035","Text":"why not make more of it?"},{"Start":"02:33.035 ","End":"02:35.765","Text":"Those would be genetic clones."},{"Start":"02:35.765 ","End":"02:39.560","Text":"At the face of it, this might appear to be a better system"},{"Start":"02:39.560 ","End":"02:44.250","Text":"than continually mixing up the genome."},{"Start":"02:44.300 ","End":"02:50.480","Text":"Another thing is that sexual reproduction requires another organism of the opposite sex."},{"Start":"02:50.480 ","End":"02:55.715","Text":"Let\u0027s say, your well-adapted organism living out in the middle of nowhere"},{"Start":"02:55.715 ","End":"03:02.450","Text":"and there are very few organisms that are of the same species as you,"},{"Start":"03:02.450 ","End":"03:05.689","Text":"you may not be able to find a mate and therefore,"},{"Start":"03:05.689 ","End":"03:10.050","Text":"the genes that are so well adapted in you could die out."},{"Start":"03:10.050 ","End":"03:12.180","Text":"Maybe that\u0027s a disadvantage."},{"Start":"03:12.180 ","End":"03:16.060","Text":"Furthermore, of course, there\u0027s a slow growth rate of a population like this."},{"Start":"03:16.060 ","End":"03:19.325","Text":"It doesn\u0027t happen very quickly if all you have to do is"},{"Start":"03:19.325 ","End":"03:22.940","Text":"just double yourself through mitosis or something like that,"},{"Start":"03:22.940 ","End":"03:24.160","Text":"just to clone yourself,"},{"Start":"03:24.160 ","End":"03:26.195","Text":"that could maybe happen very quickly."},{"Start":"03:26.195 ","End":"03:28.864","Text":"But if you have to find a mate each time,"},{"Start":"03:28.864 ","End":"03:34.520","Text":"it can happen very slowly and we all know about that when it comes to"},{"Start":"03:34.520 ","End":"03:37.940","Text":"sometimes people getting older in life and never finding"},{"Start":"03:37.940 ","End":"03:42.600","Text":"a mate and they then don\u0027t have children."},{"Start":"03:42.830 ","End":"03:47.085","Text":"Sexual reproduction and why it\u0027s so good,"},{"Start":"03:47.085 ","End":"03:56.045","Text":"why it\u0027s so important as a reproductive strategy is a central question in biology."},{"Start":"03:56.045 ","End":"03:59.665","Text":"Let\u0027s see if we can answer this central question in biology."},{"Start":"03:59.665 ","End":"04:01.760","Text":"Let\u0027s look, for instance, let\u0027s say,"},{"Start":"04:01.760 ","End":"04:05.690","Text":"at a bug that has some mutation that"},{"Start":"04:05.690 ","End":"04:09.695","Text":"occurs in it and now it becomes resistant to pesticides,"},{"Start":"04:09.695 ","End":"04:12.725","Text":"well, clearly that\u0027s an advantage for it."},{"Start":"04:12.725 ","End":"04:19.450","Text":"A different bug may have some mutation in it that causes it to be better camouflaged,"},{"Start":"04:19.450 ","End":"04:21.945","Text":"well, that gives an advantage,"},{"Start":"04:21.945 ","End":"04:26.990","Text":"but if their sexual reproduction between these 2 bugs and they can make"},{"Start":"04:26.990 ","End":"04:32.585","Text":"a new bug that\u0027s got both camouflage and pesticide resistance,"},{"Start":"04:32.585 ","End":"04:36.650","Text":"then this bug is doing much better than any of its parents."},{"Start":"04:36.650 ","End":"04:42.080","Text":"It\u0027s this combination really of new traits that arise by"},{"Start":"04:42.080 ","End":"04:49.425","Text":"mutation which can give this new bug advantage because of sexual reproduction."},{"Start":"04:49.425 ","End":"04:52.970","Text":"The variation among offspring is"},{"Start":"04:52.970 ","End":"04:57.225","Text":"very important to the survival and reproduction of the population."},{"Start":"04:57.225 ","End":"05:00.320","Text":"There could be variation of, let\u0027s say,"},{"Start":"05:00.320 ","End":"05:06.490","Text":"this new mutation such that it is not present in a new bug in the babies of this bug,"},{"Start":"05:06.490 ","End":"05:08.090","Text":"but it could be present,"},{"Start":"05:08.090 ","End":"05:09.335","Text":"the same thing could be here."},{"Start":"05:09.335 ","End":"05:11.140","Text":"There\u0027s tremendous variation,"},{"Start":"05:11.140 ","End":"05:12.410","Text":"as we mentioned earlier,"},{"Start":"05:12.410 ","End":"05:16.520","Text":"miosis causes huge variation and therefore,"},{"Start":"05:16.520 ","End":"05:18.860","Text":"it can test the environment basically,"},{"Start":"05:18.860 ","End":"05:21.470","Text":"many, many different ways."},{"Start":"05:21.470 ","End":"05:25.100","Text":"There are all sorts of combinations of traits that may give"},{"Start":"05:25.100 ","End":"05:30.770","Text":"an organism an advantage in the surrounding environment,"},{"Start":"05:30.770 ","End":"05:34.660","Text":"and therefore, it might survive better."},{"Start":"05:34.660 ","End":"05:41.750","Text":"This sexual reproduction allows a tremendous variation among offspring"},{"Start":"05:41.750 ","End":"05:48.865","Text":"that is not possible in simple clonal reproduction or simple divisions."},{"Start":"05:48.865 ","End":"05:52.340","Text":"In fact, in asexual organisms,"},{"Start":"05:52.340 ","End":"05:54.845","Text":"that is those that just divide,"},{"Start":"05:54.845 ","End":"06:01.730","Text":"the only source of variation it\u0027s a mutation and not this variation in the offspring."},{"Start":"06:01.730 ","End":"06:07.205","Text":"Of course, in sexually reproducing organisms like this bug,"},{"Start":"06:07.205 ","End":"06:09.139","Text":"there are also mutations."},{"Start":"06:09.139 ","End":"06:13.370","Text":"I just showed you an example of how these mutations can come together"},{"Start":"06:13.370 ","End":"06:18.695","Text":"to produce more of a superbug if you like superbug."},{"Start":"06:18.695 ","End":"06:22.595","Text":"In contrast to mutations during asexual reproduction,"},{"Start":"06:22.595 ","End":"06:25.999","Text":"that is non-sexual asexual reproduction."},{"Start":"06:25.999 ","End":"06:28.910","Text":"Mutations during sexual reproduction can be"},{"Start":"06:28.910 ","End":"06:32.360","Text":"continually reshuffled as it\u0027s being done with"},{"Start":"06:32.360 ","End":"06:35.000","Text":"this bug from 1 generation to the next when"},{"Start":"06:35.000 ","End":"06:39.770","Text":"different parents combine their genomes and therefore,"},{"Start":"06:39.770 ","End":"06:43.820","Text":"new environmental conditions that arise may be able to be dealt"},{"Start":"06:43.820 ","End":"06:49.045","Text":"with more efficiently than with an asexual reproduction."},{"Start":"06:49.045 ","End":"06:52.860","Text":"Since sex is so good,"},{"Start":"06:52.860 ","End":"06:57.945","Text":"it turns out that lots of different kinds of organisms, in fact,"},{"Start":"06:57.945 ","End":"07:01.730","Text":"most eukaryotic organisms as we said earlier do engage"},{"Start":"07:01.730 ","End":"07:06.745","Text":"in some form of sex but they do it somewhat differently."},{"Start":"07:06.745 ","End":"07:10.515","Text":"The way mammals do it we\u0027re quite familiar."},{"Start":"07:10.515 ","End":"07:16.515","Text":"In mammals, most of our cells in our bodies are 2n,"},{"Start":"07:16.515 ","End":"07:18.180","Text":"they\u0027ve got 2 sets of the chromosomes,"},{"Start":"07:18.180 ","End":"07:19.780","Text":"as we mentioned earlier,"},{"Start":"07:19.780 ","End":"07:25.380","Text":"we have the formation of gametes via meiosis."},{"Start":"07:25.380 ","End":"07:28.935","Text":"Then if we look at just 1 of those gametes,"},{"Start":"07:28.935 ","End":"07:34.340","Text":"it does not undergo mitosis as it does in some of the other systems."},{"Start":"07:34.340 ","End":"07:35.900","Text":"It does not divide,"},{"Start":"07:35.900 ","End":"07:40.160","Text":"it just sits around and waits until it can be used in"},{"Start":"07:40.160 ","End":"07:45.370","Text":"fertilization to make another zygote, which is 2n."},{"Start":"07:45.370 ","End":"07:51.095","Text":"That\u0027s what we know about most of the cells of our body are 2n"},{"Start":"07:51.095 ","End":"07:57.976","Text":"in mitosis and the dominant situation then is diploid."},{"Start":"07:57.976 ","End":"08:03.715","Text":"We\u0027ll see in a minute that other organisms do this a little bit differently."},{"Start":"08:03.715 ","End":"08:08.530","Text":"If we just look at what we\u0027re most familiar with these mammals,"},{"Start":"08:08.530 ","End":"08:13.195","Text":"then we have 2 life cycles, really."},{"Start":"08:13.195 ","End":"08:18.970","Text":"We have a 2n life cycle and we have a n life cycle."},{"Start":"08:18.970 ","End":"08:23.740","Text":"That\u0027s more pronounced in lower organisms than in mammals."},{"Start":"08:23.740 ","End":"08:27.175","Text":"As we know, meiosis divides the chromosome number by half"},{"Start":"08:27.175 ","End":"08:30.400","Text":"and fertilization restores the diploid condition,"},{"Start":"08:30.400 ","End":"08:34.690","Text":"and therefore, all of these figures can be drawn as a circle."},{"Start":"08:34.690 ","End":"08:38.980","Text":"The 3 main type sexual life cycles that are presented"},{"Start":"08:38.980 ","End":"08:43.045","Text":"here differ in the timing of meiosis and fertilization."},{"Start":"08:43.045 ","End":"08:46.375","Text":"There\u0027s really not much of a difference between"},{"Start":"08:46.375 ","End":"08:51.130","Text":"very simple organisms and us in most of these respects."},{"Start":"08:51.130 ","End":"08:55.074","Text":"The differences are really just in the details."},{"Start":"08:55.074 ","End":"09:00.550","Text":"Let\u0027s start out again by looking at mammals."},{"Start":"09:00.550 ","End":"09:03.985","Text":"Most employ a diploid dominant strategy."},{"Start":"09:03.985 ","End":"09:07.375","Text":"Most of the cells in the body are diploid and"},{"Start":"09:07.375 ","End":"09:13.074","Text":"only haploid cells are produced in the course of making gametes."},{"Start":"09:13.074 ","End":"09:15.565","Text":"At the embryonic stage,"},{"Start":"09:15.565 ","End":"09:21.430","Text":"then specialized diploid germ cells are produced within the gonads. What\u0027s this about?"},{"Start":"09:21.430 ","End":"09:24.190","Text":"So, how are these gametes made?"},{"Start":"09:24.190 ","End":"09:30.040","Text":"Actually when we are embryos in our mother\u0027s womb, then of course,"},{"Start":"09:30.040 ","End":"09:33.460","Text":"those cells then differentiate into different cell types,"},{"Start":"09:33.460 ","End":"09:38.620","Text":"1 of the cell types that they develop into are called germ cells."},{"Start":"09:38.620 ","End":"09:40.480","Text":"That doesn\u0027t mean that they\u0027re sick."},{"Start":"09:40.480 ","End":"09:46.105","Text":"On the contrary, it means that those germ cells are going to differentiate"},{"Start":"09:46.105 ","End":"09:52.840","Text":"later into either eggs or sperm depending on the sex of the embryo."},{"Start":"09:52.840 ","End":"09:57.295","Text":"The germ cells are capable of mitosis so that they"},{"Start":"09:57.295 ","End":"10:02.530","Text":"make more and more and more of the precursors to the sperm and eggs,"},{"Start":"10:02.530 ","End":"10:06.160","Text":"and they perpetuate the germ cell line until"},{"Start":"10:06.160 ","End":"10:10.360","Text":"meiosis occurs that produces the haploid gametes,"},{"Start":"10:10.360 ","End":"10:14.005","Text":"the haploid sperm and egg."},{"Start":"10:14.005 ","End":"10:17.980","Text":"There is no multicellular haploid life stage."},{"Start":"10:17.980 ","End":"10:19.660","Text":"Well, we don\u0027t quite understand what that is,"},{"Start":"10:19.660 ","End":"10:24.700","Text":"but let\u0027s wait until we see how ferns do it, for instance,"},{"Start":"10:24.700 ","End":"10:30.535","Text":"and then we\u0027ll understand that there is a multicellular haploid life stage in ferns,"},{"Start":"10:30.535 ","End":"10:32.485","Text":"but not in us."},{"Start":"10:32.485 ","End":"10:35.500","Text":"Fertilization occurs when the fusion of 2 gametes,"},{"Start":"10:35.500 ","End":"10:37.779","Text":"usually from different individuals."},{"Start":"10:37.779 ","End":"10:40.615","Text":"We know about fertilization."},{"Start":"10:40.615 ","End":"10:43.375","Text":"Now let\u0027s look at another extreme."},{"Start":"10:43.375 ","End":"10:47.350","Text":"Let\u0027s look now at sexual reproduction in plants"},{"Start":"10:47.350 ","End":"10:51.325","Text":"and in some algae who do it somewhat differently, and in particular,"},{"Start":"10:51.325 ","End":"10:57.085","Text":"let\u0027s think about an organism that is single-celled,"},{"Start":"10:57.085 ","End":"11:00.430","Text":"as a good example, for instance, yeast."},{"Start":"11:00.430 ","End":"11:09.430","Text":"Yeast can be either haploid or it can be diploid."},{"Start":"11:09.430 ","End":"11:14.665","Text":"In other words, a single cell that we find can be either diploid or haploid."},{"Start":"11:14.665 ","End":"11:16.330","Text":"What happens then,"},{"Start":"11:16.330 ","End":"11:21.160","Text":"the diploid actually can undergo mitosis like normal,"},{"Start":"11:21.160 ","End":"11:23.005","Text":"make many of them,"},{"Start":"11:23.005 ","End":"11:26.410","Text":"then it can undergo meiosis such that there\u0027s"},{"Start":"11:26.410 ","End":"11:30.175","Text":"a reduction in the chromosomes so that it only has 1 copy of each of them,"},{"Start":"11:30.175 ","End":"11:32.110","Text":"and there are things that you might"},{"Start":"11:32.110 ","End":"11:36.055","Text":"consider gametes that are produced and let\u0027s follow 1 of them."},{"Start":"11:36.055 ","End":"11:39.205","Text":"It can also undergo mitosis."},{"Start":"11:39.205 ","End":"11:43.120","Text":"This is different than we had,"},{"Start":"11:43.120 ","End":"11:46.060","Text":"for instance in humans or in mammals."},{"Start":"11:46.060 ","End":"11:50.290","Text":"The gametes did not undergo mitosis."},{"Start":"11:50.290 ","End":"11:53.920","Text":"But in the yeast they can undergo mitosis and they can"},{"Start":"11:53.920 ","End":"11:57.550","Text":"do this for many generations until they"},{"Start":"11:57.550 ","End":"12:05.140","Text":"meet up with another cell of the opposite mating type of the opposite sex,"},{"Start":"12:05.140 ","End":"12:07.539","Text":"if you like, and then there can be fertilization."},{"Start":"12:07.539 ","End":"12:09.100","Text":"There\u0027s a fusion between the cells,"},{"Start":"12:09.100 ","End":"12:10.540","Text":"fusion between the nuclei,"},{"Start":"12:10.540 ","End":"12:16.000","Text":"and again, the formation of a 2n organism."},{"Start":"12:16.000 ","End":"12:23.755","Text":"Note this 2n organism is probably better served in its environment than a n,"},{"Start":"12:23.755 ","End":"12:28.060","Text":"because a mutation in 1 of the chromosomes in"},{"Start":"12:28.060 ","End":"12:32.890","Text":"the 2n may not kill it even if that mutation"},{"Start":"12:32.890 ","End":"12:36.880","Text":"is lethal because it\u0027s got an additional chromosome"},{"Start":"12:36.880 ","End":"12:42.175","Text":"that might encode the protein that is defective in the mutation,"},{"Start":"12:42.175 ","End":"12:45.220","Text":"so 2n survives a little bit better."},{"Start":"12:45.220 ","End":"12:53.320","Text":"But again, we\u0027ve got 2 different cycles here and we\u0027ve got an alternation of generation."},{"Start":"12:53.320 ","End":"12:58.930","Text":"We have a blend of the haploid dominant and diploid dominant extremes,"},{"Start":"12:58.930 ","End":"13:04.405","Text":"yes, in haploid and diploid multicellular organisms as part of their life cycle."},{"Start":"13:04.405 ","End":"13:08.110","Text":"Here we\u0027re looking actually at single cell organisms,"},{"Start":"13:08.110 ","End":"13:12.610","Text":"but multi-cell organisms can do this sometimes as well."},{"Start":"13:12.610 ","End":"13:16.255","Text":"In some cases in these diploid organisms,"},{"Start":"13:16.255 ","End":"13:21.925","Text":"the diploid organisms make something that are called spores, haploid spores."},{"Start":"13:21.925 ","End":"13:25.390","Text":"Those organisms are called sporophytes,"},{"Start":"13:25.390 ","End":"13:34.570","Text":"and they grow by mitosis into a haploid organism that\u0027s called a gametophyte."},{"Start":"13:34.570 ","End":"13:38.275","Text":"That\u0027s this duplication over here."},{"Start":"13:38.275 ","End":"13:41.230","Text":"Since it\u0027s a multicellular organism,"},{"Start":"13:41.230 ","End":"13:44.695","Text":"then it will be a little bit different than yeast."},{"Start":"13:44.695 ","End":"13:49.059","Text":"Gametophyte makes haploid gametes by mitosis."},{"Start":"13:49.059 ","End":"13:53.050","Text":"So we\u0027ll see that there can be some differentiation also."},{"Start":"13:53.050 ","End":"13:57.925","Text":"Fertilization of gametes results in a diploid sporophyte."},{"Start":"13:57.925 ","End":"14:03.250","Text":"The sporophyte is diploid and the gametophyte is haploid."},{"Start":"14:03.250 ","End":"14:05.860","Text":"Those are the 2 generations,"},{"Start":"14:05.860 ","End":"14:08.200","Text":"the alterations of generations."},{"Start":"14:08.200 ","End":"14:10.885","Text":"Let\u0027s see this for instance,"},{"Start":"14:10.885 ","End":"14:13.510","Text":"in a different a picture."},{"Start":"14:13.510 ","End":"14:16.525","Text":"Here we have the body of the organism,"},{"Start":"14:16.525 ","End":"14:21.055","Text":"so here it\u0027s a multi cellular organism in this,"},{"Start":"14:21.055 ","End":"14:24.130","Text":"for instance, ferns will do this."},{"Start":"14:24.130 ","End":"14:26.485","Text":"It\u0027s a gametophyte."},{"Start":"14:26.485 ","End":"14:31.780","Text":"These cells are haploid and this looks like a plant here,"},{"Start":"14:31.780 ","End":"14:34.030","Text":"and it also does the same story."},{"Start":"14:34.030 ","End":"14:38.290","Text":"The haploid cells can undergo"},{"Start":"14:38.290 ","End":"14:43.990","Text":"mitosis and differentiate into something that looks like an organism,"},{"Start":"14:43.990 ","End":"14:50.215","Text":"but there can be, by specialized organs,"},{"Start":"14:50.215 ","End":"14:56.800","Text":"there can be fertilization of these gametes into making a 2n organism."},{"Start":"14:56.800 ","End":"15:03.610","Text":"The 2n organism may look somewhat similar to the n organism,"},{"Start":"15:03.610 ","End":"15:06.865","Text":"except that it will have"},{"Start":"15:06.865 ","End":"15:15.970","Text":"a diploid multicellular structure that can undergo meiosis making these spores again."},{"Start":"15:15.970 ","End":"15:19.120","Text":"These plants, if you like,"},{"Start":"15:19.120 ","End":"15:22.570","Text":"make spores, when they are fertilized,"},{"Start":"15:22.570 ","End":"15:24.790","Text":"when they come together,"},{"Start":"15:24.790 ","End":"15:29.650","Text":"they will make another form of the organism which is diploid."},{"Start":"15:29.650 ","End":"15:33.880","Text":"Again, here we have 2 different forms of the organism,"},{"Start":"15:33.880 ","End":"15:38.980","Text":"and those mating types can be called plus and minus."},{"Start":"15:38.980 ","End":"15:42.910","Text":"The zygote, then which is formed immediately"},{"Start":"15:42.910 ","End":"15:47.995","Text":"undergoes meiosis to form 4 haploid cells that are called spores."},{"Start":"15:47.995 ","End":"15:57.155","Text":"This meiosis is going to form 4 haploid cells just as we saw in normal meiosis."},{"Start":"15:57.155 ","End":"16:03.080","Text":"The spores form multicellular haploid structures through many rounds of mitosis."},{"Start":"16:03.080 ","End":"16:06.920","Text":"In this section, we learned how to explain that meiosis"},{"Start":"16:06.920 ","End":"16:10.215","Text":"and sexual reproduction are highly evolved traits,"},{"Start":"16:10.215 ","End":"16:15.545","Text":"in this last picture here you can see this is very evolved,"},{"Start":"16:15.545 ","End":"16:19.250","Text":"we identify variation among offspring as"},{"Start":"16:19.250 ","End":"16:24.085","Text":"a potential evolutionary advantage of sexual reproduction and we stressed that,"},{"Start":"16:24.085 ","End":"16:28.850","Text":"and we described the 3 different life-cycle types among sexually"},{"Start":"16:28.850 ","End":"16:35.190","Text":"reproducing multicellular organisms. Hope you enjoyed it."}],"ID":26320},{"Watched":false,"Name":"Exercise 1","Duration":"1m 1s","ChapterTopicVideoID":27028,"CourseChapterTopicPlaylistID":237418,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:05.445","Text":"Now that we\u0027ve watched the number of videos regarding meiosis and sexual reproduction,"},{"Start":"00:05.445 ","End":"00:11.730","Text":"let\u0027s see if we can remember what we\u0027ve learned by doing the following exercises."},{"Start":"00:11.730 ","End":"00:16.830","Text":"Meiosis usually produces what kinds of cells?"},{"Start":"00:16.830 ","End":"00:19.290","Text":"Are they, 2 haploid cells,"},{"Start":"00:19.290 ","End":"00:22.395","Text":"2 diploid cells, 4 haploid cells,"},{"Start":"00:22.395 ","End":"00:24.615","Text":"or 4 diploid cells?"},{"Start":"00:24.615 ","End":"00:29.610","Text":"Well, clearly they\u0027re not haploid, 2 of them."},{"Start":"00:29.610 ","End":"00:32.835","Text":"They\u0027re not 2 diploid cells."},{"Start":"00:32.835 ","End":"00:35.445","Text":"They\u0027re not 4 diploid cells."},{"Start":"00:35.445 ","End":"00:38.640","Text":"There are 4 haploid cells which are produced,"},{"Start":"00:38.640 ","End":"00:42.510","Text":"often those are going to be gametes."},{"Start":"00:42.510 ","End":"00:51.600","Text":"Remember, there is Meiosis 1 and Meiosis 2 that will produce in the end 1,"},{"Start":"00:51.600 ","End":"00:56.730","Text":"2, 3, 4 gametes."},{"Start":"00:56.730 ","End":"01:02.140","Text":"They\u0027ll be 4 haploid cells that will be produced."}],"ID":28153},{"Watched":false,"Name":"Exercise 2","Duration":"1m 15s","ChapterTopicVideoID":27029,"CourseChapterTopicPlaylistID":237418,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:05.490","Text":"What structure is most important in forming the tetrads?"},{"Start":"00:05.490 ","End":"00:07.160","Text":"Is it the centromere,"},{"Start":"00:07.160 ","End":"00:09.545","Text":"is it the synaptonemal complex,"},{"Start":"00:09.545 ","End":"00:11.330","Text":"is it the chiasma,"},{"Start":"00:11.330 ","End":"00:13.360","Text":"or is it the kinetochore?"},{"Start":"00:13.360 ","End":"00:16.500","Text":"Now let\u0027s remember what each of these is."},{"Start":"00:16.500 ","End":"00:20.925","Text":"Well, the centromere is a sequence of DNA at which"},{"Start":"00:20.925 ","End":"00:27.660","Text":"the proteins bind that keep the chromosomes together just before anaphase."},{"Start":"00:27.660 ","End":"00:30.450","Text":"The synaptonemal complex, is that the answer?"},{"Start":"00:30.450 ","End":"00:33.345","Text":"Well, we\u0027ll see. Is it the chiasma?"},{"Start":"00:33.345 ","End":"00:35.235","Text":"No, it\u0027s not the chiasma."},{"Start":"00:35.235 ","End":"00:39.210","Text":"The chiasma are what holds the tetrads together,"},{"Start":"00:39.210 ","End":"00:41.030","Text":"and it\u0027s not the kinetochore."},{"Start":"00:41.030 ","End":"00:43.655","Text":"The kinetochore is what\u0027s bound to the centromere."},{"Start":"00:43.655 ","End":"00:49.261","Text":"So it is the synaptonemal complex,"},{"Start":"00:49.261 ","End":"00:58.530","Text":"this entire complex, which is holding the tetrads together and that forms these tetrads."},{"Start":"00:58.530 ","End":"01:03.890","Text":"We\u0027ll see a little bit in further exercises, other structures."},{"Start":"01:03.890 ","End":"01:06.980","Text":"Remember we said that it\u0027s not the kinetochore."},{"Start":"01:06.980 ","End":"01:15.240","Text":"Yes, the kinetochore is what\u0027s holding them together just before anaphase."}],"ID":28154},{"Watched":false,"Name":"Exercise 3","Duration":"59s","ChapterTopicVideoID":27030,"CourseChapterTopicPlaylistID":237418,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:05.175","Text":"At which stage of meiosis are sister chromatids separated from each other?"},{"Start":"00:05.175 ","End":"00:07.475","Text":"Is it prophase 1,"},{"Start":"00:07.475 ","End":"00:13.135","Text":"prophase 2, anaphase 1, or anaphase 2?"},{"Start":"00:13.135 ","End":"00:16.935","Text":"Well, we\u0027re talking about separation,"},{"Start":"00:16.935 ","End":"00:19.445","Text":"which are they separated from each other?"},{"Start":"00:19.445 ","End":"00:23.270","Text":"In prophase, the chromatids are not separated,"},{"Start":"00:23.270 ","End":"00:26.495","Text":"so it can\u0027t be prophase 1 and it can\u0027t be prophase 2."},{"Start":"00:26.495 ","End":"00:32.380","Text":"We\u0027re now asking what about anaphase 1 or anaphase 2?"},{"Start":"00:32.380 ","End":"00:35.420","Text":"It\u0027s not anaphase 1 if you remember,"},{"Start":"00:35.420 ","End":"00:40.040","Text":"because the sister chromatids are not separated at that stage."},{"Start":"00:40.040 ","End":"00:43.235","Text":"It\u0027s only in anaphase 2."},{"Start":"00:43.235 ","End":"00:48.830","Text":"Remember in prophase, there\u0027s no separation of the chromatids."},{"Start":"00:48.830 ","End":"00:55.055","Text":"It\u0027s only the separation that it\u0027s occurring here in anaphase 2,"},{"Start":"00:55.055 ","End":"00:59.400","Text":"in which the sister chromatids are separated."}],"ID":28155},{"Watched":false,"Name":"Exercise 4","Duration":"59s","ChapterTopicVideoID":27031,"CourseChapterTopicPlaylistID":237418,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:02.340","Text":"At metaphase 1,"},{"Start":"00:02.340 ","End":"00:06.690","Text":"homologous chromosomes are connected only at what structures?"},{"Start":"00:06.690 ","End":"00:10.334","Text":"At Chiasmata, at recombination nodules,"},{"Start":"00:10.334 ","End":"00:13.980","Text":"at microtubules or at kinetochores."},{"Start":"00:13.980 ","End":"00:18.960","Text":"Well, recombination nodules are things that we can see,"},{"Start":"00:18.960 ","End":"00:23.594","Text":"and clearly we know that they are connected in numerous places."},{"Start":"00:23.594 ","End":"00:25.425","Text":"Those are going to be the Chiasmata,"},{"Start":"00:25.425 ","End":"00:27.450","Text":"not the microtubules for sure,"},{"Start":"00:27.450 ","End":"00:30.915","Text":"they are what pull the chromosomes apart."},{"Start":"00:30.915 ","End":"00:33.510","Text":"The kinetochores, as we discussed earlier,"},{"Start":"00:33.510 ","End":"00:34.890","Text":"are only at the centromeres."},{"Start":"00:34.890 ","End":"00:37.215","Text":"So it must be the Chiasmata."},{"Start":"00:37.215 ","End":"00:45.440","Text":"Remember, the Chiasmata where crossing over is going to occur."},{"Start":"00:47.420 ","End":"00:50.910","Text":"We\u0027re talking again at metaphase 1."},{"Start":"00:50.910 ","End":"00:52.545","Text":"This is metaphase 1,"},{"Start":"00:52.545 ","End":"00:55.100","Text":"when the chromosomes are lined up."},{"Start":"00:55.100 ","End":"01:00.150","Text":"What\u0027s holding them together at these positions are going to be the Chiasmata."}],"ID":28156},{"Watched":false,"Name":"Exercise 5","Duration":"1m 19s","ChapterTopicVideoID":27032,"CourseChapterTopicPlaylistID":237418,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.200","Text":"Which of the following is not true in regard to crossover?"},{"Start":"00:04.200 ","End":"00:10.050","Text":"Spindle microtubules guide the transfer of DNA across the synaptonemal complex."},{"Start":"00:10.050 ","End":"00:14.265","Text":"Non-sister chromatids exchange genetic material."},{"Start":"00:14.265 ","End":"00:16.365","Text":"Chiasmata are formed."},{"Start":"00:16.365 ","End":"00:20.850","Text":"Or recombination nodules mark the crossover points."},{"Start":"00:20.850 ","End":"00:23.550","Text":"Well, let\u0027s see."},{"Start":"00:23.550 ","End":"00:25.860","Text":"We\u0027ll come back to A but."},{"Start":"00:25.860 ","End":"00:29.700","Text":"Non-sister chromatids exchange genetic material, well,"},{"Start":"00:29.700 ","End":"00:35.970","Text":"we\u0027re talking about crossing over and we\u0027re saying what\u0027s not true."},{"Start":"00:35.970 ","End":"00:41.520","Text":"Yes, so clearly there\u0027s an exchange of genetic material in crossing over."},{"Start":"00:41.520 ","End":"00:43.845","Text":"Chiasmata are formed."},{"Start":"00:43.845 ","End":"00:45.315","Text":"Yes, they are formed,"},{"Start":"00:45.315 ","End":"00:48.770","Text":"but we\u0027re talking about what\u0027s not true."},{"Start":"00:48.770 ","End":"00:52.440","Text":"Recombination nodules mark the crossover point,"},{"Start":"00:52.440 ","End":"00:55.160","Text":"these nodules are things that we can see,"},{"Start":"00:55.160 ","End":"00:57.980","Text":"yes, where there is crossing over."},{"Start":"00:57.980 ","End":"01:00.610","Text":"Again, we\u0027re looking for what\u0027s not true."},{"Start":"01:00.610 ","End":"01:04.010","Text":"What\u0027s not true is that spindle microtubules guide"},{"Start":"01:04.010 ","End":"01:07.460","Text":"the transfer of DNA across the synaptonemal complex."},{"Start":"01:07.460 ","End":"01:14.960","Text":"The microtubules are what are going to be pulling the chromosomes apart,"},{"Start":"01:14.960 ","End":"01:18.840","Text":"not guiding the crossing over."}],"ID":28157},{"Watched":false,"Name":"Exercise 6","Duration":"1m 28s","ChapterTopicVideoID":27033,"CourseChapterTopicPlaylistID":237418,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:05.985","Text":"What phase of mitotic interface is missing from meiotic interkinesis?"},{"Start":"00:05.985 ","End":"00:08.653","Text":"Is it the G_0 phase,"},{"Start":"00:08.653 ","End":"00:10.384","Text":"is it a G_1 phase,"},{"Start":"00:10.384 ","End":"00:11.970","Text":"is it the S phase,"},{"Start":"00:11.970 ","End":"00:14.835","Text":"or is it the G_2 phase?"},{"Start":"00:14.835 ","End":"00:22.830","Text":"I think we have to know what interkinesis is. Let\u0027s see."},{"Start":"00:22.830 ","End":"00:27.295","Text":"It\u0027s not G_0, it\u0027s not G_1, it\u0027s not G_2."},{"Start":"00:27.295 ","End":"00:29.870","Text":"So what happens at S phase?"},{"Start":"00:29.870 ","End":"00:35.240","Text":"S phase is DNA replication. That\u0027s right."},{"Start":"00:35.240 ","End":"00:39.020","Text":"We\u0027re talking about the phase of mitotic interface"},{"Start":"00:39.020 ","End":"00:43.140","Text":"which is missing from meiotic interkinesis."},{"Start":"00:43.140 ","End":"00:46.760","Text":"Interkinesis is interphase II."},{"Start":"00:46.760 ","End":"00:49.130","Text":"It\u0027s another word for interphase II."},{"Start":"00:49.130 ","End":"00:53.930","Text":"It\u0027s a period of rest that cells of some species enter during meiosis,"},{"Start":"00:53.930 ","End":"00:58.110","Text":"between meiosis I and meiosis II."},{"Start":"00:58.110 ","End":"01:01.175","Text":"At this stage, there can be a rest,"},{"Start":"01:01.175 ","End":"01:05.330","Text":"and the cells can stay after meiosis I for long periods."},{"Start":"01:05.330 ","End":"01:12.635","Text":"In fact, egg cells in humans undergo meiosis I in the developing fetus,"},{"Start":"01:12.635 ","End":"01:18.275","Text":"but they do not undergo meiosis II until later in life."},{"Start":"01:18.275 ","End":"01:20.750","Text":"So there\u0027s a long period there,"},{"Start":"01:20.750 ","End":"01:22.639","Text":"called the interkinesis,"},{"Start":"01:22.639 ","End":"01:25.700","Text":"and of course there is no duplication of DNA."},{"Start":"01:25.700 ","End":"01:28.260","Text":"That\u0027s the S phase."}],"ID":28158},{"Watched":false,"Name":"Exercise 7","Duration":"1m 13s","ChapterTopicVideoID":27034,"CourseChapterTopicPlaylistID":237418,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:05.415","Text":"The part of meiosis that is similar to mitosis is?"},{"Start":"00:05.415 ","End":"00:10.020","Text":"What in mitosis is similar to meiosis?"},{"Start":"00:10.020 ","End":"00:12.615","Text":"Meiosis I, anaphase I,"},{"Start":"00:12.615 ","End":"00:16.275","Text":"meiosis II, or interkinesis."},{"Start":"00:16.275 ","End":"00:18.810","Text":"Clearly, it\u0027s not meiosis I,"},{"Start":"00:18.810 ","End":"00:26.250","Text":"because that\u0027s where we have a decrease in the number of chromosomes,"},{"Start":"00:26.250 ","End":"00:29.520","Text":"and that is not what happens in mitosis."},{"Start":"00:29.520 ","End":"00:31.860","Text":"It\u0027s not anaphase I."},{"Start":"00:31.860 ","End":"00:38.900","Text":"Actually, anaphase is quite similar in both anaphase I and in anaphase II,"},{"Start":"00:38.900 ","End":"00:41.935","Text":"and it\u0027s quite similar to mitosis."},{"Start":"00:41.935 ","End":"00:44.390","Text":"It\u0027s not interkinesis. As we said,"},{"Start":"00:44.390 ","End":"00:46.820","Text":"that\u0027s between meiosis I and meiosis II,"},{"Start":"00:46.820 ","End":"00:48.785","Text":"so that has nothing to do with mitosis."},{"Start":"00:48.785 ","End":"00:51.170","Text":"It\u0027s meiosis II."},{"Start":"00:51.170 ","End":"00:58.490","Text":"Remember, we\u0027re asking what part of meiosis is similar to mitosis?"},{"Start":"00:58.490 ","End":"01:08.900","Text":"It\u0027s in this stage of meiosis that we get a similar division,"},{"Start":"01:08.900 ","End":"01:13.230","Text":"which is very similar to mitosis."}],"ID":28159},{"Watched":false,"Name":"Exercise 8","Duration":"1m 38s","ChapterTopicVideoID":27035,"CourseChapterTopicPlaylistID":237418,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:05.970","Text":"If a muscle cell of a typical organism has 32 chromosomes,"},{"Start":"00:06.700 ","End":"00:12.165","Text":"how many chromosomes will be in a gamete of the same organism?"},{"Start":"00:12.165 ","End":"00:15.285","Text":"A gamete is going to be haploid."},{"Start":"00:15.285 ","End":"00:19.200","Text":"The typical organism has 32,"},{"Start":"00:19.200 ","End":"00:22.200","Text":"so is it 8,"},{"Start":"00:22.200 ","End":"00:25.490","Text":"16, 32, or 64?"},{"Start":"00:25.490 ","End":"00:28.040","Text":"Well, they\u0027re going to be half the number."},{"Start":"00:28.040 ","End":"00:29.870","Text":"That\u0027s not 8."},{"Start":"00:29.870 ","End":"00:32.900","Text":"It\u0027s not 32, it\u0027s not 64."},{"Start":"00:32.900 ","End":"00:35.300","Text":"It\u0027s going to have to be 16,"},{"Start":"00:35.300 ","End":"00:37.580","Text":"as we saw in the example of humans,"},{"Start":"00:37.580 ","End":"00:43.025","Text":"where the diploid is 46 and half of that is 23 in the haploid."},{"Start":"00:43.025 ","End":"00:47.090","Text":"Which statement best describes the genetic content of"},{"Start":"00:47.090 ","End":"00:51.520","Text":"2 daughter cells in prophase II of meiosis?"},{"Start":"00:51.520 ","End":"00:55.580","Text":"Is it haploid with 1 copy of each gene?"},{"Start":"00:55.580 ","End":"00:59.015","Text":"Is it haploid with 2 copies of each gene,"},{"Start":"00:59.015 ","End":"01:01.880","Text":"is it a diploid with 2 copies of each gene,"},{"Start":"01:01.880 ","End":"01:05.105","Text":"or is it a diploid with 4 copies of each gene?"},{"Start":"01:05.105 ","End":"01:08.300","Text":"It\u0027s not haploid with 1 copy of each gene"},{"Start":"01:08.300 ","End":"01:11.870","Text":"because we\u0027re asking which statement best describes"},{"Start":"01:11.870 ","End":"01:19.850","Text":"the genetic contents of the 2 daughter cells in when prophase II of meiosis."},{"Start":"01:19.850 ","End":"01:23.990","Text":"It\u0027s not diploid for sure because we\u0027re in prophase II."},{"Start":"01:23.990 ","End":"01:26.525","Text":"The last 2 clearly can\u0027t be right."},{"Start":"01:26.525 ","End":"01:30.170","Text":"It\u0027s going to be haploid with 2 copies of each gene."},{"Start":"01:30.170 ","End":"01:38.340","Text":"Of course, haploid with 2 copies of each gene in the daughter cells."}],"ID":28160},{"Watched":false,"Name":"Exercise 9","Duration":"1m 8s","ChapterTopicVideoID":27036,"CourseChapterTopicPlaylistID":237418,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.020","Text":"The pea plants used in Mendel\u0027s genetic inheritance studies were"},{"Start":"00:04.020 ","End":"00:08.020","Text":"diploid with 14 chromosomes in somatic cells."},{"Start":"00:08.020 ","End":"00:10.695","Text":"Assuming no crossing over events occur,"},{"Start":"00:10.695 ","End":"00:15.255","Text":"how many unique gametes could 1 pea plant produce?"},{"Start":"00:15.255 ","End":"00:18.195","Text":"Would it be 28?"},{"Start":"00:18.195 ","End":"00:23.475","Text":"No. Clearly there are not going to be double the number of gametes."},{"Start":"00:23.475 ","End":"00:26.295","Text":"Would it be 128?"},{"Start":"00:26.295 ","End":"00:30.390","Text":"No. Is it 196?"},{"Start":"00:30.390 ","End":"00:34.920","Text":"Well, actually it\u0027s 16,384."},{"Start":"00:34.920 ","End":"00:36.210","Text":"Because what are we doing?"},{"Start":"00:36.210 ","End":"00:41.550","Text":"We\u0027re asking for how many unique gametes there could be in 1 pea plant,"},{"Start":"00:41.550 ","End":"00:46.830","Text":"and the number of chromosomes is 14."},{"Start":"00:46.830 ","End":"00:51.825","Text":"It would be 2^14 would be the answer,"},{"Start":"00:51.825 ","End":"00:56.950","Text":"and that is 16,384."},{"Start":"00:57.490 ","End":"01:01.370","Text":"Because we\u0027re asking for how many unique gametes there could be."},{"Start":"01:01.370 ","End":"01:08.340","Text":"It would be 2^14."}],"ID":28161},{"Watched":false,"Name":"Exercise 10","Duration":"1m 45s","ChapterTopicVideoID":27037,"CourseChapterTopicPlaylistID":237418,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.410 ","End":"00:07.170","Text":"How do telophase I and telophase II differ during meiosis in animal cells?"},{"Start":"00:07.170 ","End":"00:11.070","Text":"Telophase I and telophase II,"},{"Start":"00:11.070 ","End":"00:14.700","Text":"we\u0027re talking about meiosis I and meiosis II,"},{"Start":"00:14.700 ","End":"00:18.360","Text":"and how are they different in animal cells?"},{"Start":"00:18.360 ","End":"00:21.660","Text":"Cells remain diploid at the end of telophase I,"},{"Start":"00:21.660 ","End":"00:24.570","Text":"but are haploid at the end of telophase II,"},{"Start":"00:24.570 ","End":"00:27.900","Text":"daughter cells form a cell plate to divide"},{"Start":"00:27.900 ","End":"00:31.710","Text":"during telophase I but divide by cytokinesis during telophase II."},{"Start":"00:31.710 ","End":"00:35.510","Text":"Cells enter interphase after telophase I,"},{"Start":"00:35.510 ","End":"00:38.010","Text":"but not after telophase II,"},{"Start":"00:38.010 ","End":"00:41.780","Text":"chromosomes can remain condensed at the end of telophase I,"},{"Start":"00:41.780 ","End":"00:46.195","Text":"but decondense after telophase II."},{"Start":"00:46.195 ","End":"00:52.275","Text":"Clearly cells don\u0027t remain diploid at the end of telophase I,"},{"Start":"00:52.275 ","End":"00:55.020","Text":"they\u0027re haploid, so that can\u0027t be."},{"Start":"00:55.020 ","End":"01:00.346","Text":"Clearly, daughter cells form a cell plate to divide during telophase I, right?"},{"Start":"01:00.346 ","End":"01:03.440","Text":"Because we\u0027re talking about animal cells."},{"Start":"01:03.440 ","End":"01:07.340","Text":"Animal cells don\u0027t have a cell plate."},{"Start":"01:07.340 ","End":"01:11.930","Text":"How about cells enter interphase after telophase I,"},{"Start":"01:11.930 ","End":"01:14.060","Text":"but not after telophase II?"},{"Start":"01:14.060 ","End":"01:20.870","Text":"Now, clearly that\u0027s not right because they do enter interphase after telophase II."},{"Start":"01:20.870 ","End":"01:24.905","Text":"Chromosomes can remain condensed at the end of telophase I,"},{"Start":"01:24.905 ","End":"01:27.455","Text":"but decondense after telophase II."},{"Start":"01:27.455 ","End":"01:32.725","Text":"Remember at the end of telophase I,"},{"Start":"01:32.725 ","End":"01:35.370","Text":"yes, during meiosis,"},{"Start":"01:35.370 ","End":"01:39.605","Text":"they don\u0027t always, but they can remain condensed"},{"Start":"01:39.605 ","End":"01:45.420","Text":"if they go quickly into telophase into meiosis II."}],"ID":28162},{"Watched":false,"Name":"Exercise 11","Duration":"1m 26s","ChapterTopicVideoID":27038,"CourseChapterTopicPlaylistID":237418,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:06.360","Text":"What is a likely evolutionary advantage of sexual reproduction over asexual reproduction?"},{"Start":"00:06.360 ","End":"00:08.985","Text":"So we\u0027re comparing sexual with"},{"Start":"00:08.985 ","End":"00:15.000","Text":"asexual reproduction and asking about evolutionary advantages."},{"Start":"00:15.000 ","End":"00:19.230","Text":"Is it that sexual reproduction involves fewer steps?"},{"Start":"00:19.230 ","End":"00:23.895","Text":"Is it that there is a lower chance of using up the resources in a given environment?"},{"Start":"00:23.895 ","End":"00:28.085","Text":"Is it sexual reproduction results in variation in the offspring?"},{"Start":"00:28.085 ","End":"00:32.570","Text":"Or sexual reproduction is more cost-effective?"},{"Start":"00:32.570 ","End":"00:36.950","Text":"Clearly, sexual reproduction does not involve fewer steps,"},{"Start":"00:36.950 ","End":"00:39.530","Text":"it involves more steps."},{"Start":"00:39.530 ","End":"00:44.885","Text":"There is not a lower chance of using up the resources in a given environment,"},{"Start":"00:44.885 ","End":"00:48.400","Text":"it really doesn\u0027t have anything to do with the resources."},{"Start":"00:48.400 ","End":"00:51.750","Text":"How about c? We\u0027ll come back to it."},{"Start":"00:51.750 ","End":"00:54.775","Text":"Sexual reproduction is more cost-effective,"},{"Start":"00:54.775 ","End":"01:00.480","Text":"I\u0027m not sure what cost-effective really means in a biological setting."},{"Start":"01:00.480 ","End":"01:05.675","Text":"Clearly, sexual reproduction results in variation in the offspring."},{"Start":"01:05.675 ","End":"01:11.750","Text":"Each of the parents contributed beneficial traits to this new bug,"},{"Start":"01:11.750 ","End":"01:15.680","Text":"the pesticide resistance in this case, or the camouflage."},{"Start":"01:15.680 ","End":"01:19.385","Text":"That is the result of sexual reproduction,"},{"Start":"01:19.385 ","End":"01:26.670","Text":"which is an evolutionary advantage for the sexual reproduction."}],"ID":28163},{"Watched":false,"Name":"Exercise 12","Duration":"1m 12s","ChapterTopicVideoID":27025,"CourseChapterTopicPlaylistID":237418,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:06.360","Text":"Which type of life cycle has both a haploid and diploid multicellular stage?"},{"Start":"00:06.360 ","End":"00:10.200","Text":"Asexual life cycles, most animal life cycles,"},{"Start":"00:10.200 ","End":"00:11.955","Text":"most fungal life cycles,"},{"Start":"00:11.955 ","End":"00:15.090","Text":"or alternation of generations."},{"Start":"00:15.090 ","End":"00:18.600","Text":"Well, it\u0027s alternation of generations."},{"Start":"00:18.600 ","End":"00:26.790","Text":"You may remember that there are some kinds of organisms like ferns, for instance,"},{"Start":"00:26.790 ","End":"00:33.375","Text":"that have both a haploid multicellular stage in their lives and"},{"Start":"00:33.375 ","End":"00:43.500","Text":"a diploid stage in their lives and that is the alternation of generations."},{"Start":"00:43.570 ","End":"00:49.580","Text":"What is the ploidy of the most conspicuous form of most fungi?"},{"Start":"00:49.580 ","End":"00:52.489","Text":"Well, is it diploid, haploid,"},{"Start":"00:52.489 ","End":"00:56.450","Text":"alternation of generations, or asexual."},{"Start":"00:56.450 ","End":"00:58.670","Text":"Well, as we\u0027ll see,"},{"Start":"00:58.670 ","End":"01:01.880","Text":"it\u0027s again alternation of generations."},{"Start":"01:01.880 ","End":"01:03.890","Text":"So both of these forms,"},{"Start":"01:03.890 ","End":"01:06.530","Text":"both the haploid and the diploid forms,"},{"Start":"01:06.530 ","End":"01:12.990","Text":"can be seen and since there\u0027s an alternation, they\u0027re both conspicuous."}],"ID":28164},{"Watched":false,"Name":"Exercise 13","Duration":"1m 48s","ChapterTopicVideoID":27026,"CourseChapterTopicPlaylistID":237418,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:03.990","Text":"A diploid, multicellular life-cycle stage that gives"},{"Start":"00:03.990 ","End":"00:07.590","Text":"rise to haploid cells by meiosis is called?"},{"Start":"00:07.590 ","End":"00:10.545","Text":"A sporophyte, gametophyte,"},{"Start":"00:10.545 ","End":"00:12.570","Text":"a spore or gamete?"},{"Start":"00:12.570 ","End":"00:17.295","Text":"Well, it is going to be a sporophyte,"},{"Start":"00:17.295 ","End":"00:19.110","Text":"so it\u0027s none of the others."},{"Start":"00:19.110 ","End":"00:26.310","Text":"The sporophyte is what we call the diploid multicellular organism."},{"Start":"00:26.310 ","End":"00:28.920","Text":"That\u0027s what our question asked."},{"Start":"00:28.920 ","End":"00:32.800","Text":"A diploid multicellular life stage."},{"Start":"00:33.170 ","End":"00:37.775","Text":"Hydras and jellyfish both live in a freshwater lake"},{"Start":"00:37.775 ","End":"00:42.575","Text":"that is slowly being acidified by the runoff from a chemical plants built upstream."},{"Start":"00:42.575 ","End":"00:49.985","Text":"Which population is predicted to be better able to cope with the changing environment?"},{"Start":"00:49.985 ","End":"00:54.775","Text":"The possibilities are jellyfish and hydra and"},{"Start":"00:54.775 ","End":"00:57.530","Text":"the other possibilities that were given in the question are"},{"Start":"00:57.530 ","End":"01:00.665","Text":"the populations will be able to equally cope,"},{"Start":"01:00.665 ","End":"01:03.140","Text":"or both populations will die."},{"Start":"01:03.140 ","End":"01:07.390","Text":"What\u0027s the difference between jellyfish and hydra?"},{"Start":"01:07.390 ","End":"01:13.430","Text":"What\u0027s relevant to this question will be that jellyfish reproduce"},{"Start":"01:13.430 ","End":"01:19.395","Text":"sexually and hydra reproduce primarily asexually."},{"Start":"01:19.395 ","End":"01:25.130","Text":"Which one gives better ability to cope with the changing environment?"},{"Start":"01:25.130 ","End":"01:26.795","Text":"It\u0027s going to be the one that has"},{"Start":"01:26.795 ","End":"01:32.165","Text":"more sexual reproduction and that will be the jellyfish."},{"Start":"01:32.165 ","End":"01:36.020","Text":"That\u0027s the reason, remember we talked about the bugs"},{"Start":"01:36.020 ","End":"01:39.950","Text":"and that sexual reproduction introduces"},{"Start":"01:39.950 ","End":"01:43.760","Text":"beneficial traits more quickly into organisms"},{"Start":"01:43.760 ","End":"01:48.840","Text":"and therefore able to cope with the changing environment better."}],"ID":28165},{"Watched":false,"Name":"Exercise 14","Duration":"1m 33s","ChapterTopicVideoID":27027,"CourseChapterTopicPlaylistID":237418,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:03.660","Text":"Many farmers are worried about decreasing genetic diversity in"},{"Start":"00:03.660 ","End":"00:07.530","Text":"plants associated with generations of artificial selection and inbreeding."},{"Start":"00:07.530 ","End":"00:09.735","Text":"Those are the things that are done in farming."},{"Start":"00:09.735 ","End":"00:14.835","Text":"Why is limiting random sexual reproduction of food crops concerning?"},{"Start":"00:14.835 ","End":"00:16.650","Text":"Why is this concerning?"},{"Start":"00:16.650 ","End":"00:21.465","Text":"Is it that mutations during asexual reproduction decrease plants fitness?"},{"Start":"00:21.465 ","End":"00:25.040","Text":"Is it that the consumers do not trust identical appearing produce?"},{"Start":"00:25.040 ","End":"00:27.290","Text":"Is it that larger proportions of"},{"Start":"00:27.290 ","End":"00:30.425","Text":"the plant populations are susceptible to the same diseases?"},{"Start":"00:30.425 ","End":"00:35.395","Text":"Or that spores are not viable in an agricultural setting?"},{"Start":"00:35.395 ","End":"00:41.900","Text":"It may be that mutations during asexual reproduction decrease plant fitness,"},{"Start":"00:41.900 ","End":"00:44.450","Text":"but that\u0027s not the main concern."},{"Start":"00:44.450 ","End":"00:49.310","Text":"Consumers really don\u0027t usually care about identical appearing produce,"},{"Start":"00:49.310 ","End":"00:52.780","Text":"so that\u0027s probably not it and spores"},{"Start":"00:52.780 ","End":"00:57.530","Text":"are sometimes viable in an agricultural setting so that can\u0027t be it,"},{"Start":"00:57.530 ","End":"01:03.980","Text":"but surely larger proportions of the plant populations are susceptible to"},{"Start":"01:03.980 ","End":"01:08.300","Text":"the same disease if there are generations"},{"Start":"01:08.300 ","End":"01:12.955","Text":"of artificial selection and especially this inbreeding."},{"Start":"01:12.955 ","End":"01:19.580","Text":"In inbreeding, remember we cross progeny to each other so that there is"},{"Start":"01:19.580 ","End":"01:23.330","Text":"a limitation of the gene pool and what we really"},{"Start":"01:23.330 ","End":"01:27.860","Text":"need to increase fitness is going to be an increase in the gene pool,"},{"Start":"01:27.860 ","End":"01:32.070","Text":"which is accomplished via sexual reproduction."}],"ID":28166}],"Thumbnail":null,"ID":237418},{"Name":"Menel\u0027s Experiments and Heredity","TopicPlaylistFirstVideoID":0,"Duration":null,"Videos":[{"Watched":false,"Name":"Mendel\u0027s Experiments and Heredity","Duration":"4m 14s","ChapterTopicVideoID":25543,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.260 ","End":"00:05.235","Text":"Welcome back. In our discussions until now,"},{"Start":"00:05.235 ","End":"00:08.835","Text":"we\u0027ve discussed the heredity of single cells basically."},{"Start":"00:08.835 ","End":"00:13.350","Text":"In mitosis about how the genetic information is split between 2 different cells."},{"Start":"00:13.350 ","End":"00:19.220","Text":"In meiosis, how the genetic information is rearranged by crossing"},{"Start":"00:19.220 ","End":"00:25.745","Text":"over and then independently segregated in meiosis to produce the gametes."},{"Start":"00:25.745 ","End":"00:28.025","Text":"Then after fertilization, of course,"},{"Start":"00:28.025 ","End":"00:37.515","Text":"we have a new cell which inherited it\u0027s traits from the 2 gametes."},{"Start":"00:37.515 ","End":"00:40.160","Text":"In higher organisms, those gametes then"},{"Start":"00:40.160 ","End":"00:43.565","Text":"we\u0027ll divide and differentiate into a higher organism,"},{"Start":"00:43.565 ","End":"00:45.545","Text":"such as you and me,"},{"Start":"00:45.545 ","End":"00:48.665","Text":"or plants or anything of that sort."},{"Start":"00:48.665 ","End":"00:55.355","Text":"Now we\u0027re going to look more at that heredity and try to understand how that comes about."},{"Start":"00:55.355 ","End":"01:00.050","Text":"Now people used to think really that heredity in"},{"Start":"01:00.050 ","End":"01:04.910","Text":"higher organisms were a mix between the parents."},{"Start":"01:04.910 ","End":"01:10.249","Text":"The traits, we\u0027re not discrete traits,"},{"Start":"01:10.249 ","End":"01:11.915","Text":"but rather they could blend."},{"Start":"01:11.915 ","End":"01:13.850","Text":"For instance, of course,"},{"Start":"01:13.850 ","End":"01:16.774","Text":"a light color person,"},{"Start":"01:16.774 ","End":"01:20.780","Text":"if they are married to a dark-colored person,"},{"Start":"01:20.780 ","End":"01:26.660","Text":"then the progeny of that union will be somewhere in the middle between dark and light."},{"Start":"01:26.660 ","End":"01:30.770","Text":"They thought the same thing about all the traits."},{"Start":"01:30.770 ","End":"01:32.270","Text":"It turns out by the way,"},{"Start":"01:32.270 ","End":"01:35.300","Text":"that the reason for"},{"Start":"01:35.300 ","End":"01:40.550","Text":"the color mixture is that the color of our skin is not determined by a single gene."},{"Start":"01:40.550 ","End":"01:43.280","Text":"It\u0027s determined by many genes and it\u0027s"},{"Start":"01:43.280 ","End":"01:47.180","Text":"the mixture of those different genes that will result in the skin color,"},{"Start":"01:47.180 ","End":"01:49.235","Text":"but that\u0027s really not for now."},{"Start":"01:49.235 ","End":"01:53.390","Text":"What we\u0027re going to do here is we\u0027re going to discuss Mendel."},{"Start":"01:53.390 ","End":"01:57.425","Text":"Mendel, who will see just a little bit about in a minute."},{"Start":"01:57.425 ","End":"02:07.475","Text":"Who very early on looked at traits in various organisms and particularly in the P,"},{"Start":"02:07.475 ","End":"02:11.000","Text":"That\u0027s the plant, the P. He looked at various traits of"},{"Start":"02:11.000 ","End":"02:16.075","Text":"them and he tried to understand how that heredity occurred."},{"Start":"02:16.075 ","End":"02:21.050","Text":"Let\u0027s look at Mendel\u0027s experiments and try to"},{"Start":"02:21.050 ","End":"02:27.110","Text":"get a little bit of insight into what Mendel might\u0027ve been thinking back in the day."},{"Start":"02:27.110 ","End":"02:30.785","Text":"Mendel really was studying genetics."},{"Start":"02:30.785 ","End":"02:34.315","Text":"Genetics is the study of heredity."},{"Start":"02:34.315 ","End":"02:38.090","Text":"Johann Gregor Mendel was an Austrian monk."},{"Start":"02:38.090 ","End":"02:44.350","Text":"In those days, scientists were usually also religious people,"},{"Start":"02:44.350 ","End":"02:48.920","Text":"and he set the framework for genetics."},{"Start":"02:48.920 ","End":"02:53.465","Text":"In fact, the work that he did though and that he published was not appreciated all"},{"Start":"02:53.465 ","End":"03:00.740","Text":"until after he died and was only rediscovered about in the year 1900."},{"Start":"03:00.740 ","End":"03:08.035","Text":"Mendel conducted methodical quantitative analysis using large sample sizes."},{"Start":"03:08.035 ","End":"03:13.627","Text":"That\u0027s going to require the understanding of some statistics."},{"Start":"03:13.627 ","End":"03:16.790","Text":"We\u0027re going to be talking a little bit later about"},{"Start":"03:16.790 ","End":"03:22.000","Text":"some simple statistics that gave some insights into heredity,"},{"Start":"03:22.000 ","End":"03:24.620","Text":"and you\u0027ll understand that a bit later."},{"Start":"03:24.620 ","End":"03:29.180","Text":"His work actually revealed the very fundamental principles"},{"Start":"03:29.180 ","End":"03:33.410","Text":"of heredity that we understand to this very day."},{"Start":"03:33.410 ","End":"03:39.440","Text":"We know that there are basic functional units of heredity,"},{"Start":"03:39.440 ","End":"03:47.030","Text":"single units of heredity that he understood from the work that he did on his peas."},{"Start":"03:47.030 ","End":"03:52.915","Text":"Here\u0027s a stamp from the Vatican that has Gregor Mendel\u0027s picture on it."},{"Start":"03:52.915 ","End":"03:59.885","Text":"His experiments then serve as an excellent starting point for thinking about inheritance."},{"Start":"03:59.885 ","End":"04:05.450","Text":"Just as Mendel began to understand the inheritance through his own experiments,"},{"Start":"04:05.450 ","End":"04:07.310","Text":"we in the same way,"},{"Start":"04:07.310 ","End":"04:14.070","Text":"we\u0027ll begin to understand heredity by looking at his experiments."}],"ID":26360},{"Watched":false,"Name":"Laws of Probability Part a1","Duration":"5m 30s","ChapterTopicVideoID":25538,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.200 ","End":"00:06.015","Text":"Now let\u0027s dive into Mendel\u0027s experiments and the laws of probability,"},{"Start":"00:06.015 ","End":"00:08.475","Text":"and there\u0027s a little bit of statistics."},{"Start":"00:08.475 ","End":"00:10.605","Text":"By the end of this section,"},{"Start":"00:10.605 ","End":"00:13.260","Text":"you should be able to describe the scientific reasons for"},{"Start":"00:13.260 ","End":"00:16.200","Text":"the success of Mendel\u0027s experimental work,"},{"Start":"00:16.200 ","End":"00:19.725","Text":"you should be able to describe the expected outcomes of"},{"Start":"00:19.725 ","End":"00:25.065","Text":"monohybrid crosses involving dominant and recessive alleles,"},{"Start":"00:25.065 ","End":"00:28.470","Text":"you should know what dominant and recessive means and"},{"Start":"00:28.470 ","End":"00:31.980","Text":"what alleles mean by the end of this video,"},{"Start":"00:31.980 ","End":"00:38.040","Text":"and you should be able to apply the sum and product rules to calculate probabilities."},{"Start":"00:38.040 ","End":"00:40.320","Text":"Now all this is actually quite a bit,"},{"Start":"00:40.320 ","End":"00:44.760","Text":"so we\u0027ve divided it into 2 videos."},{"Start":"00:44.760 ","End":"00:48.415","Text":"Let\u0027s start with the first part."},{"Start":"00:48.415 ","End":"00:50.870","Text":"As I mentioned before,"},{"Start":"00:50.870 ","End":"00:54.960","Text":"Mendel\u0027s model system was a pea."},{"Start":"00:54.960 ","End":"00:59.270","Text":"A pea is actually are quite interesting because 1 of the things that they do,"},{"Start":"00:59.270 ","End":"01:02.840","Text":"which is different than a lot of plants,"},{"Start":"01:02.840 ","End":"01:05.615","Text":"is that they fertilize themselves."},{"Start":"01:05.615 ","End":"01:11.465","Text":"They have both the male and the female genitalia,"},{"Start":"01:11.465 ","End":"01:15.470","Text":"that is, they have anthers, they make pollen,"},{"Start":"01:15.470 ","End":"01:22.085","Text":"and they have the carpel or the stamen which can be fertilized,"},{"Start":"01:22.085 ","End":"01:26.930","Text":"that\u0027s the female part of the flower by the pollen."},{"Start":"01:26.930 ","End":"01:31.775","Text":"But what usually happens is that they fertilize themselves"},{"Start":"01:31.775 ","End":"01:36.530","Text":"and so that you don\u0027t have cross-pollination between different flowers."},{"Start":"01:36.530 ","End":"01:38.170","Text":"What that means is,"},{"Start":"01:38.170 ","End":"01:40.550","Text":"and you have to take it for granted at this point,"},{"Start":"01:40.550 ","End":"01:45.050","Text":"that over many generations what happens is that the peas"},{"Start":"01:45.050 ","End":"01:50.685","Text":"become completely the same in their 2 different chromosomes."},{"Start":"01:50.685 ","End":"01:56.005","Text":"The homologous chromosomes are not only homologous, but they\u0027re identical."},{"Start":"01:56.005 ","End":"01:58.760","Text":"Mendel was a bit lucky actually,"},{"Start":"01:58.760 ","End":"02:03.980","Text":"in that he chose this plant to work with, otherwise,"},{"Start":"02:03.980 ","End":"02:06.950","Text":"his experiments would not have been so clear,"},{"Start":"02:06.950 ","End":"02:10.085","Text":"they would have been a lot more difficult to interpret."},{"Start":"02:10.085 ","End":"02:16.430","Text":"Actually, he realized that they had both the anthers and the stamen,"},{"Start":"02:16.430 ","End":"02:23.135","Text":"and he realized that he could cross-pollinate between 2 different flowers."},{"Start":"02:23.135 ","End":"02:27.800","Text":"Here, for instance, we have a purple flower and we have a white flower,"},{"Start":"02:27.800 ","End":"02:30.260","Text":"and what he does is he can cross-pollinate."},{"Start":"02:30.260 ","End":"02:32.870","Text":"In this case, he\u0027s taking some pollen from the white flower,"},{"Start":"02:32.870 ","End":"02:41.570","Text":"putting it on a little brush and then pollinating the carpel here of the purple flowers."},{"Start":"02:41.570 ","End":"02:43.400","Text":"That\u0027s how he does the cross between them."},{"Start":"02:43.400 ","End":"02:45.275","Text":"But before he can do that,"},{"Start":"02:45.275 ","End":"02:50.540","Text":"what he needs to do is very carefully cut off all the anthers"},{"Start":"02:50.540 ","End":"02:53.330","Text":"from all of his flowers that are going to"},{"Start":"02:53.330 ","End":"02:57.050","Text":"be fertilized so that they don\u0027t fertilize themselves."},{"Start":"02:57.050 ","End":"03:02.340","Text":"He\u0027s got a very well-controlled system here in which he keeps"},{"Start":"03:02.340 ","End":"03:10.795","Text":"these flowers from self pollinating and he can pollinate them as he wishes."},{"Start":"03:10.795 ","End":"03:18.290","Text":"This is very important, starting material that he starts with is completely uniform."},{"Start":"03:18.290 ","End":"03:23.670","Text":"He performed hybridizations mating to individuals that have different traits."},{"Start":"03:23.670 ","End":"03:24.950","Text":"You can see in this case,"},{"Start":"03:24.950 ","End":"03:30.260","Text":"we have this trait of a purple flower and another trait of a white flower,"},{"Start":"03:30.260 ","End":"03:33.335","Text":"and there\u0027s going to be a mating between the 2 of them."},{"Start":"03:33.335 ","End":"03:36.005","Text":"Then with time, of course,"},{"Start":"03:36.005 ","End":"03:37.220","Text":"in the same season,"},{"Start":"03:37.220 ","End":"03:39.455","Text":"the flowers then bear fruits."},{"Start":"03:39.455 ","End":"03:42.440","Text":"The fruits in this case is a pod of peas,"},{"Start":"03:42.440 ","End":"03:48.770","Text":"and he can then take that pod of peas and the next season can plant them and then have"},{"Start":"03:48.770 ","End":"03:55.555","Text":"a look and see what is the color of the flowers that this cross produced."},{"Start":"03:55.555 ","End":"03:58.465","Text":"Let\u0027s call the first generation,"},{"Start":"03:58.465 ","End":"04:02.210","Text":"the parental generation P for parental,"},{"Start":"04:02.210 ","End":"04:09.825","Text":"and let\u0027s call the next generation F_1."},{"Start":"04:09.825 ","End":"04:12.690","Text":"That is self fertilized naturally,"},{"Start":"04:12.690 ","End":"04:15.530","Text":"because what happened here was,"},{"Start":"04:15.530 ","End":"04:18.290","Text":"is that after he did the initial crossing,"},{"Start":"04:18.290 ","End":"04:20.930","Text":"then they grow and they will self"},{"Start":"04:20.930 ","End":"04:24.660","Text":"pollinate each other if he doesn\u0027t cut off their anthers."},{"Start":"04:24.660 ","End":"04:26.900","Text":"In his experiments, he did not cut off"},{"Start":"04:26.900 ","End":"04:31.570","Text":"the anthers beyond the first generation in the parental generation,"},{"Start":"04:31.570 ","End":"04:35.025","Text":"and then he could continue with this treatment,"},{"Start":"04:35.025 ","End":"04:37.445","Text":"getting F_2 plants,"},{"Start":"04:37.445 ","End":"04:40.920","Text":"and F_3, and F_4 generations and so on,"},{"Start":"04:40.920 ","End":"04:44.135","Text":"and he can count now the number of"},{"Start":"04:44.135 ","End":"04:47.860","Text":"flowers that are purple and the number of flowers that are white."},{"Start":"04:47.860 ","End":"04:50.790","Text":"Furthermore, he can see actually,"},{"Start":"04:50.790 ","End":"04:52.685","Text":"and what he saw right away was,"},{"Start":"04:52.685 ","End":"04:57.365","Text":"is that these flowers were either purple or white."},{"Start":"04:57.365 ","End":"05:00.470","Text":"The progeny were either purple or white,"},{"Start":"05:00.470 ","End":"05:02.755","Text":"they were not anywhere in-between."},{"Start":"05:02.755 ","End":"05:05.329","Text":"As I mentioned in the introduction,"},{"Start":"05:05.329 ","End":"05:07.730","Text":"that human skin color can be."},{"Start":"05:07.730 ","End":"05:10.100","Text":"Because as it turns out,"},{"Start":"05:10.100 ","End":"05:14.315","Text":"the color of the flower in the case of peas,"},{"Start":"05:14.315 ","End":"05:21.345","Text":"is controlled by 1 gene, by 1 locus."},{"Start":"05:21.345 ","End":"05:26.290","Text":"Mendel was lucky that he chose this organism to work with,"},{"Start":"05:26.290 ","End":"05:31.079","Text":"and that helped him understand the early genetics."}],"ID":26355},{"Watched":false,"Name":"Laws of Probability Part a2","Duration":"7m 14s","ChapterTopicVideoID":25540,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.200 ","End":"00:06.300","Text":"Now let\u0027s dive into Mendel\u0027s experiments and the laws of probability."},{"Start":"00:06.300 ","End":"00:08.474","Text":"There\u0027s a little bit of statistics."},{"Start":"00:08.474 ","End":"00:10.605","Text":"By the end of this section,"},{"Start":"00:10.605 ","End":"00:13.260","Text":"you should be able to describe the scientific reasons for"},{"Start":"00:13.260 ","End":"00:16.200","Text":"the success of Mendel\u0027s experimental work."},{"Start":"00:16.200 ","End":"00:19.725","Text":"You should be able to describe the expected outcomes of"},{"Start":"00:19.725 ","End":"00:25.065","Text":"monohybrid crosses involving dominant and recessive alleles."},{"Start":"00:25.065 ","End":"00:28.470","Text":"You should know what dominant and recessive means and"},{"Start":"00:28.470 ","End":"00:31.800","Text":"what alleles mean by the end of this video,"},{"Start":"00:31.800 ","End":"00:38.040","Text":"and you should be able to apply the sum and product rules to calculate probabilities."},{"Start":"00:38.040 ","End":"00:40.320","Text":"Now all this is actually quite a bit,"},{"Start":"00:40.320 ","End":"00:44.760","Text":"so we\u0027ve divided it into two videos."},{"Start":"00:44.760 ","End":"00:48.415","Text":"Let\u0027s start with the first part."},{"Start":"00:48.415 ","End":"00:50.870","Text":"As I mentioned before,"},{"Start":"00:50.870 ","End":"00:55.170","Text":"Mendel\u0027s model system was a P. A"},{"Start":"00:55.170 ","End":"00:59.270","Text":"Ps actually are quite interesting because one of the things that they do,"},{"Start":"00:59.270 ","End":"01:02.840","Text":"which is different than a lot of plants,"},{"Start":"01:02.840 ","End":"01:05.390","Text":"is that they fertilize themselves."},{"Start":"01:05.390 ","End":"01:11.465","Text":"They have both the male and the female genitalia."},{"Start":"01:11.465 ","End":"01:19.624","Text":"That is, they have anthers that make pollen and they have the carpel or the stamen,"},{"Start":"01:19.624 ","End":"01:22.085","Text":"which can be fertilized,"},{"Start":"01:22.085 ","End":"01:26.930","Text":"that\u0027s the female part of the flower by the pollen."},{"Start":"01:26.930 ","End":"01:31.775","Text":"But what usually happens is that they fertilize themselves"},{"Start":"01:31.775 ","End":"01:36.545","Text":"and so that you don\u0027t have cross-pollination between different flowers."},{"Start":"01:36.545 ","End":"01:39.500","Text":"What that means is you\u0027ll have to take it for"},{"Start":"01:39.500 ","End":"01:42.980","Text":"granted at this point that over many generations what happens"},{"Start":"01:42.980 ","End":"01:50.684","Text":"is that the P\u0027s become completely the same in their two different chromosomes."},{"Start":"01:50.684 ","End":"01:55.990","Text":"The homologous chromosomes are not only homologous but they\u0027re identical."},{"Start":"01:55.990 ","End":"02:02.945","Text":"Mendel was a bit lucky actually in that he chose this plant to work with."},{"Start":"02:02.945 ","End":"02:06.950","Text":"Otherwise, his experiments would not have been so clear,"},{"Start":"02:06.950 ","End":"02:10.085","Text":"they would\u0027ve been a lot more difficult to interpret."},{"Start":"02:10.085 ","End":"02:16.430","Text":"Actually, he realized that they had both the anthers and the stamen,"},{"Start":"02:16.430 ","End":"02:23.135","Text":"and he realized that he could cross-pollinate between two different flowers."},{"Start":"02:23.135 ","End":"02:26.195","Text":"Here, for instance, we have a purple flower and we have"},{"Start":"02:26.195 ","End":"02:30.260","Text":"a white flower and what he does is he can cross-pollinate."},{"Start":"02:30.260 ","End":"02:32.870","Text":"In this case, he\u0027s taking some pollen from the white flower,"},{"Start":"02:32.870 ","End":"02:35.465","Text":"putting it on a little brush,"},{"Start":"02:35.465 ","End":"02:40.590","Text":"and then pollinating the stamen, the carpel here."},{"Start":"02:41.290 ","End":"02:45.335","Text":"Here\u0027s what he did. When Mendel crossed"},{"Start":"02:45.335 ","End":"02:50.840","Text":"contrasting true-breeding white and purple-flowered pea plants,"},{"Start":"02:50.840 ","End":"02:54.920","Text":"true-breeding means that it\u0027s that earlier generation,"},{"Start":"02:54.920 ","End":"03:01.390","Text":"this first generation that had never been bred previously was only self-bred."},{"Start":"03:01.390 ","End":"03:03.680","Text":"As I mentioned before, everything,"},{"Start":"03:03.680 ","End":"03:08.210","Text":"all the genes on both homologous chromosomes will be the same."},{"Start":"03:08.210 ","End":"03:15.065","Text":"He discovered after mating a white with a purple that all the plants had purple flowers."},{"Start":"03:15.065 ","End":"03:25.015","Text":"Then after self or cross-pollination then what he found in the F2 generation was"},{"Start":"03:25.015 ","End":"03:30.410","Text":"that he got 7 in the experiment that he did and he published has he had"},{"Start":"03:30.410 ","End":"03:36.710","Text":"7 and 5 purple-flowered plants and 224 white-flowered plants."},{"Start":"03:36.710 ","End":"03:43.550","Text":"First of all, these purple flowers after breeding actually"},{"Start":"03:43.550 ","End":"03:50.390","Text":"with themselves with the self-fertilization could generate the white phenotype,"},{"Start":"03:50.390 ","End":"03:55.040","Text":"the white characteristic, the white trait again."},{"Start":"03:55.040 ","End":"04:04.655","Text":"That then gave him a basis for the experiments that he did further to try to understand,"},{"Start":"04:04.655 ","End":"04:08.395","Text":"the numbers here turn out to be important."},{"Start":"04:08.395 ","End":"04:12.370","Text":"He discovered that there was a ratio of"},{"Start":"04:12.370 ","End":"04:18.400","Text":"roughly 3 purple flowers to 1 white flower in the F2 generation,"},{"Start":"04:18.400 ","End":"04:21.230","Text":"regardless of how many times he did this."},{"Start":"04:21.230 ","End":"04:26.050","Text":"Not only that, there were other traits in the P that he could follow."},{"Start":"04:26.050 ","End":"04:28.720","Text":"For instance, he could follow seed color,"},{"Start":"04:28.720 ","End":"04:31.225","Text":"he could follow the seed shape."},{"Start":"04:31.225 ","End":"04:32.935","Text":"Those are the Ps that are in the pod."},{"Start":"04:32.935 ","End":"04:37.295","Text":"They could be either round like this or they could be wrinkled."},{"Start":"04:37.295 ","End":"04:39.565","Text":"In each of these,"},{"Start":"04:39.565 ","End":"04:44.875","Text":"when he did the experiment that he did before with the color,"},{"Start":"04:44.875 ","End":"04:51.375","Text":"what he found was that he continued to get this 3 to 1 ratio,"},{"Start":"04:51.375 ","End":"04:53.895","Text":"very close to 3 to 1 ratio."},{"Start":"04:53.895 ","End":"04:56.855","Text":"You can see some of his numbers were enormous."},{"Start":"04:56.855 ","End":"04:58.070","Text":"Just imagine him cutting"},{"Start":"04:58.070 ","End":"05:02.135","Text":"all those anthers in all of these flowers and then at the beginning,"},{"Start":"05:02.135 ","End":"05:04.450","Text":"but it was a lot of work."},{"Start":"05:04.450 ","End":"05:08.420","Text":"It led to a very consistent result,"},{"Start":"05:08.420 ","End":"05:12.980","Text":"which meant that there has to be something going on behind this."},{"Start":"05:12.980 ","End":"05:18.305","Text":"He was smart enough to say that in each of these cases,"},{"Start":"05:18.305 ","End":"05:21.230","Text":"there is a dominant trait."},{"Start":"05:21.230 ","End":"05:23.915","Text":"Purple would be the dominant trait or"},{"Start":"05:23.915 ","End":"05:28.220","Text":"yellow seed color will be the dominant trait and round is the dominant trait."},{"Start":"05:28.220 ","End":"05:32.895","Text":"Each of these traits can be either dominant or recessive."},{"Start":"05:32.895 ","End":"05:36.650","Text":"Furthermore, the factor for the white flowers was not"},{"Start":"05:36.650 ","End":"05:40.760","Text":"diluted or destroyed because it reappeared in the F2 generation."},{"Start":"05:40.760 ","End":"05:43.430","Text":"In other words, after this was formed in"},{"Start":"05:43.430 ","End":"05:48.710","Text":"the F1 generation after we had the F1 generation,"},{"Start":"05:48.710 ","End":"05:50.270","Text":"the F2 generation,"},{"Start":"05:50.270 ","End":"05:52.760","Text":"this white color didn\u0027t disappear."},{"Start":"05:52.760 ","End":"05:57.530","Text":"It reappeared, and so it was not diluted."},{"Start":"05:57.530 ","End":"06:01.400","Text":"Furthermore, he observed the same pattern of inheritance"},{"Start":"06:01.400 ","End":"06:06.080","Text":"in 6 pea plants and characteristics."},{"Start":"06:06.080 ","End":"06:09.365","Text":"Not only the two additional ones that I\u0027ve shown you here."},{"Start":"06:09.365 ","End":"06:12.170","Text":"Each of them was represented by 2 traits."},{"Start":"06:12.170 ","End":"06:16.640","Text":"In all of them, he got this 3 to 1 ratio."},{"Start":"06:16.640 ","End":"06:20.720","Text":"Mendel didn\u0027t know about genes."},{"Start":"06:20.720 ","End":"06:22.850","Text":"He didn\u0027t know about DNA."},{"Start":"06:22.850 ","End":"06:27.485","Text":"He didn\u0027t really know anything about heredity and what its basis was."},{"Start":"06:27.485 ","End":"06:31.204","Text":"But he saw that there was some heritable factor."},{"Start":"06:31.204 ","End":"06:32.590","Text":"That\u0027s what he called it."},{"Start":"06:32.590 ","End":"06:38.180","Text":"That heritable factor turned out to be what we now call a gene."},{"Start":"06:38.180 ","End":"06:40.980","Text":"He continued his experiments with"},{"Start":"06:40.980 ","End":"06:47.120","Text":"this heritable factor and try to understand better what was going on."},{"Start":"06:47.120 ","End":"06:50.630","Text":"He developed a hypothesis now to explain"},{"Start":"06:50.630 ","End":"06:55.370","Text":"the 3 to 1 inheritance pattern that he observed in the F2 offspring."},{"Start":"06:55.370 ","End":"07:00.110","Text":"There are four related concepts that make up this model."},{"Start":"07:00.110 ","End":"07:04.430","Text":"These concepts can be related to what we now know about genes and chromosomes."},{"Start":"07:04.430 ","End":"07:08.375","Text":"In fact, it\u0027s a little bit easier to explain if we explain it"},{"Start":"07:08.375 ","End":"07:14.610","Text":"knowing about genes and chromosomes and that\u0027s what we\u0027re going to do here."}],"ID":26357},{"Watched":false,"Name":"Laws of Probability Part a3","Duration":"5m 11s","ChapterTopicVideoID":25542,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.200 ","End":"00:06.480","Text":"First, using modern understanding of what happens in heredity,"},{"Start":"00:06.480 ","End":"00:13.230","Text":"what we now understand is that the particular genes can have mutations in them."},{"Start":"00:13.230 ","End":"00:14.850","Text":"They can have changes."},{"Start":"00:14.850 ","End":"00:17.790","Text":"For instance, here\u0027s a gene that\u0027s represented by"},{"Start":"00:17.790 ","End":"00:21.765","Text":"a particular sequence and you could see that this gene,"},{"Start":"00:21.765 ","End":"00:25.800","Text":"which is found at a particular locus on the chromosomes,"},{"Start":"00:25.800 ","End":"00:31.215","Text":"so this is a condensed chromosome and this area is just a small part of that chromosome,"},{"Start":"00:31.215 ","End":"00:36.420","Text":"that locus can have 2 separate sequences."},{"Start":"00:36.420 ","End":"00:39.540","Text":"The code for the same thing,"},{"Start":"00:39.540 ","End":"00:42.030","Text":"or it\u0027s possible that one of them"},{"Start":"00:42.030 ","End":"00:45.560","Text":"has a mutation in it that makes it not code for anything."},{"Start":"00:45.560 ","End":"00:47.270","Text":"Like it says here, absence of enzyme,"},{"Start":"00:47.270 ","End":"00:49.085","Text":"but they don\u0027t have to be this way."},{"Start":"00:49.085 ","End":"00:55.230","Text":"These different coding sequences now are going to be called alleles."},{"Start":"00:55.360 ","End":"01:01.700","Text":"We\u0027re talking now about a purple allele and a white allele."},{"Start":"01:01.700 ","End":"01:03.245","Text":"That\u0027s how we discuss it."},{"Start":"01:03.245 ","End":"01:06.095","Text":"Again, going now back to what we understand about"},{"Start":"01:06.095 ","End":"01:11.540","Text":"modern biology then one of those alleles may"},{"Start":"01:11.540 ","End":"01:14.690","Text":"code for a particular enzyme or"},{"Start":"01:14.690 ","End":"01:20.300","Text":"a particular protein and here\u0027s that protein and down the line that may be,"},{"Start":"01:20.300 ","End":"01:23.720","Text":"let\u0027s say, what\u0027s giving the flower the purple color."},{"Start":"01:23.720 ","End":"01:29.420","Text":"Whereas a different allele at this position will not be able to make the enzyme,"},{"Start":"01:29.420 ","End":"01:32.975","Text":"or it\u0027ll make a defective enzyme or it\u0027ll make a defective protein."},{"Start":"01:32.975 ","End":"01:38.830","Text":"In any case, it\u0027ll be unable to make the purple color."},{"Start":"01:38.830 ","End":"01:44.405","Text":"Therefore, the flowers will be white because they won\u0027t have the color."},{"Start":"01:44.405 ","End":"01:50.050","Text":"To repeat now the alternative versions of a gene are called alleles."},{"Start":"01:50.050 ","End":"01:54.305","Text":"This is some modern understanding of what\u0027s going on."},{"Start":"01:54.305 ","End":"01:59.539","Text":"We already discussed the locus that\u0027s on these chromosomes."},{"Start":"01:59.539 ","End":"02:02.135","Text":"Now looking at the chromosomes again,"},{"Start":"02:02.135 ","End":"02:07.700","Text":"remember we said that the parental pea plants were the"},{"Start":"02:07.700 ","End":"02:15.145","Text":"same on the 2 homologous chromosomes and you can see that in this diagram."},{"Start":"02:15.145 ","End":"02:18.200","Text":"He didn\u0027t know about chromosomes and like I said,"},{"Start":"02:18.200 ","End":"02:21.590","Text":"he was lucky that these peas fertilize"},{"Start":"02:21.590 ","End":"02:26.070","Text":"themselves and are therefore what are called inbred."},{"Start":"02:26.590 ","End":"02:30.415","Text":"That\u0027s 1 word. For each character,"},{"Start":"02:30.415 ","End":"02:33.610","Text":"it turns out that an organism inherits 2 alleles,"},{"Start":"02:33.610 ","End":"02:39.460","Text":"1 from each parent right when the gametes come together after fertilization."},{"Start":"02:39.460 ","End":"02:45.865","Text":"Mendel was able to make this deduction without knowing about the chromosomes at all."},{"Start":"02:45.865 ","End":"02:50.050","Text":"The 2 alleles at a locus may be identical or they can differ."},{"Start":"02:50.050 ","End":"02:51.820","Text":"For instance, in the F_1s,"},{"Start":"02:51.820 ","End":"02:57.070","Text":"we had a heterologous pair because we had 1 purple and"},{"Start":"02:57.070 ","End":"03:00.370","Text":"1 white parent and so at this position there were"},{"Start":"03:00.370 ","End":"03:04.510","Text":"2 different alleles at this particular position."},{"Start":"03:04.510 ","End":"03:08.580","Text":"The third thing we need to understand that Mendel"},{"Start":"03:08.580 ","End":"03:12.755","Text":"understood was that if the 2 alleles at a locus differ,"},{"Start":"03:12.755 ","End":"03:17.195","Text":"only the dominant allele will determine the organism\u0027s appearance;"},{"Start":"03:17.195 ","End":"03:22.895","Text":"the phenotype, and the other recessive allele parenterally not there."},{"Start":"03:22.895 ","End":"03:25.550","Text":"It has no noticeable effect on the appearance."},{"Start":"03:25.550 ","End":"03:30.260","Text":"The appearance of these 2 purple flowers in the parental generation,"},{"Start":"03:30.260 ","End":"03:33.815","Text":"in the F_1 generation will look the same,"},{"Start":"03:33.815 ","End":"03:36.590","Text":"but in terms of their genotype,"},{"Start":"03:36.590 ","End":"03:39.470","Text":"in terms of the DNA that they contain,"},{"Start":"03:39.470 ","End":"03:44.930","Text":"the parental ones will be homologous on both the 2 chromosomes."},{"Start":"03:44.930 ","End":"03:47.540","Text":"They\u0027ll have the same alleles on the 2 homologous chromosomes,"},{"Start":"03:47.540 ","End":"03:56.300","Text":"whereas the F_1 generation in this case will be heterologous at this locus."},{"Start":"03:57.350 ","End":"04:01.240","Text":"In this case the F_1 plants had"},{"Start":"04:01.240 ","End":"04:06.280","Text":"purple flowers because the alleles for that trait is dominant."},{"Start":"04:06.280 ","End":"04:11.080","Text":"Now there\u0027s 1 more thing that we need to know and that is"},{"Start":"04:11.080 ","End":"04:16.405","Text":"that Mendel realized that there is something called a law of segregation,"},{"Start":"04:16.405 ","End":"04:21.565","Text":"that is that each of the alleles segregate independently."},{"Start":"04:21.565 ","End":"04:26.210","Text":"What does that mean? That means that during meiosis,"},{"Start":"04:26.350 ","End":"04:31.675","Text":"the 2 different alleles can separate independently."},{"Start":"04:31.675 ","End":"04:36.410","Text":"Well, we know that from our previous videos,"},{"Start":"04:36.410 ","End":"04:40.970","Text":"but Mendel didn\u0027t know it and he was able to deduce it from"},{"Start":"04:40.970 ","End":"04:47.720","Text":"his experiments that there was independent segregation of the traits."},{"Start":"04:47.720 ","End":"04:51.050","Text":"This corresponds to the distribution of"},{"Start":"04:51.050 ","End":"04:57.060","Text":"homologous chromosomes that are found in the plant."},{"Start":"04:57.800 ","End":"05:01.190","Text":"His model, and we\u0027ll see this a bit later,"},{"Start":"05:01.190 ","End":"05:06.890","Text":"accounts for the 3:1 ratio observed in the F_2 generation."},{"Start":"05:06.890 ","End":"05:11.550","Text":"At this point, we\u0027ll go on to the next video."}],"ID":26359},{"Watched":false,"Name":"Laws of Probability Part b1","Duration":"5m 45s","ChapterTopicVideoID":25539,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.710 ","End":"00:05.130","Text":"Welcome back. Let\u0027s continue now with"},{"Start":"00:05.130 ","End":"00:09.660","Text":"Mendel\u0027s experiments in the laws of probability and look at"},{"Start":"00:09.660 ","End":"00:14.940","Text":"the F_2 generation in which we found that"},{"Start":"00:14.940 ","End":"00:20.985","Text":"there was a 3:1 between the purple and the white flowers."},{"Start":"00:20.985 ","End":"00:28.275","Text":"Let\u0027s see if we can understand why that might be and this is what Mendel suggested."},{"Start":"00:28.275 ","End":"00:31.485","Text":"He suggested we make something called a Punnett"},{"Start":"00:31.485 ","End":"00:36.290","Text":"square after the person Punnett who decided to present things in this way,"},{"Start":"00:36.290 ","End":"00:39.390","Text":"so these squares are called Punnett squares."},{"Start":"00:39.390 ","End":"00:44.240","Text":"What we do there is, on 1 axis,"},{"Start":"00:44.240 ","End":"00:49.610","Text":"we\u0027ll put the sperm from the heterologous F_1 plant."},{"Start":"00:49.610 ","End":"00:52.480","Text":"You\u0027ll see there\u0027s a purple and a white."},{"Start":"00:52.480 ","End":"00:55.185","Text":"Those will be from the pollen."},{"Start":"00:55.185 ","End":"01:02.945","Text":"Then the eggs from the female plant will also be heterologous."},{"Start":"01:02.945 ","End":"01:08.060","Text":"It\u0027s actually the same plant in this case because it\u0027s going to be self-fertilizing."},{"Start":"01:08.060 ","End":"01:11.915","Text":"But in any case, the eggs will be purple and white."},{"Start":"01:11.915 ","End":"01:15.515","Text":"In other words, they have those traits in them."},{"Start":"01:15.515 ","End":"01:19.490","Text":"Then if a purple fertilizes a purple,"},{"Start":"01:19.490 ","End":"01:21.485","Text":"then we\u0027ll get a purple plant."},{"Start":"01:21.485 ","End":"01:24.785","Text":"If a purple fertilizes a white,"},{"Start":"01:24.785 ","End":"01:26.510","Text":"we\u0027ll still get a purple plant."},{"Start":"01:26.510 ","End":"01:32.340","Text":"Why? Because remember that the purple trait is dominant."},{"Start":"01:32.340 ","End":"01:37.100","Text":"Again, we have the same thing if we look at it with the purple sperm,"},{"Start":"01:37.100 ","End":"01:41.000","Text":"with the white traded egg, still purple."},{"Start":"01:41.000 ","End":"01:47.480","Text":"The only way we\u0027re going to get a white plant is if there is no purple traits around."},{"Start":"01:47.480 ","End":"01:53.945","Text":"In other words, both the sperm and the egg don\u0027t encode the purple color,"},{"Start":"01:53.945 ","End":"01:55.070","Text":"then we\u0027ll get a white."},{"Start":"01:55.070 ","End":"01:57.980","Text":"As you can see, there are 4 possibilities,"},{"Start":"01:57.980 ","End":"02:03.750","Text":"but only 3 of them will create a purple flower."},{"Start":"02:03.750 ","End":"02:08.417","Text":"That was the insight that Mendel had."},{"Start":"02:08.417 ","End":"02:14.030","Text":"First thing that gave him insight to understand that each of these traits then"},{"Start":"02:14.030 ","End":"02:20.750","Text":"is independent and that there is such a thing as dominance."},{"Start":"02:20.750 ","End":"02:23.435","Text":"Now in our representation,"},{"Start":"02:23.435 ","End":"02:30.440","Text":"we will represent a dominant allele as being in a capital letter,"},{"Start":"02:30.440 ","End":"02:37.590","Text":"whereas a recessive one will be in a lowercase letter."},{"Start":"02:37.590 ","End":"02:42.225","Text":"Here we\u0027ve got P for purple that\u0027s dominant"},{"Start":"02:42.225 ","End":"02:48.115","Text":"and letter p that is not dominant and that will be white."},{"Start":"02:48.115 ","End":"02:51.025","Text":"Lowercase is recessive allele."},{"Start":"02:51.025 ","End":"02:54.725","Text":"Let\u0027s look a little bit of probability."},{"Start":"02:54.725 ","End":"02:56.300","Text":"You all know, for instance,"},{"Start":"02:56.300 ","End":"02:58.640","Text":"that if you flip a coin a whole bunch of times,"},{"Start":"02:58.640 ","End":"03:00.485","Text":"sometimes it\u0027ll come up heads,"},{"Start":"03:00.485 ","End":"03:02.450","Text":"sometimes it\u0027ll come up tails."},{"Start":"03:02.450 ","End":"03:06.294","Text":"There\u0027s some probability that it\u0027s going to come up this way sometimes,"},{"Start":"03:06.294 ","End":"03:08.690","Text":"another probability is going to come up the other way sometimes"},{"Start":"03:08.690 ","End":"03:11.000","Text":"and if the coin is a fair coin,"},{"Start":"03:11.000 ","End":"03:14.900","Text":"irregular coin, then it\u0027ll come up half and a half each way."},{"Start":"03:14.900 ","End":"03:17.255","Text":"The same thing with a die."},{"Start":"03:17.255 ","End":"03:20.930","Text":"A particular die if it\u0027s not weighted,"},{"Start":"03:20.930 ","End":"03:24.020","Text":"then if it\u0027s a fair good die,"},{"Start":"03:24.020 ","End":"03:30.930","Text":"then there\u0027s a 1 in 6 chance that it will come up with any particular side up."},{"Start":"03:31.130 ","End":"03:38.195","Text":"For each thing, there is a likelihood that something is going to happen."},{"Start":"03:38.195 ","End":"03:40.400","Text":"It can be either impossible,"},{"Start":"03:40.400 ","End":"03:42.560","Text":"like if you\u0027re flipping a coin,"},{"Start":"03:42.560 ","End":"03:46.580","Text":"it\u0027s not going to come up anything other than heads or tails,"},{"Start":"03:46.580 ","End":"03:52.355","Text":"or it can be certain that it\u0027s always going to turn up the same way, for instance."},{"Start":"03:52.355 ","End":"03:55.145","Text":"But usually there\u0027s something in the middle."},{"Start":"03:55.145 ","End":"04:00.635","Text":"This is an empirical probability that\u0027s the number of times the event occurs,"},{"Start":"04:00.635 ","End":"04:05.420","Text":"divided by the total number of opportunities for the event to occur."},{"Start":"04:05.420 ","End":"04:09.745","Text":"If you\u0027ve, let say flip the coin 10 times"},{"Start":"04:09.745 ","End":"04:14.925","Text":"and it comes up heads 4 times and tails 6 times,"},{"Start":"04:14.925 ","End":"04:18.840","Text":"so it would be 4 divided by 10."},{"Start":"04:18.840 ","End":"04:21.030","Text":"Because 10 is a total number of opportunities,"},{"Start":"04:21.030 ","End":"04:25.010","Text":"the probability of it happening,"},{"Start":"04:25.010 ","End":"04:28.340","Text":"you would say would be 0.4."},{"Start":"04:28.340 ","End":"04:34.525","Text":"It would be the empirical probability that you got out of the experiment."},{"Start":"04:34.525 ","End":"04:37.555","Text":"But there are also theoretical probabilities."},{"Start":"04:37.555 ","End":"04:42.850","Text":"The theoretical probability is the number of times that event is expected to occur."},{"Start":"04:42.850 ","End":"04:47.710","Text":"You expect when you flip a coin that it\u0027s going to be 50, 50,"},{"Start":"04:47.710 ","End":"04:50.580","Text":"it\u0027s going to be 50 percent of the time,"},{"Start":"04:50.580 ","End":"04:55.405","Text":"one way and 50 percent the other divided by the number of times that it could occur."},{"Start":"04:55.405 ","End":"04:57.295","Text":"In the example that I gave,"},{"Start":"04:57.295 ","End":"05:00.520","Text":"the theoretical probability would be 0.5."},{"Start":"05:00.520 ","End":"05:05.170","Text":"Whereas the empirical probability with the particular experiment that we did,"},{"Start":"05:05.170 ","End":"05:10.160","Text":"we only flipped it 10 times, was 0.4."},{"Start":"05:10.310 ","End":"05:17.205","Text":"The total probability of something happening for certain is 1,"},{"Start":"05:17.205 ","End":"05:20.360","Text":"because they would be 1 over the other,"},{"Start":"05:20.360 ","End":"05:21.695","Text":"1 divided by the other is 1."},{"Start":"05:21.695 ","End":"05:27.965","Text":"The event is guaranteed to occur and the probability is 0 if it will never occur."},{"Start":"05:27.965 ","End":"05:31.220","Text":"Mendel then, using his experiments,"},{"Start":"05:31.220 ","End":"05:34.415","Text":"was able to calculate the probabilities of"},{"Start":"05:34.415 ","End":"05:37.880","Text":"the particular outcomes that he got and used these to"},{"Start":"05:37.880 ","End":"05:45.540","Text":"predict both the outcomes of recessive and dominant traits crosses."}],"ID":26356},{"Watched":false,"Name":"Laws of Probability Part b2","Duration":"8m 26s","ChapterTopicVideoID":25541,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.350 ","End":"00:05.580","Text":"Now we\u0027re going to look a little bit into the laws of probability and we\u0027re going to"},{"Start":"00:05.580 ","End":"00:10.485","Text":"distinguish between the product rule and the sum rule."},{"Start":"00:10.485 ","End":"00:17.955","Text":"What does that mean? If we\u0027ve got 2 independent things going on,"},{"Start":"00:17.955 ","End":"00:23.000","Text":"we have the traits of A and the traits of B,"},{"Start":"00:23.000 ","End":"00:27.315","Text":"we\u0027re going to want to know what is the probability,"},{"Start":"00:27.315 ","End":"00:32.130","Text":"let\u0027s say of both of those things happening at the same time."},{"Start":"00:32.130 ","End":"00:34.555","Text":"Let\u0027s look at something like that."},{"Start":"00:34.555 ","End":"00:37.950","Text":"Mendel demonstrated that pea plants transmit"},{"Start":"00:37.950 ","End":"00:41.730","Text":"characteristics as discrete units as we mentioned,"},{"Start":"00:41.730 ","End":"00:45.620","Text":"those discrete units are genes from parents to offspring."},{"Start":"00:45.620 ","End":"00:51.510","Text":"He also determined that different characteristics were transmitted independently."},{"Start":"00:51.510 ","End":"01:00.245","Text":"For example, when he performed a cross between a plant with a green wrinkled seeds."},{"Start":"01:00.245 ","End":"01:03.395","Text":"Those are 2 different characteristics both green and wrinkled,"},{"Start":"01:03.395 ","End":"01:06.740","Text":"and a plant with yellow round seeds,"},{"Start":"01:06.740 ","End":"01:08.825","Text":"so the characteristics are different,"},{"Start":"01:08.825 ","End":"01:14.780","Text":"still produced an offspring that had a 3-1 ratio of green to yellow seeds."},{"Start":"01:14.780 ","End":"01:17.825","Text":"That was something that he saw empirically."},{"Start":"01:17.825 ","End":"01:20.210","Text":"Notice the word, and."},{"Start":"01:20.210 ","End":"01:22.850","Text":"He had a cross between a plant with"},{"Start":"01:22.850 ","End":"01:29.165","Text":"green wrinkled seeds and a plant with yellow round seeds."},{"Start":"01:29.165 ","End":"01:36.545","Text":"The product rule says that the probability of 2 independent events occurring together,"},{"Start":"01:36.545 ","End":"01:39.485","Text":"that\u0027s the and, the both are happening."},{"Start":"01:39.485 ","End":"01:44.420","Text":"Then what you need to do is to multiply the individual probabilities."},{"Start":"01:44.420 ","End":"01:51.025","Text":"We need to multiply the individual probabilities of each event occurring alone."},{"Start":"01:51.025 ","End":"01:56.210","Text":"Yes, so the probability of both A and B happening,"},{"Start":"01:56.210 ","End":"01:58.940","Text":"P is this probability here in this case."},{"Start":"01:58.940 ","End":"02:03.890","Text":"Yes, is the product of the probability of A times"},{"Start":"02:03.890 ","End":"02:09.565","Text":"the probability of B in the case of the dice here."},{"Start":"02:09.565 ","End":"02:16.075","Text":"There\u0027s a 1 in 6 probability that we\u0027ll get any one of the faces in both cases."},{"Start":"02:16.075 ","End":"02:18.780","Text":"You\u0027ll be 1/6 times 1/6,"},{"Start":"02:18.780 ","End":"02:24.080","Text":"which turns out to be this 0.0278 number."},{"Start":"02:24.080 ","End":"02:25.790","Text":"That\u0027s the probability that,"},{"Start":"02:25.790 ","End":"02:32.160","Text":"let\u0027s say you\u0027d get a 63. That\u0027s the probability."},{"Start":"02:32.470 ","End":"02:40.610","Text":"Let\u0027s see how this really works in greater detail."},{"Start":"02:40.610 ","End":"02:44.810","Text":"Let\u0027s say for the product rule that we\u0027re rolling"},{"Start":"02:44.810 ","End":"02:49.700","Text":"a 6 sided die and we\u0027re flipping a penny at the same time,"},{"Start":"02:49.700 ","End":"02:53.405","Text":"not 2 dice but 1 die and 1 penny."},{"Start":"02:53.405 ","End":"02:56.465","Text":"The penny here is either heads or tails."},{"Start":"02:56.465 ","End":"03:00.480","Text":"Heads or tails, PH, PT."},{"Start":"03:00.480 ","End":"03:02.288","Text":"But the dice can be either 1,"},{"Start":"03:02.288 ","End":"03:04.530","Text":"2, 3, 4, 5, 6."},{"Start":"03:04.530 ","End":"03:07.055","Text":"These are all the various possibilities."},{"Start":"03:07.055 ","End":"03:09.215","Text":"If you\u0027re rolling a die and flipping a penny,"},{"Start":"03:09.215 ","End":"03:12.660","Text":"you could get the die to show up with 1 and it could be"},{"Start":"03:12.660 ","End":"03:16.550","Text":"heads or it could be 1 and the penny could be tails,"},{"Start":"03:16.550 ","End":"03:20.045","Text":"and if you do this all of these times it turns out"},{"Start":"03:20.045 ","End":"03:24.565","Text":"that you have 12 different possibilities."},{"Start":"03:24.565 ","End":"03:30.300","Text":"The die roll any number from 1-6,"},{"Start":"03:30.300 ","End":"03:34.955","Text":"and the penny can be either heads or a tails."},{"Start":"03:34.955 ","End":"03:40.280","Text":"The outcome of rolling the die and flipping the penny is independent in this case."},{"Start":"03:40.280 ","End":"03:42.125","Text":"If you flip the die one way,"},{"Start":"03:42.125 ","End":"03:47.715","Text":"it\u0027s not going to affect how the penny is going to flip and vice versa."},{"Start":"03:47.715 ","End":"03:50.330","Text":"These are independent events."},{"Start":"03:50.330 ","End":"03:52.190","Text":"As I mentioned, there are 12 different outcomes and"},{"Start":"03:52.190 ","End":"03:55.145","Text":"each event is expected to occur with equal probability."},{"Start":"03:55.145 ","End":"03:57.305","Text":"In the product rule for instance,"},{"Start":"03:57.305 ","End":"04:01.030","Text":"if you wanted to come up with a 2, let\u0027s see."},{"Start":"04:01.030 ","End":"04:08.220","Text":"The die has a 2 out of 12 or a 1/6 probability obviously of rolling a 2."},{"Start":"04:08.220 ","End":"04:14.480","Text":"The penny has a 1/2 probability of coming up heads."},{"Start":"04:14.480 ","End":"04:20.161","Text":"The probability outcome of getting a 2 and"},{"Start":"04:20.161 ","End":"04:26.535","Text":"heads would be the first probability 1/6 times 1/2,"},{"Start":"04:26.535 ","End":"04:28.365","Text":"which is 1/12,"},{"Start":"04:28.365 ","End":"04:32.000","Text":"and that\u0027s what we see here in this example."},{"Start":"04:32.000 ","End":"04:34.355","Text":"But if we\u0027re looking at plants,"},{"Start":"04:34.355 ","End":"04:36.425","Text":"which is what Mendel was looking at,"},{"Start":"04:36.425 ","End":"04:40.130","Text":"the probability of having both dominant traits in"},{"Start":"04:40.130 ","End":"04:44.510","Text":"the F2 progeny there would be, what would it be?"},{"Start":"04:44.510 ","End":"04:52.260","Text":"It would be 3/4 because we said that\u0027s 3 out of 4, 3-1."},{"Start":"04:52.260 ","End":"04:59.160","Text":"It\u0027s 3 out of 4 times 3/4, which equals 9/16."},{"Start":"04:59.160 ","End":"05:02.550","Text":"That\u0027s what he found with the 2 separate traits,"},{"Start":"05:02.550 ","End":"05:06.020","Text":"so the traits then segregated independently and he was"},{"Start":"05:06.020 ","End":"05:09.935","Text":"able to deduce that from the results that he"},{"Start":"05:09.935 ","End":"05:13.520","Text":"got by counting this colored flowers and"},{"Start":"05:13.520 ","End":"05:18.290","Text":"the other traits that he was looking at at the same time."},{"Start":"05:18.290 ","End":"05:20.555","Text":"Now what\u0027s the sum rule?"},{"Start":"05:20.555 ","End":"05:23.600","Text":"In the sum rule, flipping a penny and a quarter,"},{"Start":"05:23.600 ","End":"05:24.755","Text":"let\u0027s say for instance,"},{"Start":"05:24.755 ","End":"05:28.340","Text":"we might ask what is the probability of 1 coin coming up"},{"Start":"05:28.340 ","End":"05:33.030","Text":"heads and 1 coin coming up tails?"},{"Start":"05:33.770 ","End":"05:40.110","Text":"That is 1 coin coming up heads and 1 coin coming up tails."},{"Start":"05:40.110 ","End":"05:46.420","Text":"The penny may be heads and the quarter may be tails or not heads,"},{"Start":"05:46.420 ","End":"05:49.095","Text":"or the quarter may be heads,"},{"Start":"05:49.095 ","End":"05:52.545","Text":"and the penny may be tails either way."},{"Start":"05:52.545 ","End":"05:58.670","Text":"It turns that would be the first probability that we discussed before"},{"Start":"05:58.670 ","End":"06:04.250","Text":"with the product rule plus the other probabilities,"},{"Start":"06:04.250 ","End":"06:08.720","Text":"the probability of heads and the quarter tails and the probability"},{"Start":"06:08.720 ","End":"06:14.565","Text":"of the quarter one way heads and penny tails."},{"Start":"06:14.565 ","End":"06:22.825","Text":"Each of those is a 1/2 times a 1/2 which is a 1/4 plus the opposite situation,"},{"Start":"06:22.825 ","End":"06:25.680","Text":"so a 1/4 plus a 1/4 is a 1/2."},{"Start":"06:25.680 ","End":"06:28.550","Text":"If we do the same thing in"},{"Start":"06:28.550 ","End":"06:34.310","Text":"the F2 generation with the dihybrid cross just as we had done earlier,"},{"Start":"06:34.310 ","End":"06:40.534","Text":"so the probability of having just 1 dominant traits in the F2 generation,"},{"Start":"06:40.534 ","End":"06:43.980","Text":"probably of having just 1 not having both,"},{"Start":"06:43.980 ","End":"06:48.480","Text":"but just 1 would be 3/16 times"},{"Start":"06:48.480 ","End":"06:55.185","Text":"3/4 which equals 15/16."},{"Start":"06:55.185 ","End":"06:57.740","Text":"To summarize now, the product rule and the sum rule and"},{"Start":"06:57.740 ","End":"07:02.555","Text":"the product rule for independent events A and B."},{"Start":"07:02.555 ","End":"07:05.420","Text":"These are the names of the events A and B."},{"Start":"07:05.420 ","End":"07:09.080","Text":"The probability P of them both occurring,"},{"Start":"07:09.080 ","End":"07:17.180","Text":"that is A and B is the probability of A times the probability of B."},{"Start":"07:17.180 ","End":"07:21.710","Text":"Whereas in the sum rule for mutually exclusive events A and B,"},{"Start":"07:21.710 ","End":"07:24.753","Text":"that means that they can\u0027t happen at the same time,"},{"Start":"07:24.753 ","End":"07:28.785","Text":"the probability that at least 1 occurs,"},{"Start":"07:28.785 ","End":"07:36.440","Text":"A or B is the probability of A plus the probability of B."},{"Start":"07:36.440 ","End":"07:38.825","Text":"Now in this section,"},{"Start":"07:38.825 ","End":"07:40.250","Text":"you learned how to describe"},{"Start":"07:40.250 ","End":"07:43.220","Text":"the scientific reasons for the success of Mendel\u0027s experimental work,"},{"Start":"07:43.220 ","End":"07:49.160","Text":"that he understood the probability and the independent assortments,"},{"Start":"07:49.160 ","End":"07:52.174","Text":"and then each of those things were discrete."},{"Start":"07:52.174 ","End":"07:54.440","Text":"He described the expected outcomes of"},{"Start":"07:54.440 ","End":"07:57.920","Text":"mono hybrid crosses involving dominant and recessive alleles."},{"Start":"07:57.920 ","End":"08:04.160","Text":"We saw that and he understood the concepts of dominance and recessive,"},{"Start":"08:04.160 ","End":"08:06.665","Text":"but didn\u0027t call them alleles quite."},{"Start":"08:06.665 ","End":"08:13.009","Text":"We now understand how the sum and product rules can calculate probabilities,"},{"Start":"08:13.009 ","End":"08:18.380","Text":"and we know that Mendel results fit well with"},{"Start":"08:18.380 ","End":"08:21.530","Text":"the laws of probability and from that he"},{"Start":"08:21.530 ","End":"08:26.070","Text":"could deduce what the background was in the biology."}],"ID":26358},{"Watched":false,"Name":"Characteristics and Traits Part a1","Duration":"4m 31s","ChapterTopicVideoID":25544,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:06.885","Text":"Welcome back. So far we\u0027ve been looking at Mendel\u0027s experiments on the P,"},{"Start":"00:06.885 ","End":"00:13.530","Text":"and we\u0027ve understood how he came to some of his ideas about heredity."},{"Start":"00:13.530 ","End":"00:17.475","Text":"In this section, we\u0027re going to speak about this more."},{"Start":"00:17.475 ","End":"00:19.620","Text":"We\u0027ll expand it and we\u0027ll speak about"},{"Start":"00:19.620 ","End":"00:23.505","Text":"the various characteristics and traits that organisms might have,"},{"Start":"00:23.505 ","End":"00:28.020","Text":"will expand his ideas to other organisms as well."},{"Start":"00:28.020 ","End":"00:29.715","Text":"By the end of this section,"},{"Start":"00:29.715 ","End":"00:32.130","Text":"you\u0027ll be able to explain the relationship between"},{"Start":"00:32.130 ","End":"00:36.620","Text":"genotypes and phenotypes in dominant and recessive gene systems."},{"Start":"00:36.620 ","End":"00:39.290","Text":"You\u0027ll be able to develop a Punnett square to calculate"},{"Start":"00:39.290 ","End":"00:44.080","Text":"the expected proportions of genotypes and phenotypes in a monohybrid cross."},{"Start":"00:44.080 ","End":"00:47.250","Text":"We\u0027ll understand better what a monohybrid cross is."},{"Start":"00:47.250 ","End":"00:51.140","Text":"We\u0027ll explain the purpose and methods of a test cross."},{"Start":"00:51.140 ","End":"00:57.440","Text":"This is a cross we haven\u0027t seen yet and will identify non-Mendelian inheritance patterns,"},{"Start":"00:57.440 ","End":"00:59.955","Text":"such as incomplete dominance."},{"Start":"00:59.955 ","End":"01:03.905","Text":"With Mendelian inheritance, we always have dominance,"},{"Start":"01:03.905 ","End":"01:05.735","Text":"but sometimes it\u0027s incomplete."},{"Start":"01:05.735 ","End":"01:09.020","Text":"Or there could be codominance or there can be"},{"Start":"01:09.020 ","End":"01:12.845","Text":"recessive lethal multiple alleles and sex linkage."},{"Start":"01:12.845 ","End":"01:15.530","Text":"Mendel was lucky that he didn\u0027t see these"},{"Start":"01:15.530 ","End":"01:18.840","Text":"in the P otherwise it would\u0027ve confused him a lot."},{"Start":"01:18.920 ","End":"01:24.625","Text":"All plants and animals are diploid organisms."},{"Start":"01:24.625 ","End":"01:30.575","Text":"Diploid organisms produce haploid gametes that create a diploid zygote."},{"Start":"01:30.575 ","End":"01:34.580","Text":"Yes, diploid organisms produce haploid gametes that"},{"Start":"01:34.580 ","End":"01:38.690","Text":"create a diploid zygote. What does that mean?"},{"Start":"01:38.690 ","End":"01:43.340","Text":"It means that there are 2 homologous chromosomes,"},{"Start":"01:43.340 ","End":"01:46.655","Text":"each of which came from a single parent as we know."},{"Start":"01:46.655 ","End":"01:50.015","Text":"When a single gene controls a single characteristic,"},{"Start":"01:50.015 ","End":"01:55.310","Text":"then a diploid organism has 2 genetic copies of that characteristic,"},{"Start":"01:55.310 ","End":"01:58.295","Text":"1 from the mother and 1 from the father."},{"Start":"01:58.295 ","End":"02:00.200","Text":"Here is C2 chromosomes."},{"Start":"02:00.200 ","End":"02:06.785","Text":"Yes, and they\u0027re at specific traits encoded by specific genes at particular places."},{"Start":"02:06.785 ","End":"02:14.719","Text":"Here they\u0027re denoted by large letters for dominant or small letters for recessive genes."},{"Start":"02:14.719 ","End":"02:17.780","Text":"Gene variance that arise by mutation and exist at"},{"Start":"02:17.780 ","End":"02:22.505","Text":"the same relative locations on homologous chromosomes are called alleles."},{"Start":"02:22.505 ","End":"02:24.005","Text":"What does that mean?"},{"Start":"02:24.005 ","End":"02:25.850","Text":"That means, as we just said,"},{"Start":"02:25.850 ","End":"02:27.950","Text":"that there can be a dominant or recessive,"},{"Start":"02:27.950 ","End":"02:33.185","Text":"or actually, there can be many different mutations at this particular gene."},{"Start":"02:33.185 ","End":"02:40.480","Text":"Each of those genes with different mutations are called different alleles."},{"Start":"02:40.480 ","End":"02:42.590","Text":"It is very common to encounter"},{"Start":"02:42.590 ","End":"02:46.250","Text":"more than 2 alleles for any given gene in a natural population."},{"Start":"02:46.250 ","End":"02:48.575","Text":"You can have, let\u0027s say,"},{"Start":"02:48.575 ","End":"02:52.400","Text":"a stretch of DNA that encodes there is part"},{"Start":"02:52.400 ","End":"02:56.180","Text":"of a particular gene or an entire gene and the mutations can"},{"Start":"02:56.180 ","End":"03:05.150","Text":"be all along that piece and each mutation then will cause the creation of a new allele."},{"Start":"03:05.150 ","End":"03:10.595","Text":"Now let\u0027s distinguish here between phenotypes and genotypes."},{"Start":"03:10.595 ","End":"03:13.730","Text":"We\u0027ve been talking about the various traits like the color,"},{"Start":"03:13.730 ","End":"03:15.065","Text":"for instance, in a flower."},{"Start":"03:15.065 ","End":"03:20.105","Text":"Those are observable traits and those are called phenotypes."},{"Start":"03:20.105 ","End":"03:23.000","Text":"On the other hand, a genotype is"},{"Start":"03:23.000 ","End":"03:28.700","Text":"the organism\u0027s DNA that encodes both physically visible and non expressed alleles."},{"Start":"03:28.700 ","End":"03:31.640","Text":"You can have an allele, for instance,"},{"Start":"03:31.640 ","End":"03:38.659","Text":"it\u0027s not expressed an- particular mutation might be encoded in its genotype."},{"Start":"03:38.659 ","End":"03:42.530","Text":"The genotype will be expressed sometimes"},{"Start":"03:42.530 ","End":"03:47.270","Text":"as a non-expressed allele depends upon the particular gene."},{"Start":"03:47.270 ","End":"03:50.810","Text":"Mendel\u0027s hybridization experiments demonstrated"},{"Start":"03:50.810 ","End":"03:53.750","Text":"the difference between phenotype and genotype."},{"Start":"03:53.750 ","End":"03:59.780","Text":"Because you can have a genotype that is homozygous or heterozygous."},{"Start":"03:59.780 ","End":"04:02.180","Text":"Homozygous means that they\u0027re the same,"},{"Start":"04:02.180 ","End":"04:04.855","Text":"PP, both dominant."},{"Start":"04:04.855 ","End":"04:09.905","Text":"Whereas when the phenotype can still be the same in his Ps,"},{"Start":"04:09.905 ","End":"04:15.790","Text":"and B and the genotype B heterozygous, B, Pp."},{"Start":"04:15.790 ","End":"04:20.200","Text":"That\u0027s the symbols for the 2 different chromosomes."},{"Start":"04:20.200 ","End":"04:25.415","Text":"You\u0027ll remember that when P1 plants with contrasting traits were cross-fertilized,"},{"Start":"04:25.415 ","End":"04:31.140","Text":"all the offspring were heterozygous for the contrasting traits."}],"ID":26361},{"Watched":false,"Name":"Characteristics and Traits Part a2","Duration":"6m 50s","ChapterTopicVideoID":25545,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.530 ","End":"00:03.867","Text":"Let\u0027s look now at, again,"},{"Start":"00:03.867 ","End":"00:07.470","Text":"dominant and recessive alleles in a little bit more detail."},{"Start":"00:07.470 ","End":"00:12.285","Text":"In all 7 pea plant characteristics that Mendel looked at,"},{"Start":"00:12.285 ","End":"00:17.104","Text":"1 of the 2 contrasting alleles was dominant and the other was recessive."},{"Start":"00:17.104 ","End":"00:22.275","Text":"Mendel called the dominant allele the expressed unit factor whereas the recessive allele,"},{"Start":"00:22.275 ","End":"00:25.230","Text":"he called the latent unit factor."},{"Start":"00:25.230 ","End":"00:29.369","Text":"For a genus expressed in a dominant and recessive pattern,"},{"Start":"00:29.369 ","End":"00:34.095","Text":"homozygous dominant and heterozygous organisms will look identical."},{"Start":"00:34.095 ","End":"00:36.770","Text":"Those purple flowers that we saw earlier,"},{"Start":"00:36.770 ","End":"00:41.650","Text":"it could be either homozygous dominant or heterozygous."},{"Start":"00:41.650 ","End":"00:48.185","Text":"Hence, the recessive allele will only be observed in a homozygous recessive individual,"},{"Start":"00:48.185 ","End":"00:52.325","Text":"like the whites had small y, small y."},{"Start":"00:52.325 ","End":"00:55.460","Text":"Now, what\u0027s a mono-hybrid cross?"},{"Start":"00:55.460 ","End":"01:02.705","Text":"A mono-hybrid cross is a cross in which the fertilization between 2 parents,"},{"Start":"01:02.705 ","End":"01:06.000","Text":"a mono-hybrid cross is the cross"},{"Start":"01:06.000 ","End":"01:10.850","Text":"between 2 parents that differ in only one characteristic,"},{"Start":"01:10.850 ","End":"01:15.185","Text":"let\u0027s say the color of the flower or"},{"Start":"01:15.185 ","End":"01:21.335","Text":"the color of the pea or the wrinkled the pea might be,"},{"Start":"01:21.335 ","End":"01:22.370","Text":"but each of them will have"},{"Start":"01:22.370 ","End":"01:26.690","Text":"only one characteristic and those will be called mono-hybrid crosses,"},{"Start":"01:26.690 ","End":"01:28.610","Text":"you\u0027re crossing between 2 parents that"},{"Start":"01:28.610 ","End":"01:31.048","Text":"dimer in only one characteristic, and as we know,"},{"Start":"01:31.048 ","End":"01:35.842","Text":"the upper and lowercase letters represent dominant and recessive alleles respectively."},{"Start":"01:35.842 ","End":"01:38.735","Text":"For instance, if you have a dominant seed color yellow,"},{"Start":"01:38.735 ","End":"01:40.325","Text":"here we\u0027re repeating, yes,"},{"Start":"01:40.325 ","End":"01:45.590","Text":"the dominant seed would be the Y."},{"Start":"01:45.590 ","End":"01:54.258","Text":"The parental genotypes would be YY or if the seeds were green,"},{"Start":"01:54.258 ","End":"01:55.886","Text":"they would be yy,"},{"Start":"01:55.886 ","End":"01:59.058","Text":"that\u0027s the notation that we\u0027re using."},{"Start":"01:59.058 ","End":"02:08.232","Text":"Obviously, all the resulting peas in the cross F1 generation would be Yy."},{"Start":"02:08.232 ","End":"02:13.028","Text":"We can see that in a punnett square that is shown down below."},{"Start":"02:13.028 ","End":"02:15.185","Text":"This says something, as we learned,"},{"Start":"02:15.185 ","End":"02:20.090","Text":"that helps to predict the expected frequencies of a genetic cross or mating."},{"Start":"02:20.090 ","End":"02:24.830","Text":"Then all the possible combinations of the parental alleles are listed along one side of"},{"Start":"02:24.830 ","End":"02:28.430","Text":"the grid and the other side of the grid and"},{"Start":"02:28.430 ","End":"02:33.549","Text":"each box inside represents the diploid genotype of a possible zygote."},{"Start":"02:33.549 ","End":"02:36.650","Text":"Because each possibility is equally likely,"},{"Start":"02:36.650 ","End":"02:39.158","Text":"then the genotypic ratios can be determined."},{"Start":"02:39.158 ","End":"02:47.470","Text":"We can count these up, in this case the phenotypic ratios would be 3:1 as we saw early,"},{"Start":"02:47.470 ","End":"02:51.035","Text":"but the genotypic ratios can be determined as well."},{"Start":"02:51.035 ","End":"02:56.085","Text":"The genotypic ratios would be 1 YY,"},{"Start":"02:56.085 ","End":"03:04.630","Text":"2 Yy, and 1 yy."},{"Start":"03:04.630 ","End":"03:07.940","Text":"The pattern of inheritance is known,"},{"Start":"03:07.940 ","End":"03:12.470","Text":"then the phenotypic ratios can be inferred as well as we said before."},{"Start":"03:12.470 ","End":"03:17.300","Text":"For a monohybrid cross of 2 true breeding parents, that is,"},{"Start":"03:17.300 ","End":"03:21.680","Text":"that they are homozygous for the particular allele that we\u0027re looking at,"},{"Start":"03:21.680 ","End":"03:24.740","Text":"each parent contributes one type of allele."},{"Start":"03:24.740 ","End":"03:27.260","Text":"If again, it\u0027s a monohybrid,"},{"Start":"03:27.260 ","End":"03:34.140","Text":"you\u0027ll have either Y that it\u0027s going to contribute or if it\u0027s monozygous,"},{"Start":"03:34.140 ","End":"03:37.601","Text":"if it\u0027s true breeding parents, it\u0027s green,"},{"Start":"03:37.601 ","End":"03:43.825","Text":"then you\u0027ll have yy and each of these contributes one type of allele."},{"Start":"03:43.825 ","End":"03:50.270","Text":"Of course, the recessive dominant ratio at F2 as we saw is, again,"},{"Start":"03:50.270 ","End":"03:55.970","Text":"this 3:1 in the phenotype and the genotype we discussed already before."},{"Start":"03:55.970 ","End":"03:58.820","Text":"When Mendel self crossed the plants expressing green seeds,"},{"Start":"03:58.820 ","End":"04:01.160","Text":"all the offspring had green seeds,"},{"Start":"04:01.160 ","End":"04:06.295","Text":"confirming they had a homozygous yy."},{"Start":"04:06.295 ","End":"04:10.380","Text":"He self crossed the green seeds,"},{"Start":"04:10.380 ","End":"04:12.840","Text":"he always got y back."},{"Start":"04:12.840 ","End":"04:15.523","Text":"When the F2 plants self crossed,"},{"Start":"04:15.523 ","End":"04:18.825","Text":"1/3 of the plants bred true,"},{"Start":"04:18.825 ","End":"04:22.545","Text":"1/3 of these,"},{"Start":"04:22.545 ","End":"04:28.400","Text":"of this particular genotype will breed true to,"},{"Start":"04:28.400 ","End":"04:35.690","Text":"means that it\u0027ll be homozygous and 2/3 of the plants"},{"Start":"04:35.690 ","End":"04:39.605","Text":"segregated will be able to give green seeds later"},{"Start":"04:39.605 ","End":"04:44.180","Text":"when they cross with themselves, when they self pollinate."},{"Start":"04:44.180 ","End":"04:47.510","Text":"Yes, so the true-breeding plants are homozygous"},{"Start":"04:47.510 ","End":"04:51.740","Text":"and the segregating plants will be heterozygous."},{"Start":"04:51.740 ","End":"04:53.780","Text":"When these plants self-fertilize,"},{"Start":"04:53.780 ","End":"05:01.519","Text":"the outcome was likely the F1 self fertilizing cross as you can understand."},{"Start":"05:01.519 ","End":"05:05.300","Text":"Now let\u0027s see what a test cross is,"},{"Start":"05:05.300 ","End":"05:07.519","Text":"this should be 2 words, test cross."},{"Start":"05:07.519 ","End":"05:11.180","Text":"A way to determine whether a dominant phenotype is"},{"Start":"05:11.180 ","End":"05:15.965","Text":"a heterozygote or a homozygote is a test cross."},{"Start":"05:15.965 ","End":"05:18.890","Text":"That\u0027s what the test cross does and what do we do?"},{"Start":"05:18.890 ","End":"05:22.640","Text":"An organism is crossed that we don\u0027t know whether it\u0027s a homozygous or"},{"Start":"05:22.640 ","End":"05:28.250","Text":"heterozygous is crossed with a homozygous recessive plant."},{"Start":"05:28.250 ","End":"05:32.810","Text":"Let\u0027s say we had a purple flower and we didn\u0027t know whether it was"},{"Start":"05:32.810 ","End":"05:39.240","Text":"homozygous PP or it was heterozygous Pp."},{"Start":"05:39.240 ","End":"05:44.130","Text":"Well, if it was homozygous PP,"},{"Start":"05:44.130 ","End":"05:46.235","Text":"so let\u0027s look here."},{"Start":"05:46.235 ","End":"05:47.510","Text":"Then what would happen?"},{"Start":"05:47.510 ","End":"05:50.510","Text":"All the flowers would be purple,"},{"Start":"05:50.510 ","End":"05:56.575","Text":"because every flower would have in it a large P,"},{"Start":"05:56.575 ","End":"06:00.065","Text":"would have a dominant allele,"},{"Start":"06:00.065 ","End":"06:02.240","Text":"and therefore, all the flowers would be purple."},{"Start":"06:02.240 ","End":"06:05.360","Text":"However, if it was heterozygous,"},{"Start":"06:05.360 ","End":"06:08.495","Text":"if this purple flower were heterozygous,"},{"Start":"06:08.495 ","End":"06:13.445","Text":"then we would get some white flowers out as well and we\u0027d get half of them."},{"Start":"06:13.445 ","End":"06:17.660","Text":"If the dominant expressing organism is a homozygote then"},{"Start":"06:17.660 ","End":"06:23.210","Text":"all the F1 offspring will be heterozygous expressing the dominant trait."},{"Start":"06:23.210 ","End":"06:24.740","Text":"That\u0027s what we see on the left."},{"Start":"06:24.740 ","End":"06:26.660","Text":"If any of the offspring display"},{"Start":"06:26.660 ","End":"06:30.290","Text":"the recessive phenotype and that\u0027s what we see here on the right,"},{"Start":"06:30.290 ","End":"06:33.440","Text":"the tested parent must be heterozygous."},{"Start":"06:33.440 ","End":"06:36.005","Text":"That\u0027s what this test cross tells us."},{"Start":"06:36.005 ","End":"06:38.510","Text":"The test cross further validates"},{"Start":"06:38.510 ","End":"06:43.250","Text":"Mendel\u0027s postulate that pairs of unit factors segregate equally."},{"Start":"06:43.250 ","End":"06:45.425","Text":"But it wouldn\u0027t work, this test cross,"},{"Start":"06:45.425 ","End":"06:49.860","Text":"if Mendel\u0027s postulate were wrong."}],"ID":26362},{"Watched":false,"Name":"Characteristics and Traits Part a3","Duration":"4m 56s","ChapterTopicVideoID":25530,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.290 ","End":"00:02.835","Text":"Let\u0027s continue looking at"},{"Start":"00:02.835 ","End":"00:08.580","Text":"genetically inherited diseases now this time in people and not in peas."},{"Start":"00:08.580 ","End":"00:14.460","Text":"In particular, let\u0027s look at a disease called alkaptonuria,"},{"Start":"00:14.460 ","End":"00:17.400","Text":"which is a disease that causes black urine."},{"Start":"00:17.400 ","End":"00:19.755","Text":"Not terribly serious."},{"Start":"00:19.755 ","End":"00:21.210","Text":"But in any case,"},{"Start":"00:21.210 ","End":"00:25.515","Text":"it too, just like the examples that we saw in peas,"},{"Start":"00:25.515 ","End":"00:28.995","Text":"is inherited in a dominant and recessive form."},{"Start":"00:28.995 ","End":"00:31.815","Text":"There can be people who are affected."},{"Start":"00:31.815 ","End":"00:37.230","Text":"They\u0027ll be in blue in this pedigree analysis."},{"Start":"00:37.230 ","End":"00:42.935","Text":"There will be people whose phenotype is normal, unaffected."},{"Start":"00:42.935 ","End":"00:48.755","Text":"Now of course, an affected individual must be aa."},{"Start":"00:48.755 ","End":"00:52.850","Text":"Must have both recessive genes from each of his parents."},{"Start":"00:52.850 ","End":"00:58.460","Text":"Whereas someone who is unaffected could be either homozygous."},{"Start":"00:58.460 ","End":"01:01.850","Text":"They could be either homozygous for"},{"Start":"01:01.850 ","End":"01:09.025","Text":"the dominant normal alleles or it could be heterozygous like in this case."},{"Start":"01:09.025 ","End":"01:15.005","Text":"Let\u0027s see how we can tell what the genotype is of the people."},{"Start":"01:15.005 ","End":"01:20.690","Text":"In this case, we started out with a couple in which the male,"},{"Start":"01:20.690 ","End":"01:23.385","Text":"denoted by a box,"},{"Start":"01:23.385 ","End":"01:25.460","Text":"was affected, had the disease."},{"Start":"01:25.460 ","End":"01:29.285","Text":"That means that he must have been aa."},{"Start":"01:29.285 ","End":"01:31.160","Text":"Well, what about the female?"},{"Start":"01:31.160 ","End":"01:35.280","Text":"The female could either be the homozygous,"},{"Start":"01:35.280 ","End":"01:39.240","Text":"AA or heterozygous, Aa."},{"Start":"01:39.240 ","End":"01:41.250","Text":"Well, we can tell."},{"Start":"01:41.250 ","End":"01:46.010","Text":"Because if she were homozygous,"},{"Start":"01:46.010 ","End":"01:50.735","Text":"AA, then she could not have progeny who are affected."},{"Start":"01:50.735 ","End":"01:54.890","Text":"She must have been Aa."},{"Start":"01:54.890 ","End":"02:00.300","Text":"Let\u0027s look at another example in this pedigree analysis."},{"Start":"02:00.300 ","End":"02:02.285","Text":"In this particular case,"},{"Start":"02:02.285 ","End":"02:09.444","Text":"we have 2 unaffected individuals who have a child that is affected."},{"Start":"02:09.444 ","End":"02:18.680","Text":"That means each of them must have donated a, a recessive gene."},{"Start":"02:18.680 ","End":"02:26.110","Text":"Therefore, each of them must have been heterozygous, Aa."},{"Start":"02:26.110 ","End":"02:29.150","Text":"In this case, for instance, we can\u0027t tell whether"},{"Start":"02:29.150 ","End":"02:35.780","Text":"this unaffected individual is heterozygous or homozygous. Could be homozygous."},{"Start":"02:35.780 ","End":"02:37.856","Text":"Could have gotten a A and another A,"},{"Start":"02:37.856 ","End":"02:39.680","Text":"each of her parents."},{"Start":"02:39.680 ","End":"02:43.230","Text":"But in any case, we don\u0027t know."},{"Start":"02:43.230 ","End":"02:48.275","Text":"A recessive genetic order certainly can pass through generations."},{"Start":"02:48.275 ","End":"02:55.470","Text":"Here\u0027s an example where the recessive affected phenotype was not found in 1 generation,"},{"Start":"02:55.470 ","End":"02:59.970","Text":"but the genetic disorder of course was passed through generations."},{"Start":"02:59.970 ","End":"03:04.010","Text":"The only way to tell exactly what\u0027s going on here is to use"},{"Start":"03:04.010 ","End":"03:09.245","Text":"this pedigree analysis to study the inheritance pattern of human genetic diseases."},{"Start":"03:09.245 ","End":"03:15.140","Text":"Many times genetic counselors will use family histories in order to advise"},{"Start":"03:15.140 ","End":"03:22.415","Text":"couples on what their genotypes might be regarding particular diseases."},{"Start":"03:22.415 ","End":"03:27.265","Text":"Let\u0027s look now at alternatives to dominance and recessiveness."},{"Start":"03:27.265 ","End":"03:31.550","Text":"Mendel didn\u0027t know anything about alternatives to"},{"Start":"03:31.550 ","End":"03:35.240","Text":"dominance and recessiveness because in the experiments that he performed,"},{"Start":"03:35.240 ","End":"03:38.900","Text":"he only was looking at traits that were either dominant or recessive."},{"Start":"03:38.900 ","End":"03:40.895","Text":"We can find for instance,"},{"Start":"03:40.895 ","End":"03:43.655","Text":"in different kinds of matings that we can have"},{"Start":"03:43.655 ","End":"03:46.880","Text":"either complete dominance like Mendel saw,"},{"Start":"03:46.880 ","End":"03:50.180","Text":"but we can also have incomplete dominance where"},{"Start":"03:50.180 ","End":"03:54.560","Text":"the F1 generation may have some sort of an intermediate phenotype."},{"Start":"03:54.560 ","End":"04:00.545","Text":"In this case, the red flower was homozygous, RR."},{"Start":"04:00.545 ","End":"04:05.870","Text":"The white flower was a different allele,"},{"Start":"04:05.870 ","End":"04:10.490","Text":"which was big white, big white, WW."},{"Start":"04:10.490 ","End":"04:12.110","Text":"When these came together,"},{"Start":"04:12.110 ","End":"04:18.555","Text":"we got an intermediate phenotype which was RW,"},{"Start":"04:18.555 ","End":"04:20.250","Text":"and it\u0027s pink in this case."},{"Start":"04:20.250 ","End":"04:22.220","Text":"That\u0027s incomplete dominance."},{"Start":"04:22.220 ","End":"04:24.140","Text":"We could also have codominance."},{"Start":"04:24.140 ","End":"04:29.445","Text":"2 dominant alleles affect the phenotype in separate distinguishable ways."},{"Start":"04:29.445 ","End":"04:35.330","Text":"Here we have both the white which appears in a certain kind of"},{"Start":"04:35.330 ","End":"04:41.060","Text":"way in the product and the red looks a different way."},{"Start":"04:41.060 ","End":"04:46.400","Text":"But in the F1 generation we get a flower which doesn\u0027t look like either of them."},{"Start":"04:46.400 ","End":"04:48.480","Text":"We have codominance."},{"Start":"04:48.480 ","End":"04:56.460","Text":"Some of the flowers are red and some flowers or some parts of the flower are white."}],"ID":26347},{"Watched":false,"Name":"Characteristics and Traits Part b1","Duration":"5m 33s","ChapterTopicVideoID":25531,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.050 ","End":"00:03.885","Text":"Hi. In this video,"},{"Start":"00:03.885 ","End":"00:09.750","Text":"we\u0027re going to continue our previous discussion of alleles and expand it a bit"},{"Start":"00:09.750 ","End":"00:16.260","Text":"to see that in a population there may be many different alleles,"},{"Start":"00:16.260 ","End":"00:19.785","Text":"not just a dominant and recessive 1."},{"Start":"00:19.785 ","End":"00:22.709","Text":"In dominant organisms,"},{"Start":"00:22.709 ","End":"00:25.305","Text":"they have 2 alleles for a given gene,"},{"Start":"00:25.305 ","End":"00:28.185","Text":"each one of them on a separate chromosome."},{"Start":"00:28.185 ","End":"00:30.650","Text":"But if we look at those alleles,"},{"Start":"00:30.650 ","End":"00:36.380","Text":"then there may be multiple alleles for that gene that exist in the population as a whole."},{"Start":"00:36.380 ","End":"00:40.505","Text":"We discuss the most common 1 as wild-type."},{"Start":"00:40.505 ","End":"00:42.560","Text":"That\u0027s the terminology that we use."},{"Start":"00:42.560 ","End":"00:48.620","Text":"Wild-type is the most common phenotype or genotype among wild animals."},{"Start":"00:48.620 ","End":"00:53.600","Text":"We can use this term wild-type both for phenotype and for genotype."},{"Start":"00:53.600 ","End":"00:55.850","Text":"That\u0027s an important point."},{"Start":"00:55.850 ","End":"00:58.340","Text":"This is the case for wild animals,"},{"Start":"00:58.340 ","End":"01:00.800","Text":"animals that are observed in nature,"},{"Start":"01:00.800 ","End":"01:05.630","Text":"and a lot of times we will denote that with a plus sign."},{"Start":"01:05.630 ","End":"01:08.480","Text":"Then there are variance, for instance,"},{"Start":"01:08.480 ","End":"01:11.465","Text":"the recessive variant that we talked about before."},{"Start":"01:11.465 ","End":"01:13.970","Text":"But in this case we\u0027re saying that there are many variants,"},{"Start":"01:13.970 ","End":"01:17.060","Text":"the other phenotypes or genotypes that may be"},{"Start":"01:17.060 ","End":"01:20.630","Text":"recessive or dominant to the wild-type alleles."},{"Start":"01:20.630 ","End":"01:26.105","Text":"The dominant allele is not necessarily the dominant 1."},{"Start":"01:26.105 ","End":"01:30.470","Text":"Often it is, but it\u0027s certainly not necessarily the case."},{"Start":"01:30.470 ","End":"01:35.960","Text":"Now let\u0027s look at these rabbits, for instance."},{"Start":"01:35.960 ","End":"01:42.620","Text":"In this case, they have several different genotypes and phenotypes."},{"Start":"01:42.620 ","End":"01:45.590","Text":"We can find these rabbits that have"},{"Start":"01:45.590 ","End":"01:51.830","Text":"either black or chinchilla or Himalayan or albino coloring. What does that come from?"},{"Start":"01:51.830 ","End":"02:01.100","Text":"It turns out that it comes from different alleles in this gene C. If the C is plus,"},{"Start":"02:01.100 ","End":"02:05.914","Text":"the wild-type, and it\u0027s homozygous wild-type,"},{"Start":"02:05.914 ","End":"02:09.635","Text":"then those rabbits will have brown fur."},{"Start":"02:09.635 ","End":"02:11.195","Text":"If on the other hand,"},{"Start":"02:11.195 ","End":"02:14.720","Text":"we have the ch allele, homozygous,"},{"Start":"02:14.720 ","End":"02:17.545","Text":"which is a recessive traits,"},{"Start":"02:17.545 ","End":"02:20.695","Text":"then we\u0027ll get a different kind of color,"},{"Start":"02:20.695 ","End":"02:25.325","Text":"this chinchilla color, which has black tipped white fur."},{"Start":"02:25.325 ","End":"02:28.535","Text":"Then there\u0027s the Himalayan has another recessive allele,"},{"Start":"02:28.535 ","End":"02:34.670","Text":"h. That one has black fur at the extremities and white fur elsewhere."},{"Start":"02:34.670 ","End":"02:37.925","Text":"Finally the albino, that will be"},{"Start":"02:37.925 ","End":"02:44.665","Text":"just this small c in this denotation and it has white fur."},{"Start":"02:44.665 ","End":"02:48.500","Text":"The dominant in this case, as I mentioned,"},{"Start":"02:48.500 ","End":"02:53.270","Text":"is the wild-type and it\u0027s dominant over all the others."},{"Start":"02:53.270 ","End":"02:57.380","Text":"But how do these genotypes"},{"Start":"02:57.380 ","End":"03:02.275","Text":"interact with each other if the wild-type is not in the picture."},{"Start":"03:02.275 ","End":"03:08.420","Text":"It turns out that chinchilla is incompletely dominant over Himalayan and albino."},{"Start":"03:08.420 ","End":"03:12.515","Text":"That means you can get rabbits besides these 4,"},{"Start":"03:12.515 ","End":"03:15.955","Text":"you can get some an intermediate color."},{"Start":"03:15.955 ","End":"03:22.325","Text":"We\u0027ll describe that as incompletely dominant."},{"Start":"03:22.325 ","End":"03:27.080","Text":"The chinchilla will be incompletely dominant over Himalayan and albino,"},{"Start":"03:27.080 ","End":"03:30.840","Text":"whereas Himalayan is dominant over albino."},{"Start":"03:30.840 ","End":"03:34.490","Text":"It\u0027s not important that you remember precisely what\u0027s dominant over what,"},{"Start":"03:34.490 ","End":"03:37.040","Text":"but the point is that there is"},{"Start":"03:37.040 ","End":"03:43.940","Text":"this incomplete dominance for some alleles and complete dominance for others."},{"Start":"03:43.940 ","End":"03:47.960","Text":"There\u0027s actually a hierarchy that\u0027s revealed in observing"},{"Start":"03:47.960 ","End":"03:51.990","Text":"the phenotypes for each of these heterozygote offspring."},{"Start":"03:51.990 ","End":"03:57.500","Text":"The only way we really can determine this hierarchy is by observation."},{"Start":"03:57.500 ","End":"04:00.860","Text":"By observation, so we see what the various colors of the rabbits"},{"Start":"04:00.860 ","End":"04:04.985","Text":"are that are the results of particular crosses."},{"Start":"04:04.985 ","End":"04:10.550","Text":"Likewise, in humans, there are multiple alleles."},{"Start":"04:10.550 ","End":"04:12.890","Text":"For blood types, for instance,"},{"Start":"04:12.890 ","End":"04:15.665","Text":"that\u0027s something that you\u0027re probably familiar with."},{"Start":"04:15.665 ","End":"04:17.960","Text":"There are 4 blood types."},{"Start":"04:17.960 ","End":"04:19.610","Text":"You are either A,"},{"Start":"04:19.610 ","End":"04:23.300","Text":"or B, or AB, or O."},{"Start":"04:23.300 ","End":"04:26.315","Text":"That\u0027s your blood type, will be one of those 4 things."},{"Start":"04:26.315 ","End":"04:28.730","Text":"What does that results from?"},{"Start":"04:28.730 ","End":"04:32.405","Text":"It results from different carbohydrates"},{"Start":"04:32.405 ","End":"04:36.035","Text":"that are attached to the outside of red blood cells."},{"Start":"04:36.035 ","End":"04:38.900","Text":"That\u0027s denoted as either I^A,"},{"Start":"04:38.900 ","End":"04:41.960","Text":"I^B, or i."},{"Start":"04:41.960 ","End":"04:48.230","Text":"Actually the genotypes will be denoted as AIB or i."},{"Start":"04:48.230 ","End":"04:49.400","Text":"What does it result from?"},{"Start":"04:49.400 ","End":"04:54.875","Text":"It results from a particular enzyme that has 3 different alleles,"},{"Start":"04:54.875 ","End":"04:57.110","Text":"the I^A, I^B and i."},{"Start":"04:57.110 ","End":"05:00.590","Text":"Those 3 alleles will determine whether"},{"Start":"05:00.590 ","End":"05:04.890","Text":"the A carbohydrate is attached to the outsides of the cells,"},{"Start":"05:04.890 ","End":"05:10.640","Text":"or the B carbohydrate is attached to the outside of the cells,"},{"Start":"05:10.640 ","End":"05:13.355","Text":"or nothing will be attached."},{"Start":"05:13.355 ","End":"05:16.830","Text":"That\u0027s what we see over here."},{"Start":"05:17.230 ","End":"05:23.540","Text":"The enzyme encoded by the i allele adds the A carbohydrate."},{"Start":"05:23.540 ","End":"05:28.624","Text":"I^B allele will encode the enzyme that will add the B carbohydrate,"},{"Start":"05:28.624 ","End":"05:31.490","Text":"and the i allele adds neither,"},{"Start":"05:31.490 ","End":"05:33.930","Text":"as we just explained."}],"ID":26348},{"Watched":false,"Name":"Characteristics and Traits Part b2","Duration":"5m 36s","ChapterTopicVideoID":25532,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:10.095","Text":"The incomplete dominance can be sometimes really the result of a dosage effect."},{"Start":"00:10.095 ","End":"00:19.080","Text":"What does that mean? Well, we\u0027ve got the 2 homologous chromosomes and on each chromosome,"},{"Start":"00:19.080 ","End":"00:21.330","Text":"at a particular locus,"},{"Start":"00:21.330 ","End":"00:25.380","Text":"there is a particular gene and they may be the same as you can see here,"},{"Start":"00:25.380 ","End":"00:28.050","Text":"or they may be different one from the other."},{"Start":"00:28.050 ","End":"00:31.245","Text":"They may be have different alleles."},{"Start":"00:31.245 ","End":"00:34.490","Text":"They could be dominant as you see here,"},{"Start":"00:34.490 ","End":"00:37.490","Text":"or in this case wild-type or they could"},{"Start":"00:37.490 ","End":"00:41.000","Text":"be some mutation that might be found on both alleles."},{"Start":"00:41.000 ","End":"00:46.310","Text":"Now, let\u0027s look at the results in terms of how much protein there"},{"Start":"00:46.310 ","End":"00:53.820","Text":"is as a result of these different alleles that might be found in the DNA."},{"Start":"00:54.500 ","End":"00:59.420","Text":"The different alleles might supply the correct amount"},{"Start":"00:59.420 ","End":"01:03.725","Text":"of gene products if they\u0027re found in 2 copies."},{"Start":"01:03.725 ","End":"01:08.000","Text":"In other cases, we find that if there\u0027s a heterozygote,"},{"Start":"01:08.000 ","End":"01:13.299","Text":"then only 1 copy of the chromosome will be around in the heterozygote that is normal,"},{"Start":"01:13.299 ","End":"01:15.230","Text":"and therefore there may not be"},{"Start":"01:15.230 ","End":"01:21.305","Text":"sufficient amounts of protein in the end which is produced from the heterozygotes."},{"Start":"01:21.305 ","End":"01:27.050","Text":"Alternatively however, 1 mutant allele may be completely dominant over other phenotypes."},{"Start":"01:27.050 ","End":"01:29.419","Text":"That means that it is supplying"},{"Start":"01:29.419 ","End":"01:35.945","Text":"the sufficient amounts of protein even from just 1 copy of the chromosome."},{"Start":"01:35.945 ","End":"01:37.220","Text":"It can work both ways."},{"Start":"01:37.220 ","End":"01:38.510","Text":"Either it may or may not."},{"Start":"01:38.510 ","End":"01:43.280","Text":"It depends completely upon which gene we\u0027re talking about."},{"Start":"01:43.280 ","End":"01:46.565","Text":"A third possibility is that"},{"Start":"01:46.565 ","End":"01:51.260","Text":"the mutant allele actually interferes with the genetic message."},{"Start":"01:51.260 ","End":"01:56.760","Text":"Even in a heterozygote with 1 wild-type allele,"},{"Start":"01:56.760 ","End":"02:02.810","Text":"the mutant phenotype is the one that\u0027s expressed because the mutant may be"},{"Start":"02:02.810 ","End":"02:09.635","Text":"somehow preventing the normal gene copy from behaving normally."},{"Start":"02:09.635 ","End":"02:12.215","Text":"There are different possibilities."},{"Start":"02:12.215 ","End":"02:19.310","Text":"Either that we can have a dosage effect in which we have enough of 1 copy of"},{"Start":"02:19.310 ","End":"02:22.565","Text":"the chromosome producing enough of"},{"Start":"02:22.565 ","End":"02:27.890","Text":"the protein or we may have a case where it is not producing enough,"},{"Start":"02:27.890 ","End":"02:34.195","Text":"therefore you get some incomplete dominance or it may be even that it interferes."},{"Start":"02:34.195 ","End":"02:37.960","Text":"Really cool and interesting example of"},{"Start":"02:37.960 ","End":"02:42.875","Text":"this dosage effect can be found in Drosophila, in the fruit fly."},{"Start":"02:42.875 ","End":"02:48.910","Text":"Fruit flies normally have antenna that come out of their heads."},{"Start":"02:48.910 ","End":"02:52.660","Text":"But there\u0027s an interesting mutation which is called"},{"Start":"02:52.660 ","End":"02:59.590","Text":"antennapedia which instead of having antenna coming out of their heads,"},{"Start":"02:59.590 ","End":"03:02.095","Text":"they have an additional pair of legs."},{"Start":"03:02.095 ","End":"03:06.400","Text":"Isn\u0027t that weird? There\u0027s additional pair of legs that come out of their head."},{"Start":"03:06.400 ","End":"03:12.830","Text":"All of that is the result of only 1 mutation in a particular gene."},{"Start":"03:12.830 ","End":"03:14.620","Text":"It\u0027s a particular allele,"},{"Start":"03:14.620 ","End":"03:20.861","Text":"a mutant allele that expands the distribution of a particular gene product and"},{"Start":"03:20.861 ","End":"03:23.060","Text":"that gene product in"},{"Start":"03:23.060 ","End":"03:27.995","Text":"the heterozygote develops legs on its head where the antenna should be."},{"Start":"03:27.995 ","End":"03:29.600","Text":"Now what is that gene product?"},{"Start":"03:29.600 ","End":"03:31.385","Text":"It\u0027s a regulatory protein."},{"Start":"03:31.385 ","End":"03:36.725","Text":"It\u0027s a protein which affects the transcription of other genes."},{"Start":"03:36.725 ","End":"03:43.819","Text":"But nonetheless, it\u0027s only 1 allele in 1 copy of the chromosome,"},{"Start":"03:43.819 ","End":"03:47.405","Text":"and it can have an extremely dramatic effect."},{"Start":"03:47.405 ","End":"03:50.450","Text":"The sex chromosomes, as you know,"},{"Start":"03:50.450 ","End":"03:53.885","Text":"are the X and the Y chromosomes."},{"Start":"03:53.885 ","End":"03:57.280","Text":"Remember, we discussed the homologous chromosomes and said"},{"Start":"03:57.280 ","End":"04:01.400","Text":"that all the chromosomes are homologous 1 to the other,"},{"Start":"04:01.400 ","End":"04:04.730","Text":"except for the X and Y chromosomes,"},{"Start":"04:04.730 ","End":"04:06.590","Text":"except for the sex chromosomes."},{"Start":"04:06.590 ","End":"04:11.000","Text":"They are also different sizes very often,"},{"Start":"04:11.000 ","End":"04:14.315","Text":"and they encode different genes on them."},{"Start":"04:14.315 ","End":"04:17.390","Text":"If you think about this in a male,"},{"Start":"04:17.390 ","End":"04:20.020","Text":"let\u0027s say of a mammal, let\u0027s say us,"},{"Start":"04:20.020 ","End":"04:25.280","Text":"we\u0027ve got only 1 copy of particular genes that are on"},{"Start":"04:25.280 ","End":"04:31.325","Text":"the X chromosome and 1 copy of genes that are on the Y chromosome."},{"Start":"04:31.325 ","End":"04:37.350","Text":"On the other hand, in a female that has 2 X chromosomes,"},{"Start":"04:37.350 ","End":"04:44.080","Text":"there\u0027ll be 2 copies of each of these genes and no copies of these genes."},{"Start":"04:44.080 ","End":"04:51.125","Text":"It turns out that the sex of the organism is determined by these 2 copies and you can see"},{"Start":"04:51.125 ","End":"04:53.615","Text":"that there\u0027s a sex determination gene called"},{"Start":"04:53.615 ","End":"04:58.580","Text":"SRY that\u0027s found on the Y chromosome in humans."},{"Start":"04:58.580 ","End":"05:01.850","Text":"As we said, human females have 2 X chromosomes,"},{"Start":"05:01.850 ","End":"05:07.025","Text":"whereas males have an XY chromosome that\u0027s in mammals."},{"Start":"05:07.025 ","End":"05:10.555","Text":"Will see later that sometimes it\u0027s not quite like this."},{"Start":"05:10.555 ","End":"05:16.010","Text":"The Y chromosome is much shorter and contains fewer genes."},{"Start":"05:16.010 ","End":"05:19.865","Text":"When a gene is present on the X chromosome,"},{"Start":"05:19.865 ","End":"05:24.470","Text":"and not on the Y chromosome is called X-linked."},{"Start":"05:24.470 ","End":"05:28.670","Text":"It\u0027s X-linked because it\u0027s on the X chromosome."},{"Start":"05:28.670 ","End":"05:32.045","Text":"Obviously, and that you\u0027ll see has implications"},{"Start":"05:32.045 ","End":"05:36.630","Text":"as far as who can carry a particular gene."}],"ID":26349},{"Watched":false,"Name":"Characteristics and Traits Part b3","Duration":"7m 3s","ChapterTopicVideoID":25533,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.380 ","End":"00:04.650","Text":"Let\u0027s now look at Drosophila."},{"Start":"00:04.650 ","End":"00:07.410","Text":"Drosophila, like us, have"},{"Start":"00:07.410 ","End":"00:14.205","Text":"XY chromosome pairs if they\u0027re male and they have XX if they\u0027re female."},{"Start":"00:14.205 ","End":"00:21.225","Text":"Let\u0027s look at a particular gene that expresses a red color in some flies."},{"Start":"00:21.225 ","End":"00:24.375","Text":"If there\u0027s this gene called X,"},{"Start":"00:24.375 ","End":"00:28.005","Text":"if there\u0027s a particular dominant allele,"},{"Start":"00:28.005 ","End":"00:30.870","Text":"which is expressed here with a W,"},{"Start":"00:30.870 ","End":"00:33.015","Text":"a large W,"},{"Start":"00:33.015 ","End":"00:35.700","Text":"then the eye color will be red."},{"Start":"00:35.700 ","End":"00:41.285","Text":"I agree it\u0027s a little bit confusing to call this dominant W for white."},{"Start":"00:41.285 ","End":"00:45.920","Text":"But the phenotype that was first discovered was that"},{"Start":"00:45.920 ","End":"00:51.890","Text":"the eyes of these mutants were white and so they gave the name white to the gene."},{"Start":"00:51.890 ","End":"00:55.060","Text":"But in fact it really encodes red."},{"Start":"00:55.060 ","End":"00:58.460","Text":"The red is dominant to the white."},{"Start":"00:58.460 ","End":"01:00.965","Text":"Because the gene is X-linked,"},{"Start":"01:00.965 ","End":"01:07.370","Text":"reciprocal crosses do not produce the same offspring ratios as might be expected."},{"Start":"01:07.370 ","End":"01:12.830","Text":"We can draw Punnett squares to analyze what happens."},{"Start":"01:12.830 ","End":"01:19.355","Text":"What happens will depend upon whether the gametes are female or male."},{"Start":"01:19.355 ","End":"01:21.575","Text":"Let\u0027s see why that is."},{"Start":"01:21.575 ","End":"01:26.570","Text":"It\u0027s because male genotype can only have 1 chromosome,"},{"Start":"01:26.570 ","End":"01:30.110","Text":"the X chromosome because males are XY,"},{"Start":"01:30.110 ","End":"01:35.450","Text":"so they will contain only 1 copy of the gene."},{"Start":"01:35.450 ","End":"01:40.400","Text":"It will be either dominant for red or it will be white,"},{"Start":"01:40.400 ","End":"01:42.470","Text":"small w for whites."},{"Start":"01:42.470 ","End":"01:51.245","Text":"However, the females carry 2 X chromosomes and therefore they can be big W for red,"},{"Start":"01:51.245 ","End":"01:54.140","Text":"or it\u0027s possible, for instance,"},{"Start":"01:54.140 ","End":"01:59.480","Text":"that a female that has red eyes will also carry the recessive allele."},{"Start":"01:59.480 ","End":"02:02.705","Text":"That\u0027s something that a male can do."},{"Start":"02:02.705 ","End":"02:04.340","Text":"If he\u0027s read it,"},{"Start":"02:04.340 ","End":"02:05.484","Text":"got red eyes,"},{"Start":"02:05.484 ","End":"02:11.195","Text":"he\u0027s got to be carrying 1 copy of the red allele,"},{"Start":"02:11.195 ","End":"02:14.350","Text":"but he\u0027s not carrying a copy of the white allele."},{"Start":"02:14.350 ","End":"02:16.505","Text":"That\u0027s different in females."},{"Start":"02:16.505 ","End":"02:22.685","Text":"The genotypes of the F1 and F2 offspring depend on whether the recessive trait,"},{"Start":"02:22.685 ","End":"02:30.535","Text":"this small w, was expressed by the male or the female in the first parental generation."},{"Start":"02:30.535 ","End":"02:36.430","Text":"Now in humans, this X linkage as well of course,"},{"Start":"02:36.430 ","End":"02:41.680","Text":"and there are certain phenotypes like colorblindness,"},{"Start":"02:41.680 ","End":"02:45.055","Text":"or hemophilia or muscular dystrophy,"},{"Start":"02:45.055 ","End":"02:47.200","Text":"particular kind of muscular dystrophy."},{"Start":"02:47.200 ","End":"02:50.650","Text":"Those are all X-linked. What does that mean?"},{"Start":"02:50.650 ","End":"02:56.605","Text":"It means that if there are mutations in the appropriate genes on the X chromosome,"},{"Start":"02:56.605 ","End":"03:00.235","Text":"we will get these different phenotypes."},{"Start":"03:00.235 ","End":"03:06.265","Text":"Let\u0027s look at these examples in which we\u0027ll have an unaffected father,"},{"Start":"03:06.265 ","End":"03:11.485","Text":"an unaffected father in which he will have the normal alleles,"},{"Start":"03:11.485 ","End":"03:15.274","Text":"the wild-type alleles on his X chromosome."},{"Start":"03:15.274 ","End":"03:22.550","Text":"However, if he is married to a carrier mother, that is,"},{"Start":"03:22.550 ","End":"03:27.140","Text":"the mother has affected allele on one of her X\u0027s,"},{"Start":"03:27.140 ","End":"03:32.780","Text":"she probably has a normal phenotype in the case of these 3 phenotypes"},{"Start":"03:32.780 ","End":"03:39.080","Text":"shall be normal because she carries a normal gene on her other X chromosome."},{"Start":"03:39.080 ","End":"03:42.470","Text":"Now the progeny of this cross between"},{"Start":"03:42.470 ","End":"03:46.340","Text":"an unaffected father and the carrier mother will produce the following things."},{"Start":"03:46.340 ","End":"03:50.105","Text":"Let\u0027s look first at the affected son."},{"Start":"03:50.105 ","End":"03:53.420","Text":"He\u0027s going to get his X chromosome, of course,"},{"Start":"03:53.420 ","End":"03:57.125","Text":"his affected chromosome from his mother."},{"Start":"03:57.125 ","End":"03:59.795","Text":"Because if he\u0027s a boy,"},{"Start":"03:59.795 ","End":"04:03.470","Text":"he\u0027s necessarily gotten an X from his mother and because he\u0027s"},{"Start":"04:03.470 ","End":"04:07.835","Text":"gotten his Y from his father, he\u0027ll be affected."},{"Start":"04:07.835 ","End":"04:11.120","Text":"On the other hand, we could have another son, for instance,"},{"Start":"04:11.120 ","End":"04:13.820","Text":"who is completely normal because if he got"},{"Start":"04:13.820 ","End":"04:17.735","Text":"his X chromosome from his mother that was unaffected,"},{"Start":"04:17.735 ","End":"04:21.410","Text":"he won\u0027t be affected and he certainly won\u0027t be a carrier."},{"Start":"04:21.410 ","End":"04:24.125","Text":"When we say affected, we mean that he\u0027s got the disease."},{"Start":"04:24.125 ","End":"04:26.960","Text":"On the other hand, let\u0027s look at the girls."},{"Start":"04:26.960 ","End":"04:32.480","Text":"The girls are going to get an X from their father and an X from their mother."},{"Start":"04:32.480 ","End":"04:35.230","Text":"It\u0027s going to depend upon whether they got"},{"Start":"04:35.230 ","End":"04:40.210","Text":"the mutants or where they got the wild-type allele from their mother."},{"Start":"04:40.210 ","End":"04:41.620","Text":"From their father of course,"},{"Start":"04:41.620 ","End":"04:45.085","Text":"they\u0027re going to get the non-mutant, the wild-type."},{"Start":"04:45.085 ","End":"04:47.425","Text":"Let\u0027s look at this girl for instance."},{"Start":"04:47.425 ","End":"04:52.810","Text":"She\u0027s gotten her normal X chromosome from her father,"},{"Start":"04:52.810 ","End":"04:56.265","Text":"and she\u0027s gotten her mutant one from her mother."},{"Start":"04:56.265 ","End":"04:58.870","Text":"She too, like her mother is a carrier."},{"Start":"04:58.870 ","End":"05:02.590","Text":"On the other hand, the daughter may not be a carrier at all"},{"Start":"05:02.590 ","End":"05:06.475","Text":"because if she gets the normal X chromosome,"},{"Start":"05:06.475 ","End":"05:09.340","Text":"the wild-type X chromosome from her mother,"},{"Start":"05:09.340 ","End":"05:11.720","Text":"then together with her father\u0027s normal,"},{"Start":"05:11.720 ","End":"05:16.370","Text":"she\u0027ll be normal as well and not be a carrier."},{"Start":"05:16.370 ","End":"05:18.980","Text":"If the father, on the other hand,"},{"Start":"05:18.980 ","End":"05:20.615","Text":"is affected and not the mother,"},{"Start":"05:20.615 ","End":"05:28.325","Text":"then we get a similar arrangement that is easy to understand."},{"Start":"05:28.325 ","End":"05:33.530","Text":"Females who are heterologous and are carriers, yes,"},{"Start":"05:33.530 ","End":"05:38.750","Text":"they\u0027ll be carriers and they may not exhibit any phenotypic effects because they"},{"Start":"05:38.750 ","End":"05:45.410","Text":"have this normal allele on the other X chromosome."},{"Start":"05:45.410 ","End":"05:50.060","Text":"But they may pass the disease to half their sons,"},{"Start":"05:50.060 ","End":"05:54.140","Text":"and they\u0027ll pass the carriers to half their daughters."},{"Start":"05:54.140 ","End":"05:59.750","Text":"Recessive X-linked traits then appear more frequently in males."},{"Start":"05:59.750 ","End":"06:04.220","Text":"They appear, that means there\u0027s disease more frequently in males and females."},{"Start":"06:04.220 ","End":"06:07.205","Text":"We can understand that from this."},{"Start":"06:07.205 ","End":"06:10.864","Text":"How would we get an affected female?"},{"Start":"06:10.864 ","End":"06:13.910","Text":"Well, we would get a diseased female if"},{"Start":"06:13.910 ","End":"06:18.980","Text":"an affected father were to mate with a carrier mother,"},{"Start":"06:18.980 ","End":"06:20.780","Text":"something that\u0027s not shown here."},{"Start":"06:20.780 ","End":"06:27.965","Text":"If an affected, a diseased father was to have a child with a carrier mother,"},{"Start":"06:27.965 ","End":"06:36.080","Text":"then it\u0027s possible that they would produce a female daughter who is not well either."},{"Start":"06:36.080 ","End":"06:39.065","Text":"But that\u0027s a lot rarer because for one thing,"},{"Start":"06:39.065 ","End":"06:44.450","Text":"usually people that have these severe diseases not so much with hemophilia,"},{"Start":"06:44.450 ","End":"06:49.340","Text":"but it\u0027s certainly the case with muscular dystrophy,"},{"Start":"06:49.340 ","End":"06:55.280","Text":"then it\u0027s rare that those people reach an age where they"},{"Start":"06:55.280 ","End":"07:03.030","Text":"reproduce or at least they usually have disability that they often don\u0027t have children."}],"ID":26350},{"Watched":false,"Name":"Characteristics and Traits Part b4","Duration":"5m 39s","ChapterTopicVideoID":25534,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.740 ","End":"00:04.230","Text":"Now, in birds, there\u0027s an interesting situation,"},{"Start":"00:04.230 ","End":"00:06.690","Text":"it\u0027s a bit opposite of ours."},{"Start":"00:06.690 ","End":"00:12.840","Text":"In birds, males are homologous for sex chromosomes rather than females."},{"Start":"00:12.840 ","End":"00:17.400","Text":"The males have 2 what are called Z chromosomes,"},{"Start":"00:17.400 ","End":"00:21.465","Text":"and the females will be ZW."},{"Start":"00:21.465 ","End":"00:24.750","Text":"A female can produce different eggs."},{"Start":"00:24.750 ","End":"00:27.240","Text":"One can be Z, one can be W,"},{"Start":"00:27.240 ","End":"00:30.450","Text":"whereas the male sperm will all be Z,"},{"Start":"00:30.450 ","End":"00:33.570","Text":"if we\u0027re looking at the sex chromosomes."},{"Start":"00:33.570 ","End":"00:34.950","Text":"They\u0027re not called XY,"},{"Start":"00:34.950 ","End":"00:36.060","Text":"in the case of birds,"},{"Start":"00:36.060 ","End":"00:39.930","Text":"they\u0027re called Z or ZW."},{"Start":"00:39.930 ","End":"00:43.700","Text":"In this case, it\u0027s just the opposite as we had in males."},{"Start":"00:43.700 ","End":"00:46.640","Text":"Sex linked traits will be more likely to appear in"},{"Start":"00:46.640 ","End":"00:51.200","Text":"the female in which they are hemizygous."},{"Start":"00:51.200 ","End":"00:53.915","Text":"In other words, they\u0027re heterologous."},{"Start":"00:53.915 ","End":"00:58.475","Text":"They\u0027re not homozygous, they\u0027re hemi half zygous."},{"Start":"00:58.475 ","End":"01:01.640","Text":"Recessive disorders exist typically"},{"Start":"01:01.640 ","End":"01:04.730","Text":"they\u0027re associated with infertility in males and are therefore,"},{"Start":"01:04.730 ","End":"01:08.645","Text":"not transmitted to subsequent generations."},{"Start":"01:08.645 ","End":"01:13.790","Text":"Now let\u0027s look at recessive lethal alleles."},{"Start":"01:13.790 ","End":"01:21.265","Text":"Recessive lethal allele would be an allele that is lethal only in the homozygous."},{"Start":"01:21.265 ","End":"01:24.405","Text":"That is homozygous little a,"},{"Start":"01:24.405 ","End":"01:31.285","Text":"while heterozygotes may be normal or they could have some altered non-lethal phenotype."},{"Start":"01:31.285 ","End":"01:34.850","Text":"In crosses between heterozygous individuals"},{"Start":"01:34.850 ","End":"01:38.135","Text":"with a recessive lethal allele that causes death before birth,"},{"Start":"01:38.135 ","End":"01:41.810","Text":"only wild-type homozygous and"},{"Start":"01:41.810 ","End":"01:45.980","Text":"heterozygotes would be observed because if they\u0027re homozygous,"},{"Start":"01:45.980 ","End":"01:48.095","Text":"in the small letter,"},{"Start":"01:48.095 ","End":"01:52.130","Text":"say here a small c, they wouldn\u0027t live."},{"Start":"01:52.130 ","End":"01:58.980","Text":"Therefore, we would get a genotypic ratio of 2:1."},{"Start":"01:58.980 ","End":"02:03.045","Text":"Because we could have 2 of heterozygotes,"},{"Start":"02:03.045 ","End":"02:04.920","Text":"big C, little c,"},{"Start":"02:04.920 ","End":"02:06.820","Text":"or it could be little c. Big C,"},{"Start":"02:06.820 ","End":"02:11.470","Text":"depending on which parent was donating each allele."},{"Start":"02:11.470 ","End":"02:14.315","Text":"You could have 2 possibilities for this,"},{"Start":"02:14.315 ","End":"02:19.315","Text":"and 1 possibility of the homozygous wild-type."},{"Start":"02:19.315 ","End":"02:22.665","Text":"The genotypic ratio would be 2:1."},{"Start":"02:22.665 ","End":"02:25.145","Text":"The recessive allele, however,"},{"Start":"02:25.145 ","End":"02:31.085","Text":"might also exhibit a dominant but not lethal phenotype in the heterozygote,"},{"Start":"02:31.085 ","End":"02:32.510","Text":"like we see in this case."},{"Start":"02:32.510 ","End":"02:36.050","Text":"In this case, what we see is there\u0027s a curly allele."},{"Start":"02:36.050 ","End":"02:38.420","Text":"That\u0027s why it\u0027s called C in drosophila,"},{"Start":"02:38.420 ","End":"02:40.640","Text":"which affects the wing shape."},{"Start":"02:40.640 ","End":"02:42.980","Text":"Notice the wing here is curled,"},{"Start":"02:42.980 ","End":"02:46.670","Text":"so these flies are viable,"},{"Start":"02:46.670 ","End":"02:54.190","Text":"but they have a different form if they\u0027re in the heterozygous state."},{"Start":"02:54.190 ","End":"02:59.990","Text":"In this case, it\u0027s lethal in the homozygotes with this allele."},{"Start":"02:59.990 ","End":"03:09.770","Text":"But this allele is dominant in its phenotypic effect in that it causes this curly wing."},{"Start":"03:09.770 ","End":"03:14.720","Text":"Let\u0027s look at another case of dominant lethal alleles."},{"Start":"03:14.720 ","End":"03:20.810","Text":"When allele is lethal both in the homozygote and in the heterozygote,"},{"Start":"03:20.810 ","End":"03:24.530","Text":"will call that a dominant lethal allele."},{"Start":"03:24.530 ","End":"03:30.680","Text":"Normally, of course, you will have a dominance which will cause something good,"},{"Start":"03:30.680 ","End":"03:35.719","Text":"or something which is more advantageous for the individual."},{"Start":"03:35.719 ","End":"03:40.490","Text":"But sometimes we\u0027ll find that there\u0027s an allele which is less advantageous."},{"Start":"03:40.490 ","End":"03:44.450","Text":"This is the case for Huntington\u0027s disease."},{"Start":"03:44.450 ","End":"03:47.570","Text":"Then in there, we have an allele that is"},{"Start":"03:47.570 ","End":"03:51.725","Text":"lethal both in the homozygote and in the heterozygote."},{"Start":"03:51.725 ","End":"03:55.970","Text":"Now, this kind of allele can only be transmitted if"},{"Start":"03:55.970 ","End":"04:00.245","Text":"the lethality phenotype occurs after the reproductive age."},{"Start":"04:00.245 ","End":"04:06.380","Text":"Because if it is expressed before the reproductive age,"},{"Start":"04:06.380 ","End":"04:09.665","Text":"before the organism can reproduce,"},{"Start":"04:09.665 ","End":"04:12.485","Text":"then it won\u0027t be passed on further."},{"Start":"04:12.485 ","End":"04:15.530","Text":"The only way that it can be transmitted is"},{"Start":"04:15.530 ","End":"04:18.920","Text":"if a phenotype occurs after the reproductive age."},{"Start":"04:18.920 ","End":"04:23.300","Text":"Of course, these are not expressed until the reproductive age,"},{"Start":"04:23.300 ","End":"04:29.910","Text":"and therefore, they are unknowingly passed on to the next generation."},{"Start":"04:30.340 ","End":"04:34.145","Text":"In Huntington\u0027s disease, for instance,"},{"Start":"04:34.145 ","End":"04:37.310","Text":"in which the nervous system gradually wastes away,"},{"Start":"04:37.310 ","End":"04:39.980","Text":"we find that it rarely occurs until"},{"Start":"04:39.980 ","End":"04:44.390","Text":"age 40 when afflicted persons may have already passed on the allele"},{"Start":"04:44.390 ","End":"04:47.945","Text":"to about 50 percent of their offspring because"},{"Start":"04:47.945 ","End":"04:52.025","Text":"those people are going to be heterozygous,"},{"Start":"04:52.025 ","End":"04:57.660","Text":"so 50 percent of their offspring are going to get the affected gene."},{"Start":"04:57.770 ","End":"05:00.725","Text":"In the last 2 videos,"},{"Start":"05:00.725 ","End":"05:04.045","Text":"we have been looking at characteristics and traits."},{"Start":"05:04.045 ","End":"05:07.070","Text":"We learned how to explain the relationship between"},{"Start":"05:07.070 ","End":"05:10.790","Text":"genotypes and phenotypes in dominant and recessive gene systems."},{"Start":"05:10.790 ","End":"05:14.330","Text":"We now know how to develop a Punnett square to calculate"},{"Start":"05:14.330 ","End":"05:19.505","Text":"the expected proportions of genotypes and phenotypes in a monohybrid cross."},{"Start":"05:19.505 ","End":"05:23.675","Text":"We know how to explain the purpose and methods of a test cross."},{"Start":"05:23.675 ","End":"05:26.580","Text":"These 3 things were in the previous video."},{"Start":"05:26.580 ","End":"05:27.870","Text":"In this video,"},{"Start":"05:27.870 ","End":"05:33.440","Text":"we looked at non-Mendelian inheritance patterns such as incomplete dominance,"},{"Start":"05:33.440 ","End":"05:35.855","Text":"codominance, recessive alleles,"},{"Start":"05:35.855 ","End":"05:39.780","Text":"multiple alleles, and sex linkage."}],"ID":26351},{"Watched":false,"Name":"Laws of Inheritance Part a1","Duration":"7m 7s","ChapterTopicVideoID":25535,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.200 ","End":"00:05.520","Text":"Congratulations, you\u0027ve reached the last section that deals"},{"Start":"00:05.520 ","End":"00:10.455","Text":"with Mendel\u0027s experiments and heredity in the laws of inheritance."},{"Start":"00:10.455 ","End":"00:12.270","Text":"In this final video,"},{"Start":"00:12.270 ","End":"00:16.095","Text":"we\u0027ll review what we\u0027ve learned until now rather quickly."},{"Start":"00:16.095 ","End":"00:21.110","Text":"Then we\u0027ll go on to more complicated issues that deal"},{"Start":"00:21.110 ","End":"00:26.280","Text":"with recombination and with epistatic effects between genes."},{"Start":"00:26.280 ","End":"00:27.755","Text":"By the end of this section,"},{"Start":"00:27.755 ","End":"00:31.520","Text":"you should be able to explain Mendel\u0027s laws of segregation and independent assortment in"},{"Start":"00:31.520 ","End":"00:35.880","Text":"terms of the genetics and the events of meiosis."},{"Start":"00:35.880 ","End":"00:38.690","Text":"You should be able to use something different than"},{"Start":"00:38.690 ","End":"00:42.410","Text":"a Punnett square called a forked-line method and the probability"},{"Start":"00:42.410 ","End":"00:45.020","Text":"rules to calculate the probabilities of"},{"Start":"00:45.020 ","End":"00:49.880","Text":"particular genotypes and phenotypes from multiple gene crosses."},{"Start":"00:49.880 ","End":"00:52.730","Text":"You should be able to explain the effect of linkage and"},{"Start":"00:52.730 ","End":"00:55.960","Text":"recombination on gamete genotypes."},{"Start":"00:55.960 ","End":"01:03.350","Text":"You should be able to explain the phenotypic outcomes of epistatic effects between genes."},{"Start":"01:03.350 ","End":"01:10.570","Text":"Now let\u0027s go back and very quickly review what we already know about Mendel\u0027s laws."},{"Start":"01:10.570 ","End":"01:14.432","Text":"We know paired unit factors of"},{"Start":"01:14.432 ","End":"01:17.540","Text":"heredity right there on"},{"Start":"01:17.540 ","End":"01:20.990","Text":"each chromosome are transmitted faithfully from generation to generation."},{"Start":"01:20.990 ","End":"01:23.570","Text":"We know that these factors must be inherited as"},{"Start":"01:23.570 ","End":"01:28.340","Text":"discrete units because right there encoded on particular genes,"},{"Start":"01:28.340 ","End":"01:31.825","Text":"on discrete and particular genes."},{"Start":"01:31.825 ","End":"01:38.150","Text":"This contradicted the previous belief that parental traits were blended in the offspring,"},{"Start":"01:38.150 ","End":"01:40.939","Text":"and therefore we could have a genotype."},{"Start":"01:40.939 ","End":"01:47.410","Text":"There was either homozygous or heterozygous that produced the same phenotype."},{"Start":"01:47.410 ","End":"01:51.026","Text":"It\u0027s the same phenotype, not a blended phenotype,"},{"Start":"01:51.026 ","End":"01:55.985","Text":"that led to the idea that alleles can be dominant or recessive."},{"Start":"01:55.985 ","End":"02:01.855","Text":"Now, this holds true in flowers and it may also hold true even in phenotypes of people."},{"Start":"02:01.855 ","End":"02:03.980","Text":"In a heterozygote, for instance,"},{"Start":"02:03.980 ","End":"02:08.615","Text":"1 trait can conceal the presence of another trade for the same characteristics."},{"Start":"02:08.615 ","End":"02:13.850","Text":"The dark skin either in a homozygote or heterozygote,"},{"Start":"02:13.850 ","End":"02:19.010","Text":"will shield the light-skinned allele and"},{"Start":"02:19.010 ","End":"02:26.180","Text":"only a homozygous light-skinned allele can produce this albino child in Africa."},{"Start":"02:26.180 ","End":"02:32.630","Text":"The dominant allele will be expressed exclusively the recessive 1 will not."},{"Start":"02:32.630 ","End":"02:36.215","Text":"The recessive allele, though, will remain latent."},{"Start":"02:36.215 ","End":"02:39.635","Text":"Of course, it\u0027s transmitted just like the dominant allele,"},{"Start":"02:39.635 ","End":"02:46.335","Text":"but it may not be seen in subsequent generations because of the recessive phenotype."},{"Start":"02:46.335 ","End":"02:49.550","Text":"The recessive trait will be expressed only by"},{"Start":"02:49.550 ","End":"02:53.255","Text":"offspring that have 2 copies of this recessive allele,"},{"Start":"02:53.255 ","End":"02:55.115","Text":"as you can see in this picture."},{"Start":"02:55.115 ","End":"02:59.420","Text":"The fact though is that researchers have found that the laws of"},{"Start":"02:59.420 ","End":"03:04.040","Text":"dominance do not always hold true and as we saw in the previous video,"},{"Start":"03:04.040 ","End":"03:07.690","Text":"sometimes we can have things like codominance."},{"Start":"03:07.690 ","End":"03:12.560","Text":"Now, we also know that each of the genes can"},{"Start":"03:12.560 ","End":"03:17.500","Text":"segregate or do segregate independently usually."},{"Start":"03:17.500 ","End":"03:22.085","Text":"Paired unit factors or genes must segregate equally into gametes,"},{"Start":"03:22.085 ","End":"03:27.860","Text":"such that offspring have an equal likelihood of inheriting either factor,"},{"Start":"03:27.860 ","End":"03:29.405","Text":"that\u0027s usually the case."},{"Start":"03:29.405 ","End":"03:35.135","Text":"For instance, if we have 3 pairs of chromosomes when they segregate independently,"},{"Start":"03:35.135 ","End":"03:40.850","Text":"we could get a whole bunch of different possible gametes here we only show 4 of them,"},{"Start":"03:40.850 ","End":"03:44.420","Text":"but there can be others as well of course."},{"Start":"03:44.420 ","End":"03:47.059","Text":"We saw that in the case of flowers,"},{"Start":"03:47.059 ","End":"03:50.525","Text":"the F_2 generation of a monohybrid cross."},{"Start":"03:50.525 ","End":"03:52.100","Text":"Remember a monohybrid cross."},{"Start":"03:52.100 ","End":"03:55.550","Text":"We\u0027re only talking about 1, that\u0027s the mono,"},{"Start":"03:55.550 ","End":"04:03.129","Text":"1 trait would be that we get a homozygous dominant,"},{"Start":"04:03.130 ","End":"04:09.970","Text":"we could get heterozygous plants that have the same phenotype as the dominant one,"},{"Start":"04:09.970 ","End":"04:15.690","Text":"and we have a homozygous recessive alleles that will be different."},{"Start":"04:15.690 ","End":"04:20.145","Text":"We have the 3 to 1 phenotypic expression."},{"Start":"04:20.145 ","End":"04:22.580","Text":"In the laws of segregation,"},{"Start":"04:22.580 ","End":"04:25.640","Text":"we get this 3 to 1 phenotypic ratio,"},{"Start":"04:25.640 ","End":"04:33.615","Text":"as we just mentioned and it can be expressed by looking at this understanding,"},{"Start":"04:33.615 ","End":"04:35.840","Text":"what we get in this figure,"},{"Start":"04:35.840 ","End":"04:37.160","Text":"as we\u0027ve mentioned earlier,"},{"Start":"04:37.160 ","End":"04:40.265","Text":"that describes the segregation of meiosis,"},{"Start":"04:40.265 ","End":"04:44.465","Text":"where the separation of the chromosomes happens,"},{"Start":"04:44.465 ","End":"04:47.540","Text":"particularly at the first division."},{"Start":"04:47.540 ","End":"04:49.220","Text":"Remember at the first division of meiosis,"},{"Start":"04:49.220 ","End":"04:50.690","Text":"there are 2 different divisions."},{"Start":"04:50.690 ","End":"04:55.265","Text":"At the first division is when the segregation occurs."},{"Start":"04:55.265 ","End":"05:00.920","Text":"Meiotic segregation of chromosomes though was unknown during Mendel\u0027s thought lifetime."},{"Start":"05:00.920 ","End":"05:08.435","Text":"He was lucky that the traits that he looked at really did segregate independently."},{"Start":"05:08.435 ","End":"05:11.764","Text":"Now, let\u0027s look at genes"},{"Start":"05:11.764 ","End":"05:16.100","Text":"that do not influence other regarding the sorting of alleles into"},{"Start":"05:16.100 ","End":"05:19.580","Text":"gametes as opposed to others that we will see a bit later in"},{"Start":"05:19.580 ","End":"05:24.290","Text":"this video that do affect the expression of each other."},{"Start":"05:24.290 ","End":"05:26.375","Text":"Most genes, in fact,"},{"Start":"05:26.375 ","End":"05:29.660","Text":"do not influence each other with regarding to the alleles into gametes."},{"Start":"05:29.660 ","End":"05:32.525","Text":"That makes the math relatively simple."},{"Start":"05:32.525 ","End":"05:37.595","Text":"Every possible combination of alleles for every gene is likely to occur as we saw"},{"Start":"05:37.595 ","End":"05:43.565","Text":"earlier and in a dihybrid cross that we will see in the next slide,"},{"Start":"05:43.565 ","End":"05:47.839","Text":"the independent assortment of genes can be illustrated."},{"Start":"05:47.839 ","End":"05:54.500","Text":"Here we have, instead of having 4 different possibilities,"},{"Start":"05:54.500 ","End":"06:00.130","Text":"we\u0027re going to have 16 different possibilities in the Punnett square."},{"Start":"06:00.130 ","End":"06:03.590","Text":"Across between 2 true breeding parents,"},{"Start":"06:03.590 ","End":"06:09.570","Text":"remember that means that they\u0027re going to be homozygous in each trait."},{"Start":"06:09.570 ","End":"06:14.150","Text":"Those are true breeding parents express different traits with 2 characteristics."},{"Start":"06:14.150 ","End":"06:16.865","Text":"The F_1 generation will be"},{"Start":"06:16.865 ","End":"06:21.920","Text":"heterozygous in each of them and then in the following meetings,"},{"Start":"06:21.920 ","End":"06:26.305","Text":"we will get 16 different possibilities."},{"Start":"06:26.305 ","End":"06:30.200","Text":"They will be able to look at each of them in"},{"Start":"06:30.200 ","End":"06:34.450","Text":"the phenotype of each of them and each of the traits."},{"Start":"06:34.450 ","End":"06:40.930","Text":"Here we have color or whether the seed is wrinkled or not will assort independently."},{"Start":"06:40.930 ","End":"06:46.850","Text":"We can count the phenotypic ratio that we get in each of these,"},{"Start":"06:46.850 ","End":"06:55.820","Text":"which will be 9 to 3 to 3 to 1 of the phenotypes"},{"Start":"06:55.820 ","End":"07:00.890","Text":"of each of these combinations in the Punnett square"},{"Start":"07:00.890 ","End":"07:06.810","Text":"that has 16 equally likely genotypic combinations."}],"ID":26352},{"Watched":false,"Name":"Laws of Inheritance Part a2","Duration":"8m 36s","ChapterTopicVideoID":25536,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.305","Text":"Now, let\u0027s look at it again in"},{"Start":"00:04.305 ","End":"00:09.690","Text":"this other figure where we have a better explanation of what\u0027s going on."},{"Start":"00:09.690 ","End":"00:14.160","Text":"The basis of this lies in meiosis 1, as we said,"},{"Start":"00:14.160 ","End":"00:21.210","Text":"where we have the random separation of the chromosomes at anaphase."},{"Start":"00:21.210 ","End":"00:25.410","Text":"The law applies only to genes however,"},{"Start":"00:25.410 ","End":"00:29.910","Text":"that are on different non-homologous chromosomes."},{"Start":"00:29.910 ","End":"00:36.740","Text":"If we have 2 genes that are on the same chromosome and they are close together,"},{"Start":"00:36.740 ","End":"00:41.585","Text":"they will not, of course, segregate separately."},{"Start":"00:41.585 ","End":"00:44.165","Text":"They will separate together,"},{"Start":"00:44.165 ","End":"00:46.235","Text":"and that will complicate the story."},{"Start":"00:46.235 ","End":"00:49.205","Text":"However, remember that there is also crossing over."},{"Start":"00:49.205 ","End":"00:53.734","Text":"So if they\u0027re very far apart but still on the same chromosome,"},{"Start":"00:53.734 ","End":"01:00.830","Text":"then they still probably will assort separately, independently."},{"Start":"01:00.830 ","End":"01:05.375","Text":"Genes located close to each other on the same chromosome do"},{"Start":"01:05.375 ","End":"01:11.000","Text":"tend to be inherited together and that may well complicate our story."},{"Start":"01:11.000 ","End":"01:15.620","Text":"Until now, we\u0027ve been looking at only two different traits."},{"Start":"01:15.620 ","End":"01:19.045","Text":"Well, what if there are more than two different traits?"},{"Start":"01:19.045 ","End":"01:22.880","Text":"Then the mass begins to get a little bit more complicated and it"},{"Start":"01:22.880 ","End":"01:26.945","Text":"becomes a little bit more difficult to draw these large Punnett squares."},{"Start":"01:26.945 ","End":"01:29.989","Text":"Instead, a different method was invented,"},{"Start":"01:29.989 ","End":"01:32.805","Text":"something called the forked-line method."},{"Start":"01:32.805 ","End":"01:34.639","Text":"This is actually pretty easy."},{"Start":"01:34.639 ","End":"01:39.230","Text":"With more than 2 genes this method is the preferred method over the Punnett square."},{"Start":"01:39.230 ","End":"01:44.030","Text":"All we do is we create rows equal to the number of genes being considered."},{"Start":"01:44.030 ","End":"01:47.690","Text":"Here we\u0027ve got yellow or green, that\u0027s the color."},{"Start":"01:47.690 ","End":"01:50.525","Text":"We\u0027ve got the shape either round or wrinkled,"},{"Start":"01:50.525 ","End":"01:53.066","Text":"and we have whether they\u0027re large or small."},{"Start":"01:53.066 ","End":"01:56.170","Text":"We\u0027ll call that tall or dwarfed plants."},{"Start":"01:56.170 ","End":"02:00.045","Text":"In each of them they segregate independently,"},{"Start":"02:00.045 ","End":"02:06.540","Text":"so we\u0027ll get 3-1 in each case, 3-1, 3-1."},{"Start":"02:06.540 ","End":"02:11.175","Text":"That\u0027s the case for all of the traits. That\u0027s pretty simple."},{"Start":"02:11.175 ","End":"02:14.780","Text":"We segregate the alleles in each row on the forked lines according"},{"Start":"02:14.780 ","End":"02:18.085","Text":"to the probabilities for the individual monohybrid crosses."},{"Start":"02:18.085 ","End":"02:19.500","Text":"That\u0027s 3-1."},{"Start":"02:19.500 ","End":"02:22.925","Text":"Then all we do is multiply the values along"},{"Start":"02:22.925 ","End":"02:27.160","Text":"each fork path to obtain the F_2 offspring possibilities."},{"Start":"02:27.160 ","End":"02:29.490","Text":"We would get, for instance,"},{"Start":"02:29.490 ","End":"02:35.025","Text":"a 3 times 3 times 3 would be 27,"},{"Start":"02:35.025 ","End":"02:42.455","Text":"3 times 3 is 9 times 3 is 27 yellow round and tall plants."},{"Start":"02:42.455 ","End":"02:46.475","Text":"However, look at yellow round and dwarf."},{"Start":"02:46.475 ","End":"02:54.530","Text":"It would be 3 times 3 is 9 times 1 because the size was 3-1 here."},{"Start":"02:54.530 ","End":"02:57.320","Text":"We were looking at the recessive dream gene and that would give"},{"Start":"02:57.320 ","End":"03:01.845","Text":"us 9 yellow round dwarfed plants."},{"Start":"03:01.845 ","End":"03:07.805","Text":"If we look now finally at all of these numbers for a try hybrid cross,"},{"Start":"03:07.805 ","End":"03:10.295","Text":"the F_2 phenotype ratio would be"},{"Start":"03:10.295 ","End":"03:20.130","Text":"27-9-9-9-3-3-3-1."},{"Start":"03:20.130 ","End":"03:22.140","Text":"That\u0027s the forked line method."},{"Start":"03:22.140 ","End":"03:25.190","Text":"Now let\u0027s look at a little bit more of"},{"Start":"03:25.190 ","End":"03:29.450","Text":"a mathematical method that is called the probability method."},{"Start":"03:29.450 ","End":"03:32.330","Text":"The probability method gives the proportions of"},{"Start":"03:32.330 ","End":"03:36.020","Text":"the offspring expected to exhibit each phenotype or"},{"Start":"03:36.020 ","End":"03:42.775","Text":"genotype without the added visual assistance that we had in the previous slide."},{"Start":"03:42.775 ","End":"03:46.970","Text":"Well, that turns out to be pretty simple as well."},{"Start":"03:46.970 ","End":"03:49.340","Text":"Let\u0027s give an example,"},{"Start":"03:49.340 ","End":"03:51.740","Text":"for a tetrahybrid cross that\u0027s with"},{"Start":"03:51.740 ","End":"03:54.920","Text":"four different possibilities between"},{"Start":"03:54.920 ","End":"03:58.470","Text":"individuals that are heterozygous for all four genes."},{"Start":"03:58.470 ","End":"04:01.430","Text":"That would be that F_1 right after the true breeding,"},{"Start":"04:01.430 ","End":"04:03.350","Text":"but in four different traits or"},{"Start":"04:03.350 ","End":"04:07.370","Text":"four different genes and in which all four genes are assorting independently."},{"Start":"04:07.370 ","End":"04:11.480","Text":"Well, that you remember is a given for all of these."},{"Start":"04:11.480 ","End":"04:14.300","Text":"In a dominant and recessive pattern, again,"},{"Start":"04:14.300 ","End":"04:16.910","Text":"a given what we\u0027re asking,"},{"Start":"04:16.910 ","End":"04:20.585","Text":"what proportion of the offspring will be expected to be homozygous"},{"Start":"04:20.585 ","End":"04:26.560","Text":"recessive for all four alleles?"},{"Start":"04:26.560 ","End":"04:29.660","Text":"Well, let\u0027s see. For each gene,"},{"Start":"04:29.660 ","End":"04:33.290","Text":"the fraction of the homozygous recessive for each of"},{"Start":"04:33.290 ","End":"04:37.430","Text":"the offspring will be 1/4 because it\u0027s 3-1,"},{"Start":"04:37.430 ","End":"04:39.050","Text":"so it\u0027s of the four,"},{"Start":"04:39.050 ","End":"04:40.580","Text":"only one in four,"},{"Start":"04:40.580 ","End":"04:44.120","Text":"so 1/4 will be homozygous recessive."},{"Start":"04:44.120 ","End":"04:46.715","Text":"For each of the genes, it\u0027s the same thing."},{"Start":"04:46.715 ","End":"04:51.799","Text":"In order to find out how many of the total number,"},{"Start":"04:51.799 ","End":"04:54.995","Text":"and of course, that would be 256,"},{"Start":"04:54.995 ","End":"04:59.765","Text":"would be quadruply homozygous recessive,"},{"Start":"04:59.765 ","End":"05:03.590","Text":"all we have to do is multiply a 1/4 by 1/4 by 1/4,"},{"Start":"05:03.590 ","End":"05:08.470","Text":"and we get 1 in 256."},{"Start":"05:08.470 ","End":"05:10.110","Text":"That\u0027s how we would do"},{"Start":"05:10.110 ","End":"05:15.305","Text":"such a probability method calculation"},{"Start":"05:15.305 ","End":"05:20.980","Text":"looking for a quadruply homozygous recessive alleles."},{"Start":"05:20.980 ","End":"05:23.543","Text":"For the same tetrahybrid cross,"},{"Start":"05:23.543 ","End":"05:27.230","Text":"let\u0027s ask now what is the expected proportion of offspring that"},{"Start":"05:27.230 ","End":"05:31.220","Text":"have the dominant phenotype at all four loci?"},{"Start":"05:31.220 ","End":"05:33.125","Text":"Well, that\u0027s not so hard."},{"Start":"05:33.125 ","End":"05:36.830","Text":"Let\u0027s do it again by using genotypic proportions."},{"Start":"05:36.830 ","End":"05:40.550","Text":"We ask, what is the proportion or what are the proportion of"},{"Start":"05:40.550 ","End":"05:45.250","Text":"offspring that are homozygous dominant at A,"},{"Start":"05:45.250 ","End":"05:46.980","Text":"of course, they have to have the A,"},{"Start":"05:46.980 ","End":"05:50.340","Text":"or heterozygous at A?"},{"Start":"05:50.340 ","End":"05:55.880","Text":"If they\u0027re either that is they\u0027re homozygous dominant or they\u0027re heterozygous,"},{"Start":"05:55.880 ","End":"05:59.270","Text":"they\u0027re going to have the same phenotype for each particular trait."},{"Start":"05:59.270 ","End":"06:00.950","Text":"We want to know how many of them."},{"Start":"06:00.950 ","End":"06:04.370","Text":"Well, of course, we know how many that\u0027s going to be."},{"Start":"06:04.370 ","End":"06:07.735","Text":"That\u0027s going to be 3 out of the 4 for each of them."},{"Start":"06:07.735 ","End":"06:09.800","Text":"We\u0027ll do the same thing for B,"},{"Start":"06:09.800 ","End":"06:12.215","Text":"and for C, and for D, and so on."},{"Start":"06:12.215 ","End":"06:16.010","Text":"The probability of a homozygous dominant is"},{"Start":"06:16.010 ","End":"06:20.960","Text":"1/4 and if the heterozygote is going to be 2/4 or 1/2."},{"Start":"06:20.960 ","End":"06:25.680","Text":"Total, it\u0027ll be 3/4 as we just said."},{"Start":"06:25.840 ","End":"06:30.080","Text":"The probability of a dominant phenotype at A,"},{"Start":"06:30.080 ","End":"06:31.610","Text":"and B, and C,"},{"Start":"06:31.610 ","End":"06:36.645","Text":"and D would simply be multiplying those 3/4 four times."},{"Start":"06:36.645 ","End":"06:45.870","Text":"So 3/4 times 3/4 times 3/4 times 3/4 would be 27/64."},{"Start":"06:45.870 ","End":"06:47.840","Text":"You just use a little bit of"},{"Start":"06:47.840 ","End":"06:52.820","Text":"common sense to be able to figure out what these probabilities are."},{"Start":"06:52.820 ","End":"06:57.095","Text":"This can be determined more mathematically as well."},{"Start":"06:57.095 ","End":"07:02.420","Text":"Simply, all we need to do is look at the rules for multi hybrid crosses."},{"Start":"07:02.420 ","End":"07:07.445","Text":"What we do is we ask several questions."},{"Start":"07:07.445 ","End":"07:14.665","Text":"First of all, we want to know what the number of a heterozygous gene pairs are."},{"Start":"07:14.665 ","End":"07:17.780","Text":"They must be heterozygous."},{"Start":"07:17.780 ","End":"07:21.290","Text":"Yes, so it has to be, for instance,"},{"Start":"07:21.290 ","End":"07:25.400","Text":"here we would have two because we have big A little a,"},{"Start":"07:25.400 ","End":"07:26.840","Text":"big B, little b,"},{"Start":"07:26.840 ","End":"07:28.815","Text":"big A, little a,"},{"Start":"07:28.815 ","End":"07:30.540","Text":"big B, little b."},{"Start":"07:30.540 ","End":"07:36.680","Text":"There are two different genes here that can be both A and B and those are heterozygous,"},{"Start":"07:36.680 ","End":"07:41.560","Text":"so the n in our calculation will be 2."},{"Start":"07:41.560 ","End":"07:45.600","Text":"On the other hand, if we have big A,"},{"Start":"07:45.600 ","End":"07:49.130","Text":"big A and the other parent is also big A,"},{"Start":"07:49.130 ","End":"07:53.940","Text":"big A, then that is not heterozygous, that\u0027s homozygous."},{"Start":"07:53.940 ","End":"07:56.395","Text":"Therefore the cross, the n,"},{"Start":"07:56.395 ","End":"08:02.645","Text":"in this case in the cross would be only 1 because A is not heterozygous."},{"Start":"08:02.645 ","End":"08:07.775","Text":"Of course, if A is homozygous in both cases,"},{"Start":"08:07.775 ","End":"08:13.165","Text":"then we don\u0027t get differences between the offspring."},{"Start":"08:13.165 ","End":"08:20.750","Text":"The general rules are that the number of different F_1 gametes would be n squared."},{"Start":"08:20.750 ","End":"08:27.305","Text":"The number of different F_2 genotypes would be n^3."},{"Start":"08:27.305 ","End":"08:29.720","Text":"Given dominant and recessive inheritance,"},{"Start":"08:29.720 ","End":"08:36.120","Text":"the number of different F_2 phenotypes would be n^2."}],"ID":26353},{"Watched":false,"Name":"Laws of Inheritance Part b","Duration":"10m 28s","ChapterTopicVideoID":25537,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.140 ","End":"00:04.065","Text":"Let\u0027s continue with the laws of inheritance."},{"Start":"00:04.065 ","End":"00:09.165","Text":"Until now, we\u0027ve spoken about independent assortment."},{"Start":"00:09.165 ","End":"00:14.370","Text":"Each of the genes that we\u0027ve been looking at, assorts independently."},{"Start":"00:14.370 ","End":"00:19.560","Text":"That dependent on the fact that the genes were on separate chromosomes,"},{"Start":"00:19.560 ","End":"00:23.070","Text":"or at least they were far enough apart so that crossing"},{"Start":"00:23.070 ","End":"00:28.065","Text":"over was very significant and happened about half the time."},{"Start":"00:28.065 ","End":"00:32.970","Text":"Therefore, there was an independent assortment of each of the alleles and we could draw"},{"Start":"00:32.970 ","End":"00:39.780","Text":"a Punnett square in which each of the possibilities was of equal likelihood."},{"Start":"00:39.780 ","End":"00:46.440","Text":"However, what would happen if the genes were linked?"},{"Start":"00:49.370 ","End":"00:56.419","Text":"What does that mean? That would mean that they would be on the same chromosome."},{"Start":"00:56.419 ","End":"01:00.265","Text":"What would happen if they were linked?"},{"Start":"01:00.265 ","End":"01:03.285","Text":"What does linked mean?"},{"Start":"01:03.285 ","End":"01:08.910","Text":"That would mean that both A and B are on"},{"Start":"01:08.910 ","End":"01:15.440","Text":"the same chromosome so when the 2 chromosomes split from each other during meiosis,"},{"Start":"01:15.440 ","End":"01:18.530","Text":"the 2 alleles that are on the same chromosome would"},{"Start":"01:18.530 ","End":"01:22.355","Text":"segregate together, not independently."},{"Start":"01:22.355 ","End":"01:27.835","Text":"They segregate together, they would be linked."},{"Start":"01:27.835 ","End":"01:33.350","Text":"Linkage means that genes that are located too close to"},{"Start":"01:33.350 ","End":"01:38.440","Text":"each other on the same chromosome are more likely to be inherited together."},{"Start":"01:38.440 ","End":"01:42.560","Text":"Of course, the result of that would be that the Punnett square that"},{"Start":"01:42.560 ","End":"01:47.495","Text":"we get would have far fewer possibilities in it."},{"Start":"01:47.495 ","End":"01:51.305","Text":"That complicates the things significantly."},{"Start":"01:51.305 ","End":"01:54.860","Text":"Now in addition, there are other complications."},{"Start":"01:54.860 ","End":"02:01.170","Text":"For instance, several genes can contribute to aspects of a common phenotype,"},{"Start":"02:01.250 ","End":"02:08.905","Text":"but several different genes without their gene products ever directly interacting."},{"Start":"02:08.905 ","End":"02:12.470","Text":"During organ development, for example,"},{"Start":"02:12.470 ","End":"02:15.460","Text":"genes may be expressed sequentially,"},{"Start":"02:15.460 ","End":"02:17.365","Text":"not all at the same time,"},{"Start":"02:17.365 ","End":"02:20.155","Text":"but one after the other."},{"Start":"02:20.155 ","End":"02:22.180","Text":"This is a different way, for instance,"},{"Start":"02:22.180 ","End":"02:24.970","Text":"during organ development that genes can be"},{"Start":"02:24.970 ","End":"02:30.325","Text":"expressed because they work on a timeline, they\u0027re expressed sequentially."},{"Start":"02:30.325 ","End":"02:35.665","Text":"Genes may also function complementary or synergistic fashions. What does that mean?"},{"Start":"02:35.665 ","End":"02:41.140","Text":"That means that 1 gene may help the expression of another one."},{"Start":"02:41.140 ","End":"02:42.730","Text":"That\u0027s what synergy is,"},{"Start":"02:42.730 ","End":"02:44.310","Text":"that they help each other."},{"Start":"02:44.310 ","End":"02:48.655","Text":"On the other hand, they could also oppose each other."},{"Start":"02:48.655 ","End":"02:55.010","Text":"Let\u0027s look now at another behavior of the genes."},{"Start":"02:55.010 ","End":"03:04.250","Text":"They can act in epistatic ways through a process called epistasis. What does that mean?"},{"Start":"03:04.250 ","End":"03:10.055","Text":"That means that there could be antagonistic interaction where 1 gene masks or"},{"Start":"03:10.055 ","End":"03:15.980","Text":"interferes with the expression of another gene."},{"Start":"03:15.980 ","End":"03:20.300","Text":"What we\u0027d say is that gene B, for instance,"},{"Start":"03:20.300 ","End":"03:26.930","Text":"down here, influences the effect of gene or the expression of gene A."},{"Start":"03:26.930 ","End":"03:32.900","Text":"Therefore, we say that gene B is epistatic to A."},{"Start":"03:32.900 ","End":"03:35.330","Text":"That\u0027s the terminology."},{"Start":"03:35.330 ","End":"03:37.805","Text":"The genes that are masked,"},{"Start":"03:37.805 ","End":"03:41.180","Text":"those are the ones, like gene A in this particular case,"},{"Start":"03:41.180 ","End":"03:43.085","Text":"are called hypostatic,"},{"Start":"03:43.085 ","End":"03:49.055","Text":"the masked alleles are hypostatic to the epistatic alleles that are doing the masking."},{"Start":"03:49.055 ","End":"03:54.950","Text":"Finally, the expression of 1 gene therefore is dependent on the function of"},{"Start":"03:54.950 ","End":"04:01.525","Text":"another gene that precedes or possibly follows it in the pathway,"},{"Start":"04:01.525 ","End":"04:04.100","Text":"like the pathway of development."},{"Start":"04:04.100 ","End":"04:09.100","Text":"Let\u0027s look at an example now of epistasis in mice."},{"Start":"04:09.100 ","End":"04:12.570","Text":"In the fur color of mice."},{"Start":"04:12.570 ","End":"04:17.555","Text":"Here we\u0027re going to see that there are going to be more than 1 gene."},{"Start":"04:17.555 ","End":"04:19.310","Text":"They\u0027re going to affect each other."},{"Start":"04:19.310 ","End":"04:24.500","Text":"Now, the wild coat color of the gene would be called agouti,"},{"Start":"04:24.500 ","End":"04:26.675","Text":"and it\u0027s AA,"},{"Start":"04:26.675 ","End":"04:32.225","Text":"and that\u0027s dominant to aa which gives a solid-colored fur."},{"Start":"04:32.225 ","End":"04:36.275","Text":"This agouti coat color is modeled."},{"Start":"04:36.275 ","End":"04:38.870","Text":"In any case, that\u0027s the wild-type."},{"Start":"04:38.870 ","End":"04:42.020","Text":"It turns out though, however,"},{"Start":"04:42.020 ","End":"04:46.100","Text":"that there\u0027s another gene called C,"},{"Start":"04:46.100 ","End":"04:49.500","Text":"which is necessary for pigment production."},{"Start":"04:49.500 ","End":"04:54.680","Text":"What does that mean? That means that if the C allele is recessive,"},{"Start":"04:54.680 ","End":"04:57.005","Text":"there is no pigment whatsoever,"},{"Start":"04:57.005 ","End":"05:05.375","Text":"and then the mice will be albino regardless of the allele present at locus A."},{"Start":"05:05.375 ","End":"05:09.520","Text":"If we cross 2 heterozygotes,"},{"Start":"05:09.520 ","End":"05:12.155","Text":"Aa, Cc,"},{"Start":"05:12.155 ","End":"05:13.940","Text":"one with the other,"},{"Start":"05:13.940 ","End":"05:16.010","Text":"we can draw a Punnett square, of course,"},{"Start":"05:16.010 ","End":"05:19.760","Text":"but what we find on the bottom here is that"},{"Start":"05:19.760 ","End":"05:24.855","Text":"the ratios are not what we expected from the previous crosses that we learned."},{"Start":"05:24.855 ","End":"05:30.950","Text":"4 of the 16 are going to be albino because they\u0027re homozygous,"},{"Start":"05:30.950 ","End":"05:33.790","Text":"recessive in the C gene."},{"Start":"05:33.790 ","End":"05:36.020","Text":"In this case,"},{"Start":"05:36.020 ","End":"05:40.610","Text":"we say that the C gene is epistatic to the aging because"},{"Start":"05:40.610 ","End":"05:49.020","Text":"the expression of the aging is dependent on the expression of the C gene."},{"Start":"05:49.630 ","End":"05:53.405","Text":"This epistasis, however, can be a little bit different."},{"Start":"05:53.405 ","End":"06:00.535","Text":"The epistasis can be by a dominant allele that masks a separate gene."},{"Start":"06:00.535 ","End":"06:03.560","Text":"There\u0027s dominant allele masking at a separate gene."},{"Start":"06:03.560 ","End":"06:07.430","Text":"Let\u0027s look at an example of this in squash."},{"Start":"06:07.430 ","End":"06:10.565","Text":"Fruit color in summer squash depends on 2 genes,"},{"Start":"06:10.565 ","End":"06:16.730","Text":"W and Y. W, ww,"},{"Start":"06:16.730 ","End":"06:24.530","Text":"coupled to YY or Yy,"},{"Start":"06:24.530 ","End":"06:27.515","Text":"either way produces yellow fruits."},{"Start":"06:27.515 ","End":"06:35.375","Text":"Homozygous recessive in both genes is the only way we can get a green fruit."},{"Start":"06:35.375 ","End":"06:42.680","Text":"Because if there is any W at all in the whole cross,"},{"Start":"06:42.680 ","End":"06:49.595","Text":"we\u0027re going to get a white or yellow fruit."},{"Start":"06:49.595 ","End":"06:55.285","Text":"The only way to get a green is if everything if all the alleles are recessive."},{"Start":"06:55.285 ","End":"07:04.805","Text":"A WW or a Ww will generate white fruit regardless of the Y allele."},{"Start":"07:04.805 ","End":"07:13.530","Text":"Now a cross between a white heterozygotes for both genes, Ww,"},{"Start":"07:13.530 ","End":"07:18.200","Text":"Yy in both cases would produce offspring with a phenotypic ratio of"},{"Start":"07:18.200 ","End":"07:23.075","Text":"12 whites to 3 yellow to 1 green."},{"Start":"07:23.075 ","End":"07:25.900","Text":"Just look at this Punnett square."},{"Start":"07:25.900 ","End":"07:28.860","Text":"Now let\u0027s look at another epistasis."},{"Start":"07:28.860 ","End":"07:31.770","Text":"It\u0027s called reciprocal epistasis."},{"Start":"07:31.770 ","End":"07:36.980","Text":"In this case, either gene in either dominant or recessive form,"},{"Start":"07:36.980 ","End":"07:39.290","Text":"what we saw before was just dominant."},{"Start":"07:39.290 ","End":"07:42.350","Text":"Here it could be in either dominant or recessive form,"},{"Start":"07:42.350 ","End":"07:44.795","Text":"expresses the same phenotype."},{"Start":"07:44.795 ","End":"07:48.710","Text":"In this case, we\u0027ll look at fruits that are either"},{"Start":"07:48.710 ","End":"07:53.795","Text":"triangular or the fruit has an ovoid shape."},{"Start":"07:53.795 ","End":"07:57.605","Text":"In this case, in shepherd\u0027s purse plant,"},{"Start":"07:57.605 ","End":"08:04.640","Text":"the seed shape is controlled by 2 genes in a dominant epistatic relationship."},{"Start":"08:04.640 ","End":"08:06.230","Text":"What do we mean by that?"},{"Start":"08:06.230 ","End":"08:12.740","Text":"When genes A and B are ab in all the alleles,"},{"Start":"08:12.740 ","End":"08:16.295","Text":"only then are the seeds ovoid."},{"Start":"08:16.295 ","End":"08:19.360","Text":"This is the only case where we see that."},{"Start":"08:19.360 ","End":"08:21.110","Text":"In all the other cases,"},{"Start":"08:21.110 ","End":"08:24.665","Text":"the seed shape will be triangular."},{"Start":"08:24.665 ","End":"08:28.295","Text":"If a dominant allele for either gene is present,"},{"Start":"08:28.295 ","End":"08:30.650","Text":"the seed will be triangular."},{"Start":"08:30.650 ","End":"08:35.510","Text":"Therefore, every possible genotype other than aa,"},{"Start":"08:35.510 ","End":"08:39.645","Text":"bb results in triangular seeds."},{"Start":"08:39.645 ","End":"08:43.010","Text":"The calculation will be of course,"},{"Start":"08:43.010 ","End":"08:45.710","Text":"that we\u0027re going to have 15 triangular"},{"Start":"08:45.710 ","End":"08:49.444","Text":"to 1 ovoid shape if we\u0027re looking at the phenotypes."},{"Start":"08:49.444 ","End":"08:55.315","Text":"There are a few important notes though to keep in mind in all of these cases."},{"Start":"08:55.315 ","End":"08:59.960","Text":"Let\u0027s keep in mind that any single characteristic that results in a phenotype ratio that"},{"Start":"08:59.960 ","End":"09:05.299","Text":"totals 16 is typical of a 2-gene interaction."},{"Start":"09:05.299 ","End":"09:09.155","Text":"It might not be clear to us how many genes were involved."},{"Start":"09:09.155 ","End":"09:15.185","Text":"But if there is a total of 16 different possibilities,"},{"Start":"09:15.185 ","End":"09:19.515","Text":"then we know that there are only 2 genes involved."},{"Start":"09:19.515 ","End":"09:23.840","Text":"Second, remember the phenotypic inheritance pattern"},{"Start":"09:23.840 ","End":"09:26.960","Text":"for Mendel\u0027s dihybrid cross that involved,"},{"Start":"09:26.960 ","End":"09:33.635","Text":"for instance, 2 non-interacting genes that the ratio was 9:3:3:1."},{"Start":"09:33.635 ","End":"09:37.925","Text":"Similarly, we would expect interacting gene pairs to also exhibit"},{"Start":"09:37.925 ","End":"09:43.060","Text":"ratios that are expressed in 16 parts in all cases."},{"Start":"09:43.060 ","End":"09:45.950","Text":"We are assuming that the interacting genes are not linked in"},{"Start":"09:45.950 ","End":"09:50.695","Text":"all those cases and they are assorting independently into gametes."},{"Start":"09:50.695 ","End":"09:56.300","Text":"In this section, we learned to explain Mendel\u0027s law of"},{"Start":"09:56.300 ","End":"10:01.775","Text":"segregation and independent assortment in terms of genetics and the events of meiosis."},{"Start":"10:01.775 ","End":"10:05.810","Text":"We learned the use of the forked-line method and"},{"Start":"10:05.810 ","End":"10:08.360","Text":"the probability rules to calculate the probability of"},{"Start":"10:08.360 ","End":"10:12.050","Text":"genotypes and phenotypes from multiple gene crosses."},{"Start":"10:12.050 ","End":"10:15.230","Text":"In addition, we explained the effect of linkage and"},{"Start":"10:15.230 ","End":"10:19.460","Text":"recombination on gamete genotypes, and finally,"},{"Start":"10:19.460 ","End":"10:21.965","Text":"explained the phenotypic outcomes of"},{"Start":"10:21.965 ","End":"10:28.710","Text":"epistatic events and epistatic effects between genes."}],"ID":26354},{"Watched":false,"Name":"Exercise 1","Duration":"50s","ChapterTopicVideoID":27131,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.095","Text":"Mendel performed hybridizations by transferring pollen"},{"Start":"00:04.095 ","End":"00:08.160","Text":"from what of the male plant to the female ova."},{"Start":"00:08.160 ","End":"00:13.905","Text":"Is that anther, pistil, stigma or seed?"},{"Start":"00:13.905 ","End":"00:16.005","Text":"Well, so let\u0027s see."},{"Start":"00:16.005 ","End":"00:18.150","Text":"If you remember this slide,"},{"Start":"00:18.150 ","End":"00:21.870","Text":"the way that Mendel performed hybridizations was that he"},{"Start":"00:21.870 ","End":"00:25.965","Text":"took a brush and he moved pollen from something,"},{"Start":"00:25.965 ","End":"00:27.180","Text":"what was it called?"},{"Start":"00:27.180 ","End":"00:32.640","Text":"Well, it\u0027s not the pistil because that\u0027s a female part."},{"Start":"00:32.640 ","End":"00:33.870","Text":"Not the stigma,"},{"Start":"00:33.870 ","End":"00:37.934","Text":"that\u0027s female as well and it\u0027s certainly not the seed,"},{"Start":"00:37.934 ","End":"00:42.420","Text":"so it must be the anther,"},{"Start":"00:42.420 ","End":"00:50.460","Text":"the anther is this little piece in which the pollen sits on the flower."}],"ID":28254},{"Watched":false,"Name":"Exercise 2","Duration":"47s","ChapterTopicVideoID":27132,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:05.624","Text":"Which is 1 of the 7 characteristics that Mendel observed in pea plants?"},{"Start":"00:05.624 ","End":"00:08.625","Text":"Is it flower size,"},{"Start":"00:08.625 ","End":"00:10.814","Text":"is it seed texture,"},{"Start":"00:10.814 ","End":"00:12.360","Text":"is it leaf shape,"},{"Start":"00:12.360 ","End":"00:15.255","Text":"or is it stem color?"},{"Start":"00:15.255 ","End":"00:17.945","Text":"If you remember, this slide,"},{"Start":"00:17.945 ","End":"00:20.885","Text":"there were various characteristics that we dealt with."},{"Start":"00:20.885 ","End":"00:22.520","Text":"There were 7 of them altogether,"},{"Start":"00:22.520 ","End":"00:23.765","Text":"that Mendel dealt with."},{"Start":"00:23.765 ","End":"00:26.570","Text":"These are the ones that we dealt with."},{"Start":"00:26.570 ","End":"00:32.479","Text":"So clearly, it is not flower size,"},{"Start":"00:32.479 ","End":"00:34.970","Text":"it is not leaf shape,"},{"Start":"00:34.970 ","End":"00:36.455","Text":"it is not stem color."},{"Start":"00:36.455 ","End":"00:40.490","Text":"It must be seed texture, right?"},{"Start":"00:40.490 ","End":"00:47.160","Text":"The seed texture was whether it was round or wrinkled."}],"ID":28255},{"Watched":false,"Name":"Exercise 3","Duration":"1m 19s","ChapterTopicVideoID":27133,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:06.105","Text":"Imagine you are performing a cross involving seed color in garden pea plants."},{"Start":"00:06.105 ","End":"00:12.660","Text":"What F_1 offspring would you expect if you cross true breeding parents"},{"Start":"00:12.660 ","End":"00:21.190","Text":"with green seeds and yellow seeds where yellow seed color is dominant over green."},{"Start":"00:23.150 ","End":"00:28.845","Text":"Would it be a 100% yellow-green seeds, 100% yellow seeds,"},{"Start":"00:28.845 ","End":"00:36.090","Text":"50% of each, or 25% green, 75% yellow seeds?"},{"Start":"00:36.090 ","End":"00:37.710","Text":"So since we\u0027re talking about"},{"Start":"00:37.710 ","End":"00:42.770","Text":"true breeding parents and we\u0027re talking about the F_1 generation."},{"Start":"00:42.770 ","End":"00:45.545","Text":"So here are the true breeding parents."},{"Start":"00:45.545 ","End":"00:51.060","Text":"The F_1 generation is this plants here."},{"Start":"00:51.060 ","End":"00:56.300","Text":"In this case we had dominant purple over white flowers."},{"Start":"00:56.300 ","End":"00:58.173","Text":"In the case we\u0027re talking about,"},{"Start":"00:58.173 ","End":"01:02.405","Text":"we have yellow being dominant over green."},{"Start":"01:02.405 ","End":"01:05.510","Text":"We see that it\u0027s 100% of something."},{"Start":"01:05.510 ","End":"01:08.425","Text":"We can certainly cross out these two."},{"Start":"01:08.425 ","End":"01:12.170","Text":"Since yellow is dominant over green,"},{"Start":"01:12.170 ","End":"01:19.320","Text":"our answers should be 100% yellow seeds."}],"ID":28256},{"Watched":false,"Name":"Exercise 4","Duration":"1m 25s","ChapterTopicVideoID":27134,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:05.080","Text":"Consider across to investigate that pea pod texture trade"},{"Start":"00:05.080 ","End":"00:10.320","Text":"involving constricted or inflated pods."},{"Start":"00:10.320 ","End":"00:11.795","Text":"Those are the 2 traits."},{"Start":"00:11.795 ","End":"00:14.500","Text":"Mendel found that the traits behave according to"},{"Start":"00:14.500 ","End":"00:19.015","Text":"a dominant recessive pattern in which inflated pods were dominant."},{"Start":"00:19.015 ","End":"00:21.900","Text":"Inflated pods, dominant."},{"Start":"00:21.900 ","End":"00:29.815","Text":"If you perform this cross and obtained 650 inflated pod plants in the F2 generation,"},{"Start":"00:29.815 ","End":"00:34.990","Text":"approximately how many constricted pod plants would you expect to have?"},{"Start":"00:34.990 ","End":"00:39.955","Text":"Well, we\u0027re talking about the F2 generation."},{"Start":"00:39.955 ","End":"00:41.750","Text":"In the F2 generation,"},{"Start":"00:41.750 ","End":"00:44.390","Text":"there can be 4 phenotypes."},{"Start":"00:44.390 ","End":"00:47.120","Text":"What\u0027s the phenotype we\u0027re looking for?"},{"Start":"00:47.120 ","End":"00:50.495","Text":"It\u0027s the constricted pod plants."},{"Start":"00:50.495 ","End":"00:55.885","Text":"The constricted pod plants are recessive."},{"Start":"00:55.885 ","End":"00:59.630","Text":"That is similar then to this situation."},{"Start":"00:59.630 ","End":"01:02.560","Text":"It would be 1/4 of the total."},{"Start":"01:02.560 ","End":"01:09.290","Text":"We had 650 inflated pod plants in the F2 generation."},{"Start":"01:09.290 ","End":"01:16.460","Text":"The answer would be a quarter of them or 162.5,"},{"Start":"01:16.460 ","End":"01:20.090","Text":"but that of course is not precise numbers,"},{"Start":"01:20.090 ","End":"01:25.290","Text":"so we\u0027ll choose the closest one, 165."}],"ID":28257},{"Watched":false,"Name":"Exercise 5","Duration":"33s","ChapterTopicVideoID":27135,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.020 ","End":"00:06.603","Text":"The observable traits expressed by an organism are described as its,"},{"Start":"00:06.603 ","End":"00:10.035","Text":"phenotype, and we\u0027re talking about observable traits."},{"Start":"00:10.035 ","End":"00:12.022","Text":"Is it phenotype,"},{"Start":"00:12.022 ","End":"00:13.500","Text":"is it genotype,"},{"Start":"00:13.500 ","End":"00:15.960","Text":"alleles, or zygote?"},{"Start":"00:15.960 ","End":"00:21.030","Text":"Remember this figure with phenotypes and genotypes."},{"Start":"00:21.030 ","End":"00:23.940","Text":"We have the observable traits,"},{"Start":"00:23.940 ","End":"00:25.860","Text":"that is the color of the flower,"},{"Start":"00:25.860 ","End":"00:29.250","Text":"and we call that phenotype."},{"Start":"00:29.250 ","End":"00:34.000","Text":"The correct answer will be phenotype."}],"ID":28258},{"Watched":false,"Name":"Exercise 6","Duration":"44s","ChapterTopicVideoID":27136,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:06.585","Text":"A recessive trait will be observed in individuals that are what for that trait."},{"Start":"00:06.585 ","End":"00:10.590","Text":"A recessive trait is observed."},{"Start":"00:10.590 ","End":"00:12.803","Text":"Is it heterozygous,"},{"Start":"00:12.803 ","End":"00:15.530","Text":"homozygous or heterozygous,"},{"Start":"00:15.530 ","End":"00:18.495","Text":"homozygous, or diploid?"},{"Start":"00:18.495 ","End":"00:20.720","Text":"Well, if you recall,"},{"Start":"00:20.720 ","End":"00:25.460","Text":"we have dominant and recessive phenotypes."},{"Start":"00:25.460 ","End":"00:33.935","Text":"We will only see the recessive phenotype if it is homozygous for the recessive allele."},{"Start":"00:33.935 ","End":"00:39.080","Text":"The answer then has to be homozygous."},{"Start":"00:39.080 ","End":"00:44.610","Text":"Not homozygous or heterozygous, but just homozygous."}],"ID":28259},{"Watched":false,"Name":"Exercise 7","Duration":"1m 3s","ChapterTopicVideoID":27137,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.200 ","End":"00:08.790","Text":"If black and white true breeding mice are mated and the result is all gray offspring,"},{"Start":"00:08.790 ","End":"00:12.510","Text":"what inheritance pattern would this be indicative of?"},{"Start":"00:12.510 ","End":"00:18.570","Text":"We\u0027ve got black and white are the true breeding mice."},{"Start":"00:18.570 ","End":"00:20.183","Text":"Those are the parents,"},{"Start":"00:20.183 ","End":"00:22.950","Text":"and they\u0027re both homozygous because they\u0027re true breeding."},{"Start":"00:22.950 ","End":"00:26.475","Text":"The result is neither black nor white."},{"Start":"00:26.475 ","End":"00:28.545","Text":"It\u0027s all gray."},{"Start":"00:28.545 ","End":"00:30.360","Text":"Well, what\u0027s that like?"},{"Start":"00:30.360 ","End":"00:33.150","Text":"It\u0027s like the flowers that we studied,"},{"Start":"00:33.150 ","End":"00:36.255","Text":"red flowers and white flowers."},{"Start":"00:36.255 ","End":"00:38.430","Text":"Both of them are true breeding."},{"Start":"00:38.430 ","End":"00:40.020","Text":"You see they\u0027re homozygous."},{"Start":"00:40.020 ","End":"00:46.355","Text":"But the heterozygote has neither of those 2 phenotypes."},{"Start":"00:46.355 ","End":"00:49.220","Text":"Was this called dominance?"},{"Start":"00:49.220 ","End":"00:51.545","Text":"Well, I don\u0027t think so."},{"Start":"00:51.545 ","End":"00:55.415","Text":"Was it called codominance? No, it wasn\u0027t."},{"Start":"00:55.415 ","End":"00:57.485","Text":"Was it multiple alleles?"},{"Start":"00:57.485 ","End":"00:59.090","Text":"No. Wasn\u0027t that either."},{"Start":"00:59.090 ","End":"01:03.300","Text":"It was incomplete dominance."}],"ID":28260},{"Watched":false,"Name":"Exercise 8","Duration":"2m 6s","ChapterTopicVideoID":27138,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.200 ","End":"00:06.765","Text":"The ABO blood groups in humans are expressed as the IA,"},{"Start":"00:06.765 ","End":"00:10.440","Text":"IB and i alleles."},{"Start":"00:10.440 ","End":"00:14.669","Text":"The IA allele encodes the A blood group antigen,"},{"Start":"00:14.669 ","End":"00:18.660","Text":"the IB encodes the B blood group antigen,"},{"Start":"00:18.660 ","End":"00:23.700","Text":"and the i encodes O or neither A nor B."},{"Start":"00:23.700 ","End":"00:26.610","Text":"Both A and B are dominant."},{"Start":"00:26.610 ","End":"00:29.865","Text":"Both are dominant to O."},{"Start":"00:29.865 ","End":"00:33.560","Text":"If a heterozygous blood group type A parent,"},{"Start":"00:33.560 ","End":"00:41.355","Text":"that would be IA and then i and heterozygous blood type B parent,"},{"Start":"00:41.355 ","End":"00:44.190","Text":"that would be IBi, mate,"},{"Start":"00:44.190 ","End":"00:49.330","Text":"1/4 of their offspring will have AB blood type,"},{"Start":"00:49.330 ","End":"00:53.780","Text":"in which both antigens are expressed equally."},{"Start":"00:53.780 ","End":"00:58.580","Text":"Therefore, ABO blood groups are an example of which of the following?"},{"Start":"00:58.580 ","End":"01:02.135","Text":"Is it multiple alleles and incomplete dominance,"},{"Start":"01:02.135 ","End":"01:04.995","Text":"co-dominance and incomplete dominance,"},{"Start":"01:04.995 ","End":"01:07.235","Text":"incomplete dominance only,"},{"Start":"01:07.235 ","End":"01:11.868","Text":"or multiple alleles and codominance?"},{"Start":"01:11.868 ","End":"01:16.560","Text":"Remember the 3 blood groups that we just described,"},{"Start":"01:16.560 ","End":"01:18.425","Text":"and what are the phenotypes?"},{"Start":"01:18.425 ","End":"01:28.035","Text":"Well, the phenotypes are that you can have either A by itself,"},{"Start":"01:28.035 ","End":"01:31.745","Text":"B by itself, or you could have both together."},{"Start":"01:31.745 ","End":"01:34.340","Text":"Both together as you see here."},{"Start":"01:34.340 ","End":"01:40.460","Text":"That would mean that you have to have codominance."},{"Start":"01:40.460 ","End":"01:48.515","Text":"It\u0027s got to be either this last D or maybe it would be B."},{"Start":"01:48.515 ","End":"01:54.875","Text":"But you can\u0027t have both codominance and incomplete dominance at the same time."},{"Start":"01:54.875 ","End":"02:00.130","Text":"The answer must be D, multiple alleles,"},{"Start":"02:00.130 ","End":"02:07.270","Text":"you\u0027ve got the A and the B, and codominance."}],"ID":28261},{"Watched":false,"Name":"Exercise 9","Duration":"1m 16s","ChapterTopicVideoID":27139,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:05.460","Text":"In a mating between 2 individuals that are heterozygous for"},{"Start":"00:05.460 ","End":"00:13.485","Text":"a recessive lethal allele that is expressed in utero,"},{"Start":"00:13.485 ","End":"00:15.341","Text":"what genotypic ratio,"},{"Start":"00:15.341 ","End":"00:21.900","Text":"homozygous dominant: heterozygous: homozygous recessive,"},{"Start":"00:21.900 ","End":"00:24.600","Text":"would you expect to observe in the offspring?"},{"Start":"00:24.600 ","End":"00:27.580","Text":"Would it be 1:2:1,"},{"Start":"00:27.580 ","End":"00:33.525","Text":"3:1:1, 1:2:0, or 0:2:1?"},{"Start":"00:33.525 ","End":"00:36.495","Text":"Let\u0027s see which of these it must be."},{"Start":"00:36.495 ","End":"00:40.010","Text":"You have a homozygous recessive,"},{"Start":"00:40.010 ","End":"00:43.250","Text":"which we know is lethal."},{"Start":"00:43.250 ","End":"00:45.740","Text":"That\u0027s got to be 0."},{"Start":"00:45.740 ","End":"00:51.380","Text":"The only one that has 0 here would be C. Therefore,"},{"Start":"00:51.380 ","End":"00:53.540","Text":"none of the others is correct."},{"Start":"00:53.540 ","End":"00:58.115","Text":"Yes, and we remember this from our studies of the fly"},{"Start":"00:58.115 ","End":"01:03.605","Text":"where the recessive homozygote was lethal."},{"Start":"01:03.605 ","End":"01:08.120","Text":"In that case, we saw 1:2:0."},{"Start":"01:08.120 ","End":"01:10.470","Text":"In this case, it\u0027s 1:2:0."},{"Start":"01:11.020 ","End":"01:15.390","Text":"They\u0027re reversed in the way they are shown on the slide."}],"ID":28262},{"Watched":false,"Name":"Exercise 10","Duration":"1m 22s","ChapterTopicVideoID":27140,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:03.130","Text":"Assuming no gene linkage,"},{"Start":"00:03.130 ","End":"00:06.085","Text":"in a dihybrid cross of,"},{"Start":"00:06.085 ","End":"00:08.544","Text":"now notice these 2 crosses here,"},{"Start":"00:08.544 ","End":"00:18.843","Text":"AABB crossed with aabb,"},{"Start":"00:18.843 ","End":"00:27.980","Text":"that\u0027s going to be 1 cross which is clearly going to produce Aa,"},{"Start":"00:27.980 ","End":"00:30.070","Text":"yes, and Bb,"},{"Start":"00:30.070 ","End":"00:33.985","Text":"with the same thing,"},{"Start":"00:33.985 ","End":"00:37.570","Text":"Aa, Bb, F1 heterozygotes."},{"Start":"00:37.570 ","End":"00:40.780","Text":"What is the ratio of the F1 gametes?"},{"Start":"00:40.780 ","End":"00:41.980","Text":"That\u0027s what we\u0027re asking about,"},{"Start":"00:41.980 ","End":"00:43.140","Text":"is the gametes,"},{"Start":"00:43.140 ","End":"00:46.305","Text":"the ratio of the gametes, AA,"},{"Start":"00:46.305 ","End":"00:49.910","Text":"aB, Ab,"},{"Start":"00:49.910 ","End":"00:54.485","Text":"ab, that will give rise to the F2 offspring."},{"Start":"00:54.485 ","End":"00:57.250","Text":"What is the ratio of the gametes?"},{"Start":"00:57.250 ","End":"01:03.110","Text":"That is essentially what we\u0027ve seen in this picture where we"},{"Start":"01:03.110 ","End":"01:10.215","Text":"have a big Bb, and Aa."},{"Start":"01:10.215 ","End":"01:11.960","Text":"What are the gametes that are produced?"},{"Start":"01:11.960 ","End":"01:18.645","Text":"Well, it\u0027s one of each in the same ratio to each other."},{"Start":"01:18.645 ","End":"01:22.780","Text":"That\u0027s got to be the first answer."}],"ID":28263},{"Watched":false,"Name":"Exercise 11","Duration":"1m 24s","ChapterTopicVideoID":27141,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:05.315","Text":"The forked line and probability methods make use of what probability rule?"},{"Start":"00:05.315 ","End":"00:07.650","Text":"Forked line method."},{"Start":"00:07.650 ","End":"00:10.350","Text":"Is it the test cross, the product rule,"},{"Start":"00:10.350 ","End":"00:13.335","Text":"monohybrid rule, or the sum rule?"},{"Start":"00:13.335 ","End":"00:17.145","Text":"Let\u0027s remember what the forked line method was."},{"Start":"00:17.145 ","End":"00:19.050","Text":"If you\u0027ll remember, it was"},{"Start":"00:19.050 ","End":"00:23.880","Text":"this diagram in which we had these various forks and then there was"},{"Start":"00:23.880 ","End":"00:30.675","Text":"the probability that we had to calculate for each of these various possibilities."},{"Start":"00:30.675 ","End":"00:31.980","Text":"Notice, by the way,"},{"Start":"00:31.980 ","End":"00:35.760","Text":"that there are these x\u0027s,"},{"Start":"00:35.760 ","End":"00:39.745","Text":"these products, that\u0027s going to help us with our answer."},{"Start":"00:39.745 ","End":"00:42.910","Text":"Let\u0027s first look and see what the test cross is."},{"Start":"00:42.910 ","End":"00:46.070","Text":"Well, the test cross was a way to determine whether"},{"Start":"00:46.070 ","End":"00:50.641","Text":"a dominant phenotype is a heterozygote or a homozygote,"},{"Start":"00:50.641 ","End":"00:54.500","Text":"and the organism is crossed with a homozygous recessive organism."},{"Start":"00:54.500 ","End":"00:56.540","Text":"Well, that\u0027s not quite what happens."},{"Start":"00:56.540 ","End":"01:02.005","Text":"Remember, this is what the test cross looked like."},{"Start":"01:02.005 ","End":"01:05.915","Text":"So it\u0027s not going to be the test cross."},{"Start":"01:05.915 ","End":"01:11.515","Text":"We already discussed the product rule so maybe that\u0027s what it is."},{"Start":"01:11.515 ","End":"01:14.970","Text":"Not the monohybrid rule,"},{"Start":"01:14.970 ","End":"01:17.610","Text":"and it\u0027s certainly not the sum."},{"Start":"01:17.610 ","End":"01:19.755","Text":"So we\u0027ll cross these two out."},{"Start":"01:19.755 ","End":"01:23.830","Text":"It\u0027s going to be the product rule."}],"ID":28264},{"Watched":false,"Name":"Exercise 12","Duration":"1m 19s","ChapterTopicVideoID":27142,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:08.520","Text":"How many different offspring genotypes are expected in a trihybrid cross between"},{"Start":"00:08.520 ","End":"00:12.390","Text":"parents heterozygous for all three traits"},{"Start":"00:12.390 ","End":"00:17.970","Text":"when the traits behave in a dominant and recessive pattern."},{"Start":"00:17.970 ","End":"00:21.180","Text":"We\u0027re going to know how many phenotypes as well."},{"Start":"00:21.180 ","End":"00:25.590","Text":"How many genotypes and how many phenotypes?"},{"Start":"00:25.590 ","End":"00:27.900","Text":"Is it the first, the second,"},{"Start":"00:27.900 ","End":"00:31.050","Text":"the third or the fourth of these?"},{"Start":"00:31.050 ","End":"00:34.530","Text":"Well, let\u0027s recall that the general rule is"},{"Start":"00:34.530 ","End":"00:39.320","Text":"the number of different gametes would be n^2. What\u0027s n?"},{"Start":"00:39.320 ","End":"00:40.610","Text":"N is 3,"},{"Start":"00:40.610 ","End":"00:44.140","Text":"because it\u0027s a trihybrid cross."},{"Start":"00:44.140 ","End":"00:47.930","Text":"How many genotypes will there be in the F2?"},{"Start":"00:47.930 ","End":"00:49.940","Text":"There will be 3^3."},{"Start":"00:49.940 ","End":"00:54.705","Text":"So that\u0027s 3 times 3 is 9,"},{"Start":"00:54.705 ","End":"00:56.300","Text":"times 3 is 27."},{"Start":"00:56.300 ","End":"00:59.590","Text":"That\u0027s the number of genotypes."},{"Start":"00:59.590 ","End":"01:02.880","Text":"It\u0027s going to have to be d here."},{"Start":"01:02.880 ","End":"01:04.700","Text":"Let\u0027s see, what about the phenotypes?"},{"Start":"01:04.700 ","End":"01:07.340","Text":"If we look at the number of phenotypes,"},{"Start":"01:07.340 ","End":"01:09.510","Text":"we\u0027ve got 1, 2,"},{"Start":"01:09.510 ","End":"01:11.505","Text":"3, 4, 5, 6,"},{"Start":"01:11.505 ","End":"01:15.275","Text":"7, 8 different phenotypes."},{"Start":"01:15.275 ","End":"01:19.440","Text":"So our answer is going to be d."}],"ID":28265},{"Watched":false,"Name":"Exercise 13","Duration":"1m 52s","ChapterTopicVideoID":27126,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:05.219","Text":"A scientist pollinates a true-breeding pea plant with violet,"},{"Start":"00:05.219 ","End":"00:11.685","Text":"terminal flowers with pollen from a true-breeding pea plant with white, axial flowers."},{"Start":"00:11.685 ","End":"00:13.470","Text":"We\u0027ve got 2 traits here."},{"Start":"00:13.470 ","End":"00:19.980","Text":"We have the color and we have whether the flowers are terminal or axial."},{"Start":"00:19.980 ","End":"00:25.890","Text":"Which of the following observations would most accurately describe the F2 generation?"},{"Start":"00:25.890 ","End":"00:30.930","Text":"Would it be 75 percent violet flowers;"},{"Start":"00:30.930 ","End":"00:32.670","Text":"75 percent terminal flowers,"},{"Start":"00:32.670 ","End":"00:36.540","Text":"75 percent white flowers in a terminal position,"},{"Start":"00:36.540 ","End":"00:39.150","Text":"75 percent violet flowers;"},{"Start":"00:39.150 ","End":"00:41.550","Text":"75 percent axial flowers,"},{"Start":"00:41.550 ","End":"00:46.100","Text":"or 75 percent violet flowers in an axial position?"},{"Start":"00:46.100 ","End":"00:52.700","Text":"Let\u0027s recall that for a particular trait,"},{"Start":"00:52.700 ","End":"00:56.780","Text":"in the F2 generation,"},{"Start":"00:56.780 ","End":"01:01.620","Text":"we\u0027re going to have 3:1 ratio,"},{"Start":"01:01.620 ","End":"01:03.690","Text":"so the total of 4."},{"Start":"01:03.690 ","End":"01:09.015","Text":"So it\u0027s going to be 75 percent of the dominant color."},{"Start":"01:09.015 ","End":"01:15.740","Text":"Here, the flower color in this example was purple and white,"},{"Start":"01:15.740 ","End":"01:17.480","Text":"where purple was dominant."},{"Start":"01:17.480 ","End":"01:20.165","Text":"We also had something we hadn\u0027t seen before,"},{"Start":"01:20.165 ","End":"01:27.430","Text":"which is whether the flowers were terminal or axial."},{"Start":"01:27.430 ","End":"01:35.750","Text":"What we need to know here actually is that the axial flowers are going to be dominant,"},{"Start":"01:35.750 ","End":"01:41.215","Text":"but each of these will be independently segregated."},{"Start":"01:41.215 ","End":"01:46.875","Text":"So the answer needs to be 75 percent for both."},{"Start":"01:46.875 ","End":"01:52.150","Text":"Well, that is going to be answer C."}],"ID":28266},{"Watched":false,"Name":"Exercise 14","Duration":"1m 25s","ChapterTopicVideoID":27127,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:07.305","Text":"Labrador retriever\u0027s fur color is controlled by 2 alleles that are called E and B."},{"Start":"00:07.305 ","End":"00:11.325","Text":"Any dog with the ee,"},{"Start":"00:11.325 ","End":"00:15.630","Text":"anything, genotype develops into a yellow lab."},{"Start":"00:15.630 ","End":"00:20.880","Text":"It\u0027s any dog with that genotype develops into yellow lab."},{"Start":"00:20.880 ","End":"00:28.275","Text":"While B anything, E anything dogs become black labs and the bbE,"},{"Start":"00:28.275 ","End":"00:30.870","Text":"little anything dogs become chocolate labs."},{"Start":"00:30.870 ","End":"00:34.050","Text":"This is an example of, is it epistasis,"},{"Start":"00:34.050 ","End":"00:39.143","Text":"codominance, incomplete dominance, or linkage?"},{"Start":"00:39.143 ","End":"00:40.875","Text":"Well, let\u0027s see here."},{"Start":"00:40.875 ","End":"00:47.125","Text":"It\u0027s got to be epistasis because it\u0027s any dog."},{"Start":"00:47.125 ","End":"00:53.320","Text":"Remember, epistasis is where a particular gene influences the effect of"},{"Start":"00:53.320 ","End":"01:00.235","Text":"another gene and the first gene is said to be epistatic to the second one."},{"Start":"01:00.235 ","End":"01:03.270","Text":"We had 2 examples over here,"},{"Start":"01:03.270 ","End":"01:07.660","Text":"so what we\u0027re talking here about is epistasis"},{"Start":"01:07.660 ","End":"01:13.975","Text":"since any dog with that genotype develops into a yellow dog,"},{"Start":"01:13.975 ","End":"01:18.580","Text":"it\u0027s the e gene, the e genotype,"},{"Start":"01:18.580 ","End":"01:25.550","Text":"which is going to influence the other genes regardless of what they are."}],"ID":28267},{"Watched":false,"Name":"Exercise 15","Duration":"1m 39s","ChapterTopicVideoID":27128,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:08.460","Text":"Which of the following situations does not follow the Law of Independent Assortment."},{"Start":"00:08.460 ","End":"00:13.440","Text":"Is it a blond man and a brunette woman produce 3 offspring over time,"},{"Start":"00:13.440 ","End":"00:15.810","Text":"all of whom have blonde hair?"},{"Start":"00:15.810 ","End":"00:20.972","Text":"A white cow crossed with a brown bull produces roan cattle?"},{"Start":"00:20.972 ","End":"00:24.795","Text":"Mating a hog with a sow produces 6 female piglets,"},{"Start":"00:24.795 ","End":"00:32.101","Text":"or that men are more likely to experience hemophilia than women?"},{"Start":"00:32.101 ","End":"00:36.120","Text":"We\u0027re asking which does not follow the Law of Independent Assortment."},{"Start":"00:36.120 ","End":"00:38.980","Text":"Well, in each of the first 3,"},{"Start":"00:38.980 ","End":"00:45.590","Text":"we have specific results of a particular cross of a blond man,"},{"Start":"00:45.590 ","End":"00:48.170","Text":"a white cow, a hog."},{"Start":"00:48.170 ","End":"00:51.125","Text":"We\u0027re not talking about what\u0027s more likely or less likely,"},{"Start":"00:51.125 ","End":"00:52.580","Text":"the only one we\u0027re talking about,"},{"Start":"00:52.580 ","End":"00:54.965","Text":"and that\u0027s more likely or less likely,"},{"Start":"00:54.965 ","End":"00:56.396","Text":"is the last one,"},{"Start":"00:56.396 ","End":"01:01.745","Text":"that men are more likely to experience hemophilia than women."},{"Start":"01:01.745 ","End":"01:04.700","Text":"That is sex linkage."},{"Start":"01:04.700 ","End":"01:08.360","Text":"If you remember, in the case of hemophilia,"},{"Start":"01:08.360 ","End":"01:10.040","Text":"we spoke about that,"},{"Start":"01:10.040 ","End":"01:15.290","Text":"that men are more likely to experience it because it is linked to"},{"Start":"01:15.290 ","End":"01:19.410","Text":"the X chromosome of which there is"},{"Start":"01:19.410 ","End":"01:26.430","Text":"only 1 copy in a man as opposed to 2 in a woman,"},{"Start":"01:26.430 ","End":"01:28.385","Text":"so we do not have"},{"Start":"01:28.385 ","End":"01:33.470","Text":"independent assortment in that case because there\u0027s only 1 X chromosome."},{"Start":"01:33.470 ","End":"01:35.645","Text":"Our answer is D,"},{"Start":"01:35.645 ","End":"01:40.050","Text":"men are more likely to experience hemophilia than women."}],"ID":28268},{"Watched":false,"Name":"Exercise 16","Duration":"56s","ChapterTopicVideoID":27129,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:05.099","Text":"If the allele encoding palette ductile that is 6 fingers is dominant,"},{"Start":"00:05.099 ","End":"00:06.731","Text":"the allele is dominant,"},{"Start":"00:06.731 ","End":"00:09.420","Text":"why do most people have only 5 fingers?"},{"Start":"00:09.420 ","End":"00:12.615","Text":"Is it the genetic elements suppress the polydactyl gene,"},{"Start":"00:12.615 ","End":"00:15.705","Text":"that polydactyl is embryonic lethal,"},{"Start":"00:15.705 ","End":"00:18.255","Text":"that the 6th finger is removed at birth,"},{"Start":"00:18.255 ","End":"00:22.649","Text":"or that the polydactyl allele is very rare in the human population?"},{"Start":"00:22.649 ","End":"00:25.185","Text":"Well, so let\u0027s think about this for a moment."},{"Start":"00:25.185 ","End":"00:28.350","Text":"If it were embryonic lethal,"},{"Start":"00:28.350 ","End":"00:31.305","Text":"then we wouldn\u0027t see it at all ever."},{"Start":"00:31.305 ","End":"00:33.345","Text":"That doesn\u0027t make any sense,"},{"Start":"00:33.345 ","End":"00:36.120","Text":"and in any case, it\u0027s dominant."},{"Start":"00:36.120 ","End":"00:38.910","Text":"The 6th finger is removed at birth."},{"Start":"00:38.910 ","End":"00:40.830","Text":"Well, that has nothing to do with genetics."},{"Start":"00:40.830 ","End":"00:42.480","Text":"We can cross that off."},{"Start":"00:42.480 ","End":"00:46.640","Text":"Possibly genetic elements suppress the polydactyl gene,"},{"Start":"00:46.640 ","End":"00:48.425","Text":"but we\u0027d have to know more about that."},{"Start":"00:48.425 ","End":"00:54.455","Text":"It\u0027s really more likely that the polydactyl allele is very rare in the population."},{"Start":"00:54.455 ","End":"00:56.760","Text":"That\u0027s the case."}],"ID":28269},{"Watched":false,"Name":"Exercise 17","Duration":"2m 52s","ChapterTopicVideoID":27130,"CourseChapterTopicPlaylistID":237672,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:03.690","Text":"A farmer raises black and white chickens,"},{"Start":"00:03.690 ","End":"00:08.010","Text":"so we have black and white chickens."},{"Start":"00:08.010 ","End":"00:09.329","Text":"Those are the two phenotypes."},{"Start":"00:09.329 ","End":"00:12.180","Text":"To his surprise, when the first-generation of eggs hatch,"},{"Start":"00:12.180 ","End":"00:16.545","Text":"all the chickens are black with white speckles throughout their feathers."},{"Start":"00:16.545 ","End":"00:21.065","Text":"That is a third phenotype: black with white speckles."},{"Start":"00:21.065 ","End":"00:24.905","Text":"What should the farmer expect when the eggs laid after interbreeding,"},{"Start":"00:24.905 ","End":"00:27.615","Text":"the speckled chickens hatch."},{"Start":"00:27.615 ","End":"00:29.960","Text":"We\u0027re interbreeding the speckled chickens,"},{"Start":"00:29.960 ","End":"00:32.870","Text":"they\u0027re being mated to each other."},{"Start":"00:32.870 ","End":"00:35.510","Text":"Would it be that all the offspring will be speckled,"},{"Start":"00:35.510 ","End":"00:38.810","Text":"75 percent will be speckled and 25 will be black."},{"Start":"00:38.810 ","End":"00:41.330","Text":"Then 50 percent of the offspring will be speckled,"},{"Start":"00:41.330 ","End":"00:42.410","Text":"25 will be black,"},{"Start":"00:42.410 ","End":"00:44.285","Text":"and 25 percent will be white,"},{"Start":"00:44.285 ","End":"00:47.730","Text":"or that 50 percent of the offspring will be black and"},{"Start":"00:47.730 ","End":"00:51.510","Text":"50 percent of the offspring will be white."},{"Start":"00:51.510 ","End":"00:56.330","Text":"This must be a case of codominance that is"},{"Start":"00:56.330 ","End":"01:02.240","Text":"similar to this picture here with the flowers."},{"Start":"01:02.240 ","End":"01:06.590","Text":"Remember when we have red flowers and white flowers, in this case,"},{"Start":"01:06.590 ","End":"01:09.410","Text":"when they are mated to each other,"},{"Start":"01:09.410 ","End":"01:11.360","Text":"the RR and the WW,"},{"Start":"01:11.360 ","End":"01:14.930","Text":"we get codominance, we get both red and white flowers."},{"Start":"01:14.930 ","End":"01:19.265","Text":"Both colors are expressed in this flower."},{"Start":"01:19.265 ","End":"01:22.039","Text":"This case is similar."},{"Start":"01:22.039 ","End":"01:24.275","Text":"In that case if you remember,"},{"Start":"01:24.275 ","End":"01:26.480","Text":"then in the F2 generation,"},{"Start":"01:26.480 ","End":"01:29.240","Text":"when these are bred to each other,"},{"Start":"01:29.240 ","End":"01:33.195","Text":"then 50 percent of the offspring would be this."},{"Start":"01:33.195 ","End":"01:37.185","Text":"RW, 25 would be black or,"},{"Start":"01:37.185 ","End":"01:41.235","Text":"well, it\u0027d be red, and 25 percent would be white."},{"Start":"01:41.235 ","End":"01:45.210","Text":"That\u0027s what\u0027s similar in this case."},{"Start":"01:45.210 ","End":"01:50.600","Text":"The answer would be C. When alleles are co-dominant,"},{"Start":"01:50.600 ","End":"01:54.650","Text":"both are expressed equally in heterozygous individuals,"},{"Start":"01:54.650 ","End":"01:57.290","Text":"like we saw in this flower."},{"Start":"01:57.290 ","End":"02:00.950","Text":"Chickens for example have co-dominant alleles for feather color."},{"Start":"02:00.950 ","End":"02:04.385","Text":"That\u0027s what gave the black and white speckles."},{"Start":"02:04.385 ","End":"02:09.285","Text":"Alleles code for either W or B feathers,"},{"Start":"02:09.285 ","End":"02:11.375","Text":"white or black feathers,"},{"Start":"02:11.375 ","End":"02:16.325","Text":"heterozygous chickens or speckled having feathers that are both white and black,"},{"Start":"02:16.325 ","End":"02:19.370","Text":"similar to the white and red in this picture,"},{"Start":"02:19.370 ","End":"02:20.720","Text":"but not great,"},{"Start":"02:20.720 ","End":"02:24.300","Text":"that would indicate incomplete dominance instead."},{"Start":"02:24.300 ","End":"02:34.190","Text":"Homozygous big B or big W. Big W would be black or white respectively."},{"Start":"02:34.190 ","End":"02:40.085","Text":"Heterozygous BW or WB would be speckled."},{"Start":"02:40.085 ","End":"02:44.765","Text":"Of course, since you could have it either way BW or WB,"},{"Start":"02:44.765 ","End":"02:52.170","Text":"you would have twice as many of those chickens as the pure colored ones."}],"ID":28270}],"Thumbnail":null,"ID":237672},{"Name":"Modern Understandings of Inheritance","TopicPlaylistFirstVideoID":0,"Duration":null,"Videos":[{"Watched":false,"Name":"Modern Understandings of Inheritance","Duration":"1m 15s","ChapterTopicVideoID":25550,"CourseChapterTopicPlaylistID":237673,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.050 ","End":"00:04.110","Text":"Hi, welcome back. To this point,"},{"Start":"00:04.110 ","End":"00:08.730","Text":"we\u0027ve been discussing inheritance in terms of Mendel\u0027s terms, primarily,"},{"Start":"00:08.730 ","End":"00:11.355","Text":"not so much thinking about it in modern terms,"},{"Start":"00:11.355 ","End":"00:13.410","Text":"but from here on,"},{"Start":"00:13.410 ","End":"00:16.230","Text":"let\u0027s think about inheritance with"},{"Start":"00:16.230 ","End":"00:21.420","Text":"our modern understanding and try to explain things using our current tools."},{"Start":"00:21.420 ","End":"00:26.730","Text":"What we\u0027ll see is that the genes are actually a physical unit of inheritance,"},{"Start":"00:26.730 ","End":"00:30.150","Text":"they\u0027re a piece of DNA that those genes are arranged in"},{"Start":"00:30.150 ","End":"00:33.990","Text":"a linear order on the chromosomes and that the chromosomes"},{"Start":"00:33.990 ","End":"00:38.460","Text":"themselves or their behavior and their interaction with each other during"},{"Start":"00:38.460 ","End":"00:43.190","Text":"meiosis explain the inheritance patterns observed in populations."},{"Start":"00:43.190 ","End":"00:44.960","Text":"Mendel thought that was the case,"},{"Start":"00:44.960 ","End":"00:50.840","Text":"but we understand that better now and we\u0027ll explain it more in the coming videos."},{"Start":"00:50.840 ","End":"00:57.860","Text":"Furthermore, genetic disorders, which we find in various organisms,"},{"Start":"00:57.860 ","End":"01:01.880","Text":"can arise many times because of changes of"},{"Start":"01:01.880 ","End":"01:05.870","Text":"chromosome number or the changes in the structure"},{"Start":"01:05.870 ","End":"01:09.200","Text":"of the chromosome and those changes can have"},{"Start":"01:09.200 ","End":"01:14.130","Text":"dramatic effects on the phenotypes of the organisms."}],"ID":26367},{"Watched":false,"Name":"Chromosomal Theory and Genetic Linkage a","Duration":"8m 36s","ChapterTopicVideoID":25547,"CourseChapterTopicPlaylistID":237673,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.620","Text":"Hi. Until now we\u0027ve been"},{"Start":"00:04.620 ","End":"00:10.005","Text":"studying Mendel\u0027s theories of evolution and we\u0027re now going to look"},{"Start":"00:10.005 ","End":"00:12.840","Text":"more deeply into modern understandings of"},{"Start":"00:12.840 ","End":"00:16.620","Text":"inheritance and particularly how chromosomal theory"},{"Start":"00:16.620 ","End":"00:24.210","Text":"and genetic linkage that Mendel understood to some degree at least come together."},{"Start":"00:24.210 ","End":"00:26.175","Text":"By the end of this section,"},{"Start":"00:26.175 ","End":"00:30.840","Text":"you should be able to discuss Sutton\u0027s chromosomal theory of inheritance."},{"Start":"00:30.840 ","End":"00:33.990","Text":"You should be able to describe the genetic linkage,"},{"Start":"00:33.990 ","End":"00:37.185","Text":"and you should be able to explain the process"},{"Start":"00:37.185 ","End":"00:41.595","Text":"of homologous recombination or crossing over."},{"Start":"00:41.595 ","End":"00:47.420","Text":"First of all, let\u0027s now look at Mendel\u0027s ideas in brief,"},{"Start":"00:47.420 ","End":"00:48.740","Text":"just to remind you."},{"Start":"00:48.740 ","End":"00:51.920","Text":"He is considered the father of modern genetics."},{"Start":"00:51.920 ","End":"00:56.915","Text":"He began studying heredity in 1843."},{"Start":"00:56.915 ","End":"01:00.020","Text":"Of course, not knowing anything about DNA,"},{"Start":"01:00.020 ","End":"01:04.735","Text":"and not knowing anything at all about chromosomes even."},{"Start":"01:04.735 ","End":"01:09.170","Text":"He just observed traits after crosses as we learned."},{"Start":"01:09.170 ","End":"01:12.995","Text":"But later improved microscopic techniques"},{"Start":"01:12.995 ","End":"01:16.945","Text":"allowed people to observe cell division and meiosis."},{"Start":"01:16.945 ","End":"01:21.995","Text":"Particularly, they could stain the cells and see chromosomes."},{"Start":"01:21.995 ","End":"01:24.485","Text":"With each mitotic division,"},{"Start":"01:24.485 ","End":"01:27.425","Text":"chromosomes that they saw replicated,"},{"Start":"01:27.425 ","End":"01:31.770","Text":"condensed, and migrated to separate cellular poles."},{"Start":"01:31.770 ","End":"01:34.640","Text":"They notice these chromosomes."},{"Start":"01:34.640 ","End":"01:39.770","Text":"They call them chromosomes because they were stained."},{"Start":"01:39.770 ","End":"01:41.570","Text":"Chromo means color."},{"Start":"01:41.570 ","End":"01:45.350","Text":"They could see them colored when they looked at"},{"Start":"01:45.350 ","End":"01:49.955","Text":"cells that had been stained in a particular way."},{"Start":"01:49.955 ","End":"01:57.185","Text":"Now, the speculation was that chromosomes might be the key to heredity,"},{"Start":"01:57.185 ","End":"02:03.155","Text":"because of the way they moved during meiotic and mitotic divisions."},{"Start":"02:03.155 ","End":"02:05.840","Text":"Several scientists began to examine"},{"Start":"02:05.840 ","End":"02:09.980","Text":"Mendel\u0027s publications and see if they could put 2 and 2 together."},{"Start":"02:09.980 ","End":"02:14.315","Text":"If they could understand the movement of the chromosomes with Mendel\u0027s ideas."},{"Start":"02:14.315 ","End":"02:19.355","Text":"In particular, Theodor Boveri in 1902,"},{"Start":"02:19.355 ","End":"02:23.795","Text":"noticed that proper sea urchin embryonic development"},{"Start":"02:23.795 ","End":"02:28.115","Text":"does not occur unless all the chromosomes are present."},{"Start":"02:28.115 ","End":"02:32.270","Text":"Yes. If there was a problem in our language today,"},{"Start":"02:32.270 ","End":"02:36.725","Text":"during anaphase in which the chromosomes didn\u0027t separate properly,"},{"Start":"02:36.725 ","End":"02:39.560","Text":"maybe all the chromosomes wouldn\u0027t be present, and then,"},{"Start":"02:39.560 ","End":"02:43.415","Text":"if that were the case, embryonic development did not occur properly."},{"Start":"02:43.415 ","End":"02:48.529","Text":"Maybe there\u0027s a connection between the chromosomes and development."},{"Start":"02:48.529 ","End":"02:52.220","Text":"Walter Sutton in the same year, 1902,"},{"Start":"02:52.220 ","End":"02:59.140","Text":"said that the chromosomes separate into daughter cells during meiosis."},{"Start":"02:59.140 ","End":"03:03.740","Text":"Sutton then looked at the chromosomes and"},{"Start":"03:03.740 ","End":"03:07.830","Text":"he saw that they separated into daughter cells during meiosis."},{"Start":"03:07.830 ","End":"03:11.810","Text":"This led to the chromosomal theory of inheritance in"},{"Start":"03:11.810 ","End":"03:16.220","Text":"which they said that chromosomes are the genetic material."},{"Start":"03:16.220 ","End":"03:18.890","Text":"There was material, there was the genetic material,"},{"Start":"03:18.890 ","End":"03:24.935","Text":"something physical that was responsible for the Mendelian inheritance."},{"Start":"03:24.935 ","End":"03:30.110","Text":"Now, during meiosis, homologous chromosomes they saw migrate"},{"Start":"03:30.110 ","End":"03:35.045","Text":"as discrete structures that are independent of other chromosome pairs."},{"Start":"03:35.045 ","End":"03:38.355","Text":"They could see this by looking through the microscope,"},{"Start":"03:38.355 ","End":"03:41.330","Text":"and the chromosomes sorting from each homologous pair"},{"Start":"03:41.330 ","End":"03:45.955","Text":"into pre gametes appears to be random."},{"Start":"03:45.955 ","End":"03:49.220","Text":"That was just by visualization, and of course,"},{"Start":"03:49.220 ","End":"03:53.435","Text":"that jive very nicely with Mendel\u0027s ideas."},{"Start":"03:53.435 ","End":"04:00.980","Text":"Each parent then synthesizes gametes that contain only half their chromosomal complement,"},{"Start":"04:00.980 ","End":"04:03.900","Text":"as we learned earlier."},{"Start":"04:04.090 ","End":"04:07.465","Text":"Even though male and female gametes,"},{"Start":"04:07.465 ","End":"04:10.475","Text":"sperm and egg differ in size and morphology."},{"Start":"04:10.475 ","End":"04:16.510","Text":"Yes, the sperm are much smaller and they certainly look different than the egg."},{"Start":"04:16.510 ","End":"04:19.340","Text":"Both of them are haploid."},{"Start":"04:19.340 ","End":"04:21.160","Text":"Yes. Both of them are haploid."},{"Start":"04:21.160 ","End":"04:24.325","Text":"That is, they contain the same number of chromosomes,"},{"Start":"04:24.325 ","End":"04:28.390","Text":"half the number that is found in the diploid zygote,"},{"Start":"04:28.390 ","End":"04:33.040","Text":"and that\u0027s suggested equal genetic contributions from each parent."},{"Start":"04:33.040 ","End":"04:37.990","Text":"Of course, the gametic chromosomes combined during fertilization to produce"},{"Start":"04:37.990 ","End":"04:43.675","Text":"offspring that had the same chromosome number as their parents, the 2n."},{"Start":"04:43.675 ","End":"04:46.340","Text":"Yes, as we learned before."},{"Start":"04:46.340 ","End":"04:50.525","Text":"Scientists proposed the chromosomal theory of inheritance,"},{"Start":"04:50.525 ","End":"04:55.685","Text":"long before there was any direct evidence that chromosomes carried traits."},{"Start":"04:55.685 ","End":"04:58.265","Text":"All these were indirect,"},{"Start":"04:58.265 ","End":"05:04.220","Text":"circumstantial reasoning that made people think that these things they saw,"},{"Start":"05:04.220 ","End":"05:08.029","Text":"those chromosomes, in fact, carried traits."},{"Start":"05:08.029 ","End":"05:09.575","Text":"But there were critics,"},{"Start":"05:09.575 ","End":"05:14.060","Text":"and the critics said that they saw that individuals had far"},{"Start":"05:14.060 ","End":"05:19.105","Text":"more independently segregating traits than they had chromosomes."},{"Start":"05:19.105 ","End":"05:23.990","Text":"People were thinking maybe each chromosome only had 1 trait."},{"Start":"05:23.990 ","End":"05:29.945","Text":"But here people saw that there were many independently segregating traits."},{"Start":"05:29.945 ","End":"05:32.810","Text":"If several traits might be on the same chromosome,"},{"Start":"05:32.810 ","End":"05:35.315","Text":"so they should not segregate independently."},{"Start":"05:35.315 ","End":"05:40.020","Text":"But in fact, people did see that they segregated independently."},{"Start":"05:40.020 ","End":"05:42.630","Text":"There were critical thinkers that"},{"Start":"05:42.630 ","End":"05:46.055","Text":"were worried about the chromosomal theory of inheritance."},{"Start":"05:46.055 ","End":"05:50.610","Text":"But Thomas Morgan, who worked on Drosophila Melanogaster."},{"Start":"05:50.610 ","End":"05:53.200","Text":"Drosophila are the common fruit fly,"},{"Start":"05:53.200 ","End":"05:58.420","Text":"provided experimental evidence to support the chromosomal theory of inheritance."},{"Start":"05:58.420 ","End":"06:01.890","Text":"Let\u0027s go back for a moment to Mendel."},{"Start":"06:01.890 ","End":"06:07.315","Text":"Mendel\u0027s work suggested that traits are inherited independently of each other."},{"Start":"06:07.315 ","End":"06:11.390","Text":"If we go through across here with"},{"Start":"06:11.390 ","End":"06:19.910","Text":"the same homozygous flies and then dihybrid test crosses that we saw before."},{"Start":"06:19.910 ","End":"06:24.515","Text":"Then if we look at 2 different traits, the b trait,"},{"Start":"06:24.515 ","End":"06:31.345","Text":"which is something that encodes for the body color of these flies,"},{"Start":"06:31.345 ","End":"06:36.380","Text":"and this vg or vestigial wings traits,"},{"Start":"06:36.380 ","End":"06:42.180","Text":"that is either the wings could be long like this normal or they could be just very short."},{"Start":"06:42.180 ","End":"06:47.374","Text":"If you do these crosses with homozygous plus"},{"Start":"06:47.374 ","End":"06:52.570","Text":"wild-type in both of those traits together with negatives in both traits,"},{"Start":"06:52.570 ","End":"06:56.810","Text":"then of course you get an F1 hybrid in which you will have"},{"Start":"06:56.810 ","End":"07:02.300","Text":"all the various combination of eggs that will come out of that across."},{"Start":"07:02.300 ","End":"07:04.190","Text":"Now if you mate that,"},{"Start":"07:04.190 ","End":"07:09.350","Text":"or each of these together with a bb,"},{"Start":"07:09.350 ","End":"07:12.080","Text":"in other words, in vgvg,"},{"Start":"07:12.080 ","End":"07:16.790","Text":"that is, these are the black body vestigial wings,"},{"Start":"07:16.790 ","End":"07:19.595","Text":"that\u0027s not the wild-type male,"},{"Start":"07:19.595 ","End":"07:22.190","Text":"then there are actually 4 possibilities of"},{"Start":"07:22.190 ","End":"07:25.035","Text":"flies that you\u0027ll get out and they\u0027re listed over here."},{"Start":"07:25.035 ","End":"07:26.430","Text":"You would expect, of course,"},{"Start":"07:26.430 ","End":"07:28.235","Text":"each of them according to Mendel,"},{"Start":"07:28.235 ","End":"07:33.980","Text":"to be found in a 1:1:1:1 ratio."},{"Start":"07:33.980 ","End":"07:38.644","Text":"However, when this was done by Morgan,"},{"Start":"07:38.644 ","End":"07:44.315","Text":"he did not find that they were in a 1:1:1:1 ratio."},{"Start":"07:44.315 ","End":"07:46.625","Text":"But that is not what he found."},{"Start":"07:46.625 ","End":"07:52.625","Text":"What he found was a 965: 944: 206: 185."},{"Start":"07:52.625 ","End":"07:56.675","Text":"Let\u0027s see if that could be explained."},{"Start":"07:56.675 ","End":"08:02.810","Text":"It seems actually from this and Morgan saw that it\u0027s not"},{"Start":"08:02.810 ","End":"08:10.210","Text":"a discrete segregation like Mendel saw but rather you could have something in the middle."},{"Start":"08:10.210 ","End":"08:13.700","Text":"His suggestion was that alleles,"},{"Start":"08:13.700 ","End":"08:19.415","Text":"that is, particular traits could be very close to each other on the same chromosome,"},{"Start":"08:19.415 ","End":"08:25.410","Text":"or potentially they could be far apart from each other on the same chromosome,"},{"Start":"08:25.410 ","End":"08:30.720","Text":"and that would lead to different kinds of segregation."},{"Start":"08:30.720 ","End":"08:36.570","Text":"Let\u0027s pause here and continue with this in the next video."}],"ID":26364},{"Watched":false,"Name":"Chromosomal Theory and Genetic Linkage b","Duration":"6m 13s","ChapterTopicVideoID":25548,"CourseChapterTopicPlaylistID":237673,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:05.941","Text":"We\u0027ve been discussing chromosomal theory and genetic linkage,"},{"Start":"00:05.941 ","End":"00:09.488","Text":"and we\u0027ve seen that Morgan suggested that"},{"Start":"00:09.488 ","End":"00:15.786","Text":"random chromosome segregation was the physical basis of Mendel\u0027s model."},{"Start":"00:15.786 ","End":"00:18.841","Text":"Now what he saw was that, sometimes,"},{"Start":"00:18.841 ","End":"00:22.820","Text":"the segregation did not occur as was expected."},{"Start":"00:22.820 ","End":"00:26.910","Text":"Sometimes different genes were partly linked."},{"Start":"00:26.910 ","End":"00:29.163","Text":"In trying to explain this,"},{"Start":"00:29.163 ","End":"00:36.869","Text":"we know that it was demonstrated that linked genes disrupt Mendel\u0027s predicted outcomes,"},{"Start":"00:36.869 ","End":"00:39.960","Text":"that\u0027s what we just saw from Morgan,"},{"Start":"00:39.960 ","End":"00:45.021","Text":"and that each chromosome can then carry many linked genes."},{"Start":"00:45.021 ","End":"00:52.902","Text":"Some of the researchers suggested that the alleles positioned on the same chromosome were"},{"Start":"00:52.902 ","End":"00:56.856","Text":"not always inherited together because there"},{"Start":"00:56.856 ","End":"01:00.922","Text":"were more traits than there were chromosomes,"},{"Start":"01:00.922 ","End":"01:04.894","Text":"so they may not always be inherited together,"},{"Start":"01:04.894 ","End":"01:09.402","Text":"and we remember the idea of crossing over such that,"},{"Start":"01:09.402 ","End":"01:14.344","Text":"during meiosis, linked genes somehow become unlinked."},{"Start":"01:14.344 ","End":"01:18.350","Text":"We know that that\u0027s really via crossing over."},{"Start":"01:18.350 ","End":"01:23.111","Text":"Now the genes that are located distant to each other on"},{"Start":"01:23.111 ","End":"01:30.017","Text":"the same chromosome can have a recombination frequency of nearly 50 percent,"},{"Start":"01:30.017 ","End":"01:33.642","Text":"as if they were on separate chromosomes,"},{"Start":"01:33.642 ","End":"01:37.062","Text":"and such genes are physically linked,"},{"Start":"01:37.062 ","End":"01:39.525","Text":"but genetically unlinked,"},{"Start":"01:39.525 ","End":"01:45.108","Text":"and they behave as if they\u0027re found on different chromosomes."},{"Start":"01:45.108 ","End":"01:49.632","Text":"Now let\u0027s try to understand how that might happen."},{"Start":"01:49.632 ","End":"01:53.199","Text":"If we have the homologous chromosomes,"},{"Start":"01:53.199 ","End":"01:56.667","Text":"remember each of them is duplicated in"},{"Start":"01:56.667 ","End":"02:03.087","Text":"a homologous way because they have been duplicated during the S phase,"},{"Start":"02:03.087 ","End":"02:06.805","Text":"so we\u0027ll have in this case 2 genes, G and A,"},{"Start":"02:06.805 ","End":"02:12.849","Text":"which will denote if they\u0027re dominant as being large G and large A,"},{"Start":"02:12.849 ","End":"02:15.832","Text":"as opposed to small g and small a."},{"Start":"02:15.832 ","End":"02:21.825","Text":"You would expect that these would be inherited together or that,"},{"Start":"02:21.825 ","End":"02:25.837","Text":"during meiosis, they would stay together."},{"Start":"02:25.837 ","End":"02:27.288","Text":"In other words,"},{"Start":"02:27.288 ","End":"02:30.424","Text":"a large G would stay with a large A."},{"Start":"02:30.424 ","End":"02:36.167","Text":"But sometimes we can get gametes that are not quite like that."},{"Start":"02:36.167 ","End":"02:41.494","Text":"We can sometimes get a large G with a small a, for example."},{"Start":"02:41.494 ","End":"02:44.000","Text":"Now why might that happen?"},{"Start":"02:44.000 ","End":"02:50.985","Text":"It might happen if there were crossing over like this between the 2 genes."},{"Start":"02:50.985 ","End":"02:56.057","Text":"Now the probability of the 2 genes staying together,"},{"Start":"02:56.057 ","End":"03:01.968","Text":"therefore, would be a function of the distance between them."},{"Start":"03:01.968 ","End":"03:03.248","Text":"In this case,"},{"Start":"03:03.248 ","End":"03:08.160","Text":"we would have the G that might be far away from the A,"},{"Start":"03:08.160 ","End":"03:10.986","Text":"that was not here but up here,"},{"Start":"03:10.986 ","End":"03:18.567","Text":"and therefore, when there is a crossing over anywhere along the chromosome,"},{"Start":"03:18.567 ","End":"03:22.857","Text":"then they would segregate independently,"},{"Start":"03:22.857 ","End":"03:28.246","Text":"and that is something that Morgan saw and understood."},{"Start":"03:28.246 ","End":"03:34.149","Text":"Therefore, there is a possibility of mapping these genes,"},{"Start":"03:34.149 ","End":"03:37.300","Text":"as we\u0027ll see in a minute because"},{"Start":"03:37.300 ","End":"03:43.895","Text":"the higher the frequency the 2 genes are not inherited together,"},{"Start":"03:43.895 ","End":"03:48.447","Text":"even though they\u0027re on the same chromosome,"},{"Start":"03:48.447 ","End":"03:52.158","Text":"then the more distance they must be."},{"Start":"03:52.158 ","End":"03:57.139","Text":"In 1909, Frans Janssen observed the chiasmata."},{"Start":"03:57.139 ","End":"03:59.890","Text":"Chiasmata, you remember,"},{"Start":"03:59.890 ","End":"04:07.322","Text":"are these areas in meiotic chromosomes that appear to stick together,"},{"Start":"04:07.322 ","End":"04:11.648","Text":"and it turned out that at this chiasmata,"},{"Start":"04:11.648 ","End":"04:16.649","Text":"there was this crossing over events that led to"},{"Start":"04:16.649 ","End":"04:23.266","Text":"this crossing over event that we can see denoted on the right."},{"Start":"04:23.266 ","End":"04:28.121","Text":"He suggested that alleles become unlinked,"},{"Start":"04:28.121 ","End":"04:34.341","Text":"and the chromosomes physically now exchange segments."},{"Start":"04:34.341 ","End":"04:39.280","Text":"As chromosomes paired with their homologs,"},{"Start":"04:39.280 ","End":"04:45.076","Text":"they appeared to interact at very distinct points."},{"Start":"04:45.076 ","End":"04:51.489","Text":"Janssen then suggested that these points correspond to"},{"Start":"04:51.489 ","End":"04:59.807","Text":"the regions where the chromosomes segments exchanged or crossed over,"},{"Start":"04:59.807 ","End":"05:04.179","Text":"so this is this crossing over and that"},{"Start":"05:04.179 ","End":"05:12.780","Text":"when synapsed homologous chromosomes undergo reciprocal exchanges,"},{"Start":"05:12.780 ","End":"05:21.395","Text":"homologous recombination, or another word for that is crossing over."},{"Start":"05:21.395 ","End":"05:27.099","Text":"Let\u0027s now look at homologous recombination."},{"Start":"05:27.099 ","End":"05:33.822","Text":"Consider a heterozygous individual that inherited"},{"Start":"05:33.822 ","End":"05:42.028","Text":"dominant maternal alleles for 2 genes on the same chromosome,"},{"Start":"05:42.028 ","End":"05:45.996","Text":"such as large A and large B and"},{"Start":"05:45.996 ","End":"05:53.504","Text":"2 recessive paternal alleles for those same genes,"},{"Start":"05:53.504 ","End":"05:56.834","Text":"like small a, small b,"},{"Start":"05:56.834 ","End":"06:01.221","Text":"and that\u0027s we can see here."},{"Start":"06:01.221 ","End":"06:05.653","Text":"On the same chromosome,"},{"Start":"06:05.653 ","End":"06:08.645","Text":"we have large A"},{"Start":"06:08.645 ","End":"06:12.200","Text":"and large B. On the other chromosome that is homologous,"},{"Start":"06:12.200 ","End":"06:12.201","Text":"we have a, b and of course when those cells undergo meiosis,"},{"Start":"06:12.201 ","End":"06:12.202","Text":"we\u0027ll get A and B together and a and b together."},{"Start":"06:12.202 ","End":"06:12.203","Text":"But that\u0027s under the condition that there\u0027s no crossing over."},{"Start":"06:12.203 ","End":"06:12.204","Text":"If the genes are linked, then that\u0027s what we\u0027ll get."},{"Start":"06:12.204 ","End":"06:12.205","Text":"On the other hand, if there is crossing over and the genes are unlinked in some form,"},{"Start":"06:12.205 ","End":"06:12.206","Text":"then we can get a,"},{"Start":"06:12.206 ","End":"06:12.207","Text":"B and we can also get A, b,"},{"Start":"06:12.207 ","End":"06:12.208","Text":"as well as a,"},{"Start":"06:12.208 ","End":"06:12.209","Text":"b and A,"},{"Start":"06:12.209 ","End":"06:12.210","Text":"B with equal frequencies if they\u0027re totally unlinked and those"},{"Start":"06:12.210 ","End":"06:12.211","Text":"would be parental and non-parental alleles."},{"Start":"06:12.211 ","End":"06:12.212","Text":"There would be the parental and the non parental types."},{"Start":"06:12.212 ","End":"06:13.200","Text":"This led to the formation of genetic maps and we\u0027ll see that in the next video."}],"ID":26365},{"Watched":false,"Name":"Chromosomal Theory and Genetic Linkage c","Duration":"6m 30s","ChapterTopicVideoID":25549,"CourseChapterTopicPlaylistID":237673,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.590 ","End":"00:03.210","Text":"At the end of the last video,"},{"Start":"00:03.210 ","End":"00:07.170","Text":"we proposed the possibility that the frequency of crossing"},{"Start":"00:07.170 ","End":"00:12.090","Text":"over is something that can be related to the distance between genes."},{"Start":"00:12.090 ","End":"00:16.500","Text":"Now let\u0027s see how people arrived at that idea and how they began"},{"Start":"00:16.500 ","End":"00:20.460","Text":"to map different genes or different traits,"},{"Start":"00:20.460 ","End":"00:28.410","Text":"different phenotypes along a particular thread or a particular piece of chromatin."},{"Start":"00:28.410 ","End":"00:31.470","Text":"Particular chromosome at the end of the day."},{"Start":"00:31.470 ","End":"00:36.875","Text":"Alfred Sturtevant constructed a genetic map."},{"Start":"00:36.875 ","End":"00:39.320","Text":"A genetic map that is"},{"Start":"00:39.320 ","End":"00:44.170","Text":"a linear representation of gene order and relative distance on a chromosome."},{"Start":"00:44.170 ","End":"00:47.165","Text":"You can see what this looks like over here."},{"Start":"00:47.165 ","End":"00:49.265","Text":"He gave them numbers."},{"Start":"00:49.265 ","End":"00:55.265","Text":"Because the numbers, the distances between the genes can be expressed as map units."},{"Start":"00:55.265 ","End":"00:58.025","Text":"That\u0027s a comparative distance and order,"},{"Start":"00:58.025 ","End":"01:01.340","Text":"but not the exact positions of the genes."},{"Start":"01:01.340 ","End":"01:02.960","Text":"We now know by the way,"},{"Start":"01:02.960 ","End":"01:05.420","Text":"that the frequency of crossing over is"},{"Start":"01:05.420 ","End":"01:08.000","Text":"definitely related to the distance between the genes."},{"Start":"01:08.000 ","End":"01:10.430","Text":"But sometimes the frequency of crossing over at"},{"Start":"01:10.430 ","End":"01:14.315","Text":"1 part of the chromosome might be different than at a different part of the chromosome."},{"Start":"01:14.315 ","End":"01:16.175","Text":"The actual distances,"},{"Start":"01:16.175 ","End":"01:18.530","Text":"as in terms of DNA sequence,"},{"Start":"01:18.530 ","End":"01:24.280","Text":"may not be precisely what we see as map units when we map genetically."},{"Start":"01:24.280 ","End":"01:30.515","Text":"One map unit signifies a 1 percent recombination frequency."},{"Start":"01:30.515 ","End":"01:33.860","Text":"Those are going to be called centimorgans,"},{"Start":"01:33.860 ","End":"01:39.410","Text":"as we will see for Mr. Morgan that brought up this idea in the first place."},{"Start":"01:39.410 ","End":"01:43.790","Text":"The value of the map distances in centimorgans and they"},{"Start":"01:43.790 ","End":"01:47.815","Text":"correspond to recombination frequencies in percent."},{"Start":"01:47.815 ","End":"01:49.410","Text":"To construct a map,"},{"Start":"01:49.410 ","End":"01:53.510","Text":"Sturtevant assumed that the genes were ordered serially."},{"Start":"01:53.510 ","End":"01:58.700","Text":"That\u0027s 1 after the other on a thread-like chromosome that turned out to be correct."},{"Start":"01:58.700 ","End":"02:03.545","Text":"He also assumed that the incidence of recombination between 2 homologous chromosomes"},{"Start":"02:03.545 ","End":"02:09.110","Text":"could occur with equal likelihood anywhere along the chromosomes length."},{"Start":"02:09.110 ","End":"02:12.275","Text":"I just told you that\u0027s not a 100 percent true,"},{"Start":"02:12.275 ","End":"02:16.385","Text":"but pretty close. He was good with that."},{"Start":"02:16.385 ","End":"02:22.645","Text":"The recombination frequency then correlated with the physical distance between genes."},{"Start":"02:22.645 ","End":"02:25.520","Text":"Let\u0027s look for a moment at"},{"Start":"02:25.520 ","End":"02:30.850","Text":"the example of the cross between 2 flies that we see here on the right."},{"Start":"02:30.850 ","End":"02:37.185","Text":"We can calculate the recombinations frequency of body color and wing shape."},{"Start":"02:37.185 ","End":"02:39.140","Text":"Those were 2 different traits,"},{"Start":"02:39.140 ","End":"02:42.710","Text":"turned out to be encoded by 2 different genes."},{"Start":"02:42.710 ","End":"02:48.455","Text":"The way we might do this is look at all the possibilities"},{"Start":"02:48.455 ","End":"02:54.525","Text":"of a wild type with a black vestigial cross."},{"Start":"02:54.525 ","End":"02:57.200","Text":"Male will be this black vestigial as we saw before,"},{"Start":"02:57.200 ","End":"03:02.330","Text":"that would be just a homozygous individual that"},{"Start":"03:02.330 ","End":"03:07.920","Text":"is recessive in both genes and so all of its sperm would be the same."},{"Start":"03:07.920 ","End":"03:11.595","Text":"The female here is not homozygous."},{"Start":"03:11.595 ","End":"03:18.690","Text":"It\u0027s heterozygous in the sense that one of the chromosomes is B, Vg."},{"Start":"03:18.690 ","End":"03:22.310","Text":"It\u0027s dominant on 1 chromosome and recessive in those 2 genes."},{"Start":"03:22.310 ","End":"03:24.305","Text":"In the other chromosome, of course,"},{"Start":"03:24.305 ","End":"03:29.465","Text":"in this case there are 4 different eggs that it can produce 4 different combinations."},{"Start":"03:29.465 ","End":"03:35.840","Text":"Therefore, when each of them is mated with this black vestigial male,"},{"Start":"03:35.840 ","End":"03:38.750","Text":"we can get 4 different possibilities."},{"Start":"03:38.750 ","End":"03:42.290","Text":"That ought to be 1:1:1:1,"},{"Start":"03:42.290 ","End":"03:43.670","Text":"as we had mentioned before."},{"Start":"03:43.670 ","End":"03:47.300","Text":"But in fact, the number of individuals that you get when you make"},{"Start":"03:47.300 ","End":"03:52.465","Text":"a cross like this would be out of 2300 total offspring,"},{"Start":"03:52.465 ","End":"03:56.445","Text":"we get 944 of black vestigial,"},{"Start":"03:56.445 ","End":"03:58.890","Text":"965 gray normal,"},{"Start":"03:58.890 ","End":"04:00.779","Text":"206 of gray vestigial,"},{"Start":"04:00.779 ","End":"04:04.620","Text":"and 185 black to normal."},{"Start":"04:04.620 ","End":"04:08.720","Text":"The parental phenotypes. If you look at these,"},{"Start":"04:08.720 ","End":"04:11.180","Text":"these are parental phenotypes."},{"Start":"04:11.180 ","End":"04:14.690","Text":"This was what the male was and this is what the female was."},{"Start":"04:14.690 ","End":"04:18.110","Text":"That altogether, we can combine those together"},{"Start":"04:18.110 ","End":"04:21.650","Text":"and we can combine together the recombinant non-parental ones."},{"Start":"04:21.650 ","End":"04:24.020","Text":"If we look at the non-parental ones,"},{"Start":"04:24.020 ","End":"04:26.450","Text":"so it\u0027s 206 plus 185 makes"},{"Start":"04:26.450 ","End":"04:33.320","Text":"391 recombinants different parental phenotypes over the total number of offspring."},{"Start":"04:33.320 ","End":"04:41.585","Text":"We see that it\u0027s 0.17 and that would be the recombination frequency."},{"Start":"04:41.585 ","End":"04:46.295","Text":"The likelihood of a crossover between genes B,"},{"Start":"04:46.295 ","End":"04:54.450","Text":"b and the 2 vestigial genes was 0.17 or 17%."},{"Start":"04:54.470 ","End":"04:59.600","Text":"In likewise way, we can do all sorts of different crosses and"},{"Start":"04:59.600 ","End":"05:04.190","Text":"measure distances and the genes that were definitely linked,"},{"Start":"05:04.190 ","End":"05:07.660","Text":"but there were far enough away for crossovers to occasionally occur,"},{"Start":"05:07.660 ","End":"05:10.250","Text":"would lead us to be able to map and the"},{"Start":"05:10.250 ","End":"05:13.265","Text":"genetic map units or centimorgans, as we said before."},{"Start":"05:13.265 ","End":"05:18.830","Text":"A 0.01 recombination frequency corresponds to 1 centimorgan."},{"Start":"05:18.830 ","End":"05:21.425","Text":"If genes are totally unlinked,"},{"Start":"05:21.425 ","End":"05:24.780","Text":"then recombination frequency would be 0.5."},{"Start":"05:24.780 ","End":"05:28.405","Text":"There\u0027s no way of mapping genes that are that far apart."},{"Start":"05:28.405 ","End":"05:33.050","Text":"Perfectly unlinked genes then correspond to Mendel\u0027s prediction of"},{"Start":"05:33.050 ","End":"05:37.915","Text":"independent assortment in dihybrid cross."},{"Start":"05:37.915 ","End":"05:40.410","Text":"In the traits that Mendel mapped,"},{"Start":"05:40.410 ","End":"05:44.915","Text":"homologous recombination is a common genetic process."},{"Start":"05:44.915 ","End":"05:48.170","Text":"But in fact, he\u0027d never observed it."},{"Start":"05:48.170 ","End":"05:50.750","Text":"As I said before,"},{"Start":"05:50.750 ","End":"05:57.005","Text":"he may have been lucky in this respect because all the genes that he examined"},{"Start":"05:57.005 ","End":"06:00.140","Text":"are either on separate chromosomes or sufficiently"},{"Start":"06:00.140 ","End":"06:04.030","Text":"far apart to be statistically unlinked."},{"Start":"06:04.030 ","End":"06:07.415","Text":"Mendel, in fact was very lucky."},{"Start":"06:07.415 ","End":"06:12.590","Text":"Some people say that maybe Mendel discarded some data that suggested linkage."},{"Start":"06:12.590 ","End":"06:15.305","Text":"But we\u0027ll never really know."},{"Start":"06:15.305 ","End":"06:18.290","Text":"Now, by the end of this section,"},{"Start":"06:18.290 ","End":"06:22.430","Text":"we learned how to discuss Sutton\u0027s chromosomal theory of inheritance."},{"Start":"06:22.430 ","End":"06:25.580","Text":"We described genetic linkage and we explain"},{"Start":"06:25.580 ","End":"06:30.360","Text":"the process of homologous recombination or crossing over."}],"ID":26366},{"Watched":false,"Name":"Chromosomal Basis of Inherited Disorders part a","Duration":"6m 7s","ChapterTopicVideoID":25551,"CourseChapterTopicPlaylistID":237673,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.725","Text":"In this section, the Modern Understanding of Inheritance,"},{"Start":"00:04.725 ","End":"00:09.855","Text":"we\u0027re going to be discussing Chromosomal Basis of Inherited Disorders."},{"Start":"00:09.855 ","End":"00:17.250","Text":"We\u0027ll see here what disorders can occur when there are gross changes."},{"Start":"00:17.250 ","End":"00:21.164","Text":"Not mutations, but gross changes to the chromosomes."},{"Start":"00:21.164 ","End":"00:26.741","Text":"By the end of this section, you should be able to describe how a karyogram is created,"},{"Start":"00:26.741 ","End":"00:28.500","Text":"you should be able to explain how"},{"Start":"00:28.500 ","End":"00:33.015","Text":"non-disjunction leads to disorders in chromosome number,"},{"Start":"00:33.015 ","End":"00:35.520","Text":"you should be able to compare disorders that"},{"Start":"00:35.520 ","End":"00:38.955","Text":"aneuploidy causes and know what aneuploidy means,"},{"Start":"00:38.955 ","End":"00:42.320","Text":"and you should be able to describe how errors in chromosome structure"},{"Start":"00:42.320 ","End":"00:46.870","Text":"occur through inversions and translocations."},{"Start":"00:46.870 ","End":"00:53.120","Text":"Let\u0027s now look at different inherited disorders and how we can detect them."},{"Start":"00:53.120 ","End":"00:59.480","Text":"First of all, they can arise when chromosomes behave abnormally during meiosis,"},{"Start":"00:59.480 ","End":"01:06.350","Text":"so that the process of meiosis then does not occur exactly properly and there may"},{"Start":"01:06.350 ","End":"01:09.410","Text":"be an improper number of"},{"Start":"01:09.410 ","End":"01:14.090","Text":"chromosomes that separate during the different meiotic divisions."},{"Start":"01:14.090 ","End":"01:19.150","Text":"That would cause them abnormalities in chromosome number."},{"Start":"01:19.150 ","End":"01:24.065","Text":"Furthermore, there could be abnormalities in chromosomal structure"},{"Start":"01:24.065 ","End":"01:30.695","Text":"because there could be structural rearrangements in the chromosomes as we\u0027ll see later."},{"Start":"01:30.695 ","End":"01:33.770","Text":"Furthermore, chromosomal disorders are"},{"Start":"01:33.770 ","End":"01:37.630","Text":"characteristically dramatic and of course, often fatal."},{"Start":"01:37.630 ","End":"01:40.115","Text":"If you have major changes in the chromosome,"},{"Start":"01:40.115 ","End":"01:43.415","Text":"it\u0027s not surprising that they are often fatal,"},{"Start":"01:43.415 ","End":"01:47.195","Text":"but not always as we\u0027ll see soon."},{"Start":"01:47.195 ","End":"01:54.800","Text":"How do we identify these chromosomes and what do we see when we look in the microscope?"},{"Start":"01:54.800 ","End":"01:58.550","Text":"Chromosome isolation and microscopic observation is"},{"Start":"01:58.550 ","End":"02:03.260","Text":"the primary method to detect chromosomal abnormalities in humans."},{"Start":"02:03.260 ","End":"02:04.700","Text":"That\u0027s still the case."},{"Start":"02:04.700 ","End":"02:09.205","Text":"What we do is we make something called a karyotype."},{"Start":"02:09.205 ","End":"02:14.030","Text":"What we do is we force the cells to all"},{"Start":"02:14.030 ","End":"02:18.890","Text":"stop in the M phase by using a chemical called cytochalasin B."},{"Start":"02:18.890 ","End":"02:21.835","Text":"Then we stain the cells."},{"Start":"02:21.835 ","End":"02:24.800","Text":"When we stain the cells with a proper stain,"},{"Start":"02:24.800 ","End":"02:29.003","Text":"we can see the banding pattern in the chromosomes that we have mentioned before,"},{"Start":"02:29.003 ","End":"02:31.250","Text":"and we can see the chromosomal length,"},{"Start":"02:31.250 ","End":"02:35.525","Text":"as well as the banding pattern and we can see the centromere position."},{"Start":"02:35.525 ","End":"02:38.360","Text":"Now since each of the chromosomes,"},{"Start":"02:38.360 ","End":"02:41.360","Text":"in this case, we\u0027ve got 23 chromosomes."},{"Start":"02:41.360 ","End":"02:45.965","Text":"There are 22 autosomes and the 2 sex chromosomes, X and Y."},{"Start":"02:45.965 ","End":"02:49.130","Text":"Each of them looks a little bit different."},{"Start":"02:49.130 ","End":"02:51.215","Text":"In what respect are they different?"},{"Start":"02:51.215 ","End":"02:57.290","Text":"They\u0027re different in the lengths and the banding pattern and where"},{"Start":"02:57.290 ","End":"03:03.665","Text":"the centromere is along the chromosome."},{"Start":"03:03.665 ","End":"03:06.485","Text":"We can divide them into metacentric,"},{"Start":"03:06.485 ","End":"03:12.965","Text":"submetacentric an acrocentric depending on where the centromere is."},{"Start":"03:12.965 ","End":"03:16.355","Text":"The chromosomes will vary in number, size,"},{"Start":"03:16.355 ","End":"03:21.635","Text":"centromere position, and banding patterns between the different chromosomes."},{"Start":"03:21.635 ","End":"03:27.445","Text":"Interestingly, we\u0027ll see that these are different as well between species."},{"Start":"03:27.445 ","End":"03:33.320","Text":"In the karyotype, the autosomes are generally organized by size."},{"Start":"03:33.320 ","End":"03:35.225","Text":"The numbering is 1,"},{"Start":"03:35.225 ","End":"03:37.655","Text":"2, 3, 4, and so on."},{"Start":"03:37.655 ","End":"03:41.480","Text":"As you can see, they get smaller as the number goes up."},{"Start":"03:41.480 ","End":"03:43.010","Text":"In most of the cases,"},{"Start":"03:43.010 ","End":"03:44.621","Text":"there is 1 exception,"},{"Start":"03:44.621 ","End":"03:49.880","Text":"and that is the chromosome 21 is shorter than chromosome 22."},{"Start":"03:49.880 ","End":"03:54.911","Text":"Chromosome arms, that\u0027s what is projecting from the centromere,"},{"Start":"03:54.911 ","End":"03:57.650","Text":"can be either long or they can be,"},{"Start":"03:57.650 ","End":"04:00.020","Text":"let\u0027s say here, very short."},{"Start":"04:00.020 ","End":"04:03.605","Text":"In addition, we have some nomenclature for that."},{"Start":"04:03.605 ","End":"04:04.955","Text":"The short arm,"},{"Start":"04:04.955 ","End":"04:08.560","Text":"\u0027petite\u0027 would be we\u0027ll call it p."},{"Start":"04:08.560 ","End":"04:15.050","Text":"The longer arm we\u0027ll call q because q follows p alphabetically."},{"Start":"04:15.050 ","End":"04:21.790","Text":"We have p and q arms in the notation for each of these chromosomes."},{"Start":"04:21.790 ","End":"04:25.100","Text":"Then there are numbers which will often add to that,"},{"Start":"04:25.100 ","End":"04:29.695","Text":"that further subdivided and denote each arm."},{"Start":"04:29.695 ","End":"04:34.302","Text":"The karyogram may reveal genetic abnormalities,"},{"Start":"04:34.302 ","End":"04:38.570","Text":"but there can be minor abnormalities that we can\u0027t see."},{"Start":"04:38.570 ","End":"04:45.695","Text":"In addition, there may be too many or too few chromosomes in the cell."},{"Start":"04:45.695 ","End":"04:49.060","Text":"We all have heard of Down syndrome for instance,"},{"Start":"04:49.060 ","End":"04:52.565","Text":"which is called trisomy 21."},{"Start":"04:52.565 ","End":"05:01.820","Text":"Which means that there are 3 copies in these individuals of chromosome 21."},{"Start":"05:01.820 ","End":"05:07.175","Text":"It\u0027s actually surprising at least to me that they live at all, but they do."},{"Start":"05:07.175 ","End":"05:10.420","Text":"Another example is Turner\u0027s syndrome."},{"Start":"05:10.420 ","End":"05:16.125","Text":"In Turner\u0027s syndrome there is 1 fewer chromosome in women."},{"Start":"05:16.125 ","End":"05:19.550","Text":"There\u0027s only 1 X chromosome in these women."},{"Start":"05:19.550 ","End":"05:23.420","Text":"In addition, there can be deletions or insertions of"},{"Start":"05:23.420 ","End":"05:27.940","Text":"large DNA fragments inside a particular chromosome."},{"Start":"05:27.940 ","End":"05:32.000","Text":"There\u0027s another syndrome called Jacobsen syndrome,"},{"Start":"05:32.000 ","End":"05:36.860","Text":"in which case there is a deletion on chromosome 11."},{"Start":"05:36.860 ","End":"05:42.050","Text":"There are also pinpoint translocations, very small translocations."},{"Start":"05:42.050 ","End":"05:46.400","Text":"It\u0027s a segment of genetic material breaks off from 1 chromosome and then can"},{"Start":"05:46.400 ","End":"05:51.885","Text":"reattach to another chromosome or to a different part of the same chromosome."},{"Start":"05:51.885 ","End":"05:58.870","Text":"There can be all translocations that we\u0027ll see a little bit about that later."},{"Start":"05:58.870 ","End":"06:06.060","Text":"Let\u0027s now break this video and we\u0027ll continue on the next 1."}],"ID":26368},{"Watched":false,"Name":"Chromosomal Basis of Inherited Disorders part b","Duration":"5m 31s","ChapterTopicVideoID":25552,"CourseChapterTopicPlaylistID":237673,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:03.300","Text":"Let\u0027s continue with this section."},{"Start":"00:03.300 ","End":"00:05.070","Text":"In the previous video,"},{"Start":"00:05.070 ","End":"00:09.345","Text":"we were talking about different syndromes that were the results of"},{"Start":"00:09.345 ","End":"00:12.185","Text":"various kinds of changes in the chromosome where there"},{"Start":"00:12.185 ","End":"00:15.390","Text":"was an additional copy to make trisomy,"},{"Start":"00:15.390 ","End":"00:19.950","Text":"or the presence of only 1 chromosome instead of 2."},{"Start":"00:19.950 ","End":"00:22.800","Text":"Now let\u0027s go on to the next slide,"},{"Start":"00:22.800 ","End":"00:28.410","Text":"and we\u0027ll talk about how these chromosome number disorders may occur."},{"Start":"00:28.410 ","End":"00:35.400","Text":"They could include duplicating or losing entire chromosomes and they can be changes in"},{"Start":"00:35.400 ","End":"00:38.840","Text":"the number of complete sets of chromosomes that are caused"},{"Start":"00:38.840 ","End":"00:42.980","Text":"by chromosomal nondisjunction during meiosis."},{"Start":"00:42.980 ","End":"00:46.965","Text":"They can occur either during meiosis I,"},{"Start":"00:46.965 ","End":"00:50.070","Text":"or they can occur during meiosis II."},{"Start":"00:50.070 ","End":"00:51.420","Text":"Meiosis I, you\u0027ll remember,"},{"Start":"00:51.420 ","End":"01:01.075","Text":"is the first meiosis and the second 1 is down here after there is duplication of the DNA."},{"Start":"01:01.075 ","End":"01:03.465","Text":"Let\u0027s look at meiosis I."},{"Start":"01:03.465 ","End":"01:04.730","Text":"In that case, for instance,"},{"Start":"01:04.730 ","End":"01:06.950","Text":"we could have nondisjunction."},{"Start":"01:06.950 ","End":"01:12.795","Text":"The pair of chromosomes would not separate when it should, and therefore,"},{"Start":"01:12.795 ","End":"01:18.350","Text":"1 cell when the cell divides would get 3 copies of this particular chromosome,"},{"Start":"01:18.350 ","End":"01:20.485","Text":"and the other 1 would get only 1."},{"Start":"01:20.485 ","End":"01:25.880","Text":"Another possibility is that the separation would be normal in this case."},{"Start":"01:25.880 ","End":"01:29.630","Text":"However, in meiosis II,"},{"Start":"01:29.630 ","End":"01:31.895","Text":"there would not be the appropriate separation,"},{"Start":"01:31.895 ","End":"01:36.005","Text":"and that would lead to a different set of chromosomes."},{"Start":"01:36.005 ","End":"01:39.980","Text":"We can talk about these cells being either you euploid,"},{"Start":"01:39.980 ","End":"01:43.595","Text":"that will be a zygote with the appropriate number of chromosomes for its species."},{"Start":"01:43.595 ","End":"01:48.372","Text":"For instance, these would be euploid"},{"Start":"01:48.372 ","End":"01:54.290","Text":"because they are the gametes that have 2 different chromosomes."},{"Start":"01:54.290 ","End":"01:59.120","Text":"In this case, each of them has the appropriate number."},{"Start":"01:59.120 ","End":"02:01.070","Text":"There are 2 different chromosomes,"},{"Start":"02:01.070 ","End":"02:02.620","Text":"but there\u0027s 1 of each."},{"Start":"02:02.620 ","End":"02:05.560","Text":"Whereas in aneuploids,"},{"Start":"02:05.560 ","End":"02:08.525","Text":"which is what we see all these others are,"},{"Start":"02:08.525 ","End":"02:12.080","Text":"they\u0027ll have either too many or not enough"},{"Start":"02:12.080 ","End":"02:16.655","Text":"chromosomes as opposed to the euploid, the normal situation."},{"Start":"02:16.655 ","End":"02:20.960","Text":"We can discuss a term called monosomy in"},{"Start":"02:20.960 ","End":"02:24.950","Text":"which we have only 1 chromosome. How did that arise?"},{"Start":"02:24.950 ","End":"02:27.680","Text":"Well, because there was 1 chromosome that was lost,"},{"Start":"02:27.680 ","End":"02:31.450","Text":"or we can have trisomy as we saw before in Down syndrome,"},{"Start":"02:31.450 ","End":"02:34.730","Text":"in trisomy 21, in which there was"},{"Start":"02:34.730 ","End":"02:40.220","Text":"the gain of an extra chromosome that we saw in these cases."},{"Start":"02:40.220 ","End":"02:43.325","Text":"Let\u0027s look at different kinds of aneuploidy."},{"Start":"02:43.325 ","End":"02:46.730","Text":"We can have monosomic human zygotes,"},{"Start":"02:46.730 ","End":"02:48.170","Text":"that is new autosomes,"},{"Start":"02:48.170 ","End":"02:51.065","Text":"not in the X or Y chromosomes."},{"Start":"02:51.065 ","End":"02:53.735","Text":"But if they\u0027re monosomic,"},{"Start":"02:53.735 ","End":"02:56.835","Text":"they only have 1 of the 2 chromosomes,"},{"Start":"02:56.835 ","End":"02:59.570","Text":"they invariably fail to develop to birth."},{"Start":"02:59.570 ","End":"03:02.140","Text":"That\u0027s certainly the case in humans."},{"Start":"03:02.140 ","End":"03:06.170","Text":"Most autosomal trisomy also fails to develop to birth,"},{"Start":"03:06.170 ","End":"03:07.880","Text":"as I said before."},{"Start":"03:07.880 ","End":"03:10.910","Text":"But there are exceptions like, for instance,"},{"Start":"03:10.910 ","End":"03:15.050","Text":"trisomy 21, the Down syndrome,"},{"Start":"03:15.050 ","End":"03:16.505","Text":"but there are others as well."},{"Start":"03:16.505 ","End":"03:18.920","Text":"Some of the smaller chromosomes like 13, 15,"},{"Start":"03:18.920 ","End":"03:21.560","Text":"18, or even 22,"},{"Start":"03:21.560 ","End":"03:26.390","Text":"can result in offspring that do survive either for several weeks or even years,"},{"Start":"03:26.390 ","End":"03:28.205","Text":"like in the case of 21."},{"Start":"03:28.205 ","End":"03:35.704","Text":"Interestingly, the risk of Down syndrome in live births goes up with the mother\u0027s age,"},{"Start":"03:35.704 ","End":"03:37.055","Text":"and as you can see here,"},{"Start":"03:37.055 ","End":"03:39.950","Text":"goes up quite dramatically over the age of 40."},{"Start":"03:39.950 ","End":"03:45.080","Text":"The reason for that is that the meiosis becomes less perfect"},{"Start":"03:45.080 ","End":"03:51.380","Text":"as the mother\u0027s age gets older as she goes, does meiosis II."},{"Start":"03:51.380 ","End":"03:57.570","Text":"Trisomy 21 is the most common among viable births."},{"Start":"03:57.610 ","End":"04:00.925","Text":"You can see that there is quite a high risk,"},{"Start":"04:00.925 ","End":"04:07.665","Text":"about 3.75% or close to 4% as women get older."},{"Start":"04:07.665 ","End":"04:12.440","Text":"Now let\u0027s look at other kinds of aneuploidy."},{"Start":"04:12.440 ","End":"04:16.265","Text":"We can have something called polyploidy."},{"Start":"04:16.265 ","End":"04:22.370","Text":"Polyploidy would mean that we have multiples of all the chromosomes."},{"Start":"04:22.370 ","End":"04:24.995","Text":"The normal situation is that we have"},{"Start":"04:24.995 ","End":"04:30.274","Text":"a haploid and we know about a diploid in which we have multiples,"},{"Start":"04:30.274 ","End":"04:31.985","Text":"but we can have triploid,"},{"Start":"04:31.985 ","End":"04:33.425","Text":"have 3 of each,"},{"Start":"04:33.425 ","End":"04:35.360","Text":"tetraploid, 4 of each,"},{"Start":"04:35.360 ","End":"04:37.580","Text":"even 6 of each."},{"Start":"04:37.580 ","End":"04:40.160","Text":"This is extremely rare in animals."},{"Start":"04:40.160 ","End":"04:43.250","Text":"But in some of the flatworms, crustaceans,"},{"Start":"04:43.250 ","End":"04:45.035","Text":"amphibians, and fish, and lizards,"},{"Start":"04:45.035 ","End":"04:47.285","Text":"it can be more common."},{"Start":"04:47.285 ","End":"04:48.950","Text":"In plants, actually,"},{"Start":"04:48.950 ","End":"04:52.700","Text":"it\u0027s very common, as we\u0027ll see in a minute."},{"Start":"04:52.700 ","End":"04:55.610","Text":"However, polyploid animals,"},{"Start":"04:55.610 ","End":"04:56.975","Text":"that would be sterile."},{"Start":"04:56.975 ","End":"04:59.690","Text":"Because if they separate,"},{"Start":"04:59.690 ","End":"05:01.365","Text":"let\u0027s say they are tetraploid,"},{"Start":"05:01.365 ","End":"05:04.760","Text":"then once they go through meiosis,"},{"Start":"05:04.760 ","End":"05:08.385","Text":"they would end up with 2n, and not 1n,"},{"Start":"05:08.385 ","End":"05:12.649","Text":"as they should in order to produce normal gametes."},{"Start":"05:12.649 ","End":"05:16.450","Text":"There\u0027s something called haplodiploid species,"},{"Start":"05:16.450 ","End":"05:22.940","Text":"in which some of the gametes are indeed haploid and others are diploid."},{"Start":"05:22.940 ","End":"05:28.180","Text":"Those are very specific species that go through a specific developmental program,"},{"Start":"05:28.180 ","End":"05:31.989","Text":"and those are exceptions to the rule."}],"ID":26369},{"Watched":false,"Name":"Chromosomal Basis of Inherited Disorders part c","Duration":"5m ","ChapterTopicVideoID":25553,"CourseChapterTopicPlaylistID":237673,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.785","Text":"We left off in the previous video of this section talking about"},{"Start":"00:04.785 ","End":"00:12.150","Text":"polyploidy and we mentioned that gametes usually are haploid."},{"Start":"00:12.150 ","End":"00:15.060","Text":"In normal cells like in humans,"},{"Start":"00:15.060 ","End":"00:17.700","Text":"for instance, the autosomes will be 2n,"},{"Start":"00:17.700 ","End":"00:26.025","Text":"but there can be polyploidy as well in various organisms and especially in plants."},{"Start":"00:26.025 ","End":"00:29.070","Text":"It\u0027s very common in the plant kingdom,"},{"Start":"00:29.070 ","End":"00:34.935","Text":"about 60 percent of all flowering plants are polyploidy."},{"Start":"00:34.935 ","End":"00:37.215","Text":"They are often tetraploid,"},{"Start":"00:37.215 ","End":"00:38.550","Text":"that means that they\u0027ve got"},{"Start":"00:38.550 ","End":"00:47.115","Text":"4 homologous chromosomes altogether and they can arise in different ways."},{"Start":"00:47.115 ","End":"00:53.070","Text":"It depends on exactly which kinds of plants were mated to each other."},{"Start":"00:53.070 ","End":"00:55.650","Text":"Polyploid plants tend to be larger and more"},{"Start":"00:55.650 ","End":"00:58.920","Text":"robust than euploids of their species and therefore,"},{"Start":"00:58.920 ","End":"01:03.435","Text":"it\u0027s a major force in the evolution of both wild-type and cultivated plants."},{"Start":"01:03.435 ","End":"01:08.310","Text":"Often cultivated plants will be bred on purpose to cause"},{"Start":"01:08.310 ","End":"01:11.310","Text":"these tetraploid plants because they are more"},{"Start":"01:11.310 ","End":"01:15.270","Text":"robust and sometimes they\u0027ll produce better fruits as well."},{"Start":"01:15.270 ","End":"01:19.980","Text":"In fact, many seedless fruit varieties are seedless"},{"Start":"01:19.980 ","End":"01:26.310","Text":"because they are sterile and those are our results of polyploidy and of course,"},{"Start":"01:26.310 ","End":"01:31.020","Text":"seedless fruits can be very useful for us in industry."},{"Start":"01:31.020 ","End":"01:34.300","Text":"Now let\u0027s go back to humans."},{"Start":"01:34.940 ","End":"01:40.200","Text":"In humans, there can be sex chromosome non-disjunction."},{"Start":"01:40.200 ","End":"01:44.295","Text":"We\u0027re now talking about the X or the Y chromosomes,"},{"Start":"01:44.295 ","End":"01:46.440","Text":"before we were talking about autosomes."},{"Start":"01:46.440 ","End":"01:53.190","Text":"The variations in the number of human sex chromosomes actually occurs fairly frequently."},{"Start":"01:53.190 ","End":"01:58.710","Text":"It can occur maybe surprisingly with relatively mild effects."},{"Start":"01:58.710 ","End":"02:01.440","Text":"That\u0027s in part because of the molecular process"},{"Start":"02:01.440 ","End":"02:05.115","Text":"of X inactivation. Now, what does that mean?"},{"Start":"02:05.115 ","End":"02:07.920","Text":"Well, in X activation,"},{"Start":"02:07.920 ","End":"02:13.020","Text":"there is the inactivation of 1 of the 2 X chromosomes."},{"Start":"02:13.020 ","End":"02:14.865","Text":"Of course, we get 1 X chromosome."},{"Start":"02:14.865 ","End":"02:19.440","Text":"If we\u0027re a female, we get a 1 X chromosome from our mother and 1 from our father."},{"Start":"02:19.440 ","End":"02:20.760","Text":"But if we were male,"},{"Start":"02:20.760 ","End":"02:22.515","Text":"we would get only 1 X chromosome."},{"Start":"02:22.515 ","End":"02:26.490","Text":"Females have 2 copies of the X chromosome,"},{"Start":"02:26.490 ","End":"02:28.830","Text":"whereas males have only 1."},{"Start":"02:28.830 ","End":"02:34.110","Text":"But there are plenty of genes on there that are really designed to work only in 1 copy."},{"Start":"02:34.110 ","End":"02:35.740","Text":"How does that work?"},{"Start":"02:35.740 ","End":"02:38.090","Text":"What happens is that,"},{"Start":"02:38.090 ","End":"02:41.510","Text":"let\u0027s roughly say the thousandth cell stage"},{"Start":"02:41.510 ","End":"02:45.390","Text":"after the zygote begins to divide and develop,"},{"Start":"02:45.390 ","End":"02:50.655","Text":"then 1 of those 2 chromosomes becomes inactivated."},{"Start":"02:50.655 ","End":"02:58.470","Text":"It becomes more condensed and is then not going to be expressed in the animal."},{"Start":"02:58.470 ","End":"03:04.830","Text":"The genes on that chromosome will not be expressed on the animal and by this process,"},{"Start":"03:04.830 ","End":"03:09.404","Text":"females compensate for their double genetic dose"},{"Start":"03:09.404 ","End":"03:14.295","Text":"of the X chromosome and they become something called the mosaics."},{"Start":"03:14.295 ","End":"03:16.920","Text":"Now it\u0027s interesting in cats, for instance,"},{"Start":"03:16.920 ","End":"03:18.825","Text":"we\u0027ve seen cats that look like this,"},{"Start":"03:18.825 ","End":"03:21.885","Text":"a tortoiseshell cat or a calico cat."},{"Start":"03:21.885 ","End":"03:24.840","Text":"These cats are all female."},{"Start":"03:24.840 ","End":"03:30.930","Text":"They\u0027re all female because the gene for coat color is located on the X chromosome"},{"Start":"03:30.930 ","End":"03:38.670","Text":"and 1 of their X chromosomes has been inactivated in each of their cells."},{"Start":"03:38.670 ","End":"03:40.320","Text":"Cells, for instance,"},{"Start":"03:40.320 ","End":"03:43.950","Text":"that are clones of a particular cell that lost"},{"Start":"03:43.950 ","End":"03:48.030","Text":"the cell color will be white, like in this region."},{"Start":"03:48.030 ","End":"03:53.310","Text":"Cells that are descendant from those that lost the next chromosome that"},{"Start":"03:53.310 ","End":"03:59.055","Text":"has a brown color will be this brown color and so on."},{"Start":"03:59.055 ","End":"04:04.110","Text":"So the random inactivation of 1 of the 2 X chromosomes in each cell results"},{"Start":"04:04.110 ","End":"04:09.225","Text":"in this tortoiseshell pattern if the cats have 2 different alleles for coat color."},{"Start":"04:09.225 ","End":"04:11.880","Text":"They could have 1 allele. Here you\u0027ve got 2 alleles,"},{"Start":"04:11.880 ","End":"04:13.800","Text":"you\u0027ve got black and brown,"},{"Start":"04:13.800 ","End":"04:17.565","Text":"and that causes for the 3 different colors because we could have either none,"},{"Start":"04:17.565 ","End":"04:21.090","Text":"or 1, or the other."},{"Start":"04:21.090 ","End":"04:22.890","Text":"Male cats, of course,"},{"Start":"04:22.890 ","End":"04:24.315","Text":"have only 1 X chromosome,"},{"Start":"04:24.315 ","End":"04:28.230","Text":"and so they never inhibit this tortoiseshell coat color."},{"Start":"04:28.230 ","End":"04:36.660","Text":"Even inactivated X chromosomes do continue to express just a few of the genes."},{"Start":"04:36.660 ","End":"04:38.490","Text":"For example, X chromosomes must"},{"Start":"04:38.490 ","End":"04:43.020","Text":"reactivate in order for proper maturation of female ovaries,"},{"Start":"04:43.020 ","End":"04:44.400","Text":"and as a result,"},{"Start":"04:44.400 ","End":"04:47.745","Text":"X chromosomal abnormalities typically occur with"},{"Start":"04:47.745 ","End":"04:52.340","Text":"mild mental and physical defects as well as sterility."},{"Start":"04:52.340 ","End":"04:55.565","Text":"Now, if the X chromosome is absent altogether,"},{"Start":"04:55.565 ","End":"04:59.520","Text":"the individual does not develop."}],"ID":26370},{"Watched":false,"Name":"Chromosomal Basis of Inherited Disorders part d","Duration":"7m 17s","ChapterTopicVideoID":25554,"CourseChapterTopicPlaylistID":237673,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:03.000","Text":"In the previous video of this section,"},{"Start":"00:03.000 ","End":"00:05.880","Text":"we were talking about X-inactivation."},{"Start":"00:05.880 ","End":"00:12.210","Text":"Now, let\u0027s go on to talk about aneuploidy of sex chromosomes."},{"Start":"00:12.210 ","End":"00:13.950","Text":"As we mentioned before,"},{"Start":"00:13.950 ","End":"00:16.920","Text":"individuals can be triplo-X."},{"Start":"00:16.920 ","End":"00:19.124","Text":"Those would be females,"},{"Start":"00:19.124 ","End":"00:21.375","Text":"they would phenotypically be female,"},{"Start":"00:21.375 ","End":"00:26.220","Text":"but they express developmental delays and reduced fertility."},{"Start":"00:26.220 ","End":"00:31.635","Text":"On the other hand, we can have an XXY genotype,"},{"Start":"00:31.635 ","End":"00:35.195","Text":"and that\u0027s called the Klinefelter syndrome."},{"Start":"00:35.195 ","End":"00:40.295","Text":"Interestingly, they appear more or less male in their phenotype,"},{"Start":"00:40.295 ","End":"00:44.113","Text":"but it\u0027s actually much more common,"},{"Start":"00:44.113 ","End":"00:45.710","Text":"you can see what we have over here."},{"Start":"00:45.710 ","End":"00:48.650","Text":"It\u0027s much more common than you might think."},{"Start":"00:48.650 ","End":"00:54.180","Text":"About 1 in 1,100 males is actually XYY."},{"Start":"00:54.180 ","End":"01:00.095","Text":"But very rarely, males could have 3 or even 4 X chromosomes."},{"Start":"01:00.095 ","End":"01:04.699","Text":"But these individuals are generally severely retarded."},{"Start":"01:04.699 ","End":"01:07.400","Text":"Now, in phenotypically female,"},{"Start":"01:07.400 ","End":"01:10.130","Text":"we can have another problem."},{"Start":"01:10.130 ","End":"01:16.040","Text":"That would be an X0 genotype in which they are aneuploid,"},{"Start":"01:16.040 ","End":"01:20.100","Text":"these individuals, and have only 1 X chromosome."},{"Start":"01:20.100 ","End":"01:23.290","Text":"This results in a syndrome called the Turner syndrome,"},{"Start":"01:23.290 ","End":"01:25.010","Text":"and it\u0027s also fairly common,"},{"Start":"01:25.010 ","End":"01:28.550","Text":"it\u0027s about 1 in 1,000 females and they have"},{"Start":"01:28.550 ","End":"01:33.755","Text":"various kinds of phenotypes that are discussed here."},{"Start":"01:33.755 ","End":"01:37.670","Text":"This most commonly occurs due to a random event during"},{"Start":"01:37.670 ","End":"01:42.559","Text":"the formation of an egg or sperm cell in the parent prior to conception."},{"Start":"01:42.559 ","End":"01:47.750","Text":"Most women with Turner syndrome cannot get pregnant naturally and"},{"Start":"01:47.750 ","End":"01:53.845","Text":"the primary therapies for them are growth hormone therapy, estrogen therapy."},{"Start":"01:53.845 ","End":"01:59.640","Text":"Now let\u0027s look at defects in the chromosomes themselves."},{"Start":"01:59.640 ","End":"02:04.245","Text":"We\u0027ll look at duplications and deletions."},{"Start":"02:04.245 ","End":"02:11.305","Text":"Chromosomal segments may duplicate or they may get lost altogether."},{"Start":"02:11.305 ","End":"02:13.685","Text":"The offspring may survive,"},{"Start":"02:13.685 ","End":"02:18.215","Text":"but exhibit physical and mental abnormalities."},{"Start":"02:18.215 ","End":"02:21.055","Text":"Let\u0027s look at an example of that."},{"Start":"02:21.055 ","End":"02:23.390","Text":"We can see down below over here,"},{"Start":"02:23.390 ","End":"02:25.189","Text":"we can have a deletion,"},{"Start":"02:25.189 ","End":"02:29.460","Text":"for instance or we could have a duplication."},{"Start":"02:29.460 ","End":"02:31.065","Text":"Let\u0027s look at a deletion."},{"Start":"02:31.065 ","End":"02:36.080","Text":"The sequence of the genes on this chromosome would be A, B, C, D, E,"},{"Start":"02:36.080 ","End":"02:38.840","Text":"F. But if there were deletion of the D,"},{"Start":"02:38.840 ","End":"02:41.460","Text":"we could end up with A, B, C,"},{"Start":"02:41.460 ","End":"02:47.170","Text":"E, F, without the D. Or possibly we could have a duplication,"},{"Start":"02:47.170 ","End":"02:52.880","Text":"and they could fuse in these chromosomes and we could have an A,"},{"Start":"02:52.880 ","End":"02:54.230","Text":"B, C and then the B,"},{"Start":"02:54.230 ","End":"02:55.707","Text":"C would be duplicated, so A,"},{"Start":"02:55.707 ","End":"02:57.845","Text":"B, C, B, C, D,"},{"Start":"02:57.845 ","End":"03:02.270","Text":"E, that would lead to a longer chromosome."},{"Start":"03:02.270 ","End":"03:07.130","Text":"It\u0027s also possible that these duplications could go free in the nucleus,"},{"Start":"03:07.130 ","End":"03:11.644","Text":"but of course they won\u0027t divide unless there\u0027s a centromere attached."},{"Start":"03:11.644 ","End":"03:16.720","Text":"Interestingly, there\u0027s a syndrome called Cri-du-chat,"},{"Start":"03:16.720 ","End":"03:18.710","Text":"that\u0027s French for a cry of the cat."},{"Start":"03:18.710 ","End":"03:21.275","Text":"This is in humans, not in cats,"},{"Start":"03:21.275 ","End":"03:25.730","Text":"and results from a specific deletion in chromosome number 5."},{"Start":"03:25.730 ","End":"03:31.040","Text":"It results with a nervous system abnormalities and identifiable physical features."},{"Start":"03:31.040 ","End":"03:34.820","Text":"But the main thing that\u0027s characteristic is that"},{"Start":"03:34.820 ","End":"03:38.701","Text":"the infants emit a characteristic high-pitched cry,"},{"Start":"03:38.701 ","End":"03:43.490","Text":"therefore, the name of this syndrome, the Cri-du-chat."},{"Start":"03:43.490 ","End":"03:45.800","Text":"Now in certain cancers,"},{"Start":"03:45.800 ","End":"03:48.950","Text":"then we find that they are also caused by"},{"Start":"03:48.950 ","End":"03:54.724","Text":"either translocations or deletions or various changes in the chromosome."},{"Start":"03:54.724 ","End":"03:57.865","Text":"But translocations are quite common."},{"Start":"03:57.865 ","End":"04:02.580","Text":"Rearrangements that we saw can be of all sorts."},{"Start":"04:02.580 ","End":"04:05.170","Text":"They can be either deletions or duplications,"},{"Start":"04:05.170 ","End":"04:07.945","Text":"but they can also be inversions,"},{"Start":"04:07.945 ","End":"04:12.010","Text":"and they can be these other kinds of translocations."},{"Start":"04:12.010 ","End":"04:14.500","Text":"Let\u0027s see in this example, for instance,"},{"Start":"04:14.500 ","End":"04:17.080","Text":"we can have an inversion of an entire piece of"},{"Start":"04:17.080 ","End":"04:20.140","Text":"DNA so that instead of the sequence being A,"},{"Start":"04:20.140 ","End":"04:21.505","Text":"B, C, D, E,"},{"Start":"04:21.505 ","End":"04:23.350","Text":"the sequence would be A,"},{"Start":"04:23.350 ","End":"04:24.775","Text":"D C, B,"},{"Start":"04:24.775 ","End":"04:31.705","Text":"E because this darker colored piece of the chromosome has flipped, it has inverted."},{"Start":"04:31.705 ","End":"04:33.100","Text":"Or, for instance,"},{"Start":"04:33.100 ","End":"04:34.810","Text":"we could have a translocation,"},{"Start":"04:34.810 ","End":"04:38.143","Text":"let\u0027s say they moves a segment from one chromosome to another,"},{"Start":"04:38.143 ","End":"04:40.015","Text":"that could be non-homologous."},{"Start":"04:40.015 ","End":"04:41.825","Text":"We could have, for instance,"},{"Start":"04:41.825 ","End":"04:45.214","Text":"let\u0027s say a piece of DNA,"},{"Start":"04:45.214 ","End":"04:47.535","Text":"this A, B, C, D,"},{"Start":"04:47.535 ","End":"04:55.260","Text":"E would be translocated from another chromosome such that the M, N,"},{"Start":"04:55.260 ","End":"04:58.257","Text":"O would replace the A, B,"},{"Start":"04:58.257 ","End":"05:00.995","Text":"there will be a reciprocal translocation,"},{"Start":"05:00.995 ","End":"05:03.395","Text":"and then we\u0027d have 2 chromosomes that are messed up."},{"Start":"05:03.395 ","End":"05:05.480","Text":"One of them would be M, N,"},{"Start":"05:05.480 ","End":"05:07.080","Text":"O, and then C,"},{"Start":"05:07.080 ","End":"05:09.345","Text":"D, E and the other one would be A, B,"},{"Start":"05:09.345 ","End":"05:17.245","Text":"P, Q, R. This would be a reciprocal translocation and it\u0027s non homologous of course."},{"Start":"05:17.245 ","End":"05:21.530","Text":"If the genes on the 2 homologs are not oriented correctly,"},{"Start":"05:21.530 ","End":"05:24.515","Text":"a recombination event could result in losing genes"},{"Start":"05:24.515 ","End":"05:28.355","Text":"from one chromosome and gaining genes on the other."},{"Start":"05:28.355 ","End":"05:33.590","Text":"That of course, would produce aneuploid gametes because they would not"},{"Start":"05:33.590 ","End":"05:40.565","Text":"be normal with respect to how many copies they have of each of these genes."},{"Start":"05:40.565 ","End":"05:47.239","Text":"Chromosome inversions can happen in which the detachment is 180 degrees,"},{"Start":"05:47.239 ","End":"05:49.681","Text":"and then reinsertion part of the chromosome,"},{"Start":"05:49.681 ","End":"05:52.790","Text":"that\u0027s what we saw before with the B,"},{"Start":"05:52.790 ","End":"05:55.085","Text":"C, D becoming inverted."},{"Start":"05:55.085 ","End":"05:57.050","Text":"But they can also occur,"},{"Start":"05:57.050 ","End":"06:01.560","Text":"or they do occur as a result of mechanical shear in"},{"Start":"06:01.560 ","End":"06:06.920","Text":"addition to being caused by things called transposable elements."},{"Start":"06:06.920 ","End":"06:09.980","Text":"There are transposable elements which are pieces of DNA"},{"Start":"06:09.980 ","End":"06:13.160","Text":"that have actually enzymology that are built into them"},{"Start":"06:13.160 ","End":"06:20.795","Text":"to cause pieces of DNA to be excised from one place and then moved to some place else,"},{"Start":"06:20.795 ","End":"06:27.430","Text":"something that is called jumping genes and that too is not that infrequent."},{"Start":"06:27.430 ","End":"06:31.830","Text":"Unless these translocations though cause disruption,"},{"Start":"06:31.830 ","End":"06:33.480","Text":"unless they disrupted gene sequence,"},{"Start":"06:33.480 ","End":"06:36.950","Text":"inversions have much more mild effects than"},{"Start":"06:36.950 ","End":"06:41.280","Text":"aneuploid errors because the copy number stays the same,"},{"Start":"06:41.280 ","End":"06:45.005","Text":"and they may continue to be expressed."},{"Start":"06:45.005 ","End":"06:48.980","Text":"However, alter gene orientation can cause functional changes of"},{"Start":"06:48.980 ","End":"06:53.240","Text":"regulators of gene expression because sometimes one piece of DNA,"},{"Start":"06:53.240 ","End":"06:55.215","Text":"let\u0027s say this E piece,"},{"Start":"06:55.215 ","End":"06:58.875","Text":"may influence that D that\u0027s right next to it."},{"Start":"06:58.875 ","End":"07:00.500","Text":"If there is an inversion,"},{"Start":"07:00.500 ","End":"07:07.870","Text":"then this E piece will be far away from the D and not regulated as it\u0027s supposed to."},{"Start":"07:07.870 ","End":"07:12.260","Text":"Altered gene orientation can cause functional changes of regulators of"},{"Start":"07:12.260 ","End":"07:17.550","Text":"gene expression and cause aberrant levels of gene products."}],"ID":26371},{"Watched":false,"Name":"Chromosomal Basis of Inherited Disorders part e","Duration":"4m 40s","ChapterTopicVideoID":25546,"CourseChapterTopicPlaylistID":237673,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:02.250","Text":"In the previous video,"},{"Start":"00:02.250 ","End":"00:05.985","Text":"we were talking about chromosome inversions."},{"Start":"00:05.985 ","End":"00:10.800","Text":"Now of course, these chromosome inversions can occur either"},{"Start":"00:10.800 ","End":"00:17.940","Text":"outside or away from the centromere or they can include the centromere,"},{"Start":"00:17.940 ","End":"00:22.560","Text":"pericentric, that\u0027s P-R-I centric,"},{"Start":"00:22.560 ","End":"00:25.350","Text":"and versions do include the centromere."},{"Start":"00:25.350 ","End":"00:32.445","Text":"But para, P-A-R-A centric inversions occur outside the centromere."},{"Start":"00:32.445 ","End":"00:35.325","Text":"Now what\u0027s the difference between them?"},{"Start":"00:35.325 ","End":"00:38.730","Text":"A pericentric inversion can change"},{"Start":"00:38.730 ","End":"00:45.500","Text":"the chromosome arms relative lengths because if c and d are not exactly the same length,"},{"Start":"00:45.500 ","End":"00:47.075","Text":"which they usually won\u0027t be."},{"Start":"00:47.075 ","End":"00:49.370","Text":"Although in this figure it looks like they are,"},{"Start":"00:49.370 ","End":"00:50.975","Text":"but often they\u0027re not."},{"Start":"00:50.975 ","End":"00:55.835","Text":"Then the chromosomes arms will change the relative lengths."},{"Start":"00:55.835 ","End":"01:00.370","Text":"This is probably going to be visible on a karyotype."},{"Start":"01:00.370 ","End":"01:05.630","Text":"On the other hand, a paracentric inversion that occurs"},{"Start":"01:05.630 ","End":"01:10.775","Text":"outside the centromere will not change the relative lengths of the chromosome arms."},{"Start":"01:10.775 ","End":"01:14.870","Text":"That won\u0027t be as visible in a karyotype unless we look at"},{"Start":"01:14.870 ","End":"01:20.540","Text":"the bands specifically that are on eat on the pieces that got turned around."},{"Start":"01:20.540 ","End":"01:23.330","Text":"Asymmetric conversions about the centromere can"},{"Start":"01:23.330 ","End":"01:26.330","Text":"change the chromosome arms relative lengths,"},{"Start":"01:26.330 ","End":"01:29.870","Text":"making these inversions easily identifiable,"},{"Start":"01:29.870 ","End":"01:32.180","Text":"as we said just before."},{"Start":"01:32.180 ","End":"01:38.425","Text":"Let\u0027s see what happens during meiosis if there is inversion."},{"Start":"01:38.425 ","End":"01:41.030","Text":"In a heterozygote though, for instance,"},{"Start":"01:41.030 ","End":"01:43.655","Text":"where there\u0027s an inversion in 1 of the chromosomes,"},{"Start":"01:43.655 ","End":"01:46.175","Text":"there\u0027s going to be troubled during meiosis."},{"Start":"01:46.175 ","End":"01:49.685","Text":"When 1 homologous chromosome undergoes an inversion,"},{"Start":"01:49.685 ","End":"01:51.380","Text":"but the other does not,"},{"Start":"01:51.380 ","End":"01:56.120","Text":"then we\u0027re going to have to make a very particular structure."},{"Start":"01:56.120 ","End":"02:00.110","Text":"To maintain a point for point synapses during meiosis,"},{"Start":"02:00.110 ","End":"02:06.115","Text":"1 homolog must form a loop and the other homolog must mold around it."},{"Start":"02:06.115 ","End":"02:11.360","Text":"There\u0027s this loop in order to maintain the homology of G with G, F with F,"},{"Start":"02:11.360 ","End":"02:18.260","Text":"E with E, because in 1 of the chromosomes there was this inversion."},{"Start":"02:18.260 ","End":"02:21.740","Text":"That it wouldn\u0027t pair if we just had them be straight,"},{"Start":"02:21.740 ","End":"02:23.825","Text":"1 right next to the other."},{"Start":"02:23.825 ","End":"02:27.500","Text":"This ensures that the genes will correctly aligned,"},{"Start":"02:27.500 ","End":"02:34.985","Text":"but it also forces the homologs to stretch and can occur with imprecise synapsis regions"},{"Start":"02:34.985 ","End":"02:43.420","Text":"making there be a possibility of improper meiosis and possibly gene breakage."},{"Start":"02:43.420 ","End":"02:46.970","Text":"Now let\u0027s look at translocations."},{"Start":"02:46.970 ","End":"02:49.670","Text":"When a chromosome segment dissociates and then"},{"Start":"02:49.670 ","End":"02:52.955","Text":"reattaches to a difference non-homologous chromosome,"},{"Start":"02:52.955 ","End":"02:55.325","Text":"we\u0027re going to call that translocation."},{"Start":"02:55.325 ","End":"02:58.780","Text":"We had seen something like that before in previous videos."},{"Start":"02:58.780 ","End":"03:04.010","Text":"This piece of DNA might translocate now to another chromosome."},{"Start":"03:04.010 ","End":"03:06.275","Text":"If it is reciprocal,"},{"Start":"03:06.275 ","End":"03:11.015","Text":"then we\u0027re going to get the yellow 1 on the blue 1,"},{"Start":"03:11.015 ","End":"03:13.446","Text":"and the blue 1 on the yellow 1 as you can see."},{"Start":"03:13.446 ","End":"03:16.970","Text":"There\u0027s no gain or loss of genetic information unless"},{"Start":"03:16.970 ","End":"03:23.650","Text":"the brake or the brakes are at a place that are going to disrupt a gene."},{"Start":"03:23.650 ","End":"03:27.370","Text":"It can be benign or it can actually have"},{"Start":"03:27.370 ","End":"03:30.940","Text":"these devastating effects depending on how the positions of the genes are"},{"Start":"03:30.940 ","End":"03:34.539","Text":"altered with respect to the regulatory sequences"},{"Start":"03:34.539 ","End":"03:38.935","Text":"that may be outside the part that was translocated."},{"Start":"03:38.935 ","End":"03:45.505","Text":"Specific translocations have occurred with several cancers and also with schizophrenia."},{"Start":"03:45.505 ","End":"03:49.960","Text":"Of course, all of these translocations can have"},{"Start":"03:49.960 ","End":"03:55.765","Text":"very dramatic effects on offspring if they occur in the germ cells."},{"Start":"03:55.765 ","End":"03:59.590","Text":"If this occurs in the gametes they are going to lead to a new organism."},{"Start":"03:59.590 ","End":"04:04.060","Text":"That can have interesting implications evolutionarily,"},{"Start":"04:04.060 ","End":"04:06.260","Text":"when that\u0027s rarely happens."},{"Start":"04:06.260 ","End":"04:10.250","Text":"Reciprocal translocations exchanging chromosomes segments"},{"Start":"04:10.250 ","End":"04:16.669","Text":"between 2 non-homologous chromosomes can have these interesting effects."},{"Start":"04:16.669 ","End":"04:19.895","Text":"In this section of all these videos,"},{"Start":"04:19.895 ","End":"04:23.315","Text":"we learned how to describe how a karyogram is created."},{"Start":"04:23.315 ","End":"04:28.370","Text":"We learned how to explain how non-disjunction leads to disorders in chromosome number."},{"Start":"04:28.370 ","End":"04:32.510","Text":"We compared disorders that aneuploidy causes,"},{"Start":"04:32.510 ","End":"04:34.880","Text":"and we described how errors in"},{"Start":"04:34.880 ","End":"04:40.500","Text":"chromosome structure occur through inversions and translocations."}],"ID":26363},{"Watched":false,"Name":"Exercise 1","Duration":"1m 14s","ChapterTopicVideoID":27171,"CourseChapterTopicPlaylistID":237673,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:06.105","Text":"X-linked recessive traits in humans or in Drosophila are observed."},{"Start":"00:06.105 ","End":"00:12.000","Text":"Talking here about X-linked recessive traits in more males than females,"},{"Start":"00:12.000 ","End":"00:13.485","Text":"in more females than males,"},{"Start":"00:13.485 ","End":"00:14.895","Text":"in males and females,"},{"Start":"00:14.895 ","End":"00:19.860","Text":"equally, or in different distributions depending on the trait."},{"Start":"00:19.860 ","End":"00:24.915","Text":"Remember we spoke about this when we discussed X linkage."},{"Start":"00:24.915 ","End":"00:30.900","Text":"You remember that if there\u0027s a mutation"},{"Start":"00:30.900 ","End":"00:36.570","Text":"on the X chromosome then a female has 2 copies of it,"},{"Start":"00:36.570 ","End":"00:42.645","Text":"whereas a male has only one because a male has only 1 X chromosome."},{"Start":"00:42.645 ","End":"00:47.450","Text":"Most of the affected people are going to be males."},{"Start":"00:47.450 ","End":"00:55.485","Text":"Yes, it affected son because a girl has 2 X chromosomes."},{"Start":"00:55.485 ","End":"00:57.060","Text":"If there\u0027s a recessive gene,"},{"Start":"00:57.060 ","End":"00:59.900","Text":"a recessive allele on one of them,"},{"Start":"00:59.900 ","End":"01:02.570","Text":"then the dominant one,"},{"Start":"01:02.570 ","End":"01:06.140","Text":"the non-mutated one, will compensate."},{"Start":"01:06.140 ","End":"01:14.580","Text":"Therefore, in more males than females is our answer."}],"ID":28271},{"Watched":false,"Name":"Exercise 2","Duration":"47s","ChapterTopicVideoID":27172,"CourseChapterTopicPlaylistID":237673,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.830","Text":"The first suggestion that chromosomes may physically exchange segments"},{"Start":"00:04.830 ","End":"00:09.890","Text":"came from the microscopic identification of what of the following,"},{"Start":"00:09.890 ","End":"00:14.970","Text":"of synapsis, sister chromatids, chiasmata, or alleles."},{"Start":"00:14.970 ","End":"00:21.930","Text":"We\u0027re talking here about physically exchanging segments,"},{"Start":"00:21.930 ","End":"00:26.145","Text":"and we\u0027re talking about microscopic identification."},{"Start":"00:26.145 ","End":"00:30.810","Text":"If you remember that in 1909,"},{"Start":"00:30.810 ","End":"00:35.355","Text":"Fronds Johnson observed chiasmata."},{"Start":"00:35.355 ","End":"00:43.854","Text":"Yes, those are the places where homologous chromosomes undergo crossing over."},{"Start":"00:43.854 ","End":"00:47.800","Text":"So our answer then will be chiasmata."}],"ID":28272},{"Watched":false,"Name":"Exercise 3","Duration":"41s","ChapterTopicVideoID":27173,"CourseChapterTopicPlaylistID":237673,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:03.675","Text":"Which recombination frequency corresponds to"},{"Start":"00:03.675 ","End":"00:10.095","Text":"independent assortment and the absence of linkage?"},{"Start":"00:10.095 ","End":"00:12.775","Text":"Is it 0, 0.25,"},{"Start":"00:12.775 ","End":"00:15.900","Text":"0.5, or 0.75?"},{"Start":"00:15.900 ","End":"00:20.115","Text":"When we discussed chromosomal theory and genetic linkage,"},{"Start":"00:20.115 ","End":"00:23.445","Text":"we said that genes can range from linking perfectly,"},{"Start":"00:23.445 ","End":"00:26.970","Text":"in which we say that the recombination frequency is 0"},{"Start":"00:26.970 ","End":"00:30.860","Text":"because they are linking perfectly, to unlinking perfectly."},{"Start":"00:30.860 ","End":"00:37.170","Text":"Then, the recombination frequency is 0.5."},{"Start":"00:37.170 ","End":"00:41.620","Text":"That is our answer, 0.5."}],"ID":28273},{"Watched":false,"Name":"Exercise 4","Duration":"25s","ChapterTopicVideoID":27174,"CourseChapterTopicPlaylistID":237673,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:03.615","Text":"Which recombination frequency corresponds to"},{"Start":"00:03.615 ","End":"00:07.500","Text":"perfect linkage and violates the law of independent assortment?"},{"Start":"00:07.500 ","End":"00:10.080","Text":"If 2 genes are very, very close to each other,"},{"Start":"00:10.080 ","End":"00:12.585","Text":"then there is perfect linkage."},{"Start":"00:12.585 ","End":"00:19.530","Text":"We said then that perfect linkage has a recombination frequency of 0,"},{"Start":"00:19.530 ","End":"00:25.540","Text":"and therefore, our answer is a, 0."}],"ID":28274},{"Watched":false,"Name":"Exercise 5","Duration":"1m 9s","ChapterTopicVideoID":27175,"CourseChapterTopicPlaylistID":237673,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:09.945","Text":"Which of the following codes describes position 12 on the long arm of chromosome 13?"},{"Start":"00:09.945 ","End":"00:11.595","Text":"It\u0027s the long arm."},{"Start":"00:11.595 ","End":"00:13.605","Text":"Is it 13p12?"},{"Start":"00:13.605 ","End":"00:15.405","Text":"Is it 13q12?"},{"Start":"00:15.405 ","End":"00:18.000","Text":"Is it 12p13?"},{"Start":"00:18.000 ","End":"00:21.550","Text":"Or is it 12q13?"},{"Start":"00:21.650 ","End":"00:26.100","Text":"If you remember the names of the chromosomes or"},{"Start":"00:26.100 ","End":"00:32.744","Text":"the chromosome identification starts with the chromosome number"},{"Start":"00:32.744 ","End":"00:39.890","Text":"and then there is either a p for petite or q"},{"Start":"00:39.890 ","End":"00:44.270","Text":"for the longer arm because it follows p. The longer arm is"},{"Start":"00:44.270 ","End":"00:48.620","Text":"q and that\u0027s what we were asked in the question, the long arm."},{"Start":"00:48.620 ","End":"00:51.200","Text":"It\u0027s going to be q."},{"Start":"00:51.200 ","End":"00:59.940","Text":"It\u0027s clearly not one of these with a p. Then it was chromosome 13."},{"Start":"00:59.940 ","End":"01:03.540","Text":"Clearly, our answer then must be"},{"Start":"01:03.540 ","End":"01:09.660","Text":"b 13q12 because we start with the name of the chromosome."}],"ID":28275},{"Watched":false,"Name":"Exercise 6","Duration":"38s","ChapterTopicVideoID":27176,"CourseChapterTopicPlaylistID":237673,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:03.795","Text":"In agriculture, polyploid crops,"},{"Start":"00:03.795 ","End":"00:05.655","Text":"that is as opposed a diploid,"},{"Start":"00:05.655 ","End":"00:08.550","Text":"polyploid crops like coffee,"},{"Start":"00:08.550 ","End":"00:11.554","Text":"strawberries, or bananas tend to produce which of the following?"},{"Start":"00:11.554 ","End":"00:13.635","Text":"More uniformity, more variety,"},{"Start":"00:13.635 ","End":"00:17.040","Text":"larger yields or smaller yields?"},{"Start":"00:17.040 ","End":"00:18.720","Text":"Well, when we discussed this,"},{"Start":"00:18.720 ","End":"00:22.890","Text":"we said that polyploidy is first of all, very common."},{"Start":"00:22.890 ","End":"00:27.570","Text":"But the polyploid plants tend to be larger and"},{"Start":"00:27.570 ","End":"00:32.730","Text":"more robust than euploids of their same species."},{"Start":"00:32.730 ","End":"00:39.190","Text":"Therefore, our answer must be larger yields."}],"ID":28276},{"Watched":false,"Name":"Exercise 7","Duration":"1m 22s","ChapterTopicVideoID":27177,"CourseChapterTopicPlaylistID":237673,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.230 ","End":"00:03.165","Text":"Abnormalities in the number of"},{"Start":"00:03.165 ","End":"00:08.655","Text":"X chromosomes tends to have"},{"Start":"00:08.655 ","End":"00:14.265","Text":"milder phenotypic effects than the same abnormalities in autosomes,"},{"Start":"00:14.265 ","End":"00:16.530","Text":"because of which of the following?"},{"Start":"00:16.530 ","End":"00:20.640","Text":"What are we doing here? We\u0027re asked about abnormalities in the number of"},{"Start":"00:20.640 ","End":"00:27.450","Text":"X chromosomes as compared to the same abnormalities in autosomes,"},{"Start":"00:27.450 ","End":"00:29.670","Text":"in other words, not the sex chromosomes."},{"Start":"00:29.670 ","End":"00:33.405","Text":"This is because of deletions, nonhomologous recombination,"},{"Start":"00:33.405 ","End":"00:37.635","Text":"synapsis or X inactivation."},{"Start":"00:37.635 ","End":"00:43.970","Text":"Well, if you remember, X inactivation is that in females, particularly,"},{"Start":"00:43.970 ","End":"00:48.065","Text":"for example in males where there are 2 X chromosomes,"},{"Start":"00:48.065 ","End":"00:51.730","Text":"there is a random inactivation,"},{"Start":"00:51.730 ","End":"00:56.330","Text":"so some of the chromosomes do not express themselves,"},{"Start":"00:56.330 ","End":"00:59.420","Text":"or most of what\u0027s on the chromosome does not express itself."},{"Start":"00:59.420 ","End":"01:04.715","Text":"In fact, despite the fact that there might be additional chromosomes here,"},{"Start":"01:04.715 ","End":"01:09.050","Text":"additional X chromosomes, they may be inactivated."},{"Start":"01:09.050 ","End":"01:13.790","Text":"If they\u0027re inactivated, it\u0027s more likely therefore that"},{"Start":"01:13.790 ","End":"01:18.715","Text":"we\u0027re going to have milder phenotypic effects."},{"Start":"01:18.715 ","End":"01:22.840","Text":"Our answer is X inactivation."}],"ID":28277},{"Watched":false,"Name":"Exercise 8","Duration":"1m 2s","ChapterTopicVideoID":27168,"CourseChapterTopicPlaylistID":237673,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:09.630","Text":"Assume a pericentric inversion occurred in 1 of the 2 homologs prior to meiosis."},{"Start":"00:09.630 ","End":"00:11.720","Text":"The other homolog remains normal."},{"Start":"00:11.720 ","End":"00:15.315","Text":"We\u0027ve got an inversion in 1 chromosome, but not the other."},{"Start":"00:15.315 ","End":"00:17.730","Text":"During meiosis, what structure, if any,"},{"Start":"00:17.730 ","End":"00:23.715","Text":"would these homologs assume in order to pair accurately along their lengths?"},{"Start":"00:23.715 ","End":"00:25.890","Text":"Would it be V formation, cruciform,"},{"Start":"00:25.890 ","End":"00:31.005","Text":"loop or that pairing would not be possible in any case."},{"Start":"00:31.005 ","End":"00:35.655","Text":"We\u0027ve got 1 chromosome that has an inversion."},{"Start":"00:35.655 ","End":"00:39.060","Text":"In this case we would have, here\u0027s our inversion."},{"Start":"00:39.060 ","End":"00:41.600","Text":"We have A, B, C, D,"},{"Start":"00:41.600 ","End":"00:45.885","Text":"but then we\u0027ve got inverted piece over here."},{"Start":"00:45.885 ","End":"00:47.970","Text":"It would be G, F, E,"},{"Start":"00:47.970 ","End":"00:52.490","Text":"H. In order for it to pair with a homologous chromosome,"},{"Start":"00:52.490 ","End":"00:58.095","Text":"simply there could be a loop in the homologous chromosome."},{"Start":"00:58.095 ","End":"01:03.100","Text":"Therefore, our answer would be loop."}],"ID":28278},{"Watched":false,"Name":"Exercise 9","Duration":"1m 14s","ChapterTopicVideoID":27169,"CourseChapterTopicPlaylistID":237673,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:07.620","Text":"The genotype XXY corresponds to which of the following?"},{"Start":"00:07.620 ","End":"00:10.485","Text":"The Klinefelter syndrome, the turner syndrome,"},{"Start":"00:10.485 ","End":"00:14.610","Text":"triplo-X or the Jacobsen syndrome."},{"Start":"00:14.610 ","End":"00:17.055","Text":"This is something we just need to know."},{"Start":"00:17.055 ","End":"00:20.295","Text":"We\u0027re talking here about too many chromosomes,"},{"Start":"00:20.295 ","End":"00:23.415","Text":"yes, an additional X chromosome."},{"Start":"00:23.415 ","End":"00:25.650","Text":"You might remember that,"},{"Start":"00:25.650 ","End":"00:28.770","Text":"the karyogram will reveal genetic abnormalities of"},{"Start":"00:28.770 ","End":"00:33.030","Text":"either too many or too few chromosomes in the cell,"},{"Start":"00:33.030 ","End":"00:36.480","Text":"and if we\u0027re talking about autosomic chromosomes,"},{"Start":"00:36.480 ","End":"00:38.970","Text":"then we can talk about down syndrome, turner syndrome,"},{"Start":"00:38.970 ","End":"00:43.385","Text":"Jacobsen syndrome, or sometimes they\u0027re pinpoint translocations."},{"Start":"00:43.385 ","End":"00:44.960","Text":"But in any case,"},{"Start":"00:44.960 ","End":"00:50.375","Text":"when we\u0027re talking about sex chromosomes and that\u0027s the X that we\u0027re talking about,"},{"Start":"00:50.375 ","End":"00:52.570","Text":"the XXY genotype,"},{"Start":"00:52.570 ","End":"00:54.395","Text":"and this is just something you need to remember,"},{"Start":"00:54.395 ","End":"00:58.265","Text":"is called the Klinefelter syndrome."},{"Start":"00:58.265 ","End":"01:04.019","Text":"Surprisingly actually, about 1 in 1,100 males is XXY,"},{"Start":"01:04.019 ","End":"01:05.510","Text":"that\u0027s an awful lot, right?"},{"Start":"01:05.510 ","End":"01:08.720","Text":"That\u0027s 0.1%. But in any case,"},{"Start":"01:08.720 ","End":"01:14.460","Text":"the answer here for this question is called the Klinefelter syndrome."}],"ID":28279},{"Watched":false,"Name":"Exercise 10","Duration":"33s","ChapterTopicVideoID":27170,"CourseChapterTopicPlaylistID":237673,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:08.190","Text":"By definition, a pericentric inversion includes which of the following?"},{"Start":"00:08.190 ","End":"00:09.915","Text":"The centromere, the chiasma,"},{"Start":"00:09.915 ","End":"00:12.945","Text":"telomere or the synapse."},{"Start":"00:12.945 ","End":"00:19.530","Text":"If you remember, a pericentric inversion"},{"Start":"00:19.530 ","End":"00:25.980","Text":"is going to include the centromere because it spans the centromere."},{"Start":"00:25.980 ","End":"00:29.550","Text":"That\u0027s the definition of a pericentric inversion."},{"Start":"00:29.550 ","End":"00:33.069","Text":"Our answer then is centromere."}],"ID":28280}],"Thumbnail":null,"ID":237673},{"Name":"DNA Structure And Function","TopicPlaylistFirstVideoID":0,"Duration":null,"Videos":[{"Watched":false,"Name":"DNA and RNA primary structure","Duration":"4m 30s","ChapterTopicVideoID":27039,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.770","Text":"In this section, we\u0027re going to discuss DNA structure and function,"},{"Start":"00:04.770 ","End":"00:08.100","Text":"and you\u0027ll see this is really quite an amazing story."},{"Start":"00:08.100 ","End":"00:12.090","Text":"First, let\u0027s look at the building blocks of DNA,"},{"Start":"00:12.090 ","End":"00:14.370","Text":"which are called nucleotides,"},{"Start":"00:14.370 ","End":"00:16.800","Text":"and look at the chemical composition."},{"Start":"00:16.800 ","End":"00:20.565","Text":"First of all, we conveniently"},{"Start":"00:20.565 ","End":"00:25.710","Text":"separate the structure of these nucleotides into 3 different groups."},{"Start":"00:25.710 ","End":"00:28.575","Text":"There\u0027s the phosphate group,"},{"Start":"00:28.575 ","End":"00:31.650","Text":"there is a sugar which is a pentose,"},{"Start":"00:31.650 ","End":"00:36.090","Text":"it\u0027s pentose because it\u0027s got 5 different carbons, let\u0027s count them,"},{"Start":"00:36.090 ","End":"00:37.620","Text":"1, 2,"},{"Start":"00:37.620 ","End":"00:41.120","Text":"3, 4, 5."},{"Start":"00:41.120 ","End":"00:43.805","Text":"The last carbon is outside the ring,"},{"Start":"00:43.805 ","End":"00:47.705","Text":"and we have a nitrogenous base,"},{"Start":"00:47.705 ","End":"00:50.840","Text":"which as you\u0027ll see, can be different."},{"Start":"00:50.840 ","End":"00:55.865","Text":"There are 4 different nitrogenous bases that can make up different nucleotides."},{"Start":"00:55.865 ","End":"00:59.735","Text":"The nucleotide structure contains a nitrogenous base,"},{"Start":"00:59.735 ","End":"01:03.575","Text":"a 5-carbon sugar, and a phosphate group."},{"Start":"01:03.575 ","End":"01:05.315","Text":"In addition to that,"},{"Start":"01:05.315 ","End":"01:09.040","Text":"the nucleotide that we discuss is"},{"Start":"01:09.040 ","End":"01:14.050","Text":"named depending on which nitrogenous base it has, as I said."},{"Start":"01:14.050 ","End":"01:21.005","Text":"In DNA, there are 4 different nitrogenous bases: there\u0027s a cytosine,"},{"Start":"01:21.005 ","End":"01:22.970","Text":"which is abbreviated C,"},{"Start":"01:22.970 ","End":"01:28.500","Text":"there is a Thymine which is abbreviated with a T,"},{"Start":"01:28.500 ","End":"01:31.940","Text":"there is an Adenine, abbreviated A,"},{"Start":"01:31.940 ","End":"01:34.250","Text":"and there is a Guanine,"},{"Start":"01:34.250 ","End":"01:37.325","Text":"it\u0027s abbreviated G. Now,"},{"Start":"01:37.325 ","End":"01:39.440","Text":"notice that in DNA,"},{"Start":"01:39.440 ","End":"01:42.890","Text":"the Thymine is replaced by a uracil,"},{"Start":"01:42.890 ","End":"01:47.015","Text":"and if you look at them, the Thymine and Uracil, they\u0027re very similar."},{"Start":"01:47.015 ","End":"01:50.075","Text":"The main difference is that the Thymine has"},{"Start":"01:50.075 ","End":"01:55.760","Text":"a methyl group that is sitting on this carbon over here,"},{"Start":"01:55.760 ","End":"01:57.710","Text":"but they\u0027re very similar and as you\u0027ll see,"},{"Start":"01:57.710 ","End":"02:00.680","Text":"they behave in very similar ways."},{"Start":"02:00.680 ","End":"02:05.810","Text":"The nucleotide is the name that depending on its nitrogenous base,"},{"Start":"02:05.810 ","End":"02:07.040","Text":"and as you can see,"},{"Start":"02:07.040 ","End":"02:10.430","Text":"there are rings in these nitrogenous bases that are either"},{"Start":"02:10.430 ","End":"02:14.170","Text":"made up of 1 ring or a double ring,"},{"Start":"02:14.170 ","End":"02:20.350","Text":"and they are called Purines and Pyrimidines."},{"Start":"02:21.400 ","End":"02:32.160","Text":"The purines have a double ring structure and they are either Adenine and Guanine, A,"},{"Start":"02:32.160 ","End":"02:37.265","Text":"G, and the pyrimidines are cytosine and thymine,"},{"Start":"02:37.265 ","End":"02:47.720","Text":"C or T. The sugar is deoxyribose in DNA and ribose in RNA."},{"Start":"02:47.720 ","End":"02:48.890","Text":"Here are the sugars,"},{"Start":"02:48.890 ","End":"02:50.870","Text":"let\u0027s look at the difference."},{"Start":"02:50.870 ","End":"02:57.500","Text":"In DNA, it\u0027s deoxy ribose because it does not"},{"Start":"02:57.500 ","End":"03:03.965","Text":"have the hydroxyl group on sugar 2 prime."},{"Start":"03:03.965 ","End":"03:13.835","Text":"The sugars in DNA and RNA have their carbons that are numbered 1 prime, 2 prime,"},{"Start":"03:13.835 ","End":"03:15.680","Text":"3 prime, 4 prime,"},{"Start":"03:15.680 ","End":"03:17.605","Text":"and 5 prime,"},{"Start":"03:17.605 ","End":"03:23.120","Text":"and it\u0027s the 2 prime sugar that either does not have a hydroxyl group on it,"},{"Start":"03:23.120 ","End":"03:25.835","Text":"or does, it\u0027s a ribose."},{"Start":"03:25.835 ","End":"03:30.260","Text":"That\u0027s really the main difference between DNA and RNA."},{"Start":"03:30.260 ","End":"03:35.385","Text":"It\u0027s this hydroxyl group that is on the 2 prime carbon."},{"Start":"03:35.385 ","End":"03:39.180","Text":"The connections are 5 prime to 3 prime."},{"Start":"03:39.180 ","End":"03:42.320","Text":"The 3 prime sugar is here,"},{"Start":"03:42.320 ","End":"03:43.550","Text":"as we\u0027ve seen before,"},{"Start":"03:43.550 ","End":"03:46.610","Text":"and the 5 prime sugar is outside the ring,"},{"Start":"03:46.610 ","End":"03:50.970","Text":"and that connects through the phosphate group,"},{"Start":"03:50.970 ","End":"03:52.185","Text":"as you can see here,"},{"Start":"03:52.185 ","End":"04:00.735","Text":"phosphate sugar in a polynucleotide."},{"Start":"04:00.735 ","End":"04:05.750","Text":"Therefore, at 1 end of the chain we\u0027ll have a 5 prime and,"},{"Start":"04:05.750 ","End":"04:09.095","Text":"the 5 prime free phosphate,"},{"Start":"04:09.095 ","End":"04:11.300","Text":"as you can see here, and on the other hand,"},{"Start":"04:11.300 ","End":"04:14.710","Text":"we\u0027ll have a 3 prime hydroxyl group,"},{"Start":"04:14.710 ","End":"04:19.285","Text":"which is on the 3 prime sugar."},{"Start":"04:19.285 ","End":"04:24.500","Text":"So that means therefore that a chain in DNA and"},{"Start":"04:24.500 ","End":"04:31.120","Text":"RNA has a 5 prime end and a 3 prime end."}],"ID":28167},{"Watched":false,"Name":"DNA packaging in cells","Duration":"5m 25s","ChapterTopicVideoID":27040,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:05.925","Text":"Hi there. We\u0027ve been looking at the structure of DNA,"},{"Start":"00:05.925 ","End":"00:08.774","Text":"and we talked a bit about how it\u0027s sequenced."},{"Start":"00:08.774 ","End":"00:13.305","Text":"Now, let\u0027s think a little bit about how the DNA is packaged inside cells."},{"Start":"00:13.305 ","End":"00:16.785","Text":"Some of this we\u0027ve seen a little bit earlier in our introductions,"},{"Start":"00:16.785 ","End":"00:19.415","Text":"but we\u0027ll repeat a little bit of it."},{"Start":"00:19.415 ","End":"00:26.205","Text":"Remember that prokaryotes or things like bacteria are much simpler than eukaryotes."},{"Start":"00:26.205 ","End":"00:28.815","Text":"They\u0027re much smaller for one thing,"},{"Start":"00:28.815 ","End":"00:33.495","Text":"and they don\u0027t have a nucleus like eukaryotes do."},{"Start":"00:33.495 ","End":"00:42.244","Text":"Thus, most prokaryotes have a single circular chromosome that is packaged somehow,"},{"Start":"00:42.244 ","End":"00:47.715","Text":"it\u0027s folded up inside this region called the nucleoid region."},{"Start":"00:47.715 ","End":"00:52.140","Text":"The DNA in that region is supercoiled,"},{"Start":"00:52.140 ","End":"00:56.420","Text":"that is, it\u0027s like you take a telephone wire which is helical,"},{"Start":"00:56.420 ","End":"00:59.075","Text":"to begin with, and you keep turning it in the same direction,"},{"Start":"00:59.075 ","End":"01:03.740","Text":"it will fold and it\u0027ll make these additional super helixes,"},{"Start":"01:03.740 ","End":"01:05.855","Text":"that\u0027s a helix of a helix."},{"Start":"01:05.855 ","End":"01:11.010","Text":"That\u0027s this supercoiling that we see in DNA."},{"Start":"01:11.010 ","End":"01:12.675","Text":"In E. coli,"},{"Start":"01:12.675 ","End":"01:16.070","Text":"just to give you an idea of how long the DNA would be,"},{"Start":"01:16.070 ","End":"01:19.000","Text":"it would be about 1.1 millimeters long,"},{"Start":"01:19.000 ","End":"01:23.080","Text":"that\u0027s pretty big if the whole bacterium is just tiny,"},{"Start":"01:23.080 ","End":"01:27.560","Text":"and it\u0027s got about 4.6 million base pairs."},{"Start":"01:27.560 ","End":"01:33.535","Text":"This supercoiled DNA then is also complexed"},{"Start":"01:33.535 ","End":"01:39.800","Text":"with a number of different proteins that helps maintain the supercoiled structure."},{"Start":"01:39.800 ","End":"01:41.720","Text":"Now, in eukaryotes,"},{"Start":"01:41.720 ","End":"01:44.825","Text":"those proteins are called histones,"},{"Start":"01:44.825 ","End":"01:50.210","Text":"and the primary package is called a nucleosome."},{"Start":"01:50.210 ","End":"01:55.370","Text":"In eukaryotes, there\u0027s also supercoiling that is"},{"Start":"01:55.370 ","End":"02:02.170","Text":"facilitated by the nucleosome proteins that are called histones."},{"Start":"02:02.170 ","End":"02:06.305","Text":"The DNA is wrapped tightly around the histone core,"},{"Start":"02:06.305 ","End":"02:08.020","Text":"as we can see here,"},{"Start":"02:08.020 ","End":"02:14.180","Text":"and it forms therefore a structure that looks in the microscope like beads on"},{"Start":"02:14.180 ","End":"02:22.474","Text":"a string where the DNA which is between the 2 nucleosomes is called linker DNA."},{"Start":"02:22.474 ","End":"02:26.915","Text":"Now, you know that during mitosis, for instance,"},{"Start":"02:26.915 ","End":"02:34.340","Text":"the metaphase chromosomes are compacted much more than this compaction,"},{"Start":"02:34.340 ","End":"02:35.930","Text":"as we\u0027ve seen earlier."},{"Start":"02:35.930 ","End":"02:38.840","Text":"That\u0027s done by the association with"},{"Start":"02:38.840 ","End":"02:42.235","Text":"additional proteins that are called scaffolding proteins."},{"Start":"02:42.235 ","End":"02:47.840","Text":"The metaphase, the chromosomes are very compact and they are considerably"},{"Start":"02:47.840 ","End":"02:54.850","Text":"wider because they\u0027re so compacted at about 700 nanometers in width."},{"Start":"02:54.850 ","End":"02:57.845","Text":"Looking at further compaction,"},{"Start":"02:57.845 ","End":"03:02.840","Text":"we have this 700 nanometers that is packed"},{"Start":"03:02.840 ","End":"03:09.160","Text":"even further in the mitotic chromosome before anaphase."},{"Start":"03:09.160 ","End":"03:17.180","Text":"Again, we see this \"Beads on a string\" structure which is very compacted together with"},{"Start":"03:17.180 ","End":"03:19.430","Text":"the scaffolding proteins and"},{"Start":"03:19.430 ","End":"03:26.644","Text":"the metaphase compaction but if we look at the area of the DNA,"},{"Start":"03:26.644 ","End":"03:29.045","Text":"at the level on top,"},{"Start":"03:29.045 ","End":"03:31.750","Text":"over here at the beads on a string level,"},{"Start":"03:31.750 ","End":"03:39.275","Text":"then we will see that it actually can be separated into 2 distinct regions of compaction."},{"Start":"03:39.275 ","End":"03:41.705","Text":"There is a region which is more compact,"},{"Start":"03:41.705 ","End":"03:44.200","Text":"which is called heterochromatin,"},{"Start":"03:44.200 ","End":"03:50.405","Text":"and there is a section which is less compact called euchromatin."},{"Start":"03:50.405 ","End":"03:54.560","Text":"We have a less compacted region and a more compacted region."},{"Start":"03:54.560 ","End":"04:01.625","Text":"It turns out that these different regions of compaction are correlated,"},{"Start":"04:01.625 ","End":"04:07.835","Text":"which with whether the genes in those areas are expressed or not expressed."},{"Start":"04:07.835 ","End":"04:11.210","Text":"Of course, those that are not expressed are more"},{"Start":"04:11.210 ","End":"04:14.510","Text":"compacted into the structure called heterochromatin."},{"Start":"04:14.510 ","End":"04:17.960","Text":"It\u0027s believed that it\u0027s one of the forms of"},{"Start":"04:17.960 ","End":"04:22.220","Text":"regulation that controls whether genes will be expressed or not, that is,"},{"Start":"04:22.220 ","End":"04:26.660","Text":"if they\u0027re more compacted or the system will compact more to prevent"},{"Start":"04:26.660 ","End":"04:33.530","Text":"the RNA polymerase from transcribing regions that are more tightly packed."},{"Start":"04:36.410 ","End":"04:45.215","Text":"Again, the transcribed regions will be more open and the compacted ones less so."},{"Start":"04:45.215 ","End":"04:46.730","Text":"As you can see from here,"},{"Start":"04:46.730 ","End":"04:51.065","Text":"there are modifications that are made to the histones."},{"Start":"04:51.065 ","End":"04:53.280","Text":"In a very broad sense,"},{"Start":"04:53.280 ","End":"05:00.740","Text":"there can be methyl groups that are added to these histones which are such"},{"Start":"05:00.740 ","End":"05:08.945","Text":"that we have a lessening of the charge and a more larger compaction of the DNA,"},{"Start":"05:08.945 ","End":"05:13.130","Text":"whereas active areas can be acetylated."},{"Start":"05:13.130 ","End":"05:14.720","Text":"An acetyl group would be added,"},{"Start":"05:14.720 ","End":"05:19.490","Text":"which is negatively charged and causes the DNA to be"},{"Start":"05:19.490 ","End":"05:25.680","Text":"less compacted and therefore more transcriptionally active."}],"ID":28168},{"Watched":false,"Name":"DNA polymerase on the lagging strand","Duration":"6m 16s","ChapterTopicVideoID":27041,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:05.595","Text":"Hi. Let\u0027s continue with our discussion of replication."},{"Start":"00:05.595 ","End":"00:14.070","Text":"Where we left off, we were talking about the priming of the lagging strand,"},{"Start":"00:14.070 ","End":"00:16.860","Text":"the lagging strands of the DNA."},{"Start":"00:16.860 ","End":"00:20.310","Text":"Remember, there\u0027s both the lagging and the leading strand."},{"Start":"00:20.310 ","End":"00:24.060","Text":"The leading strand will be synthesized very simply but right now,"},{"Start":"00:24.060 ","End":"00:25.680","Text":"we\u0027re looking at the lagging strand."},{"Start":"00:25.680 ","End":"00:31.635","Text":"DNA polymerase extends the RNA primer by building a new DNA at the replication fork and"},{"Start":"00:31.635 ","End":"00:37.965","Text":"it is adding the new DNA 5\u0027 to 3\u0027,"},{"Start":"00:37.965 ","End":"00:42.270","Text":"where it\u0027s using the RNA as the primer."},{"Start":"00:42.270 ","End":"00:47.509","Text":"The rate of this elongation is about 500 nucleotides per second in bacteria,"},{"Start":"00:47.509 ","End":"00:49.520","Text":"500 nucleotides per second."},{"Start":"00:49.520 ","End":"00:52.550","Text":"That\u0027s really fast, but about 10 times slower,"},{"Start":"00:52.550 ","End":"00:55.760","Text":"50 per second in human cells."},{"Start":"00:55.760 ","End":"00:59.750","Text":"Now if we look at the entire replication area,"},{"Start":"00:59.750 ","End":"01:02.600","Text":"remember we started from an origin and we moved in"},{"Start":"01:02.600 ","End":"01:07.880","Text":"both directions having 2 replication forks,"},{"Start":"01:07.880 ","End":"01:14.464","Text":"each replication fork has on the leading strand DNA is synthesized continuously,"},{"Start":"01:14.464 ","End":"01:16.175","Text":"as you can see here."},{"Start":"01:16.175 ","End":"01:18.575","Text":"However, on the lagging strand,"},{"Start":"01:18.575 ","End":"01:21.200","Text":"DNA is synthesized in short stretches."},{"Start":"01:21.200 ","End":"01:25.759","Text":"We saw that when we were looking at the primers that were extended,"},{"Start":"01:25.759 ","End":"01:27.990","Text":"what we were looking at something similar to this."},{"Start":"01:27.990 ","End":"01:30.620","Text":"What we saw in those cases was that there were"},{"Start":"01:30.620 ","End":"01:34.460","Text":"several different primers that were formed,"},{"Start":"01:34.460 ","End":"01:37.060","Text":"each of them was extended."},{"Start":"01:37.060 ","End":"01:43.700","Text":"Each of these fragments then that are made are called Okazaki fragments."},{"Start":"01:43.700 ","End":"01:50.690","Text":"Okazaki fragments named for Okazaki who was the person that discovered them initially."},{"Start":"01:50.690 ","End":"01:57.110","Text":"DNA polymerase I is the enzyme that does the extension of the primer."},{"Start":"01:57.110 ","End":"01:59.315","Text":"Here, we\u0027re looking at it on the opposite strand."},{"Start":"01:59.315 ","End":"02:01.160","Text":"We\u0027re looking at it on the bottom strand,"},{"Start":"02:01.160 ","End":"02:04.640","Text":"previously we had seen the lagging strand on top."},{"Start":"02:04.640 ","End":"02:08.140","Text":"Here, it\u0027s on the bottom, but it\u0027s really the same thing."},{"Start":"02:08.140 ","End":"02:12.875","Text":"In each of them what we see is that DNA polymerase"},{"Start":"02:12.875 ","End":"02:18.440","Text":"I replaces the RNA primer with DNA by adding NTPs."},{"Start":"02:18.440 ","End":"02:24.710","Text":"It actually has a 5\u0027 to 3\u0027 exonuclease"},{"Start":"02:24.710 ","End":"02:29.435","Text":"because it eats the RNA which is in front of it."},{"Start":"02:29.435 ","End":"02:38.180","Text":"Yes, and it has this 5\u0027 to 3\u0027 polymerase action as well."},{"Start":"02:38.180 ","End":"02:41.720","Text":"It fills in new dNTPs."},{"Start":"02:41.720 ","End":"02:45.190","Text":"That is the DNA polymerase 1."},{"Start":"02:45.190 ","End":"02:50.705","Text":"In addition, there is another enzyme that we have to consider and that is DNA ligase."},{"Start":"02:50.705 ","End":"02:55.205","Text":"What does it do? It seals the gap between the Okazaki fragments."},{"Start":"02:55.205 ","End":"03:00.619","Text":"When the DNA polymerase I reaches the DNA,"},{"Start":"03:00.619 ","End":"03:04.455","Text":"which is in the next Okazaki fragments,"},{"Start":"03:04.455 ","End":"03:08.510","Text":"then the 2 pieces of DNA are combined together."},{"Start":"03:08.510 ","End":"03:10.534","Text":"They are ligated together,"},{"Start":"03:10.534 ","End":"03:13.865","Text":"they\u0027re stuck together by this DNA ligase,"},{"Start":"03:13.865 ","End":"03:18.650","Text":"which makes a new phosphodiester bond between the 2 fragments."},{"Start":"03:18.650 ","End":"03:21.530","Text":"Now once the chromosome has been completely replicated,"},{"Start":"03:21.530 ","End":"03:26.315","Text":"the 2 DNA copies move into 2 different cells during cell division."},{"Start":"03:26.315 ","End":"03:29.350","Text":"That\u0027s something that we learned earlier."},{"Start":"03:29.350 ","End":"03:35.825","Text":"Now, let\u0027s review what we just talked about on this lagging strand."},{"Start":"03:35.825 ","End":"03:41.525","Text":"On the lagging strand, first there\u0027s a primer which is made by the primase."},{"Start":"03:41.525 ","End":"03:48.020","Text":"The next thing that happens is that the DNA polymerase III."},{"Start":"03:48.020 ","End":"03:50.780","Text":"Yes, that\u0027s the main DNA polymerase,"},{"Start":"03:50.780 ","End":"03:53.075","Text":"makes the Okazaki fragments,"},{"Start":"03:53.075 ","End":"04:00.379","Text":"it just continues the RNA primer that was made by the primase."},{"Start":"04:00.379 ","End":"04:07.545","Text":"The next thing that happens is that the DNA polymerase III detaches, it comes off."},{"Start":"04:07.545 ","End":"04:14.855","Text":"Here it is, it comes off and it is replaced then by DNA polymerase I,"},{"Start":"04:14.855 ","End":"04:16.805","Text":"which is what we see here."},{"Start":"04:16.805 ","End":"04:19.970","Text":"What we see here, the DNA polymerase I,"},{"Start":"04:19.970 ","End":"04:24.660","Text":"and it continues to replicate the DNA."},{"Start":"04:24.660 ","End":"04:28.910","Text":"When it encounters the RNA from the Okazaki fragment,"},{"Start":"04:28.910 ","End":"04:33.035","Text":"it replaces the RNA with DNA."},{"Start":"04:33.035 ","End":"04:39.270","Text":"Finally, RNA ligase then forms bonds."},{"Start":"04:39.270 ","End":"04:43.835","Text":"It forms a new phosphodiester bond between the DNA fragments,"},{"Start":"04:43.835 ","End":"04:47.639","Text":"making the lagging strand complete."},{"Start":"04:47.770 ","End":"04:51.920","Text":"Let\u0027s now look at the various enzymes we talked about."},{"Start":"04:51.920 ","End":"04:54.455","Text":"There was DNA polymerase I,"},{"Start":"04:54.455 ","End":"04:56.090","Text":"which is the one that removes the primary,"},{"Start":"04:56.090 ","End":"04:58.455","Text":"replaces it with newly synthesized DNA."},{"Start":"04:58.455 ","End":"05:05.570","Text":"DNA polymerase III is the main enzyme that adds nucleotides in the 5\u0027 to 3\u0027 direction."},{"Start":"05:05.570 ","End":"05:07.580","Text":"There was the helicase, if remember,"},{"Start":"05:07.580 ","End":"05:12.860","Text":"which opens the DNA helix by breaking the hydrogen bonds between the nitrogenous bases."},{"Start":"05:12.860 ","End":"05:16.220","Text":"There was the ligase that seals the gaps between"},{"Start":"05:16.220 ","End":"05:20.180","Text":"the Okazaki fragments to create one continuous DNA strand."},{"Start":"05:20.180 ","End":"05:22.970","Text":"There was the primase that\u0027s synthesized,"},{"Start":"05:22.970 ","End":"05:26.630","Text":"the RNA primers that were needed to start replication."},{"Start":"05:26.630 ","End":"05:30.770","Text":"There was topoisomerase that helped relieve the strain on the DNA,"},{"Start":"05:30.770 ","End":"05:34.240","Text":"that torsional stress on the DNA when unwinding,"},{"Start":"05:34.240 ","End":"05:39.040","Text":"that would otherwise cause breaks and so what it does is it,"},{"Start":"05:39.040 ","End":"05:40.435","Text":"in a controlled way,"},{"Start":"05:40.435 ","End":"05:44.795","Text":"breaks the phosphodiester backbone and then reseals it."},{"Start":"05:44.795 ","End":"05:47.601","Text":"That relieves the strain on the DNA,"},{"Start":"05:47.601 ","End":"05:51.205","Text":"and there were the single-stranded binding proteins, the SSBs,"},{"Start":"05:51.205 ","End":"05:52.930","Text":"which binds to single-stranded DNA,"},{"Start":"05:52.930 ","End":"05:58.330","Text":"preventing the DNA from rewinding whatever\u0027s in the replication fork."},{"Start":"05:58.330 ","End":"06:00.010","Text":"Now in addition to these,"},{"Start":"06:00.010 ","End":"06:04.495","Text":"there is the sliding clamp that we had not really mentioned before."},{"Start":"06:04.495 ","End":"06:09.610","Text":"It is in the form of a ring which goes around"},{"Start":"06:09.610 ","End":"06:12.820","Text":"the entire complex and this helps to hold the DNA polymerase in"},{"Start":"06:12.820 ","End":"06:17.420","Text":"place when the nucleotides are being added."}],"ID":28169},{"Watched":false,"Name":"DNA repair mechanisms","Duration":"4m 22s","ChapterTopicVideoID":27042,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.710 ","End":"00:05.370","Text":"We\u0027ve discussed DNA replication until now,"},{"Start":"00:05.370 ","End":"00:09.570","Text":"but we have not at all considered what happens if mistakes are made when"},{"Start":"00:09.570 ","End":"00:14.385","Text":"the DNA is replicated or possibly even afterwards."},{"Start":"00:14.385 ","End":"00:20.835","Text":"Uncorrected mistakes may sometimes lead to very serious consequences."},{"Start":"00:20.835 ","End":"00:26.490","Text":"Repair mechanisms will correct those mistakes but in rare cases,"},{"Start":"00:26.490 ","End":"00:31.035","Text":"mistakes are not corrected and this leads to mutations."},{"Start":"00:31.035 ","End":"00:36.330","Text":"In other cases, repair enzymes themselves can be mutated or defective,"},{"Start":"00:36.330 ","End":"00:39.690","Text":"and that of course, will make it such that there will"},{"Start":"00:39.690 ","End":"00:44.200","Text":"be many more mutations throughout the cell."},{"Start":"00:44.330 ","End":"00:47.710","Text":"How are these mistakes usually corrected?"},{"Start":"00:47.710 ","End":"00:52.550","Text":"While there are varying methods for that and the most of the mistakes that occur"},{"Start":"00:52.550 ","End":"00:58.040","Text":"during replication are very promptly corrected by the DNA polymerase itself."},{"Start":"00:58.040 ","End":"01:03.980","Text":"The polymerase checks whether the newly added base pairs are correctly paired"},{"Start":"01:03.980 ","End":"01:10.235","Text":"with the base in the template strand if they do not pair exactly the way they should,"},{"Start":"01:10.235 ","End":"01:14.315","Text":"and of course the DNA will not be straight."},{"Start":"01:14.315 ","End":"01:18.500","Text":"There will be a bulge in it and that can be recognized by"},{"Start":"01:18.500 ","End":"01:23.320","Text":"the polymerase and it cannot move forward correctly."},{"Start":"01:23.320 ","End":"01:25.910","Text":"If the right base is added,"},{"Start":"01:25.910 ","End":"01:28.745","Text":"the next nucleotide is added but if not,"},{"Start":"01:28.745 ","End":"01:31.565","Text":"the enzyme can make a cut,"},{"Start":"01:31.565 ","End":"01:33.140","Text":"as you can see here,"},{"Start":"01:33.140 ","End":"01:37.070","Text":"and it can release the wrong nucleotide."},{"Start":"01:37.070 ","End":"01:44.800","Text":"There is an exonuclease which will remove the DNA that has just been made."},{"Start":"01:44.800 ","End":"01:47.405","Text":"Once the incorrect nucleotides been removed,"},{"Start":"01:47.405 ","End":"01:50.510","Text":"it can be replaced by a correct one,"},{"Start":"01:50.510 ","End":"01:54.875","Text":"and then we just move forward and finally,"},{"Start":"01:54.875 ","End":"02:02.300","Text":"there is a ligase which will connect the break that\u0027s made in the DNA."},{"Start":"02:02.300 ","End":"02:06.275","Text":"Another possibility is mismatch repair."},{"Start":"02:06.275 ","End":"02:12.695","Text":"Mismatch repair corrects errors that get corrected only after replication is completed."},{"Start":"02:12.695 ","End":"02:15.940","Text":"It\u0027s not that the polymerase passes and corrects it,"},{"Start":"02:15.940 ","End":"02:22.880","Text":"it\u0027s that there is a mismatch now in the DNA and there is a system,"},{"Start":"02:22.880 ","End":"02:25.355","Text":"there is a repair mechanism,"},{"Start":"02:25.355 ","End":"02:27.970","Text":"which will do the following."},{"Start":"02:27.970 ","End":"02:35.360","Text":"It will recognize the mismatch and then excise an entire piece of DNA."},{"Start":"02:35.360 ","End":"02:44.870","Text":"The DNA which was here is exercised by the mechanism and notice that there is"},{"Start":"02:44.870 ","End":"02:49.880","Text":"a methyl group here that has to do with recognizing"},{"Start":"02:49.880 ","End":"02:52.355","Text":"which is the new strand and the old strands"},{"Start":"02:52.355 ","End":"02:55.460","Text":"but that we\u0027ll learn in a more advanced stage."},{"Start":"02:55.460 ","End":"03:00.650","Text":"Then the excised region is then re-synthesized."},{"Start":"03:00.650 ","End":"03:04.565","Text":"Mismatch may lead to more permanent damage when"},{"Start":"03:04.565 ","End":"03:09.305","Text":"the mismatched DNA is replicated if it is not repaired."},{"Start":"03:09.305 ","End":"03:13.055","Text":"Another mechanism is called nucleotide excision repair."},{"Start":"03:13.055 ","End":"03:15.125","Text":"This is like mismatch repair,"},{"Start":"03:15.125 ","End":"03:18.500","Text":"but it\u0027s for removing damaged bases."},{"Start":"03:18.500 ","End":"03:22.655","Text":"That is, one\u0027s the bases themselves are damaged,"},{"Start":"03:22.655 ","End":"03:25.015","Text":"note, that there is a mismatch."},{"Start":"03:25.015 ","End":"03:28.280","Text":"For instance, your UV light can create"},{"Start":"03:28.280 ","End":"03:33.170","Text":"a thymine dimer when there are 2 T\u0027s that are right next to each other."},{"Start":"03:33.170 ","End":"03:38.360","Text":"These 2 T\u0027s can be covalently connected to each other and then they don\u0027t base"},{"Start":"03:38.360 ","End":"03:40.760","Text":"pair correctly with what\u0027s on"},{"Start":"03:40.760 ","End":"03:44.420","Text":"the other side and it also changes the structure of the DNA."},{"Start":"03:44.420 ","End":"03:49.429","Text":"In this case, what happens is damaged bases are removed"},{"Start":"03:49.429 ","End":"03:55.175","Text":"and they cut out basis both on the 3 and 5\u0027 ends"},{"Start":"03:55.175 ","End":"04:01.805","Text":"of the part that is damaged and DNA polymerase then replaces the DNA"},{"Start":"04:01.805 ","End":"04:09.020","Text":"with the correctly paired nucleotides and the gap is sealed by DNA ligase."},{"Start":"04:09.020 ","End":"04:11.570","Text":"This is employed, as I mentioned before,"},{"Start":"04:11.570 ","End":"04:16.850","Text":"when ultraviolet exposure causes the formation of pyrimidine dimers,"},{"Start":"04:16.850 ","End":"04:19.400","Text":"for instance, these thymine dimers,"},{"Start":"04:19.400 ","End":"04:22.680","Text":"those are the most common ones."}],"ID":28170},{"Watched":false,"Name":"DNA secondary and tertiary structures","Duration":"7m 16s","ChapterTopicVideoID":27043,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.080 ","End":"00:07.350","Text":"Welcome back to the discussion about the structure and function of DNA."},{"Start":"00:07.350 ","End":"00:13.410","Text":"We\u0027ve looked at 1 strand of DNA and seen that it has a 5-prime end and"},{"Start":"00:13.410 ","End":"00:15.255","Text":"a 3-prime end and"},{"Start":"00:15.255 ","End":"00:22.050","Text":"the different nucleotides are connected with these phosphodiester bonds."},{"Start":"00:22.050 ","End":"00:28.235","Text":"But how do we know how these different strands of DNA connect to each other?"},{"Start":"00:28.235 ","End":"00:34.890","Text":"Well, let\u0027s look really at the work of 3 different people."},{"Start":"00:37.360 ","End":"00:41.810","Text":"First, Francis Crick and James Watson in"},{"Start":"00:41.810 ","End":"00:44.720","Text":"the very early \u002750s worked together to determine"},{"Start":"00:44.720 ","End":"00:47.825","Text":"the structure of DNA at the University of Cambridge,"},{"Start":"00:47.825 ","End":"00:50.320","Text":"England where they were post-docs."},{"Start":"00:50.320 ","End":"00:56.915","Text":"Their work was based upon the lab work that was done by this woman,"},{"Start":"00:56.915 ","End":"01:00.250","Text":"whose name was Rosalind Franklin."},{"Start":"01:00.250 ","End":"01:05.320","Text":"There were other scientists in addition to Rosalind Franklin,"},{"Start":"01:05.320 ","End":"01:08.194","Text":"Linus Pauling and Maurice Wilkins in particular,"},{"Start":"01:08.194 ","End":"01:12.530","Text":"who were using X-ray diffraction methods."},{"Start":"01:12.530 ","End":"01:14.810","Text":"These are methods that look into"},{"Start":"01:14.810 ","End":"01:21.950","Text":"the 3-dimensional structure of macro-molecules to try to understand the structure of DNA."},{"Start":"01:21.950 ","End":"01:27.395","Text":"In fact, Pauling really had been working previously on proteins."},{"Start":"01:27.395 ","End":"01:34.940","Text":"Rosalind Franklin turned her attention to DNA to try to understand the structure,"},{"Start":"01:34.940 ","End":"01:39.325","Text":"and she got this picture, as you can see here,"},{"Start":"01:39.325 ","End":"01:45.290","Text":"this is an X-ray diffraction pattern and it has the spots that are at"},{"Start":"01:45.290 ","End":"01:51.850","Text":"a particular angle of each other and the spots at particular distances from each other."},{"Start":"01:51.850 ","End":"02:00.170","Text":"This picture then was used as the basis of the understanding of the structure of DNA."},{"Start":"02:00.170 ","End":"02:04.145","Text":"It was Watson and Crick who took this structure"},{"Start":"02:04.145 ","End":"02:09.500","Text":"and could develop an idea about the structure of DNA."},{"Start":"02:09.500 ","End":"02:12.410","Text":"Her image that was called image 51,"},{"Start":"02:12.410 ","End":"02:17.660","Text":"enabled Watson in particular to infer that DNA was helical,"},{"Start":"02:17.660 ","End":"02:19.205","Text":"that was the X,"},{"Start":"02:19.205 ","End":"02:23.120","Text":"that there is a helix of DNA."},{"Start":"02:23.120 ","End":"02:28.895","Text":"Furthermore, by looking at the distances of the spots one from the other,"},{"Start":"02:28.895 ","End":"02:36.140","Text":"he could infer from that the width of the helix and the spacing of the nitrogenous bases."},{"Start":"02:36.140 ","End":"02:40.460","Text":"Remember the nitrogenous bases are attached to the backbone."},{"Start":"02:40.460 ","End":"02:43.310","Text":"This is a somewhat different picture than we saw earlier,"},{"Start":"02:43.310 ","End":"02:44.975","Text":"but it represents the same thing."},{"Start":"02:44.975 ","End":"02:52.475","Text":"Where the blue ribbon here is the sugar-phosphate backbone,"},{"Start":"02:52.475 ","End":"02:56.180","Text":"and the red are the nitrogenous bases."},{"Start":"02:56.180 ","End":"03:00.470","Text":"The pattern also suggested that there were 2 strands of DNA,"},{"Start":"03:00.470 ","End":"03:05.220","Text":"that was the X that formed a double helix."},{"Start":"03:05.220 ","End":"03:13.110","Text":"There\u0027s 1 helix and a second helix and they twist around each other."},{"Start":"03:13.110 ","End":"03:19.090","Text":"This was really a tremendous idea because it"},{"Start":"03:19.090 ","End":"03:24.580","Text":"formed really the basis for understanding how genetic material is inherited."},{"Start":"03:24.580 ","End":"03:28.030","Text":"Therefore, in 1962, Jim Watson,"},{"Start":"03:28.030 ","End":"03:32.305","Text":"Francis Crick, and Maurice Wilkins were awarded the Nobel Prize."},{"Start":"03:32.305 ","End":"03:36.280","Text":"Unfortunately, Franklin did not get the prize because she had"},{"Start":"03:36.280 ","End":"03:41.330","Text":"already died and Nobel Prizes are not awarded posthumously."},{"Start":"03:41.330 ","End":"03:44.730","Text":"Let\u0027s look at this in a bit more detail."},{"Start":"03:44.730 ","End":"03:47.585","Text":"The base pairs are such,"},{"Start":"03:47.585 ","End":"03:50.800","Text":"remember that there are purines and pyrimidines,"},{"Start":"03:50.800 ","End":"03:54.885","Text":"and at first Watson and Crick thought the 2 strands might pair"},{"Start":"03:54.885 ","End":"03:59.495","Text":"like an A with an A and a T with a T and so on."},{"Start":"03:59.495 ","End":"04:07.070","Text":"But these pairings would not give an even width of the DNA because,"},{"Start":"04:07.070 ","End":"04:10.309","Text":"you remember that the pyrimidines are smaller,"},{"Start":"04:10.309 ","End":"04:14.375","Text":"there\u0027s only 1 ring so that would make the DNA too narrow,"},{"Start":"04:14.375 ","End":"04:16.700","Text":"and that did not jive."},{"Start":"04:16.700 ","End":"04:20.135","Text":"It was not consistent with the X-ray data."},{"Start":"04:20.135 ","End":"04:24.170","Text":"However, pairing a purine with a pyrimidine,"},{"Start":"04:24.170 ","End":"04:30.885","Text":"so an A or G with a C or T did result in a constant width,"},{"Start":"04:30.885 ","End":"04:34.370","Text":"and therefore they could determine that adenine"},{"Start":"04:34.370 ","End":"04:39.140","Text":"and thymine are complimentary basis or base pairs,"},{"Start":"04:39.140 ","End":"04:43.760","Text":"and cytosine and guanine are also complimentary base pairs."},{"Start":"04:43.760 ","End":"04:45.505","Text":"Let\u0027s see what that means."},{"Start":"04:45.505 ","End":"04:47.695","Text":"You can see in this figure,"},{"Start":"04:47.695 ","End":"04:54.695","Text":"here that we have a thymine and adenine and they can hydrogen bond to each other."},{"Start":"04:54.695 ","End":"04:59.315","Text":"A guanine and cytosine can also bind to each other."},{"Start":"04:59.315 ","End":"05:01.003","Text":"Note that adenine,"},{"Start":"05:01.003 ","End":"05:04.798","Text":"and thymine have 2 hydrogen bonds between them,"},{"Start":"05:04.798 ","End":"05:07.085","Text":"and this will turn out to be important."},{"Start":"05:07.085 ","End":"05:13.220","Text":"Cytosine and guanine have 3 hydrogen bonds between them."},{"Start":"05:13.220 ","End":"05:20.070","Text":"But, the width of the DNA will be the same in both."},{"Start":"05:20.070 ","End":"05:25.100","Text":"The 2 strands therefore are anti-parallel in nature,"},{"Start":"05:25.100 ","End":"05:28.925","Text":"that means you have a 3-prime end of"},{"Start":"05:28.925 ","End":"05:36.225","Text":"1 strand which is opposite the 5-prime end of the opposite strand."},{"Start":"05:36.225 ","End":"05:38.370","Text":"We have 5-prime on one end,"},{"Start":"05:38.370 ","End":"05:40.170","Text":"3 prime on the other end."},{"Start":"05:40.170 ","End":"05:46.730","Text":"1 is going, let\u0027s say top to bottom and the other one is going bottom to top."},{"Start":"05:46.730 ","End":"05:50.490","Text":"That\u0027s the meaning of anti parallel."},{"Start":"05:50.490 ","End":"05:53.420","Text":"The nitrogenous bases stacked,"},{"Start":"05:53.420 ","End":"05:56.420","Text":"they\u0027re sitting flat, one on top of each other."},{"Start":"05:56.420 ","End":"06:05.090","Text":"These are rings which are flat and they stack one on top of the other in this structure."},{"Start":"06:05.090 ","End":"06:08.660","Text":"Furthermore, each base is separated from the next base,"},{"Start":"06:08.660 ","End":"06:16.630","Text":"that\u0027s the distance between each base by 0.34 nanometers or angstroms,"},{"Start":"06:16.630 ","End":"06:19.620","Text":"that\u0027s the distance between the bases."},{"Start":"06:19.620 ","End":"06:26.720","Text":"In fact, there is 1 turn of the double helix every 10 base pairs,"},{"Start":"06:26.720 ","End":"06:29.360","Text":"so that is 0.34 times 10."},{"Start":"06:29.360 ","End":"06:34.865","Text":"That\u0027s 3.4 nanometers is 1 turn of the helix."},{"Start":"06:34.865 ","End":"06:44.855","Text":"The helix can be designated with a figure like this, a space-filling 1."},{"Start":"06:44.855 ","End":"06:47.150","Text":"In this space-filling model,"},{"Start":"06:47.150 ","End":"06:48.770","Text":"it\u0027s clear for instance,"},{"Start":"06:48.770 ","End":"06:55.655","Text":"that the strands are close to each other as they go around forming 2 different grooves,"},{"Start":"06:55.655 ","End":"06:59.105","Text":"a major groove and a minor groove."},{"Start":"06:59.105 ","End":"07:05.365","Text":"But the overall diameter on the outside of this is 2 nanometers."},{"Start":"07:05.365 ","End":"07:10.070","Text":"The twisting of the 2 strands around each other results in the formation of"},{"Start":"07:10.070 ","End":"07:16.920","Text":"a uniformly spaced major and minor grooves as you can see here."}],"ID":28171},{"Watched":false,"Name":"DNA Structure and Function","Duration":"3m 23s","ChapterTopicVideoID":27044,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.680 ","End":"00:03.510","Text":"I\u0027m really glad you\u0027re back."},{"Start":"00:03.510 ","End":"00:09.045","Text":"We\u0027re going to discuss DNA structure and function now in the modern sense,"},{"Start":"00:09.045 ","End":"00:14.020","Text":"and also get to understand how we learned about those things."},{"Start":"00:14.390 ","End":"00:20.610","Text":"First of all, DNA is the genetic material, as you know,"},{"Start":"00:20.610 ","End":"00:26.190","Text":"and it can be retrieved from pretty much any part of the body."},{"Start":"00:26.190 ","End":"00:27.480","Text":"If we\u0027re looking at people,"},{"Start":"00:27.480 ","End":"00:28.740","Text":"it\u0027s even from hair,"},{"Start":"00:28.740 ","End":"00:30.690","Text":"from the tips of the hair, from the blood,"},{"Start":"00:30.690 ","End":"00:34.215","Text":"saliva, any other tissue that\u0027s in the body."},{"Start":"00:34.215 ","End":"00:40.625","Text":"We know that every person\u0027s DNA is unique and it\u0027s used, now,"},{"Start":"00:40.625 ","End":"00:47.270","Text":"in modern science and in industry and all sorts of different applied ways."},{"Start":"00:47.270 ","End":"00:48.830","Text":"In humans, for instance,"},{"Start":"00:48.830 ","End":"00:53.970","Text":"DNA testing is applied to forensics to be able to tell who, say,"},{"Start":"00:53.970 ","End":"00:55.830","Text":"was responsible for a crime,"},{"Start":"00:55.830 ","End":"01:01.420","Text":"in determining paternity, in tracing genealogy."},{"Start":"01:01.420 ","End":"01:06.650","Text":"You know that there are all sorts of companies that do this to trace genealogy."},{"Start":"01:06.650 ","End":"01:09.350","Text":"It\u0027s used for identifying pathogens,"},{"Start":"01:09.350 ","End":"01:11.120","Text":"for archaeological research,"},{"Start":"01:11.120 ","End":"01:13.295","Text":"that is we can look, for instance,"},{"Start":"01:13.295 ","End":"01:20.425","Text":"at the genomes of organisms which are extinct by now and tell a lot about them."},{"Start":"01:20.425 ","End":"01:23.105","Text":"We can trace the disease outbreaks."},{"Start":"01:23.105 ","End":"01:25.850","Text":"That\u0027s something that is quite current."},{"Start":"01:25.850 ","End":"01:32.440","Text":"The COVID-19 is being traced using DNA tracing, strand sequencing."},{"Start":"01:32.440 ","End":"01:36.665","Text":"We can use it to study human migration patterns over time."},{"Start":"01:36.665 ","End":"01:40.190","Text":"We can use it for diagnostics of"},{"Start":"01:40.190 ","End":"01:45.670","Text":"a new vaccine development or for cancer therapy, all things."},{"Start":"01:45.670 ","End":"01:48.590","Text":"Now we\u0027re just talking about an introduction"},{"Start":"01:48.590 ","End":"01:51.578","Text":"here and we\u0027re not getting into any details,"},{"Start":"01:51.578 ","End":"01:54.230","Text":"but each human has 2 sets of chromosomes,"},{"Start":"01:54.230 ","End":"01:56.920","Text":"as you know, one inherited from each parent."},{"Start":"01:56.920 ","End":"01:59.015","Text":"In addition to that,"},{"Start":"01:59.015 ","End":"02:02.210","Text":"there is also mitochondrial DNA."},{"Start":"02:02.210 ","End":"02:06.740","Text":"Remember the mitochondria are these organelles that are in the cell that are"},{"Start":"02:06.740 ","End":"02:13.380","Text":"responsible for energy production in the cell and they,"},{"Start":"02:13.380 ","End":"02:15.900","Text":"as it turns out, have DNA in them also."},{"Start":"02:15.900 ","End":"02:19.490","Text":"It\u0027s a circular DNA which is"},{"Start":"02:19.490 ","End":"02:25.580","Text":"very small relative to the DNA which is found in the nucleus of the cell."},{"Start":"02:25.580 ","End":"02:30.200","Text":"But it is inherited exclusively from the mother because"},{"Start":"02:30.200 ","End":"02:35.825","Text":"the mitochondria are in the ova or in the eggs of the mother,"},{"Start":"02:35.825 ","End":"02:38.150","Text":"and they\u0027re not transmitted through the sperm."},{"Start":"02:38.150 ","End":"02:41.700","Text":"The human haploid genome contains"},{"Start":"02:42.170 ","End":"02:50.870","Text":"about 3 billion base pairs and has on the order of 20-25,000 functional genes in them."},{"Start":"02:50.870 ","End":"02:54.560","Text":"Actually, the number of genes is"},{"Start":"02:54.560 ","End":"02:59.000","Text":"something which is very hard to count because each of the genes,"},{"Start":"02:59.000 ","End":"03:01.250","Text":"as you\u0027ll learn later,"},{"Start":"03:01.250 ","End":"03:04.845","Text":"can actually be spliced in various ways,"},{"Start":"03:04.845 ","End":"03:07.820","Text":"or the RNA from them can be spliced in various ways."},{"Start":"03:07.820 ","End":"03:11.615","Text":"All changes can be made that change their function."},{"Start":"03:11.615 ","End":"03:16.790","Text":"Therefore, the number of genes that are functional"},{"Start":"03:16.790 ","End":"03:23.010","Text":"with a particular sequence are on the order of between 20 and 25,000."}],"ID":28172},{"Watched":false,"Name":"Eukaryotic DNA replication and telomeres","Duration":"8m 9s","ChapterTopicVideoID":27045,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:06.220","Text":"Let\u0027s continue now looking at DNA replication in eukaryotes."},{"Start":"00:06.500 ","End":"00:12.100","Text":"We\u0027ve talked about the various enzymes that work in eukaryotes,"},{"Start":"00:12.100 ","End":"00:17.970","Text":"and now let\u0027s continue by looking at what\u0027s going on on the lagging strands."},{"Start":"00:17.970 ","End":"00:23.115","Text":"To begin with, the helicase has to open the DNA helix as it does in prokaryotes,"},{"Start":"00:23.115 ","End":"00:27.525","Text":"and that is sits at the replication fork."},{"Start":"00:27.525 ","End":"00:30.975","Text":"Here is the helicase opening the DNA."},{"Start":"00:30.975 ","End":"00:36.360","Text":"There is a topoisomerase that stabilizes the single strands"},{"Start":"00:36.360 ","End":"00:42.165","Text":"because it relieves the tension as it does in prokaryotes."},{"Start":"00:42.165 ","End":"00:45.635","Text":"RNA primers are formed by primase,"},{"Start":"00:45.635 ","End":"00:48.485","Text":"as is done in prokaryotes,"},{"Start":"00:48.485 ","End":"00:52.655","Text":"and it adds RNA nucleotides one at a time using the parental DNA as a template."},{"Start":"00:52.655 ","End":"00:57.725","Text":"This is very similar to what happens in prokaryotes."},{"Start":"00:57.725 ","End":"01:02.660","Text":"The short primers and the 3\u0027 end serve as a starting point for"},{"Start":"01:02.660 ","End":"01:10.715","Text":"the new DNA strand again as in prokaryotes but in eukaryotes,"},{"Start":"01:10.715 ","End":"01:14.960","Text":"the DNA polymerases are called Alpha,"},{"Start":"01:14.960 ","End":"01:17.135","Text":"Delta, and Epsilon."},{"Start":"01:17.135 ","End":"01:21.110","Text":"They catalyze the synthesis of new DNA at the replication fork."},{"Start":"01:21.110 ","End":"01:27.175","Text":"That\u0027s as opposed to polymerase 3 in prokaryotes."},{"Start":"01:27.175 ","End":"01:31.945","Text":"DNA polymerase Alpha adds to begin with,"},{"Start":"01:31.945 ","End":"01:37.100","Text":"shorts 20-30 nucleotides to the DNA fragments on both strands and"},{"Start":"01:37.100 ","End":"01:43.325","Text":"then it hands off the polymerization to other polymerases."},{"Start":"01:43.325 ","End":"01:45.350","Text":"The rate of elongation,"},{"Start":"01:45.350 ","End":"01:46.625","Text":"as we said before,"},{"Start":"01:46.625 ","End":"01:52.235","Text":"is much faster in bacteria than in eukaryotes,"},{"Start":"01:52.235 ","End":"01:56.905","Text":"about by a factor of 10 when compared with human cells."},{"Start":"01:56.905 ","End":"02:01.025","Text":"However, the overall mechanism is not"},{"Start":"02:01.025 ","End":"02:05.060","Text":"different really in prokaryotes and eukaryotes and therefore,"},{"Start":"02:05.060 ","End":"02:10.115","Text":"prokaryotes are a good model system to study replication."},{"Start":"02:10.115 ","End":"02:14.035","Text":"Again, this is the diagram that we saw earlier,"},{"Start":"02:14.035 ","End":"02:16.610","Text":"and so while the leading slant strand is continuously"},{"Start":"02:16.610 ","End":"02:20.285","Text":"synthesized by the enzyme polymerase Delta,"},{"Start":"02:20.285 ","End":"02:25.205","Text":"the lagging strand now is synthesized by polymerase Epsilon."},{"Start":"02:25.205 ","End":"02:30.770","Text":"That\u0027s another difference that there is between prokaryotes and eukaryotes."},{"Start":"02:30.770 ","End":"02:34.880","Text":"Then there\u0027s this sliding clamp that we talked about,"},{"Start":"02:34.880 ","End":"02:38.640","Text":"it actually has something that sits here."},{"Start":"02:38.640 ","End":"02:43.700","Text":"It\u0027s a ring of proteins which sits over the area where the replication"},{"Start":"02:43.700 ","End":"02:49.205","Text":"takes place over the replication fork which holds the DNA polymerases in place."},{"Start":"02:49.205 ","End":"02:55.010","Text":"As polymerase Delta runs into the primer on the lagging strands,"},{"Start":"02:55.010 ","End":"02:59.960","Text":"it displaces it from the DNA template and it"},{"Start":"02:59.960 ","End":"03:04.865","Text":"is digested by RNAs H as we had mentioned before."},{"Start":"03:04.865 ","End":"03:09.410","Text":"The displaced RNA then is replaced with DNA nucleotides."},{"Start":"03:09.410 ","End":"03:13.790","Text":"The Okazaki fragments are joined together by a ligase in"},{"Start":"03:13.790 ","End":"03:18.755","Text":"a very similar way that they are in prokaryotes."},{"Start":"03:18.755 ","End":"03:24.470","Text":"This is the ligase. There\u0027s a big difference"},{"Start":"03:24.470 ","End":"03:27.690","Text":"between chromosomes in prokaryotes and eukaryotes."},{"Start":"03:27.690 ","End":"03:33.485","Text":"The big difference is that prokaryotes usually have circular chromosomes,"},{"Start":"03:33.485 ","End":"03:38.480","Text":"but in eukaryotes the chromosomes are linear."},{"Start":"03:38.480 ","End":"03:47.885","Text":"So that presents a problem because DNA can add nucleotides only in the 5\u0027-3\u0027 direction."},{"Start":"03:47.885 ","End":"03:52.460","Text":"They are always adding something,"},{"Start":"03:52.460 ","End":"04:00.125","Text":"5\u0027-3\u0027 and that creates a problem at the very ends."},{"Start":"04:00.125 ","End":"04:03.260","Text":"Now let\u0027s see why. Because in the lagging strand there\u0027s"},{"Start":"04:03.260 ","End":"04:06.960","Text":"no way to replace the primer at the 5\u0027 end."},{"Start":"04:06.960 ","End":"04:11.765","Text":"The primer, you\u0027ll remember always starts further down"},{"Start":"04:11.765 ","End":"04:17.345","Text":"on the fragment or if it can\u0027t start further down on the fragment,"},{"Start":"04:17.345 ","End":"04:22.970","Text":"then what\u0027s going to happen is that the DNA at the ends of the chromosome,"},{"Start":"04:22.970 ","End":"04:24.890","Text":"that\u0027s called the telomeres,"},{"Start":"04:24.890 ","End":"04:28.115","Text":"they will remain unpaired."},{"Start":"04:28.115 ","End":"04:31.790","Text":"The solution to that will be that something"},{"Start":"04:31.790 ","End":"04:36.475","Text":"called telomeres specialized structures will be formed,"},{"Start":"04:36.475 ","End":"04:39.680","Text":"and if they\u0027re not formed then the ends will get"},{"Start":"04:39.680 ","End":"04:43.115","Text":"progressively shorter as cells continue to divide."},{"Start":"04:43.115 ","End":"04:49.175","Text":"Of course, in prokaryotes is not a problem because they have these circular chromosomes."},{"Start":"04:49.175 ","End":"04:52.445","Text":"Now let\u0027s see what is it that\u0027s added to the ends."},{"Start":"04:52.445 ","End":"04:54.755","Text":"It\u0027s, as I mentioned, a telomere."},{"Start":"04:54.755 ","End":"05:01.880","Text":"It\u0027s the addition of certain nucleotides that do not encode anything in particular."},{"Start":"05:01.880 ","End":"05:03.425","Text":"In humans in fact,"},{"Start":"05:03.425 ","End":"05:08.320","Text":"the sequence that\u0027s added is TTAGGG,"},{"Start":"05:08.320 ","End":"05:13.745","Text":"and it\u0027s repeated many times, 100-1,000 times."},{"Start":"05:13.745 ","End":"05:17.285","Text":"It is added by a telomerase."},{"Start":"05:17.285 ","End":"05:21.155","Text":"It is added by a particular enzyme that adds"},{"Start":"05:21.155 ","End":"05:26.564","Text":"this particular sequence by just attaching it to the end."},{"Start":"05:26.564 ","End":"05:33.020","Text":"This protects the genes from getting shorter as the cells continue to divide."},{"Start":"05:33.020 ","End":"05:36.665","Text":"As we mentioned, this is the enzyme telomerase,"},{"Start":"05:36.665 ","End":"05:38.974","Text":"which adds these pieces."},{"Start":"05:38.974 ","End":"05:43.160","Text":"It\u0027s interesting though that this telomerase knows how to"},{"Start":"05:43.160 ","End":"05:47.630","Text":"add this TTAGGG sequence because as"},{"Start":"05:47.630 ","End":"05:56.225","Text":"part of the enzyme it contains an RNA template which is homologous to the TTAGGG,"},{"Start":"05:56.225 ","End":"06:03.235","Text":"and therefore it can polymerize this particular sequence over and over."},{"Start":"06:03.235 ","End":"06:12.495","Text":"These telomerase attach at these telomeres to the end of this sequence,"},{"Start":"06:12.495 ","End":"06:14.580","Text":"and it attaches to the end of the chromosome,"},{"Start":"06:14.580 ","End":"06:17.990","Text":"and the DNA nucleotides complimentary to the RNA are added"},{"Start":"06:17.990 ","End":"06:21.790","Text":"on the 3\u0027 end of the DNA strand,"},{"Start":"06:21.790 ","End":"06:27.890","Text":"such that once the 3\u0027 end of the lagging strand is sufficiently elongated,"},{"Start":"06:27.890 ","End":"06:29.855","Text":"so now it increases,"},{"Start":"06:29.855 ","End":"06:32.820","Text":"it adds to the 3\u0027 end."},{"Start":"06:32.820 ","End":"06:35.250","Text":"It adds this additional piece."},{"Start":"06:35.250 ","End":"06:40.265","Text":"DNA polymerase now can add a regular primer,"},{"Start":"06:40.265 ","End":"06:46.450","Text":"as you can see here and fill in the end of the chromosome."},{"Start":"06:46.450 ","End":"06:51.650","Text":"This is the way that the chromosomes are replicated."},{"Start":"06:51.650 ","End":"06:54.320","Text":"Now interestingly, in most cells,"},{"Start":"06:54.320 ","End":"07:01.158","Text":"the telomeres get shorter as the somatic cells do not make telomerase."},{"Start":"07:01.158 ","End":"07:03.695","Text":"As the somatic cells divide,"},{"Start":"07:03.695 ","End":"07:06.710","Text":"the telomeres that you can see here on the end,"},{"Start":"07:06.710 ","End":"07:12.025","Text":"actually get shorter and shorter with aging and"},{"Start":"07:12.025 ","End":"07:18.220","Text":"thus people thought that maybe the shortening is a measure of age."},{"Start":"07:18.220 ","End":"07:23.870","Text":"In fact in 2010 and experiment was done in which they reversed"},{"Start":"07:23.870 ","End":"07:29.870","Text":"this shortening by increasing the amount of telomerase in some mice,"},{"Start":"07:29.870 ","End":"07:34.160","Text":"and they found that some of the age-related conditions in"},{"Start":"07:34.160 ","End":"07:38.975","Text":"mice could be reversed by making the telomeres longer."},{"Start":"07:38.975 ","End":"07:46.100","Text":"Of course, this may have potential in regenerative medicine and reversal of aging."},{"Start":"07:46.100 ","End":"07:48.830","Text":"It\u0027s an exciting idea, but in fact,"},{"Start":"07:48.830 ","End":"07:52.015","Text":"it turns out to be significantly more complicated than that,"},{"Start":"07:52.015 ","End":"07:58.280","Text":"and there is not a uniformity of opinion in the field about whether"},{"Start":"07:58.280 ","End":"08:05.390","Text":"telomerase is really the core or the lack of telomerase is the cause of aging,"},{"Start":"08:05.390 ","End":"08:06.950","Text":"the shortening of these telomeres,"},{"Start":"08:06.950 ","End":"08:10.320","Text":"or whether it\u0027s a combination with something else."}],"ID":28173},{"Watched":false,"Name":"First steps in Eukaryotic DNA replication","Duration":"5m 16s","ChapterTopicVideoID":27046,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.290 ","End":"00:08.100","Text":"Welcome back. We\u0027ve been discussing DNA replication in prokaryotes till now."},{"Start":"00:08.100 ","End":"00:11.730","Text":"Now, let\u0027s see what happens in eukaryotes."},{"Start":"00:11.730 ","End":"00:14.820","Text":"Yes, unlike in prokaryotes,"},{"Start":"00:14.820 ","End":"00:18.300","Text":"eukaryotes have several different linear chromosomes."},{"Start":"00:18.300 ","End":"00:22.545","Text":"You\u0027ll remember that in prokaryotes we had 1 chromosome,"},{"Start":"00:22.545 ","End":"00:26.865","Text":"usually with 1 origin of replication."},{"Start":"00:26.865 ","End":"00:32.655","Text":"However, in eukaryotes, there is a problem because for instance,"},{"Start":"00:32.655 ","End":"00:42.635","Text":"in humans, there are about 6 billion base pairs that are replicated during the S phase."},{"Start":"00:42.635 ","End":"00:48.004","Text":"You\u0027ll remember also that the DNA is replicated more slowly,"},{"Start":"00:48.004 ","End":"00:50.060","Text":"about tenfold more slowly."},{"Start":"00:50.060 ","End":"00:55.415","Text":"In order to have all the DNA replicated during the S phase,"},{"Start":"00:55.415 ","End":"00:59.300","Text":"then what happens is that there are about or"},{"Start":"00:59.300 ","End":"01:03.140","Text":"up to about a 100,000 origins of replication."},{"Start":"01:03.140 ","End":"01:06.500","Text":"Not 1, but up to about a 100,000 that are"},{"Start":"01:06.500 ","End":"01:10.675","Text":"across the genome on the different chromosomes."},{"Start":"01:10.675 ","End":"01:19.485","Text":"What that does is that it allows the entire genome to be replicated during the S phase."},{"Start":"01:19.485 ","End":"01:23.865","Text":"Here you can see in this figure there are 2 origins of replication."},{"Start":"01:23.865 ","End":"01:26.069","Text":"There was 1 here and 1 here,"},{"Start":"01:26.069 ","End":"01:28.125","Text":"making 2 replication forks,"},{"Start":"01:28.125 ","End":"01:32.600","Text":"and they will then meet each other as replication occurs."},{"Start":"01:32.600 ","End":"01:34.300","Text":"That\u0027s what we can see here."},{"Start":"01:34.300 ","End":"01:39.065","Text":"Then of course afterwards the sister chromatids are going to be separated during mitosis."},{"Start":"01:39.065 ","End":"01:44.480","Text":"Remembering also that the rate of replication is much slower in eukaryotes,"},{"Start":"01:44.480 ","End":"01:50.420","Text":"than it is in prokaryotes but there are additional things to consider."},{"Start":"01:50.420 ","End":"01:52.220","Text":"There are additional problems."},{"Start":"01:52.220 ","End":"01:55.550","Text":"For instance, you\u0027ll remember that in eukaryotes,"},{"Start":"01:55.550 ","End":"01:58.715","Text":"the DNA in eukaryotes is packaged in"},{"Start":"01:58.715 ","End":"02:03.510","Text":"nucleosomes and then there\u0027s further higher level of packaging as well."},{"Start":"02:03.510 ","End":"02:06.710","Text":"So the replication has to deal with all this packaging,"},{"Start":"02:06.710 ","End":"02:10.475","Text":"is going to have to open all these packages and then"},{"Start":"02:10.475 ","End":"02:15.130","Text":"close them again as the replication machinery passes."},{"Start":"02:15.130 ","End":"02:17.659","Text":"Before replication can start,"},{"Start":"02:17.659 ","End":"02:22.114","Text":"even the DNA has to be made available as a template."},{"Start":"02:22.114 ","End":"02:24.440","Text":"Because as we mentioned,"},{"Start":"02:24.440 ","End":"02:27.230","Text":"eukaryotic DNA forms these nucleosomes that must be"},{"Start":"02:27.230 ","End":"02:31.070","Text":"removed and then replaced during the replication process."},{"Start":"02:31.070 ","End":"02:35.590","Text":"That certainly lowers the replication rate."},{"Start":"02:35.590 ","End":"02:38.574","Text":"Let\u0027s look at what the differences are,"},{"Start":"02:38.574 ","End":"02:41.870","Text":"some of the smaller differences actually that there are between"},{"Start":"02:41.870 ","End":"02:46.150","Text":"prokaryotic and eukaryotic DNA replication."},{"Start":"02:46.150 ","End":"02:49.890","Text":"First of all, in eukaryotes at the origin replication,"},{"Start":"02:49.890 ","End":"02:54.440","Text":"there is something called a pre-replication complex that is made"},{"Start":"02:54.440 ","End":"02:59.825","Text":"with various initiator proteins that are not found in bacteria."},{"Start":"02:59.825 ","End":"03:04.430","Text":"The formation of the pre-replication complex is"},{"Start":"03:04.430 ","End":"03:09.050","Text":"definitely required for this replication to occur."},{"Start":"03:09.050 ","End":"03:12.110","Text":"Then there is the helicase and there are other proteins that are"},{"Start":"03:12.110 ","End":"03:15.885","Text":"recruited to start the replication process."},{"Start":"03:15.885 ","End":"03:20.960","Text":"You can see here that we have various proteins that we\u0027ve not discussed before that are"},{"Start":"03:20.960 ","End":"03:29.420","Text":"important in each of these replication initiation sites."},{"Start":"03:29.420 ","End":"03:31.958","Text":"Yes, these initiator proteins."},{"Start":"03:31.958 ","End":"03:37.280","Text":"They together are something that are called a replisome complex."},{"Start":"03:37.280 ","End":"03:41.780","Text":"The entire complex that contains all the various proteins that are necessary"},{"Start":"03:41.780 ","End":"03:46.735","Text":"for replication is called a replisome."},{"Start":"03:46.735 ","End":"03:49.610","Text":"Let\u0027s now look at the differences between"},{"Start":"03:49.610 ","End":"03:54.770","Text":"DNA replication in prokaryotes and eukaryotes in a simplistic form."},{"Start":"03:54.770 ","End":"03:57.980","Text":"First of all, in prokaryotes it\u0027s only 1 origin replication,"},{"Start":"03:57.980 ","End":"04:00.095","Text":"whereas in eukaryotes there are multiple ones."},{"Start":"04:00.095 ","End":"04:01.280","Text":"The speed is different."},{"Start":"04:01.280 ","End":"04:04.685","Text":"The rate of replication is quite different in the two of them."},{"Start":"04:04.685 ","End":"04:08.945","Text":"The numbers of different DNA polymerases is different."},{"Start":"04:08.945 ","End":"04:13.370","Text":"We discussed only 2 different DNA polymerases in prokaryotes,"},{"Start":"04:13.370 ","End":"04:14.539","Text":"and some of them, they have more,"},{"Start":"04:14.539 ","End":"04:15.830","Text":"up to about 5."},{"Start":"04:15.830 ","End":"04:17.390","Text":"In eukaryotes, there are many more,"},{"Start":"04:17.390 ","End":"04:22.175","Text":"up to about 14 different DNA polymerases."},{"Start":"04:22.175 ","End":"04:26.480","Text":"The telomerase is not present in prokaryotes."},{"Start":"04:26.480 ","End":"04:27.890","Text":"We\u0027ll get to that in a minute."},{"Start":"04:27.890 ","End":"04:33.005","Text":"In eukaryotes it is, that has to do with what happens at the ends of the chromosomes."},{"Start":"04:33.005 ","End":"04:39.605","Text":"The RNA primer is removed by DNA pol I in prokaryotes, as we mentioned."},{"Start":"04:39.605 ","End":"04:44.765","Text":"In eukaryotes, it\u0027s called RNase H. It\u0027s actually not a polymerase,"},{"Start":"04:44.765 ","End":"04:48.600","Text":"it is an enzyme called RNase H,"},{"Start":"04:48.600 ","End":"04:52.395","Text":"so it destroys RNA that is double-stranded."},{"Start":"04:52.395 ","End":"04:54.980","Text":"The elongation of the DNA,"},{"Start":"04:54.980 ","End":"04:57.695","Text":"the main strand elongation of the DNA"},{"Start":"04:57.695 ","End":"05:02.075","Text":"is of course done by DNA polymerase III in prokaryotes,"},{"Start":"05:02.075 ","End":"05:07.970","Text":"whereas in eukaryotes, there are numerous polymerases."},{"Start":"05:07.970 ","End":"05:11.975","Text":"Actually, there are 3 polymerases that are given Greek letters,"},{"Start":"05:11.975 ","End":"05:16.320","Text":"Alpha, Delta, and Epsilon."}],"ID":28174},{"Watched":false,"Name":"Historical Basis of Modern Understanding Part a","Duration":"9m ","ChapterTopicVideoID":27047,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.635","Text":"Now we\u0027re going to continue studying DNA structure and function."},{"Start":"00:04.635 ","End":"00:12.315","Text":"We\u0027re going to focus on the historical basis of the modern understanding of DNA,"},{"Start":"00:12.315 ","End":"00:14.430","Text":"try to understand the history."},{"Start":"00:14.430 ","End":"00:15.690","Text":"By the end of this section,"},{"Start":"00:15.690 ","End":"00:18.330","Text":"you\u0027ll be able to explain transformation of DNA,"},{"Start":"00:18.330 ","End":"00:22.440","Text":"something that was discovered in the course of understanding DNA."},{"Start":"00:22.440 ","End":"00:27.780","Text":"Describe the key experiments that help identify DNA as the genetic material."},{"Start":"00:27.780 ","End":"00:32.325","Text":"Finally, state and explain Chargaff\u0027s rules."},{"Start":"00:32.325 ","End":"00:37.035","Text":"Chargaff\u0027s rules they help to explain something about the function of the DNA."},{"Start":"00:37.035 ","End":"00:44.640","Text":"Let\u0027s start with Johannes Friedrich Miescher in 1869."},{"Start":"00:44.640 ","End":"00:47.925","Text":"He was a Swiss physician and biologist."},{"Start":"00:47.925 ","End":"00:52.500","Text":"He isolated some phosphates-rich chemicals that he"},{"Start":"00:52.500 ","End":"00:57.515","Text":"called nuclein from white blood cells, from leukocytes."},{"Start":"00:57.515 ","End":"01:01.010","Text":"Of course, we know now that DNA has lots of phosphate in it."},{"Start":"01:01.010 ","End":"01:04.490","Text":"That\u0027s what he was isolating."},{"Start":"01:04.490 ","End":"01:09.911","Text":"It was the first time that someone had some DNA in their hand,"},{"Start":"01:09.911 ","End":"01:14.180","Text":"wasn\u0027t quite isolated as clean as it would be now,"},{"Start":"01:14.180 ","End":"01:16.070","Text":"but this isolation procedure,"},{"Start":"01:16.070 ","End":"01:19.565","Text":"that Miescher did was very formative."},{"Start":"01:19.565 ","End":"01:25.210","Text":"He, therefore, was the first to identify DNA as a distinct molecule."},{"Start":"01:25.210 ","End":"01:27.410","Text":"He didn\u0027t know yet what it does."},{"Start":"01:27.410 ","End":"01:32.375","Text":"This was then the discovery of nucleic acids and"},{"Start":"01:32.375 ","End":"01:38.640","Text":"the DNA that he isolated was from the nucleus of a cell."},{"Start":"01:38.990 ","End":"01:44.965","Text":"That was a major contribution to discovery of the genetic code."},{"Start":"01:44.965 ","End":"01:50.220","Text":"Next was Frederick Griffith in 1928."},{"Start":"01:50.220 ","End":"01:52.125","Text":"Quite a long time passed."},{"Start":"01:52.125 ","End":"01:56.620","Text":"He was the first to demonstrate something called transformation."},{"Start":"01:56.620 ","End":"02:01.055","Text":"He was a term that he gave that was called transformation."},{"Start":"02:01.055 ","End":"02:07.235","Text":"He showed that bacteria are capable of transferring genetic information."},{"Start":"02:07.235 ","End":"02:09.970","Text":"This was done with bacteria."},{"Start":"02:09.970 ","End":"02:13.335","Text":"He used 2 bacterial strains."},{"Start":"02:13.335 ","End":"02:17.660","Text":"There were 2 strains of pneumococcus of a bacterium"},{"Start":"02:17.660 ","End":"02:21.770","Text":"that caused basically pneumonia in mice and killed them."},{"Start":"02:21.770 ","End":"02:27.020","Text":"One of these strains was rough in the sense that the colonies"},{"Start":"02:27.020 ","End":"02:29.975","Text":"were of this bacterium when they were plated on"},{"Start":"02:29.975 ","End":"02:33.110","Text":"agar were rough and they weren\u0027t non-pathogenic,"},{"Start":"02:33.110 ","End":"02:34.610","Text":"they don\u0027t cause disease."},{"Start":"02:34.610 ","End":"02:40.255","Text":"Then there was another pathogenic one which created smooth colonies."},{"Start":"02:40.255 ","End":"02:43.895","Text":"The reason was that those had a capsule outside"},{"Start":"02:43.895 ","End":"02:49.330","Text":"the cell wall and that can be seen that this capsule was made of various carbohydrates."},{"Start":"02:49.330 ","End":"02:55.055","Text":"When mice were injected with the living S strain, they died."},{"Start":"02:55.055 ","End":"02:56.980","Text":"I said it was disease-causing."},{"Start":"02:56.980 ","End":"02:58.948","Text":"They died of pneumonia,"},{"Start":"02:58.948 ","End":"03:02.460","Text":"but the R injected mice survived."},{"Start":"03:02.460 ","End":"03:04.445","Text":"That\u0027s what we can see here in the picture."},{"Start":"03:04.445 ","End":"03:07.910","Text":"The S cells caused the mice to die,"},{"Start":"03:07.910 ","End":"03:12.485","Text":"whereas the R cells had no effect on the mice."},{"Start":"03:12.485 ","End":"03:15.575","Text":"Now, the next thing he did, Griffith,"},{"Start":"03:15.575 ","End":"03:20.770","Text":"was that he heat-killed the living S cells."},{"Start":"03:20.770 ","End":"03:23.645","Text":"Remember, they had caused the mouse to die,"},{"Start":"03:23.645 ","End":"03:26.135","Text":"but when he killed those bacteria,"},{"Start":"03:26.135 ","End":"03:30.460","Text":"maybe not surprisingly, the mice did not die."},{"Start":"03:30.460 ","End":"03:38.000","Text":"Up to here, nothing really is particularly interesting and doesn\u0027t really relate to DNA."},{"Start":"03:38.000 ","End":"03:41.015","Text":"However, in a third set of experiments,"},{"Start":"03:41.015 ","End":"03:47.810","Text":"what he did is he took mice that were injected with a mixture of live R strains,"},{"Start":"03:47.810 ","End":"03:49.865","Text":"the ones that keep them healthy,"},{"Start":"03:49.865 ","End":"03:52.025","Text":"and the heat killed S strain,"},{"Start":"03:52.025 ","End":"03:55.205","Text":"which also made them healthy."},{"Start":"03:55.205 ","End":"03:57.410","Text":"When he made this mixture,"},{"Start":"03:57.410 ","End":"03:58.985","Text":"the mice did die."},{"Start":"03:58.985 ","End":"04:04.565","Text":"Now notice each of them individually did not make the mice die, and furthermore,"},{"Start":"04:04.565 ","End":"04:10.410","Text":"the bacteria that he recovered from these mice,"},{"Start":"04:10.850 ","End":"04:15.455","Text":"were S strain bacteria."},{"Start":"04:15.455 ","End":"04:19.835","Text":"S strain bacteria, the ones that caused mice to die,"},{"Start":"04:19.835 ","End":"04:23.755","Text":"they were smooth when he plated them on plates."},{"Start":"04:23.755 ","End":"04:28.100","Text":"When this isolated S strain was injected into fresh mice now,"},{"Start":"04:28.100 ","End":"04:32.345","Text":"it was just like any other S strain, the mice died."},{"Start":"04:32.345 ","End":"04:36.410","Text":"What he said was that something had passed from"},{"Start":"04:36.410 ","End":"04:40.670","Text":"the heat killed S strain into the live R strain,"},{"Start":"04:40.670 ","End":"04:44.440","Text":"we know now that that was DNA and transformed it,"},{"Start":"04:44.440 ","End":"04:46.500","Text":"use that word transformed,"},{"Start":"04:46.500 ","End":"04:49.605","Text":"it transformed it into the pathogenic S strain."},{"Start":"04:49.605 ","End":"04:53.640","Text":"He called this the transforming principle."},{"Start":"04:53.640 ","End":"04:59.705","Text":"Now there was another scientist named Avery a bit later in 1944."},{"Start":"04:59.705 ","End":"05:05.485","Text":"His group was interested in exploring this transforming principle a bit further."},{"Start":"05:05.485 ","End":"05:10.160","Text":"He wanted to know what was it that was causing this transformation?"},{"Start":"05:10.160 ","End":"05:12.020","Text":"Was it polysaccharide?"},{"Start":"05:12.020 ","End":"05:13.685","Text":"Was it lipid?"},{"Start":"05:13.685 ","End":"05:16.520","Text":"Was it RNA? Was it protein?"},{"Start":"05:16.520 ","End":"05:19.369","Text":"Or was it DNA?"},{"Start":"05:19.369 ","End":"05:23.450","Text":"What he did is he isolated protein, RNA,"},{"Start":"05:23.450 ","End":"05:27.470","Text":"and DNA of the S strain from dead mice,"},{"Start":"05:27.470 ","End":"05:32.545","Text":"and then he used enzymes that specifically degraded each component."},{"Start":"05:32.545 ","End":"05:38.465","Text":"He used each mixture separately to transform the R strain."},{"Start":"05:38.465 ","End":"05:40.385","Text":"Remember it\u0027s the S strain,"},{"Start":"05:40.385 ","End":"05:42.455","Text":"which is the one that\u0027s virulent."},{"Start":"05:42.455 ","End":"05:46.100","Text":"That\u0027s where he got all these components and he used it to transform."},{"Start":"05:46.100 ","End":"05:50.195","Text":"He mixed all these components with the R strain. What did he get?"},{"Start":"05:50.195 ","End":"05:52.985","Text":"He got that when the DNA was degraded,"},{"Start":"05:52.985 ","End":"05:55.250","Text":"only the DNA was degraded,"},{"Start":"05:55.250 ","End":"05:57.680","Text":"he had enzymes against all these other things,"},{"Start":"05:57.680 ","End":"06:02.195","Text":"the resulting mixture was no longer able to transform the bacteria."},{"Start":"06:02.195 ","End":"06:08.300","Text":"Since it was the DNA when destroyed did not allow recovery of the S strain,"},{"Start":"06:08.300 ","End":"06:14.275","Text":"then the transforming principle must have been the DNA."},{"Start":"06:14.275 ","End":"06:18.710","Text":"However, there was a lot of skepticism about this because DNA"},{"Start":"06:18.710 ","End":"06:23.390","Text":"after all was a rather simple molecule or so it seemed,"},{"Start":"06:23.390 ","End":"06:28.570","Text":"because it only carried really 4 different sub-units,"},{"Start":"06:28.570 ","End":"06:30.665","Text":"as we\u0027ll learn a little bit later,"},{"Start":"06:30.665 ","End":"06:34.220","Text":"whereas proteins people thought was a better candidate to be"},{"Start":"06:34.220 ","End":"06:39.115","Text":"the genetic material since it had 20 different sub-units called amino acids."},{"Start":"06:39.115 ","End":"06:43.700","Text":"That was more likely to be what the people thought,"},{"Start":"06:43.700 ","End":"06:48.025","Text":"at least that would be the more likely candidate for the genetic material."},{"Start":"06:48.025 ","End":"06:52.400","Text":"Along came Hershey and Chase, Alfred Hershey,"},{"Start":"06:52.400 ","End":"06:56.595","Text":"and Martha Chase that are pictured here in 1952."},{"Start":"06:56.595 ","End":"06:59.450","Text":"They were studying bacteriophages."},{"Start":"06:59.450 ","End":"07:03.770","Text":"Bacteriophages are viruses that infect bacteria."},{"Start":"07:03.770 ","End":"07:12.530","Text":"What they did is they knew that DNA contains phosphate in it,"},{"Start":"07:12.530 ","End":"07:20.465","Text":"contains phosphorus molecule, and they also knew that proteins had sulfur in them."},{"Start":"07:20.465 ","End":"07:23.615","Text":"But DNA did not have sulfur in it,"},{"Start":"07:23.615 ","End":"07:28.010","Text":"and proteins did not have phosphorous in them."},{"Start":"07:28.010 ","End":"07:30.420","Text":"Now, we\u0027re talking about 1952."},{"Start":"07:30.420 ","End":"07:33.800","Text":"1952 is already in the atomic age."},{"Start":"07:33.800 ","End":"07:41.130","Text":"Remember the atomic bomb was dropped on Japan 7 years earlier."},{"Start":"07:41.130 ","End":"07:46.290","Text":"It was possible then to radio-label sulfur,"},{"Start":"07:46.290 ","End":"07:50.610","Text":"that is to make it radioactive S-35,"},{"Start":"07:50.610 ","End":"07:55.345","Text":"and the same thing with phosphorus to use P-32."},{"Start":"07:55.345 ","End":"08:03.645","Text":"Those things could label the protein or the DNA differentially. Here\u0027s what they did."},{"Start":"08:03.645 ","End":"08:06.285","Text":"They did 2 experiments."},{"Start":"08:06.285 ","End":"08:14.065","Text":"One is they labeled the bacteriophage either with S-35 or with P-32."},{"Start":"08:14.065 ","End":"08:17.590","Text":"Then they looked to see what was in"},{"Start":"08:17.590 ","End":"08:22.940","Text":"the cells that might sink after bacteria were infected."},{"Start":"08:22.940 ","End":"08:26.600","Text":"In other words, did the material that was labeled go"},{"Start":"08:26.600 ","End":"08:31.745","Text":"into the bacteria or did it stay on the outside?"},{"Start":"08:31.745 ","End":"08:35.495","Text":"In other words, was it in the supermanant?"},{"Start":"08:35.495 ","End":"08:39.170","Text":"What they found was that only P-32,"},{"Start":"08:39.170 ","End":"08:41.750","Text":"that is the DNA,"},{"Start":"08:41.750 ","End":"08:44.345","Text":"then enter the bacterial cells."},{"Start":"08:44.345 ","End":"08:48.829","Text":"That then was the most important experiments"},{"Start":"08:48.829 ","End":"08:53.765","Text":"that indicated that DNA is the genetic material."},{"Start":"08:53.765 ","End":"09:00.180","Text":"Then we\u0027ll look at the following experiments in the next video."}],"ID":28175},{"Watched":false,"Name":"Historical Basis of Modern Understanding Part b","Duration":"2m 30s","ChapterTopicVideoID":27048,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:03.420","Text":"About the same time, Erwin Chargaff,"},{"Start":"00:03.420 ","End":"00:10.155","Text":"that\u0027s in 1950, examined the content of DNA in different species."},{"Start":"00:10.155 ","End":"00:19.875","Text":"He found that there was a very interesting rule that he could make and that was"},{"Start":"00:19.875 ","End":"00:30.164","Text":"that we know that there are 4 different components for different nucleotides in DNA."},{"Start":"00:30.164 ","End":"00:32.069","Text":"That is, there\u0027s,"},{"Start":"00:32.069 ","End":"00:34.755","Text":"A, adenine, there\u0027s guanine."},{"Start":"00:34.755 ","End":"00:37.005","Text":"Adenine and guanine are,"},{"Start":"00:37.005 ","End":"00:43.575","Text":"each of them are called purines because they have this structure in their basis."},{"Start":"00:43.575 ","End":"00:47.030","Text":"In addition to that, there is thymine, T,"},{"Start":"00:47.030 ","End":"00:50.225","Text":"and cytosine that are called pyrimidines,"},{"Start":"00:50.225 ","End":"00:52.985","Text":"or we have A and G for short."},{"Start":"00:52.985 ","End":"00:54.635","Text":"Those are the purines,"},{"Start":"00:54.635 ","End":"00:57.230","Text":"and we have T and C for short,"},{"Start":"00:57.230 ","End":"00:58.564","Text":"those are the pyrimidines."},{"Start":"00:58.564 ","End":"01:06.710","Text":"What Chargaff saw and understood was that A plus G In other words,"},{"Start":"01:06.710 ","End":"01:11.840","Text":"the number of purines was always equal to the number of"},{"Start":"01:11.840 ","End":"01:17.810","Text":"pyrimidines in DNA that he extracted from any species."},{"Start":"01:17.810 ","End":"01:21.140","Text":"The DNAs based composition, however,"},{"Start":"01:21.140 ","End":"01:27.035","Text":"varies from one species to the next but the rule is always the same."},{"Start":"01:27.035 ","End":"01:36.960","Text":"The rule was that the amount of A equals T and the amount of G always equals C. Now,"},{"Start":"01:36.960 ","End":"01:40.335","Text":"that is really interesting."},{"Start":"01:40.335 ","End":"01:45.890","Text":"Those rules were the basis then for what"},{"Start":"01:45.890 ","End":"01:51.500","Text":"Watson and Crick revealed by looking at some X-ray crystallography."},{"Start":"01:51.500 ","End":"01:56.740","Text":"That\u0027s a technique in which we can look at structure of a molecule."},{"Start":"01:56.740 ","End":"02:04.425","Text":"They had this insights already that A equals T and G is equal C and help them"},{"Start":"02:04.425 ","End":"02:12.180","Text":"understand the structure that they deduced from X-ray cystography."},{"Start":"02:12.180 ","End":"02:14.174","Text":"Now, in this section,"},{"Start":"02:14.174 ","End":"02:18.600","Text":"we learnt how to explain transformation of DNA,"},{"Start":"02:18.600 ","End":"02:23.355","Text":"describe the key experiment that helped identify that DNA is a genetic material"},{"Start":"02:23.355 ","End":"02:30.220","Text":"and we know to state and explain Chargaff\u0027s rules."}],"ID":28176},{"Watched":false,"Name":"Initiation of DNA replication","Duration":"6m 37s","ChapterTopicVideoID":27049,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:06.015","Text":"Hi there. We\u0027ve been discussing the structure of DNA,"},{"Start":"00:06.015 ","End":"00:11.010","Text":"and now what we\u0027d like to do is to see how it\u0027s replicated."},{"Start":"00:11.010 ","End":"00:17.985","Text":"What are the steps and what are the enzymes that are required to replicate DNA?"},{"Start":"00:17.985 ","End":"00:22.950","Text":"To start with, we\u0027ll look at prokaryotes, that is bacteria,"},{"Start":"00:22.950 ","End":"00:28.065","Text":"because in prokaryotes the system is a little bit simpler than it is in eukaryotes,"},{"Start":"00:28.065 ","End":"00:30.240","Text":"but the basics are the same."},{"Start":"00:30.240 ","End":"00:32.549","Text":"In E. coli, for example,"},{"Start":"00:32.549 ","End":"00:36.600","Text":"which is the model system for prokaryotes that\u0027s typically been used,"},{"Start":"00:36.600 ","End":"00:41.220","Text":"we see that E. coli has about 4.6 million base"},{"Start":"00:41.220 ","End":"00:47.705","Text":"pairs in its DNA and it forms a single circular chromosome,"},{"Start":"00:47.705 ","End":"00:49.715","Text":"as we\u0027ve seen earlier."},{"Start":"00:49.715 ","End":"00:53.090","Text":"Let\u0027s look at what it might look like."},{"Start":"00:53.090 ","End":"00:56.540","Text":"We have a circular double helix,"},{"Start":"00:56.540 ","End":"01:01.100","Text":"which is then going to replicate in some fashion that we\u0027ll describe."},{"Start":"01:01.100 ","End":"01:05.595","Text":"The replication is going to start at"},{"Start":"01:05.595 ","End":"01:11.990","Text":"an origin of replication that you can see here."},{"Start":"01:11.990 ","End":"01:19.730","Text":"That means that the DNA replication enzymes are going to start at"},{"Start":"01:19.730 ","End":"01:23.555","Text":"this origin and they are going to"},{"Start":"01:23.555 ","End":"01:27.984","Text":"add nucleotides in 2 directions, as we\u0027re going to see."},{"Start":"01:27.984 ","End":"01:34.205","Text":"The replication goes both to the left and to the right from this sequence,"},{"Start":"01:34.205 ","End":"01:36.950","Text":"which is the origin application."},{"Start":"01:36.950 ","End":"01:42.275","Text":"There are approximately are a thousand nucleotides that are added per second,"},{"Start":"01:42.275 ","End":"01:45.815","Text":"that\u0027s the speed in E. coli,"},{"Start":"01:45.815 ","End":"01:49.040","Text":"and the processes quite rapid, therefore,"},{"Start":"01:49.040 ","End":"01:52.400","Text":"and occurs without many mistakes being made."},{"Start":"01:52.400 ","End":"01:56.005","Text":"There are some mistakes made, but not many."},{"Start":"01:56.005 ","End":"02:01.595","Text":"What we see is that replication goes in both directions and so that the new DNA,"},{"Start":"02:01.595 ","End":"02:06.285","Text":"as we\u0027ll see, is being made on both strands,"},{"Start":"02:06.285 ","End":"02:08.690","Text":"so the DNA is replicated."},{"Start":"02:08.690 ","End":"02:10.715","Text":"We\u0027ve got that new strand,"},{"Start":"02:10.715 ","End":"02:14.810","Text":"which is homologous to the old strand both on this top piece and on"},{"Start":"02:14.810 ","End":"02:19.460","Text":"the lower piece, it moves down."},{"Start":"02:19.460 ","End":"02:23.690","Text":"Sometimes this is called a Theta because this structure looks like the Greek letter"},{"Start":"02:23.690 ","End":"02:28.100","Text":"Theta until eventually these 2 replication, for example,"},{"Start":"02:28.100 ","End":"02:33.240","Text":"sides arrive at the bottom and then"},{"Start":"02:33.240 ","End":"02:38.940","Text":"the 2 circles of DNA are resolved one from the other."},{"Start":"02:38.940 ","End":"02:40.589","Text":"Then when the cell divides,"},{"Start":"02:40.589 ","End":"02:48.155","Text":"then 1 chromosome will go into one cell and the other chromosome will go into the other."},{"Start":"02:48.155 ","End":"02:53.150","Text":"Now let\u0027s look at a different representation of the DNA."},{"Start":"02:53.150 ","End":"02:57.995","Text":"We are going to be looking just at area such as this."},{"Start":"02:57.995 ","End":"02:59.885","Text":"That\u0027s a replication fork."},{"Start":"02:59.885 ","End":"03:03.125","Text":"That\u0027s what we see here."},{"Start":"03:03.125 ","End":"03:07.490","Text":"It turns out that there are many enzymes that take part in this replication,"},{"Start":"03:07.490 ","End":"03:09.245","Text":"as we\u0027ll see in a few minutes."},{"Start":"03:09.245 ","End":"03:14.690","Text":"It\u0027s a quite a complicated process."},{"Start":"03:14.690 ","End":"03:19.160","Text":"Some of the enzymes actually are a real enzymes,"},{"Start":"03:19.160 ","End":"03:24.235","Text":"and some of them are structural proteins that hold things together."},{"Start":"03:24.235 ","End":"03:29.955","Text":"The main enzyme that we deal with is called DNA polymerase,"},{"Start":"03:29.955 ","End":"03:34.640","Text":"and it adds nucleotides to the growing chain."},{"Start":"03:34.640 ","End":"03:39.200","Text":"What we\u0027ll see is that there is more than 1 kind of DNA polymerase,"},{"Start":"03:39.200 ","End":"03:44.685","Text":"we\u0027ll talk about DNA polymerase 3 as being the main enzyme."},{"Start":"03:44.685 ","End":"03:47.895","Text":"Here it is DNA polymerase 3."},{"Start":"03:47.895 ","End":"03:52.022","Text":"We\u0027ll talk about another DNA polymerase called DNA polymerase 1,"},{"Start":"03:52.022 ","End":"03:54.890","Text":"they have slightly different functions,"},{"Start":"03:54.890 ","End":"03:59.630","Text":"but both of them add nucleotides to the growing DNA chain."},{"Start":"03:59.630 ","End":"04:06.995","Text":"The energy for this addition comes from the nucleotide triphosphates that are added,"},{"Start":"04:06.995 ","End":"04:10.350","Text":"whether they\u0027d be the ATP, the GTP,"},{"Start":"04:10.350 ","End":"04:13.845","Text":"the TTP, and the CTP."},{"Start":"04:13.845 ","End":"04:19.710","Text":"There\u0027s actually deoxy tri nucleosides that are being added."},{"Start":"04:19.710 ","End":"04:23.790","Text":"Let\u0027s look at it now in greater detail."},{"Start":"04:23.790 ","End":"04:27.294","Text":"First of all, let\u0027s start with the origin replication,"},{"Start":"04:27.294 ","End":"04:31.735","Text":"how does the replication machinery know from where to begin?"},{"Start":"04:31.735 ","End":"04:35.150","Text":"Well, it begins at the specific nucleotide sequence"},{"Start":"04:35.150 ","End":"04:41.090","Text":"that we mentioned earlier that is called the origin of replication,"},{"Start":"04:41.090 ","End":"04:46.663","Text":"it\u0027s this one particular sequence that we saw,"},{"Start":"04:46.663 ","End":"04:51.215","Text":"is in only one position in the E. coli genome."},{"Start":"04:51.215 ","End":"04:56.630","Text":"It is recognized by certain proteins that will bind to"},{"Start":"04:56.630 ","End":"05:03.440","Text":"that site and will facilitate the addition of the other enzymes which are needed,"},{"Start":"05:03.440 ","End":"05:08.015","Text":"and in particular DNA polymerase 3."},{"Start":"05:08.015 ","End":"05:12.665","Text":"In addition, there is this enzyme called helicase."},{"Start":"05:12.665 ","End":"05:16.865","Text":"Helicase, here it\u0027s represented by this green arrow."},{"Start":"05:16.865 ","End":"05:18.512","Text":"Of course, we\u0027ve got 2 origins,"},{"Start":"05:18.512 ","End":"05:22.770","Text":"we\u0027ve got 2 directions, 2 replication forks,"},{"Start":"05:22.770 ","End":"05:29.130","Text":"1 going to the left and 1 going to the right in this diagram."},{"Start":"05:29.130 ","End":"05:37.614","Text":"We have 2 helicase enzymes and their function is to unwind the DNA strands."},{"Start":"05:37.614 ","End":"05:44.045","Text":"Unwind the DNA so that the enzymes that are operating here,"},{"Start":"05:44.045 ","End":"05:48.250","Text":"particularly again, the DNA polymerase, can function."},{"Start":"05:48.250 ","End":"05:54.005","Text":"We have 2 Y-shaped replication forks that are formed at the origin replication,"},{"Start":"05:54.005 ","End":"05:58.130","Text":"and they get extended bi-directionally because we\u0027re going both"},{"Start":"05:58.130 ","End":"06:02.425","Text":"to the left and the right as replication proceeds."},{"Start":"06:02.425 ","End":"06:09.470","Text":"Single-stranded binding proteins that bind to the single-stranded DNA,"},{"Start":"06:09.470 ","End":"06:16.415","Text":"prevent the single-stranded DNA which is created from winding back into a double-helix."},{"Start":"06:16.415 ","End":"06:20.030","Text":"Of course, the double-helix is quite stable because of"},{"Start":"06:20.030 ","End":"06:24.020","Text":"all the hydrogen bonds that there are between the 2 strands."},{"Start":"06:24.020 ","End":"06:30.935","Text":"The single-stranded binding proteins prevent that formation of a double helix again,"},{"Start":"06:30.935 ","End":"06:38.130","Text":"until time comes when the DNA needs to be fully double-stranded."}],"ID":28177},{"Watched":false,"Name":"Mutation types 1","Duration":"5m 56s","ChapterTopicVideoID":27050,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:05.640","Text":"We\u0027ve discussed several different mutations and now we\u0027ll learn about additional kinds."},{"Start":"00:05.640 ","End":"00:08.880","Text":"First of all, there are induced mutations."},{"Start":"00:08.880 ","End":"00:13.950","Text":"That\u0027s the kind that we just discussed in the previous video when we said that they were"},{"Start":"00:13.950 ","End":"00:19.920","Text":"thymine dimers that were created because of UV rays or ultraviolet light,"},{"Start":"00:19.920 ","End":"00:22.575","Text":"but they can result also from exposure or"},{"Start":"00:22.575 ","End":"00:25.829","Text":"different mutations can result from an exposure to chemicals,"},{"Start":"00:25.829 ","End":"00:28.860","Text":"to x-rays, other environmental agents,"},{"Start":"00:28.860 ","End":"00:31.470","Text":"let\u0027s say cigarette smoke."},{"Start":"00:31.470 ","End":"00:38.075","Text":"There can be spontaneous mutations that result just because of simple,"},{"Start":"00:38.075 ","End":"00:40.565","Text":"rare mistakes that the polymerase makes."},{"Start":"00:40.565 ","End":"00:44.990","Text":"Those are natural reactions that take place within the body; spontaneous mutations."},{"Start":"00:44.990 ","End":"00:49.640","Text":"There can be point mutations which change just a single nucleotide,"},{"Start":"00:49.640 ","End":"00:53.075","Text":"and of course, those are usually detrimental."},{"Start":"00:53.075 ","End":"00:59.045","Text":"But occasionally, they can be good and that will be a source"},{"Start":"00:59.045 ","End":"01:05.875","Text":"of evolution that might improve the species over time,"},{"Start":"01:05.875 ","End":"01:08.570","Text":"but that\u0027s an evolutionary scale."},{"Start":"01:08.570 ","End":"01:10.640","Text":"There are frameshift mutations,"},{"Start":"01:10.640 ","End":"01:14.225","Text":"additions or deletions of several nucleotides,"},{"Start":"01:14.225 ","End":"01:15.755","Text":"could be 1 or more,"},{"Start":"01:15.755 ","End":"01:18.445","Text":"that cause a shift in the reading frame."},{"Start":"01:18.445 ","End":"01:25.490","Text":"When DNA is transcribed into RNA and then the RNA is translated into protein,"},{"Start":"01:25.490 ","End":"01:27.500","Text":"there\u0027s something called a reading frame."},{"Start":"01:27.500 ","End":"01:34.805","Text":"Each 3 nucleotides is read into an amino or it\u0027s translated into an amino acid,"},{"Start":"01:34.805 ","End":"01:41.825","Text":"each 3 nucleotides is read independently and encodes 1 amino acid in the protein."},{"Start":"01:41.825 ","End":"01:48.060","Text":"If there\u0027s an additional nucleotide that is inserted or 1 is deleted, then, of course,"},{"Start":"01:48.060 ","End":"01:50.895","Text":"this reading frame will be shifted,"},{"Start":"01:50.895 ","End":"01:54.260","Text":"so those are frameshift mutations."},{"Start":"01:54.260 ","End":"01:58.385","Text":"There are transition substitutions in which"},{"Start":"01:58.385 ","End":"02:02.900","Text":"a purine or pyrimidine is replaced by a base of the same kinds."},{"Start":"02:02.900 ","End":"02:05.720","Text":"In other words, a purine is replaced by a purine or"},{"Start":"02:05.720 ","End":"02:09.290","Text":"pyrimidine is replaced by a pyrimidine, however,"},{"Start":"02:09.290 ","End":"02:17.495","Text":"transversion substitutions or a purine being replaced by a pyrimidine or vice versa."},{"Start":"02:17.495 ","End":"02:22.085","Text":"Now, these mutations can either be silent."},{"Start":"02:22.085 ","End":"02:24.950","Text":"That means those are point mutations which are not"},{"Start":"02:24.950 ","End":"02:28.295","Text":"expressed as changes in the encoded protein."},{"Start":"02:28.295 ","End":"02:34.310","Text":"That means usually that there is a substitution in the third base of a codon."},{"Start":"02:34.310 ","End":"02:39.245","Text":"Remember I said that there was reading of the RNA in 3 \u0027s,"},{"Start":"02:39.245 ","End":"02:41.420","Text":"so here\u0027s 3 \u0027s."},{"Start":"02:41.420 ","End":"02:46.115","Text":"Yes, so each triplet here is red, but there\u0027s redundancy."},{"Start":"02:46.115 ","End":"02:49.715","Text":"Usually, these 3 \u0027s are called a codon."},{"Start":"02:49.715 ","End":"02:55.276","Text":"Usually it doesn\u0027t make much difference what the third nucleotide is in the codon,"},{"Start":"02:55.276 ","End":"02:57.695","Text":"it still will encode the same amino acid."},{"Start":"02:57.695 ","End":"03:01.870","Text":"Silent mutations are those mutations,"},{"Start":"03:01.870 ","End":"03:03.755","Text":"usually in the third codon,"},{"Start":"03:03.755 ","End":"03:07.460","Text":"which will not change the sequence of the protein."},{"Start":"03:07.460 ","End":"03:09.665","Text":"For instance, the protein here was Met,"},{"Start":"03:09.665 ","End":"03:10.805","Text":"Lys, Phe,"},{"Start":"03:10.805 ","End":"03:14.450","Text":"Gly and even after this mutation here,"},{"Start":"03:14.450 ","End":"03:16.325","Text":"we still have Met, Lys Phe, Gly."},{"Start":"03:16.325 ","End":"03:21.380","Text":"The glycine was not changed because it didn\u0027t matter whether at this side we"},{"Start":"03:21.380 ","End":"03:29.615","Text":"had a GC base pair or it\u0027s an AT base pair."},{"Start":"03:29.615 ","End":"03:32.660","Text":"Still, it\u0027s encodes glycine."},{"Start":"03:32.660 ","End":"03:38.485","Text":"Other point mutations can result in the replacement of 1 amino acid by another."},{"Start":"03:38.485 ","End":"03:40.230","Text":"That, of course,"},{"Start":"03:40.230 ","End":"03:43.169","Text":"will change the sequence."},{"Start":"03:43.169 ","End":"03:45.350","Text":"In this case, you can see that there was"},{"Start":"03:45.350 ","End":"03:51.825","Text":"a nuclear pair substitution that will be called a missense mutation."},{"Start":"03:51.825 ","End":"03:59.615","Text":"The A, it was now inserted instead of the G and that did change the amino acid,"},{"Start":"03:59.615 ","End":"04:03.095","Text":"so that\u0027ll be a missense mutation."},{"Start":"04:03.095 ","End":"04:05.160","Text":"There are other mutations."},{"Start":"04:05.160 ","End":"04:08.330","Text":"Nucleotide-pair substitution, the replacement of"},{"Start":"04:08.330 ","End":"04:12.380","Text":"a specific nucleotide by a different pair."},{"Start":"04:12.380 ","End":"04:18.930","Text":"As we mentioned, that can change an amino acid."},{"Start":"04:18.930 ","End":"04:22.925","Text":"In this case, in the molecule of hemoglobin,"},{"Start":"04:22.925 ","End":"04:27.140","Text":"a glutamine is replaced by a valine in"},{"Start":"04:27.140 ","End":"04:32.490","Text":"the protein because of just this 1 point mutation,"},{"Start":"04:32.490 ","End":"04:36.120","Text":"TA to AT,"},{"Start":"04:36.120 ","End":"04:41.440","Text":"and that changes the codon from GAG to GUG."},{"Start":"04:41.440 ","End":"04:43.050","Text":"Therefore, now,"},{"Start":"04:43.050 ","End":"04:47.005","Text":"we have hemoglobin has a valine where before it had a glutamine,"},{"Start":"04:47.005 ","End":"04:51.170","Text":"and that is what causes disease in"},{"Start":"04:51.170 ","End":"04:58.325","Text":"the sickle-cell anemia because the hemoglobin now has a different structure."},{"Start":"04:58.325 ","End":"05:03.830","Text":"Another possibility is nucleotide-pair substitution"},{"Start":"05:03.830 ","End":"05:07.850","Text":"that causes what\u0027s called a nonsense mutation. What is that?"},{"Start":"05:07.850 ","End":"05:10.310","Text":"It\u0027s a substitution of a single base-pair that leads"},{"Start":"05:10.310 ","End":"05:13.040","Text":"now to the appearance of a stop codon,"},{"Start":"05:13.040 ","End":"05:15.940","Text":"where previously there was a codon specifying an amino acid."},{"Start":"05:15.940 ","End":"05:20.870","Text":"As I mentioned, there are these triplets that encode amino acids,"},{"Start":"05:20.870 ","End":"05:23.015","Text":"but there are also triplets,"},{"Start":"05:23.015 ","End":"05:28.085","Text":"for instance this UAA or UAG,"},{"Start":"05:28.085 ","End":"05:30.740","Text":"which don\u0027t encode an amino acid."},{"Start":"05:30.740 ","End":"05:37.735","Text":"Rather, they tell the ribosome which is making the protein to stop synthesizing."},{"Start":"05:37.735 ","End":"05:39.510","Text":"Those are called stop codons."},{"Start":"05:39.510 ","End":"05:43.025","Text":"You could have a mutation that, for instance,"},{"Start":"05:43.025 ","End":"05:47.515","Text":"changed a TTC to an ATC,"},{"Start":"05:47.515 ","End":"05:56.820","Text":"and that will be a stop codon and a protein which will be shorter, a nonsense mutation."}],"ID":28178},{"Watched":false,"Name":"Mutation types 2","Duration":"2m 48s","ChapterTopicVideoID":27051,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.350","Text":"Let\u0027s continue with our discussion of mutations."},{"Start":"00:04.350 ","End":"00:07.710","Text":"To add to our bank of mutations,"},{"Start":"00:07.710 ","End":"00:10.245","Text":"there are deletion mutations."},{"Start":"00:10.245 ","End":"00:13.410","Text":"That\u0027s when there\u0027s a mistake in the DNA replication process,"},{"Start":"00:13.410 ","End":"00:17.280","Text":"which removes more than 1 nucleotide from the genome,"},{"Start":"00:17.280 ","End":"00:19.635","Text":"usually more than 1 nucleotide."},{"Start":"00:19.635 ","End":"00:21.559","Text":"Let\u0027s look at this example,"},{"Start":"00:21.559 ","End":"00:27.005","Text":"which we have a wild type that encodes methionine,"},{"Start":"00:27.005 ","End":"00:29.585","Text":"lysine, phenylalanine, and so on."},{"Start":"00:29.585 ","End":"00:32.600","Text":"You\u0027ll notice that there is a T,"},{"Start":"00:32.600 ","End":"00:35.615","Text":"T, C here,"},{"Start":"00:35.615 ","End":"00:41.510","Text":"which after there was a mutation that caused the deletion,"},{"Start":"00:41.510 ","End":"00:43.010","Text":"then the T, T,"},{"Start":"00:43.010 ","End":"00:48.034","Text":"C was removed or it was not replicated."},{"Start":"00:48.034 ","End":"00:50.660","Text":"In fact, there was no frameshift,"},{"Start":"00:50.660 ","End":"00:53.360","Text":"but yet, 1 amino acid is missing."},{"Start":"00:53.360 ","End":"00:57.665","Text":"The lysine in this example is missing,"},{"Start":"00:57.665 ","End":"01:00.025","Text":"so that would be a deletion."},{"Start":"01:00.025 ","End":"01:03.040","Text":"These deletions can remove a single nucleotide, of course,"},{"Start":"01:03.040 ","End":"01:08.020","Text":"that will create a frameshift or entire sequences of nucleotides,"},{"Start":"01:08.020 ","End":"01:10.180","Text":"like we saw in this example."},{"Start":"01:10.180 ","End":"01:14.725","Text":"If results in the alteration of the translational reading frame,"},{"Start":"01:14.725 ","End":"01:17.424","Text":"that is the frameshift mutation,"},{"Start":"01:17.424 ","End":"01:21.815","Text":"then the resultant protein is usually non-functional."},{"Start":"01:21.815 ","End":"01:23.840","Text":"Because it will change,"},{"Start":"01:23.840 ","End":"01:25.345","Text":"in a frameshift mutation,"},{"Start":"01:25.345 ","End":"01:27.145","Text":"everything that\u0027s downstream,"},{"Start":"01:27.145 ","End":"01:31.160","Text":"that is beyond the position that the mutation"},{"Start":"01:31.160 ","End":"01:36.280","Text":"occurred where you have a missing or sometimes even an addition of a nucleotide,"},{"Start":"01:36.280 ","End":"01:39.295","Text":"all those amino acids will be different and therefore,"},{"Start":"01:39.295 ","End":"01:43.565","Text":"the protein that\u0027s made is usually non-functional."},{"Start":"01:43.565 ","End":"01:45.835","Text":"You can have insertions,"},{"Start":"01:45.835 ","End":"01:47.005","Text":"not only deletions,"},{"Start":"01:47.005 ","End":"01:52.060","Text":"that\u0027s the addition of 1 or more nucleotide base pairs into a DNA sequence."},{"Start":"01:52.060 ","End":"01:54.640","Text":"In this case, for instance, there\u0027s an example,"},{"Start":"01:54.640 ","End":"02:01.315","Text":"there is a frameshift which is caused that added an extra A."},{"Start":"02:01.315 ","End":"02:06.340","Text":"This A was added so that in this particular case,"},{"Start":"02:06.340 ","End":"02:09.565","Text":"the example shows that there is a stop mutation, but any case,"},{"Start":"02:09.565 ","End":"02:13.135","Text":"it messed up the continuation of the translation."},{"Start":"02:13.135 ","End":"02:15.580","Text":"If there are mistakes made in the repair genes,"},{"Start":"02:15.580 ","End":"02:18.595","Text":"that is, if an error in a DNA repair gene is present,"},{"Start":"02:18.595 ","End":"02:22.125","Text":"then the mistakes that are made in other places remain"},{"Start":"02:22.125 ","End":"02:26.210","Text":"uncorrected and those become mutations."},{"Start":"02:26.210 ","End":"02:30.110","Text":"Many of those mutations can accumulate in"},{"Start":"02:30.110 ","End":"02:33.950","Text":"a somatic cell and lead to problems such as the uncontrolled cell division,"},{"Start":"02:33.950 ","End":"02:39.740","Text":"depends on what gene these mistakes are in and that can cause cancer."},{"Start":"02:39.740 ","End":"02:42.320","Text":"If the mutations are in germ cells,"},{"Start":"02:42.320 ","End":"02:43.460","Text":"that\u0027s the sex cells,"},{"Start":"02:43.460 ","End":"02:48.600","Text":"of course, they can be passed on to the next generation."}],"ID":28179},{"Watched":false,"Name":"Next generation sequencing","Duration":"3m 38s","ChapterTopicVideoID":27052,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.830 ","End":"00:04.605","Text":"As was explained in the previous video,"},{"Start":"00:04.605 ","End":"00:09.360","Text":"the Fred Sanger dideoxy chain termination method,"},{"Start":"00:09.360 ","End":"00:15.355","Text":"is the method of choice now for reading DNA sequencing."},{"Start":"00:15.355 ","End":"00:20.420","Text":"But, this technique is still pretty labor-intensive."},{"Start":"00:20.420 ","End":"00:21.500","Text":"First of all, actually,"},{"Start":"00:21.500 ","End":"00:28.970","Text":"we have to isolate a particular piece of DNA that\u0027s usually using molecular cloning,"},{"Start":"00:28.970 ","End":"00:32.585","Text":"or something called the PCR reaction,"},{"Start":"00:32.585 ","End":"00:38.135","Text":"which we have many copies of a single sequence of DNA."},{"Start":"00:38.135 ","End":"00:40.415","Text":"That\u0027s another story for another day."},{"Start":"00:40.415 ","End":"00:41.735","Text":"But in any case,"},{"Start":"00:41.735 ","End":"00:43.330","Text":"that\u0027s a lot of work."},{"Start":"00:43.330 ","End":"00:51.065","Text":"Then we have a gel which has a lane in it that we must run in order to read the sequence."},{"Start":"00:51.065 ","End":"00:53.690","Text":"That we could get a sequence of,"},{"Start":"00:53.690 ","End":"00:57.285","Text":"let\u0027s say, 500 and 600 bases."},{"Start":"00:57.285 ","End":"01:00.820","Text":"This way, it\u0027s not that much."},{"Start":"01:00.820 ","End":"01:04.355","Text":"In order to get more sequences,"},{"Start":"01:04.355 ","End":"01:08.600","Text":"another generation of sequences was developed called next-generation,"},{"Start":"01:08.600 ","End":"01:10.160","Text":"or second-generation sequencing,"},{"Start":"01:10.160 ","End":"01:12.280","Text":"sometimes it\u0027s called NGS."},{"Start":"01:12.280 ","End":"01:17.030","Text":"Several different new rapid DNA sequencing methods were implemented"},{"Start":"01:17.030 ","End":"01:23.045","Text":"by different companies and commercial DNA sequences by the year 2000 and since then,"},{"Start":"01:23.045 ","End":"01:25.990","Text":"they have improved tremendously."},{"Start":"01:25.990 ","End":"01:29.885","Text":"The Sanger method only sequences a single DNA method."},{"Start":"01:29.885 ","End":"01:34.880","Text":"The new technology in this NGS is massively parallel."},{"Start":"01:34.880 ","End":"01:36.115","Text":"How do we do that?"},{"Start":"01:36.115 ","End":"01:41.690","Text":"Well, what the companies did is they\u0027ve learned a technique in which they could bind"},{"Start":"01:41.690 ","End":"01:47.540","Text":"individual molecules to a solid supports to a solid of some sort,"},{"Start":"01:47.540 ","End":"01:50.345","Text":"let\u0027s say a piece of silicon, where it wouldn\u0027t move."},{"Start":"01:50.345 ","End":"01:56.585","Text":"Then the Sanger method polymerase would do its thing,"},{"Start":"01:56.585 ","End":"01:59.420","Text":"doing its polymerization to each molecule,"},{"Start":"01:59.420 ","End":"02:05.885","Text":"but each molecule was set in a particular place on the solid support,"},{"Start":"02:05.885 ","End":"02:08.570","Text":"making it what\u0027s called massively parallel."},{"Start":"02:08.570 ","End":"02:09.890","Text":"There are many of these."},{"Start":"02:09.890 ","End":"02:17.584","Text":"Then using microscopes and very detailed pieces of equipment,"},{"Start":"02:17.584 ","End":"02:20.720","Text":"the sequencing was such that you could sequence"},{"Start":"02:20.720 ","End":"02:25.205","Text":"millions of fragments simultaneously per run."},{"Start":"02:25.205 ","End":"02:31.010","Text":"Therefore, NGS can sequence an entire human genome even,"},{"Start":"02:31.010 ","End":"02:35.974","Text":"within a single day and that is a tremendous advance."},{"Start":"02:35.974 ","End":"02:39.710","Text":"This involves fragmenting the DNA into multiple pieces because again,"},{"Start":"02:39.710 ","End":"02:44.720","Text":"we can only read, let\u0027s say a few 100 bases on a particular piece of DNA."},{"Start":"02:44.720 ","End":"02:48.850","Text":"That fragmenting is usually done at random."},{"Start":"02:48.850 ","End":"02:52.820","Text":"Then there are all sorts of pieces that"},{"Start":"02:52.820 ","End":"02:57.490","Text":"are added to the DNA to make the sequencing more convenient."},{"Start":"02:57.490 ","End":"03:03.260","Text":"Those are called adapters and we have sequence things that are called libraries."},{"Start":"03:03.260 ","End":"03:07.440","Text":"Those are the collections of different pieces of DNA."},{"Start":"03:07.440 ","End":"03:10.640","Text":"Then each of these fragments, that is,"},{"Start":"03:10.640 ","End":"03:12.890","Text":"it\u0027s reassembled what\u0027s called in-silico,"},{"Start":"03:12.890 ","End":"03:18.405","Text":"that is using a computer to form a larger genomic sequence."},{"Start":"03:18.405 ","End":"03:22.445","Text":"Since the DNA is broken randomly,"},{"Start":"03:22.445 ","End":"03:26.210","Text":"there will be overlaps of different sequences of DNA"},{"Start":"03:26.210 ","End":"03:30.020","Text":"and the computers look for these overlaps and"},{"Start":"03:30.020 ","End":"03:39.090","Text":"then assemble large long sequences that can even be the entire human genome."}],"ID":28180},{"Watched":false,"Name":"Sanger DNA sequencing","Duration":"6m 14s","ChapterTopicVideoID":27053,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.680 ","End":"00:05.685","Text":"Welcome back to our discussion of DNA."},{"Start":"00:05.685 ","End":"00:09.240","Text":"Until now, we discussed the structure of DNA from"},{"Start":"00:09.240 ","End":"00:12.495","Text":"the perspective of what the nucleotides look like,"},{"Start":"00:12.495 ","End":"00:15.540","Text":"and how the nucleotides are connected to each other,"},{"Start":"00:15.540 ","End":"00:23.250","Text":"but it\u0027s really the sequence of the nucleotides which encodes the secret of genetics."},{"Start":"00:23.250 ","End":"00:26.370","Text":"It\u0027s the sequence of these nucleotides."},{"Start":"00:26.370 ","End":"00:30.284","Text":"In order to determine the sequence,"},{"Start":"00:30.284 ","End":"00:33.725","Text":"there was a technology that was developed"},{"Start":"00:33.725 ","End":"00:37.342","Text":"called DNA sequencing by a number of scientists,"},{"Start":"00:37.342 ","End":"00:42.666","Text":"and one of them is a man named Fred Sanger that we\u0027ll discuss in a minute."},{"Start":"00:42.666 ","End":"00:50.212","Text":"DNA sequencing may be used to determine the sequence of very short pieces of DNA."},{"Start":"00:50.212 ","End":"00:54.305","Text":"Say, individual genes or larger genetic regions, say, clusters."},{"Start":"00:54.305 ","End":"00:58.700","Text":"Actually now the technology has gotten so good that we can sequence full chromosomes,"},{"Start":"00:58.700 ","End":"01:03.345","Text":"or even the entire genomes of really any organism."},{"Start":"01:03.345 ","End":"01:06.470","Text":"Here you see an example where there\u0027s a color-coding in"},{"Start":"01:06.470 ","End":"01:10.220","Text":"addition to the sequence itself where Gs would be red,"},{"Start":"01:10.220 ","End":"01:13.765","Text":"and Ts yellow, and so on."},{"Start":"01:13.765 ","End":"01:16.160","Text":"Until the 1990s actually,"},{"Start":"01:16.160 ","End":"01:19.760","Text":"DNA sequencing was relatively expensive."},{"Start":"01:19.760 ","End":"01:22.250","Text":"It was long, and it was risky because people use"},{"Start":"01:22.250 ","End":"01:26.655","Text":"radioactive materials in the process of sequencing,"},{"Start":"01:26.655 ","End":"01:31.685","Text":"but with time it got to be significantly cheaper,"},{"Start":"01:31.685 ","End":"01:35.900","Text":"quicker, and safer using various technological advancements."},{"Start":"01:35.900 ","End":"01:41.425","Text":"Here we\u0027ll just talk a little bit about the basis for this advancement."},{"Start":"01:41.425 ","End":"01:43.545","Text":"As I mentioned, it was"},{"Start":"01:43.545 ","End":"01:49.430","Text":"Fred Sanger\u0027s dideoxy chain Termination Method that was developed further."},{"Start":"01:49.430 ","End":"01:52.820","Text":"Let\u0027s see what this chain termination method"},{"Start":"01:52.820 ","End":"01:58.130","Text":"is that Fred Sanger won the Nobel Prize for in 1980"},{"Start":"01:58.130 ","End":"02:03.035","Text":"because it\u0027s really that method which is now"},{"Start":"02:03.035 ","End":"02:08.060","Text":"the most common sequencing method that is also used commercially."},{"Start":"02:08.060 ","End":"02:13.565","Text":"It is based on the use of what are called chain terminators."},{"Start":"02:13.565 ","End":"02:21.645","Text":"Remember the nucleotides have a 3\u0027,"},{"Start":"02:21.645 ","End":"02:29.165","Text":"and a 5\u0027 connection to the phosphates in the phosphate backbone."},{"Start":"02:29.165 ","End":"02:35.045","Text":"What Sanger did is he used a polymerase chain reaction,"},{"Start":"02:35.045 ","End":"02:43.045","Text":"and that is a polymerase reaction in which DNA was added to a chain."},{"Start":"02:43.045 ","End":"02:45.225","Text":"From time to time,"},{"Start":"02:45.225 ","End":"02:48.860","Text":"he added into the mix nucleotides,"},{"Start":"02:48.860 ","End":"02:53.565","Text":"some of which were 2\u0027-dideoxy,"},{"Start":"02:53.565 ","End":"02:57.480","Text":"which meant that they had a dideoxy,"},{"Start":"02:57.480 ","End":"03:02.660","Text":"they did not contain a hydroxyl group in the 3\u0027 location,"},{"Start":"03:02.660 ","End":"03:06.755","Text":"and therefore, they would terminate a chain."},{"Start":"03:06.755 ","End":"03:14.270","Text":"Now if we fluorescently labeled each of those dideoxy nucleotides,"},{"Start":"03:14.270 ","End":"03:18.155","Text":"and we would get chains that are of varying lengths."},{"Start":"03:18.155 ","End":"03:27.535","Text":"We have a mixture of deoxynucleotide triphosphates and dideoxy, that\u0027s ddNTPs,"},{"Start":"03:27.535 ","End":"03:31.340","Text":"that\u0027s the basis of making different chain lengths,"},{"Start":"03:31.340 ","End":"03:40.535","Text":"each of which ends with a particular dideoxynucleotide that we can identify because each"},{"Start":"03:40.535 ","End":"03:50.050","Text":"of the dideoxy is fluorescently labeled with a different color of a dideoxynucleotide."},{"Start":"03:50.050 ","End":"03:55.060","Text":"By using this dideoxy,"},{"Start":"03:55.060 ","End":"03:58.595","Text":"which is added to a growing DNA strand using the polymerase,"},{"Start":"03:58.595 ","End":"04:05.045","Text":"the chain cannot extend any further and by using a predetermined ratio of"},{"Start":"04:05.045 ","End":"04:09.800","Text":"deoxyribonucleotides and deoxynucleotides is"},{"Start":"04:09.800 ","End":"04:13.865","Text":"possible to generate DNA fragments of different sizes."},{"Start":"04:13.865 ","End":"04:20.855","Text":"They actually may be deoxyribonucleotides or deoxynucleotides,"},{"Start":"04:20.855 ","End":"04:24.755","Text":"depends exactly upon the system we\u0027re using."},{"Start":"04:24.755 ","End":"04:28.280","Text":"Now, all that\u0027s left to do is to separate"},{"Start":"04:28.280 ","End":"04:34.685","Text":"the different DNA strands using a Gel electrophoresis system."},{"Start":"04:34.685 ","End":"04:39.320","Text":"It\u0027s actually uses a polyacrylamide Gel electrophoresis system."},{"Start":"04:39.320 ","End":"04:41.650","Text":"That is acrylamide,"},{"Start":"04:41.650 ","End":"04:44.945","Text":"is the basis for separating them. It\u0027s a sieve."},{"Start":"04:44.945 ","End":"04:48.020","Text":"The longer the piece of DNA,"},{"Start":"04:48.020 ","End":"04:50.900","Text":"let\u0027s say this one with a G at the end of it,"},{"Start":"04:50.900 ","End":"04:54.680","Text":"will run more slowly than one that\u0027s a little bit shorter,"},{"Start":"04:54.680 ","End":"04:56.180","Text":"than one that has an A,"},{"Start":"04:56.180 ","End":"04:58.850","Text":"and it has a C, that has a T at the end of it."},{"Start":"04:58.850 ","End":"05:03.065","Text":"Therefore, just by looking at the fluorescence of the Gel,"},{"Start":"05:03.065 ","End":"05:08.300","Text":"we will be able to tell the sequence of"},{"Start":"05:08.300 ","End":"05:15.545","Text":"the original DNA to which these dideoxynucleotides were being used."},{"Start":"05:15.545 ","End":"05:20.720","Text":"Let\u0027s look for a moment at what Gel electrophoresis is,"},{"Start":"05:20.720 ","End":"05:23.540","Text":"and we\u0027ll look at it in"},{"Start":"05:23.540 ","End":"05:26.900","Text":"the following very simple system in which"},{"Start":"05:26.900 ","End":"05:31.310","Text":"the DNA fragments are separated according to size."},{"Start":"05:31.310 ","End":"05:33.020","Text":"In the simplest case,"},{"Start":"05:33.020 ","End":"05:35.045","Text":"agarose is the medium."},{"Start":"05:35.045 ","End":"05:39.080","Text":"Of course, we discussed polyacrylamide a minute ago,"},{"Start":"05:39.080 ","End":"05:45.480","Text":"and as we said, the larger bands run more slowly than the smaller ones."},{"Start":"05:46.130 ","End":"05:49.805","Text":"This is when there is an electric current that is applied,"},{"Start":"05:49.805 ","End":"05:51.245","Text":"and of course, the DNA,"},{"Start":"05:51.245 ","End":"05:53.375","Text":"which is negatively charged,"},{"Start":"05:53.375 ","End":"05:59.555","Text":"moves from the negative electrode towards the positive electrode according to size."},{"Start":"05:59.555 ","End":"06:01.925","Text":"Once the DNA is separated,"},{"Start":"06:01.925 ","End":"06:05.090","Text":"then we can look at the DNA using techniques,"},{"Start":"06:05.090 ","End":"06:07.130","Text":"one of many different techniques."},{"Start":"06:07.130 ","End":"06:14.400","Text":"One of them uses a stain in which the DNA is specifically viewed."}],"ID":28181},{"Watched":false,"Name":"Semi-conservative DNA replication","Duration":"6m 38s","ChapterTopicVideoID":27054,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:03.570","Text":"Hi there. Now that we\u0027ve seen how Watson"},{"Start":"00:03.570 ","End":"00:07.035","Text":"and Crick figured out the 3-dimensional structure of DNA."},{"Start":"00:07.035 ","End":"00:12.375","Text":"Let\u0027s see what they considered from a genetic point of view."},{"Start":"00:12.375 ","End":"00:18.060","Text":"What they realized was that the DNA has"},{"Start":"00:18.060 ","End":"00:24.255","Text":"an A opposite of T and a C opposite a G. So that in fact,"},{"Start":"00:24.255 ","End":"00:28.560","Text":"all of the information is really encoded on 1 strands because you"},{"Start":"00:28.560 ","End":"00:33.120","Text":"couldn\u0027t get the information for the other strands simply by pairing it."},{"Start":"00:33.120 ","End":"00:37.710","Text":"Since an a always goes with a T and a T with an a and a C with a G,"},{"Start":"00:37.710 ","End":"00:41.630","Text":"and a G with a C. They wrote in their paper in"},{"Start":"00:41.630 ","End":"00:45.710","Text":"1953 that it has not escaped our notice that the"},{"Start":"00:45.710 ","End":"00:49.850","Text":"specific pairing we have postulated immediately suggests"},{"Start":"00:49.850 ","End":"00:55.430","Text":"a possible copying mechanism for the genetic material."},{"Start":"00:55.430 ","End":"01:02.590","Text":"What they were suggesting was that the 2 strands of DNA would separate."},{"Start":"01:02.590 ","End":"01:09.500","Text":"That the 2 strands of DNA would separate and then"},{"Start":"01:09.500 ","End":"01:12.710","Text":"each of them would serve as a template from which"},{"Start":"01:12.710 ","End":"01:16.133","Text":"the new complementary strands would be copied."},{"Start":"01:16.133 ","End":"01:22.540","Text":"You would have the old strands and the new strand that\u0027s created."},{"Start":"01:22.540 ","End":"01:28.460","Text":"If we look at this now in these 2 different blue colors,"},{"Start":"01:28.460 ","End":"01:31.580","Text":"the darker blue and the lighter blue."},{"Start":"01:31.580 ","End":"01:33.860","Text":"The lighter blue is the new material."},{"Start":"01:33.860 ","End":"01:36.950","Text":"Then what we see is that there actually are"},{"Start":"01:36.950 ","End":"01:41.600","Text":"several possibilities of how this replication could take place."},{"Start":"01:41.600 ","End":"01:43.430","Text":"There are 3 possibilities."},{"Start":"01:43.430 ","End":"01:44.945","Text":"There\u0027s what\u0027s called the conservative,"},{"Start":"01:44.945 ","End":"01:49.160","Text":"semi-conservative and dispersive possibilities."},{"Start":"01:49.160 ","End":"01:51.996","Text":"In conservative replication,"},{"Start":"01:51.996 ","End":"01:54.170","Text":"that\u0027s what we have here on the left,"},{"Start":"01:54.170 ","End":"02:00.830","Text":"the parental DNA remains together and the newly formed daughter strands are together."},{"Start":"02:00.830 ","End":"02:06.595","Text":"You have old DNA in the first replication and still have old DNA"},{"Start":"02:06.595 ","End":"02:13.810","Text":"in the second replication and in the first replication you\u0027ll get a new DNA."},{"Start":"02:13.810 ","End":"02:17.320","Text":"Both strands will be new and in the second replication,"},{"Start":"02:17.320 ","End":"02:20.485","Text":"you\u0027ll have 3 out of the 4 strands, which will be new."},{"Start":"02:20.485 ","End":"02:25.960","Text":"But that\u0027s not the only possibility you could have semiconservative. What does that mean?"},{"Start":"02:25.960 ","End":"02:28.750","Text":"That means that each double-stranded DNA includes"},{"Start":"02:28.750 ","End":"02:33.805","Text":"1 parental or old strand and 1 new strand, that\u0027s what we see here."},{"Start":"02:33.805 ","End":"02:36.115","Text":"We have an old strands,"},{"Start":"02:36.115 ","End":"02:39.660","Text":"the darker blue and a new strand, the lighter 1."},{"Start":"02:39.660 ","End":"02:44.430","Text":"The same thing is true of the 2 different original strands."},{"Start":"02:44.430 ","End":"02:49.340","Text":"The 2 are the same and if you look at the second replication,"},{"Start":"02:49.340 ","End":"02:52.370","Text":"then you still have old new,"},{"Start":"02:52.370 ","End":"02:54.114","Text":"like you did up here,"},{"Start":"02:54.114 ","End":"02:58.610","Text":"but you also have just new new and new new."},{"Start":"02:58.610 ","End":"03:03.035","Text":"Finally, we have a dispersive model and the dispersive model,"},{"Start":"03:03.035 ","End":"03:09.530","Text":"we have fragments of new and old on the same piece of DNA."},{"Start":"03:09.530 ","End":"03:12.380","Text":"Both copies of DNA have double-stranded fragments of"},{"Start":"03:12.380 ","End":"03:17.030","Text":"parental DNA and the newly synthesized DNA is interspersed."},{"Start":"03:17.030 ","End":"03:19.123","Text":"That means it\u0027s on the same strand,"},{"Start":"03:19.123 ","End":"03:22.885","Text":"we have both new and old DNA."},{"Start":"03:22.885 ","End":"03:25.910","Text":"How could these be distinguished from one another?"},{"Start":"03:25.910 ","End":"03:28.204","Text":"How are these models distinguished?"},{"Start":"03:28.204 ","End":"03:30.980","Text":"Meselson and Stahl did"},{"Start":"03:30.980 ","End":"03:36.155","Text":"a very clever experiment to be able to distinguish them. Here\u0027s what their experiment."},{"Start":"03:36.155 ","End":"03:44.830","Text":"First of all, they cultured E. coli in a medium that had a heavy isotope of nitrogen."},{"Start":"03:44.830 ","End":"03:47.990","Text":"It has an extra neutron, this nitrogen,"},{"Start":"03:47.990 ","End":"03:51.950","Text":"and it makes the DNA that is formed in"},{"Start":"03:51.950 ","End":"03:57.590","Text":"any other molecule that is formed there incorporates this heavy isotope in it,"},{"Start":"03:57.590 ","End":"04:02.060","Text":"heavy nitrogen in it will be more dense and 14,"},{"Start":"04:02.060 ","End":"04:06.680","Text":"the normal nitrogen that only has 7 neutrons,"},{"Start":"04:06.680 ","End":"04:09.200","Text":"as opposed to this 1 has 8."},{"Start":"04:09.200 ","End":"04:12.890","Text":"What they did is they cultured bacteria in this heavy media."},{"Start":"04:12.890 ","End":"04:17.520","Text":"All the nitrogen pretty much would be heavy and then they transferred it for"},{"Start":"04:17.520 ","End":"04:23.390","Text":"1 generation to media that has the normal lighter isotope."},{"Start":"04:23.390 ","End":"04:30.990","Text":"Then what they did is they isolated the DNA from the different samples?"},{"Start":"04:31.040 ","End":"04:35.340","Text":"After they centrifuged the cells."},{"Start":"04:35.340 ","End":"04:36.580","Text":"They would centrifuge the cells,"},{"Start":"04:36.580 ","End":"04:39.230","Text":"they would spin them out from the media"},{"Start":"04:39.230 ","End":"04:43.700","Text":"and they did this after the first and the second replication."},{"Start":"04:43.700 ","End":"04:48.050","Text":"Then what they did, they isolated the DNA and put it"},{"Start":"04:48.050 ","End":"04:52.910","Text":"into a medium which separates the 2 strands,"},{"Start":"04:52.910 ","End":"04:54.820","Text":"1 from the other."},{"Start":"04:54.820 ","End":"04:58.700","Text":"In high-speed centrifugation afterwards,"},{"Start":"04:58.700 ","End":"05:03.170","Text":"they could separate the strands by their molecular weights,"},{"Start":"05:03.170 ","End":"05:05.995","Text":"by their density essentially."},{"Start":"05:05.995 ","End":"05:08.555","Text":"What did they find out?"},{"Start":"05:08.555 ","End":"05:11.105","Text":"They found out the following;"},{"Start":"05:11.105 ","End":"05:14.075","Text":"after the first replication,"},{"Start":"05:14.075 ","End":"05:22.385","Text":"they found that they had a single band in the middle of the tube."},{"Start":"05:22.385 ","End":"05:25.099","Text":"The ones they didn\u0027t have DNA,"},{"Start":"05:25.099 ","End":"05:27.530","Text":"which was heavy heavy."},{"Start":"05:27.530 ","End":"05:31.985","Text":"That\u0027s what you\u0027d find at the bottom and they didn\u0027t have light lights,"},{"Start":"05:31.985 ","End":"05:35.165","Text":"that\u0027s what you would have at the top."},{"Start":"05:35.165 ","End":"05:39.170","Text":"The first conservative model must be"},{"Start":"05:39.170 ","End":"05:43.100","Text":"wrong because that model would predict that we would have"},{"Start":"05:43.100 ","End":"05:50.825","Text":"light light and heavy heavy but the dispersive model would give abandoned the same place."},{"Start":"05:50.825 ","End":"05:54.530","Text":"But after the second replication, you\u0027ll remember,"},{"Start":"05:54.530 ","End":"05:58.310","Text":"in the semi-conservative model,"},{"Start":"05:58.310 ","End":"06:01.325","Text":"we would have both light lights."},{"Start":"06:01.325 ","End":"06:09.905","Text":"That would be the newest DNA which has made but we also have heavy and light together,"},{"Start":"06:09.905 ","End":"06:12.605","Text":"so we still maintain the central bands."},{"Start":"06:12.605 ","End":"06:14.735","Text":"Whereas in the dispersive model,"},{"Start":"06:14.735 ","End":"06:18.720","Text":"we have heavy and light all along"},{"Start":"06:18.720 ","End":"06:22.910","Text":"and then therefore we would still have this band in the middle."},{"Start":"06:22.910 ","End":"06:24.650","Text":"It might move up a little bit,"},{"Start":"06:24.650 ","End":"06:25.940","Text":"be a little bit lighter,"},{"Start":"06:25.940 ","End":"06:29.045","Text":"but it would not be as light as light light."},{"Start":"06:29.045 ","End":"06:38.980","Text":"The semi-conservative model must be the correct 1 and indeed, it is."}],"ID":28182},{"Watched":false,"Name":"The DNA polymerase reaction","Duration":"5m 12s","ChapterTopicVideoID":27055,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.800 ","End":"00:06.629","Text":"Now, let\u0027s look at the replication in more detail."},{"Start":"00:06.629 ","End":"00:13.185","Text":"The first thing we\u0027ll do is look now at this representation of the DNA,"},{"Start":"00:13.185 ","End":"00:16.170","Text":"where we have the template strand."},{"Start":"00:16.170 ","End":"00:18.975","Text":"You can see here the sugar,"},{"Start":"00:18.975 ","End":"00:23.520","Text":"phosphate, sugar, phosphate, sugar, phosphate, backbone."},{"Start":"00:23.520 ","End":"00:28.650","Text":"Notice that there is a 5\u0027 and a 3\u0027 end."},{"Start":"00:28.650 ","End":"00:33.855","Text":"We have the new strand which is being made that it also has the 5\u0027 end"},{"Start":"00:33.855 ","End":"00:39.120","Text":"and a 3\u0027 end which is anti-parallel."},{"Start":"00:39.120 ","End":"00:42.230","Text":"You can see the 5 is the top of the new strand as"},{"Start":"00:42.230 ","End":"00:46.445","Text":"opposed to the 3\u0027 being at the top of the template strand."},{"Start":"00:46.445 ","End":"00:52.860","Text":"We are going to be adding nucleotide triphosphate,"},{"Start":"00:52.860 ","End":"00:57.420","Text":"with 3 phosphates, to 3\u0027 hydroxyl."},{"Start":"00:57.420 ","End":"01:00.125","Text":"DNA polymerase is this enzyme, as I said,"},{"Start":"01:00.125 ","End":"01:05.105","Text":"which is going to add nucleotides only in the 5 to 3\u0027 direction."},{"Start":"01:05.105 ","End":"01:06.515","Text":"It\u0027s a little bit confusing."},{"Start":"01:06.515 ","End":"01:12.875","Text":"It\u0027s 5\u0027 to 3\u0027 as the general direction of the growth,"},{"Start":"01:12.875 ","End":"01:17.090","Text":"but the addition is to the 3\u0027 end."},{"Start":"01:17.090 ","End":"01:22.465","Text":"We speak of the polymerase moving in the 5 to 3\u0027 direction."},{"Start":"01:22.465 ","End":"01:30.170","Text":"Each nucleotide that is added to a growing DNA strand is this nucleoside triphosphate."},{"Start":"01:30.170 ","End":"01:32.520","Text":"It\u0027s got 3 phosphates here."},{"Start":"01:32.520 ","End":"01:41.610","Text":"In this case we\u0027re looking at dATP, this is deoxytriphosphate."},{"Start":"01:41.610 ","End":"01:48.830","Text":"The energy that is"},{"Start":"01:48.830 ","End":"01:54.620","Text":"required for this comes from breaking this bond here,"},{"Start":"01:54.620 ","End":"02:03.235","Text":"which is about the same amount of energy that is released when ATP is used in metabolism."},{"Start":"02:03.235 ","End":"02:09.500","Text":"In fact, you\u0027ll remember that the only difference really between ATP and dATP is"},{"Start":"02:09.500 ","End":"02:17.000","Text":"the deoxy of the 3\u0027 sugar of the ribose."},{"Start":"02:17.000 ","End":"02:21.470","Text":"Each monomer then joins the strand via a dehydration reaction,"},{"Start":"02:21.470 ","End":"02:25.410","Text":"and it loses these 2 phosphates,"},{"Start":"02:25.410 ","End":"02:29.565","Text":"it\u0027s called a pyrophosphate because of the 2 phosphates."},{"Start":"02:29.565 ","End":"02:33.770","Text":"They lose this pyrophosphate in the process,"},{"Start":"02:33.770 ","End":"02:36.800","Text":"and this is called a dehydration reaction."},{"Start":"02:36.800 ","End":"02:40.565","Text":"Now, let\u0027s look at the further replication steps."},{"Start":"02:40.565 ","End":"02:44.090","Text":"To begin with, we have the DNA here represented"},{"Start":"02:44.090 ","End":"02:47.930","Text":"as the double helix with the replication fork as we\u0027ve seen before."},{"Start":"02:47.930 ","End":"02:52.950","Text":"We\u0027re going to start by looking at the lagging strand."},{"Start":"02:52.950 ","End":"02:54.600","Text":"There are 2 different strands,"},{"Start":"02:54.600 ","End":"02:56.855","Text":"one is called the leading strand,"},{"Start":"02:56.855 ","End":"02:58.579","Text":"which is the one that\u0027s at the bottom here."},{"Start":"02:58.579 ","End":"03:00.920","Text":"The other one is called the lagging strand,"},{"Start":"03:00.920 ","End":"03:04.375","Text":"we\u0027ll understand why that\u0027s the case in a bit."},{"Start":"03:04.375 ","End":"03:07.125","Text":"We\u0027re not going to discuss the lagging strand."},{"Start":"03:07.125 ","End":"03:10.400","Text":"In that one, the first nucleotide that\u0027s added by"},{"Start":"03:10.400 ","End":"03:15.090","Text":"the DNA polymerase is added to a nucleotide primer,"},{"Start":"03:15.090 ","End":"03:19.170","Text":"it\u0027s about 5 to 10 nucleotides long to a primer,"},{"Start":"03:19.170 ","End":"03:22.415","Text":"that\u0027s this piece of DNA over here,"},{"Start":"03:22.415 ","End":"03:30.170","Text":"that is actually RNA that provides a free 3\u0027 hydroxyl end."},{"Start":"03:30.170 ","End":"03:34.175","Text":"Because the DNA polymerase must add,"},{"Start":"03:34.175 ","End":"03:36.935","Text":"as you\u0027ll remember from the previous slides,"},{"Start":"03:36.935 ","End":"03:43.305","Text":"to a 3\u0027 hydroxyl end of the nucleotide."},{"Start":"03:43.305 ","End":"03:47.510","Text":"Since it must add to something,"},{"Start":"03:47.510 ","End":"03:50.210","Text":"so it adds to an RNA primer,"},{"Start":"03:50.210 ","End":"03:53.140","Text":"to the 3\u0027 end of this RNA primer."},{"Start":"03:53.140 ","End":"03:58.910","Text":"The primers themselves are synthesized by an enzyme which is called primase,"},{"Start":"03:58.910 ","End":"04:02.280","Text":"which does not require anything to add to."},{"Start":"04:02.280 ","End":"04:04.790","Text":"It can begin to add by itself."},{"Start":"04:04.790 ","End":"04:10.755","Text":"This primase then primes the DNA synthesis,"},{"Start":"04:10.755 ","End":"04:14.480","Text":"it will supply this 3\u0027 hydroxyl,"},{"Start":"04:14.480 ","End":"04:16.595","Text":"and therefore it\u0027s called a primer."},{"Start":"04:16.595 ","End":"04:18.200","Text":"Now in addition to that,"},{"Start":"04:18.200 ","End":"04:24.785","Text":"there\u0027s another enzyme called topoisomerase,"},{"Start":"04:24.785 ","End":"04:30.350","Text":"which acts on the DNA which is ahead of the replication fork."},{"Start":"04:30.350 ","End":"04:34.040","Text":"Of course, the replication fork is moving from right to left in this picture,"},{"Start":"04:34.040 ","End":"04:39.860","Text":"and it breaks and then reforms the DNA phosphate backbone ahead of"},{"Start":"04:39.860 ","End":"04:41.900","Text":"the replication fork because there is"},{"Start":"04:41.900 ","End":"04:47.825","Text":"torsional stress that is formed as the replication fork moves forward."},{"Start":"04:47.825 ","End":"04:54.345","Text":"Of course, in this picture we don\u0027t see the DNA denoted as a helix,"},{"Start":"04:54.345 ","End":"04:57.140","Text":"that is the strands go around each other,"},{"Start":"04:57.140 ","End":"05:00.200","Text":"but in fact, in real life it is a helix."},{"Start":"05:00.200 ","End":"05:05.075","Text":"As the replication fork opens, there\u0027s torsional stress,"},{"Start":"05:05.075 ","End":"05:08.450","Text":"which is being put on the DNA that\u0027s just ahead of it,"},{"Start":"05:08.450 ","End":"05:13.560","Text":"and that\u0027s relieved by the topoisomerase."}],"ID":28183},{"Watched":false,"Name":"Exercise 1","Duration":"1m 34s","ChapterTopicVideoID":27070,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:09.810","Text":"If DNA of a species was analyzed and it was found that it contains 27 percent A,"},{"Start":"00:09.810 ","End":"00:14.070","Text":"what would be the percentage of C?"},{"Start":"00:14.070 ","End":"00:23.930","Text":"Let\u0027s see here, we have 27 percent A and we\u0027re asking what the percentage of C would be."},{"Start":"00:23.930 ","End":"00:27.360","Text":"Remember Chargaff\u0027s rules."},{"Start":"00:27.360 ","End":"00:33.830","Text":"That\u0027s the results of the experiment in 1950 in which he concluded that"},{"Start":"00:33.830 ","End":"00:41.000","Text":"the amount of A equals the amount of T and the amount of G equals the amount of,"},{"Start":"00:41.000 ","End":"00:43.130","Text":"C, the percentages of each of them."},{"Start":"00:43.130 ","End":"00:51.200","Text":"A is equal to T and G is equal to C. Therefore,"},{"Start":"00:51.200 ","End":"00:53.104","Text":"we come back to our question."},{"Start":"00:53.104 ","End":"00:55.970","Text":"We want to know what the percentage of C would be."},{"Start":"00:55.970 ","End":"00:59.540","Text":"We know that the percentage of A is 27"},{"Start":"00:59.540 ","End":"01:03.530","Text":"and that therefore the percentage of T would also be 27,"},{"Start":"01:03.530 ","End":"01:08.060","Text":"so 27 times 2 is 54 percent."},{"Start":"01:08.060 ","End":"01:13.925","Text":"What\u0027s going to be left is the percentage of G and C."},{"Start":"01:13.925 ","End":"01:20.540","Text":"A 100 percent minus this 54 leaves 46 percent left and of course,"},{"Start":"01:20.540 ","End":"01:22.280","Text":"half of that,"},{"Start":"01:22.280 ","End":"01:26.175","Text":"of the 46, is 23 percent."},{"Start":"01:26.175 ","End":"01:28.586","Text":"Which of these answers is 23?"},{"Start":"01:28.586 ","End":"01:32.295","Text":"Well clearly C is."},{"Start":"01:32.295 ","End":"01:34.660","Text":"C is our answer."}],"ID":28184},{"Watched":false,"Name":"Exercise 2","Duration":"2m 23s","ChapterTopicVideoID":27069,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.080 ","End":"00:04.980","Text":"The experiments by Hershey and Chase helped confirm that DNA"},{"Start":"00:04.980 ","End":"00:09.989","Text":"was the hereditary material based on which finding?"},{"Start":"00:09.989 ","End":"00:14.130","Text":"Was it that the radioactive phage were found in the pellet,"},{"Start":"00:14.130 ","End":"00:16.740","Text":"that radioactive cells were found in the supernatant,"},{"Start":"00:16.740 ","End":"00:19.860","Text":"that radioactive sulfur was found inside the cell,"},{"Start":"00:19.860 ","End":"00:23.745","Text":"that radioactive phosphorus was found in the cell?"},{"Start":"00:23.745 ","End":"00:28.290","Text":"Let\u0027s recall the Hershey and Chase Experiment."},{"Start":"00:28.290 ","End":"00:31.130","Text":"In the Hershey and Chase experiment,"},{"Start":"00:31.130 ","End":"00:35.660","Text":"you remember that they used 2 different isotopes."},{"Start":"00:35.660 ","End":"00:43.135","Text":"They used sulfur S-35 and they used phosphorus P-32."},{"Start":"00:43.135 ","End":"00:45.185","Text":"Well, what\u0027s the difference between them?"},{"Start":"00:45.185 ","End":"00:51.830","Text":"Sulfur labels proteins because there are cystines,"},{"Start":"00:51.830 ","End":"00:55.580","Text":"amino acids in proteins and they have sulfur in them,"},{"Start":"00:55.580 ","End":"00:59.480","Text":"whereas it has no phosphorus usually."},{"Start":"00:59.480 ","End":"01:01.130","Text":"However, DNA of course,"},{"Start":"01:01.130 ","End":"01:03.890","Text":"has the sugar phosphate backbone,"},{"Start":"01:03.890 ","End":"01:06.260","Text":"so it\u0027s got lots of phosphorus in it."},{"Start":"01:06.260 ","End":"01:09.650","Text":"Basically the P-32 is going to label the DNA,"},{"Start":"01:09.650 ","End":"01:13.775","Text":"and the S-35 is going to label the protein."},{"Start":"01:13.775 ","End":"01:15.410","Text":"Now what were they asking?"},{"Start":"01:15.410 ","End":"01:21.890","Text":"They were asking, is it protein or is it DNA that is the genetic material."},{"Start":"01:21.890 ","End":"01:27.235","Text":"The genetic material obviously has to get into the cells."},{"Start":"01:27.235 ","End":"01:30.755","Text":"They found, in fact when they did this experiment,"},{"Start":"01:30.755 ","End":"01:33.395","Text":"that when they labeled with S-35,"},{"Start":"01:33.395 ","End":"01:37.520","Text":"the radioactivity, the proteins stayed outside the cells."},{"Start":"01:37.520 ","End":"01:42.650","Text":"These bacteriophages that have DNA in them, as it turns out,"},{"Start":"01:42.650 ","End":"01:46.190","Text":"injected their DNA into the cells but left the proteins on the outside,"},{"Start":"01:46.190 ","End":"01:52.250","Text":"so the radioactivity then was in the supernatant if they used S-35."},{"Start":"01:52.250 ","End":"01:57.635","Text":"However, if they used P-32, then of course,"},{"Start":"01:57.635 ","End":"02:01.550","Text":"the DNA which was inside the cell will be radioactively labeled,"},{"Start":"02:01.550 ","End":"02:04.820","Text":"then when they precipitated the cells,"},{"Start":"02:04.820 ","End":"02:09.135","Text":"they found the radio activity in the pellet."},{"Start":"02:09.135 ","End":"02:12.960","Text":"Only P-32 entered the cells."},{"Start":"02:12.960 ","End":"02:15.935","Text":"That indicated that the DNA is the genetic material."},{"Start":"02:15.935 ","End":"02:18.394","Text":"Now going back to our question,"},{"Start":"02:18.394 ","End":"02:21.879","Text":"we find that radioactive phosphorus was found in the cell,"},{"Start":"02:21.879 ","End":"02:24.390","Text":"that\u0027s our correct answer."}],"ID":28185},{"Watched":false,"Name":"Exercise 3","Duration":"1m 23s","ChapterTopicVideoID":27068,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.755","Text":"Bacterial transformation is a major concern in many medical settings."},{"Start":"00:04.755 ","End":"00:07.440","Text":"Why might healthcare providers be concerned?"},{"Start":"00:07.440 ","End":"00:12.625","Text":"We\u0027re talking here about bacterial transformation."},{"Start":"00:12.625 ","End":"00:14.865","Text":"What might be problems?"},{"Start":"00:14.865 ","End":"00:17.160","Text":"That pathogenic bacteria could introduce"},{"Start":"00:17.160 ","End":"00:20.730","Text":"disease-causing genes in non-pathogenic material."},{"Start":"00:20.730 ","End":"00:23.700","Text":"Well, that\u0027s movement of"},{"Start":"00:23.700 ","End":"00:29.085","Text":"some genetic material from one kind of bacteria to other kinds of bacteria."},{"Start":"00:29.085 ","End":"00:30.480","Text":"Well, that could be a problem."},{"Start":"00:30.480 ","End":"00:33.270","Text":"How about antibiotic resistance genes"},{"Start":"00:33.270 ","End":"00:36.540","Text":"could be introduced into new bacteria to create superbug?"},{"Start":"00:36.540 ","End":"00:41.988","Text":"Again, that\u0027s movement of particular genes from one bacteria to the other."},{"Start":"00:41.988 ","End":"00:44.570","Text":"That probably could be a problem."},{"Start":"00:44.570 ","End":"00:50.300","Text":"How about the bacteriophages could spread DNA encoding toxins to new bacteria?"},{"Start":"00:50.300 ","End":"00:52.055","Text":"Well, yes."},{"Start":"00:52.055 ","End":"00:54.530","Text":"That could be a problem as well,"},{"Start":"00:54.530 ","End":"00:59.120","Text":"because the bacteriophages could pick up some DNA from"},{"Start":"00:59.120 ","End":"01:04.865","Text":"particular bacteria and then transfer it into new bacteria."},{"Start":"01:04.865 ","End":"01:07.820","Text":"You\u0027ll remember that transformation,"},{"Start":"01:07.820 ","End":"01:10.699","Text":"which was first shown by Fred Griffith,"},{"Start":"01:10.699 ","End":"01:16.670","Text":"showed that bacteria are capable of transferring genetic information."},{"Start":"01:16.670 ","End":"01:24.300","Text":"All of the above could be concerns for health care providers."}],"ID":28186},{"Watched":false,"Name":"Exercise 4","Duration":"50s","ChapterTopicVideoID":27067,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:05.970","Text":"DNA double helix does not have which of the following?"},{"Start":"00:05.970 ","End":"00:09.210","Text":"Double helix does not have which of the following?"},{"Start":"00:09.210 ","End":"00:11.550","Text":"Is it an anti-parallel configuration,"},{"Start":"00:11.550 ","End":"00:15.735","Text":"complementary base pairing, major and minor grooves, or uracil?"},{"Start":"00:15.735 ","End":"00:18.420","Text":"Well, let\u0027s remember the double helix,"},{"Start":"00:18.420 ","End":"00:20.700","Text":"it certainly is anti-parallel."},{"Start":"00:20.700 ","End":"00:26.705","Text":"We\u0027ve got 5 prime on one end and 3 prime on the other end, that\u0027s anti-parallel."},{"Start":"00:26.705 ","End":"00:30.210","Text":"It certainly has complimentary base pairing,"},{"Start":"00:30.210 ","End":"00:34.190","Text":"a C with a G and an A with a T,"},{"Start":"00:34.190 ","End":"00:39.665","Text":"and it has major and minor grooves."},{"Start":"00:39.665 ","End":"00:43.550","Text":"The answer then is uracil."},{"Start":"00:43.550 ","End":"00:51.270","Text":"Uracil actually is found only in RNA, not DNA."}],"ID":28187},{"Watched":false,"Name":"Exercise 5","Duration":"33s","ChapterTopicVideoID":27066,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.125","Text":"In eukaryotes, what is the DNA wrapped around?"},{"Start":"00:04.125 ","End":"00:05.970","Text":"Eukaryotes, here we\u0027re talking about."},{"Start":"00:05.970 ","End":"00:08.340","Text":"Is it single-stranded binding proteins,"},{"Start":"00:08.340 ","End":"00:11.760","Text":"sliding clamp, polymerase, or histones?"},{"Start":"00:11.760 ","End":"00:20.700","Text":"Well, we\u0027ll remember that the nucleosomes are made up of histones,"},{"Start":"00:20.700 ","End":"00:24.285","Text":"of a histone core,"},{"Start":"00:24.285 ","End":"00:29.190","Text":"and it is the DNA then that wraps around this histone core."},{"Start":"00:29.190 ","End":"00:33.910","Text":"Clearly, that is our answer, histones."}],"ID":28188},{"Watched":false,"Name":"Exercise 6","Duration":"2m 8s","ChapterTopicVideoID":27065,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:07.300","Text":"Meselson and Stahl\u0027s experiments proved that DNA replicates, by which mode?"},{"Start":"00:07.300 ","End":"00:10.170","Text":"Is it conservative, semi-conservative,"},{"Start":"00:10.170 ","End":"00:13.310","Text":"dispersive, or none of the above?"},{"Start":"00:13.310 ","End":"00:18.220","Text":"We\u0027re talking here about Meselson and Stahl\u0027s experiments,"},{"Start":"00:19.370 ","End":"00:22.755","Text":"and if you remember on this slide,"},{"Start":"00:22.755 ","End":"00:28.155","Text":"what they did is they grew bacteria using N15,"},{"Start":"00:28.155 ","End":"00:30.690","Text":"heavy isotope of nitrogen,"},{"Start":"00:30.690 ","End":"00:38.105","Text":"and then they transferred it for 1 generation to a lighter isotope of nitrogen."},{"Start":"00:38.105 ","End":"00:43.630","Text":"Then they isolated the DNA,"},{"Start":"00:43.630 ","End":"00:45.725","Text":"and separated the strands,"},{"Start":"00:45.725 ","End":"00:53.945","Text":"and then ran them in a cesium chloride density centrifugation,"},{"Start":"00:53.945 ","End":"00:58.040","Text":"which separates DNA by the density,"},{"Start":"00:58.040 ","End":"01:00.665","Text":"less dense and more dense."},{"Start":"01:00.665 ","End":"01:05.360","Text":"The more dense DNA will have N15 minutes,"},{"Start":"01:05.360 ","End":"01:10.560","Text":"the less dense will have no N15 or less."},{"Start":"01:10.560 ","End":"01:14.060","Text":"In fact, there were 3 possible bands that they could get."},{"Start":"01:14.060 ","End":"01:15.485","Text":"They could get one,"},{"Start":"01:15.485 ","End":"01:18.305","Text":"which was only the lights,"},{"Start":"01:18.305 ","End":"01:23.955","Text":"only the dark or something intermediate between the 2."},{"Start":"01:23.955 ","End":"01:29.055","Text":"By looking at which bands they got after 1 generation,"},{"Start":"01:29.055 ","End":"01:32.490","Text":"and then after a second-generation,"},{"Start":"01:32.490 ","End":"01:35.840","Text":"that\u0027s a first replication and then a second replication,"},{"Start":"01:35.840 ","End":"01:43.010","Text":"they could deduce that the DNA was replicated in a semi-conservative manner."},{"Start":"01:43.010 ","End":"01:45.875","Text":"We can see that in this figure,"},{"Start":"01:45.875 ","End":"01:49.580","Text":"they ruled out both the conservative and the dispersive model."},{"Start":"01:49.580 ","End":"01:52.190","Text":"The answer was semi-conservative,"},{"Start":"01:52.190 ","End":"01:58.250","Text":"because they ended up in the second replication with the intermediate density DNA,"},{"Start":"01:58.250 ","End":"01:59.645","Text":"that\u0027s these 2,"},{"Start":"01:59.645 ","End":"02:01.580","Text":"and another band on top,"},{"Start":"02:01.580 ","End":"02:05.060","Text":"which was only the lighter DNA."},{"Start":"02:05.060 ","End":"02:08.700","Text":"So our answer was semi-conservative."}],"ID":28189},{"Watched":false,"Name":"Exercise 7","Duration":"1m 2s","ChapterTopicVideoID":27064,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:08.850","Text":"If the sequence of the 5 prime to 3 prime strand is AATGCTAC,"},{"Start":"00:08.850 ","End":"00:13.710","Text":"then the complimentary sequence has which of the following sequences,"},{"Start":"00:13.710 ","End":"00:15.300","Text":"the ones that are here?"},{"Start":"00:15.300 ","End":"00:24.375","Text":"We note that the sequence here is 5 prime to 3 prime and the answers,"},{"Start":"00:24.375 ","End":"00:30.390","Text":"we have 3 prime on the left and 5 prime on the right."},{"Start":"00:30.390 ","End":"00:35.000","Text":"If we want to write what is a complementary sequence"},{"Start":"00:35.000 ","End":"00:39.146","Text":"to the original sequence and we wanted 3 prime to 5 prime,"},{"Start":"00:39.146 ","End":"00:40.730","Text":"let\u0027s write under it."},{"Start":"00:40.730 ","End":"00:46.755","Text":"Opposite the A is T, A, C,"},{"Start":"00:46.755 ","End":"00:49.755","Text":"G, A, T,"},{"Start":"00:49.755 ","End":"00:52.815","Text":"G. That\u0027s 3 prime,"},{"Start":"00:52.815 ","End":"00:54.450","Text":"5 prime on the right."},{"Start":"00:54.450 ","End":"00:56.945","Text":"Which of these is the correct answer?"},{"Start":"00:56.945 ","End":"01:02.820","Text":"Well, let\u0027s have a look. It is the third one. That\u0027s our answer."}],"ID":28190},{"Watched":false,"Name":"Exercise 8","Duration":"1m 38s","ChapterTopicVideoID":27063,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.230 ","End":"00:06.885","Text":"How did Meselson and Stahl support the Watson and Crick double-helix model?"},{"Start":"00:06.885 ","End":"00:10.260","Text":"They demonstrated that each strand serves as a template for"},{"Start":"00:10.260 ","End":"00:13.905","Text":"synthesizing a new strand of DNA?"},{"Start":"00:13.905 ","End":"00:20.130","Text":"Or they showed that DNA strands break and recombine without losing genetic material?"},{"Start":"00:20.130 ","End":"00:22.560","Text":"Or they proved that DNA maintains"},{"Start":"00:22.560 ","End":"00:26.625","Text":"a double-helix structure while undergoing semi-conservative replication?"},{"Start":"00:26.625 ","End":"00:30.540","Text":"Or they demonstrated that conservative replication maintains"},{"Start":"00:30.540 ","End":"00:34.939","Text":"the complementary base pairing of each DNA helix."},{"Start":"00:34.939 ","End":"00:39.350","Text":"Let\u0027s recall the Meselson and Stahl experiment."},{"Start":"00:39.350 ","End":"00:41.605","Text":"In that experiment,"},{"Start":"00:41.605 ","End":"00:47.915","Text":"you\u0027ll remember that they used heavy nitrogen to label the DNA"},{"Start":"00:47.915 ","End":"00:49.640","Text":"at first and then they did"},{"Start":"00:49.640 ","End":"00:54.805","Text":"one first replication and second replication in which they asked,"},{"Start":"00:54.805 ","End":"00:59.405","Text":"what the density of the new DNA was that was being created?"},{"Start":"00:59.405 ","End":"01:03.110","Text":"For that they were looking at"},{"Start":"01:03.110 ","End":"01:08.255","Text":"what the density of the different DNAs that was created was."},{"Start":"01:08.255 ","End":"01:12.170","Text":"Therefore, demonstrated actually that each strand can"},{"Start":"01:12.170 ","End":"01:16.190","Text":"serve as a template for synthesizing a new strand of DNA."},{"Start":"01:16.190 ","End":"01:20.765","Text":"That was the semi-conservative model."},{"Start":"01:20.765 ","End":"01:28.850","Text":"That\u0027s the explanation that each DNA strand was making an entire second strand."},{"Start":"01:28.850 ","End":"01:32.060","Text":"Not dispersive where you had different pieces on"},{"Start":"01:32.060 ","End":"01:35.870","Text":"the same strand and not having 2 strands of DNA,"},{"Start":"01:35.870 ","End":"01:38.970","Text":"both of whom were new."}],"ID":28191},{"Watched":false,"Name":"Exercise 9","Duration":"1m 4s","ChapterTopicVideoID":27062,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:02.850","Text":"Which of the following components is"},{"Start":"00:02.850 ","End":"00:07.845","Text":"not involved during the formation of the replication fork?"},{"Start":"00:07.845 ","End":"00:11.130","Text":"We\u0027re talking about the formation of the replication fork,"},{"Start":"00:11.130 ","End":"00:13.650","Text":"the initiation of replication."},{"Start":"00:13.650 ","End":"00:16.740","Text":"So is it single-stranded binding proteins, helicase,"},{"Start":"00:16.740 ","End":"00:20.235","Text":"origin replication, or ligase?"},{"Start":"00:20.235 ","End":"00:23.760","Text":"Let\u0027s recall that in the beginning,"},{"Start":"00:23.760 ","End":"00:25.965","Text":"the initiation of replication,"},{"Start":"00:25.965 ","End":"00:30.330","Text":"we have several different proteins that are part of it."},{"Start":"00:30.330 ","End":"00:32.610","Text":"We\u0027ve got DNA helicase,"},{"Start":"00:32.610 ","End":"00:35.445","Text":"we have the single-stranded binding proteins,"},{"Start":"00:35.445 ","End":"00:37.200","Text":"which are binding,"},{"Start":"00:37.200 ","End":"00:42.195","Text":"we have a gyrase that relieves a strain."},{"Start":"00:42.195 ","End":"00:47.275","Text":"But there\u0027s no ligase here, is there?"},{"Start":"00:47.275 ","End":"00:49.190","Text":"What\u0027s our answer?"},{"Start":"00:49.190 ","End":"00:50.630","Text":"Of course, we\u0027ve got the origin."},{"Start":"00:50.630 ","End":"00:54.020","Text":"Yes, we\u0027ve got the origin where everything starts."},{"Start":"00:54.020 ","End":"00:58.955","Text":"Our answer then has to be ligase because we were asked"},{"Start":"00:58.955 ","End":"01:00.815","Text":"which of the following components is"},{"Start":"01:00.815 ","End":"01:04.980","Text":"not involved during the formation of the replication fork."}],"ID":28192},{"Watched":false,"Name":"Exercise 10","Duration":"52s","ChapterTopicVideoID":27061,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.110 ","End":"00:06.029","Text":"Which of the following does the enzyme primase synthesize?"},{"Start":"00:06.029 ","End":"00:09.780","Text":"Primase. Is that a DNA primer,"},{"Start":"00:09.780 ","End":"00:16.005","Text":"an RNA primer, Okazaki fragments, or phosphodiester linkage?"},{"Start":"00:16.005 ","End":"00:25.035","Text":"Let\u0027s recall the primase and recall the primer on the lagging strand of DNA."},{"Start":"00:25.035 ","End":"00:35.550","Text":"We can see from this figure that it is an RNA primer which is formed by the primase."},{"Start":"00:35.550 ","End":"00:40.065","Text":"Our answer of course will be an RNA primer."},{"Start":"00:40.065 ","End":"00:44.030","Text":"It\u0027s true that it is the beginning of an Okazaki fragment"},{"Start":"00:44.030 ","End":"00:48.304","Text":"and it\u0027s true that there is DNA which is synthesized further,"},{"Start":"00:48.304 ","End":"00:53.130","Text":"but the original primer is made of RNA."}],"ID":28193},{"Watched":false,"Name":"Exercise 11","Duration":"36s","ChapterTopicVideoID":27060,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:03.765","Text":"In which direction does DNA replication take place?"},{"Start":"00:03.765 ","End":"00:07.050","Text":"Is it 5\u0027 to 3\u0027,"},{"Start":"00:07.050 ","End":"00:09.615","Text":"3\u0027 to 5\u0027, and then it just says 5\u0027 and 3\u0027?"},{"Start":"00:09.615 ","End":"00:12.270","Text":"Well, those can\u0027t really be right, can they?"},{"Start":"00:12.270 ","End":"00:15.225","Text":"It\u0027s got to be either a or b."},{"Start":"00:15.225 ","End":"00:20.560","Text":"Let\u0027s recall that we have an addition to the 3\u0027 end."},{"Start":"00:20.560 ","End":"00:24.720","Text":"Yes, we have the nucleotide which is added to the 3\u0027 end."},{"Start":"00:24.720 ","End":"00:33.300","Text":"But the overall direction of replication is from the 5\u0027 to the 3\u0027 and therefore,"},{"Start":"00:33.300 ","End":"00:36.970","Text":"a will be our answer, 5\u0027 to 3\u0027."}],"ID":28194},{"Watched":false,"Name":"Exercise 12","Duration":"1m 18s","ChapterTopicVideoID":27059,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:05.170","Text":"A scientist randomly mutates the DNA of a bacterium."},{"Start":"00:05.170 ","End":"00:09.240","Text":"She then sequences the bacterium\u0027s daughter cells and finds that"},{"Start":"00:09.240 ","End":"00:13.830","Text":"the daughters have many errors in their replicated DNA;"},{"Start":"00:13.830 ","End":"00:16.800","Text":"many errors in their replicated DNA."},{"Start":"00:16.800 ","End":"00:21.885","Text":"The parent\u0027s bacterium likely acquired a mutation in which enzyme?"},{"Start":"00:21.885 ","End":"00:23.370","Text":"Would it be DNA ligase,"},{"Start":"00:23.370 ","End":"00:25.245","Text":"DNA polymerase II,"},{"Start":"00:25.245 ","End":"00:29.280","Text":"primase, or DNA polymerase I?"},{"Start":"00:29.280 ","End":"00:35.235","Text":"If you recall, there is proofreading by DNA polymerase,"},{"Start":"00:35.235 ","End":"00:37.965","Text":"and which DNA polymerase is that?"},{"Start":"00:37.965 ","End":"00:43.665","Text":"Is it DNA polymerase I, II, III?"},{"Start":"00:43.665 ","End":"00:49.400","Text":"Well, in bacteria you\u0027ll remember we have polymerase I and polymerase III."},{"Start":"00:49.400 ","End":"00:55.485","Text":"Polymerase III is the main enzyme which is doing most of the polymerization,"},{"Start":"00:55.485 ","End":"01:02.425","Text":"and polymerase I has to do with the formation of the Okazaki fragments,"},{"Start":"01:02.425 ","End":"01:05.525","Text":"and it also has some repair activity."},{"Start":"01:05.525 ","End":"01:07.235","Text":"What is our answer?"},{"Start":"01:07.235 ","End":"01:16.160","Text":"Our answer is DNA polymerase I because we don\u0027t have any polymerase III in our question,"},{"Start":"01:16.160 ","End":"01:19.470","Text":"so it\u0027s DNA polymerase I."}],"ID":28195},{"Watched":false,"Name":"Exercise 13","Duration":"34s","ChapterTopicVideoID":27058,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:03.390","Text":"Now we\u0027re going to be talking about eukaryotes because"},{"Start":"00:03.390 ","End":"00:08.055","Text":"we\u0027re asking about the ends of the linear chromosomes: That\u0027s in eukaryotes,"},{"Start":"00:08.055 ","End":"00:09.840","Text":"are maintained by what?"},{"Start":"00:09.840 ","End":"00:12.885","Text":"The ends of the chromosomes."},{"Start":"00:12.885 ","End":"00:14.370","Text":"Is it helicase, primase,"},{"Start":"00:14.370 ","End":"00:17.280","Text":"DNA polymerase or Telomerase."},{"Start":"00:17.280 ","End":"00:23.565","Text":"Well, recall that the ends of the chromosomes in eukaryotes are called"},{"Start":"00:23.565 ","End":"00:30.360","Text":"telomerase and it is the enzyme telomerase that adds those telomerase."},{"Start":"00:30.360 ","End":"00:34.870","Text":"Clearly, our answer must be telomerase."}],"ID":28196},{"Watched":false,"Name":"Exercise 14","Duration":"1m 40s","ChapterTopicVideoID":27057,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.110","Text":"Which of the following is not a true statement"},{"Start":"00:04.110 ","End":"00:08.730","Text":"comparing prokaryotic and eukaryotic DNA replication?"},{"Start":"00:08.730 ","End":"00:12.810","Text":"Comparing prokaryotes and eukaryotes."},{"Start":"00:12.810 ","End":"00:19.785","Text":"Both eukaryotic and prokaryotic DNA polymerases build off RNA primers made by primase."},{"Start":"00:19.785 ","End":"00:22.335","Text":"Is that true? Yes, it is true."},{"Start":"00:22.335 ","End":"00:24.240","Text":"we\u0027ll cross that off."},{"Start":"00:24.240 ","End":"00:28.530","Text":"Eukaryotic DNA replication requires multiple replication forks,"},{"Start":"00:28.530 ","End":"00:31.110","Text":"while prokaryotic replication uses"},{"Start":"00:31.110 ","End":"00:35.040","Text":"a single origin to rapidly replicate the entire genome."},{"Start":"00:35.040 ","End":"00:36.825","Text":"That\u0027s certainly true,"},{"Start":"00:36.825 ","End":"00:38.700","Text":"because there are many chromosomes,"},{"Start":"00:38.700 ","End":"00:43.070","Text":"so there are many multiple replication forks in the DNA is so"},{"Start":"00:43.070 ","End":"00:48.230","Text":"large and it replicates so slowly that it needs multiple replication forks,"},{"Start":"00:48.230 ","End":"00:50.285","Text":"whereas in bacteria there\u0027s only one."},{"Start":"00:50.285 ","End":"00:53.765","Text":"Since we\u0027re looking for a wrong answer, we\u0027ll cross that out."},{"Start":"00:53.765 ","End":"00:58.775","Text":"DNA replication always occurs in the nucleus."},{"Start":"00:58.775 ","End":"01:04.910","Text":"Well, there\u0027s a nucleus only in eukaryotes, not in prokaryotes."},{"Start":"01:04.910 ","End":"01:09.220","Text":"We\u0027re looking for what\u0027s not true."},{"Start":"01:09.220 ","End":"01:14.480","Text":"That might be it. Let\u0027s look at the last answer and see whether that could be true."},{"Start":"01:14.480 ","End":"01:19.745","Text":"Eukaryotic DNA replication involves more polymerases than prokaryotic replication."},{"Start":"01:19.745 ","End":"01:21.375","Text":"Yes, we saw that,"},{"Start":"01:21.375 ","End":"01:28.810","Text":"that in eukaryotes we have Alpha, Epsilon, Delta."},{"Start":"01:28.810 ","End":"01:30.800","Text":"There are more polymerases."},{"Start":"01:30.800 ","End":"01:33.770","Text":"They were about 14 of them actually in eukaryotes."},{"Start":"01:33.770 ","End":"01:35.330","Text":"That\u0027s a true statement."},{"Start":"01:35.330 ","End":"01:37.070","Text":"We\u0027ve got a cross that off."},{"Start":"01:37.070 ","End":"01:41.460","Text":"Clearly, our answer then is going to be C."}],"ID":28197},{"Watched":false,"Name":"Exercise 15","Duration":"39s","ChapterTopicVideoID":27056,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:05.010","Text":"During proofreading, which of the following enzymes reads the DNA?"},{"Start":"00:05.010 ","End":"00:10.875","Text":"Primase, topoisomerase, DNA polymerase, or a helicase."},{"Start":"00:10.875 ","End":"00:13.185","Text":"Well, that\u0027s really pretty easy."},{"Start":"00:13.185 ","End":"00:19.155","Text":"Remember, the DNA polymerase is the proofreading molecule,"},{"Start":"00:19.155 ","End":"00:23.835","Text":"is the proofreading enzyme and as it polymerizes,"},{"Start":"00:23.835 ","End":"00:25.380","Text":"if a mistake is made,"},{"Start":"00:25.380 ","End":"00:29.280","Text":"then it backs up with an exonuclease and"},{"Start":"00:29.280 ","End":"00:34.305","Text":"replaces the nucleotide that\u0027s wrong and then fills in."},{"Start":"00:34.305 ","End":"00:39.880","Text":"So clearly our answer must be DNA polymerase."}],"ID":28198},{"Watched":false,"Name":"Exercise 16","Duration":"28s","ChapterTopicVideoID":27072,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:05.865","Text":"The initial mechanism for repairing nucleotide errors in DNA is mismatch repair,"},{"Start":"00:05.865 ","End":"00:12.615","Text":"DNA polymerase proofreading, nucleotide excision repair, or thymine dimers?"},{"Start":"00:12.615 ","End":"00:15.810","Text":"The initial mechanism is for repairing,"},{"Start":"00:15.810 ","End":"00:18.720","Text":"so that\u0027s during replication."},{"Start":"00:18.720 ","End":"00:23.507","Text":"The DNA polymerase itself does the proofreading,"},{"Start":"00:23.507 ","End":"00:28.450","Text":"so that\u0027s got to be the answer, DNA polymerase proofreading."}],"ID":28199},{"Watched":false,"Name":"Exercise 17","Duration":"1m 59s","ChapterTopicVideoID":27071,"CourseChapterTopicPlaylistID":261640,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:05.820","Text":"A scientist creates fruit fly larvae with a mutation that"},{"Start":"00:05.820 ","End":"00:11.430","Text":"eliminates the 5\u0027-3\u0027 exonuclease function of the DNA polymerase III."},{"Start":"00:11.430 ","End":"00:16.030","Text":"This is exonuclease function of DNA polymerase III."},{"Start":"00:16.030 ","End":"00:19.230","Text":"That\u0027s the main enzyme that\u0027s doing the polymerization."},{"Start":"00:19.230 ","End":"00:21.840","Text":"Which prediction about the mutational load in"},{"Start":"00:21.840 ","End":"00:24.885","Text":"the adult fruit flies is most likely to be correct?"},{"Start":"00:24.885 ","End":"00:26.880","Text":"Is it that the adults with"},{"Start":"00:26.880 ","End":"00:31.275","Text":"DNA polymerase III mutation will have significantly more mutations than average,"},{"Start":"00:31.275 ","End":"00:33.420","Text":"that the adults with DNA polymerase mutation will have"},{"Start":"00:33.420 ","End":"00:36.870","Text":"slightly more mutations than average,"},{"Start":"00:36.870 ","End":"00:39.330","Text":"that the adults were the DNA polymerase mutation will have"},{"Start":"00:39.330 ","End":"00:43.528","Text":"the same number of mutations as average,"},{"Start":"00:43.528 ","End":"00:49.810","Text":"and that the adults with DNA polymerase III mutation will have fewer mutations?"},{"Start":"00:49.810 ","End":"00:51.330","Text":"Is it fewer, more,"},{"Start":"00:51.330 ","End":"00:54.251","Text":"or the same really?"},{"Start":"00:54.251 ","End":"01:00.844","Text":"Recall that we\u0027re talking about the proofreading of by DNA polymerase,"},{"Start":"01:00.844 ","End":"01:07.610","Text":"and that when a nucleotide is put in by mistake, then the polymerase,"},{"Start":"01:07.610 ","End":"01:15.035","Text":"which is moving in the 5\u0027-3\u0027 direction,"},{"Start":"01:15.035 ","End":"01:18.130","Text":"then the polymerase is moving in this direction."},{"Start":"01:18.130 ","End":"01:19.760","Text":"When a mistake is made,"},{"Start":"01:19.760 ","End":"01:23.975","Text":"it has to back up, go 3\u0027-5\u0027."},{"Start":"01:23.975 ","End":"01:28.735","Text":"That would be the 3\u0027-5\u0027 exo."},{"Start":"01:28.735 ","End":"01:39.605","Text":"In our question, we were asking about 5\u0027-3\u0027 exonuclease, not 3\u0027-5\u0027."},{"Start":"01:39.605 ","End":"01:46.344","Text":"Since it\u0027s the 3\u0027-5\u0027 exonuclease activity that corrects things,"},{"Start":"01:46.344 ","End":"01:53.645","Text":"if no corrections are made because of the mutation in that 5\u0027-3\u0027 exo,"},{"Start":"01:53.645 ","End":"02:00.180","Text":"then we would have the same number of mutations as average."}],"ID":28200}],"Thumbnail":null,"ID":261640},{"Name":"Genes And Proteins","TopicPlaylistFirstVideoID":0,"Duration":null,"Videos":[{"Watched":false,"Name":"Termination and processing of translated proteins","Duration":"4m 53s","ChapterTopicVideoID":27073,"CourseChapterTopicPlaylistID":261641,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.260","Text":"Now that we know a lot about elongation,"},{"Start":"00:04.260 ","End":"00:05.955","Text":"let\u0027s go to the next stage,"},{"Start":"00:05.955 ","End":"00:09.045","Text":"which is termination of translation."},{"Start":"00:09.045 ","End":"00:10.635","Text":"How does all this end?"},{"Start":"00:10.635 ","End":"00:12.360","Text":"Well, it occurs, of course,"},{"Start":"00:12.360 ","End":"00:15.450","Text":"when a nonsense that is a stop codon,"},{"Start":"00:15.450 ","End":"00:18.540","Text":"which you will remember there are 3 of them, UAA,"},{"Start":"00:18.540 ","End":"00:23.310","Text":"UAG or UGA, is encountered."},{"Start":"00:23.310 ","End":"00:25.080","Text":"There were these 2 sites."},{"Start":"00:25.080 ","End":"00:30.105","Text":"Remember the aminoacyl site and the peptidyl site, the P site."},{"Start":"00:30.105 ","End":"00:36.920","Text":"The A site, the amino acyl site can also accept something called a release factor,"},{"Start":"00:36.920 ","End":"00:40.335","Text":"that\u0027s this pink molecule."},{"Start":"00:40.335 ","End":"00:42.950","Text":"Instead of an amino acid going into here,"},{"Start":"00:42.950 ","End":"00:44.255","Text":"a charged amino acid,"},{"Start":"00:44.255 ","End":"00:46.130","Text":"if there is a stop codon there,"},{"Start":"00:46.130 ","End":"00:50.630","Text":"it will not accept an amino acid tRNA,"},{"Start":"00:50.630 ","End":"00:56.915","Text":"but rather it will accept a release factor into that position,"},{"Start":"00:56.915 ","End":"01:00.785","Text":"and that causes the addition of a water molecule to"},{"Start":"01:00.785 ","End":"01:06.650","Text":"the peptide and its carboxyl and instead of an amino acid."},{"Start":"01:06.650 ","End":"01:08.960","Text":"It\u0027s not adding an amino acid,"},{"Start":"01:08.960 ","End":"01:14.050","Text":"and then that forces the P site here"},{"Start":"01:14.050 ","End":"01:20.000","Text":"to detach from its tRNA and the newly-made protein is released."},{"Start":"01:20.000 ","End":"01:25.490","Text":"The small and large ribosomal subunits will then dissociate one from the other,"},{"Start":"01:25.490 ","End":"01:27.290","Text":"and then almost immediately,"},{"Start":"01:27.290 ","End":"01:33.155","Text":"they\u0027ll reattach into a new RNA to initiate translation."},{"Start":"01:33.155 ","End":"01:36.289","Text":"Again, after the translation is completed,"},{"Start":"01:36.289 ","End":"01:40.040","Text":"the messenger RNA is degraded and the nucleotides"},{"Start":"01:40.040 ","End":"01:43.920","Text":"are reused in another transcription reaction."},{"Start":"01:43.920 ","End":"01:49.390","Text":"The messenger RNA then has done its job if it\u0027s not translated again."},{"Start":"01:49.390 ","End":"01:55.150","Text":"In fact, these ribosomes protect the messenger RNA from degradation."},{"Start":"01:55.150 ","End":"01:59.690","Text":"Now what happens to the protein after it\u0027s made?"},{"Start":"01:59.690 ","End":"02:03.320","Text":"Well, it folds on itself,"},{"Start":"02:03.320 ","End":"02:04.520","Text":"sometimes with some help."},{"Start":"02:04.520 ","End":"02:06.635","Text":"It can be modified,"},{"Start":"02:06.635 ","End":"02:08.850","Text":"that is chemically modified in various ways,"},{"Start":"02:08.850 ","End":"02:13.595","Text":"and it needs to be targeted to get to the right place in the cell or sometimes,"},{"Start":"02:13.595 ","End":"02:16.760","Text":"out of the cell in order to do its function."},{"Start":"02:16.760 ","End":"02:18.800","Text":"In eukaryotes now,"},{"Start":"02:18.800 ","End":"02:24.485","Text":"the synthesis finishes in the cytosol, unless that,"},{"Start":"02:24.485 ","End":"02:27.890","Text":"but it\u0027s on the cytosol side of the ER,"},{"Start":"02:27.890 ","End":"02:31.535","Text":"that\u0027s the endoplasmic reticulum that\u0027s shown here in blue,"},{"Start":"02:31.535 ","End":"02:34.565","Text":"so it\u0027s in the cytosol part,"},{"Start":"02:34.565 ","End":"02:39.710","Text":"and sometimes there is a polypeptide signal,"},{"Start":"02:39.710 ","End":"02:43.445","Text":"a particular sequence in the protein,"},{"Start":"02:43.445 ","End":"02:45.920","Text":"which is called a signal peptide,"},{"Start":"02:45.920 ","End":"02:49.130","Text":"depends on, was encoded for this particular protein,"},{"Start":"02:49.130 ","End":"02:52.640","Text":"but for some proteins that are going to have to go through a membrane"},{"Start":"02:52.640 ","End":"02:56.300","Text":"or be embedded in the membrane or move to a specific place in the cell,"},{"Start":"02:56.300 ","End":"03:03.035","Text":"they will have this signal peptide at the N-terminus of the protein."},{"Start":"03:03.035 ","End":"03:06.650","Text":"The polypeptides that are destined for the ER or"},{"Start":"03:06.650 ","End":"03:11.435","Text":"the endoplasmic reticulum or for secretion are marked with the signal peptide,"},{"Start":"03:11.435 ","End":"03:13.175","Text":"as we just said."},{"Start":"03:13.175 ","End":"03:23.000","Text":"Now, that sequence then is recognized by a signal recognition particle, this SRP,"},{"Start":"03:23.000 ","End":"03:25.490","Text":"and it binds to the peptide,"},{"Start":"03:25.490 ","End":"03:30.200","Text":"and that\u0027s then the SRP is recognized by a,"},{"Start":"03:30.200 ","End":"03:38.205","Text":"here\u0027s the receptor protein that is in the membrane of the endoplasmic reticulum."},{"Start":"03:38.205 ","End":"03:42.924","Text":"Once the protein reaches that position,"},{"Start":"03:42.924 ","End":"03:46.475","Text":"it will then be pushed through."},{"Start":"03:46.475 ","End":"03:52.340","Text":"It will translate right through the membrane and will find"},{"Start":"03:52.340 ","End":"03:58.820","Text":"itself at the end of the day inside the lumen of the endoplasmic reticulum,"},{"Start":"03:58.820 ","End":"04:06.235","Text":"and very often the signal peptide will be clipped off as it says here."},{"Start":"04:06.235 ","End":"04:13.085","Text":"Many proteins, after they\u0027ve either gotten into the lumen of the ER or maybe not,"},{"Start":"04:13.085 ","End":"04:17.390","Text":"then fold into a 3-dimensional structure."},{"Start":"04:17.390 ","End":"04:20.225","Text":"And sometimes, often actually,"},{"Start":"04:20.225 ","End":"04:26.090","Text":"that folding is helped by other molecules that are usually proteins"},{"Start":"04:26.090 ","End":"04:32.010","Text":"themselves that are called chaperones because they chaperone the folding of the proteins."},{"Start":"04:32.010 ","End":"04:36.350","Text":"Of course, the 3-dimensional structure of the protein is going to be very"},{"Start":"04:36.350 ","End":"04:43.115","Text":"important for its function and will also prevent its aggregation."},{"Start":"04:43.115 ","End":"04:47.510","Text":"Abnormal temperatures or pH conditions can"},{"Start":"04:47.510 ","End":"04:54.000","Text":"prevent the correct folding and cause dysfunctional proteins."}],"ID":28201},{"Watched":false,"Name":"The central genetic dogma","Duration":"6m 40s","ChapterTopicVideoID":27074,"CourseChapterTopicPlaylistID":261641,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.290 ","End":"00:06.030","Text":"Well, now that we\u0027ve looked at the structure of DNA and how it\u0027s replicated."},{"Start":"00:06.030 ","End":"00:07.835","Text":"Let\u0027s see how it\u0027s used."},{"Start":"00:07.835 ","End":"00:11.625","Text":"We\u0027ll start by talking about the genetic code."},{"Start":"00:11.625 ","End":"00:16.770","Text":"There is a particular code that is used throughout"},{"Start":"00:16.770 ","End":"00:22.575","Text":"biology and there is a central dogma of DNA to protein synthesis."},{"Start":"00:22.575 ","End":"00:24.915","Text":"What is this dogma?"},{"Start":"00:24.915 ","End":"00:27.840","Text":"The dogma is that DNA,"},{"Start":"00:27.840 ","End":"00:31.560","Text":"double-stranded DNA that we know is transcribed."},{"Start":"00:31.560 ","End":"00:35.340","Text":"It\u0027s copying into messenger RNA."},{"Start":"00:35.340 ","End":"00:37.850","Text":"Transcription, is what this is called."},{"Start":"00:37.850 ","End":"00:43.070","Text":"Transcription generates messenger RNA and messenger RNA is"},{"Start":"00:43.070 ","End":"00:49.640","Text":"a mobile molecular copy of 1 or more genes with an alphabet of A,"},{"Start":"00:49.640 ","End":"00:52.100","Text":"C, G, and U."},{"Start":"00:52.100 ","End":"00:56.080","Text":"Remember the DNA had the alphabet of A,"},{"Start":"00:56.080 ","End":"00:58.860","Text":"C, G and T,"},{"Start":"00:58.860 ","End":"01:01.034","Text":"where A was adenine,"},{"Start":"01:01.034 ","End":"01:02.355","Text":"C was cytosine,"},{"Start":"01:02.355 ","End":"01:06.059","Text":"G was guanosine, and T was thymine,"},{"Start":"01:06.059 ","End":"01:12.484","Text":"but in RNA, thymine is replaced by uracil and if you\u0027ll look at the chemistry,"},{"Start":"01:12.484 ","End":"01:14.585","Text":"they\u0027re actually quite similar."},{"Start":"01:14.585 ","End":"01:19.770","Text":"So DNA is replicated and then"},{"Start":"01:19.770 ","End":"01:25.070","Text":"it\u0027s transcribed but rarely in biology is it reversed transcribed."},{"Start":"01:25.070 ","End":"01:30.380","Text":"In other words, the information goes from messenger RNA to DNA."},{"Start":"01:30.380 ","End":"01:33.395","Text":"It does happen in some cases, but rarely."},{"Start":"01:33.395 ","End":"01:36.935","Text":"Now after the messenger RNA is transcribed,"},{"Start":"01:36.935 ","End":"01:45.145","Text":"it is then used as a template on these machines that are called ribosomes."},{"Start":"01:45.145 ","End":"01:50.660","Text":"Ribosomes are a combination of proteins and a different kind of RNA,"},{"Start":"01:50.660 ","End":"01:54.470","Text":"a structural RNA that converts or translates,"},{"Start":"01:54.470 ","End":"01:57.440","Text":"this is called translation,"},{"Start":"01:57.440 ","End":"02:02.680","Text":"the nucleotide based genetic information into a protein product."},{"Start":"02:02.680 ","End":"02:06.230","Text":"Now what is the language of the proteins?"},{"Start":"02:06.230 ","End":"02:12.365","Text":"The language of the DNA and RNA are the nucleotides A, C, G,"},{"Start":"02:12.365 ","End":"02:21.105","Text":"and T or U but the language of proteins is amino acids and there were 4,"},{"Start":"02:21.105 ","End":"02:23.330","Text":"if you remember, nucleotides A, C, G,"},{"Start":"02:23.330 ","End":"02:30.305","Text":"and U but there are 20 different amino acids, 20 different letters."},{"Start":"02:30.305 ","End":"02:32.585","Text":"Now, the difference amino acids have"},{"Start":"02:32.585 ","End":"02:37.235","Text":"different chemistries and different structural constraints,"},{"Start":"02:37.235 ","End":"02:41.120","Text":"but they have a number of things which are in common."},{"Start":"02:41.120 ","End":"02:46.700","Text":"Let\u0027s see what\u0027s common and what\u0027s different and it\u0027s actually this difference,"},{"Start":"02:46.700 ","End":"02:48.860","Text":"the variation in amino acid sequence,"},{"Start":"02:48.860 ","End":"02:54.830","Text":"which will be the key to the protein\u0027s structure and functional variation."},{"Start":"02:54.830 ","End":"02:57.790","Text":"Let\u0027s first look at what\u0027s common."},{"Start":"02:57.790 ","End":"03:01.970","Text":"Each amino acid is composed of an amino acid group."},{"Start":"03:01.970 ","End":"03:03.290","Text":"Let\u0027s look at 1 of them."},{"Start":"03:03.290 ","End":"03:06.200","Text":"Here\u0027s the amine group."},{"Start":"03:06.200 ","End":"03:09.140","Text":"You\u0027ll see that this is on each of the amino acids that"},{"Start":"03:09.140 ","End":"03:12.710","Text":"are shown here and a carboxyl group."},{"Start":"03:12.710 ","End":"03:14.975","Text":"Here\u0027s the carboxyl group,"},{"Start":"03:14.975 ","End":"03:17.540","Text":"which is found in every amino acid."},{"Start":"03:17.540 ","End":"03:25.100","Text":"Now notice between the amino group and the carboxyl group is 1 carbon and this carbon,"},{"Start":"03:25.100 ","End":"03:27.230","Text":"the central carbon here,"},{"Start":"03:27.230 ","End":"03:30.710","Text":"has something else attached to it in each amino acids,"},{"Start":"03:30.710 ","End":"03:35.165","Text":"something different, which is called an R group."},{"Start":"03:35.165 ","End":"03:45.270","Text":"It\u0027s a group which is going to be on the side of each of these amino acids."},{"Start":"03:45.270 ","End":"03:49.195","Text":"That\u0027s the side chain of each of them and"},{"Start":"03:49.195 ","End":"03:53.780","Text":"in this example are colored different ways depending on"},{"Start":"03:53.780 ","End":"03:56.900","Text":"whether they are hydrophobic or"},{"Start":"03:56.900 ","End":"04:03.115","Text":"hydrophilic or whether they\u0027re negatively charged or positively charged and so on."},{"Start":"04:03.115 ","End":"04:04.670","Text":"As we just mentioned,"},{"Start":"04:04.670 ","End":"04:07.010","Text":"the side chain can be either polar,"},{"Start":"04:07.010 ","End":"04:12.500","Text":"nonpolar charged and it can be large as you can see here or it can be small."},{"Start":"04:12.500 ","End":"04:15.095","Text":"They\u0027re all sorts of variations."},{"Start":"04:15.095 ","End":"04:16.760","Text":"In the central dogma, again,"},{"Start":"04:16.760 ","End":"04:21.845","Text":"DNA encodes RNA, and the RNA encodes protein."},{"Start":"04:21.845 ","End":"04:29.615","Text":"We have a flow of genetic information which goes from DNA to messenger RNA to protein."},{"Start":"04:29.615 ","End":"04:36.680","Text":"Yes we have DNA which is transcribed into 2 and RNA,"},{"Start":"04:36.680 ","End":"04:41.315","Text":"which is then translated into protein."},{"Start":"04:41.315 ","End":"04:45.830","Text":"Messenger RNA copies, all these different copies."},{"Start":"04:45.830 ","End":"04:50.450","Text":"Of course several copies can be made from 1 piece of DNA."},{"Start":"04:50.450 ","End":"04:53.525","Text":"These mRNA copies of the information in the DNA"},{"Start":"04:53.525 ","End":"04:56.870","Text":"are made and then they\u0027re used for protein synthesis"},{"Start":"04:56.870 ","End":"05:03.530","Text":"or their service templates for the protein synthesis while the DNA itself up here yes,"},{"Start":"05:03.530 ","End":"05:05.600","Text":"is kept, it\u0027s not changed."},{"Start":"05:05.600 ","End":"05:08.945","Text":"It\u0027s kept intact and it\u0027s protected."},{"Start":"05:08.945 ","End":"05:13.550","Text":"The copying of the DNA to RNA is done by"},{"Start":"05:13.550 ","End":"05:16.160","Text":"1 nucleotide is added to"},{"Start":"05:16.160 ","End":"05:19.550","Text":"the messenger RNA stranded every nucleotide read in the DNA strand."},{"Start":"05:19.550 ","End":"05:24.185","Text":"Very similar to replication where we have 1 nucleotide"},{"Start":"05:24.185 ","End":"05:33.120","Text":"added to the next with a primer and such very much like trend in replication of the DNA."},{"Start":"05:33.120 ","End":"05:36.920","Text":"But in translation of the messenger RNA to protein,"},{"Start":"05:36.920 ","End":"05:40.310","Text":"it is not a 1-1 correspondence."},{"Start":"05:40.310 ","End":"05:45.635","Text":"There are 3 messenger RNA nucleotides that\u0027s called a codon."},{"Start":"05:45.635 ","End":"05:50.175","Text":"Here\u0027s 3, 3 and so on."},{"Start":"05:50.175 ","End":"05:56.955","Text":"Each of these 3 is called a codon and each of them correspond to 1 amino acid."},{"Start":"05:56.955 ","End":"06:03.275","Text":"Here\u0027s the 1 amino acid for this 1 codon, and so on."},{"Start":"06:03.275 ","End":"06:06.170","Text":"Each of them corresponds to 1 amino acid in"},{"Start":"06:06.170 ","End":"06:11.839","Text":"the polypeptide sequence and of course this translation is systematic."},{"Start":"06:11.839 ","End":"06:13.730","Text":"You have 1 after the other,"},{"Start":"06:13.730 ","End":"06:17.615","Text":"after the other after the other and it is colinear."},{"Start":"06:17.615 ","End":"06:21.230","Text":"Colinear, that means that if you draw them out,"},{"Start":"06:21.230 ","End":"06:24.440","Text":"you can draw them out in 1 line."},{"Start":"06:24.440 ","End":"06:27.890","Text":"It\u0027s a 2 dimensional sequence;"},{"Start":"06:27.890 ","End":"06:35.585","Text":"goes backwards and forwards but it is not 3 dimensional at this stage."},{"Start":"06:35.585 ","End":"06:37.520","Text":"It doesn\u0027t pack into anything,"},{"Start":"06:37.520 ","End":"06:41.310","Text":"at least not at this stage."}],"ID":28202},{"Watched":false,"Name":"The prokaryotic promoter","Duration":"5m 54s","ChapterTopicVideoID":27075,"CourseChapterTopicPlaylistID":261641,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:07.590","Text":"In prokaryotic transcription, let\u0027s now look at the enzyme that does the transcription."},{"Start":"00:07.590 ","End":"00:11.235","Text":"It\u0027s quite a complicated molecule actually,"},{"Start":"00:11.235 ","End":"00:16.574","Text":"the prokaryotic RNA polymerase,"},{"Start":"00:16.574 ","End":"00:22.350","Text":"and what we find is that the same RNA polymerase is used to transcribe all of"},{"Start":"00:22.350 ","End":"00:26.235","Text":"the prokaryotic genes that\u0027s going to be different from"},{"Start":"00:26.235 ","End":"00:30.420","Text":"eukaryotes in which there is more than 1 RNA polymerase."},{"Start":"00:30.420 ","End":"00:35.614","Text":"Let\u0027s look in more detail at this RNA polymerase in prokaryotes."},{"Start":"00:35.614 ","End":"00:44.285","Text":"We just see that the entire enzyme here is composed of several different sub-units."},{"Start":"00:44.285 ","End":"00:46.055","Text":"There\u0027s what\u0027s called Alpha,"},{"Start":"00:46.055 ","End":"00:48.160","Text":"Beta, Beta prime,"},{"Start":"00:48.160 ","End":"00:50.080","Text":"and a Sigma,"},{"Start":"00:50.080 ","End":"00:55.175","Text":"all of which are going to form something called the holoenzyme."},{"Start":"00:55.175 ","End":"00:56.930","Text":"Let\u0027s look at that, again,"},{"Start":"00:56.930 ","End":"00:59.905","Text":"there are 5 polypeptide subunits,"},{"Start":"00:59.905 ","End":"01:01.335","Text":"2 of them notice,"},{"Start":"01:01.335 ","End":"01:02.430","Text":"they are identical,"},{"Start":"01:02.430 ","End":"01:08.285","Text":"there\u0027s a dimer of Alpha subunits and they\u0027re denoted Alpha,"},{"Start":"01:08.285 ","End":"01:09.770","Text":"Beta, Beta prime,"},{"Start":"01:09.770 ","End":"01:12.615","Text":"and as we said, the Sigma,"},{"Start":"01:12.615 ","End":"01:20.480","Text":"but these 4 polypeptides together are called the core enzyme."},{"Start":"01:20.480 ","End":"01:24.185","Text":"The Sigma is going to be used for promoter recognition,"},{"Start":"01:24.185 ","End":"01:27.620","Text":"it\u0027s really a regulatory subunit,"},{"Start":"01:27.620 ","End":"01:29.950","Text":"not an enzymatic one,"},{"Start":"01:29.950 ","End":"01:33.255","Text":"and therefore it\u0027s not part of the core."},{"Start":"01:33.255 ","End":"01:37.190","Text":"The subunits assemble every time a gene is transcribed,"},{"Start":"01:37.190 ","End":"01:41.270","Text":"and then they disassemble once transcription is complete,"},{"Start":"01:41.270 ","End":"01:42.800","Text":"and as we mentioned,"},{"Start":"01:42.800 ","End":"01:52.450","Text":"the polymerase that contains all 5 subunits is called the holo or complete enzyme."},{"Start":"01:52.730 ","End":"01:57.110","Text":"Now we\u0027re going to look at the Beta subunit."},{"Start":"01:57.110 ","End":"02:01.415","Text":"The Beta sub-unit binds to the ribonucleoside triphosphate"},{"Start":"02:01.415 ","End":"02:06.020","Text":"that will become part of the nascent messenger RNA molecule."},{"Start":"02:06.020 ","End":"02:07.805","Text":"We use this word nascent,"},{"Start":"02:07.805 ","End":"02:11.675","Text":"which means that it\u0027s in the process of being formed."},{"Start":"02:11.675 ","End":"02:14.510","Text":"Nascent messenger RNA molecule is in"},{"Start":"02:14.510 ","End":"02:17.990","Text":"the middle of its transcription, so here for instance,"},{"Start":"02:17.990 ","End":"02:21.170","Text":"we see a nascent messenger RNA molecule,"},{"Start":"02:21.170 ","End":"02:26.905","Text":"it\u0027s being transcribed in this bubble in the DNA."},{"Start":"02:26.905 ","End":"02:34.005","Text":"The Beta prime subunit binds the DNA strand,"},{"Start":"02:34.005 ","End":"02:37.670","Text":"so we\u0027ve got 1 of them binding the ribonucleoside triphosphate,"},{"Start":"02:37.670 ","End":"02:40.510","Text":"the other 1 binding the DNA strands."},{"Start":"02:40.510 ","End":"02:43.810","Text":"Then we have this Sigma subunits,"},{"Start":"02:43.810 ","End":"02:45.280","Text":"sometimes it\u0027s Sigma 70,"},{"Start":"02:45.280 ","End":"02:47.920","Text":"it depends, that\u0027s the molecular weight of the Sigma,"},{"Start":"02:47.920 ","End":"02:52.190","Text":"it depends exactly on where the Sigma is coming from,"},{"Start":"02:52.190 ","End":"02:55.130","Text":"and what organism it is, but in any case,"},{"Start":"02:55.130 ","End":"02:59.420","Text":"this fifth sub-unit is involved in transcription initiation,"},{"Start":"02:59.420 ","End":"03:03.440","Text":"yet it helps with the signaling as we\u0027ll see later,"},{"Start":"03:03.440 ","End":"03:10.725","Text":"and it confers transcriptional specificity and is removed during the elongation process."},{"Start":"03:10.725 ","End":"03:15.100","Text":"There is first the recognition of the promoter;"},{"Start":"03:15.100 ","End":"03:19.370","Text":"the promoter is the region of the DNA that is"},{"Start":"03:19.370 ","End":"03:24.770","Text":"recognized as the position for starting the transcription, that\u0027s called initiation,"},{"Start":"03:24.770 ","End":"03:25.910","Text":"the start of the transcription,"},{"Start":"03:25.910 ","End":"03:28.460","Text":"and then later there\u0027s going to be elongation"},{"Start":"03:28.460 ","End":"03:33.260","Text":"as the transcriptional bubble moves down the DNA,"},{"Start":"03:33.260 ","End":"03:37.685","Text":"and the Sigma will then be released at that point."},{"Start":"03:37.685 ","End":"03:39.260","Text":"Without the Sigma,"},{"Start":"03:39.260 ","End":"03:41.980","Text":"the core enzyme would transcribe from random sites,"},{"Start":"03:41.980 ","End":"03:46.880","Text":"so it\u0027s the specificity of initiation given by the Sigma, and that would produce,"},{"Start":"03:46.880 ","End":"03:52.280","Text":"of course, messenger RNAs that would specify just gibberish in the protein."},{"Start":"03:52.280 ","End":"03:54.350","Text":"So what is that promoter?"},{"Start":"03:54.350 ","End":"03:55.495","Text":"What does it look like?"},{"Start":"03:55.495 ","End":"04:01.670","Text":"The promoter or the DNA sequence onto which the transcription unit binds,"},{"Start":"04:01.670 ","End":"04:07.955","Text":"the transcriptional start is going to be determined by the promoter,"},{"Start":"04:07.955 ","End":"04:09.710","Text":"it\u0027s going to initiate transcription."},{"Start":"04:09.710 ","End":"04:10.970","Text":"What does it look like?"},{"Start":"04:10.970 ","End":"04:14.030","Text":"First of all, where is it located?"},{"Start":"04:14.030 ","End":"04:18.085","Text":"Well, it\u0027s located upstream of the genes that are regulated."},{"Start":"04:18.085 ","End":"04:19.310","Text":"Here\u0027s our plus 1,"},{"Start":"04:19.310 ","End":"04:24.440","Text":"and we\u0027ll notice that at minus 10 and at minus 35,"},{"Start":"04:24.440 ","End":"04:26.390","Text":"roughly in those regions,"},{"Start":"04:26.390 ","End":"04:31.260","Text":"there are consensus sequences in prokaryotes."},{"Start":"04:31.260 ","End":"04:37.490","Text":"Pro consensus sequences that are going to be important for the start of transcription,"},{"Start":"04:37.490 ","End":"04:40.910","Text":"they\u0027re going to be recognized by the Sigma factor."},{"Start":"04:40.910 ","End":"04:45.070","Text":"Not only that, notice that these sequences are consensus sequences,"},{"Start":"04:45.070 ","End":"04:48.748","Text":"so not in every promoter do we have exactly the same sequence,"},{"Start":"04:48.748 ","End":"04:51.380","Text":"they can be more similar to what is"},{"Start":"04:51.380 ","End":"04:54.410","Text":"shown here or a little bit different from what\u0027s shown here,"},{"Start":"04:54.410 ","End":"04:59.030","Text":"and depending on how similar they are to the consensus or different to the consensus,"},{"Start":"04:59.030 ","End":"05:02.960","Text":"can determine the degree of transcription,"},{"Start":"05:02.960 ","End":"05:05.710","Text":"in other words, how much transcription is going to be."},{"Start":"05:05.710 ","End":"05:09.950","Text":"Not all genes are transcribed in the same amount,"},{"Start":"05:09.950 ","End":"05:16.645","Text":"and there are a few elements actually that are conserved in prokaryotic species."},{"Start":"05:16.645 ","End":"05:19.660","Text":"Of course, these 2 elements are particularly conserved,"},{"Start":"05:19.660 ","End":"05:23.465","Text":"that means the different prokaryotes have the same sequences."},{"Start":"05:23.465 ","End":"05:25.445","Text":"So as it says here,"},{"Start":"05:25.445 ","End":"05:30.275","Text":"at the minus 10 and minus 35 regions upstream of the initiation site,"},{"Start":"05:30.275 ","End":"05:33.135","Text":"it has these 2 consensus regions,"},{"Start":"05:33.135 ","End":"05:38.220","Text":"T-A-T-A-A-T, and there is the"},{"Start":"05:38.220 ","End":"05:45.200","Text":"T-T-G-A-C-A that is found at the minus 35."},{"Start":"05:45.200 ","End":"05:48.830","Text":"These sites then are recognized as I mentioned by the Sigma,"},{"Start":"05:48.830 ","End":"05:55.110","Text":"and they determine where the core enzyme will bind."}],"ID":28203},{"Watched":false,"Name":"The three eukaryotic RNA polymerases","Duration":"5m 34s","ChapterTopicVideoID":27076,"CourseChapterTopicPlaylistID":261641,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:06.360","Text":"Hi, welcome back. We\u0027ve been discussing transcription first in prokaryotes,"},{"Start":"00:06.360 ","End":"00:09.405","Text":"and now we\u0027ll move to eukaryotes."},{"Start":"00:09.405 ","End":"00:13.095","Text":"As you know, eukaryotes contain a nucleus and organelles,"},{"Start":"00:13.095 ","End":"00:16.860","Text":"but prokaryotes do not."},{"Start":"00:16.860 ","End":"00:21.225","Text":"If you\u0027re looking at prokaryotic cell for instance,"},{"Start":"00:21.225 ","End":"00:28.199","Text":"we\u0027ve got both transcription and translation happening simultaneously in the same space."},{"Start":"00:28.199 ","End":"00:33.435","Text":"Whereas in eukaryotes, the transcription occurs in the nucleus,"},{"Start":"00:33.435 ","End":"00:39.825","Text":"but it cannot be translated until it is transported into the cytoplasm."},{"Start":"00:39.825 ","End":"00:45.970","Text":"There\u0027s a separation of the 2 spatially and so they cannot occur at the same time either."},{"Start":"00:45.970 ","End":"00:50.420","Text":"A eukaryotic cell needs to transport it\u0027s messenger RNA to the cytoplasm,"},{"Start":"00:50.420 ","End":"00:55.910","Text":"as we said and it also must protect it from being degraded before translation."},{"Start":"00:55.910 ","End":"01:00.710","Text":"Now in addition, there are 3 different RNA polymerases in"},{"Start":"01:00.710 ","End":"01:06.845","Text":"eukaryotes that are employed and each of them transcribes a different subset of genes."},{"Start":"01:06.845 ","End":"01:11.690","Text":"Furthermore, eukaryotic messenger RNAs are usually monogenic."},{"Start":"01:11.690 ","End":"01:14.390","Text":"That is, they encode a single protein,"},{"Start":"01:14.390 ","End":"01:20.270","Text":"whereas in prokaryotes, you\u0027ll remember there were polycistronic messages."},{"Start":"01:20.270 ","End":"01:23.570","Text":"Now let\u0027s look at the 3 stages of"},{"Start":"01:23.570 ","End":"01:28.130","Text":"transcription that are both in eukaryotes and prokaryotes."},{"Start":"01:28.130 ","End":"01:33.075","Text":"There\u0027s initiation, elongation and termination."},{"Start":"01:33.075 ","End":"01:38.305","Text":"What we\u0027ll do is we\u0027ll look at each of these individually now in the eukaryotes."},{"Start":"01:38.305 ","End":"01:41.045","Text":"To remind you, in prokaryotes,"},{"Start":"01:41.045 ","End":"01:44.960","Text":"the polymerase can bind to the DNA templates on its own."},{"Start":"01:44.960 ","End":"01:49.190","Text":"Yes, there were the sequences at minus 10 and minus 35,"},{"Start":"01:49.190 ","End":"01:52.130","Text":"roughly and the sigma factor bound there."},{"Start":"01:52.130 ","End":"01:57.650","Text":"However, in eukaryotes, the polymerase requires several different transcription factors,"},{"Start":"01:57.650 ","End":"02:02.795","Text":"actually many different transcription factors to first bind the promoter region,"},{"Start":"02:02.795 ","End":"02:06.680","Text":"and then to help recruit the appropriate polymerase,"},{"Start":"02:06.680 ","End":"02:08.775","Text":"that\u0027s in the initiation."},{"Start":"02:08.775 ","End":"02:13.310","Text":"Eukaryotes have, as we mentioned, 3 different polymerases,"},{"Start":"02:13.310 ","End":"02:19.040","Text":"and each of those is made of 10 subunits or more."},{"Start":"02:19.040 ","End":"02:22.340","Text":"The polymerases require a distinct set"},{"Start":"02:22.340 ","End":"02:25.250","Text":"of transcription factors to bring it to the DNA templates,"},{"Start":"02:25.250 ","End":"02:27.695","Text":"of course, different from in prokaryotes."},{"Start":"02:27.695 ","End":"02:34.320","Text":"In fact, each of those polymerases requires different set of transcription factors."},{"Start":"02:34.320 ","End":"02:36.125","Text":"The RNA polymerase II,"},{"Start":"02:36.125 ","End":"02:39.815","Text":"which is responsible for making the messenger RNA,"},{"Start":"02:39.815 ","End":"02:45.530","Text":"you will see it can have many different kinds of transcription factors that bind."},{"Start":"02:45.530 ","End":"02:49.580","Text":"Now let\u0027s look at the polymerase itself."},{"Start":"02:49.580 ","End":"02:52.418","Text":"The bacterial RNA polymerase itself,"},{"Start":"02:52.418 ","End":"02:58.335","Text":"you remember the holoenzyme was made of 2 Alpha subunits,"},{"Start":"02:58.335 ","End":"03:03.455","Text":"a beta, a beta prime and this omega that we hadn\u0027t mentioned much before."},{"Start":"03:03.455 ","End":"03:04.670","Text":"But in any case,"},{"Start":"03:04.670 ","End":"03:10.960","Text":"this holoenzyme is quite different than eukaryotic RNA polymerase II,"},{"Start":"03:10.960 ","End":"03:14.180","Text":"which is made up of many different subunits,"},{"Start":"03:14.180 ","End":"03:17.520","Text":"at least 10 different subunits."},{"Start":"03:17.520 ","End":"03:23.030","Text":"In addition, it requires all sorts of transcription factors in addition to these subunits"},{"Start":"03:23.030 ","End":"03:28.580","Text":"to first bind the promoter region and then to help recruit the appropriate polymerase."},{"Start":"03:28.580 ","End":"03:34.145","Text":"As we mentioned, there are these 3 polymerases and they require"},{"Start":"03:34.145 ","End":"03:40.220","Text":"this distinct sets of transcription factors to bring the DNA to the templates."},{"Start":"03:40.220 ","End":"03:47.330","Text":"Let\u0027s first look at RNA polymerase I. RNA polymerase I is located in the nucleolus,"},{"Start":"03:47.330 ","End":"03:49.325","Text":"that\u0027s inside the nucleus."},{"Start":"03:49.325 ","End":"03:55.475","Text":"But the nucleolus is primarily the place where ribosomes are put together"},{"Start":"03:55.475 ","End":"04:01.700","Text":"and the ribosomal RNA is transcribed by RNA polymerase I."},{"Start":"04:01.700 ","End":"04:05.780","Text":"That\u0027s actually makes up about 95% of the RNA in the cell."},{"Start":"04:05.780 ","End":"04:12.450","Text":"But this RNA polymerase then transcribes this specific structural RNA,"},{"Start":"04:12.450 ","End":"04:17.765","Text":"that we\u0027ll a little bit more about in a minute and it is involved also in its processing"},{"Start":"04:17.765 ","End":"04:24.125","Text":"and its assembly together with ribosomal proteins to make mature ribosomes."},{"Start":"04:24.125 ","End":"04:28.460","Text":"Ribosomal RNAs are structural RNAs."},{"Start":"04:28.460 ","End":"04:32.135","Text":"That is, they are not translated into protein."},{"Start":"04:32.135 ","End":"04:34.580","Text":"On the other hand, RNA polymerase II,"},{"Start":"04:34.580 ","End":"04:36.815","Text":"so this is a different RNA polymerase,"},{"Start":"04:36.815 ","End":"04:41.510","Text":"is located outside the nucleolus in the nucleus and it"},{"Start":"04:41.510 ","End":"04:47.060","Text":"synthesizes all of the protein encoding nuclear pre-mRNAs."},{"Start":"04:47.060 ","End":"04:50.975","Text":"The RNA polymerase II is responsible for transcribing"},{"Start":"04:50.975 ","End":"04:55.490","Text":"most eukaryotic genes but in terms of the amount of it,"},{"Start":"04:55.490 ","End":"04:59.300","Text":"it is only about 5 percent of the RNA."},{"Start":"04:59.300 ","End":"05:02.255","Text":"Ribosomal RNA is the vast majority."},{"Start":"05:02.255 ","End":"05:09.855","Text":"But the more interesting RNA is transcribed by RNA polymerase II."},{"Start":"05:09.855 ","End":"05:12.800","Text":"RNA polymerase III is also outside"},{"Start":"05:12.800 ","End":"05:17.855","Text":"the nucleolus and it transcribes a variety of other structural RNAs,"},{"Start":"05:17.855 ","End":"05:25.060","Text":"including RNAs that are called 5S pre RNAs and small nuclear RNA."},{"Start":"05:25.060 ","End":"05:28.820","Text":"Here you can see a summary of the different polymerases,"},{"Start":"05:28.820 ","End":"05:34.680","Text":"the cellular compartment that they act and what they transcribe."}],"ID":28204},{"Watched":false,"Name":"Transcription elongation and rho dependent termination","Duration":"5m 19s","ChapterTopicVideoID":27077,"CourseChapterTopicPlaylistID":261641,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:07.530","Text":"Now, let\u0027s continue discussing the prokaryotic promoters and remember that we have this"},{"Start":"00:07.530 ","End":"00:11.895","Text":"minus 35 and minus 10 elements"},{"Start":"00:11.895 ","End":"00:16.935","Text":"that have consensus sequences that are recognized by the Sigma factor."},{"Start":"00:16.935 ","End":"00:19.560","Text":"Now what are they more specifically?"},{"Start":"00:19.560 ","End":"00:25.140","Text":"First of all, notice the minus 10 region is very A-T-rich."},{"Start":"00:25.140 ","End":"00:28.470","Text":"Remember between A and T there are"},{"Start":"00:28.470 ","End":"00:34.260","Text":"only 2 hydrogen bonds and that facilitates unwinding of the DNA template."},{"Start":"00:34.260 ","End":"00:40.175","Text":"It\u0027s easier to separate AT strands from GC and therefore,"},{"Start":"00:40.175 ","End":"00:42.340","Text":"then what happens is that after the DNA opens,"},{"Start":"00:42.340 ","End":"00:47.845","Text":"there\u0027ll several phosphodiester bonds of the new RNA are made."},{"Start":"00:47.845 ","End":"00:52.150","Text":"The RNA polymerase then binds to the promoter region."},{"Start":"00:52.150 ","End":"00:55.520","Text":"It\u0027s a Sigma factor that determines where the promoter is"},{"Start":"00:55.520 ","End":"00:58.730","Text":"or recognizes the promoter and unwinds the DNA to"},{"Start":"00:58.730 ","End":"01:05.940","Text":"initiate transcription and the DNA opening occurs at the minus 10 region."},{"Start":"01:05.940 ","End":"01:09.110","Text":"At this site, the strands are easier to separate as I said because of"},{"Start":"01:09.110 ","End":"01:14.750","Text":"the As and Ts as opposed to Gs and Cs."},{"Start":"01:14.750 ","End":"01:16.820","Text":"Now when we get to elongation,"},{"Start":"01:16.820 ","End":"01:21.860","Text":"the transcription elongation phase begins with the release of the Sigma,"},{"Start":"01:21.860 ","End":"01:26.650","Text":"as I\u0027ve mentioned before from the polymerase and the dissociation of"},{"Start":"01:26.650 ","End":"01:29.560","Text":"Sigma allows the core enzyme to proceed along"},{"Start":"01:29.560 ","End":"01:33.085","Text":"the DNA template, synthesizing messenger RNA."},{"Start":"01:33.085 ","End":"01:37.405","Text":"Notice in the 5\u0027 to 3\u0027 direction,"},{"Start":"01:37.405 ","End":"01:44.380","Text":"the RNA that is made is 5\u0027 to 3\u0027."},{"Start":"01:44.380 ","End":"01:49.435","Text":"The addition is always to the 3\u0027 end and the rate of"},{"Start":"01:49.435 ","End":"01:55.165","Text":"transcription is roughly 40 nucleotides per second in bacteria,"},{"Start":"01:55.165 ","End":"01:57.685","Text":"40 nucleotides per second;"},{"Start":"01:57.685 ","End":"01:59.590","Text":"that\u0027s a very rough estimate."},{"Start":"01:59.590 ","End":"02:09.260","Text":"If the DNA is continuously unwound ahead of the core enzyme and then it\u0027s rewound behind."},{"Start":"02:09.260 ","End":"02:13.940","Text":"The RNA polymerase then acts as a stable linker between"},{"Start":"02:13.940 ","End":"02:16.400","Text":"the DNA template and the nascent RNA strands to"},{"Start":"02:16.400 ","End":"02:19.065","Text":"ensure that elongation is not interrupted prematurely."},{"Start":"02:19.065 ","End":"02:21.375","Text":"What does that mean? What it really means is that"},{"Start":"02:21.375 ","End":"02:24.200","Text":"the enzyme is not exactly the way it\u0027s shown here."},{"Start":"02:24.200 ","End":"02:27.110","Text":"It wraps all around the DNA."},{"Start":"02:27.110 ","End":"02:32.720","Text":"The DNA goes right through it and so does the RNA and it holds the whole complex"},{"Start":"02:32.720 ","End":"02:38.330","Text":"together so that it doesn\u0027t just fall apart here and there prematurely."},{"Start":"02:38.330 ","End":"02:43.700","Text":"It\u0027s important that this be a very processive reaction."},{"Start":"02:43.700 ","End":"02:48.230","Text":"That means that something is added and added and added and added to an end."},{"Start":"02:48.230 ","End":"02:54.469","Text":"That\u0027s the nucleotides that are added without it stopping before it gets to a terminator."},{"Start":"02:54.469 ","End":"02:58.220","Text":"Here the terminator is shown in green."},{"Start":"02:58.220 ","End":"03:01.534","Text":"Now, what happens at this terminator?"},{"Start":"03:01.534 ","End":"03:07.490","Text":"Well, there are termination signals just like there were initiation signals and so"},{"Start":"03:07.490 ","End":"03:11.420","Text":"the prokaryotic polymerase needs to be instructed where to dissociate from"},{"Start":"03:11.420 ","End":"03:16.360","Text":"the DNA template and liberate the newly made messenger RNA."},{"Start":"03:16.360 ","End":"03:20.120","Text":"Now, there are actually 2 kinds of termination signals."},{"Start":"03:20.120 ","End":"03:25.460","Text":"There\u0027s something which is called Rho-dependent termination and that\u0027s protein-based."},{"Start":"03:25.460 ","End":"03:28.190","Text":"That means that there\u0027s a specific protein,"},{"Start":"03:28.190 ","End":"03:32.850","Text":"it\u0027s called Rho actually and there\u0027s Rho independent termination."},{"Start":"03:32.850 ","End":"03:35.885","Text":"That\u0027s intrinsic to the DNA sequence."},{"Start":"03:35.885 ","End":"03:39.110","Text":"These 2 methods work somewhat differently."},{"Start":"03:39.110 ","End":"03:40.520","Text":"Let\u0027s see how they look."},{"Start":"03:40.520 ","End":"03:42.545","Text":"They don\u0027t work at the same time."},{"Start":"03:42.545 ","End":"03:45.950","Text":"Some RNAs are released by the Rho factor and"},{"Start":"03:45.950 ","End":"03:51.310","Text":"other RNAs are released because of the sequence at the termination site."},{"Start":"03:51.310 ","End":"03:55.040","Text":"If it\u0027s controlled, if we have Rho-dependent termination,"},{"Start":"03:55.040 ","End":"03:58.505","Text":"the termination is controlled by the Rho protein,"},{"Start":"03:58.505 ","End":"04:04.700","Text":"which is found on the RNA and it moves along"},{"Start":"04:04.700 ","End":"04:11.495","Text":"the RNA as the RNA is being made and it tracks behind the polymerase."},{"Start":"04:11.495 ","End":"04:14.321","Text":"It\u0027s an ATP-dependent helicase,"},{"Start":"04:14.321 ","End":"04:19.850","Text":"a helicase which breaks a helix and it binds to"},{"Start":"04:19.850 ","End":"04:22.400","Text":"the exposed region of the single-stranded RNA that\u0027s"},{"Start":"04:22.400 ","End":"04:26.630","Text":"following the polymerase as we mentioned."},{"Start":"04:26.630 ","End":"04:28.789","Text":"Now near the end of the gene,"},{"Start":"04:28.789 ","End":"04:35.720","Text":"the polymerase encounters the termination sites on the DNA template and it stalls"},{"Start":"04:35.720 ","End":"04:38.420","Text":"because it can\u0027t move as quickly through"},{"Start":"04:38.420 ","End":"04:42.800","Text":"that region in the termination sites because of the way the sequence is,"},{"Start":"04:42.800 ","End":"04:47.795","Text":"it\u0027s very rich in Gs and Cs and so it somewhat stalls and that allows the Rho"},{"Start":"04:47.795 ","End":"04:53.535","Text":"to catch up and collide with the RNA polymerase."},{"Start":"04:53.535 ","End":"04:56.210","Text":"That then because it\u0027s a helicase,"},{"Start":"04:56.210 ","End":"05:00.065","Text":"releases the messenger RNA from the transcription bubble"},{"Start":"05:00.065 ","End":"05:07.800","Text":"and the transcriptional complex falls apart and then the RNA is released, of course."},{"Start":"05:07.800 ","End":"05:12.935","Text":"That is Rho-dependent termination."},{"Start":"05:12.935 ","End":"05:14.495","Text":"In the next video,"},{"Start":"05:14.495 ","End":"05:19.289","Text":"we will look at Rho independent termination."}],"ID":28205},{"Watched":false,"Name":"Transcription initiation","Duration":"6m 34s","ChapterTopicVideoID":27078,"CourseChapterTopicPlaylistID":261641,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:03.600","Text":"Welcome back. Now, we\u0027ve talked about"},{"Start":"00:03.600 ","End":"00:08.009","Text":"the way RNA is translated into protein and triplets."},{"Start":"00:08.009 ","End":"00:13.230","Text":"But let\u0027s now go back and look at transcription in more detail and start with"},{"Start":"00:13.230 ","End":"00:19.680","Text":"prokaryotes because they serve as the model system really in all the systems,"},{"Start":"00:19.680 ","End":"00:21.810","Text":"in replication, and in transcription,"},{"Start":"00:21.810 ","End":"00:24.320","Text":"and translation, and so on because it\u0027s simpler there."},{"Start":"00:24.320 ","End":"00:26.459","Text":"Then we\u0027ll go on a little bit to eukaryotes."},{"Start":"00:26.459 ","End":"00:30.824","Text":"Prokaryotes, that includes bacteria and archaea,"},{"Start":"00:30.824 ","End":"00:35.145","Text":"are mostly single-celled organisms and they lack membrane-bound nuclei,"},{"Start":"00:35.145 ","End":"00:37.970","Text":"as well as other organelles, of course."},{"Start":"00:37.970 ","End":"00:42.885","Text":"The bacterial chromosome is called the genophore,"},{"Start":"00:42.885 ","End":"00:44.330","Text":"and as we\u0027ve mentioned earlier,"},{"Start":"00:44.330 ","End":"00:49.220","Text":"it\u0027s circular and it\u0027s not organized around histone proteins."},{"Start":"00:49.220 ","End":"00:50.840","Text":"In addition to the genophore,"},{"Start":"00:50.840 ","End":"00:53.450","Text":"there are the plasmids which are shorter,"},{"Start":"00:53.450 ","End":"00:56.375","Text":"of course, this is not drawn to scale and by any means,"},{"Start":"00:56.375 ","End":"00:57.740","Text":"they\u0027re much shorter,"},{"Start":"00:57.740 ","End":"01:00.750","Text":"also circular DNA molecules and many of them"},{"Start":"01:00.750 ","End":"01:04.445","Text":"have one or a few genes which can be transferred independently."},{"Start":"01:04.445 ","End":"01:06.740","Text":"We know that often they can carry traits."},{"Start":"01:06.740 ","End":"01:12.140","Text":"These plasmids can carry trades such as those involved with antibiotic resistance."},{"Start":"01:12.140 ","End":"01:15.020","Text":"Let\u0027s look at the transcription now in prokaryotes."},{"Start":"01:15.020 ","End":"01:19.165","Text":"As I mentioned, it actually serves as a model for eukaryotes as well."},{"Start":"01:19.165 ","End":"01:20.990","Text":"Transcription, of course,"},{"Start":"01:20.990 ","End":"01:27.800","Text":"requires that the DNA be partially unwind in the region of messenger RNA synthesis."},{"Start":"01:27.800 ","End":"01:30.140","Text":"Yes, and that creates a bubble."},{"Start":"01:30.140 ","End":"01:35.075","Text":"The DNA is double-stranded on each side of this bubble,"},{"Start":"01:35.075 ","End":"01:38.870","Text":"but the DNA then is pulled apart."},{"Start":"01:38.870 ","End":"01:43.940","Text":"It has to be opened so that the transcriptional machinery can read,"},{"Start":"01:43.940 ","End":"01:45.920","Text":"as it turns out, only one of the strands,"},{"Start":"01:45.920 ","End":"01:47.435","Text":"and we\u0027ll see how that happens,"},{"Start":"01:47.435 ","End":"01:49.940","Text":"and do the actual transcription."},{"Start":"01:49.940 ","End":"01:53.750","Text":"Here the RNA is in this yellow orange color,"},{"Start":"01:53.750 ","End":"01:56.510","Text":"and of course the DNA is in blue."},{"Start":"01:56.510 ","End":"01:59.389","Text":"There are 2 strands of the DNA."},{"Start":"01:59.389 ","End":"02:07.295","Text":"There\u0027s a template strands that is going to be the template upon which the RNA is made."},{"Start":"02:07.295 ","End":"02:12.975","Text":"Here\u0027s our template strands of DNA."},{"Start":"02:12.975 ","End":"02:18.410","Text":"The RNA is going to be made by reading this template strand."},{"Start":"02:18.410 ","End":"02:24.770","Text":"The transcription always proceeds from the same strand of DNA for each gene."},{"Start":"02:24.770 ","End":"02:29.389","Text":"The messenger RNA product is complimentary to the template,"},{"Start":"02:29.389 ","End":"02:30.950","Text":"of course, opposite the T and A,"},{"Start":"02:30.950 ","End":"02:32.060","Text":"opposite the A and U,"},{"Start":"02:32.060 ","End":"02:33.990","Text":"opposite the G and C,"},{"Start":"02:33.990 ","End":"02:38.480","Text":"and so on and is almost identical to the other DNA strands."},{"Start":"02:38.480 ","End":"02:40.235","Text":"If you look at it, for instance,"},{"Start":"02:40.235 ","End":"02:42.320","Text":"here we have C, A, U,"},{"Start":"02:42.320 ","End":"02:43.490","Text":"C, C,"},{"Start":"02:43.490 ","End":"02:44.625","Text":"A, well,"},{"Start":"02:44.625 ","End":"02:47.280","Text":"T because T and U are interchangeable,"},{"Start":"02:47.280 ","End":"02:49.530","Text":"T is the DNA, U is in the RNA,"},{"Start":"02:49.530 ","End":"02:51.195","Text":"C, and so on."},{"Start":"02:51.195 ","End":"02:53.660","Text":"The messenger RNA is complementary to the template,"},{"Start":"02:53.660 ","End":"02:55.760","Text":"is almost identical to the other DNA strand,"},{"Start":"02:55.760 ","End":"02:58.130","Text":"that\u0027s the non template strand and sometimes"},{"Start":"02:58.130 ","End":"03:03.180","Text":"that non template strand is called the coding strand."},{"Start":"03:03.190 ","End":"03:05.480","Text":"Of course, in messenger RNA,"},{"Start":"03:05.480 ","End":"03:09.310","Text":"the T\u0027s are replaced with U\u0027s."},{"Start":"03:09.500 ","End":"03:15.425","Text":"Occasionally, we\u0027ll find that the RNA itself that is made"},{"Start":"03:15.425 ","End":"03:20.905","Text":"can form a double helix on its own if there is the appropriate sequence there."},{"Start":"03:20.905 ","End":"03:27.040","Text":"In that case a U binds an A just like a T binds in a U,"},{"Start":"03:27.040 ","End":"03:29.530","Text":"form hydrogen bonds between the minutes,"},{"Start":"03:29.530 ","End":"03:35.365","Text":"2 hydrogen bonds just as it is between an A and a T. Now let\u0027s see,"},{"Start":"03:35.365 ","End":"03:39.250","Text":"how does the machinery know from where to start?"},{"Start":"03:39.250 ","End":"03:42.040","Text":"Well, if you remember in replication,"},{"Start":"03:42.040 ","End":"03:48.445","Text":"there was a sequence which formed the origin of replication."},{"Start":"03:48.445 ","End":"03:54.438","Text":"Similarly, in transcription, there is an initiation site"},{"Start":"03:54.438 ","End":"04:01.700","Text":"and that is where the DNA begins the transcription."},{"Start":"04:01.700 ","End":"04:07.040","Text":"Now it\u0027s the first 5\u0027 messenger"},{"Start":"04:07.040 ","End":"04:09.110","Text":"RNA nucleotide is the position from which"},{"Start":"04:09.110 ","End":"04:12.905","Text":"the first messenger RNA nucleotide is transcribed."},{"Start":"04:12.905 ","End":"04:15.710","Text":"Now when we write these down,"},{"Start":"04:15.710 ","End":"04:20.180","Text":"we talk about upstream and downstream regions of the DNA."},{"Start":"04:20.180 ","End":"04:23.150","Text":"The nucleotides in the DNA that precede"},{"Start":"04:23.150 ","End":"04:27.940","Text":"the initiation site are denoted with a minus sign."},{"Start":"04:27.940 ","End":"04:34.490","Text":"We\u0027ll say that something is minus 25 nucleotides from the initiation site,"},{"Start":"04:34.490 ","End":"04:36.755","Text":"or minus 80, or minus 100 whatever,"},{"Start":"04:36.755 ","End":"04:38.430","Text":"and then we could do the same thing,"},{"Start":"04:38.430 ","End":"04:40.235","Text":"plus on the other side,"},{"Start":"04:40.235 ","End":"04:42.770","Text":"those are nucleotides that are following"},{"Start":"04:42.770 ","End":"04:47.014","Text":"the initiation site and they\u0027re denoted with plus and those are called downstream,"},{"Start":"04:47.014 ","End":"04:48.755","Text":"as we just mentioned."},{"Start":"04:48.755 ","End":"04:51.365","Text":"We can have upstream and downstream."},{"Start":"04:51.365 ","End":"04:53.090","Text":"We don\u0027t have a 0,"},{"Start":"04:53.090 ","End":"04:54.870","Text":"we have a plus 1."},{"Start":"04:54.870 ","End":"05:00.230","Text":"We\u0027ll have minus something that is minus from upstream of the initiation site."},{"Start":"05:00.230 ","End":"05:03.845","Text":"Initiation site itself is called plus 1."},{"Start":"05:03.845 ","End":"05:06.845","Text":"Of course, in bacteria,"},{"Start":"05:06.845 ","End":"05:08.640","Text":"there are no nuclei,"},{"Start":"05:08.640 ","End":"05:12.560","Text":"so that allows transcription and translation to occur"},{"Start":"05:12.560 ","End":"05:18.380","Text":"simultaneously in because the RNA, which is made,"},{"Start":"05:18.380 ","End":"05:24.530","Text":"as we\u0027ll see, can immediately be translated into protein before it\u0027s even"},{"Start":"05:24.530 ","End":"05:32.105","Text":"finished because the 2 processes work in the same direction, 5\u0027 to 3\u0027."},{"Start":"05:32.105 ","End":"05:35.225","Text":"We\u0027ll detail that a little bit more further."},{"Start":"05:35.225 ","End":"05:38.705","Text":"Furthermore, the genome is very compact."},{"Start":"05:38.705 ","End":"05:40.820","Text":"In bacteria and the transcription,"},{"Start":"05:40.820 ","End":"05:45.280","Text":"the transcripts then can cover more than 1 gene."},{"Start":"05:45.280 ","End":"05:47.030","Text":"In this example, for instance,"},{"Start":"05:47.030 ","End":"05:49.310","Text":"in prokaryotic messenger RNA,"},{"Start":"05:49.310 ","End":"05:51.776","Text":"we have 1 piece of RNA,"},{"Start":"05:51.776 ","End":"05:55.850","Text":"so we have an untranslated region that encodes Protein 1,"},{"Start":"05:55.850 ","End":"05:58.640","Text":"Protein 2, and Protein 3,"},{"Start":"05:58.640 ","End":"06:02.555","Text":"all of them on the same messenger RNA,"},{"Start":"06:02.555 ","End":"06:06.100","Text":"and that would be called a cistron."},{"Start":"06:06.100 ","End":"06:10.340","Text":"This is what we find in prokaryotes as opposed to"},{"Start":"06:10.340 ","End":"06:14.930","Text":"eukaryotes where we don\u0027t find polycistronic messages,"},{"Start":"06:14.930 ","End":"06:19.970","Text":"that means more than one protein that are encoded by the same messenger RNA."},{"Start":"06:19.970 ","End":"06:26.095","Text":"In eukaryotes we only have a single protein which is made."},{"Start":"06:26.095 ","End":"06:28.520","Text":"These in bacteria as we said,"},{"Start":"06:28.520 ","End":"06:35.610","Text":"are polycistronic messenger RNAs which produce more than one kind of protein."}],"ID":28206},{"Watched":false,"Name":"Transcription through chromatin and termination","Duration":"2m 36s","ChapterTopicVideoID":27079,"CourseChapterTopicPlaylistID":261641,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.320 ","End":"00:05.330","Text":"Now, let\u0027s consider something that is really specific to eukaryotes,"},{"Start":"00:05.330 ","End":"00:08.475","Text":"and that is the way the DNA is packaged."},{"Start":"00:08.475 ","End":"00:12.840","Text":"As you\u0027ll remember, the DNA is packaged in these nucleosomes that"},{"Start":"00:12.840 ","End":"00:17.760","Text":"include 146 nucleotides that are wrapped around the histones."},{"Start":"00:17.760 ","End":"00:19.890","Text":"Here are these nucleotides."},{"Start":"00:19.890 ","End":"00:24.000","Text":"Of course, the transcription complex must"},{"Start":"00:24.000 ","End":"00:29.070","Text":"move through the chromatin and deal somehow with"},{"Start":"00:29.070 ","End":"00:33.840","Text":"these histones and maybe other proteins as well that are"},{"Start":"00:33.840 ","End":"00:39.375","Text":"already bound to the DNA because it\u0027s going to need to open up the DNA,"},{"Start":"00:39.375 ","End":"00:42.500","Text":"make it available to this enormous complex."},{"Start":"00:42.500 ","End":"00:46.745","Text":"In fact, the RNA polymerase complex together with all of its proteins,"},{"Start":"00:46.745 ","End":"00:50.855","Text":"can make up as many as say 60 different proteins."},{"Start":"00:50.855 ","End":"00:53.165","Text":"There has to be room for all that."},{"Start":"00:53.165 ","End":"00:55.180","Text":"How does that happen?"},{"Start":"00:55.180 ","End":"00:58.310","Text":"The transcriptional machinery must move through"},{"Start":"00:58.310 ","End":"01:02.450","Text":"those histones when it encounters the nucleosome."},{"Start":"01:02.450 ","End":"01:05.165","Text":"There is a special protein complex,"},{"Start":"01:05.165 ","End":"01:06.730","Text":"which is called FACT,"},{"Start":"01:06.730 ","End":"01:10.130","Text":"short for facilitates chromatin transcription."},{"Start":"01:10.130 ","End":"01:12.237","Text":"This FACT complex,"},{"Start":"01:12.237 ","End":"01:14.998","Text":"contains a number of different proteins,"},{"Start":"01:14.998 ","End":"01:20.725","Text":"somehow pulls the histones away from the DNA template as the polymerase moves along it."},{"Start":"01:20.725 ","End":"01:23.690","Text":"Then once the pre-messenger RNA is synthesized,"},{"Start":"01:23.690 ","End":"01:26.990","Text":"the FACT complex actually is involved in"},{"Start":"01:26.990 ","End":"01:31.855","Text":"replacement of the histones to recreate the nucleosomes."},{"Start":"01:31.855 ","End":"01:35.510","Text":"The structure is displaced or changed"},{"Start":"01:35.510 ","End":"01:41.105","Text":"as the RNA polymerase moves through and then it\u0027s restored."},{"Start":"01:41.105 ","End":"01:43.940","Text":"Then finally at the very end of transcription,"},{"Start":"01:43.940 ","End":"01:46.160","Text":"we have eukaryotic termination,"},{"Start":"01:46.160 ","End":"01:51.050","Text":"which actually is a bit less interesting than in prokaryotes."},{"Start":"01:51.050 ","End":"01:56.710","Text":"The transcription termination is not as specific as it is in prokaryotes."},{"Start":"01:56.710 ","End":"01:58.650","Text":"For the case of RNA polymerase I,"},{"Start":"01:58.650 ","End":"02:00.530","Text":"the genes transcribed do contain"},{"Start":"02:00.530 ","End":"02:04.955","Text":"a specific 18-nucleotide sequence that is recognized by a termination protein."},{"Start":"02:04.955 ","End":"02:06.635","Text":"But in RNA polymerase II,"},{"Start":"02:06.635 ","End":"02:12.125","Text":"termination involves the recognition of a variable sequence at the end of the gene,"},{"Start":"02:12.125 ","End":"02:17.150","Text":"but there\u0027s no need for extra factors like there are in prokaryotes,"},{"Start":"02:17.150 ","End":"02:22.340","Text":"just to make the RNA polymerase fall off the DNA and stop the transcription."},{"Start":"02:22.340 ","End":"02:24.470","Text":"In the case of RNA polymerase III,"},{"Start":"02:24.470 ","End":"02:29.824","Text":"termination does involve messenger RNA hairpin that is not unlike"},{"Start":"02:29.824 ","End":"02:36.730","Text":"the Rho-independent termination of transcription in prokaryotes."}],"ID":28207},{"Watched":false,"Name":"tRNAs","Duration":"5m 6s","ChapterTopicVideoID":27080,"CourseChapterTopicPlaylistID":261641,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:03.930","Text":"Let\u0027s continue with our discussion of protein synthesis."},{"Start":"00:03.930 ","End":"00:06.510","Text":"We had been discussing ribosomes."},{"Start":"00:06.510 ","End":"00:09.150","Text":"Now let\u0027s discuss tRNAs,"},{"Start":"00:09.150 ","End":"00:12.600","Text":"which of course are very important for the translation."},{"Start":"00:12.600 ","End":"00:16.260","Text":"They are structural RNA molecules that are transcribed from"},{"Start":"00:16.260 ","End":"00:21.225","Text":"genes by RNA polymerase III as we had mentioned earlier,"},{"Start":"00:21.225 ","End":"00:27.150","Text":"there are about 40-60 different types of tRNAs that exist in the cytoplasm,"},{"Start":"00:27.150 ","End":"00:29.040","Text":"depending on the species."},{"Start":"00:29.040 ","End":"00:33.905","Text":"Each of those tRNAs carries a specific amino acid."},{"Start":"00:33.905 ","End":"00:37.640","Text":"Remember there are 20 different amino acids."},{"Start":"00:37.640 ","End":"00:39.695","Text":"Now in this representation,"},{"Start":"00:39.695 ","End":"00:42.770","Text":"you see the tRNA in two-dimensions,"},{"Start":"00:42.770 ","End":"00:44.540","Text":"as we discussed earlier with"},{"Start":"00:44.540 ","End":"00:48.755","Text":"the hydrogen bonding in the stems and the loops that are created."},{"Start":"00:48.755 ","End":"00:54.780","Text":"Notice there\u0027s some stars here because there are some altered nucleotides into tRNA."},{"Start":"00:54.780 ","End":"01:01.040","Text":"This structure can fold on itself into a three-dimensional structure,"},{"Start":"01:01.040 ","End":"01:04.230","Text":"leaving the anticodon, the part that\u0027s at the bottom over here."},{"Start":"01:04.230 ","End":"01:08.995","Text":"It is going to interact with the messenger RNA exposed."},{"Start":"01:08.995 ","End":"01:12.755","Text":"On the other ends, another sequence exposed,"},{"Start":"01:12.755 ","End":"01:16.310","Text":"the amino acid attachment site that you can see"},{"Start":"01:16.310 ","End":"01:20.500","Text":"that is on the three-prime end of this tRNA."},{"Start":"01:20.500 ","End":"01:26.765","Text":"A third representation, which is a lot simpler and a lot more schematic,"},{"Start":"01:26.765 ","End":"01:33.190","Text":"shows just the anticodon and the amino acid attachment site on one end."},{"Start":"01:33.190 ","End":"01:39.755","Text":"This will be the symbol that we\u0027re going to use in the upcoming slides."},{"Start":"01:39.755 ","End":"01:44.960","Text":"Here are the tRNAs that are sitting in a ribosome."},{"Start":"01:44.960 ","End":"01:50.855","Text":"There are amino acids that are attached to the attachment site as you can see here."},{"Start":"01:50.855 ","End":"01:53.330","Text":"Now what does the attachment?"},{"Start":"01:53.330 ","End":"02:01.010","Text":"There is an enzyme called aminoacyl-tRNA transferase that we\u0027ll discuss in"},{"Start":"02:01.010 ","End":"02:09.245","Text":"a few minutes that binds the tRNAs to the specific amino acids."},{"Start":"02:09.245 ","End":"02:13.460","Text":"Those are called aminoacyl-tRNAs."},{"Start":"02:13.460 ","End":"02:17.720","Text":"For instance, here\u0027s an aminoacyl-tRNA,"},{"Start":"02:17.720 ","End":"02:20.290","Text":"because it has an amino acid attached to it."},{"Start":"02:20.290 ","End":"02:23.750","Text":"They bind to the ribosome and then they add"},{"Start":"02:23.750 ","End":"02:30.395","Text":"the corresponding amino acid to the polypeptide chain by having this interaction"},{"Start":"02:30.395 ","End":"02:35.750","Text":"between the codon and the anticodon that"},{"Start":"02:35.750 ","End":"02:41.705","Text":"will specify exactly which tRNA will fit into this site."},{"Start":"02:41.705 ","End":"02:45.020","Text":"You\u0027ll see it\u0027s called the aminoacyl site,"},{"Start":"02:45.020 ","End":"02:47.135","Text":"the A-site in the ribosome."},{"Start":"02:47.135 ","End":"02:52.655","Text":"Then that will bring in the appropriate amino acid."},{"Start":"02:52.655 ","End":"03:00.050","Text":"Now remember this chart in which we saw that of the 64 possible messenger RNA codons,"},{"Start":"03:00.050 ","End":"03:03.190","Text":"3 of them specify termination."},{"Start":"03:03.190 ","End":"03:12.250","Text":"These stop codons, they specify termination of the polypeptide chain and one of them,"},{"Start":"03:12.250 ","End":"03:14.514","Text":"yes, this AUG over here,"},{"Start":"03:14.514 ","End":"03:17.935","Text":"specifies the initiation of translation."},{"Start":"03:17.935 ","End":"03:21.118","Text":"It also specifies a methionine always."},{"Start":"03:21.118 ","End":"03:23.469","Text":"Each tRNA anticodon,"},{"Start":"03:23.469 ","End":"03:31.030","Text":"then we know can pair with one or more of the messenger RNA codons for its amino acid."},{"Start":"03:31.030 ","End":"03:33.550","Text":"We say more than one possibly because of"},{"Start":"03:33.550 ","End":"03:38.110","Text":"the wobble in the third nucleotide of each of the codons."},{"Start":"03:38.110 ","End":"03:45.650","Text":"Let\u0027s now look at how the appropriate amino acid is attached to each of the tRNAs."},{"Start":"03:45.650 ","End":"03:47.435","Text":"Well, that\u0027s done as I mentioned,"},{"Start":"03:47.435 ","End":"03:52.520","Text":"by an aminoacyl-tRNA synthetase of which there are"},{"Start":"03:52.520 ","End":"03:56.570","Text":"numerous ones that are specific for each of"},{"Start":"03:56.570 ","End":"04:01.055","Text":"the tRNAs and their corresponding amino acids."},{"Start":"04:01.055 ","End":"04:06.035","Text":"Pre-tRNA synthesis creates the RNA portion of the adapter molecule."},{"Start":"04:06.035 ","End":"04:08.945","Text":"Once exported to the cytoplasm,"},{"Start":"04:08.945 ","End":"04:11.990","Text":"the amino acid is added."},{"Start":"04:11.990 ","End":"04:15.080","Text":"Each tRNA molecule is linked by"},{"Start":"04:15.080 ","End":"04:19.880","Text":"addition of the amino acid and this addition is called charging."},{"Start":"04:19.880 ","End":"04:21.890","Text":"Yes, that\u0027s what we see here."},{"Start":"04:21.890 ","End":"04:23.435","Text":"It\u0027s charged."},{"Start":"04:23.435 ","End":"04:30.530","Text":"That\u0027s a term that\u0027s used really been added by this enzyme aminoacyl-tRNA synthetase."},{"Start":"04:30.530 ","End":"04:36.020","Text":"It\u0027s called charging because of the high-energy bond that is created when"},{"Start":"04:36.020 ","End":"04:42.590","Text":"the amino acid is added to the tRNA and that as we\u0027ll see,"},{"Start":"04:42.590 ","End":"04:44.390","Text":"will be used that high-energy bond,"},{"Start":"04:44.390 ","End":"04:47.810","Text":"will be used to drive the formation of the peptide bond,"},{"Start":"04:47.810 ","End":"04:50.090","Text":"which also requires quite a bit of energy."},{"Start":"04:50.090 ","End":"04:55.010","Text":"At least one type aminoacyl-tRNA synthetase exists for each of the 20 amino acids."},{"Start":"04:55.010 ","End":"04:58.535","Text":"As I said, there are numerous ones like this,"},{"Start":"04:58.535 ","End":"05:06.480","Text":"and each tRNA is named for the amino acid that is added to it."}],"ID":28208},{"Watched":false,"Name":"Capping and polyadenylation","Duration":"6m 35s","ChapterTopicVideoID":27081,"CourseChapterTopicPlaylistID":261641,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:02.610","Text":"Hi."},{"Start":"00:02.610 ","End":"00:04.125","Text":"We\u0027ve been talking about"},{"Start":"00:04.125 ","End":"00:10.335","Text":"RNA transcription in eukaryotes and now let\u0027s talk about its processing."},{"Start":"00:10.335 ","End":"00:13.650","Text":"RNA processing in eukaryotes."},{"Start":"00:13.650 ","End":"00:16.830","Text":"Because all of the RNA which is transcribed in"},{"Start":"00:16.830 ","End":"00:21.870","Text":"eukaryotes must undergo some processing before it is functional."},{"Start":"00:21.870 ","End":"00:24.135","Text":"Let\u0027s take a look at that."},{"Start":"00:24.135 ","End":"00:30.270","Text":"First of all, let\u0027s compare RNA in prokaryotes and eukaryotes."},{"Start":"00:30.270 ","End":"00:34.110","Text":"In eukaryotes the messenger RNA has"},{"Start":"00:34.110 ","End":"00:38.310","Text":"a much longer half-life than in a prokaryotic messenger RNA."},{"Start":"00:38.310 ","End":"00:42.285","Text":"That means that it lasts a much longer time."},{"Start":"00:42.285 ","End":"00:45.785","Text":"Eukaryotic messenger RNA can last for several hours."},{"Start":"00:45.785 ","End":"00:49.670","Text":"It can survive for several hours before it gets degraded while E."},{"Start":"00:49.670 ","End":"00:53.885","Text":"Coli\u0027s messenger RNA lasts on the order of about 5 minutes."},{"Start":"00:53.885 ","End":"00:55.595","Text":"It\u0027s very quick."},{"Start":"00:55.595 ","End":"01:00.275","Text":"Furthermore, the pre-messenger RNAs in"},{"Start":"01:00.275 ","End":"01:06.800","Text":"eukaryotes must undergo several processing steps before they\u0027re translated."},{"Start":"01:06.800 ","End":"01:12.259","Text":"That\u0027s true of tRNAs and ribosomal RNAs,"},{"Start":"01:12.259 ","End":"01:14.960","Text":"which also undergo processing before they can function."},{"Start":"01:14.960 ","End":"01:21.320","Text":"You\u0027ll remember that tRNAs are involved in translation of the messenger RNA into"},{"Start":"01:21.320 ","End":"01:28.190","Text":"protein and ribosomal RNAs are the structural proteins which are part of the ribosomes."},{"Start":"01:28.190 ","End":"01:33.380","Text":"The eukaryotic pre-messenger RNA contains coding sequences,"},{"Start":"01:33.380 ","End":"01:36.425","Text":"that is sequences that are going to"},{"Start":"01:36.425 ","End":"01:41.580","Text":"encode protein at the end of the day so they are called exons."},{"Start":"01:42.130 ","End":"01:45.215","Text":"Here you can see in this example,"},{"Start":"01:45.215 ","End":"01:46.775","Text":"we have 1,"},{"Start":"01:46.775 ","End":"01:50.160","Text":"2, 3 different exons."},{"Start":"01:50.160 ","End":"01:53.390","Text":"Between them, there are these sequences"},{"Start":"01:53.390 ","End":"01:56.990","Text":"which do not encode protein that are called introns."},{"Start":"01:56.990 ","End":"02:00.065","Text":"Between the 3 exons in this example,"},{"Start":"02:00.065 ","End":"02:03.330","Text":"we have 2 introns."},{"Start":"02:03.330 ","End":"02:10.080","Text":"In addition, pre-messenger RNAs are coated with RNA-stabilizing proteins,"},{"Start":"02:10.080 ","End":"02:12.310","Text":"and we\u0027re not going to talk much about them."},{"Start":"02:12.310 ","End":"02:16.735","Text":"But they\u0027re involved in the protection from degradation."},{"Start":"02:16.735 ","End":"02:19.610","Text":"That\u0027s really the reason that in eukaryotes,"},{"Start":"02:19.610 ","End":"02:25.085","Text":"the messenger RNA is so much more stable than it is in prokaryotes."},{"Start":"02:25.085 ","End":"02:27.635","Text":"Now let\u0027s look at the processing."},{"Start":"02:27.635 ","End":"02:32.600","Text":"The 3 most important steps of pre-messenger RNA processing are first"},{"Start":"02:32.600 ","End":"02:38.815","Text":"the addition of stabilizing and signaling factors at the 5\u0027 end,"},{"Start":"02:38.815 ","End":"02:43.500","Text":"here\u0027s the 5\u0027 end of the messenger RNA,"},{"Start":"02:43.500 ","End":"02:49.600","Text":"the addition of stabilizing and signaling factors at the 3\u0027 ends of the molecule,"},{"Start":"02:49.600 ","End":"02:52.250","Text":"here\u0027s the 3\u0027 end of the molecule,"},{"Start":"02:52.250 ","End":"02:56.165","Text":"and also the removal of the introns."},{"Start":"02:56.165 ","End":"02:59.930","Text":"Here are these 2 introns which are removed and they are cut"},{"Start":"02:59.930 ","End":"03:03.965","Text":"out by a process called splicing."},{"Start":"03:03.965 ","End":"03:05.690","Text":"Now in rare cases,"},{"Start":"03:05.690 ","End":"03:08.810","Text":"the messenger RNA transcript is also edited"},{"Start":"03:08.810 ","End":"03:12.290","Text":"after it\u0027s transcribed and we\u0027ll talk about that further."},{"Start":"03:12.290 ","End":"03:15.620","Text":"But that\u0027s reasonably rare event that can have"},{"Start":"03:15.620 ","End":"03:22.160","Text":"significant import into the translation of the messenger RNA."},{"Start":"03:22.160 ","End":"03:25.985","Text":"That\u0027s RNA editing, fairly new field."},{"Start":"03:25.985 ","End":"03:31.405","Text":"Let\u0027s now start by looking at what happens at the 5\u0027 end."},{"Start":"03:31.405 ","End":"03:36.905","Text":"There is a process called capping at the 5\u0027 end."},{"Start":"03:36.905 ","End":"03:44.220","Text":"There\u0027s the addition of a triphosphate nucleotide,"},{"Start":"03:44.220 ","End":"03:52.005","Text":"guanosine usually, at the 5\u0027 end via a 5\u0027 to 5\u0027 bridge."},{"Start":"03:52.005 ","End":"04:01.115","Text":"This is added at the 5\u0027 end of the growing transcript by this strange phosphates linkage."},{"Start":"04:01.115 ","End":"04:08.165","Text":"Now notice that this end then does not contain a 5\u0027-phosphate,"},{"Start":"04:08.165 ","End":"04:12.770","Text":"which might be a substrate for an exonuclease,"},{"Start":"04:12.770 ","End":"04:15.230","Text":"a 5\u0027 to 3\u0027 exonuclease."},{"Start":"04:15.230 ","End":"04:18.980","Text":"Instead, it\u0027s got this nucleotide at the 5\u0027 end and that"},{"Start":"04:18.980 ","End":"04:24.215","Text":"protects the nascent messenger RNA from degradation at the 5\u0027 end."},{"Start":"04:24.215 ","End":"04:29.000","Text":"In addition, there are factors that are involved in protein synthesis that will"},{"Start":"04:29.000 ","End":"04:34.690","Text":"recognize this cap and help initiate the translation by ribosomes in the cytoplasm."},{"Start":"04:34.690 ","End":"04:40.925","Text":"This cap is going to survive transports from the nucleus into the cytoplasm."},{"Start":"04:40.925 ","End":"04:42.615","Text":"Let\u0027s look at the 3\u0027 end."},{"Start":"04:42.615 ","End":"04:43.890","Text":"At the 3\u0027 end,"},{"Start":"04:43.890 ","End":"04:48.185","Text":"there is what\u0027s called a poly-A tail that is added."},{"Start":"04:48.185 ","End":"04:50.225","Text":"Once the elongation is complete,"},{"Start":"04:50.225 ","End":"04:57.140","Text":"the pre-messenger RNA is cleaved by an endonuclease between the sequence."},{"Start":"04:57.140 ","End":"05:01.730","Text":"You\u0027ll remember AAUAAA or something similar to it,"},{"Start":"05:01.730 ","End":"05:03.770","Text":"it\u0027s a consensus sequence."},{"Start":"05:03.770 ","End":"05:06.240","Text":"It has a consensus sequence."},{"Start":"05:06.560 ","End":"05:10.310","Text":"There\u0027s this additional GU rich sequence usually,"},{"Start":"05:10.310 ","End":"05:15.800","Text":"and that leaves the AAUAAA sequence on the pre-RNA."},{"Start":"05:15.800 ","End":"05:19.400","Text":"Then to that is added a string of"},{"Start":"05:19.400 ","End":"05:26.240","Text":"about 200 adenosine residues by an enzyme called poly-A polymerase."},{"Start":"05:26.240 ","End":"05:30.905","Text":"Then these a residues are added without a template."},{"Start":"05:30.905 ","End":"05:32.780","Text":"There is no template to add this."},{"Start":"05:32.780 ","End":"05:40.490","Text":"The RNA poly-A polymerase adds this residues and that is called the poly-A tail,"},{"Start":"05:40.490 ","End":"05:45.750","Text":"which is at the 3\u0027 end of these messenger RNAs."},{"Start":"05:45.750 ","End":"05:49.309","Text":"This further protects the messenger RNA from degradation,"},{"Start":"05:49.309 ","End":"05:55.000","Text":"this time in a 3\u0027 to 5\u0027 direction."},{"Start":"05:55.000 ","End":"06:00.165","Text":"So there are also RNA exonucleases that are 3\u0027 to 5\u0027."},{"Start":"06:00.165 ","End":"06:02.815","Text":"But if they begin to digest the poly-A,"},{"Start":"06:02.815 ","End":"06:05.315","Text":"they don\u0027t get into the coding segments."},{"Start":"06:05.315 ","End":"06:13.465","Text":"We\u0027ve got protection on the 5\u0027 end by the cap and on the 3\u0027 end by the poly-A."},{"Start":"06:13.465 ","End":"06:20.300","Text":"The binding sites for the protein necessary for exporting processing messenger RNA"},{"Start":"06:20.300 ","End":"06:27.230","Text":"also binds this poly-A so only RNA which has been complete,"},{"Start":"06:27.230 ","End":"06:35.490","Text":"that is one that has both a 5\u0027 cap and a poly-A will be exported to the cytoplasm."}],"ID":28209},{"Watched":false,"Name":"Codons and translation","Duration":"8m 13s","ChapterTopicVideoID":27082,"CourseChapterTopicPlaylistID":261641,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.050 ","End":"00:03.690","Text":"Welcome back. We\u0027ve been discussing"},{"Start":"00:03.690 ","End":"00:10.020","Text":"the central dogma of the movement of information from DNA,"},{"Start":"00:10.020 ","End":"00:14.085","Text":"which encodes RNA, and the RNA encodes protein,"},{"Start":"00:14.085 ","End":"00:21.240","Text":"and we discussed a little bit before that the translation from RNA to"},{"Start":"00:21.240 ","End":"00:29.160","Text":"protein is read in a triplet code and each of those triplets is called a codon."},{"Start":"00:29.160 ","End":"00:34.155","Text":"Each amino acid is defined by a 3 nucleotide sequence."},{"Start":"00:34.155 ","End":"00:36.050","Text":"On the right over here you see a chart,"},{"Start":"00:36.050 ","End":"00:42.453","Text":"it\u0027s a chart that you need to learn to read in which you have a first letter,"},{"Start":"00:42.453 ","End":"00:48.410","Text":"a second letter, and a third letter for each of the codons."},{"Start":"00:48.410 ","End":"00:53.540","Text":"Then each of those triplets then we\u0027ll encode a particular amino acid,"},{"Start":"00:53.540 ","End":"00:55.700","Text":"so phenylalanine, leucine, leucine,"},{"Start":"00:55.700 ","End":"00:59.200","Text":"proline, serine, tyrosine and so on."},{"Start":"00:59.200 ","End":"01:01.230","Text":"Let\u0027s see for example,"},{"Start":"01:01.230 ","End":"01:02.655","Text":"how you would read one of them."},{"Start":"01:02.655 ","End":"01:05.495","Text":"Let\u0027s take for instance, C, U,"},{"Start":"01:05.495 ","End":"01:08.365","Text":"A, so C, U,"},{"Start":"01:08.365 ","End":"01:11.115","Text":"A would be found here, C, U,"},{"Start":"01:11.115 ","End":"01:15.140","Text":"and then A, and what does that encode?"},{"Start":"01:15.140 ","End":"01:17.360","Text":"That encodes a leucine."},{"Start":"01:17.360 ","End":"01:18.875","Text":"The same thing is true,"},{"Start":"01:18.875 ","End":"01:24.320","Text":"you can find the sequence of any of the amino acids this way."},{"Start":"01:24.320 ","End":"01:29.150","Text":"There are 64 possible nucleotide triplets, of course,"},{"Start":"01:29.150 ","End":"01:30.785","Text":"if you count these all up,"},{"Start":"01:30.785 ","End":"01:34.085","Text":"and that\u0027s far more than the number of amino acids that there are;"},{"Start":"01:34.085 ","End":"01:36.005","Text":"there are 20 amino acids."},{"Start":"01:36.005 ","End":"01:39.925","Text":"Certainly there\u0027s a degree of redundancy,"},{"Start":"01:39.925 ","End":"01:43.550","Text":"and you can see for instance here that leucine, for example,"},{"Start":"01:43.550 ","End":"01:44.990","Text":"is encoded by,"},{"Start":"01:44.990 ","End":"01:47.165","Text":"well, 1, 2,"},{"Start":"01:47.165 ","End":"01:48.380","Text":"3, 4,"},{"Start":"01:48.380 ","End":"01:51.310","Text":"5, 6 different codons."},{"Start":"01:51.310 ","End":"01:54.215","Text":"Some are encoded by more and some are encoded by less,"},{"Start":"01:54.215 ","End":"01:58.550","Text":"we\u0027ll talk about that in a couple of minutes but in any case a given amino acid,"},{"Start":"01:58.550 ","End":"02:03.535","Text":"therefore, could be encoded by more than 1 nucleotide triplets."},{"Start":"02:03.535 ","End":"02:09.934","Text":"Now, 3 of those triplets are called nonsense codons."},{"Start":"02:09.934 ","End":"02:13.970","Text":"They don\u0027t encode any amino acid at all,"},{"Start":"02:13.970 ","End":"02:18.380","Text":"instead, they encode stopping translation."},{"Start":"02:18.380 ","End":"02:20.390","Text":"In other words, when the machinery,"},{"Start":"02:20.390 ","End":"02:25.790","Text":"when the ribosome gets to a codon of UAA, UAG,"},{"Start":"02:25.790 ","End":"02:31.175","Text":"or UGA, it does not put in another amino acid onto the protein,"},{"Start":"02:31.175 ","End":"02:34.580","Text":"rather what it does is it stops the translation."},{"Start":"02:34.580 ","End":"02:40.835","Text":"So these 3 codons are called stop codons."},{"Start":"02:40.835 ","End":"02:45.995","Text":"Yes? They instruct termination of protein synthesis."},{"Start":"02:45.995 ","End":"02:49.550","Text":"Now there\u0027s an additional interesting codon, if you\u0027ll notice,"},{"Start":"02:49.550 ","End":"02:54.840","Text":"which is encoded in red in this chart, AUG."},{"Start":"02:54.840 ","End":"03:02.620","Text":"If you look you\u0027ll see that AUG is the only codon that encodes methionine."},{"Start":"03:02.620 ","End":"03:04.620","Text":"It specifies methionine,"},{"Start":"03:04.620 ","End":"03:08.630","Text":"it\u0027s the only one like that but it also serves as"},{"Start":"03:08.630 ","End":"03:13.220","Text":"the start codon to initiate translation and as we\u0027ll see,"},{"Start":"03:13.220 ","End":"03:18.390","Text":"it is always the first codon in translation,"},{"Start":"03:18.390 ","End":"03:23.015","Text":"so the first amino acid in every protein will be methionine."},{"Start":"03:23.015 ","End":"03:24.500","Text":"Actually, in some cases,"},{"Start":"03:24.500 ","End":"03:27.510","Text":"it is later taken off by an enzyme,"},{"Start":"03:27.510 ","End":"03:29.930","Text":"so if you look at a mature protein,"},{"Start":"03:29.930 ","End":"03:31.610","Text":"it doesn\u0027t always start with methionine,"},{"Start":"03:31.610 ","End":"03:34.790","Text":"but it\u0027s translation always does,"},{"Start":"03:34.790 ","End":"03:36.410","Text":"in almost every system."},{"Start":"03:36.410 ","End":"03:43.230","Text":"We said that these codons are read 3 at a time."},{"Start":"03:43.230 ","End":"03:47.180","Text":"There\u0027s something that we call a reading frame for translation,"},{"Start":"03:47.180 ","End":"03:52.925","Text":"which is set by this AUG. Now notice you could have a triplet like this,"},{"Start":"03:52.925 ","End":"03:54.245","Text":"as shown over here,"},{"Start":"03:54.245 ","End":"03:56.285","Text":"but you could also read it,"},{"Start":"03:56.285 ","End":"03:58.090","Text":"let\u0027s say this way."},{"Start":"03:58.090 ","End":"04:02.375","Text":"That would be a different reading frame."},{"Start":"04:02.375 ","End":"04:04.910","Text":"I\u0027ve now shown here 2 different reading frames,"},{"Start":"04:04.910 ","End":"04:07.295","Text":"there can be 3 reading frames, of course."},{"Start":"04:07.295 ","End":"04:12.420","Text":"Yes, you could start from the G and that would be the third one."},{"Start":"04:12.420 ","End":"04:15.530","Text":"How does the cell know which one to start from?"},{"Start":"04:15.530 ","End":"04:18.200","Text":"Well, it sets by looking for"},{"Start":"04:18.200 ","End":"04:22.580","Text":"an AUG start codon near the 5-prime end of the messenger RNA."},{"Start":"04:22.580 ","End":"04:25.475","Text":"It\u0027s done differently in different organisms,"},{"Start":"04:25.475 ","End":"04:30.860","Text":"but there is a commonality that all of them do start with this AUG."},{"Start":"04:30.860 ","End":"04:36.320","Text":"The messenger RNA then is read after the reading frame is set in groups of 3"},{"Start":"04:36.320 ","End":"04:41.855","Text":"until the stop codon is encountered and that will stop the translation."},{"Start":"04:41.855 ","End":"04:44.180","Text":"Now if you look at this chart,"},{"Start":"04:44.180 ","End":"04:47.825","Text":"you\u0027ll see that there are actually different blocks of codons,"},{"Start":"04:47.825 ","End":"04:51.740","Text":"16 of them that\u0027s not so important but each of them is specified mostly by"},{"Start":"04:51.740 ","End":"04:56.225","Text":"the first and second nucleotides of the codons within a block."},{"Start":"04:56.225 ","End":"04:58.335","Text":"Here, for instance, is a block,"},{"Start":"04:58.335 ","End":"05:00.660","Text":"where all of them are the same,"},{"Start":"05:00.660 ","End":"05:03.060","Text":"in the sense that they all start with CU,"},{"Start":"05:03.060 ","End":"05:04.680","Text":"CU, CU,"},{"Start":"05:04.680 ","End":"05:06.770","Text":"they all encode leucine."},{"Start":"05:06.770 ","End":"05:08.225","Text":"Same thing would be here."},{"Start":"05:08.225 ","End":"05:09.975","Text":"We have CA, CA,"},{"Start":"05:09.975 ","End":"05:11.800","Text":"CA, CA,"},{"Start":"05:11.800 ","End":"05:15.995","Text":"and they can encode either histidine or glutamine."},{"Start":"05:15.995 ","End":"05:19.820","Text":"Yes? Some of the blocks are divided into a pyrimidine half,"},{"Start":"05:19.820 ","End":"05:23.510","Text":"that means ends with a U or C and a purine half."},{"Start":"05:23.510 ","End":"05:27.560","Text":"That was this example here, histidine and glutamine."},{"Start":"05:27.560 ","End":"05:31.475","Text":"Yes. Others of them get a whole block of 4 codon,"},{"Start":"05:31.475 ","End":"05:36.134","Text":"let\u0027s say this proline is a whole block of 4 codons."},{"Start":"05:36.134 ","End":"05:38.630","Text":"But some of them actually even have more,"},{"Start":"05:38.630 ","End":"05:40.430","Text":"as we mentioned, the leucine,"},{"Start":"05:40.430 ","End":"05:46.830","Text":"there are 6 actually codons that encode leucine."},{"Start":"05:46.830 ","End":"05:53.285","Text":"So there\u0027s no real commonality or there\u0027s no rule regarding all of these."},{"Start":"05:53.285 ","End":"05:55.595","Text":"However, if we look at the cells,"},{"Start":"05:55.595 ","End":"06:00.665","Text":"we will find that there is a codon usage bias."},{"Start":"06:00.665 ","End":"06:06.110","Text":"That means that there\u0027s a specification of a single amino acid by multiple similar codons"},{"Start":"06:06.110 ","End":"06:11.945","Text":"may be a similar mechanism to reduce the negative impact of random mutations."},{"Start":"06:11.945 ","End":"06:17.960","Text":"If there is a mutation in the last codon of some of these,"},{"Start":"06:17.960 ","End":"06:20.660","Text":"for instance, the last codon of a CU,"},{"Start":"06:20.660 ","End":"06:21.710","Text":"it doesn\u0027t really matter,"},{"Start":"06:21.710 ","End":"06:24.860","Text":"it\u0027s still going to encode a leucine,"},{"Start":"06:24.860 ","End":"06:30.925","Text":"and that\u0027s therefore will make evolution happen a little bit more slowly."},{"Start":"06:30.925 ","End":"06:35.090","Text":"Again, the codons that specify the same amino acid typically are"},{"Start":"06:35.090 ","End":"06:39.365","Text":"different by only one nucleotide and interestingly,"},{"Start":"06:39.365 ","End":"06:41.300","Text":"even beyond that, the amino acids with"},{"Start":"06:41.300 ","End":"06:46.065","Text":"chemically similar side chains are encoded by similar codons."},{"Start":"06:46.065 ","End":"06:48.735","Text":"A single nucleotide substitution,"},{"Start":"06:48.735 ","End":"06:52.580","Text":"mutation might specify the same amino acid in the end of"},{"Start":"06:52.580 ","End":"06:56.450","Text":"the day and therefore have no effect over a similar amino acid."},{"Start":"06:56.450 ","End":"07:01.370","Text":"Therefore, it will make up very similar protein preventing"},{"Start":"07:01.370 ","End":"07:07.110","Text":"the protein from being rendered completely non-functional over evolutionary time."},{"Start":"07:07.110 ","End":"07:11.480","Text":"It\u0027s also important to note that the genetic codes of different organisms are"},{"Start":"07:11.480 ","End":"07:15.230","Text":"often biased towards using one of several codons,"},{"Start":"07:15.230 ","End":"07:18.415","Text":"so not all the codons that are here."},{"Start":"07:18.415 ","End":"07:22.684","Text":"Let\u0027s say are actual used in the same amount,"},{"Start":"07:22.684 ","End":"07:26.120","Text":"you\u0027ll have a bias where let\u0027s say these 2 are used more in"},{"Start":"07:26.120 ","End":"07:30.825","Text":"a particular organism than the other 4 in the case of leucine,"},{"Start":"07:30.825 ","End":"07:34.220","Text":"so the genetic code is often biased towards using one of"},{"Start":"07:34.220 ","End":"07:38.435","Text":"the several codons that encode the same amino acid over the others."},{"Start":"07:38.435 ","End":"07:44.420","Text":"The genetic code is nearly universal with very few minor exceptions,"},{"Start":"07:44.420 ","End":"07:45.965","Text":"some of them are shown in this chart,"},{"Start":"07:45.965 ","End":"07:50.536","Text":"all species using the same genetic code for protein synthesis."},{"Start":"07:50.536 ","End":"07:52.730","Text":"This is a powerful evidence."},{"Start":"07:52.730 ","End":"07:57.620","Text":"It\u0027s powerful evidence that all life on Earth shares a common origin."},{"Start":"07:57.620 ","End":"08:00.620","Text":"That\u0027s a general belief by biologists."},{"Start":"08:00.620 ","End":"08:03.080","Text":"It\u0027s not proven, but it is good evidence,"},{"Start":"08:03.080 ","End":"08:08.030","Text":"especially considering there are about 1,084 possible combinations"},{"Start":"08:08.030 ","End":"08:14.130","Text":"of the 20 amino acids and 64 triplet codons."}],"ID":28210},{"Watched":false,"Name":"Eukaryotic transcription factors","Duration":"5m 18s","ChapterTopicVideoID":27083,"CourseChapterTopicPlaylistID":261641,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.150 ","End":"00:07.495","Text":"Let\u0027s continue now discussing eukaryotic transcription and its initiation."},{"Start":"00:07.495 ","End":"00:11.800","Text":"Eukaryotic promoters are much larger and much more"},{"Start":"00:11.800 ","End":"00:17.250","Text":"intricate than the prokaryotic promoters as we mentioned a little bit before."},{"Start":"00:17.250 ","End":"00:23.170","Text":"Notice that there is a box called a TATA box here."},{"Start":"00:23.170 ","End":"00:26.920","Text":"It has a sequence which is not always the same and in fact,"},{"Start":"00:26.920 ","End":"00:28.870","Text":"it doesn\u0027t even occur at every gene,"},{"Start":"00:28.870 ","End":"00:33.580","Text":"but it has a sequence that has a TATA,"},{"Start":"00:33.580 ","End":"00:34.990","Text":"sometimes more A\u0027s,"},{"Start":"00:34.990 ","End":"00:37.705","Text":"it\u0027s similar to this sequence."},{"Start":"00:37.705 ","End":"00:40.090","Text":"In eukaryotes, there\u0027s this TATA box with"},{"Start":"00:40.090 ","End":"00:44.150","Text":"a consensus sequence of TATAAA on the coding strand,"},{"Start":"00:44.150 ","End":"00:48.080","Text":"and it\u0027s located at about minus 25 to minus 35."},{"Start":"00:48.080 ","End":"00:49.765","Text":"It can move around a little bit,"},{"Start":"00:49.765 ","End":"00:54.500","Text":"and that\u0027s of course, relative to the plus 1 initiation site."},{"Start":"00:54.500 ","End":"00:58.040","Text":"Furthermore, instead of the simple Sigma factor that prokaryotes have,"},{"Start":"00:58.040 ","End":"01:04.700","Text":"eukaryotes assemble a large complex of transcription factors that are"},{"Start":"01:04.700 ","End":"01:11.900","Text":"required to recruit the RNA polymerase II to the proper protein-coding gene."},{"Start":"01:11.900 ","End":"01:15.955","Text":"In prokaryotes, there are only these 3 promoter elements."},{"Start":"01:15.955 ","End":"01:19.040","Text":"There\u0027s the minus 10 minus 35 that we discussed."},{"Start":"01:19.040 ","End":"01:22.325","Text":"In addition, there are occasionally some other elements called UP elements,"},{"Start":"01:22.325 ","End":"01:26.930","Text":"but eukaryotes contain a wide variety of promoter elements,"},{"Start":"01:26.930 ","End":"01:31.580","Text":"and we can see that down in this figure."},{"Start":"01:31.580 ","End":"01:38.960","Text":"Some eukaryotic promoters have this conserved CAAT box at about minus 75."},{"Start":"01:38.960 ","End":"01:43.055","Text":"It\u0027s called a CAAT box because it includes this sequence CAAT."},{"Start":"01:43.055 ","End":"01:45.080","Text":"Here you can see an example of it."},{"Start":"01:45.080 ","End":"01:47.135","Text":"It\u0027s not always exactly the same,"},{"Start":"01:47.135 ","End":"01:50.165","Text":"but it is somewhat of a consensus."},{"Start":"01:50.165 ","End":"01:52.580","Text":"Further upstream of the TATA box,"},{"Start":"01:52.580 ","End":"01:56.270","Text":"say at minus 100, something like that,"},{"Start":"01:56.270 ","End":"02:02.494","Text":"eukaryotic promoters may also contain one or more of these GC-rich boxes."},{"Start":"02:02.494 ","End":"02:10.520","Text":"For instance, GGCG or sometimes these octamer boxes that is 8 different nucleotides,"},{"Start":"02:10.520 ","End":"02:14.030","Text":"for example, ATTTGCAT,"},{"Start":"02:14.030 ","End":"02:19.940","Text":"but these sequences vary and they also vary in where they\u0027re located."},{"Start":"02:19.940 ","End":"02:23.780","Text":"Now why is that and why are they so different?"},{"Start":"02:23.780 ","End":"02:28.700","Text":"Well, you remember that DNA is the same in every tissue of the body,"},{"Start":"02:28.700 ","End":"02:32.225","Text":"but it\u0027s expressed differently in different places,"},{"Start":"02:32.225 ","End":"02:38.255","Text":"one of the ways that the body controls what is transcribed in what cell,"},{"Start":"02:38.255 ","End":"02:40.520","Text":"despite the fact that DNA is the same,"},{"Start":"02:40.520 ","End":"02:47.570","Text":"is by having different transcription factors that are available in different tissues."},{"Start":"02:47.570 ","End":"02:50.210","Text":"In skin cells, for instance,"},{"Start":"02:50.210 ","End":"02:56.870","Text":"you could have certain basal transcription factors that are applied to a particular gene."},{"Start":"02:56.870 ","End":"03:02.105","Text":"In liver cells, you could have those factors and activator proteins,"},{"Start":"03:02.105 ","End":"03:03.965","Text":"and in another cell type,"},{"Start":"03:03.965 ","End":"03:07.850","Text":"you may say in the brain you might have the same basal transcription factors,"},{"Start":"03:07.850 ","End":"03:11.315","Text":"but there are repressor proteins that are acting on them."},{"Start":"03:11.315 ","End":"03:14.435","Text":"In fact, there are sequences that are called"},{"Start":"03:14.435 ","End":"03:18.880","Text":"enhancers and other sequences called silencers that"},{"Start":"03:18.880 ","End":"03:21.830","Text":"influence the expression of the genes that are in"},{"Start":"03:21.830 ","End":"03:26.705","Text":"their vicinity very greatly together with"},{"Start":"03:26.705 ","End":"03:29.780","Text":"various transcription factors that may bind to"},{"Start":"03:29.780 ","End":"03:36.110","Text":"these enhancers upstream of the gene and occasionally even downstream of the gene,"},{"Start":"03:36.110 ","End":"03:38.600","Text":"or sometimes even within the gene."},{"Start":"03:38.600 ","End":"03:43.850","Text":"They regulate the transcription of that particular gene and they help regulate"},{"Start":"03:43.850 ","End":"03:49.355","Text":"the frequency with which pre-messenger RNA is synthesized from that gene."},{"Start":"03:49.355 ","End":"03:53.420","Text":"In other words, how often it initiates and ultimately,"},{"Start":"03:53.420 ","End":"03:57.655","Text":"therefore, how many copies of that gene are made."},{"Start":"03:57.655 ","End":"04:00.660","Text":"Now let\u0027s look at elongation."},{"Start":"04:00.660 ","End":"04:05.740","Text":"In eukaryotic elongation, there is this bubble, of course,"},{"Start":"04:05.740 ","End":"04:11.230","Text":"that occurs in unwound DNA where the RNA polymerase is using 1 strand of"},{"Start":"04:11.230 ","End":"04:13.794","Text":"the DNA as a template as it does in prokaryotes"},{"Start":"04:13.794 ","End":"04:17.020","Text":"to catalyze the synthesis of a new RNA strand,"},{"Start":"04:17.020 ","End":"04:21.995","Text":"and of course, it is in the 5\u0027 to 3\u0027 direction."},{"Start":"04:21.995 ","End":"04:25.660","Text":"For each nucleotide in the template, as in prokaryotes,"},{"Start":"04:25.660 ","End":"04:33.860","Text":"RNA polymerase adds a complementary RNA nucleotide to the 3\u0027 end of the RNA strand,"},{"Start":"04:33.860 ","End":"04:38.350","Text":"but as opposed to what might be happening in prokaryotes,"},{"Start":"04:38.350 ","End":"04:44.155","Text":"sometimes there is something which is called a pause,"},{"Start":"04:44.155 ","End":"04:46.850","Text":"right after the beginning of initiation,"},{"Start":"04:46.850 ","End":"04:49.130","Text":"there may be sometimes,"},{"Start":"04:49.130 ","End":"04:52.730","Text":"often will happen that the RNA stops,"},{"Start":"04:52.730 ","End":"04:58.220","Text":"and there is a brief time when the newly formed RNA is bound to the unwound DNA,"},{"Start":"04:58.220 ","End":"05:00.140","Text":"but it\u0027s not transcribing."},{"Start":"05:00.140 ","End":"05:04.400","Text":"Often there is an adenine at the end of that RNA."},{"Start":"05:04.400 ","End":"05:09.230","Text":"Then there\u0027s another control that may"},{"Start":"05:09.230 ","End":"05:14.360","Text":"release this RNA polymerase complex from this initiation site,"},{"Start":"05:14.360 ","End":"05:18.660","Text":"from the pause to further elongation."}],"ID":28211},{"Watched":false,"Name":"Innitiation and elongation of translation","Duration":"4m 53s","ChapterTopicVideoID":27084,"CourseChapterTopicPlaylistID":261641,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.260 ","End":"00:05.610","Text":"Now that we know what the structure of the ribosome is,"},{"Start":"00:05.610 ","End":"00:09.720","Text":"roughly and what the structure of the tRNA is, roughly."},{"Start":"00:09.720 ","End":"00:13.980","Text":"Let\u0027s look at the protein synthesis itself."},{"Start":"00:13.980 ","End":"00:19.125","Text":"Just as transcription was divided into 3 different phases."},{"Start":"00:19.125 ","End":"00:27.165","Text":"Likewise, protein synthesis is divided into initiation, elongation, and termination."},{"Start":"00:27.165 ","End":"00:33.360","Text":"The mechanism of translation is actually similar in prokaryotes and eukaryotes."},{"Start":"00:33.360 ","End":"00:36.765","Text":"As we mentioned before in the case of transcription,"},{"Start":"00:36.765 ","End":"00:39.735","Text":"we will concentrate on what it looks like"},{"Start":"00:39.735 ","End":"00:43.425","Text":"in prokaryotes because it\u0027s a little bit simpler."},{"Start":"00:43.425 ","End":"00:47.050","Text":"That\u0027s what we see here from E. coli."},{"Start":"00:47.410 ","End":"00:54.635","Text":"Translation begins at a start codon AUG that encodes for methionine."},{"Start":"00:54.635 ","End":"00:56.810","Text":"As we said, here\u0027s the methionine."},{"Start":"00:56.810 ","End":"01:03.065","Text":"Every protein is going to start with a methionine that signals the start of translation."},{"Start":"01:03.065 ","End":"01:05.880","Text":"First, a small ribosomal subunit,"},{"Start":"01:05.880 ","End":"01:08.495","Text":"just the smaller subunit the 30S,"},{"Start":"01:08.495 ","End":"01:10.850","Text":"in the case of prokaryotes,"},{"Start":"01:10.850 ","End":"01:15.620","Text":"binds with messenger RNA and this special initiator,"},{"Start":"01:15.620 ","End":"01:19.730","Text":"tRNA that has methionine attached to it."},{"Start":"01:19.730 ","End":"01:23.585","Text":"Then the small subunit moves along the messenger RNA"},{"Start":"01:23.585 ","End":"01:27.845","Text":"until it reaches the first start codon,"},{"Start":"01:27.845 ","End":"01:33.200","Text":"which is going to be AUG. Proteins that are called initiation factors,"},{"Start":"01:33.200 ","End":"01:38.315","Text":"will bring the large sub-unit that completes the translation initiation complex."},{"Start":"01:38.315 ","End":"01:40.955","Text":"Here is the large subunit,"},{"Start":"01:40.955 ","End":"01:47.734","Text":"which will then close down on the smaller subunit and it will then begin."},{"Start":"01:47.734 ","End":"01:52.200","Text":"Then the larger subunit is brought to"},{"Start":"01:52.200 ","End":"01:59.015","Text":"the smaller subunit and the initiation of translation is complete."},{"Start":"01:59.015 ","End":"02:01.970","Text":"Now let\u0027s look at elongation."},{"Start":"02:01.970 ","End":"02:04.910","Text":"During this phase, amino acids are added"},{"Start":"02:04.910 ","End":"02:09.440","Text":"one-by-one to the C-terminus of the growing chain."},{"Start":"02:09.440 ","End":"02:13.390","Text":"We had this initiation to begin with"},{"Start":"02:13.390 ","End":"02:18.905","Text":"and the messenger RNA will provide the template for the tRNA binding specificity."},{"Start":"02:18.905 ","End":"02:22.850","Text":"As we mentioned, it\u0027s the interaction between the codon and"},{"Start":"02:22.850 ","End":"02:28.660","Text":"the anticodon of the incoming tRNAs that will provide the specificity."},{"Start":"02:28.660 ","End":"02:32.840","Text":"The elongation itself can also be divided into 3 steps."},{"Start":"02:32.840 ","End":"02:36.005","Text":"First of all, there\u0027s this codon recognition, as we mentioned."},{"Start":"02:36.005 ","End":"02:42.530","Text":"There\u0027s the peptide bond formation itself that we can see here between"},{"Start":"02:42.530 ","End":"02:45.560","Text":"the incoming amino acid that was"},{"Start":"02:45.560 ","End":"02:50.300","Text":"attached to the previous tRNA and then there\u0027s translocation."},{"Start":"02:50.300 ","End":"02:56.000","Text":"There will be movement of this whole business that we can see"},{"Start":"02:56.000 ","End":"03:02.090","Text":"here in which you can see that the amino acid chain moves from the tRNA,"},{"Start":"03:02.090 ","End":"03:06.980","Text":"which was in the P site as the peptidyl site"},{"Start":"03:06.980 ","End":"03:12.270","Text":"to the aminoacyl site."},{"Start":"03:12.270 ","End":"03:16.380","Text":"In that case, there is this movement."},{"Start":"03:16.380 ","End":"03:19.070","Text":"The messenger RNA template, as we said,"},{"Start":"03:19.070 ","End":"03:24.415","Text":"provides a tRNA specificity and the elongation occurs in these 3 steps."},{"Start":"03:24.415 ","End":"03:27.110","Text":"We\u0027ve seen now the codon recognition,"},{"Start":"03:27.110 ","End":"03:32.930","Text":"the peptide bond formation, and the translocation."},{"Start":"03:32.930 ","End":"03:36.410","Text":"Now finally, after this translocation,"},{"Start":"03:36.410 ","End":"03:41.870","Text":"we return back to the original position and we\u0027re ready now to get a"},{"Start":"03:41.870 ","End":"03:48.680","Text":"new tRNA back into the aminoacyl site as the tRNA,"},{"Start":"03:48.680 ","End":"03:53.405","Text":"which is no longer charged with amino acid leaves."},{"Start":"03:53.405 ","End":"03:58.160","Text":"We\u0027ve got charged tRNAs sequentially entering and leaving"},{"Start":"03:58.160 ","End":"04:03.530","Text":"the ribosome as each new amino acid is added to the polypeptide chain and"},{"Start":"04:03.530 ","End":"04:08.870","Text":"the energy for that peptide bond which is"},{"Start":"04:08.870 ","End":"04:15.350","Text":"formed is derived from the high-energy bond that links each amino acid to its tRNA."},{"Start":"04:15.350 ","End":"04:19.535","Text":"Remember we said the tRNAs were charged with an amino acid."},{"Start":"04:19.535 ","End":"04:25.490","Text":"We\u0027re discussing that high-energy and the translation proceeds along the messenger RNA"},{"Start":"04:25.490 ","End":"04:32.465","Text":"in a 5-prime to 3-prime direction with respect to the messenger RNA."},{"Start":"04:32.465 ","End":"04:36.770","Text":"Now it\u0027s really fast this reaction or it\u0027s so complicated."},{"Start":"04:36.770 ","End":"04:43.310","Text":"It\u0027s only 0.05 seconds in bacteria to add each amino acid."},{"Start":"04:43.310 ","End":"04:44.660","Text":"That\u0027s how long it takes,"},{"Start":"04:44.660 ","End":"04:50.680","Text":"meaning that a 200 amino acid protein can be translated in about 10 seconds."},{"Start":"04:50.680 ","End":"04:53.770","Text":"That\u0027s amazingly fast."}],"ID":28212},{"Watched":false,"Name":"Outline of translation","Duration":"7m 36s","ChapterTopicVideoID":27085,"CourseChapterTopicPlaylistID":261641,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:03.000","Text":"Welcome back. For the next video."},{"Start":"00:03.000 ","End":"00:09.825","Text":"We\u0027ve been discussing RNA transcription and then RNA processing."},{"Start":"00:09.825 ","End":"00:14.010","Text":"We\u0027re now ready to discuss what that RNA is used for,"},{"Start":"00:14.010 ","End":"00:17.130","Text":"and that is primarily protein synthesis."},{"Start":"00:17.130 ","End":"00:21.300","Text":"Here we\u0027re going to discuss the mechanism of protein synthesis."},{"Start":"00:21.300 ","End":"00:26.895","Text":"Now protein synthesis consumes more of a cell\u0027s energy than any other metabolic process."},{"Start":"00:26.895 ","End":"00:32.850","Text":"Proteins are also the main mass of living organisms as you can see here,"},{"Start":"00:32.850 ","End":"00:35.610","Text":"about 16 percent water composes,"},{"Start":"00:35.610 ","End":"00:39.075","Text":"say, 60-70 percent of us."},{"Start":"00:39.075 ","End":"00:41.870","Text":"These proteins are not only structural,"},{"Start":"00:41.870 ","End":"00:44.210","Text":"but many of them also serve as"},{"Start":"00:44.210 ","End":"00:48.980","Text":"the enzymes that drive the chemical reactions that occur in the body."},{"Start":"00:48.980 ","End":"00:52.280","Text":"They\u0027re really, really important."},{"Start":"00:52.280 ","End":"00:56.090","Text":"Proteins perform virtually every function in a cell."},{"Start":"00:56.090 ","End":"01:01.525","Text":"Now, each amino acid in the protein contains an amino group,"},{"Start":"01:01.525 ","End":"01:04.055","Text":"NH_2 and a carboxyl group,"},{"Start":"01:04.055 ","End":"01:05.825","Text":"as we discussed earlier."},{"Start":"01:05.825 ","End":"01:09.260","Text":"Each amino acid, as we said,"},{"Start":"01:09.260 ","End":"01:13.790","Text":"has this amino group and this carboxyl group."},{"Start":"01:13.790 ","End":"01:20.960","Text":"Yes. The polypeptides, that is the connection between the amino acids are formed when"},{"Start":"01:20.960 ","End":"01:23.870","Text":"the amino group of the 1 amino acid forms"},{"Start":"01:23.870 ","End":"01:28.025","Text":"an amide bond with the carboxyl group of another amino acid."},{"Start":"01:28.025 ","End":"01:31.145","Text":"That\u0027s what we see happening here."},{"Start":"01:31.145 ","End":"01:35.750","Text":"Yes, there\u0027s the creation of this peptide bonds."},{"Start":"01:35.750 ","End":"01:40.220","Text":"Note in the course of making this peptide bonds,"},{"Start":"01:40.220 ","End":"01:43.055","Text":"there is water released."},{"Start":"01:43.055 ","End":"01:49.460","Text":"The reaction is catalyzed by this machinery called ribosomes."},{"Start":"01:49.460 ","End":"01:54.319","Text":"The ribosomes are the machine\u0027s really that create the peptide bonds."},{"Start":"01:54.319 ","End":"01:56.645","Text":"In the process, as we mentioned,"},{"Start":"01:56.645 ","End":"02:01.195","Text":"water is released by a process of dehydration."},{"Start":"02:01.195 ","End":"02:06.905","Text":"Let\u0027s look a little bit more closely about these machines then at these ribosomes."},{"Start":"02:06.905 ","End":"02:10.790","Text":"Many molecules actually contribute to the process of translation and"},{"Start":"02:10.790 ","End":"02:16.060","Text":"form these very complicated machines called ribosomes."},{"Start":"02:16.060 ","End":"02:20.960","Text":"Interestingly, they vary somewhat amongst species,"},{"Start":"02:20.960 ","End":"02:25.330","Text":"but in general, there\u0027s a conservation of the structure."},{"Start":"02:25.330 ","End":"02:31.040","Text":"In some organisms they may contain different numbers of ribosomal RNAs."},{"Start":"02:31.040 ","End":"02:34.100","Text":"These are the structural RNAs and polypeptides."},{"Start":"02:34.100 ","End":"02:36.515","Text":"But as I said, in general,"},{"Start":"02:36.515 ","End":"02:43.410","Text":"they are comparable even between prokaryotes and eukaryotes."},{"Start":"02:43.410 ","End":"02:48.785","Text":"The translation requires the inputs of a messenger RNA template of course,"},{"Start":"02:48.785 ","End":"02:53.000","Text":"these ribosomes, tRNAs, which we\u0027ll see"},{"Start":"02:53.000 ","End":"02:57.665","Text":"are these adaptor molecules and other enzymatic factors."},{"Start":"02:57.665 ","End":"03:00.620","Text":"Let\u0027s first look at ribosomes."},{"Start":"03:00.620 ","End":"03:05.060","Text":"Ribosomes can be thought of as a very large enzyme"},{"Start":"03:05.060 ","End":"03:11.495","Text":"whose amino acid binding sites are specified by the messenger RNA."},{"Start":"03:11.495 ","End":"03:15.815","Text":"What we\u0027re looking at over here is that nucleus of the cell in"},{"Start":"03:15.815 ","End":"03:21.110","Text":"purple with a structure in the middle called the nucleolus,"},{"Start":"03:21.110 ","End":"03:23.844","Text":"which is inside the nucleus."},{"Start":"03:23.844 ","End":"03:30.305","Text":"Then on the outside what we see is a structure called the endoplasmic reticulum."},{"Start":"03:30.305 ","End":"03:35.030","Text":"Ribosomes that we\u0027re talking about are often in eukaryotes"},{"Start":"03:35.030 ","End":"03:40.595","Text":"stuck to the outside of the endoplasmic reticulum."},{"Start":"03:40.595 ","End":"03:44.660","Text":"Now a cell must invest an awful lot of energy in order to build"},{"Start":"03:44.660 ","End":"03:49.340","Text":"these very complicated ribosomes and there are many of these ribosomes."},{"Start":"03:49.340 ","End":"03:50.840","Text":"In fact, in E-coli,"},{"Start":"03:50.840 ","End":"03:55.280","Text":"there are somewhere between 10 thousand and 70 thousand ribosomes"},{"Start":"03:55.280 ","End":"03:58.240","Text":"in every cell at any given time."},{"Start":"03:58.240 ","End":"04:02.580","Text":"That\u0027s a lot of machines to make quite a bit of protein."},{"Start":"04:02.580 ","End":"04:05.495","Text":"In eukaryotes, as we mentioned,"},{"Start":"04:05.495 ","End":"04:09.995","Text":"there is the specialized structure inside the nucleus for the synthesis"},{"Start":"04:09.995 ","End":"04:14.690","Text":"and assembly of ribosomal RNAs and in fact,"},{"Start":"04:14.690 ","End":"04:17.630","Text":"the sub-units of the ribosome."},{"Start":"04:17.630 ","End":"04:21.725","Text":"Interestingly, the ribosomes exist not only"},{"Start":"04:21.725 ","End":"04:27.490","Text":"in eukaryotic cells outside the nucleus and in prokaryotic cells,"},{"Start":"04:27.490 ","End":"04:31.445","Text":"but they are found even inside"},{"Start":"04:31.445 ","End":"04:40.150","Text":"some organelles like mitochondria and chloroplasts."},{"Start":"04:40.150 ","End":"04:44.150","Text":"These little organelles also have ribosomes in"},{"Start":"04:44.150 ","End":"04:49.100","Text":"them because they know how to make protein."},{"Start":"04:49.100 ","End":"04:54.065","Text":"Even inside mitochondria and chloroplasts,"},{"Start":"04:54.065 ","End":"04:57.560","Text":"ribosomes in general dissociate into"},{"Start":"04:57.560 ","End":"05:01.970","Text":"large and small subunits when they are not synthesizing the proteins."},{"Start":"05:01.970 ","End":"05:08.085","Text":"Prokaryotic small subunit is described as 30S."},{"Start":"05:08.085 ","End":"05:14.458","Text":"Here we\u0027re talking about a prokaryotic ribosome and on the right, a eukaryotic ribosome."},{"Start":"05:14.458 ","End":"05:18.550","Text":"The different sub-units are denoted by these S values."},{"Start":"05:18.550 ","End":"05:22.010","Text":"The 30S sub-unit in prokaryotes,"},{"Start":"05:22.010 ","End":"05:24.664","Text":"the 40 S sub unit in eukaryotes,"},{"Start":"05:24.664 ","End":"05:30.570","Text":"the entire ribosome is described as 70S in prokaryotes in 80S."},{"Start":"05:30.570 ","End":"05:36.170","Text":"In eukaryotes, this S value has to do with how quickly it\u0027s sediments."},{"Start":"05:36.170 ","End":"05:38.840","Text":"That\u0027s where the S comes from through"},{"Start":"05:38.840 ","End":"05:42.230","Text":"a sucrose gradients when it\u0027s put into a centrifuge."},{"Start":"05:42.230 ","End":"05:46.490","Text":"That means that this is a solution of sucrose."},{"Start":"05:46.490 ","End":"05:51.590","Text":"The larger and more bulky a particle,"},{"Start":"05:51.590 ","End":"05:57.405","Text":"the small slowly it will go through the sucrose gradient and the higher the number."},{"Start":"05:57.405 ","End":"06:02.855","Text":"These S values have something to do with the size of these particles."},{"Start":"06:02.855 ","End":"06:06.470","Text":"Eukaryotic ribosomes have these 40S sub-units"},{"Start":"06:06.470 ","End":"06:09.830","Text":"as we mentioned and then the larger 60S sub-units."},{"Start":"06:09.830 ","End":"06:14.200","Text":"We have 40 and 60 in the eukaryote for a total of 80."},{"Start":"06:14.200 ","End":"06:17.830","Text":"Notice that 40 and 60 don\u0027t add up to 80"},{"Start":"06:17.830 ","End":"06:21.940","Text":"because each of these values is measured independently."},{"Start":"06:21.940 ","End":"06:26.800","Text":"The small unit is responsible for binding the messenger RNA template in general,"},{"Start":"06:26.800 ","End":"06:32.805","Text":"and the large sub-unit sequentially binds the tRNAs as we\u0027ll see."},{"Start":"06:32.805 ","End":"06:36.550","Text":"Each messenger RNA molecule is simultaneously"},{"Start":"06:36.550 ","End":"06:41.445","Text":"translated by many ribosomes in the same direction."},{"Start":"06:41.445 ","End":"06:47.595","Text":"Yes, in the 5 prime to 3 prime direction of the messenger RNA."},{"Start":"06:47.595 ","End":"06:52.385","Text":"The polypeptide is synthesized from its N terminus,"},{"Start":"06:52.385 ","End":"06:59.595","Text":"that is where the amino group is to the C terminus or the carboxyl end is."},{"Start":"06:59.595 ","End":"07:04.040","Text":"You can see in this picture the growing polypeptides."},{"Start":"07:04.040 ","End":"07:06.950","Text":"Yes, the purple is the growing polypeptide that is"},{"Start":"07:06.950 ","End":"07:10.549","Text":"growing from the end that is inside the ribosome."},{"Start":"07:10.549 ","End":"07:12.850","Text":"There\u0027s an addition made."},{"Start":"07:12.850 ","End":"07:22.025","Text":"As it runs along the messenger RNA from the 5 prime end to this 3 prime end."},{"Start":"07:22.025 ","End":"07:25.789","Text":"Each of these messenger RNAs that has multiple ribosomes"},{"Start":"07:25.789 ","End":"07:29.480","Text":"on them is called a polyribosome,"},{"Start":"07:29.480 ","End":"07:37.020","Text":"because it has multiple poly ribosomes on this structure."}],"ID":28213},{"Watched":false,"Name":"Rho independent termination","Duration":"5m 6s","ChapterTopicVideoID":27086,"CourseChapterTopicPlaylistID":261641,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.590","Text":"Hi. So let\u0027s continue discussing prokaryotic transcription."},{"Start":"00:04.590 ","End":"00:06.210","Text":"We were discussing,"},{"Start":"00:06.210 ","End":"00:10.800","Text":"at the end of the last video, Rho-dependent termination."},{"Start":"00:10.800 ","End":"00:15.780","Text":"If you remember, Rho-dependent termination had to do with a particular protein,"},{"Start":"00:15.780 ","End":"00:19.290","Text":"Rho, that was involved in the termination."},{"Start":"00:19.290 ","End":"00:25.845","Text":"But transcriptional termination can also occur in bacteria without Rho."},{"Start":"00:25.845 ","End":"00:30.795","Text":"It\u0027s called, therefore, Rho-independent termination and the control of"},{"Start":"00:30.795 ","End":"00:33.540","Text":"Rho-independent termination is controlled by"},{"Start":"00:33.540 ","End":"00:38.085","Text":"specific sequences in the DNA template strand."},{"Start":"00:38.085 ","End":"00:40.465","Text":"How does that work? Well,"},{"Start":"00:40.465 ","End":"00:42.215","Text":"near the end of the gene,"},{"Start":"00:42.215 ","End":"00:49.470","Text":"the RNA polymerase encounters a region rich in C-G nucleotides."},{"Start":"00:49.470 ","End":"00:51.845","Text":"If you look at this sequence here,"},{"Start":"00:51.845 ","End":"00:56.060","Text":"there is in the DNA and then it\u0027s transcribed of course into the RNA,"},{"Start":"00:56.060 ","End":"01:01.480","Text":"a sequence which is AGCCCGCC."},{"Start":"01:01.480 ","End":"01:03.019","Text":"Then, actually,"},{"Start":"01:03.019 ","End":"01:09.410","Text":"there\u0027s another sequence GGCGGGCT and"},{"Start":"01:09.410 ","End":"01:16.415","Text":"then further along in that sequence is exactly the complementary sequence to that."},{"Start":"01:16.415 ","End":"01:23.675","Text":"What happens? The RNA which is made therefore is from this sequence,"},{"Start":"01:23.675 ","End":"01:27.080","Text":"is going to have the possibility."},{"Start":"01:27.080 ","End":"01:35.740","Text":"The transcribed RNA is going to have a possibility of a very stable loop and hairpin."},{"Start":"01:35.740 ","End":"01:39.000","Text":"The resulting messenger RNA folds back on itself,"},{"Start":"01:39.000 ","End":"01:40.490","Text":"that\u0027s what you can see here,"},{"Start":"01:40.490 ","End":"01:45.469","Text":"and the complimentary C-G nucleotides bind together creating a stable,"},{"Start":"01:45.469 ","End":"01:46.970","Text":"what\u0027s called a hairpin."},{"Start":"01:46.970 ","End":"01:51.335","Text":"This structure with a loop and a stem is called a hairpin."},{"Start":"01:51.335 ","End":"01:55.040","Text":"That causes the polymerase to stall as soon as it begins to"},{"Start":"01:55.040 ","End":"01:59.060","Text":"transcribe a region that is rich"},{"Start":"01:59.060 ","End":"02:06.705","Text":"A-T nucleotides which is adjacent to that area of the stem and loop."},{"Start":"02:06.705 ","End":"02:11.330","Text":"Now, on the one hand, you\u0027ll have something which stalls the RNA because of"},{"Start":"02:11.330 ","End":"02:15.290","Text":"this loop which has been made in"},{"Start":"02:15.290 ","End":"02:20.900","Text":"the RNA and interferes with its binding to the RNA polymerase."},{"Start":"02:20.900 ","End":"02:25.435","Text":"On the other hand, there is this U-A region"},{"Start":"02:25.435 ","End":"02:31.670","Text":"in the messenger RNA transcript that forms only a weak interaction with the template DNA."},{"Start":"02:31.670 ","End":"02:35.030","Text":"This issue coupled with the stalled polymerase"},{"Start":"02:35.030 ","End":"02:38.945","Text":"induces enough instability for the core enzyme to break away,"},{"Start":"02:38.945 ","End":"02:41.195","Text":"to disassemble, and liberate"},{"Start":"02:41.195 ","End":"02:46.960","Text":"the new messenger RNA transcript which ends up with termination."},{"Start":"02:46.960 ","End":"02:50.450","Text":"That is the completion of transcription."},{"Start":"02:50.450 ","End":"02:52.655","Text":"This can occur either through"},{"Start":"02:52.655 ","End":"02:59.750","Text":"Rho-dependent or Rho-independent termination in prokaryotes."},{"Start":"02:59.750 ","End":"03:03.420","Text":"Now, it\u0027s important to note that there is,"},{"Start":"03:03.420 ","End":"03:08.465","Text":"in prokaryotes, there is a unification of sorts between transcription and translation."},{"Start":"03:08.465 ","End":"03:11.390","Text":"Because by the time termination occurs,"},{"Start":"03:11.390 ","End":"03:14.360","Text":"the prokaryotic transcript would already have been used to begin"},{"Start":"03:14.360 ","End":"03:17.780","Text":"synthesis of numerous copies of the encoded protein."},{"Start":"03:17.780 ","End":"03:20.810","Text":"What does that mean? If this is the DNA,"},{"Start":"03:20.810 ","End":"03:23.705","Text":"the blue, and the RNA,"},{"Start":"03:23.705 ","End":"03:29.375","Text":"this orange strand is being produced by the RNA polymerase,"},{"Start":"03:29.375 ","End":"03:38.600","Text":"then the end of it can already be translated into a polypeptide,"},{"Start":"03:38.600 ","End":"03:43.175","Text":"into a protein as it\u0027s being transcribed."},{"Start":"03:43.175 ","End":"03:47.330","Text":"So all along, we have transcription which causes"},{"Start":"03:47.330 ","End":"03:55.127","Text":"longer and longer and longer pieces of RNA which is being translated at the same time."},{"Start":"03:55.127 ","End":"04:00.430","Text":"These brown things here are ribosomes creating a polyribosome,"},{"Start":"04:00.430 ","End":"04:01.905","Text":"number of them together."},{"Start":"04:01.905 ","End":"04:05.150","Text":"Each of these ribosomes then is producing more and more,"},{"Start":"04:05.150 ","End":"04:08.885","Text":"longer and longer and longer protein as"},{"Start":"04:08.885 ","End":"04:14.660","Text":"the RNA polymerase moves down the DNA transcribing more RNA,"},{"Start":"04:14.660 ","End":"04:16.490","Text":"which is then translated into proteins."},{"Start":"04:16.490 ","End":"04:19.160","Text":"So these things occur together."},{"Start":"04:19.160 ","End":"04:23.552","Text":"We call that the unification of transcription, translation,"},{"Start":"04:23.552 ","End":"04:28.970","Text":"and even what we haven\u0027t seen here is messenger RNA degradation is possible because"},{"Start":"04:28.970 ","End":"04:34.910","Text":"all of these processes occur in this same 5\u0027 to 3\u0027 direction."},{"Start":"04:34.910 ","End":"04:37.345","Text":"5\u0027 to 3\u0027."},{"Start":"04:37.345 ","End":"04:39.530","Text":"If they were to occur in opposite directions,"},{"Start":"04:39.530 ","End":"04:41.285","Text":"this would be impossible."},{"Start":"04:41.285 ","End":"04:45.770","Text":"Furthermore, there is no membranous compartmentalization in"},{"Start":"04:45.770 ","End":"04:51.230","Text":"prokaryotic cells in contrast to the nuclear membrane that is in eukaryotic cells,"},{"Start":"04:51.230 ","End":"04:57.590","Text":"in which that membrane precludes simultaneous transcription and translation because"},{"Start":"04:57.590 ","End":"05:00.920","Text":"the transcription occurs in the nucleus but"},{"Start":"05:00.920 ","End":"05:07.170","Text":"the translation in eukaryotes occurs in the cytoplasm."}],"ID":28214},{"Watched":false,"Name":"Splicing","Duration":"5m 30s","ChapterTopicVideoID":27087,"CourseChapterTopicPlaylistID":261641,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.905","Text":"Let\u0027s continue talking about RNA processing in eukaryotes."},{"Start":"00:04.905 ","End":"00:09.600","Text":"We\u0027ve discussed the addition of the cap on the 5-prime end,"},{"Start":"00:09.600 ","End":"00:14.640","Text":"and we\u0027ve discussed the addition of poly at the 3-prime end of the RNAs."},{"Start":"00:14.640 ","End":"00:17.475","Text":"But remember there are also introns"},{"Start":"00:17.475 ","End":"00:21.600","Text":"which need to be removed by a process called splicing."},{"Start":"00:21.600 ","End":"00:24.270","Text":"Eukaryotic genes are composed of course,"},{"Start":"00:24.270 ","End":"00:29.204","Text":"of exons that encode the protein"},{"Start":"00:29.204 ","End":"00:35.010","Text":"and introns which may be involved in gene regulation."},{"Start":"00:35.010 ","End":"00:38.190","Text":"In other words, sequences that are there may be involved in gene regulation,"},{"Start":"00:38.190 ","End":"00:42.225","Text":"but they\u0027re removed during the process of splicing."},{"Start":"00:42.225 ","End":"00:45.695","Text":"As we said, they don\u0027t encode functional proteins."},{"Start":"00:45.695 ","End":"00:50.840","Text":"The genes of higher eukaryotes often contain many introns."},{"Start":"00:50.840 ","End":"00:52.910","Text":"They could contain as few as 1, but usually,"},{"Start":"00:52.910 ","End":"00:56.365","Text":"they contain many many introns."},{"Start":"00:56.365 ","End":"01:01.550","Text":"As we said, they may contain regulatory sequences."},{"Start":"01:01.550 ","End":"01:07.940","Text":"Now, the biological significance of having so many introns is really not quite clear."},{"Start":"01:07.940 ","End":"01:13.205","Text":"They possibly might slow down gene expression because so much RNA has to be transcribed."},{"Start":"01:13.205 ","End":"01:17.825","Text":"They may be leftover evolutionarily from ancient genes,"},{"Start":"01:17.825 ","End":"01:20.765","Text":"maybe fusion of ancient genes, we don\u0027t know."},{"Start":"01:20.765 ","End":"01:27.575","Text":"It may be that since the sequences that have introns are much longer"},{"Start":"01:27.575 ","End":"01:35.960","Text":"than mutations that are found in these introns would not affect the protein product."},{"Start":"01:35.960 ","End":"01:39.319","Text":"Therefore it\u0027s a buffer against mutations."},{"Start":"01:39.319 ","End":"01:42.355","Text":"That\u0027s a possibility we don\u0027t really know."},{"Start":"01:42.355 ","End":"01:47.295","Text":"Let\u0027s look now at the process of splicing itself."},{"Start":"01:47.295 ","End":"01:55.835","Text":"The splicing or the intron removal must be very precise because an error of"},{"Start":"01:55.835 ","End":"01:58.970","Text":"even a single nucleotide in bringing"},{"Start":"01:58.970 ","End":"02:02.300","Text":"the 2 splice sites together will"},{"Start":"02:02.300 ","End":"02:06.380","Text":"cause a reading frame-shift and therefore a dysfunctional protein."},{"Start":"02:06.380 ","End":"02:09.500","Text":"The splicing must be quite precise,"},{"Start":"02:09.500 ","End":"02:16.050","Text":"is accomplished by a complex of proteins with small RNAs."},{"Start":"02:16.050 ","End":"02:20.870","Text":"This complex has both protein and small RNAs in it."},{"Start":"02:20.870 ","End":"02:25.475","Text":"This entire complex is called a spliceosome."},{"Start":"02:25.475 ","End":"02:31.910","Text":"The introns are removed by this process of splicing and then they\u0027re degraded fairly"},{"Start":"02:31.910 ","End":"02:35.240","Text":"rapidly while the pre-messenger RNA is"},{"Start":"02:35.240 ","End":"02:39.110","Text":"still in the nucleus and actually while it\u0027s still being transcribed,"},{"Start":"02:39.110 ","End":"02:45.170","Text":"in some cases there are even on the order of 70 introns in very large genes."},{"Start":"02:45.170 ","End":"02:52.330","Text":"Each of them must undergo the process of splicing in order to get a mature messenger RNA."},{"Start":"02:52.330 ","End":"02:56.270","Text":"But splicing occurs not only in messenger RNA,"},{"Start":"02:56.270 ","End":"03:02.630","Text":"it also occurs in tRNA and ribosomal RNA processing."},{"Start":"03:02.630 ","End":"03:08.960","Text":"Remember the tRNAs are used in translation into protein."},{"Start":"03:08.960 ","End":"03:12.680","Text":"The ribosomal RNAs are structural proteins of the ribosome."},{"Start":"03:12.680 ","End":"03:18.335","Text":"They\u0027re not translated, but they\u0027re transcribed, processed, and assembled."},{"Start":"03:18.335 ","End":"03:21.860","Text":"Yes, either if we\u0027re talking about ribosomal RNAs into"},{"Start":"03:21.860 ","End":"03:26.600","Text":"the ribosome and if we\u0027re talking about tRNAs then we\u0027re discussing,"},{"Start":"03:26.600 ","End":"03:27.815","Text":"these are tRNAs,"},{"Start":"03:27.815 ","End":"03:32.285","Text":"then they are actually going to be processed in a way"},{"Start":"03:32.285 ","End":"03:37.505","Text":"that eventually will link them to free amino acids."},{"Start":"03:37.505 ","End":"03:42.170","Text":"Those are used again in the process of translation."},{"Start":"03:42.170 ","End":"03:45.710","Text":"Now, most of the tRNAs and ribosomal RNAs that"},{"Start":"03:45.710 ","End":"03:49.490","Text":"are transcribed as these long precursor molecules"},{"Start":"03:49.490 ","End":"03:57.080","Text":"that contain within them multiple ribosomal RNAs and multiple tRNAs,"},{"Start":"03:57.080 ","End":"03:58.685","Text":"each of them individually."},{"Start":"03:58.685 ","End":"04:03.590","Text":"Then they are processed and cut up into smaller pieces,"},{"Start":"04:03.590 ","End":"04:09.540","Text":"making individual tRNAs and individual ribosomal RNAs."},{"Start":"04:09.540 ","End":"04:16.280","Text":"The tRNAs can make this hairpin structure."},{"Start":"04:16.280 ","End":"04:20.985","Text":"You can see there is base pairing and stems and loops."},{"Start":"04:20.985 ","End":"04:26.285","Text":"Of course, this 2-dimensional structure can then fold into a 3-dimensional structure,"},{"Start":"04:26.285 ","End":"04:30.635","Text":"creating a very unique structure for each tRNA."},{"Start":"04:30.635 ","End":"04:39.095","Text":"The tRNA is folded up such that there\u0027s an amino acid binding site at the end of it."},{"Start":"04:39.095 ","End":"04:44.480","Text":"A specific amino acid is attached by a specific enzyme to each of"},{"Start":"04:44.480 ","End":"04:50.450","Text":"the 20 tRNAs that are correspond to the 20 amino acids."},{"Start":"04:50.450 ","End":"04:52.460","Text":"But the anticodon,"},{"Start":"04:52.460 ","End":"04:54.530","Text":"this structure that it\u0027s at the bottom,"},{"Start":"04:54.530 ","End":"05:01.247","Text":"is left to be complementary to the messenger RNA so that it will adapt,"},{"Start":"05:01.247 ","End":"05:06.815","Text":"it serve as an adapter between the RNA with"},{"Start":"05:06.815 ","End":"05:14.720","Text":"its codon and the amino acid that will be attached to the other end of the tRNA."},{"Start":"05:14.720 ","End":"05:20.765","Text":"The tRNA will serve as an adapter molecule between the RNA,"},{"Start":"05:20.765 ","End":"05:24.920","Text":"messenger RNA and the amino acid that it\u0027s"},{"Start":"05:24.920 ","End":"05:29.670","Text":"at the other ends during the process of translation."}],"ID":28215},{"Watched":false,"Name":"Exercise 1","Duration":"1m ","ChapterTopicVideoID":27091,"CourseChapterTopicPlaylistID":261641,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:08.760","Text":"The AUC and AUA codons in messenger RNA both specify isoleucine."},{"Start":"00:08.760 ","End":"00:12.285","Text":"What feature of the genetic code explains this?"},{"Start":"00:12.285 ","End":"00:14.145","Text":"Is it complementarity?"},{"Start":"00:14.145 ","End":"00:16.215","Text":"Is it nonsense codons,"},{"Start":"00:16.215 ","End":"00:20.505","Text":"universality or degeneracy?"},{"Start":"00:20.505 ","End":"00:22.380","Text":"Well, let\u0027s see."},{"Start":"00:22.380 ","End":"00:26.700","Text":"If you remember, the genetic code has a number"},{"Start":"00:26.700 ","End":"00:31.290","Text":"of different codons that encode the same amino acid."},{"Start":"00:31.290 ","End":"00:32.549","Text":"For instance, in this case,"},{"Start":"00:32.549 ","End":"00:37.455","Text":"it was AUC and AUA,"},{"Start":"00:37.455 ","End":"00:40.800","Text":"which both encode isoleucine."},{"Start":"00:40.800 ","End":"00:42.993","Text":"What is that called?"},{"Start":"00:42.993 ","End":"00:46.080","Text":"It\u0027s certainly not complementarity."},{"Start":"00:46.080 ","End":"00:48.240","Text":"It\u0027s not nonsense codons."},{"Start":"00:48.240 ","End":"00:51.550","Text":"Nonsense codons are these 3."},{"Start":"00:52.490 ","End":"00:57.155","Text":"Universality, there\u0027s no universality here."},{"Start":"00:57.155 ","End":"01:01.050","Text":"Clearly, it\u0027s got to be degeneracy."}],"ID":28216},{"Watched":false,"Name":"Exercise 2","Duration":"30s","ChapterTopicVideoID":27092,"CourseChapterTopicPlaylistID":261641,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:06.390","Text":"How many nucleotides are in 12 mRNA codons?"},{"Start":"00:06.390 ","End":"00:08.160","Text":"Is it 12, 24,"},{"Start":"00:08.160 ","End":"00:09.645","Text":"36, or 48?"},{"Start":"00:09.645 ","End":"00:10.980","Text":"Well, the codons, you remember?"},{"Start":"00:10.980 ","End":"00:19.050","Text":"The codons are the triplets that encode the various amino acids."},{"Start":"00:19.050 ","End":"00:21.435","Text":"Each of them is a triplet."},{"Start":"00:21.435 ","End":"00:25.545","Text":"There are 12 codons in the question,"},{"Start":"00:25.545 ","End":"00:31.270","Text":"so 12x3 is 36."}],"ID":28217},{"Watched":false,"Name":"Exercise 3","Duration":"1m 37s","ChapterTopicVideoID":27093,"CourseChapterTopicPlaylistID":261641,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:06.600","Text":"Which event contradicts the central dogma of molecular biology."},{"Start":"00:06.600 ","End":"00:11.295","Text":"Is it poly-A polymerase enzymes process mRNA in the nucleus?"},{"Start":"00:11.295 ","End":"00:13.305","Text":"I don\u0027t think that\u0027s even really true."},{"Start":"00:13.305 ","End":"00:17.175","Text":"Poly-A polymerase process mRNA in the nucleus?"},{"Start":"00:17.175 ","End":"00:21.825","Text":"Well, they don\u0027t really process the mRNA, they add poly-A."},{"Start":"00:21.825 ","End":"00:27.215","Text":"Is it that endonuclease enzymes splice out and repair damaged DNA?"},{"Start":"00:27.215 ","End":"00:31.430","Text":"There are endonuclease enzymes that are"},{"Start":"00:31.430 ","End":"00:37.385","Text":"involved in repairing damaged DNA but is that the central dogma? No, it\u0027s not."},{"Start":"00:37.385 ","End":"00:43.070","Text":"Scientists use reverse transcriptase enzymes to make DNA from RNA."},{"Start":"00:43.070 ","End":"00:46.640","Text":"That really might contradict the central dogma."},{"Start":"00:46.640 ","End":"00:52.540","Text":"We\u0027ll see why in a minute. Codon specifying amino acids are degenerate and universal."},{"Start":"00:52.540 ","End":"00:55.380","Text":"Well, it\u0027s true that they\u0027re degenerate,"},{"Start":"00:55.380 ","End":"00:59.395","Text":"but what\u0027s that have to do with the central dogma?"},{"Start":"00:59.395 ","End":"01:07.385","Text":"Remember that the central dogma is that DNA is transcribed into mRNA,"},{"Start":"01:07.385 ","End":"01:12.140","Text":"which then is translated into protein."},{"Start":"01:12.140 ","End":"01:14.060","Text":"That\u0027s the central dogma."},{"Start":"01:14.060 ","End":"01:21.680","Text":"Reverse transcriptase transcribes really mRNA into DNA."},{"Start":"01:21.680 ","End":"01:25.870","Text":"There are some viruses that have reversed this transcriptase in them."},{"Start":"01:25.870 ","End":"01:28.590","Text":"That is not the central dogma,"},{"Start":"01:28.590 ","End":"01:30.900","Text":"it\u0027s reverse of the central dogma."},{"Start":"01:30.900 ","End":"01:34.070","Text":"The answer really should be that scientists use"},{"Start":"01:34.070 ","End":"01:38.250","Text":"reverse transcriptase enzymes to make DNA from RNA."}],"ID":28218},{"Watched":false,"Name":"Exercise 4","Duration":"39s","ChapterTopicVideoID":27094,"CourseChapterTopicPlaylistID":261641,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:07.620","Text":"Which subunit of the E. Coli polymerase confers specificity to the transcription?"},{"Start":"00:07.620 ","End":"00:11.070","Text":"Alpha, Beta, Beta prime, or Sigma."},{"Start":"00:11.070 ","End":"00:15.630","Text":"Well, let\u0027s recall this slide in which we"},{"Start":"00:15.630 ","End":"00:21.060","Text":"had a picture of the RNA polymerase holoenzyme,"},{"Start":"00:21.060 ","End":"00:23.320","Text":"yes, which binds to the promoter,"},{"Start":"00:23.320 ","End":"00:29.040","Text":"and what we know is that the subunit Sigma 70 is involved"},{"Start":"00:29.040 ","End":"00:35.745","Text":"in transcription initiation and it confers transcriptional specificity."},{"Start":"00:35.745 ","End":"00:39.910","Text":"Sigma must be the answer, D."}],"ID":28219},{"Watched":false,"Name":"Exercise 5","Duration":"1m 7s","ChapterTopicVideoID":27095,"CourseChapterTopicPlaylistID":261641,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.200","Text":"The minus 10 and minus 35 regions of"},{"Start":"00:04.200 ","End":"00:10.200","Text":"prokaryotic promoters are called consensus sequences because,"},{"Start":"00:10.200 ","End":"00:13.095","Text":"what\u0027s the reason for them being called consensus sequences?"},{"Start":"00:13.095 ","End":"00:15.075","Text":"The minus 10 minus 35 regions?"},{"Start":"00:15.075 ","End":"00:18.855","Text":"Because they are identical in all bacterial species?"},{"Start":"00:18.855 ","End":"00:22.215","Text":"Well, they\u0027re not identical, so that\u0027s wrong."},{"Start":"00:22.215 ","End":"00:25.350","Text":"They are similar in all bacterial species?"},{"Start":"00:25.350 ","End":"00:31.020","Text":"That might be. That they exist in all organisms? They don\u0027t really."},{"Start":"00:31.020 ","End":"00:33.345","Text":"Remember because they don\u0027t exist in eukaryotes."},{"Start":"00:33.345 ","End":"00:37.140","Text":"That they have the same function in all organisms?"},{"Start":"00:37.140 ","End":"00:40.630","Text":"Well, we just said they\u0027re not in all organisms."},{"Start":"00:40.630 ","End":"00:51.125","Text":"Recall the minus 35 and minus 10 elements in the promoters of prokaryotes,"},{"Start":"00:51.125 ","End":"00:57.990","Text":"and they are similar across all promoters in bacterial species."},{"Start":"00:57.990 ","End":"01:03.690","Text":"That\u0027s why they\u0027re called a consensus,"},{"Start":"01:03.690 ","End":"01:08.040","Text":"because they are similar in all bacterial species."}],"ID":28220},{"Watched":false,"Name":"Exercise 6","Duration":"2m 29s","ChapterTopicVideoID":27096,"CourseChapterTopicPlaylistID":261641,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:03.210","Text":"3 different bacteria species have"},{"Start":"00:03.210 ","End":"00:09.060","Text":"the following consensus sequences upstream of a conserved gene."},{"Start":"00:09.060 ","End":"00:11.265","Text":"At minus 10,"},{"Start":"00:11.265 ","End":"00:16.350","Text":"they have these sequences and at minus 35,"},{"Start":"00:16.350 ","End":"00:18.630","Text":"they have these sequences."},{"Start":"00:18.630 ","End":"00:22.470","Text":"We are asked to order the bacteria from the most to"},{"Start":"00:22.470 ","End":"00:26.865","Text":"least efficient initiation of gene transcription."},{"Start":"00:26.865 ","End":"00:29.910","Text":"The answers will look like this."},{"Start":"00:29.910 ","End":"00:33.397","Text":"Yes, A more than B more than C or B more than C"},{"Start":"00:33.397 ","End":"00:36.990","Text":"more than A and so on. What do we want to do?"},{"Start":"00:36.990 ","End":"00:39.015","Text":"This is our question again."},{"Start":"00:39.015 ","End":"00:44.040","Text":"Remember, there\u0027s the minus 35 element and the minus 10 element."},{"Start":"00:44.040 ","End":"00:49.445","Text":"The one that will be the most likely to work the best would have"},{"Start":"00:49.445 ","End":"00:56.270","Text":"a specific sequence which is most like the consensus."},{"Start":"00:56.270 ","End":"01:01.660","Text":"The consensus from minus 35 is TTGACA."},{"Start":"01:03.680 ","End":"01:09.120","Text":"This is the consensus sequence and it\u0027s the best, really."},{"Start":"01:09.120 ","End":"01:11.975","Text":"What about the minus 10 element?"},{"Start":"01:11.975 ","End":"01:21.065","Text":"Well, the sequence that is precise is TATAAT. Where is that?"},{"Start":"01:21.065 ","End":"01:25.376","Text":"TATATT."},{"Start":"01:25.376 ","End":"01:30.030","Text":"It\u0027s not quite that."},{"Start":"01:30.030 ","End":"01:33.485","Text":"Is it TATAAT?"},{"Start":"01:33.485 ","End":"01:36.910","Text":"This is fairly similar."},{"Start":"01:36.910 ","End":"01:43.345","Text":"I think it\u0027s certainly not species B, it\u0027s quite different."},{"Start":"01:43.345 ","End":"01:46.675","Text":"What was the minus 35 element there?"},{"Start":"01:46.675 ","End":"01:49.600","Text":"Well, that was actually quite different."},{"Start":"01:49.600 ","End":"01:54.250","Text":"Species B is probably going to be the one that\u0027s list good."},{"Start":"01:54.250 ","End":"01:56.410","Text":"What about species C?"},{"Start":"01:56.410 ","End":"02:04.885","Text":"Here we\u0027ve got TTGAAA this is so."},{"Start":"02:04.885 ","End":"02:06.880","Text":"What about the TATATT element?"},{"Start":"02:06.880 ","End":"02:09.655","Text":"Well, that\u0027s so also."},{"Start":"02:09.655 ","End":"02:11.480","Text":"I think judging this,"},{"Start":"02:11.480 ","End":"02:16.280","Text":"I would order the species A to be the first."},{"Start":"02:16.280 ","End":"02:18.065","Text":"This would be the first,"},{"Start":"02:18.065 ","End":"02:23.110","Text":"and the second would be C and the third would be B."},{"Start":"02:23.110 ","End":"02:30.460","Text":"So A more than C more than B."}],"ID":28221},{"Watched":false,"Name":"Exercise 7","Duration":"40s","ChapterTopicVideoID":27097,"CourseChapterTopicPlaylistID":261641,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:06.210","Text":"What transcripts will be most affected by low levels of Alpha-amanitin?"},{"Start":"00:06.210 ","End":"00:09.915","Text":"Alpha-amanitin. Well, this is something we just have to know."},{"Start":"00:09.915 ","End":"00:14.565","Text":"Would it be 18S and 28S ribosomal RNAs,"},{"Start":"00:14.565 ","End":"00:18.765","Text":"pre-messenger RNAs, 5S ribosomal RNAs and tRNAs,"},{"Start":"00:18.765 ","End":"00:21.675","Text":"or other small nuclear RNAs?"},{"Start":"00:21.675 ","End":"00:26.490","Text":"Alpha-amanitin is a repressor."},{"Start":"00:26.490 ","End":"00:28.155","Text":"It\u0027s an inhibitor, really,"},{"Start":"00:28.155 ","End":"00:31.968","Text":"of the synthesis of messenger RNA,"},{"Start":"00:31.968 ","End":"00:34.455","Text":"so our answer is going to be"},{"Start":"00:34.455 ","End":"00:41.410","Text":"pre-mRNAs that will be most affected by low levels of Alpha-amanitin."}],"ID":28222},{"Watched":false,"Name":"Exercise 8","Duration":"1m 37s","ChapterTopicVideoID":27098,"CourseChapterTopicPlaylistID":261641,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:03.950 ","End":"00:07.425","Text":"How are they different, enhancers and promoters?"},{"Start":"00:07.425 ","End":"00:09.690","Text":"Enhancers bind transcription factors to"},{"Start":"00:09.690 ","End":"00:14.610","Text":"silence gene expression while promoters activate transcription."},{"Start":"00:14.610 ","End":"00:19.935","Text":"Enhancers don\u0027t bind anything they\u0027re a sequence in the DNA,"},{"Start":"00:19.935 ","End":"00:22.665","Text":"so that\u0027s got to be wrong."},{"Start":"00:22.665 ","End":"00:27.845","Text":"Enhancers increase the efficiency of gene transcription or gene expression,"},{"Start":"00:27.845 ","End":"00:30.110","Text":"but are not essential for transcription."},{"Start":"00:30.110 ","End":"00:32.705","Text":"They\u0027re enhancers, that sounds right."},{"Start":"00:32.705 ","End":"00:38.420","Text":"Promoter recognition is essential for transcriptional initiation."},{"Start":"00:38.420 ","End":"00:40.055","Text":"That sounds right."},{"Start":"00:40.055 ","End":"00:41.420","Text":"Maybe we\u0027ll come back to that."},{"Start":"00:41.420 ","End":"00:46.370","Text":"Promoters bind transcription factors to increase the efficiency of transcription."},{"Start":"00:46.370 ","End":"00:50.150","Text":"Enhancers bind RNA polymerases to initiate transcription."},{"Start":"00:50.150 ","End":"00:57.155","Text":"No, that\u0027s wrong because the promoters bind RNA polymerase to initiate transcription."},{"Start":"00:57.155 ","End":"00:59.540","Text":"That\u0027s got to be wrong as well."},{"Start":"00:59.540 ","End":"01:02.660","Text":"There\u0027s no difference. Well, certainly there is a difference."},{"Start":"01:02.660 ","End":"01:06.605","Text":"If you remember the transcription factors."},{"Start":"01:06.605 ","End":"01:08.930","Text":"Yes, our class of protein transcription factors that"},{"Start":"01:08.930 ","End":"01:11.180","Text":"bind to a promoter and they activate transcription."},{"Start":"01:11.180 ","End":"01:15.020","Text":"And the enhancers and silencers had the ability to greatly"},{"Start":"01:15.020 ","End":"01:17.030","Text":"influenced the expression of the rate of their genes"},{"Start":"01:17.030 ","End":"01:19.295","Text":"and their facility in their vicinity."},{"Start":"01:19.295 ","End":"01:23.345","Text":"The enhancers influence but are not required."},{"Start":"01:23.345 ","End":"01:26.990","Text":"The answer indeed is b. Enhancers increase"},{"Start":"01:26.990 ","End":"01:31.100","Text":"the efficiency of gene expression but are not essential for transcription,"},{"Start":"01:31.100 ","End":"01:37.710","Text":"whereas promoter recognition is essential for transcriptional initiation."}],"ID":28223},{"Watched":false,"Name":"Exercise 9","Duration":"1m 6s","ChapterTopicVideoID":27099,"CourseChapterTopicPlaylistID":261641,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.890","Text":"Which pre-mRNA processing step is important for initiating"},{"Start":"00:04.890 ","End":"00:10.785","Text":"translation and it\u0027s a processing step of pre-messenger RNA."},{"Start":"00:10.785 ","End":"00:13.620","Text":"Is it the poly-A tail?"},{"Start":"00:13.620 ","End":"00:16.530","Text":"Is it RNA editing, splicing,"},{"Start":"00:16.530 ","End":"00:21.630","Text":"or the addition of the 7-methylguanosine cap?"},{"Start":"00:21.630 ","End":"00:25.065","Text":"We\u0027re talking about initiating translation."},{"Start":"00:25.065 ","End":"00:26.445","Text":"Well, if you remember,"},{"Start":"00:26.445 ","End":"00:30.120","Text":"the 7-methylguanosine cap is added to the 5-prime end of"},{"Start":"00:30.120 ","End":"00:35.220","Text":"the growing transcript by a phosphate linkage. What\u0027s it good for?"},{"Start":"00:35.220 ","End":"00:40.535","Text":"Among other things, it can help initiate translation by ribosomes."},{"Start":"00:40.535 ","End":"00:43.010","Text":"When this RNA goes out of the nucleus,"},{"Start":"00:43.010 ","End":"00:44.930","Text":"is transported out of the nucleus,"},{"Start":"00:44.930 ","End":"00:51.140","Text":"it will be recognized in parts by the ribosomes as something that\u0027s worthy of translation"},{"Start":"00:51.140 ","End":"00:57.650","Text":"because it is fully processed on both ends and on the 5-prime end specifically,"},{"Start":"00:57.650 ","End":"00:59.335","Text":"it has the cap."},{"Start":"00:59.335 ","End":"01:01.410","Text":"Our answer is D,"},{"Start":"01:01.410 ","End":"01:07.530","Text":"the 7-methylguanosine cap, which is important for initiating translation."}],"ID":28224},{"Watched":false,"Name":"Exercise 10","Duration":"30s","ChapterTopicVideoID":27100,"CourseChapterTopicPlaylistID":261641,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:10.590","Text":"What processing step enhances the stability of pre-tRNAs and pre-ribosomal RNAs?"},{"Start":"00:10.590 ","End":"00:13.530","Text":"What processing step enhances their stability?"},{"Start":"00:13.530 ","End":"00:18.960","Text":"Is it methylation, nucleotide modification, cleavage, or splicing?"},{"Start":"00:18.960 ","End":"00:21.785","Text":"Well, again, this is something that you just need to know."},{"Start":"00:21.785 ","End":"00:25.560","Text":"It is methylation, is the answer,"},{"Start":"00:25.560 ","End":"00:30.520","Text":"increases the stability of these RNAs."}],"ID":28225},{"Watched":false,"Name":"Exercise 11","Duration":"1m 16s","ChapterTopicVideoID":27101,"CourseChapterTopicPlaylistID":261641,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:06.359","Text":"A scientist identifies a pre-messenger RNA with the following structure."},{"Start":"00:06.359 ","End":"00:11.565","Text":"What is the predicted size of the corresponding mature messenger RNA in base pairs,"},{"Start":"00:11.565 ","End":"00:16.563","Text":"excluding the 5 prime cap and the 3 prime poly-A tail?"},{"Start":"00:16.563 ","End":"00:20.565","Text":"Well, we have here 3 exons."},{"Start":"00:20.565 ","End":"00:28.530","Text":"It\u0027s the 3 exons that are going to be included in the final RNA."},{"Start":"00:28.530 ","End":"00:30.555","Text":"It\u0027s the introns which removed,"},{"Start":"00:30.555 ","End":"00:33.165","Text":"so it\u0027s just the exons."},{"Start":"00:33.165 ","End":"00:38.965","Text":"In this case, it was 1-30 and 31-104 and105-146,"},{"Start":"00:38.965 ","End":"00:42.815","Text":"which will come together to make the entire coding segment."},{"Start":"00:42.815 ","End":"00:45.425","Text":"So what we\u0027re going need to do in our question,"},{"Start":"00:45.425 ","End":"00:48.770","Text":"is to add up the lengths of the 3 exons"},{"Start":"00:48.770 ","End":"00:52.130","Text":"and that will be the length of the entire message."},{"Start":"00:52.130 ","End":"00:54.475","Text":"So it is, let\u0027s see,"},{"Start":"00:54.475 ","End":"01:04.260","Text":"100 base pairs plus 75 base pairs plus 120 base pairs."},{"Start":"01:04.260 ","End":"01:09.140","Text":"What is that? That would be 295."},{"Start":"01:09.140 ","End":"01:12.050","Text":"Is that a possibility in our answers?"},{"Start":"01:12.050 ","End":"01:14.240","Text":"Well, yes it is. It\u0027s B."},{"Start":"01:14.240 ","End":"01:17.010","Text":"There we are, B."}],"ID":28226},{"Watched":false,"Name":"Exercise 12","Duration":"48s","ChapterTopicVideoID":27088,"CourseChapterTopicPlaylistID":261641,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:08.970","Text":"The RNA components of ribosomes are synthesized where?"},{"Start":"00:08.970 ","End":"00:10.605","Text":"In the cytoplasm,"},{"Start":"00:10.605 ","End":"00:15.555","Text":"nucleolus, or in the endoplasmic reticulum?"},{"Start":"00:15.555 ","End":"00:24.135","Text":"Let\u0027s recall what we know about where RNA components of the ribosomes are synthesized."},{"Start":"00:24.135 ","End":"00:27.540","Text":"They are in the nucleolus."},{"Start":"00:27.540 ","End":"00:31.050","Text":"Here we see the nucleolus."},{"Start":"00:31.050 ","End":"00:37.910","Text":"Remember, the endoplasmic reticulum is around it and the nucleolus is the area which is"},{"Start":"00:37.910 ","End":"00:41.180","Text":"specialized for the synthesis and assembly of"},{"Start":"00:41.180 ","End":"00:45.560","Text":"the ribosomal RNAs and actually the proteins as well."},{"Start":"00:45.560 ","End":"00:49.350","Text":"Our answer is going to be the nucleolus."}],"ID":28227},{"Watched":false,"Name":"Exercise 13","Duration":"51s","ChapterTopicVideoID":27089,"CourseChapterTopicPlaylistID":261641,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:02.370","Text":"In any given species,"},{"Start":"00:02.370 ","End":"00:09.945","Text":"there are at least how many types of aminoacyl tRNA synthetases?"},{"Start":"00:09.945 ","End":"00:11.420","Text":"Is it 20, 40,"},{"Start":"00:11.420 ","End":"00:12.690","Text":"100, or 200?"},{"Start":"00:12.690 ","End":"00:17.525","Text":"Well, aminoacyl tRNA synthetases are"},{"Start":"00:17.525 ","End":"00:24.630","Text":"the enzymes that attach the amino acids to the tRNAs,"},{"Start":"00:24.630 ","End":"00:27.730","Text":"that is the enzyme."},{"Start":"00:27.730 ","End":"00:31.115","Text":"Each of the amino acids has"},{"Start":"00:31.115 ","End":"00:38.645","Text":"at least 1 aminoacyl tRNA synthetase to attach to different tRNAs."},{"Start":"00:38.645 ","End":"00:42.079","Text":"Since there are 20 amino acids,"},{"Start":"00:42.079 ","End":"00:47.505","Text":"there has to be at least one type of aminoacyl tRNA synthetase for each of them,"},{"Start":"00:47.505 ","End":"00:52.030","Text":"so our answer must be 20."}],"ID":28228},{"Watched":false,"Name":"Exercise 14","Duration":"2m 3s","ChapterTopicVideoID":27090,"CourseChapterTopicPlaylistID":261641,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:03.480","Text":"A scientist introduces a mutation that makes"},{"Start":"00:03.480 ","End":"00:11.495","Text":"the 60S ribosomal subunit nonfunctional in a human cell line."},{"Start":"00:11.495 ","End":"00:13.670","Text":"That\u0027s a eukaryotic cell."},{"Start":"00:13.670 ","End":"00:16.860","Text":"What would be the predicted effect on translation?"},{"Start":"00:16.860 ","End":"00:21.794","Text":"There\u0027s a mutation now in the 60S ribosomal subunit."},{"Start":"00:21.794 ","End":"00:27.240","Text":"Would it be the translation stalls after the initiation AUG codon is identified,"},{"Start":"00:27.240 ","End":"00:29.940","Text":"is it that the ribosome cannot catalyze the formation of"},{"Start":"00:29.940 ","End":"00:33.705","Text":"peptide bonds between the tRNAs in the A and P sites,"},{"Start":"00:33.705 ","End":"00:36.815","Text":"is it that the ribosome cannot interact with messenger RNAs,"},{"Start":"00:36.815 ","End":"00:42.185","Text":"or is it that tRNAs cannot exist in the E site of the ribosome?"},{"Start":"00:42.185 ","End":"00:47.940","Text":"Let\u0027s recall what the large subunit,"},{"Start":"00:47.940 ","End":"00:51.870","Text":"the 60S ribosomal subunit is doing."},{"Start":"00:51.870 ","End":"00:54.865","Text":"Well, that\u0027s this subunit."},{"Start":"00:54.865 ","End":"00:57.200","Text":"What happens in initiation?"},{"Start":"00:57.200 ","End":"00:59.030","Text":"Well first, of course,"},{"Start":"00:59.030 ","End":"01:04.160","Text":"the initiator tRNA attaches to the messenger RNA,"},{"Start":"01:04.160 ","End":"01:07.620","Text":"and searches, it attaches messenger RNA,"},{"Start":"01:07.620 ","End":"01:09.630","Text":"sorry, and the small subunit,"},{"Start":"01:09.630 ","End":"01:11.265","Text":"of course, of the ribosome."},{"Start":"01:11.265 ","End":"01:15.795","Text":"Then it scans looking for the first AUG."},{"Start":"01:15.795 ","End":"01:18.710","Text":"The start codon of the signal,"},{"Start":"01:18.710 ","End":"01:23.285","Text":"and then the large ribosomal subunit will be added."},{"Start":"01:23.285 ","End":"01:26.060","Text":"But in our question, we were asked,"},{"Start":"01:26.060 ","End":"01:28.070","Text":"it says that there is a mutation,"},{"Start":"01:28.070 ","End":"01:31.985","Text":"it makes the 60S ribosomal subunit nonfunctional."},{"Start":"01:31.985 ","End":"01:33.740","Text":"So what would happen?"},{"Start":"01:33.740 ","End":"01:38.585","Text":"Well, it means that probably would not be able to join."},{"Start":"01:38.585 ","End":"01:41.990","Text":"Therefore, there must be a problem in the initiation"},{"Start":"01:41.990 ","End":"01:46.330","Text":"because the 2 subunits can\u0027t even get together."},{"Start":"01:46.330 ","End":"01:51.455","Text":"Indeed, translation stalls after the initiation codon is"},{"Start":"01:51.455 ","End":"01:57.705","Text":"identified because there\u0027s the identification here,"},{"Start":"01:57.705 ","End":"02:00.440","Text":"but then it cannot continue."},{"Start":"02:00.440 ","End":"02:03.540","Text":"So our answer is a."}],"ID":28229}],"Thumbnail":null,"ID":261641},{"Name":"Gene Expression","TopicPlaylistFirstVideoID":0,"Duration":null,"Videos":[{"Watched":false,"Name":"Transcription and post-transcription defects in cancer","Duration":"5m 32s","ChapterTopicVideoID":27102,"CourseChapterTopicPlaylistID":261642,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.170 ","End":"00:02.940","Text":"Welcome back to this video."},{"Start":"00:02.940 ","End":"00:06.930","Text":"We were discussing gene regulation as it relates to cancer,"},{"Start":"00:06.930 ","End":"00:10.050","Text":"and we had discussed tumor suppressor genes,"},{"Start":"00:10.050 ","End":"00:13.650","Text":"which of course were negative cell cycle regulators."},{"Start":"00:13.650 ","End":"00:18.360","Text":"Now we\u0027re going to continue and talk about proto-oncogenes,"},{"Start":"00:18.360 ","End":"00:23.520","Text":"which are positive cell cycle regulators."},{"Start":"00:23.520 ","End":"00:28.530","Text":"Over-expression of oncogenes due to mutation,"},{"Start":"00:28.530 ","End":"00:32.320","Text":"then can lead to uncontrolled cell growth and"},{"Start":"00:32.320 ","End":"00:36.500","Text":"cancer because they alter transcriptional activity,"},{"Start":"00:36.500 ","End":"00:39.440","Text":"stability, or protein translation of"},{"Start":"00:39.440 ","End":"00:45.360","Text":"another gene that either directly or indirectly controls cell growth."},{"Start":"00:45.360 ","End":"00:46.910","Text":"You can see here, for instance,"},{"Start":"00:46.910 ","End":"00:49.490","Text":"you could have cancer causing agents, for instance,"},{"Start":"00:49.490 ","End":"00:50.660","Text":"just as an example,"},{"Start":"00:50.660 ","End":"00:54.095","Text":"which might change this proto-oncogene."},{"Start":"00:54.095 ","End":"00:56.990","Text":"Yes, that\u0027s here in the DNA is changed."},{"Start":"00:56.990 ","End":"01:00.980","Text":"This oncogene, such that it now becomes much more activated"},{"Start":"01:00.980 ","End":"01:05.750","Text":"and turns a normal cell into a cancer cell."},{"Start":"01:05.750 ","End":"01:09.950","Text":"In addition, we can have various epigenetic alterations."},{"Start":"01:09.950 ","End":"01:14.000","Text":"Remember, epigenetic changes are changes not in the DNA sequence,"},{"Start":"01:14.000 ","End":"01:17.750","Text":"but rather either by changing the DNA itself,"},{"Start":"01:17.750 ","End":"01:18.830","Text":"I say, for instance,"},{"Start":"01:18.830 ","End":"01:23.810","Text":"doing DNA methylation or possibly acetylation or deacetylation or"},{"Start":"01:23.810 ","End":"01:26.480","Text":"phosphorylation of nucleosomes are"},{"Start":"01:26.480 ","End":"01:30.425","Text":"the proteins of the histones that are in the histone modifications."},{"Start":"01:30.425 ","End":"01:33.665","Text":"In this case, we may,"},{"Start":"01:33.665 ","End":"01:37.220","Text":"for instance, silence genes through epigenetic mechanisms."},{"Start":"01:37.220 ","End":"01:40.085","Text":"If we silence tumor suppressor genes,"},{"Start":"01:40.085 ","End":"01:45.245","Text":"then it\u0027s likely they we\u0027re going to turn a normal cell into a cancer cell."},{"Start":"01:45.245 ","End":"01:46.820","Text":"In many cancer cells,"},{"Start":"01:46.820 ","End":"01:52.595","Text":"a combination of DNA methylation and histone deacetylation is commonly found."},{"Start":"01:52.595 ","End":"01:54.830","Text":"You\u0027ll remember that both of these things,"},{"Start":"01:54.830 ","End":"02:02.330","Text":"DNA methylation and histone deacetylation will cause compaction of the chromatin."},{"Start":"02:02.330 ","End":"02:09.485","Text":"If the chromatin is compacted at a place where a tumor suppressor gene, for instance,"},{"Start":"02:09.485 ","End":"02:13.610","Text":"is transcribed, then the gene that\u0027s present there,"},{"Start":"02:13.610 ","End":"02:18.335","Text":"the tumor suppressor gene may be silenced."},{"Start":"02:18.335 ","End":"02:22.780","Text":"Now let\u0027s look at cancer and transcriptional control."},{"Start":"02:22.780 ","End":"02:26.630","Text":"There can be alterations in cells that give rise to cancer."},{"Start":"02:26.630 ","End":"02:32.960","Text":"These alterations can affect the transcriptional control of gene expression."},{"Start":"02:32.960 ","End":"02:40.145","Text":"For example, mutations in a transcription factor may promote its binding to a promoter."},{"Start":"02:40.145 ","End":"02:42.230","Text":"Remember, there are promoters and there are"},{"Start":"02:42.230 ","End":"02:45.380","Text":"all sorts of transcription factors that binds."},{"Start":"02:45.380 ","End":"02:50.840","Text":"Mutations can occur in any of these factors promoting the binding to"},{"Start":"02:50.840 ","End":"02:56.530","Text":"a promoter and may be thereby increasing transcription of a target gene."},{"Start":"02:56.530 ","End":"03:01.024","Text":"If that happens, that may affect cell growth afterwards."},{"Start":"03:01.024 ","End":"03:05.705","Text":"Alternatively, a mutation in the DNA itself at a promoter."},{"Start":"03:05.705 ","End":"03:12.200","Text":"Alternatively, a mutation in the DNA of a promoter or an enhancer region may"},{"Start":"03:12.200 ","End":"03:16.310","Text":"increase the binding ability of transcription factor leading"},{"Start":"03:16.310 ","End":"03:20.785","Text":"to abnormal gene expression and thereby cancer."},{"Start":"03:20.785 ","End":"03:27.160","Text":"Finally, there is post-transcriptional control that you might want to look at."},{"Start":"03:27.160 ","End":"03:31.595","Text":"You\u0027ll remember there are these miRNAs which"},{"Start":"03:31.595 ","End":"03:36.905","Text":"control whether particular messenger RNAs are going to be destroyed."},{"Start":"03:36.905 ","End":"03:40.100","Text":"For instance, changes in the post-transcriptional control of"},{"Start":"03:40.100 ","End":"03:43.730","Text":"a gene can also result in cancer."},{"Start":"03:43.730 ","End":"03:48.169","Text":"If oncogenic miRNA or particular"},{"Start":"03:48.169 ","End":"03:52.400","Text":"miRNAs destroy a tumor suppressor gene, we can get cancer."},{"Start":"03:52.400 ","End":"03:58.385","Text":"Or alternatively, if miRNAs that are supposed to be there are not there,"},{"Start":"03:58.385 ","End":"04:04.771","Text":"ones that normally are important in degradation of oncogene messenger RNAs,"},{"Start":"04:04.771 ","End":"04:07.375","Text":"then that too can cause cancer."},{"Start":"04:07.375 ","End":"04:14.450","Text":"Specific cancers we find often have altered expression of miRNAs."},{"Start":"04:14.450 ","End":"04:16.820","Text":"I\u0027ll remind you that miRNAs bind to"},{"Start":"04:16.820 ","End":"04:23.110","Text":"the 3\u0027 UTR untranslated region of RNA molecules to degrade them."},{"Start":"04:23.110 ","End":"04:31.445","Text":"Over-expression or under expression of miRNAs can dramatically change RNA populations,"},{"Start":"04:31.445 ","End":"04:38.000","Text":"and that can lead to abnormal protein expression and therefore cancer."},{"Start":"04:38.000 ","End":"04:41.105","Text":"Many modifications are found in cancer cells"},{"Start":"04:41.105 ","End":"04:44.480","Text":"from increased translation of protein to changes"},{"Start":"04:44.480 ","End":"04:47.570","Text":"in protein phosphorylation to alternative splice sites"},{"Start":"04:47.570 ","End":"04:51.050","Text":"or alternative splice variants of a protein,"},{"Start":"04:51.050 ","End":"04:53.000","Text":"and the expression of an alternative form of"},{"Start":"04:53.000 ","End":"04:56.779","Text":"a protein can have dramatically different outcomes."},{"Start":"04:56.779 ","End":"04:58.670","Text":"I\u0027ll give you an example here."},{"Start":"04:58.670 ","End":"05:03.545","Text":"For example, there\u0027s a colon cancer C flip protein,"},{"Start":"05:03.545 ","End":"05:06.500","Text":"which is involved in mediating the cell death pathway,"},{"Start":"05:06.500 ","End":"05:08.090","Text":"and it comes in 2 different forms."},{"Start":"05:08.090 ","End":"05:10.655","Text":"There\u0027s a long form and a short form."},{"Start":"05:10.655 ","End":"05:16.985","Text":"Both are involved in initiating controlled cell death mechanisms in normal cells."},{"Start":"05:16.985 ","End":"05:20.210","Text":"But in colon cancer cells,"},{"Start":"05:20.210 ","End":"05:27.740","Text":"expression of the long form results in increased cell growth instead of cell death,"},{"Start":"05:27.740 ","End":"05:32.790","Text":"and thus leads to the development of cancer."}],"ID":28230},{"Watched":false,"Name":"Translational and post translational regulation","Duration":"6m 31s","ChapterTopicVideoID":27103,"CourseChapterTopicPlaylistID":261642,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.080 ","End":"00:05.160","Text":"Welcome back. We\u0027re almost finished with our discussion of"},{"Start":"00:05.160 ","End":"00:10.300","Text":"the regulation of gene expression in eukaryotes."},{"Start":"00:10.300 ","End":"00:14.430","Text":"We\u0027ve discussed the chromatin modifications, the epigenetic changes,"},{"Start":"00:14.430 ","End":"00:18.539","Text":"transcriptional regulation, RNA processing regulation,"},{"Start":"00:18.539 ","End":"00:21.600","Text":"and most recently we\u0027re talking about"},{"Start":"00:21.600 ","End":"00:29.025","Text":"messenger RNA degradation and that relates to the stability of the RNA."},{"Start":"00:29.025 ","End":"00:32.870","Text":"We\u0027ve been discussing the stability of the messenger RNA."},{"Start":"00:32.870 ","End":"00:37.850","Text":"Of course, it has a very large impact on its translation into a protein."},{"Start":"00:37.850 ","End":"00:41.359","Text":"As the stability of the messenger RNAs changes,"},{"Start":"00:41.359 ","End":"00:43.939","Text":"the amount of time that it is available for translation,"},{"Start":"00:43.939 ","End":"00:46.045","Text":"of course, also changes."},{"Start":"00:46.045 ","End":"00:51.170","Text":"Let\u0027s look a little bit at the translational process itself."},{"Start":"00:51.170 ","End":"00:57.197","Text":"First, there\u0027s an initiation complex that is made if you remember,"},{"Start":"00:57.197 ","End":"01:01.820","Text":"initiation complex in which contains the 40S ribosomal subunit,"},{"Start":"01:01.820 ","End":"01:07.450","Text":"the smaller subunit of the ribosome together with other factors."},{"Start":"01:07.450 ","End":"01:14.740","Text":"In eukaryotes, the translation is initiated by binding an initiation met-tRNAi."},{"Start":"01:14.740 ","End":"01:18.920","Text":"It\u0027s of course the methionine which is attached to the appropriate"},{"Start":"01:18.920 ","End":"01:22.445","Text":"initiating tRNA to the ribosome. That\u0027s what you see here."},{"Start":"01:22.445 ","End":"01:30.390","Text":"The tRNA is brought to the ribosome by a particular initiation factor called eIF2."},{"Start":"01:32.060 ","End":"01:39.855","Text":"That\u0027s actually this green thing here which brings it to the ribosome."},{"Start":"01:39.855 ","End":"01:43.145","Text":"It binds to the high-energy molecule,"},{"Start":"01:43.145 ","End":"01:45.520","Text":"GTP in order to do that,"},{"Start":"01:45.520 ","End":"01:48.215","Text":"so this requires energy."},{"Start":"01:48.215 ","End":"01:49.550","Text":"It binds to GTP."},{"Start":"01:49.550 ","End":"01:57.015","Text":"Note that GDP is released from that and again binds to the 40S ribosome."},{"Start":"01:57.015 ","End":"02:02.795","Text":"Then this 40S ribosome then attaches to messenger RNA,"},{"Start":"02:02.795 ","End":"02:10.625","Text":"usually in eukaryotes at the end and it scans until it finds an AUG. AUG you remember"},{"Start":"02:10.625 ","End":"02:14.390","Text":"is the start codon and when the anticodon of"},{"Start":"02:14.390 ","End":"02:19.113","Text":"the initiator tRNA and the start codon aligned at this AUG,"},{"Start":"02:19.113 ","End":"02:24.901","Text":"then the GTP is hydrolyzed and the initiation factors are released,"},{"Start":"02:24.901 ","End":"02:29.235","Text":"for instance, this eIF2 and other initiation factors."},{"Start":"02:29.235 ","End":"02:32.815","Text":"The 60S ribosomal subunit binds,"},{"Start":"02:32.815 ","End":"02:37.530","Text":"and we have the beginning of translation."},{"Start":"02:38.390 ","End":"02:44.100","Text":"All of those different stages can be regulated."},{"Start":"02:44.100 ","End":"02:48.170","Text":"After translation occurs, we have"},{"Start":"02:48.170 ","End":"02:55.200","Text":"additional steps at which we can have regulation."},{"Start":"02:55.200 ","End":"02:58.130","Text":"The cell can make different chemical modifications"},{"Start":"02:58.130 ","End":"03:01.280","Text":"that influence protein activity, longevity,"},{"Start":"03:01.280 ","End":"03:05.150","Text":"and these different modifications can be"},{"Start":"03:05.150 ","End":"03:09.440","Text":"by say the addition of a methyl group of a phosphates group,"},{"Start":"03:09.440 ","End":"03:10.640","Text":"of acetyl groups,"},{"Start":"03:10.640 ","End":"03:13.940","Text":"or you\u0027ll see these little peptides that are called"},{"Start":"03:13.940 ","End":"03:18.610","Text":"ubiquitin that are going to regulate degradation."},{"Start":"03:18.610 ","End":"03:23.420","Text":"The regulation of the activity of these proteins then can"},{"Start":"03:23.420 ","End":"03:28.850","Text":"be modulated by different chemical modifications that are made."},{"Start":"03:28.850 ","End":"03:34.850","Text":"This regulates protein activity or even the length of time that they exist in the cell."},{"Start":"03:34.850 ","End":"03:38.108","Text":"Sometimes it can regulate where a protein is found,"},{"Start":"03:38.108 ","End":"03:41.795","Text":"where it\u0027s found in the nucleus and the cytoplasm membrane."},{"Start":"03:41.795 ","End":"03:48.960","Text":"These chemical modifications occur in response to all external factors,"},{"Start":"03:48.960 ","End":"03:53.360","Text":"for instance, stress or lack of nutrients or heat,"},{"Start":"03:53.360 ","End":"03:55.430","Text":"ultraviolet light exposure, all sorts of things."},{"Start":"03:55.430 ","End":"03:59.675","Text":"Those things can alter the epigenetic accessibility,"},{"Start":"03:59.675 ","End":"04:02.690","Text":"the transcription messenger RNA stability, or translation."},{"Start":"04:02.690 ","End":"04:07.730","Text":"All these things result in the changes of expression of the various genes."},{"Start":"04:07.730 ","End":"04:12.050","Text":"Of course, this is a very efficient and rapid way to change the levels of"},{"Start":"04:12.050 ","End":"04:17.705","Text":"specific proteins in response to changes in the environment."},{"Start":"04:17.705 ","End":"04:20.270","Text":"What about altering accessibility?"},{"Start":"04:20.270 ","End":"04:24.665","Text":"Because proteins are involved in every stage of gene regulation,"},{"Start":"04:24.665 ","End":"04:28.460","Text":"let\u0027s think for a moment about phosphorylation,"},{"Start":"04:28.460 ","End":"04:30.350","Text":"the addition of a phosphate group."},{"Start":"04:30.350 ","End":"04:35.950","Text":"This is a very common way that proteins are regulated."},{"Start":"04:35.950 ","End":"04:39.476","Text":"They can alter accessibility to the chromosome,"},{"Start":"04:39.476 ","End":"04:42.190","Text":"they can alter translation, for instance,"},{"Start":"04:42.190 ","End":"04:44.470","Text":"by altering transcription factor binding because"},{"Start":"04:44.470 ","End":"04:47.410","Text":"the strong negative charge that\u0027s on"},{"Start":"04:47.410 ","End":"04:51.033","Text":"the phosphates can change 3-dimensional structure of proteins,"},{"Start":"04:51.033 ","End":"04:56.044","Text":"they can alter nuclear shuttling by influencing modifications to nuclear pore complex,"},{"Start":"04:56.044 ","End":"04:57.474","Text":"they can alter stability."},{"Start":"04:57.474 ","End":"04:59.140","Text":"Pretty much anything you can think of."},{"Start":"04:59.140 ","End":"05:02.000","Text":"Translation, you can increase or decrease it."},{"Start":"05:02.000 ","End":"05:06.760","Text":"These can change post-translational modifications by adding"},{"Start":"05:06.760 ","End":"05:11.275","Text":"or removing phosphate of other molecules as well."},{"Start":"05:11.275 ","End":"05:16.445","Text":"Now finally, let\u0027s talk about degradation of"},{"Start":"05:16.445 ","End":"05:21.709","Text":"proteins and that is often controlled by ubiquitin relation."},{"Start":"05:21.709 ","End":"05:27.958","Text":"Now, what is that? If a protein is destined to be degraded,"},{"Start":"05:27.958 ","End":"05:31.342","Text":"and this again is of course going to be a regulatory mechanism,"},{"Start":"05:31.342 ","End":"05:37.234","Text":"then it turns out that there are enzymes which will add ubiquitin."},{"Start":"05:37.234 ","End":"05:41.750","Text":"This is a short peptide Subunits 1 to the other making"},{"Start":"05:41.750 ","End":"05:46.595","Text":"a chain and that will mark this protein for degradation,"},{"Start":"05:46.595 ","End":"05:50.450","Text":"then be attracted to a proteasome."},{"Start":"05:50.450 ","End":"05:54.840","Text":"This is a fancy enzyme that\u0027s the shape of a tube in which"},{"Start":"05:54.840 ","End":"05:59.900","Text":"the ubiquitin flags the protein and allows it"},{"Start":"05:59.900 ","End":"06:05.000","Text":"to go into one side of the proteasome and out the other side come amino acids."},{"Start":"06:05.000 ","End":"06:07.940","Text":"These proteins are moved to the proteasome,"},{"Start":"06:07.940 ","End":"06:10.055","Text":"the ones that are ubiquitin-related,"},{"Start":"06:10.055 ","End":"06:14.070","Text":"and they are then degraded."},{"Start":"06:15.800 ","End":"06:21.290","Text":"A final way to control gene expression is after proteins are made,"},{"Start":"06:21.290 ","End":"06:25.160","Text":"they too can be degraded and in"},{"Start":"06:25.160 ","End":"06:31.980","Text":"a controlled way which alter the longevity of the proteins."}],"ID":28231},{"Watched":false,"Name":"Defects in gene regulation can cause cancer","Duration":"6m 25s","ChapterTopicVideoID":27104,"CourseChapterTopicPlaylistID":261642,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.350 ","End":"00:06.500","Text":"Now we come to the conclusion of the subject of gene regulation."},{"Start":"00:06.500 ","End":"00:10.980","Text":"We\u0027ll look to see what happens when things go wrong"},{"Start":"00:10.980 ","End":"00:15.225","Text":"at the various levels of gene regulation."},{"Start":"00:15.225 ","End":"00:20.580","Text":"Of course, the primary thing that can go wrong is that in multicellular organisms,"},{"Start":"00:20.580 ","End":"00:23.925","Text":"we can get cases of cancer."},{"Start":"00:23.925 ","End":"00:27.090","Text":"Of course, cancer really includes many different diseases,"},{"Start":"00:27.090 ","End":"00:29.165","Text":"it\u0027s not 1 disease."},{"Start":"00:29.165 ","End":"00:31.400","Text":"But in all of them,"},{"Start":"00:31.400 ","End":"00:34.400","Text":"we\u0027re going to get some mutations,"},{"Start":"00:34.400 ","End":"00:37.280","Text":"some changes that modify cell cycle"},{"Start":"00:37.280 ","End":"00:43.145","Text":"controls and therefore the cells don\u0027t stop growing when they should."},{"Start":"00:43.145 ","End":"00:47.150","Text":"Now, this can be caused by all factors, it could be caused,"},{"Start":"00:47.150 ","End":"00:51.710","Text":"for instance, by just hereditary propensity for mistakes,"},{"Start":"00:51.710 ","End":"00:55.864","Text":"UV radiation chemicals, the cells could divide"},{"Start":"00:55.864 ","End":"01:01.583","Text":"improperly in a place where they shouldn\u0027t for all sort of reasons,"},{"Start":"01:01.583 ","End":"01:03.305","Text":"some of them we\u0027ll see later,"},{"Start":"01:03.305 ","End":"01:06.920","Text":"you can have external factors such as smoking or viruses,"},{"Start":"01:06.920 ","End":"01:08.255","Text":"all sorts of reasons."},{"Start":"01:08.255 ","End":"01:12.590","Text":"But we\u0027re going to concentrate on mutations which alter"},{"Start":"01:12.590 ","End":"01:18.965","Text":"cell growth rates because we\u0027re studying changes in gene regulation."},{"Start":"01:18.965 ","End":"01:23.075","Text":"Those changes will alter the growth rates or"},{"Start":"01:23.075 ","End":"01:27.490","Text":"at least the progression of the cell through the cell cycle."},{"Start":"01:27.490 ","End":"01:30.375","Text":"Remember, the cell cycle,"},{"Start":"01:30.375 ","End":"01:33.950","Text":"after mitosis, we have G_1."},{"Start":"01:33.950 ","End":"01:38.330","Text":"Then S phase in which the DNA is synthesized."},{"Start":"01:38.330 ","End":"01:42.260","Text":"Another stage called G_2 in which the cells grow."},{"Start":"01:42.260 ","End":"01:47.540","Text":"There are these various cell cycle checkpoints,"},{"Start":"01:47.540 ","End":"01:50.162","Text":"so 1, 2,"},{"Start":"01:50.162 ","End":"01:53.465","Text":"3 different checkpoints listed here that"},{"Start":"01:53.465 ","End":"01:59.420","Text":"ensure that the cell has properly completed previous steps and if they haven\u0027t,"},{"Start":"01:59.420 ","End":"02:03.785","Text":"the cell cycle will stop at each of these checkpoints."},{"Start":"02:03.785 ","End":"02:08.945","Text":"Now there are different proteins that are regulators of the different checkpoints,"},{"Start":"02:08.945 ","End":"02:17.765","Text":"we\u0027re going to concentrate here on cyclin B. Cyclin B can be sometimes phosphorylated."},{"Start":"02:17.765 ","End":"02:23.960","Text":"Again, cyclin B is here that is involved in regulating the M checkpoint,"},{"Start":"02:23.960 ","End":"02:26.000","Text":"the ones in mitosis."},{"Start":"02:26.000 ","End":"02:32.120","Text":"What we\u0027re going to see here is that the phosphorylation of cyclin B"},{"Start":"02:32.120 ","End":"02:39.575","Text":"sometimes can cause a post-translational event that will alter its function."},{"Start":"02:39.575 ","End":"02:42.245","Text":"As a result of the phosphorylation,"},{"Start":"02:42.245 ","End":"02:49.780","Text":"cells can improperly progress through mitosis and this might lead to cancer."},{"Start":"02:49.780 ","End":"02:53.130","Text":"Many proteins we know,"},{"Start":"02:53.130 ","End":"02:55.080","Text":"turn on or off,"},{"Start":"02:55.080 ","End":"03:00.935","Text":"and those can dramatically alter the overall cell activity."},{"Start":"03:00.935 ","End":"03:06.740","Text":"A gene can be switched on and become expressed at abnormally high levels,"},{"Start":"03:06.740 ","End":"03:08.553","Text":"or the opposite can happen,"},{"Start":"03:08.553 ","End":"03:13.745","Text":"it can be switched off and be at lower levels than it should be."},{"Start":"03:13.745 ","End":"03:21.230","Text":"As a result of a gene mutation that will change the expression of some genes,"},{"Start":"03:21.230 ","End":"03:25.895","Text":"then this gene mutation can change gene regulation."},{"Start":"03:25.895 ","End":"03:29.090","Text":"These can be either epigenetic,"},{"Start":"03:29.090 ","End":"03:30.620","Text":"they can be transcriptional changes,"},{"Start":"03:30.620 ","End":"03:32.820","Text":"post-transcriptional, translational,"},{"Start":"03:32.820 ","End":"03:36.565","Text":"or even post-translational as we\u0027ve seen earlier."},{"Start":"03:36.565 ","End":"03:44.830","Text":"These changes are often detected in different kinds of cancer."},{"Start":"03:44.830 ","End":"03:51.740","Text":"Interestingly, different forms of cancer sometimes have different defects at"},{"Start":"03:51.740 ","End":"03:59.485","Text":"different sites that each of them though control the gene expression in different ways."},{"Start":"03:59.485 ","End":"04:05.325","Text":"Now let\u0027s look at different changes that we know about."},{"Start":"04:05.325 ","End":"04:07.805","Text":"They can be histone acetylation,"},{"Start":"04:07.805 ","End":"04:10.850","Text":"activation of transcription factors by phosphorylation,"},{"Start":"04:10.850 ","End":"04:14.585","Text":"increased RNA stability, decreased RNA stability,"},{"Start":"04:14.585 ","End":"04:20.385","Text":"increased or decreased translational control, protein modifications."},{"Start":"04:20.385 ","End":"04:23.180","Text":"All of these are detected at"},{"Start":"04:23.180 ","End":"04:29.150","Text":"some different points in different kinds or various cancer cells."},{"Start":"04:29.150 ","End":"04:33.840","Text":"I\u0027ll remind you about 2 different kinds of cancer genes,"},{"Start":"04:33.840 ","End":"04:36.920","Text":"genes that can affect cancer."},{"Start":"04:36.920 ","End":"04:40.445","Text":"Some of them are called tumor suppressor genes."},{"Start":"04:40.445 ","End":"04:43.070","Text":"Those are negative genes,"},{"Start":"04:43.070 ","End":"04:45.524","Text":"and some of them are oncogenes,"},{"Start":"04:45.524 ","End":"04:47.260","Text":"they are going to be positive regulators."},{"Start":"04:47.260 ","End":"04:48.620","Text":"We have negative regulators,"},{"Start":"04:48.620 ","End":"04:49.940","Text":"the tumor suppressor genes,"},{"Start":"04:49.940 ","End":"04:52.990","Text":"and positive regulators, oncogene."},{"Start":"04:52.990 ","End":"04:59.090","Text":"In normal cells, tumor suppressor genes function to prevent inappropriate cell growth."},{"Start":"04:59.090 ","End":"05:03.035","Text":"Of course, there are many tumor suppressor genes in cells."},{"Start":"05:03.035 ","End":"05:09.350","Text":"But let\u0027s look at the one that we have studied previously p53,"},{"Start":"05:09.350 ","End":"05:14.360","Text":"which is the most studied and which functions as a transcriptional factor."},{"Start":"05:14.360 ","End":"05:18.620","Text":"It\u0027s mutated in over 50 percent of all cancer types,"},{"Start":"05:18.620 ","End":"05:23.750","Text":"so it\u0027s a really important gene. Now what does it do?"},{"Start":"05:23.750 ","End":"05:26.015","Text":"Let\u0027s look at the figure over here."},{"Start":"05:26.015 ","End":"05:30.185","Text":"If there\u0027s DNA damage during the cell cycle,"},{"Start":"05:30.185 ","End":"05:34.480","Text":"then p53 can cause cell cycle arrest,"},{"Start":"05:34.480 ","End":"05:36.200","Text":"again, in normal cells,"},{"Start":"05:36.200 ","End":"05:39.320","Text":"either causing apoptosis that\u0027s programmed cell death"},{"Start":"05:39.320 ","End":"05:42.650","Text":"to kill cells in which have these mutations,"},{"Start":"05:42.650 ","End":"05:47.105","Text":"or the DNA can be repaired and the cell cycle restarts afterwards."},{"Start":"05:47.105 ","End":"05:50.524","Text":"However, if the p53 is mutated,"},{"Start":"05:50.524 ","End":"05:55.975","Text":"then DNA damage may really stay,"},{"Start":"05:55.975 ","End":"05:57.660","Text":"not be fixed,"},{"Start":"05:57.660 ","End":"06:03.490","Text":"and the cell cycle continue and those cells may become cancerous."},{"Start":"06:03.490 ","End":"06:09.170","Text":"It binds the sites and the promoters of the genes to initiate transcription."},{"Start":"06:09.170 ","End":"06:11.030","Text":"That\u0027s what it normally does."},{"Start":"06:11.030 ","End":"06:14.125","Text":"But a mutation will dramatically alter"},{"Start":"06:14.125 ","End":"06:18.949","Text":"the transcriptional activity of the various target genes."},{"Start":"06:18.949 ","End":"06:20.390","Text":"In the next video,"},{"Start":"06:20.390 ","End":"06:25.380","Text":"we\u0027ll move on to the positive genes, to the oncogene."}],"ID":28232},{"Watched":false,"Name":"Different levels of regulation of gene expression","Duration":"6m 47s","ChapterTopicVideoID":27105,"CourseChapterTopicPlaylistID":261642,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.770","Text":"To begin our discussion of the regulation of gene expression,"},{"Start":"00:04.770 ","End":"00:08.610","Text":"we need to consider what we know about how information"},{"Start":"00:08.610 ","End":"00:13.125","Text":"is passed from DNA to RNA to protein."},{"Start":"00:13.125 ","End":"00:18.750","Text":"Of course, all of these different stages can be regulated."},{"Start":"00:18.750 ","End":"00:20.925","Text":"They can be controlled."},{"Start":"00:20.925 ","End":"00:27.690","Text":"The process of turning on a gene to produce RNA and"},{"Start":"00:27.690 ","End":"00:31.380","Text":"protein or regulating how much of these are"},{"Start":"00:31.380 ","End":"00:35.445","Text":"going to be produced is what we call gene expression."},{"Start":"00:35.445 ","End":"00:40.640","Text":"In other words, getting the information from the DNA to the protein."},{"Start":"00:40.640 ","End":"00:44.270","Text":"There are all chemical mechanisms that control"},{"Start":"00:44.270 ","End":"00:48.470","Text":"the amount of gene expression and the timing of the gene in expression,"},{"Start":"00:48.470 ","End":"00:51.814","Text":"as well as the protein synthesis."},{"Start":"00:51.814 ","End":"00:57.065","Text":"The regulation of gene expression conserves energy and space,"},{"Start":"00:57.065 ","End":"01:01.625","Text":"but the control of this is extremely complex,"},{"Start":"01:01.625 ","End":"01:04.805","Text":"especially in eukaryotes, as we will see."},{"Start":"01:04.805 ","End":"01:09.740","Text":"Therefore malfunctions in this process are very detrimental to"},{"Start":"01:09.740 ","End":"01:15.095","Text":"the cell and in many cases can lead to the development of different diseases."},{"Start":"01:15.095 ","End":"01:23.390","Text":"Cancer is a classic disease which is caused by improper gene expression."},{"Start":"01:23.390 ","End":"01:27.740","Text":"So as usual, we\u0027ll start with a model system which is relatively simple."},{"Start":"01:27.740 ","End":"01:32.000","Text":"Let\u0027s start with bacteria with prokaryotes and"},{"Start":"01:32.000 ","End":"01:36.679","Text":"look at the regulation of transcription in prokaryotes."},{"Start":"01:36.679 ","End":"01:39.920","Text":"To begin with, let\u0027s think about what\u0027s"},{"Start":"01:39.920 ","End":"01:43.325","Text":"particular about prokaryotes different from eukaryotes."},{"Start":"01:43.325 ","End":"01:49.190","Text":"First of all, the DNA is more or less floats freely in the cell cytoplasm."},{"Start":"01:49.190 ","End":"01:52.475","Text":"In other words, it\u0027s not separated from"},{"Start":"01:52.475 ","End":"01:56.750","Text":"the rest of the cytoplasm as opposed to eukaryotes."},{"Start":"01:56.750 ","End":"02:04.370","Text":"Therefore the process of transcription and translation can occur almost simultaneously"},{"Start":"02:04.370 ","End":"02:13.220","Text":"because the DNA in the process of being transcribed can translate at the same time."},{"Start":"02:13.220 ","End":"02:14.540","Text":"Because as you\u0027ll remember,"},{"Start":"02:14.540 ","End":"02:19.850","Text":"transcription and translation both go 5\u0027 to 3\u0027."},{"Start":"02:19.850 ","End":"02:23.240","Text":"The new RNA which is made can be"},{"Start":"02:23.240 ","End":"02:29.015","Text":"translated immediately even before the rest of the messenger RNA is made."},{"Start":"02:29.015 ","End":"02:33.560","Text":"Finally, when the proteins are no longer needed,"},{"Start":"02:33.560 ","End":"02:36.935","Text":"the polypeptides that are made are no longer needed by the cell,"},{"Start":"02:36.935 ","End":"02:40.040","Text":"then the way this process is stopped,"},{"Start":"02:40.040 ","End":"02:46.295","Text":"and it makes a lot of sense is that the transcription will stop."},{"Start":"02:46.295 ","End":"02:50.150","Text":"So it\u0027s the transcription is going to be regulated."},{"Start":"02:50.150 ","End":"02:55.565","Text":"The regulation of DNA transcription therefore will also stop the translation."},{"Start":"02:55.565 ","End":"02:59.480","Text":"In prokaryotes, the primary method of"},{"Start":"02:59.480 ","End":"03:03.650","Text":"gene regulation is the regulation of DNA transcription."},{"Start":"03:03.650 ","End":"03:06.200","Text":"When more protein is required,"},{"Start":"03:06.200 ","End":"03:09.295","Text":"then more transcription occurs."},{"Start":"03:09.295 ","End":"03:17.090","Text":"The control of gene expression is mostly at the transcriptional level in prokaryotes."},{"Start":"03:17.090 ","End":"03:19.595","Text":"Now, what about eukaryotes?"},{"Start":"03:19.595 ","End":"03:21.515","Text":"In eukaryotes, of course,"},{"Start":"03:21.515 ","End":"03:27.155","Text":"the DNA is contained inside the nucleus where it is transcribed into RNA."},{"Start":"03:27.155 ","End":"03:33.920","Text":"We have a nucleus that surrounds the DNA and the transcription and"},{"Start":"03:33.920 ","End":"03:36.950","Text":"translation therefore are physically separated by"},{"Start":"03:36.950 ","End":"03:41.254","Text":"this nuclear membrane which goes around the nucleus."},{"Start":"03:41.254 ","End":"03:46.340","Text":"The transcription occurs inside the nucleus and of course,"},{"Start":"03:46.340 ","End":"03:47.600","Text":"some of the processing,"},{"Start":"03:47.600 ","End":"03:50.839","Text":"whereas the translation occurs outside."},{"Start":"03:50.839 ","End":"03:53.630","Text":"So they can\u0027t occur simultaneously,"},{"Start":"03:53.630 ","End":"03:56.180","Text":"like they do in bacteria."},{"Start":"03:56.180 ","End":"04:00.635","Text":"The regulation in eukaryotes is a lot more complicated."},{"Start":"04:00.635 ","End":"04:03.965","Text":"It can occur, first of all,"},{"Start":"04:03.965 ","End":"04:07.630","Text":"in controlling the uncoiling of"},{"Start":"04:07.630 ","End":"04:11.380","Text":"the DNA from the nucleosomes so that they can bind transcription factors,"},{"Start":"04:11.380 ","End":"04:15.080","Text":"and we can call that an epigenetic level if you like."},{"Start":"04:15.080 ","End":"04:19.310","Text":"Furthermore, we can control the RNA transcription,"},{"Start":"04:19.310 ","End":"04:23.770","Text":"that transcriptional level over here, that\u0027s one."},{"Start":"04:23.770 ","End":"04:29.675","Text":"We can also control the processing of the RNA,"},{"Start":"04:29.675 ","End":"04:33.185","Text":"yes the RNA processing and it\u0027s exports."},{"Start":"04:33.185 ","End":"04:39.000","Text":"This is another place that we can control after it\u0027s transcribed,"},{"Start":"04:39.000 ","End":"04:42.060","Text":"and we\u0027ll call that a post transcriptional level."},{"Start":"04:42.060 ","End":"04:43.940","Text":"So far we\u0027ve got epigenetic,"},{"Start":"04:43.940 ","End":"04:47.600","Text":"transcriptional, and post-transcriptional level."},{"Start":"04:47.600 ","End":"04:53.835","Text":"Of course, the next thing that happens is that the RNA is translated."},{"Start":"04:53.835 ","End":"05:00.125","Text":"We could have control at this stage of translation, but actually,"},{"Start":"05:00.125 ","End":"05:02.570","Text":"we could also have the possibility that"},{"Start":"05:02.570 ","End":"05:07.285","Text":"the messenger RNA never gets to translation, that it\u0027s degraded."},{"Start":"05:07.285 ","End":"05:12.050","Text":"That would be a degradation control making inactive or usually"},{"Start":"05:12.050 ","End":"05:18.185","Text":"the RNA would be then just broke down into pieces and therefore not translated."},{"Start":"05:18.185 ","End":"05:19.925","Text":"After the protein has been made,"},{"Start":"05:19.925 ","End":"05:26.780","Text":"we have post-translational control in which sometimes the protein,"},{"Start":"05:26.780 ","End":"05:28.760","Text":"it could be modified all ways."},{"Start":"05:28.760 ","End":"05:33.035","Text":"For instance, it could be phosphorylated as a prime example,"},{"Start":"05:33.035 ","End":"05:35.390","Text":"making it into an active protein."},{"Start":"05:35.390 ","End":"05:41.615","Text":"So we have all levels of control in eukaryotes that we don\u0027t have in prokaryotes."},{"Start":"05:41.615 ","End":"05:46.130","Text":"To summarize, prokaryotes lack a membrane,"},{"Start":"05:46.130 ","End":"05:50.795","Text":"but eukaryotes contain a membrane around the nucleus."},{"Start":"05:50.795 ","End":"05:54.170","Text":"In prokaryotes, the DNA is found in the cytoplasm."},{"Start":"05:54.170 ","End":"05:58.579","Text":"It\u0027s found everywhere because there\u0027s no differentiation between nucleus and cytoplasm."},{"Start":"05:58.579 ","End":"06:01.909","Text":"But of course, in eukaryotes it\u0027s confined to the nuclear compartment."},{"Start":"06:01.909 ","End":"06:08.120","Text":"In prokaryotes, RNA transcription and protein occur almost simultaneously,"},{"Start":"06:08.120 ","End":"06:09.800","Text":"whereas in eukaryotes of course,"},{"Start":"06:09.800 ","End":"06:14.135","Text":"they have to be separated by the nuclear membrane."},{"Start":"06:14.135 ","End":"06:17.300","Text":"Finally, in prokaryotes, gene expression"},{"Start":"06:17.300 ","End":"06:20.345","Text":"is regulated primarily at the transcriptional level."},{"Start":"06:20.345 ","End":"06:25.025","Text":"While in eukaryotes, it is regulated at multiple levels,"},{"Start":"06:25.025 ","End":"06:29.495","Text":"including epigenetic transcriptional nuclear shuttling,"},{"Start":"06:29.495 ","End":"06:30.890","Text":"that is the exports from"},{"Start":"06:30.890 ","End":"06:35.930","Text":"the nucleus post-transcriptional translational, post-translational."},{"Start":"06:35.930 ","End":"06:38.615","Text":"It\u0027s a lot more complicated."},{"Start":"06:38.615 ","End":"06:43.010","Text":"In the next videos, we\u0027ll look in detail about how"},{"Start":"06:43.010 ","End":"06:48.060","Text":"the transcription in both prokaryotes and eukaryotes is regulated."}],"ID":28233},{"Watched":false,"Name":"Epigenetic regulation","Duration":"8m 8s","ChapterTopicVideoID":27106,"CourseChapterTopicPlaylistID":261642,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:06.310","Text":"Until now we\u0027ve been discussing gene regulation in prokaryotes."},{"Start":"00:06.310 ","End":"00:10.480","Text":"We looked at the details of repressors and activators and so on."},{"Start":"00:10.480 ","End":"00:12.595","Text":"But as I mentioned earlier,"},{"Start":"00:12.595 ","End":"00:14.050","Text":"in the eukaryotic cell,"},{"Start":"00:14.050 ","End":"00:20.830","Text":"things are considerably more complicated and there are a lot more levels of regulation."},{"Start":"00:20.830 ","End":"00:26.710","Text":"The first one we want to talk about is going to be called epigenetic gene regulation."},{"Start":"00:26.710 ","End":"00:31.510","Text":"Of course, eukaryotic gene expression is more complex since transcription and"},{"Start":"00:31.510 ","End":"00:37.425","Text":"translation are physically separated by the nuclear membrane as we discussed earlier."},{"Start":"00:37.425 ","End":"00:43.110","Text":"Eukaryotic cells can regulate gene expression at many different levels of course."},{"Start":"00:43.110 ","End":"00:49.010","Text":"The first epigenetic changes are inheritable changes in"},{"Start":"00:49.010 ","End":"00:54.770","Text":"gene expression that do not result from changes in the DNA sequence."},{"Start":"00:54.770 ","End":"01:00.050","Text":"There can be changes that are made in gene expression that are inherited,"},{"Start":"01:00.050 ","End":"01:06.155","Text":"but they are not changes in DNA sequence and those are called epigenetic changes."},{"Start":"01:06.155 ","End":"01:15.355","Text":"The transcriptional access to the DNA can be controlled in 2 different ways in general."},{"Start":"01:15.355 ","End":"01:19.250","Text":"First of all, we can discuss something called chromatin remodeling."},{"Start":"01:19.250 ","End":"01:25.205","Text":"That is the way the DNA is packaged can change such that"},{"Start":"01:25.205 ","End":"01:31.864","Text":"it becomes more associated or less associated with chromosomal histones."},{"Start":"01:31.864 ","End":"01:35.329","Text":"If an area is very tightly compacted,"},{"Start":"01:35.329 ","End":"01:38.150","Text":"then of course the machinery that does the transcription,"},{"Start":"01:38.150 ","End":"01:43.700","Text":"the transcriptional machinery won\u0027t have access and that can be a level of control."},{"Start":"01:43.700 ","End":"01:46.550","Text":"Whereas if it becomes more accessible,"},{"Start":"01:46.550 ","End":"01:51.320","Text":"it\u0027s opened up, then transcription might increase there."},{"Start":"01:51.320 ","End":"01:56.840","Text":"There are all sorts of different ways that the cell knows how to regulate"},{"Start":"01:56.840 ","End":"02:02.845","Text":"the chromatin remodeling and one of them is DNA methylation."},{"Start":"02:02.845 ","End":"02:06.885","Text":"DNA itself can be methylated and"},{"Start":"02:06.885 ","End":"02:11.500","Text":"that is usually associated with developmental changes and gene silencing."},{"Start":"02:11.500 ","End":"02:16.760","Text":"Of course, when a tissue is undergoing development,"},{"Start":"02:16.760 ","End":"02:18.470","Text":"then there is a change in"},{"Start":"02:18.470 ","End":"02:23.150","Text":"gene expression in the different parts of the tissue as they develop."},{"Start":"02:23.150 ","End":"02:26.870","Text":"That to some extent is regulated by"},{"Start":"02:26.870 ","End":"02:33.815","Text":"DNA methylation as some of the genes are turned off gene silencing."},{"Start":"02:33.815 ","End":"02:38.180","Text":"I\u0027ll remind you now, this diagram that you\u0027ve seen before,"},{"Start":"02:38.180 ","End":"02:41.929","Text":"the different levels of compaction of the DNA,"},{"Start":"02:41.929 ","End":"02:45.770","Text":"starting from the naked DNA to"},{"Start":"02:45.770 ","End":"02:50.780","Text":"the beads on a string in which we\u0027ve got histones that are wrapped by 146,"},{"Start":"02:50.780 ","End":"02:55.529","Text":"147 base pairs of DNA and then those are further packed and further packed of course,"},{"Start":"02:55.529 ","End":"02:59.360","Text":"in ways that we\u0027ve discussed."},{"Start":"02:59.360 ","End":"03:05.300","Text":"The human genome roughly contains about 20,000 genes or so."},{"Start":"03:05.300 ","End":"03:10.625","Text":"The DNA in the nucleus is precisely round folded, compacted into chromosomes."},{"Start":"03:10.625 ","End":"03:14.930","Text":"It\u0027s organized so the specific segments can be accessed as needed"},{"Start":"03:14.930 ","End":"03:19.995","Text":"by the specific cell type during development of course."},{"Start":"03:19.995 ","End":"03:23.105","Text":"The first level of packing"},{"Start":"03:23.105 ","End":"03:29.930","Text":"this nucleosome level is the winding of the DNA strands around the histone proteins."},{"Start":"03:29.930 ","End":"03:33.395","Text":"There are 4 different proteins that are called H2A,"},{"Start":"03:33.395 ","End":"03:37.430","Text":"H2B, H3, and H4."},{"Start":"03:37.430 ","End":"03:41.270","Text":"There are 2 of each of those and they\u0027re color-coded in these picture."},{"Start":"03:41.270 ","End":"03:43.565","Text":"Those are called core histones,"},{"Start":"03:43.565 ","End":"03:47.215","Text":"and they create a histone octamer,"},{"Start":"03:47.215 ","End":"03:50.400","Text":"which is a 8 of these proteins."},{"Start":"03:50.400 ","End":"03:52.140","Text":"4 times 2,"},{"Start":"03:52.140 ","End":"03:53.860","Text":"plus the DNA,"},{"Start":"03:53.860 ","End":"03:58.760","Text":"winds into something called beads on a string and they then can"},{"Start":"03:58.760 ","End":"04:05.255","Text":"package further that make these larger complexes."},{"Start":"04:05.255 ","End":"04:11.810","Text":"Nucleosome complexes can control the axis of the transcriptional proteins to the DNA."},{"Start":"04:11.810 ","End":"04:16.429","Text":"In addition, it turns out that these nucleosomes can move."},{"Start":"04:16.429 ","End":"04:20.180","Text":"They are at least not very sequence-specific,"},{"Start":"04:20.180 ","End":"04:22.985","Text":"and they can move along the DNA string,"},{"Start":"04:22.985 ","End":"04:26.725","Text":"exposing different sections of the DNA."},{"Start":"04:26.725 ","End":"04:30.304","Text":"Now, how is this controlled?"},{"Start":"04:30.304 ","End":"04:35.285","Text":"Well, it turns out that each of the histones has"},{"Start":"04:35.285 ","End":"04:40.370","Text":"a tail on its N-terminus that sticks out of the nucleosome."},{"Start":"04:40.370 ","End":"04:45.410","Text":"Here you can see in blue the DNA which is encircling the nucleosomes and we can"},{"Start":"04:45.410 ","End":"04:50.900","Text":"see these N-terminal tails on the histones and they,"},{"Start":"04:50.900 ","End":"04:55.445","Text":"that is, those tails are available for chemical modification."},{"Start":"04:55.445 ","End":"04:57.740","Text":"They can be, for instance, acetylated,"},{"Start":"04:57.740 ","End":"05:01.180","Text":"methylated, phosphorylated, all sorts of things can happen."},{"Start":"05:01.180 ","End":"05:03.120","Text":"What we want to know,"},{"Start":"05:03.120 ","End":"05:07.565","Text":"if we\u0027re trying to study this is how closely the histone proteins associate"},{"Start":"05:07.565 ","End":"05:12.560","Text":"with the DNA and how this is regulated by chemical signals."},{"Start":"05:12.560 ","End":"05:19.820","Text":"Genes within a highly packed heterochromatin area are usually not expressed but"},{"Start":"05:19.820 ","End":"05:22.670","Text":"sometimes there are chemical groups that are attached to"},{"Start":"05:22.670 ","End":"05:27.860","Text":"these histone tails and they can alter how tightly wound the DNA is."},{"Start":"05:27.860 ","End":"05:35.270","Text":"For example, we can see here that this histone tail might be acetylated."},{"Start":"05:35.270 ","End":"05:39.700","Text":"That\u0027s what this is trying to show, histone acetylation."},{"Start":"05:39.700 ","End":"05:43.725","Text":"Therefore, this area will be more open,"},{"Start":"05:43.725 ","End":"05:46.620","Text":"Acetyl groups of course are negatively charged,"},{"Start":"05:46.620 ","End":"05:48.640","Text":"the DNA is negatively charged."},{"Start":"05:48.640 ","End":"05:53.540","Text":"There is a decompaction of the DNA and"},{"Start":"05:53.540 ","End":"05:58.085","Text":"the genes will become active as a result of acetylation."},{"Start":"05:58.085 ","End":"06:00.665","Text":"This is relaxed chromatin."},{"Start":"06:00.665 ","End":"06:05.065","Text":"On the other hand, if the histones are methylated,"},{"Start":"06:05.065 ","End":"06:09.820","Text":"don\u0027t confuse this with DNA methylation that we discussed a minute ago,"},{"Start":"06:09.820 ","End":"06:13.160","Text":"the genes will be switched off because in general,"},{"Start":"06:13.160 ","End":"06:19.020","Text":"this condenses the chromatin and reduces the transcription."},{"Start":"06:19.520 ","End":"06:24.530","Text":"Interestingly, these changes, for instance,"},{"Start":"06:24.530 ","End":"06:26.525","Text":"the acetylation and methylation,"},{"Start":"06:26.525 ","End":"06:32.030","Text":"are inherited when a cell divides."},{"Start":"06:32.030 ","End":"06:39.210","Text":"Therefore, these really are modifications that are inherited,"},{"Start":"06:39.210 ","End":"06:42.715","Text":"they are epigenetic changes."},{"Start":"06:42.715 ","End":"06:46.535","Text":"We call this epigenetic inheritance."},{"Start":"06:46.535 ","End":"06:50.420","Text":"Even in people, the inheritance of traits is transmitted by"},{"Start":"06:50.420 ","End":"06:54.700","Text":"mechanisms that do not involve the nucleotide sequence."},{"Start":"06:54.700 ","End":"06:58.860","Text":"In some cases, genes that are silenced during the development of the gametes of"},{"Start":"06:58.860 ","End":"07:04.400","Text":"1 parent are then transmitted in a silence condition to the offspring."},{"Start":"07:04.400 ","End":"07:06.260","Text":"They could be silenced, they could be activated."},{"Start":"07:06.260 ","End":"07:14.245","Text":"For instance, if this woman was pregnant with this fetus,"},{"Start":"07:14.245 ","End":"07:16.620","Text":"has a particular diet,"},{"Start":"07:16.620 ","End":"07:18.010","Text":"or maybe she\u0027s smoking,"},{"Start":"07:18.010 ","End":"07:21.260","Text":"different kinds of environmental factors on her, maybe she\u0027s drinking,"},{"Start":"07:21.260 ","End":"07:26.915","Text":"they could affect the methylation patterns of the genes of the embryo and in particular,"},{"Start":"07:26.915 ","End":"07:34.685","Text":"if they modify the genes of the gametes of this unborn child,"},{"Start":"07:34.685 ","End":"07:37.310","Text":"then when the child is born,"},{"Start":"07:37.310 ","End":"07:40.880","Text":"it could influence then the next-generation,"},{"Start":"07:40.880 ","End":"07:43.220","Text":"which could influence the next-generation."},{"Start":"07:43.220 ","End":"07:48.320","Text":"We can see this kind of epigenetic inheritance that goes"},{"Start":"07:48.320 ","End":"07:53.215","Text":"through the mother\u0027s intergenerational transmission."},{"Start":"07:53.215 ","End":"07:56.720","Text":"You could call it multigenerational transmission if we\u0027ve got"},{"Start":"07:56.720 ","End":"08:02.480","Text":"more than 1 generation going on and certainly transgenerational transmission,"},{"Start":"08:02.480 ","End":"08:05.420","Text":"if it goes to many children,"},{"Start":"08:05.420 ","End":"08:09.420","Text":"grandchildren, and subsequent generations."}],"ID":28234},{"Watched":false,"Name":"Eukaryotic gene regulation","Duration":"9m 49s","ChapterTopicVideoID":27107,"CourseChapterTopicPlaylistID":261642,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.350 ","End":"00:05.835","Text":"We\u0027ve been discussing eukaryotic transcription control,"},{"Start":"00:05.835 ","End":"00:10.035","Text":"eukaryotic gene regulation, if you like."},{"Start":"00:10.035 ","End":"00:14.355","Text":"We started by talking about epigenetic control."},{"Start":"00:14.355 ","End":"00:20.325","Text":"That is how the DNA is packed and how the packing affects the transcription."},{"Start":"00:20.325 ","End":"00:23.550","Text":"Well, but once the DNA is unpacked,"},{"Start":"00:23.550 ","End":"00:29.070","Text":"it turns out that the system is very, very complicated."},{"Start":"00:29.070 ","End":"00:35.310","Text":"Getting the RNA polymerase onto the DNA to start transcription is going to be"},{"Start":"00:35.310 ","End":"00:44.660","Text":"a very complicated process in eukaryotes and it\u0027s in a sense like in prokaryotic cells."},{"Start":"00:44.660 ","End":"00:50.270","Text":"But the eukaryotic RNA polymerase requires other transcription factors"},{"Start":"00:50.270 ","End":"00:55.835","Text":"to facilitate transcription initiation unlike in prokaryotes,"},{"Start":"00:55.835 ","End":"00:59.765","Text":"where initiation does not require additional factors."},{"Start":"00:59.765 ","End":"01:06.545","Text":"In eukaryotes, RNA polymerase requires additional transcrip