[{"Name":"Cell Structure","TopicPlaylistFirstVideoID":0,"Duration":null,"Videos":[{"Watched":false,"Name":"Cell Theory","Duration":"3m 25s","ChapterTopicVideoID":24914,"CourseChapterTopicPlaylistID":136374,"HasSubtitles":true,"ThumbnailPath":"https://www.proprep.uk/Images/Videos_Thumbnails/24914.jpeg","UploadDate":"2021-03-04T15:20:30.5370000","DurationForVideoObject":"PT3M25S","Description":null,"MetaTitle":"Cell Theory: Video + Workbook | Proprep","MetaDescription":"Cell Structure and Function - Cell Structure. 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-structure-and-function/cell-structure/vid25827","VideoComments":[],"Subtitles":[{"Start":"00:01.430 ","End":"00:05.655","Text":"Hi. We\u0027re learning about cell structure."},{"Start":"00:05.655 ","End":"00:08.805","Text":"In this section, we\u0027ll be discussing the cell theory,"},{"Start":"00:08.805 ","End":"00:12.330","Text":"which is one of the most basic theories in Biology."},{"Start":"00:12.330 ","End":"00:14.310","Text":"By the end of this section,"},{"Start":"00:14.310 ","End":"00:18.255","Text":"you will be able to describe the role of cells and organisms,"},{"Start":"00:18.255 ","End":"00:20.505","Text":"summarize the cell theory,"},{"Start":"00:20.505 ","End":"00:24.790","Text":"and identify the common components of all cells."},{"Start":"00:25.130 ","End":"00:31.050","Text":"The cell theory states that a cell is the smallest unit of a living thing."},{"Start":"00:31.050 ","End":"00:34.755","Text":"In Biology, all living things are called organisms,"},{"Start":"00:34.755 ","End":"00:36.975","Text":"whether they\u0027re made out of 1 cell,"},{"Start":"00:36.975 ","End":"00:40.260","Text":"unicellular, like this paramecium here,"},{"Start":"00:40.260 ","End":"00:43.760","Text":"or if they\u0027re multi-cellular, like this cow."},{"Start":"00:43.760 ","End":"00:47.345","Text":"You see, all organisms are made out of cells,"},{"Start":"00:47.345 ","End":"00:51.365","Text":"whether they have only 1 cell or they\u0027re made out of many cells."},{"Start":"00:51.365 ","End":"00:55.295","Text":"The cow as an organism is made up of many organs,"},{"Start":"00:55.295 ","End":"00:56.915","Text":"such as the stomach."},{"Start":"00:56.915 ","End":"00:59.945","Text":"Organs are made out of tissue;"},{"Start":"00:59.945 ","End":"01:04.440","Text":"and tissue in turn is made out of cells."},{"Start":"01:04.630 ","End":"01:09.725","Text":"All organisms, multicellular or unicellular,"},{"Start":"01:09.725 ","End":"01:12.050","Text":"are all made out of cells."},{"Start":"01:12.050 ","End":"01:17.990","Text":"The cell is the simplest collection of matter that we described as living."},{"Start":"01:17.990 ","End":"01:23.170","Text":"All cells are related by their descent from earlier cells."},{"Start":"01:23.170 ","End":"01:28.550","Text":"If we were to see other paramecium cells or other living cells of cows,"},{"Start":"01:28.550 ","End":"01:32.765","Text":"you can know that all those cells came from a common ancestor,"},{"Start":"01:32.765 ","End":"01:37.925","Text":"and in turn, they too will give rise to the next-generation of cells."},{"Start":"01:37.925 ","End":"01:41.480","Text":"Cells can differ substantially from one another,"},{"Start":"01:41.480 ","End":"01:44.730","Text":"but they all share some common features."},{"Start":"01:45.580 ","End":"01:52.555","Text":"The 2 types of cells are Prokaryotic cells and eukaryotic cells."},{"Start":"01:52.555 ","End":"01:57.590","Text":"Prokaryotic cells are the type of cells that bacteria have."},{"Start":"01:57.590 ","End":"02:02.700","Text":"Plants, animals, and fungi are all eukaryotes."},{"Start":"02:02.990 ","End":"02:09.380","Text":"Note the difference in scale between the Prokaryotic cells and eukaryotic cells."},{"Start":"02:09.380 ","End":"02:14.600","Text":"While the Prokaryotes are between 0.1-5 micrometers,"},{"Start":"02:14.600 ","End":"02:20.035","Text":"the size of eukaryotes is between 10 and 100 micrometers."},{"Start":"02:20.035 ","End":"02:22.875","Text":"But, large and small,"},{"Start":"02:22.875 ","End":"02:29.735","Text":"all cells share 4 common components: All cells have a plasma membrane."},{"Start":"02:29.735 ","End":"02:32.450","Text":"This is an outer covering that separates"},{"Start":"02:32.450 ","End":"02:36.180","Text":"the cell\u0027s interior from its surrounding environment."},{"Start":"02:36.580 ","End":"02:39.499","Text":"All cells have DNA."},{"Start":"02:39.499 ","End":"02:43.705","Text":"The DNA is the genetic material of the cell."},{"Start":"02:43.705 ","End":"02:50.555","Text":"The cytosol is a jelly-like substance where other cellular components are located."},{"Start":"02:50.555 ","End":"02:54.064","Text":"Ribosomes synthesize proteins."},{"Start":"02:54.064 ","End":"02:57.985","Text":"These 4 components are included in all cells."},{"Start":"02:57.985 ","End":"03:03.170","Text":"However, Prokaryotes differ from eukaryotic cells in several ways,"},{"Start":"03:03.170 ","End":"03:06.060","Text":"as you can probably see in this picture."},{"Start":"03:06.280 ","End":"03:11.400","Text":"We\u0027ll be discussing these differences in the coming sections."},{"Start":"03:12.680 ","End":"03:17.374","Text":"By now, we can describe the role of cells and organisms,"},{"Start":"03:17.374 ","End":"03:19.565","Text":"we can summarize the cell theory,"},{"Start":"03:19.565 ","End":"03:23.255","Text":"and we can identify the common components of all cells."},{"Start":"03:23.255 ","End":"03:25.980","Text":"See you in the next section."}],"ID":25827},{"Watched":false,"Name":"Prokaryotic Cells","Duration":"3m 25s","ChapterTopicVideoID":24909,"CourseChapterTopicPlaylistID":136374,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:02.370 ","End":"00:05.950","Text":"Hi. We\u0027re learning about the structure of cells,"},{"Start":"00:05.950 ","End":"00:09.055","Text":"and today we\u0027ll be speaking about prokaryotic cells."},{"Start":"00:09.055 ","End":"00:10.855","Text":"By the end of this section,"},{"Start":"00:10.855 ","End":"00:15.110","Text":"you\u0027ll be able to describe the characteristics of these cells."},{"Start":"00:15.570 ","End":"00:21.145","Text":"Prokaryotic cells are what we call bacteria, or germs."},{"Start":"00:21.145 ","End":"00:25.870","Text":"Prokaryotic cells have cytosol bound by the plasma membrane."},{"Start":"00:25.870 ","End":"00:29.185","Text":"The plasma membrane, this orange layer here,"},{"Start":"00:29.185 ","End":"00:32.110","Text":"as you recall, has 2 layers."},{"Start":"00:32.110 ","End":"00:37.180","Text":"It has a hydrophilic area,"},{"Start":"00:37.180 ","End":"00:41.350","Text":"hydrophilic head, and hydrophobic tails,"},{"Start":"00:41.350 ","End":"00:44.690","Text":"hydrophobic that don\u0027t like water."},{"Start":"00:45.590 ","End":"00:48.650","Text":"The membrane is made of a double layer of these,"},{"Start":"00:48.650 ","End":"00:53.600","Text":"so we have tails facing the inside of the double layer and we"},{"Start":"00:53.600 ","End":"00:58.820","Text":"have the hydrophilic heads, like water."},{"Start":"00:58.820 ","End":"01:02.570","Text":"What we have here actually on one side is the outside of the cell."},{"Start":"01:02.570 ","End":"01:04.850","Text":"This is the outside of the cell,"},{"Start":"01:04.850 ","End":"01:07.175","Text":"and this is the inside of the cell."},{"Start":"01:07.175 ","End":"01:11.810","Text":"The hydrophilic side of the membrane is actually in water area."},{"Start":"01:11.810 ","End":"01:14.120","Text":"The inside is also in whatever area."},{"Start":"01:14.120 ","End":"01:17.960","Text":"In the middle, we have the hydrophobic area that"},{"Start":"01:17.960 ","End":"01:21.905","Text":"doesn\u0027t let hydrophilic molecules pass in-between."},{"Start":"01:21.905 ","End":"01:30.869","Text":"What watery area that"},{"Start":"01:30.869 ","End":"01:38.304","Text":"we have in the inside of the cell?"},{"Start":"01:38.304 ","End":"01:38.744","Text":"The watery substance is called the cytosol."},{"Start":"01:38.744 ","End":"01:39.551","Text":"It comprises mostly water, as I\u0027ve said, but it also hasn\u0027t dissolved ions,"},{"Start":"01:39.551 ","End":"01:41.580","Text":"large water-soluble molecules, smaller minute molecules, and other proteins."},{"Start":"01:42.640 ","End":"01:48.635","Text":"As you can see, the prokaryotic cells have no nucleus."},{"Start":"01:48.635 ","End":"01:54.600","Text":"That means that the DNA is in an unbound region called the nucleoid."},{"Start":"01:54.790 ","End":"02:00.380","Text":"Furthermore, there are no other membrane-bound organelles as you can see."},{"Start":"02:00.380 ","End":"02:03.380","Text":"The orange dots are the ribosomes."},{"Start":"02:03.380 ","End":"02:07.355","Text":"The ribosomes are minute protein factories."},{"Start":"02:07.355 ","End":"02:11.660","Text":"They synthesize other proteins by reading the code on the mRNA,"},{"Start":"02:11.660 ","End":"02:13.340","Text":"and the messenger RNA."},{"Start":"02:13.340 ","End":"02:17.465","Text":"Most prokaryotes have a peptidoglycan cell wall."},{"Start":"02:17.465 ","End":"02:21.785","Text":"Peptidoglycan is a strongly cross-link polysaccharide."},{"Start":"02:21.785 ","End":"02:26.180","Text":"The cell wall acts as an extra layer of protection for the cell."},{"Start":"02:26.180 ","End":"02:29.425","Text":"It also helps the cell to maintain its shape."},{"Start":"02:29.425 ","End":"02:33.035","Text":"It prevents dehydration by not letting water through,"},{"Start":"02:33.035 ","End":"02:38.030","Text":"and it enable the cell to attach to surfaces in its environment."},{"Start":"02:38.030 ","End":"02:40.640","Text":"An extra layer here,"},{"Start":"02:40.640 ","End":"02:44.645","Text":"the yellow layer, is the polysaccharide capsule."},{"Start":"02:44.645 ","End":"02:49.400","Text":"The capsule further protects the cell by resisting being engulfed by other cells,"},{"Start":"02:49.400 ","End":"02:52.120","Text":"such as antibodies and their immune system."},{"Start":"02:52.120 ","End":"02:55.040","Text":"Some prokaryotes have flagella."},{"Start":"02:55.040 ","End":"02:59.200","Text":"These are extensions that help the bacteria to move around."},{"Start":"02:59.200 ","End":"03:02.130","Text":"Other prokaryotes have pili."},{"Start":"03:02.130 ","End":"03:05.940","Text":"These little extensions also called fimbriae,"},{"Start":"03:09.820 ","End":"03:14.130","Text":"help the bacteria in binding the surfaces."},{"Start":"03:15.160 ","End":"03:19.055","Text":"In our next lesson, we\u0027ll learn about the eukaryotic cells."},{"Start":"03:19.055 ","End":"03:21.950","Text":"But meantime, we can describe the characteristics of"},{"Start":"03:21.950 ","End":"03:26.040","Text":"prokaryotic cells quite well. Thank you for listening."}],"ID":25822},{"Watched":false,"Name":"Cell Size","Duration":"4m 34s","ChapterTopicVideoID":24913,"CourseChapterTopicPlaylistID":136374,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:03.120","Text":"Hi, we\u0027re studying Cell structure."},{"Start":"00:03.120 ","End":"00:06.435","Text":"This section will be dedicating the cell size."},{"Start":"00:06.435 ","End":"00:08.250","Text":"By the end of this section,"},{"Start":"00:08.250 ","End":"00:12.750","Text":"you\u0027ll be able to describe the issue of surface area to volume ratio."},{"Start":"00:12.750 ","End":"00:16.450","Text":"To explain the constraints of cell size."},{"Start":"00:17.030 ","End":"00:23.415","Text":"Prokaryotic cell size is significantly smaller than eukaryotic cells."},{"Start":"00:23.415 ","End":"00:28.950","Text":"If we take the largest prokaryotes next to the smallest eukaryotes,"},{"Start":"00:28.950 ","End":"00:30.510","Text":"it might look something like this."},{"Start":"00:30.510 ","End":"00:34.890","Text":"Most prokaryotes are less smaller than 5 micrometers."},{"Start":"00:34.890 ","End":"00:38.715","Text":"Usually we get a proportion, something like this."},{"Start":"00:38.715 ","End":"00:41.310","Text":"If we look at a logarithmic scale,"},{"Start":"00:41.310 ","End":"00:46.595","Text":"we\u0027d see that these cells are actually quite constrained in their size."},{"Start":"00:46.595 ","End":"00:49.085","Text":"We see this is a logarithmic scale."},{"Start":"00:49.085 ","End":"00:53.015","Text":"Each of these ticks is 10 times the previous one."},{"Start":"00:53.015 ","End":"00:57.090","Text":"Bacteria has roughly 10,"},{"Start":"00:57.090 ","End":"01:00.115","Text":"100, 1,000,10,000,"},{"Start":"01:00.115 ","End":"01:03.620","Text":"100,000, 1,000,000 times smaller than the dog."},{"Start":"01:03.620 ","End":"01:07.595","Text":"A question is, why don\u0027t sell is just get so much bigger?"},{"Start":"01:07.595 ","End":"01:13.295","Text":"The answer is that the metabolic necessities is set the upper bounds in the cell size."},{"Start":"01:13.295 ","End":"01:16.340","Text":"The membrane is what allows ions and"},{"Start":"01:16.340 ","End":"01:19.640","Text":"organic molecules to quickly diffuse in and out of the cell."},{"Start":"01:19.640 ","End":"01:27.430","Text":"That means that the cell membrane is a door to let anything in or out of the cell."},{"Start":"01:27.430 ","End":"01:32.620","Text":"The cell ratio of surface area to volume is what limits the size of a cell."},{"Start":"01:32.620 ","End":"01:36.505","Text":"Since its volume grows proportionately more than its surface area."},{"Start":"01:36.505 ","End":"01:46.045","Text":"The area of a sphere is 4 times pi r which is the radius squared."},{"Start":"01:46.045 ","End":"01:55.255","Text":"While the volume of a sphere is 4 divided by 3 times pi r to the power of 3."},{"Start":"01:55.255 ","End":"01:58.615","Text":"That means that if we look at these 2 cells,"},{"Start":"01:58.615 ","End":"02:06.550","Text":"can say that this cell is size x and this cell it\u0027s radius would be 2x."},{"Start":"02:06.550 ","End":"02:09.800","Text":"That means that we\u0027re multiplying the area here,"},{"Start":"02:09.800 ","End":"02:11.330","Text":"by radius squared,"},{"Start":"02:11.330 ","End":"02:15.160","Text":"by 2 squared, which is 4."},{"Start":"02:16.870 ","End":"02:22.760","Text":"We\u0027re multiplying the volume by 2 to the power of 3, which is 8."},{"Start":"02:22.760 ","End":"02:24.380","Text":"That means that if in this cell,"},{"Start":"02:24.380 ","End":"02:29.150","Text":"we had a proportion of 1 cubic centimeter of"},{"Start":"02:29.150 ","End":"02:35.365","Text":"volume per each square centimeter of the membrane and the area."},{"Start":"02:35.365 ","End":"02:38.570","Text":"In this cell, we would have a volume of"},{"Start":"02:38.570 ","End":"02:45.725","Text":"8 cubic centimeters per each 4 square centimeters in the membrane,"},{"Start":"02:45.725 ","End":"02:49.730","Text":"which is actually the volume of 2 per 1."},{"Start":"02:49.730 ","End":"02:52.490","Text":"If this cell would not be twice as big as this,"},{"Start":"02:52.490 ","End":"02:56.155","Text":"and let\u0027s say it wouldn\u0027t be 4 times as big as this one."},{"Start":"02:56.155 ","End":"03:02.000","Text":"Now we would be multiplying the area by 4 squared, which is 16."},{"Start":"03:02.000 ","End":"03:06.310","Text":"We will be multiplying the volume by 4 to the power of 3,"},{"Start":"03:06.310 ","End":"03:09.775","Text":"which is 4 times 4, 64."},{"Start":"03:09.775 ","End":"03:16.190","Text":"That means that now for 64 cubic centimeters and the volume,"},{"Start":"03:16.190 ","End":"03:21.080","Text":"we only have 16 square centimeters in the outer membrane,"},{"Start":"03:21.080 ","End":"03:24.895","Text":"which is a proportion of 4 to 1."},{"Start":"03:24.895 ","End":"03:26.990","Text":"What happens here is actually,"},{"Start":"03:26.990 ","End":"03:29.180","Text":"if we take an example of a household,"},{"Start":"03:29.180 ","End":"03:32.284","Text":"we\u0027re getting more and more children in the household."},{"Start":"03:32.284 ","End":"03:33.530","Text":"The income is growing,"},{"Start":"03:33.530 ","End":"03:35.330","Text":"but it\u0027s not growing enough."},{"Start":"03:35.330 ","End":"03:41.135","Text":"At first, we had 1 child and let\u0027s say $100 to feed him."},{"Start":"03:41.135 ","End":"03:44.670","Text":"Now we have 2 children with only $100."},{"Start":"03:44.670 ","End":"03:48.005","Text":"Now we have 4 children for every $100 that we get."},{"Start":"03:48.005 ","End":"03:50.585","Text":"Even though we get more money,"},{"Start":"03:50.585 ","End":"03:53.270","Text":"we still have more mouths to feed."},{"Start":"03:53.270 ","End":"03:59.440","Text":"What happens is that the cell membrane cannot feed so much of a volume now."},{"Start":"03:59.440 ","End":"04:03.215","Text":"That\u0027s why cells don\u0027t get as big as buildings."},{"Start":"04:03.215 ","End":"04:05.525","Text":"They stay in their size."},{"Start":"04:05.525 ","End":"04:10.330","Text":"How is it that eukaryotes are so much larger than prokaryotes?"},{"Start":"04:10.330 ","End":"04:14.060","Text":"Eukaryotes cells are much larger because they\u0027ve developed"},{"Start":"04:14.060 ","End":"04:18.350","Text":"different structural adaptations that enhance intracellular transport."},{"Start":"04:18.350 ","End":"04:22.775","Text":"We\u0027ll be speaking about these adaptations in the next units."},{"Start":"04:22.775 ","End":"04:24.710","Text":"We\u0027ve finished this section,"},{"Start":"04:24.710 ","End":"04:28.820","Text":"and now we can describe the issue of surface area to volume ratio."},{"Start":"04:28.820 ","End":"04:34.110","Text":"You can also explain the constraints of cell size. Thanks for listening."}],"ID":25826},{"Watched":false,"Name":"Eukaryotic Cells","Duration":"3m 18s","ChapterTopicVideoID":24915,"CourseChapterTopicPlaylistID":136374,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.620 ","End":"00:04.950","Text":"Hi. Today we\u0027re studying cell structure."},{"Start":"00:04.950 ","End":"00:08.250","Text":"In this section we\u0027ll introduce eukaryotic cells."},{"Start":"00:08.250 ","End":"00:09.990","Text":"By the end of this section,"},{"Start":"00:09.990 ","End":"00:14.415","Text":"you\u0027ll be able to describe the basic structure of eukaryotic plant and animal cells,"},{"Start":"00:14.415 ","End":"00:17.500","Text":"and list the major cell organelles."},{"Start":"00:18.080 ","End":"00:22.244","Text":"Eukaryotic cells are divided into 2 major groups;"},{"Start":"00:22.244 ","End":"00:25.695","Text":"plant cells and animal cells."},{"Start":"00:25.695 ","End":"00:31.000","Text":"Here\u0027s the key to this illustration and soon we\u0027ll be going over many of these."},{"Start":"00:31.220 ","End":"00:35.759","Text":"Unlike prokaryotic cells, such as this bacteria,"},{"Start":"00:35.759 ","End":"00:41.070","Text":"eukaryotes have DNA bound by a double membrane forming a nucleus."},{"Start":"00:41.070 ","End":"00:42.350","Text":"So we see here that"},{"Start":"00:42.350 ","End":"00:48.005","Text":"the eukaryotic DNA is all bound by this membrane here forming a nucleus,"},{"Start":"00:48.005 ","End":"00:51.350","Text":"while the prokaryotic DNA is not bound by anything at all."},{"Start":"00:51.350 ","End":"00:55.429","Text":"Eukaryotes also have numerous membrane-bound organelles,"},{"Start":"00:55.429 ","End":"00:59.330","Text":"such as the mitochondrion which is the power plant of the cell,"},{"Start":"00:59.330 ","End":"01:02.255","Text":"the Golgi apparatus here,"},{"Start":"01:02.255 ","End":"01:05.765","Text":"and this purple endoplasmic reticulum,"},{"Start":"01:05.765 ","End":"01:08.520","Text":"which serve in protein production and export."},{"Start":"01:08.520 ","End":"01:11.600","Text":"Eukaryotes also have several chromosomes."},{"Start":"01:11.600 ","End":"01:13.745","Text":"When they\u0027re condensed, they\u0027re rod-shaped."},{"Start":"01:13.745 ","End":"01:16.970","Text":"Here we see an example of DNA being condensed."},{"Start":"01:16.970 ","End":"01:19.085","Text":"Here it looks like an X."},{"Start":"01:19.085 ","End":"01:21.170","Text":"That\u0027s because when it\u0027s condensed,"},{"Start":"01:21.170 ","End":"01:23.945","Text":"DNA really does look like a rod."},{"Start":"01:23.945 ","End":"01:26.315","Text":"But when cells are duplicated,"},{"Start":"01:26.315 ","End":"01:27.860","Text":"the DNA is duplicated too,"},{"Start":"01:27.860 ","End":"01:32.685","Text":"and therefore we get this shape here."},{"Start":"01:32.685 ","End":"01:34.470","Text":"We have several of them."},{"Start":"01:34.470 ","End":"01:39.455","Text":"While prokaryotes have a single ring-shaped DNA chromosome,"},{"Start":"01:39.455 ","End":"01:42.680","Text":"eukaryotic cells also have a cytoplasm,"},{"Start":"01:42.680 ","End":"01:46.490","Text":"which is the region between the plasma membrane and nucleus."},{"Start":"01:46.490 ","End":"01:50.630","Text":"Plant, and animal cells have an almost identical set of organelles."},{"Start":"01:50.630 ","End":"01:54.035","Text":"What is the difference between these 2 types of cells?"},{"Start":"01:54.035 ","End":"01:58.985","Text":"Well, there are organelles found only in animal cells and absent in plant cells,"},{"Start":"01:58.985 ","End":"02:02.355","Text":"such as the lysosomes here in pink,"},{"Start":"02:02.355 ","End":"02:05.160","Text":"and they serve in a cell\u0027s digestion."},{"Start":"02:05.160 ","End":"02:11.840","Text":"Animal cells also have centrosomes and centrioles which help in the cell division."},{"Start":"02:11.840 ","End":"02:14.404","Text":"Many animal cells have flagella,"},{"Start":"02:14.404 ","End":"02:16.190","Text":"such as these sperm cells,"},{"Start":"02:16.190 ","End":"02:20.190","Text":"but they are also present in some of the plants sperm cells."},{"Start":"02:20.420 ","End":"02:26.150","Text":"Other organelles are only found in plant cells and absent in animal cells."},{"Start":"02:26.150 ","End":"02:30.140","Text":"These include plastids such as these chloroplasts,"},{"Start":"02:30.140 ","End":"02:33.415","Text":"for example, where photosynthesis is carried out."},{"Start":"02:33.415 ","End":"02:37.100","Text":"A large central vacuole carries"},{"Start":"02:37.100 ","End":"02:40.655","Text":"out many of the functions performed by the lysosomes of animal cells."},{"Start":"02:40.655 ","End":"02:43.490","Text":"It also stores water."},{"Start":"02:43.490 ","End":"02:46.205","Text":"Plant cells have a cell wall,"},{"Start":"02:46.205 ","End":"02:48.170","Text":"this thick green thing."},{"Start":"02:48.170 ","End":"02:52.860","Text":"It\u0027s a thick perforated layer outside the plant cell\u0027s plasma membrane."},{"Start":"02:52.900 ","End":"02:57.200","Text":"The cell wall is dotted with a plasmodesmata,"},{"Start":"02:57.200 ","End":"03:02.520","Text":"which are microscopic channels that allow transport and communication between the cells."},{"Start":"03:02.560 ","End":"03:05.885","Text":"We\u0027ve learned about eukaryotic cells."},{"Start":"03:05.885 ","End":"03:10.453","Text":"We can now describe the basic structure of eukaryotic plant and animal cells,"},{"Start":"03:10.453 ","End":"03:12.860","Text":"and list the major cell organelles."},{"Start":"03:12.860 ","End":"03:15.005","Text":"In the following videos,"},{"Start":"03:15.005 ","End":"03:19.230","Text":"we\u0027re going to learn more about these organelles. See you then."}],"ID":25828},{"Watched":false,"Name":"The Cell\u0027s Organelles","Duration":"10m 37s","ChapterTopicVideoID":24910,"CourseChapterTopicPlaylistID":136374,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:03.510","Text":"Hi, we\u0027re studying cell structure."},{"Start":"00:03.510 ","End":"00:07.890","Text":"In this section, we\u0027ll be speaking about eukaryotes cell organelles."},{"Start":"00:07.890 ","End":"00:09.495","Text":"By the end of this section,"},{"Start":"00:09.495 ","End":"00:11.010","Text":"you\u0027ll be able to state the role of"},{"Start":"00:11.010 ","End":"00:15.225","Text":"the plasma membrane and summarize the functions of the cell organelles."},{"Start":"00:15.225 ","End":"00:17.835","Text":"First we\u0027ll speak about the plasma membrane,"},{"Start":"00:17.835 ","End":"00:20.010","Text":"which engulfs the whole cell."},{"Start":"00:20.010 ","End":"00:23.865","Text":"Here\u0027s a close-up image of the phospholipid bilayer."},{"Start":"00:23.865 ","End":"00:27.780","Text":"The function of the plasma membrane is to control the passage of"},{"Start":"00:27.780 ","End":"00:31.860","Text":"organic molecules and wastes into and out of the cell."},{"Start":"00:31.860 ","End":"00:36.510","Text":"Like prokaryotes, the plasma membrane of eukaryotic cells contains"},{"Start":"00:36.510 ","End":"00:40.020","Text":"a phospholipid bilayer with embedded proteins that separate"},{"Start":"00:40.020 ","End":"00:44.135","Text":"the internal contents of the cell from its surrounding environment."},{"Start":"00:44.135 ","End":"00:49.577","Text":"A quick reminder, the phospholipid is a lipid molecule with 2 fatty acid chains,1,"},{"Start":"00:49.577 ","End":"00:53.575","Text":"2, and a phosphate-containing group."},{"Start":"00:53.575 ","End":"00:55.700","Text":"The 2 fatty acid chains, of course,"},{"Start":"00:55.700 ","End":"01:00.425","Text":"are hydrophobic, which means that they do not like water."},{"Start":"01:00.425 ","End":"01:08.840","Text":"While the phosphate head is hydrophilic. Loving water."},{"Start":"01:08.840 ","End":"01:13.175","Text":"If we take here the bilayer, double layer of them,"},{"Start":"01:13.175 ","End":"01:18.515","Text":"and the inside and the outside are both hydrophilic."},{"Start":"01:18.515 ","End":"01:24.810","Text":"The outside of the cell and the inside of the cell are both watery environments."},{"Start":"01:25.130 ","End":"01:31.590","Text":"The center of the bilayer here is, of course, hydrophobic."},{"Start":"01:32.020 ","End":"01:34.820","Text":"Let\u0027s have a look now at the inside of the cell."},{"Start":"01:34.820 ","End":"01:36.830","Text":"The cytoplasm."},{"Start":"01:36.830 ","End":"01:39.710","Text":"This is the region between the plasma membrane and"},{"Start":"01:39.710 ","End":"01:42.860","Text":"the nuclear envelope. This is the nuclear envelope."},{"Start":"01:42.860 ","End":"01:49.220","Text":"Essentially all what is inside the cell except for the nucleus is the cytoplasm."},{"Start":"01:49.220 ","End":"01:54.245","Text":"It\u0027s made up of organelles suspended in gel-like cytosol."},{"Start":"01:54.245 ","End":"01:59.510","Text":"It has a semi-solid consistency which comes from the proteins within it."},{"Start":"01:59.510 ","End":"02:03.320","Text":"Many metabolic reactions, including protein synthesis,"},{"Start":"02:03.320 ","End":"02:05.900","Text":"take place in the cytoplasm."},{"Start":"02:05.900 ","End":"02:10.520","Text":"Let\u0027s have a look at the biggest and the most prominent structure in the cell."},{"Start":"02:10.520 ","End":"02:14.885","Text":"The nucleus. Close-up image."},{"Start":"02:14.885 ","End":"02:18.274","Text":"The nucleus is bound by the nuclear envelope."},{"Start":"02:18.274 ","End":"02:20.975","Text":"This whole dark purple structure."},{"Start":"02:20.975 ","End":"02:24.665","Text":"It constitutes the outermost portion of the nucleus."},{"Start":"02:24.665 ","End":"02:28.490","Text":"Nuclear pores in the nuclear envelope allow substances"},{"Start":"02:28.490 ","End":"02:32.700","Text":"to enter and exit the nucleus. These are the pores here."},{"Start":"02:34.840 ","End":"02:39.500","Text":"The nuclear envelope control the passage of ions, molecules,"},{"Start":"02:39.500 ","End":"02:43.750","Text":"and RNA between the nucleoplasm and the cytoplasm."},{"Start":"02:43.750 ","End":"02:47.914","Text":"The nuclear membrane is continuous with the endoplasmic reticulum,"},{"Start":"02:47.914 ","End":"02:50.930","Text":"which we will speak about in the following section."},{"Start":"02:50.930 ","End":"02:54.830","Text":"Now let\u0027s have a look and see the inner part of the nucleus."},{"Start":"02:54.830 ","End":"03:00.815","Text":"The nucleoplasm is a semi-solid fluid inside the nucleus."},{"Start":"03:00.815 ","End":"03:06.815","Text":"Here we have it. That\u0027s where the chromatin and the nucleolus are located."},{"Start":"03:06.815 ","End":"03:11.720","Text":"This is the nucleolus and the chromatin, these strings."},{"Start":"03:11.720 ","End":"03:15.770","Text":"The nucleolus is the site where ribosomes synthesis occurs."},{"Start":"03:15.770 ","End":"03:21.950","Text":"A chromatin is organized in the separate units called chromosomes."},{"Start":"03:21.950 ","End":"03:25.225","Text":"Let\u0027s have a look at chromosomes and see what they are."},{"Start":"03:25.225 ","End":"03:28.745","Text":"The chromosomes are structures within the nucleus."},{"Start":"03:28.745 ","End":"03:30.200","Text":"They\u0027re made up of DNA,"},{"Start":"03:30.200 ","End":"03:32.360","Text":"which is the hereditary material."},{"Start":"03:32.360 ","End":"03:37.385","Text":"In prokaryotes, DNA is organized into a single circular chromosome."},{"Start":"03:37.385 ","End":"03:41.645","Text":"While in eukaryotes, chromosomes are linear structures."},{"Start":"03:41.645 ","End":"03:44.975","Text":"In prokaryotes like germs,"},{"Start":"03:44.975 ","End":"03:48.110","Text":"we have a single ring of DNA."},{"Start":"03:48.110 ","End":"03:54.335","Text":"While in eukaryotes, this is of course the double helix of DNA."},{"Start":"03:54.335 ","End":"03:55.910","Text":"When the DNA is condensed,"},{"Start":"03:55.910 ","End":"04:01.550","Text":"we get a single linear structure."},{"Start":"04:01.550 ","End":"04:03.680","Text":"Before the cell division,"},{"Start":"04:03.680 ","End":"04:06.500","Text":"this single chromosome is duplicated,"},{"Start":"04:06.500 ","End":"04:10.310","Text":"and then we get this X-like structure,"},{"Start":"04:10.310 ","End":"04:13.490","Text":"which is what you all imagine when you hear chromosomes."},{"Start":"04:13.490 ","End":"04:18.270","Text":"A chromosome is actually a single linear structure."},{"Start":"04:18.820 ","End":"04:21.740","Text":"Every eukaryotic species has"},{"Start":"04:21.740 ","End":"04:26.370","Text":"a specific number of chromosomes in the nuclei of its body\u0027s cell."},{"Start":"04:26.410 ","End":"04:31.204","Text":"The DNA structure is supported by proteins called histones."},{"Start":"04:31.204 ","End":"04:33.810","Text":"Here these are the histones here."},{"Start":"04:33.820 ","End":"04:39.810","Text":"The unwound protein chromosome complexes are called chromatin."},{"Start":"04:41.080 ","End":"04:49.760","Text":"This unwind chromatin looks like just a lot of strings is what is inside the nucleus."},{"Start":"04:49.760 ","End":"04:52.835","Text":"Next, we\u0027ll speak about ribosomes."},{"Start":"04:52.835 ","End":"04:57.905","Text":"These are the cellular structures that are responsible for protein synthesis."},{"Start":"04:57.905 ","End":"05:02.030","Text":"Of course, ribosomes occur also in prokaryotes,"},{"Start":"05:02.030 ","End":"05:06.245","Text":"but eukaryotes, we can find them positioned in 2 locations."},{"Start":"05:06.245 ","End":"05:12.530","Text":"Number 1, attached to the outside of the endoplasmic reticulum or the nuclear envelope."},{"Start":"05:12.530 ","End":"05:15.245","Text":"These are called bound ribosomes."},{"Start":"05:15.245 ","End":"05:16.790","Text":"Here you see it\u0027s all these dots here."},{"Start":"05:16.790 ","End":"05:23.220","Text":"It\u0027s what makes the outside of the endoplasmic reticulum rough."},{"Start":"05:23.700 ","End":"05:27.274","Text":"Other ribosomes are free in the cytosol."},{"Start":"05:27.274 ","End":"05:29.890","Text":"We call them free ribosomes."},{"Start":"05:29.890 ","End":"05:36.100","Text":"The next organelle we\u0027ll speak about is the mitochondria, that\u0027s in plural."},{"Start":"05:36.100 ","End":"05:39.035","Text":"In single we say mitochondrion,"},{"Start":"05:39.035 ","End":"05:41.585","Text":"and let\u0027s have a close look at the mitochondrion."},{"Start":"05:41.585 ","End":"05:46.250","Text":"This is an oval-shaped, double membrane-bound organelle."},{"Start":"05:46.250 ","End":"05:49.880","Text":"Mitochondria have their own ribosomes and DNA."},{"Start":"05:49.880 ","End":"05:53.825","Text":"You can see here the little squiggles of the DNA,"},{"Start":"05:53.825 ","End":"05:57.230","Text":"and these ribosomes, all these dots."},{"Start":"05:57.230 ","End":"06:03.890","Text":"The mitochondria are the sites of the cellular respiration,"},{"Start":"06:03.890 ","End":"06:09.634","Text":"that\u0027s a metabolic process that uses oxygen and sugar to generate ATP."},{"Start":"06:09.634 ","End":"06:15.130","Text":"ATP is the energetic coin used in cells for anything needed."},{"Start":"06:15.130 ","End":"06:18.830","Text":"Some cells have a single large mitochondrion."},{"Start":"06:18.830 ","End":"06:22.640","Text":"More often a cell has a hundreds or even thousands of mitochondria."},{"Start":"06:22.640 ","End":"06:25.700","Text":"They can move around and change their shape and fuse,"},{"Start":"06:25.700 ","End":"06:27.455","Text":"or even divide in 2,"},{"Start":"06:27.455 ","End":"06:30.380","Text":"for example, muscle cells that need a lot of"},{"Start":"06:30.380 ","End":"06:34.010","Text":"energy have a very high concentration of mitochondria."},{"Start":"06:34.010 ","End":"06:36.800","Text":"Next we\u0027ll speak about peroxisomes."},{"Start":"06:36.800 ","End":"06:39.200","Text":"These pinkish balls."},{"Start":"06:39.200 ","End":"06:46.130","Text":"Peroxisomes carry out oxidation reactions that break down fatty acids and amino acids."},{"Start":"06:46.130 ","End":"06:50.030","Text":"They detoxify many poisons that may enter the body,"},{"Start":"06:50.030 ","End":"06:52.260","Text":"and the cells of course."},{"Start":"06:52.390 ","End":"06:56.790","Text":"Glyoxysomes are peroxisomes found in plants."},{"Start":"06:56.790 ","End":"06:59.645","Text":"They convert stored fats into sugars."},{"Start":"06:59.645 ","End":"07:02.120","Text":"Vesicles and vacuoles are"},{"Start":"07:02.120 ","End":"07:06.635","Text":"membrane-bound sacs that function in storage and transport in the cell."},{"Start":"07:06.635 ","End":"07:09.445","Text":"Vacuoles are a bit larger than vesicles."},{"Start":"07:09.445 ","End":"07:13.040","Text":"One of the big differences between vacuoles and vesicles is that"},{"Start":"07:13.040 ","End":"07:17.765","Text":"vacuole membranes do not fuse with the membranes of other cellular components."},{"Start":"07:17.765 ","End":"07:23.015","Text":"While vesicle membranes can fuse with these enzymes within plant vacuoles,"},{"Start":"07:23.015 ","End":"07:25.205","Text":"can break down macromolecules too."},{"Start":"07:25.205 ","End":"07:28.580","Text":"Contractile vacuoles are utilized for pumping"},{"Start":"07:28.580 ","End":"07:31.865","Text":"water out of the cell in many freshwater protists."},{"Start":"07:31.865 ","End":"07:35.815","Text":"The central vacuole, found only in plant cells,"},{"Start":"07:35.815 ","End":"07:38.390","Text":"is a large vacuole that regulates"},{"Start":"07:38.390 ","End":"07:42.530","Text":"the cells concentration of water and changing environmental conditions."},{"Start":"07:42.530 ","End":"07:44.915","Text":"When a plant cell absorbs a lot of water,"},{"Start":"07:44.915 ","End":"07:48.305","Text":"this water is contained in the vacuole that gets really big,"},{"Start":"07:48.305 ","End":"07:50.960","Text":"takes most of the cellular area."},{"Start":"07:50.960 ","End":"07:53.360","Text":"When a plant loses its water,"},{"Start":"07:53.360 ","End":"07:57.845","Text":"the water leaves the vacuole and the whole cell shrinks."},{"Start":"07:57.845 ","End":"08:01.385","Text":"The centrosome, and here you can see it in this animal cell."},{"Start":"08:01.385 ","End":"08:03.445","Text":"Let\u0027s have a close look."},{"Start":"08:03.445 ","End":"08:10.175","Text":"The centrosome is a micro-tubule organizing center found near the nuclei of animal cells."},{"Start":"08:10.175 ","End":"08:14.955","Text":"It contains a pair of centrioles 1 and 2."},{"Start":"08:14.955 ","End":"08:18.260","Text":"These are 2 structures that lie perpendicular to each other."},{"Start":"08:18.260 ","End":"08:22.870","Text":"The central is a cylinder of 9 triplets microtubules."},{"Start":"08:22.870 ","End":"08:25.935","Text":"Here we have 1 triplet, second triplet,"},{"Start":"08:25.935 ","End":"08:27.399","Text":"3, 4, 5,"},{"Start":"08:27.399 ","End":"08:29.370","Text":"6, 7, 8 and 9."},{"Start":"08:29.370 ","End":"08:32.795","Text":"This tube is made of 9 triplets of microtubules."},{"Start":"08:32.795 ","End":"08:38.515","Text":"Centrioles appear to have some role in pulling the chromosomes during cell division."},{"Start":"08:38.515 ","End":"08:41.275","Text":"Next comes the cell wall."},{"Start":"08:41.275 ","End":"08:44.470","Text":"Here it\u0027s this green outer part of the cell."},{"Start":"08:44.470 ","End":"08:49.465","Text":"Let\u0027s scoop the whole inside of the cell out and just see the cell wall."},{"Start":"08:49.465 ","End":"08:52.480","Text":"Here we have 2 cell walls,"},{"Start":"08:52.480 ","End":"08:54.385","Text":"or the walls of 2 cells."},{"Start":"08:54.385 ","End":"08:56.905","Text":"What the cell wall is actually,"},{"Start":"08:56.905 ","End":"09:01.195","Text":"it\u0027s a rigid covering structure external to the plasma membrane."},{"Start":"09:01.195 ","End":"09:03.050","Text":"The yellow part here,"},{"Start":"09:03.050 ","End":"09:08.190","Text":"this is the plasma membrane."},{"Start":"09:10.430 ","End":"09:14.740","Text":"The outer part is the cell wall."},{"Start":"09:17.740 ","End":"09:20.044","Text":"It\u0027s found in plant,"},{"Start":"09:20.044 ","End":"09:23.135","Text":"fungal, and some protists cells."},{"Start":"09:23.135 ","End":"09:27.530","Text":"The function of the cell wall is first to protect the cells,"},{"Start":"09:27.530 ","End":"09:29.930","Text":"and second to provide structural support."},{"Start":"09:29.930 ","End":"09:33.290","Text":"In prokaryotic cells,"},{"Start":"09:33.290 ","End":"09:36.275","Text":"it\u0027s mainly composed of peptidoglycan,"},{"Start":"09:36.275 ","End":"09:39.305","Text":"a polymer of sugar and amino acids."},{"Start":"09:39.305 ","End":"09:42.965","Text":"On the other hand, in plants and some other protists,"},{"Start":"09:42.965 ","End":"09:45.004","Text":"it\u0027s mainly composed of cellulose,"},{"Start":"09:45.004 ","End":"09:47.390","Text":"which is a change in highly branched sugar."},{"Start":"09:47.390 ","End":"09:54.965","Text":"The last organelle we\u0027ll discuss in this section is the chloroplast found in plant cells."},{"Start":"09:54.965 ","End":"09:57.650","Text":"Here\u0027s a close-up image of them."},{"Start":"09:57.650 ","End":"10:03.935","Text":"The chloroplasts are the site where photosynthesis takes place in plants and algae cells."},{"Start":"10:03.935 ","End":"10:09.500","Text":"Similar to mitochondria, they have their own DNA and ribosomes."},{"Start":"10:09.500 ","End":"10:13.340","Text":"Some bacteria also perform photosynthesis,"},{"Start":"10:13.340 ","End":"10:16.835","Text":"but note that they do not have chloroplasts."},{"Start":"10:16.835 ","End":"10:20.330","Text":"In bacteria, the photosynthetic pigments are"},{"Start":"10:20.330 ","End":"10:24.680","Text":"located in the thylakoid membrane within the cell itself."},{"Start":"10:25.100 ","End":"10:30.230","Text":"We\u0027ve discussed the organelles of eukaryotic cells and by now you can"},{"Start":"10:30.230 ","End":"10:34.805","Text":"state the role of the plasma membrane and summarize the functions of the cell organelles."},{"Start":"10:34.805 ","End":"10:37.260","Text":"See you in the next section."}],"ID":25823},{"Watched":false,"Name":"The Endomembrane System","Duration":"6m 53s","ChapterTopicVideoID":24912,"CourseChapterTopicPlaylistID":136374,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:02.190","Text":"Hi, and welcome back."},{"Start":"00:02.190 ","End":"00:04.304","Text":"We\u0027re studying cell structure."},{"Start":"00:04.304 ","End":"00:08.445","Text":"In this section, we\u0027ll be speaking about the endomembrane system."},{"Start":"00:08.445 ","End":"00:10.320","Text":"By the end of this section,"},{"Start":"00:10.320 ","End":"00:14.100","Text":"you\u0027ll be able to list the components of the endomembrane system and to"},{"Start":"00:14.100 ","End":"00:19.000","Text":"recognize the relationship between these components and their functions."},{"Start":"00:19.250 ","End":"00:22.755","Text":"What is the endomembrane system?"},{"Start":"00:22.755 ","End":"00:29.700","Text":"This system consists of the plasma membrane here in yellow wrapping the cell."},{"Start":"00:29.700 ","End":"00:34.330","Text":"The nuclear envelope here in purple wrapping the nucleus."},{"Start":"00:34.330 ","End":"00:36.750","Text":"The endoplasmic reticulum,"},{"Start":"00:36.750 ","End":"00:40.445","Text":"these purple folds coming out of the nucleus."},{"Start":"00:40.445 ","End":"00:42.970","Text":"The Golgi apparatus,"},{"Start":"00:42.970 ","End":"00:45.450","Text":"this organelle here in turquoise."},{"Start":"00:45.450 ","End":"00:51.410","Text":"Vacuoles and vesicles, such as the lysosomes here in pink."},{"Start":"00:51.410 ","End":"00:56.470","Text":"If we take a close look at the plasma membrane, what would we see?"},{"Start":"00:56.470 ","End":"00:58.080","Text":"From previous sections,"},{"Start":"00:58.080 ","End":"01:01.460","Text":"we already know we\u0027d see a bi-layer of phospholipids,"},{"Start":"01:01.460 ","End":"01:07.445","Text":"a phospholipid with a hydrophilic head and 2 hydrophobic tails."},{"Start":"01:07.445 ","End":"01:14.240","Text":"In this bi-layer, the hydrophilic heads are pointing both to the outside of the cell and"},{"Start":"01:14.240 ","End":"01:20.710","Text":"to the inside of the cell where the area is of watery medium and in between,"},{"Start":"01:20.710 ","End":"01:24.350","Text":"we have a barrier of the hydrophobic tails,"},{"Start":"01:24.350 ","End":"01:28.985","Text":"which don\u0027t let many molecules pass through."},{"Start":"01:28.985 ","End":"01:35.305","Text":"Unlike prokaryotes, eukaryotes have many membranous organelles."},{"Start":"01:35.305 ","End":"01:41.735","Text":"All these organelles, the same bi-layer of phospholipids is present."},{"Start":"01:41.735 ","End":"01:44.885","Text":"Let\u0027s start with the endoplasmic reticulum."},{"Start":"01:44.885 ","End":"01:46.560","Text":"In the previous section,"},{"Start":"01:46.560 ","End":"01:50.090","Text":"we spoke about the plasma membrane and the nuclear envelope."},{"Start":"01:50.090 ","End":"01:54.625","Text":"Therefore here it will go straight to speaking about the endoplasmic reticulum."},{"Start":"01:54.625 ","End":"01:59.600","Text":"The endoplasmic reticulum is this whole organelle here."},{"Start":"01:59.600 ","End":"02:02.465","Text":"Let\u0027s have a look at it without the rest of the cell."},{"Start":"02:02.465 ","End":"02:05.900","Text":"We can see that it\u0027s continuous with the nuclear envelope."},{"Start":"02:05.900 ","End":"02:08.360","Text":"This is the nuclear envelope and here we have"},{"Start":"02:08.360 ","End":"02:12.920","Text":"the endoplasmic reticulum and also abbreviated as ER."},{"Start":"02:12.920 ","End":"02:17.855","Text":"What it does is it modifies proteins and synthesizes lipids."},{"Start":"02:17.855 ","End":"02:22.385","Text":"The endoplasmic reticulum is divided into 2 separate areas."},{"Start":"02:22.385 ","End":"02:27.425","Text":"The first of them is the rough ER or the rough endoplasmic reticulum."},{"Start":"02:27.425 ","End":"02:28.790","Text":"We can see it here."},{"Start":"02:28.790 ","End":"02:30.800","Text":"It\u0027s studded with ribosomes."},{"Start":"02:30.800 ","End":"02:34.570","Text":"These ribosomes give it a rough look."},{"Start":"02:34.570 ","End":"02:36.795","Text":"Ribosomes, as we know,"},{"Start":"02:36.795 ","End":"02:38.955","Text":"are what synthesize proteins."},{"Start":"02:38.955 ","End":"02:40.640","Text":"This is actually what happens."},{"Start":"02:40.640 ","End":"02:46.190","Text":"The mRNA coming out of the nucleus is used by these ribosomes to synthesize proteins."},{"Start":"02:46.190 ","End":"02:49.760","Text":"The proteins are folded into the ER lumen,"},{"Start":"02:49.760 ","End":"02:53.584","Text":"which is the space here between the membranes."},{"Start":"02:53.584 ","End":"02:56.210","Text":"The smooth ER, on the other hand here,"},{"Start":"02:56.210 ","End":"02:58.760","Text":"doesn\u0027t have any ribosomes on it."},{"Start":"02:58.760 ","End":"03:01.730","Text":"That\u0027s why it looks smooth in the microscope."},{"Start":"03:01.730 ","End":"03:04.990","Text":"As we said, it has few or no ribosomes at all."},{"Start":"03:04.990 ","End":"03:07.680","Text":"The smooth ER synthesizes carbohydrates,"},{"Start":"03:07.680 ","End":"03:10.780","Text":"lipids, and steroid hormones."},{"Start":"03:10.780 ","End":"03:14.915","Text":"These lipids, they are actually phospholipids and eventually,"},{"Start":"03:14.915 ","End":"03:17.924","Text":"they\u0027re going to be building the cell\u0027s membranes."},{"Start":"03:17.924 ","End":"03:23.830","Text":"It also detoxifies different drugs and poisons that may come into the cell."},{"Start":"03:23.830 ","End":"03:27.350","Text":"In muscle cells, there\u0027s a special area in"},{"Start":"03:27.350 ","End":"03:30.980","Text":"the smooth ER called the sarcoplasmic reticulum."},{"Start":"03:30.980 ","End":"03:34.220","Text":"This stores calcium ions."},{"Start":"03:34.220 ","End":"03:39.215","Text":"The membrane of the ER can actually form these bubbles"},{"Start":"03:39.215 ","End":"03:43.850","Text":"just closes upon itself with the materials synthesized inside,"},{"Start":"03:43.850 ","End":"03:47.185","Text":"and that\u0027s how they\u0027re moved to the next place where they need to get."},{"Start":"03:47.185 ","End":"03:49.340","Text":"If these materials are already matured,"},{"Start":"03:49.340 ","End":"03:51.350","Text":"they can move to their final destination."},{"Start":"03:51.350 ","End":"03:52.850","Text":"But in most cases,"},{"Start":"03:52.850 ","End":"03:55.595","Text":"they move to the Golgi apparatus."},{"Start":"03:55.595 ","End":"04:01.595","Text":"Here we can see the Golgi apparatus receiving these vesicles with molecules inside."},{"Start":"04:01.595 ","End":"04:06.065","Text":"We can see them here being processed inside the Golgi apparatus."},{"Start":"04:06.065 ","End":"04:08.660","Text":"In the end, they are shipped right out."},{"Start":"04:08.660 ","End":"04:11.015","Text":"What does the Golgi apparatus do?"},{"Start":"04:11.015 ","End":"04:15.910","Text":"It executes the final processing steps of many lipids and proteins."},{"Start":"04:15.910 ","End":"04:17.840","Text":"It stores, sorts,"},{"Start":"04:17.840 ","End":"04:21.485","Text":"and ships these macromolecules to their final destinations."},{"Start":"04:21.485 ","End":"04:25.370","Text":"The Golgi apparatus synthesizes polysaccharides and"},{"Start":"04:25.370 ","End":"04:29.720","Text":"phosphate groups and then uses them to modify proteins and lipids."},{"Start":"04:29.720 ","End":"04:32.780","Text":"An example that would be glycoproteins."},{"Start":"04:32.780 ","End":"04:35.690","Text":"Glyco is sugar and proteins are proteins."},{"Start":"04:35.690 ","End":"04:40.490","Text":"These are proteins with modifications of sugar groups."},{"Start":"04:40.490 ","End":"04:46.790","Text":"The Golgi apparatus afterwards categorizes and packages all these materials."},{"Start":"04:46.790 ","End":"04:51.335","Text":"Then it secretes them via transport vesicles in these vesicles,"},{"Start":"04:51.335 ","End":"04:54.784","Text":"and it\u0027s transported to the final destination."},{"Start":"04:54.784 ","End":"05:01.925","Text":"What is really amazing with this whole system is that just like we can blow soap bubbles,"},{"Start":"05:01.925 ","End":"05:05.280","Text":"and then we can attach these bubbles to one another,"},{"Start":"05:05.280 ","End":"05:08.875","Text":"the same thing happens in the cell with all these vesicles and vacuoles,"},{"Start":"05:08.875 ","End":"05:12.515","Text":"they\u0027re move from one organelle in the endomembrane system to another."},{"Start":"05:12.515 ","End":"05:15.530","Text":"They can be moved from the ER straight to the Golgi"},{"Start":"05:15.530 ","End":"05:18.750","Text":"where they just attach and let the materials in."},{"Start":"05:18.750 ","End":"05:23.270","Text":"They can move right out to the plasma membrane or to anywhere they need to go."},{"Start":"05:23.270 ","End":"05:26.750","Text":"In each place, these vesicles they just attach and they go on."},{"Start":"05:26.750 ","End":"05:32.600","Text":"The phospholipids turn to be part of the membrane of the new organelle that they reach."},{"Start":"05:32.600 ","End":"05:36.998","Text":"1 of the more important vesicles of the cell is the lysosome,"},{"Start":"05:36.998 ","End":"05:39.270","Text":"here depicted in pink."},{"Start":"05:39.820 ","End":"05:42.420","Text":"You can see the lysosome."},{"Start":"05:42.420 ","End":"05:45.590","Text":"If we look inside it, we\u0027d see it\u0027s filled with digestive enzymes."},{"Start":"05:45.590 ","End":"05:48.910","Text":"These enzymes can digest different macromolecules."},{"Start":"05:48.910 ","End":"05:51.335","Text":"They aid to break down proteins,"},{"Start":"05:51.335 ","End":"05:55.085","Text":"polysaccharides, lipids, and nucleic acids."},{"Start":"05:55.085 ","End":"05:56.810","Text":"How does this work?"},{"Start":"05:56.810 ","End":"06:01.775","Text":"Again, we said that the membrane can close itself into a bubble."},{"Start":"06:01.775 ","End":"06:04.340","Text":"In this example of phagocytosis,"},{"Start":"06:04.340 ","End":"06:09.980","Text":"the outer cell membrane is closing upon this food."},{"Start":"06:09.980 ","End":"06:13.520","Text":"The food is brought into the cell and it needs to be digested."},{"Start":"06:13.520 ","End":"06:18.320","Text":"The food vacuole is united with this lysosome."},{"Start":"06:18.320 ","End":"06:24.400","Text":"Again, the membrane of both these vesicles just unites, tends to be 1."},{"Start":"06:24.400 ","End":"06:28.715","Text":"The digestive enzymes then digest the different macromolecules of food,"},{"Start":"06:28.715 ","End":"06:32.945","Text":"whether they\u0027re lipids, nucleic acids, or polysaccharides."},{"Start":"06:32.945 ","End":"06:35.599","Text":"The lysosomes are also used to destroy"},{"Start":"06:35.599 ","End":"06:39.240","Text":"disease-causing organisms that might enter the cell."},{"Start":"06:39.610 ","End":"06:42.905","Text":"We learned about the endomembrane system."},{"Start":"06:42.905 ","End":"06:46.340","Text":"Now we can list the components of the endomembrane system and"},{"Start":"06:46.340 ","End":"06:50.855","Text":"recognize the relationship between these components and their functions."},{"Start":"06:50.855 ","End":"06:53.730","Text":"I\u0027ll see you in the next section."}],"ID":25825},{"Watched":false,"Name":"The Cytoskeleton","Duration":"4m 2s","ChapterTopicVideoID":24911,"CourseChapterTopicPlaylistID":136374,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:03.650","Text":"Hey, there, we\u0027re studying the cell structure."},{"Start":"00:03.650 ","End":"00:06.885","Text":"This section we\u0027ll be speaking about the cytoskeleton."},{"Start":"00:06.885 ","End":"00:11.190","Text":"This internal cellular structure helps the cell maintain its shape,"},{"Start":"00:11.190 ","End":"00:12.885","Text":"move from place to place,"},{"Start":"00:12.885 ","End":"00:17.325","Text":"or even move organelles and different molecules inside the cell itself."},{"Start":"00:17.325 ","End":"00:18.975","Text":"By the end of this section,"},{"Start":"00:18.975 ","End":"00:21.525","Text":"you\u0027ll be able to describe the cytoskeleton,"},{"Start":"00:21.525 ","End":"00:23.865","Text":"compare the roles of microfilaments,"},{"Start":"00:23.865 ","End":"00:27.093","Text":"intermediate filaments, and microtubules,"},{"Start":"00:27.093 ","End":"00:28.260","Text":"and recognize the structure,"},{"Start":"00:28.260 ","End":"00:31.125","Text":"and function of cilia and flagella."},{"Start":"00:31.125 ","End":"00:34.830","Text":"The cytoskeleton is present in the cytoplasm is all cells"},{"Start":"00:34.830 ","End":"00:38.485","Text":"including eukaryotes as well as prokaryotes."},{"Start":"00:38.485 ","End":"00:44.030","Text":"Here we\u0027ll describe eukaryotic structure of the cytoskeleton."},{"Start":"00:44.030 ","End":"00:46.280","Text":"The cytoskeleton is a network of"},{"Start":"00:46.280 ","End":"00:51.530","Text":"interlocking protein filaments that extend from the cell nucleus to the cell membrane."},{"Start":"00:51.530 ","End":"00:57.410","Text":"It\u0027s capable of rapid growth or disassembly depending on the cell\u0027s requirements."},{"Start":"00:57.410 ","End":"01:02.420","Text":"The cytoskeleton of eukaryotes is composed of 3 main proteins."},{"Start":"01:02.420 ","End":"01:05.885","Text":"Microfilaments, also called actin filaments,"},{"Start":"01:05.885 ","End":"01:08.090","Text":"are the thinnest components."},{"Start":"01:08.090 ","End":"01:14.090","Text":"Intermediate filaments are the most stable of the 3 components of the cytoskeleton."},{"Start":"01:14.090 ","End":"01:18.595","Text":"Microtubules are the thickest of these components."},{"Start":"01:18.595 ","End":"01:22.530","Text":"Let\u0027s have a closer look at the components of the cytoskeleton."},{"Start":"01:22.530 ","End":"01:28.770","Text":"Microfilaments, here in this picture we can see fluorescence staining of cells,"},{"Start":"01:28.770 ","End":"01:30.475","Text":"in red we see the nuclei,"},{"Start":"01:30.475 ","End":"01:33.005","Text":"and in yellow the microfilaments."},{"Start":"01:33.005 ","End":"01:36.999","Text":"Microfilaments function in a cellular movement."},{"Start":"01:36.999 ","End":"01:41.590","Text":"Microfilaments are comprised of 2 intertwined strands formed from"},{"Start":"01:41.590 ","End":"01:46.570","Text":"globular sub-unit proteins called actin. As you can see here."},{"Start":"01:46.570 ","End":"01:53.125","Text":"This thin filament serves as a track for the movement of a motor protein, myosin."},{"Start":"01:53.125 ","End":"01:57.040","Text":"Microfilaments engage in cellular events requiring"},{"Start":"01:57.040 ","End":"02:01.520","Text":"motion such as cell division, and muscle contractions."},{"Start":"02:01.520 ","End":"02:06.800","Text":"The second component will refer to are the intermediate filaments."},{"Start":"02:06.800 ","End":"02:12.185","Text":"These are built of several strands of fibrous proteins that are wound together."},{"Start":"02:12.185 ","End":"02:15.400","Text":"Their function is purely structural."},{"Start":"02:15.400 ","End":"02:19.460","Text":"They bear tension fast maintaining the cell shape."},{"Start":"02:19.460 ","End":"02:24.020","Text":"They also anchor the nucleus and other organelles in place."},{"Start":"02:24.020 ","End":"02:27.530","Text":"Last but not least, are the microtubules."},{"Start":"02:27.530 ","End":"02:30.665","Text":"These are the thickest element in a cytoskeleton."},{"Start":"02:30.665 ","End":"02:34.009","Text":"They\u0027re built as small hollow tubes."},{"Start":"02:34.009 ","End":"02:37.250","Text":"They help resist cell compression."},{"Start":"02:37.250 ","End":"02:41.600","Text":"They also provide a track along with vesicles move through the cells,"},{"Start":"02:41.600 ","End":"02:45.244","Text":"similarly to the microfilaments that we\u0027ve seen previously."},{"Start":"02:45.244 ","End":"02:50.500","Text":"They can also pull replicated chromosomes to opposite ends of a dividing cell."},{"Start":"02:50.500 ","End":"02:53.930","Text":"In cell division microtubules are used to pull"},{"Start":"02:53.930 ","End":"02:58.620","Text":"replicated chromosomes to opposite ends of a dividing cell."},{"Start":"02:58.930 ","End":"03:04.970","Text":"They also build structural elements of flagella, cilia, and centrioles."},{"Start":"03:04.970 ","End":"03:08.330","Text":"Let\u0027s have a closer look at the flagella and cilia."},{"Start":"03:08.330 ","End":"03:11.105","Text":"Flagella and cilia."},{"Start":"03:11.105 ","End":"03:15.920","Text":"These are long hair-like structures that enable an entire cell to move."},{"Start":"03:15.920 ","End":"03:20.225","Text":"Cells can have a single flagellum or a few flagella."},{"Start":"03:20.225 ","End":"03:25.310","Text":"In mammals, the only cell that has a flagellum is a sperm cell."},{"Start":"03:25.310 ","End":"03:29.630","Text":"Flagellum helps the cell swim from place to place."},{"Start":"03:29.630 ","End":"03:32.090","Text":"On the other hand, when present,"},{"Start":"03:32.090 ","End":"03:36.155","Text":"there are many cilia that extend along the plasma membranes, entire surface."},{"Start":"03:36.155 ","End":"03:39.200","Text":"Like in these human bronchi cells."},{"Start":"03:39.200 ","End":"03:43.670","Text":"Many cilia and what they do is that they all move together,"},{"Start":"03:43.670 ","End":"03:48.870","Text":"they help to push the mucus and other things out of their airway."},{"Start":"03:49.850 ","End":"03:52.910","Text":"We can now describe the cytoskeleton,"},{"Start":"03:52.910 ","End":"03:54.890","Text":"compare the roles of microfilaments,"},{"Start":"03:54.890 ","End":"03:57.260","Text":"intermediate filaments, and microtubules,"},{"Start":"03:57.260 ","End":"04:02.310","Text":"and recognize the structure and function of cilia and flagella."}],"ID":25824},{"Watched":false,"Name":"Major Types of Intercellular Junctions","Duration":"2m 1s","ChapterTopicVideoID":24908,"CourseChapterTopicPlaylistID":136374,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.170 ","End":"00:03.840","Text":"Hi, we\u0027re studying Cell structure."},{"Start":"00:03.840 ","End":"00:09.495","Text":"In this section we\u0027ll be speaking about the major types of intercellular junctions."},{"Start":"00:09.495 ","End":"00:11.940","Text":"By the end of this section,"},{"Start":"00:11.940 ","End":"00:13.470","Text":"you\u0027ll be able to describe"},{"Start":"00:13.470 ","End":"00:18.015","Text":"the intercellular junctions and compare the roles of plasmodesmata,"},{"Start":"00:18.015 ","End":"00:22.785","Text":"tight junctions, gap junctions, and desmosomes."},{"Start":"00:22.785 ","End":"00:26.100","Text":"The cells can communicate with each other via"},{"Start":"00:26.100 ","End":"00:30.075","Text":"direct contact, or intercellular junctions."},{"Start":"00:30.075 ","End":"00:35.130","Text":"In plant cells, this communication is performed through plasmodesmata."},{"Start":"00:35.130 ","End":"00:39.059","Text":"Animal cells contact each other through tight junctions,"},{"Start":"00:39.059 ","End":"00:42.690","Text":"gap junctions, and desmosomes."},{"Start":"00:42.690 ","End":"00:45.735","Text":"Let\u0027s have a look at the plant cells."},{"Start":"00:45.735 ","End":"00:48.613","Text":"The plasmodesmata, or singular,"},{"Start":"00:48.613 ","End":"00:53.690","Text":"plasmodesma, are built from channels that perforate the cell walls."},{"Start":"00:53.690 ","End":"00:59.450","Text":"They enable passage of water and small solutes between neighboring cells."},{"Start":"00:59.450 ","End":"01:03.860","Text":"In animal cells, we find tight junctions which bind cells"},{"Start":"01:03.860 ","End":"01:09.005","Text":"together by specific proteins forming continuous seals around the cell."},{"Start":"01:09.005 ","End":"01:11.570","Text":"Tight junctions prevent leakage of"},{"Start":"01:11.570 ","End":"01:16.160","Text":"extra cellular fluid across layers of epithelial cells."},{"Start":"01:16.160 ","End":"01:20.104","Text":"Desmosomes, also called anchoring junctions,"},{"Start":"01:20.104 ","End":"01:22.292","Text":"are found only in animal cells."},{"Start":"01:22.292 ","End":"01:26.930","Text":"They connect cells together into very strong sheets."},{"Start":"01:26.930 ","End":"01:34.460","Text":"Gap junctions in animal cells have similar function as plasmodesmata do in plant cells."},{"Start":"01:34.460 ","End":"01:39.695","Text":"These are channels between adjacent cells that allow for transporting ions,"},{"Start":"01:39.695 ","End":"01:43.745","Text":"nutrients, and other substances between the cells."},{"Start":"01:43.745 ","End":"01:48.260","Text":"They\u0027re particularly important in cardiac muscles."},{"Start":"01:48.260 ","End":"01:50.690","Text":"After listening to this section,"},{"Start":"01:50.690 ","End":"01:53.405","Text":"we can describe the intracellular junctions,"},{"Start":"01:53.405 ","End":"01:56.465","Text":"and compare the roles of plasmodesmata and plant cells,"},{"Start":"01:56.465 ","End":"01:58.430","Text":"tight junctions, gap junctions,"},{"Start":"01:58.430 ","End":"02:01.140","Text":"and desmosomes in animal cells."}],"ID":25821},{"Watched":false,"Name":"Exercise 1","Duration":"1m 25s","ChapterTopicVideoID":26992,"CourseChapterTopicPlaylistID":136374,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:07.029","Text":"In this question, we\u0027re asked which of the following answers is present in all cells?"},{"Start":"00:07.029 ","End":"00:11.770","Text":"The endoplasmic reticulum, plasma membrane,"},{"Start":"00:11.770 ","End":"00:14.910","Text":"the nucleus, or mitochondria."},{"Start":"00:14.910 ","End":"00:18.670","Text":"Well, at first glance, it may seem that all the answers are right."},{"Start":"00:18.670 ","End":"00:21.140","Text":"Let\u0027s have a look at this sketch of a cell here."},{"Start":"00:21.140 ","End":"00:24.130","Text":"We see the nucleus and the mitochondria."},{"Start":"00:24.130 ","End":"00:26.005","Text":"But here\u0027s the catch."},{"Start":"00:26.005 ","End":"00:28.285","Text":"This is a eukaryotic cell."},{"Start":"00:28.285 ","End":"00:31.825","Text":"Many organisms are prokaryotes."},{"Start":"00:31.825 ","End":"00:35.485","Text":"Other than the big size difference between the cells,"},{"Start":"00:35.485 ","End":"00:37.330","Text":"prokaryotes are a lot smaller,"},{"Start":"00:37.330 ","End":"00:39.400","Text":"there\u0027s a structural difference because"},{"Start":"00:39.400 ","End":"00:42.815","Text":"prokaryotes don\u0027t have membrane-encased organelles."},{"Start":"00:42.815 ","End":"00:47.570","Text":"In fact, the only 4 components that are present in both prokaryotes and"},{"Start":"00:47.570 ","End":"00:52.325","Text":"eukaryotes are the plasma membrane which encases all cells,"},{"Start":"00:52.325 ","End":"00:54.200","Text":"the DNA or chromatin,"},{"Start":"00:54.200 ","End":"00:58.310","Text":"which carries the genetic information in all cells, the cytosol,"},{"Start":"00:58.310 ","End":"01:01.863","Text":"which is the jelly-like liquid that fills the cells,"},{"Start":"01:01.863 ","End":"01:04.070","Text":"and the ribosomes here,"},{"Start":"01:04.070 ","End":"01:06.200","Text":"these little brown dots,"},{"Start":"01:06.200 ","End":"01:11.390","Text":"which translate the RNA into the protein sequence of the amino acids."},{"Start":"01:11.390 ","End":"01:14.630","Text":"Therefore, we can cross out the endoplasmic reticulum,"},{"Start":"01:14.630 ","End":"01:16.549","Text":"the nucleus, and the mitochondria,"},{"Start":"01:16.549 ","End":"01:19.355","Text":"which are not present in prokaryotic cells."},{"Start":"01:19.355 ","End":"01:25.740","Text":"The correct answer is a plasma membrane present in the cells of all living organisms."}],"ID":28127},{"Watched":false,"Name":"Exercise 2","Duration":"1m 50s","ChapterTopicVideoID":26993,"CourseChapterTopicPlaylistID":136374,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.560 ","End":"00:04.260","Text":"In this question, we\u0027re asked whether any of"},{"Start":"00:04.260 ","End":"00:09.765","Text":"the following answers makes locomotion possible in prokaryotes cells?"},{"Start":"00:09.765 ","End":"00:16.860","Text":"Ribosomes, lysosomes, flagella, or desmosomes."},{"Start":"00:16.860 ","End":"00:20.730","Text":"Let\u0027s bring up an illustration of a prokaryote cell."},{"Start":"00:20.730 ","End":"00:23.685","Text":"Ribosomes appear in prokaryotes,"},{"Start":"00:23.685 ","End":"00:26.220","Text":"but they function in translating RNA to"},{"Start":"00:26.220 ","End":"00:30.015","Text":"proteins have nothing whatsoever to do with locomotion."},{"Start":"00:30.015 ","End":"00:32.625","Text":"We can cross that ribosomes."},{"Start":"00:32.625 ","End":"00:35.310","Text":"B. Lysosomes."},{"Start":"00:35.310 ","End":"00:38.685","Text":"We don\u0027t have any lysosomes in the prokaryote cell."},{"Start":"00:38.685 ","End":"00:41.595","Text":"Let\u0027s have a look at the eukaryotic cell."},{"Start":"00:41.595 ","End":"00:44.300","Text":"Here we\u0027ve got the lysosomes here."},{"Start":"00:44.300 ","End":"00:47.799","Text":"These are membranous sacs full of digestive enzymes."},{"Start":"00:47.799 ","End":"00:52.670","Text":"Lysosomes are fused with food vacuoles there are swallowed in phagocytosis."},{"Start":"00:52.670 ","End":"00:56.465","Text":"The digestive enzymes then digest the food."},{"Start":"00:56.465 ","End":"01:01.550","Text":"This has nothing to do with locomotion and doesn\u0027t occur in prokaryotes cells at all."},{"Start":"01:01.550 ","End":"01:04.588","Text":"We can cross out lysosomes too."},{"Start":"01:04.588 ","End":"01:06.225","Text":"C is flagella."},{"Start":"01:06.225 ","End":"01:09.365","Text":"We have flagella here and the answer is"},{"Start":"01:09.365 ","End":"01:14.360","Text":"both flagella and cilia in different cells make locomotion possible."},{"Start":"01:14.360 ","End":"01:17.555","Text":"That looks right, but before we circle an answer,"},{"Start":"01:17.555 ","End":"01:19.670","Text":"we should always look at all the answers."},{"Start":"01:19.670 ","End":"01:22.009","Text":"Let\u0027s have a look at D. Desmosomes."},{"Start":"01:22.009 ","End":"01:23.720","Text":"What are desmosomes?"},{"Start":"01:23.720 ","End":"01:26.330","Text":"We don\u0027t see any in this illustration and that\u0027s because"},{"Start":"01:26.330 ","End":"01:29.480","Text":"desmosomes don\u0027t appear in prokaryotes cells at all."},{"Start":"01:29.480 ","End":"01:32.510","Text":"In fact, they appear only in certain animal cells."},{"Start":"01:32.510 ","End":"01:36.755","Text":"The desmosomes function in holding cells together very tightly,"},{"Start":"01:36.755 ","End":"01:39.975","Text":"forming strong untearable layers of tissue."},{"Start":"01:39.975 ","End":"01:42.260","Text":"Desmosomes too, don\u0027t appear in"},{"Start":"01:42.260 ","End":"01:45.110","Text":"prokaryotes at all and don\u0027t have anything to do with local motion."},{"Start":"01:45.110 ","End":"01:50.160","Text":"We can cross them out and circle our correct answer, flagella."}],"ID":28128},{"Watched":false,"Name":"Exercise 3","Duration":"3m 26s","ChapterTopicVideoID":26994,"CourseChapterTopicPlaylistID":136374,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.110 ","End":"00:04.980","Text":"Which of the following has 2 phospholipid bilayers?"},{"Start":"00:04.980 ","End":"00:07.875","Text":"A, the lysosome, B,"},{"Start":"00:07.875 ","End":"00:10.110","Text":"the nucleus, C,"},{"Start":"00:10.110 ","End":"00:11.745","Text":"the Golgi apparatus,"},{"Start":"00:11.745 ","End":"00:13.649","Text":"and D, the vacuole."},{"Start":"00:13.649 ","End":"00:17.295","Text":"Well, a quick reminder about the phospholipid bilayer."},{"Start":"00:17.295 ","End":"00:20.400","Text":"What is a phospholipid and what is the bilayer of this?"},{"Start":"00:20.400 ","End":"00:30.600","Text":"The phospholipid is a molecule that has a hydrophilic head,"},{"Start":"00:30.600 ","End":"00:33.840","Text":"which means water loving."},{"Start":"00:33.840 ","End":"00:43.325","Text":"This molecule also has 2 hydrophobic tails."},{"Start":"00:43.325 ","End":"00:47.675","Text":"Hydrophobic means water repelling."},{"Start":"00:47.675 ","End":"00:49.760","Text":"If you\u0027d take a hint,"},{"Start":"00:49.760 ","End":"00:53.375","Text":"follow these phospholipid molecules and throw into a cup of water."},{"Start":"00:53.375 ","End":"00:58.340","Text":"You would probably find them setting themselves up in a way that the hydrophobic tails"},{"Start":"00:58.340 ","End":"01:03.290","Text":"all face each other as they are repelled by the water and the hydrophilic,"},{"Start":"01:03.290 ","End":"01:07.295","Text":"water loving heads all face the aqueous environment."},{"Start":"01:07.295 ","End":"01:11.330","Text":"The phospholipid bilayer is the very stable structure that"},{"Start":"01:11.330 ","End":"01:15.530","Text":"separates between the inside of the cell and the outer environment."},{"Start":"01:15.530 ","End":"01:19.655","Text":"Now the question is which of the following has 2 phospholipid bi-layers,"},{"Start":"01:19.655 ","End":"01:21.920","Text":"the lysosome, the nucleus, the Golgi apparatus,"},{"Start":"01:21.920 ","End":"01:27.079","Text":"or the vacuole and since only eukaryotic cells have membrane engulfed organelles,"},{"Start":"01:27.079 ","End":"01:29.275","Text":"let\u0027s have a look at the eukaryotic cell,"},{"Start":"01:29.275 ","End":"01:31.895","Text":"and here we see the lysosomes."},{"Start":"01:31.895 ","End":"01:35.705","Text":"These are membranous sacs which carry digestive enzymes."},{"Start":"01:35.705 ","End":"01:38.990","Text":"They fuse with food vacuoles swallowed by the cell"},{"Start":"01:38.990 ","End":"01:42.715","Text":"in the process of phagocytosis and then digest the food."},{"Start":"01:42.715 ","End":"01:45.630","Text":"In order for the membranes to fuse with one another,"},{"Start":"01:45.630 ","End":"01:48.500","Text":"we can kind of think of soap bubbles fusing with one another"},{"Start":"01:48.500 ","End":"01:52.220","Text":"and you couldn\u0027t do that so easily with double membrane layer,"},{"Start":"01:52.220 ","End":"01:54.709","Text":"with a double phospholipid bilayer."},{"Start":"01:54.709 ","End":"01:56.960","Text":"Therefore, all the structures in"},{"Start":"01:56.960 ","End":"02:01.865","Text":"the intermembrane system tend to have only one phospholipid bilayer."},{"Start":"02:01.865 ","End":"02:03.995","Text":"That way they can fuse, for example,"},{"Start":"02:03.995 ","End":"02:06.065","Text":"with the membrane of the food vacuole,"},{"Start":"02:06.065 ","End":"02:09.395","Text":"which actually bubbles out of the cell outer membrane."},{"Start":"02:09.395 ","End":"02:12.815","Text":"The lysosome only has one phospholipid bilayer."},{"Start":"02:12.815 ","End":"02:18.515","Text":"We can cross that out and the vacuole to only has one phospholipid bilayer,"},{"Start":"02:18.515 ","End":"02:20.605","Text":"we can cross this out also."},{"Start":"02:20.605 ","End":"02:25.955","Text":"Another component of the cells intermembrane system is the Golgi apparatus."},{"Start":"02:25.955 ","End":"02:32.390","Text":"This system also receives and sends membrane incase sacs with proteins,"},{"Start":"02:32.390 ","End":"02:36.950","Text":"for example, they may later fuse with the outer cell membrane."},{"Start":"02:36.950 ","End":"02:38.970","Text":"All the membranous sacs in"},{"Start":"02:38.970 ","End":"02:43.735","Text":"the intermembrane system include only one phospholipid bilayer."},{"Start":"02:43.735 ","End":"02:46.275","Text":"We crossed out the Golgi apparatus too."},{"Start":"02:46.275 ","End":"02:47.791","Text":"We\u0027re left with the nucleus."},{"Start":"02:47.791 ","End":"02:52.550","Text":"The nucleus in fact does have 2 phospholipid bilayers."},{"Start":"02:52.550 ","End":"02:55.370","Text":"It\u0027s a double membrane organelle."},{"Start":"02:55.370 ","End":"02:58.550","Text":"The inner membrane and engulfs all the chromatin and"},{"Start":"02:58.550 ","End":"03:02.525","Text":"the outer membrane also stands out to make the ER,"},{"Start":"03:02.525 ","End":"03:04.400","Text":"or the endoplasmic reticulum."},{"Start":"03:04.400 ","End":"03:11.584","Text":"In fact, the cell has 3 main structures that have a double phospholipid bilayer;"},{"Start":"03:11.584 ","End":"03:14.615","Text":"the nucleus, the mitochondria,"},{"Start":"03:14.615 ","End":"03:18.080","Text":"and any of the plastids including the chloroplasts that of course we"},{"Start":"03:18.080 ","End":"03:21.920","Text":"can\u0027t see in this animal cell because they appear only in plant cells."},{"Start":"03:21.920 ","End":"03:25.409","Text":"The correct answer is, the nucleus."}],"ID":28129},{"Watched":false,"Name":"Exercise 4","Duration":"2m 24s","ChapterTopicVideoID":26995,"CourseChapterTopicPlaylistID":136374,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.140 ","End":"00:02.460","Text":"The rough ER, or"},{"Start":"00:02.460 ","End":"00:08.715","Text":"the rough endoplasmic reticulum got its name from something attached to it."},{"Start":"00:08.715 ","End":"00:10.495","Text":"What is that something?"},{"Start":"00:10.495 ","End":"00:13.485","Text":"A, the nucleolus, B,"},{"Start":"00:13.485 ","End":"00:16.290","Text":"the Golgi apparatus, C,"},{"Start":"00:16.290 ","End":"00:18.420","Text":"the ribosomes or,"},{"Start":"00:18.420 ","End":"00:20.370","Text":"D, the chromosomes."},{"Start":"00:20.370 ","End":"00:23.405","Text":"Let\u0027s have a good look at our cell."},{"Start":"00:23.405 ","End":"00:25.775","Text":"Here we have the outer membrane."},{"Start":"00:25.775 ","End":"00:27.319","Text":"We have here many organelles,"},{"Start":"00:27.319 ","End":"00:31.070","Text":"Golgi apparatus, mitochondria, lysosomes."},{"Start":"00:31.070 ","End":"00:36.995","Text":"We have the cell nucleus and out of the cell nucleus we have the endoplasmic reticulum,"},{"Start":"00:36.995 ","End":"00:42.230","Text":"which has a smooth part known as the smooth ER and a rough part."},{"Start":"00:42.230 ","End":"00:46.565","Text":"You see all these rough dots here called the rough ER."},{"Start":"00:46.565 ","End":"00:49.410","Text":"What are these bumps here?"},{"Start":"00:50.030 ","End":"00:57.560","Text":"A, tells us that might be the nucleolus but the nucleolus is right here."},{"Start":"00:57.560 ","End":"01:02.585","Text":"Therefore, this cannot be what\u0027s giving to the bumps to the rough ER."},{"Start":"01:02.585 ","End":"01:05.105","Text":"We can cross out nucleolus."},{"Start":"01:05.105 ","End":"01:07.715","Text":"As we\u0027re already looking inside the nucleus."},{"Start":"01:07.715 ","End":"01:13.370","Text":"Let\u0027s have a look at this spin guinea hair-like structure here. What are these?"},{"Start":"01:13.370 ","End":"01:18.335","Text":"Well, this is actually the unfolded chromosomes."},{"Start":"01:18.335 ","End":"01:22.730","Text":"It\u0027s called chromatin when it\u0027s not condensed to this chromosome shape."},{"Start":"01:22.730 ","End":"01:25.010","Text":"Again, these chromosomes are inside"},{"Start":"01:25.010 ","End":"01:29.180","Text":"the nucleus and it certainly cannot give the bumps to the rough ER,"},{"Start":"01:29.180 ","End":"01:31.830","Text":"cross out the chromosomes."},{"Start":"01:32.840 ","End":"01:36.965","Text":"We can get now to answer B, the Golgi apparatus."},{"Start":"01:36.965 ","End":"01:41.075","Text":"The Golgi apparatus is right here, and again,"},{"Start":"01:41.075 ","End":"01:44.515","Text":"we can see that it\u0027s not the bumps on the rough ER,"},{"Start":"01:44.515 ","End":"01:48.325","Text":"which leaves us only answers C, the ribosomes."},{"Start":"01:48.325 ","End":"01:52.610","Text":"The ribosomes can be found in 2 areas in the cell."},{"Start":"01:52.610 ","End":"01:59.840","Text":"The free ribosomes in the cytosol and the ribosomes that are connected to the rough ER."},{"Start":"01:59.840 ","End":"02:02.060","Text":"Look at them closely here."},{"Start":"02:02.060 ","End":"02:06.425","Text":"You can see here how the rough ER and the mRNA,"},{"Start":"02:06.425 ","End":"02:11.570","Text":"which is secreted to the inside of the endoplasmic reticulum is"},{"Start":"02:11.570 ","End":"02:14.420","Text":"processed by all these ribosomes which are"},{"Start":"02:14.420 ","End":"02:17.920","Text":"connected to the membrane of the endoplasmic reticulum,"},{"Start":"02:17.920 ","End":"02:20.470","Text":"making it the ER, rough,"},{"Start":"02:20.470 ","End":"02:24.560","Text":"and correct answer is C, ribosomes."}],"ID":28130},{"Watched":false,"Name":"Exercise 5","Duration":"1m 14s","ChapterTopicVideoID":26996,"CourseChapterTopicPlaylistID":136374,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.380 ","End":"00:05.265","Text":"Which of the following exists only in animal cells?"},{"Start":"00:05.265 ","End":"00:07.605","Text":"A: The centrosome."},{"Start":"00:07.605 ","End":"00:09.930","Text":"B: Nucleoplasm."},{"Start":"00:09.930 ","End":"00:12.495","Text":"C: Envelope membrane,"},{"Start":"00:12.495 ","End":"00:15.330","Text":"or D: Golgi apparatus."},{"Start":"00:15.330 ","End":"00:18.750","Text":"If you want to see the structure of animal cells or else plant cells,"},{"Start":"00:18.750 ","End":"00:21.375","Text":"let\u0027s have a look at this illustration."},{"Start":"00:21.375 ","End":"00:25.485","Text":"All eukaryotic cells have a nucleus."},{"Start":"00:25.485 ","End":"00:29.610","Text":"The inner area of the nucleus including the nucleolus and"},{"Start":"00:29.610 ","End":"00:33.450","Text":"the chromatin are called the nucleoplasm."},{"Start":"00:33.450 ","End":"00:38.160","Text":"Nucleoplasm appears in both animal and plant cells."},{"Start":"00:38.160 ","End":"00:40.590","Text":"We can cross out answer B."},{"Start":"00:40.590 ","End":"00:46.595","Text":"Well, all cells have an envelope membrane around them. So C is wrong."},{"Start":"00:46.595 ","End":"00:49.160","Text":"We can see that the Golgi apparatus,"},{"Start":"00:49.160 ","End":"00:52.475","Text":"which processes proteins and sends them to the right target,"},{"Start":"00:52.475 ","End":"00:55.055","Text":"appears in both cells."},{"Start":"00:55.055 ","End":"00:58.084","Text":"That leaves us with a centrosome."},{"Start":"00:58.084 ","End":"01:03.515","Text":"The centrosome is involved in the process of cell division only in animal cells."},{"Start":"01:03.515 ","End":"01:07.880","Text":"Therefore, our correct answer is A, the centrosome."},{"Start":"01:07.880 ","End":"01:14.760","Text":"This is the only option out of the 4 structures given that exists only in animal cells."}],"ID":28131},{"Watched":false,"Name":"Exercise 6","Duration":"2m 4s","ChapterTopicVideoID":26997,"CourseChapterTopicPlaylistID":136374,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.380 ","End":"00:06.195","Text":"What is the dark zone in the nucleus that produces ribosomes?"},{"Start":"00:06.195 ","End":"00:11.940","Text":"A, the rough ER or endoplasmic reticulum, B,"},{"Start":"00:11.940 ","End":"00:14.505","Text":"the nucleolus, C,"},{"Start":"00:14.505 ","End":"00:17.190","Text":"the smooth endoplasmic reticulum,"},{"Start":"00:17.190 ","End":"00:20.055","Text":"or D, chromosomes."},{"Start":"00:20.055 ","End":"00:22.590","Text":"Let\u0027s have a look at the cells."},{"Start":"00:22.590 ","End":"00:24.645","Text":"We see here liver cells,"},{"Start":"00:24.645 ","End":"00:28.530","Text":"and in the center of the cell we see the dark nucleus."},{"Start":"00:28.530 ","End":"00:32.460","Text":"But the nucleus itself has a condense darker part."},{"Start":"00:32.460 ","End":"00:36.735","Text":"The question is, what is this condensed darker part?"},{"Start":"00:36.735 ","End":"00:40.335","Text":"You already tell us that it produces ribosomes."},{"Start":"00:40.335 ","End":"00:45.730","Text":"The question we\u0027re told that this darker area produces the ribosomes."},{"Start":"00:45.730 ","End":"00:48.635","Text":"Here we have an illustration of the cell."},{"Start":"00:48.635 ","End":"00:50.270","Text":"We have the nucleus,"},{"Start":"00:50.270 ","End":"00:54.185","Text":"and in the center we have this extra dark zone."},{"Start":"00:54.185 ","End":"00:56.850","Text":"Let\u0027s zoom in on it."},{"Start":"00:56.920 ","End":"01:00.215","Text":"Here we got the nucleus."},{"Start":"01:00.215 ","End":"01:05.465","Text":"The nuclear envelope stems out to the endoplasmic reticulum,"},{"Start":"01:05.465 ","End":"01:07.040","Text":"which has 2 parts."},{"Start":"01:07.040 ","End":"01:10.640","Text":"The rough endoplasmic reticulum with all these dots,"},{"Start":"01:10.640 ","End":"01:12.590","Text":"which are actually the ribosomes,"},{"Start":"01:12.590 ","End":"01:15.350","Text":"and we have here the smooth area that doesn\u0027t"},{"Start":"01:15.350 ","End":"01:19.045","Text":"have ribosomes called the smooth endoplasmic reticulum."},{"Start":"01:19.045 ","End":"01:23.515","Text":"Inside the nucleus, we have chromatin,"},{"Start":"01:23.515 ","End":"01:26.465","Text":"which are the unconvinced chromosomes."},{"Start":"01:26.465 ","End":"01:30.050","Text":"In the center, we have the nucleolus,"},{"Start":"01:30.050 ","End":"01:33.455","Text":"which is the area where the ribosomal RNA forms,"},{"Start":"01:33.455 ","End":"01:37.490","Text":"eventually forming the ribosomes will indicted here."},{"Start":"01:37.490 ","End":"01:42.210","Text":"Some of them are actually also free in the cell."},{"Start":"01:42.970 ","End":"01:47.125","Text":"What is the dark zone and the nucleus that produces the ribosomes?"},{"Start":"01:47.125 ","End":"01:51.380","Text":"Well, it\u0027s not the rough endoplasmic reticulum, which is this area."},{"Start":"01:51.380 ","End":"01:54.380","Text":"It\u0027s not the smooth endoplasmic reticulum either."},{"Start":"01:54.380 ","End":"01:56.330","Text":"It can\u0027t be the chromosomes either."},{"Start":"01:56.330 ","End":"01:59.915","Text":"Here we have the unconvinced chromatin that really doesn\u0027t show up."},{"Start":"01:59.915 ","End":"02:02.300","Text":"Therefore, we\u0027re left with the nucleolus,"},{"Start":"02:02.300 ","End":"02:04.560","Text":"which is the correct answer."}],"ID":28132},{"Watched":false,"Name":"Exercise 7","Duration":"3m 12s","ChapterTopicVideoID":26989,"CourseChapterTopicPlaylistID":136374,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.530 ","End":"00:04.710","Text":"Diseased animal cells may produce molecules that"},{"Start":"00:04.710 ","End":"00:09.150","Text":"activate death cascades to kill the cells in a controlled manner."},{"Start":"00:09.150 ","End":"00:13.980","Text":"Why would neighboring healthy cells also die in this process?"},{"Start":"00:13.980 ","End":"00:18.135","Text":"A, the death molecule is passed through desmosomes."},{"Start":"00:18.135 ","End":"00:22.440","Text":"B, the death molecules pass through plasmodesmata."},{"Start":"00:22.440 ","End":"00:26.805","Text":"C, the death molecule disrupts the extracellular matrix."},{"Start":"00:26.805 ","End":"00:33.555","Text":"Or d, the death molecule passes through gap junctions. What\u0027s the story here?"},{"Start":"00:33.555 ","End":"00:34.805","Text":"We have a cell here,"},{"Start":"00:34.805 ","End":"00:37.245","Text":"let\u0027s theoretically say it\u0027s the cell,"},{"Start":"00:37.245 ","End":"00:40.620","Text":"and it has a problem,"},{"Start":"00:40.620 ","End":"00:42.140","Text":"some disease tactic,"},{"Start":"00:42.140 ","End":"00:44.090","Text":"and decides to kill itself,"},{"Start":"00:44.090 ","End":"00:46.645","Text":"so the disease will stop to spread."},{"Start":"00:46.645 ","End":"00:49.230","Text":"It has this death molecule,"},{"Start":"00:49.230 ","End":"00:56.395","Text":"and scientists noticed that also the cells around the disease cells are starting to die."},{"Start":"00:56.395 ","End":"01:00.140","Text":"The question is, how is the death molecule passing out of"},{"Start":"01:00.140 ","End":"01:05.735","Text":"the first cell and then reaching the other cells?"},{"Start":"01:05.735 ","End":"01:09.560","Text":"Our options are through desmosomes,"},{"Start":"01:09.560 ","End":"01:13.850","Text":"plasmodesmata, by disrupting the extracellular matrix,"},{"Start":"01:13.850 ","End":"01:15.860","Text":"or through the gap junctions."},{"Start":"01:15.860 ","End":"01:18.245","Text":"Let\u0027s have a look at these structures."},{"Start":"01:18.245 ","End":"01:20.780","Text":"Here we\u0027ve got cell tissue within"},{"Start":"01:20.780 ","End":"01:24.920","Text":"cellular cells and here we\u0027re looking at one specific cell,"},{"Start":"01:24.920 ","End":"01:26.450","Text":"we\u0027re looking at the inside of it."},{"Start":"01:26.450 ","End":"01:29.599","Text":"There are several types of intercellular junctions."},{"Start":"01:29.599 ","End":"01:32.735","Text":"Here we\u0027re asked about the desmosomes."},{"Start":"01:32.735 ","End":"01:36.395","Text":"The desmosomes are also known as anchoring junctions."},{"Start":"01:36.395 ","End":"01:39.530","Text":"They connect adjacent cells very tightly,"},{"Start":"01:39.530 ","End":"01:43.760","Text":"forming strong sheets of tissue that can withstand a lot of pressure."},{"Start":"01:43.760 ","End":"01:50.180","Text":"The desmosomes hold the cells together rather than passing death molecules around."},{"Start":"01:50.180 ","End":"01:52.690","Text":"Therefore, we can cross out a."},{"Start":"01:52.690 ","End":"01:54.800","Text":"Now where are plasmodesmata?"},{"Start":"01:54.800 ","End":"01:56.295","Text":"We don\u0027t see them at all here."},{"Start":"01:56.295 ","End":"02:00.665","Text":"That\u0027s because plasmodesmata don\u0027t appear in animal cells at all."},{"Start":"02:00.665 ","End":"02:05.285","Text":"These are indeed perforated channels between adjacent cells,"},{"Start":"02:05.285 ","End":"02:10.265","Text":"allowing adjacent cells to share water and other molecules with each other."},{"Start":"02:10.265 ","End":"02:13.955","Text":"But the plasmodesmata exists only in plant cells."},{"Start":"02:13.955 ","End":"02:20.225","Text":"Therefore, the plasmodesmata cannot explain a death molecule moving within animal cells."},{"Start":"02:20.225 ","End":"02:22.500","Text":"So we can cross out B too."},{"Start":"02:22.500 ","End":"02:26.705","Text":"C, the death molecule disrupts the extracellular matrix."},{"Start":"02:26.705 ","End":"02:30.260","Text":"So we\u0027re back to the other illustration, the animal cells,"},{"Start":"02:30.260 ","End":"02:33.710","Text":"and the extracellular matrix is,"},{"Start":"02:33.710 ","End":"02:35.345","Text":"well, it\u0027s out of the cells."},{"Start":"02:35.345 ","End":"02:38.555","Text":"So even if the extracellular matrix is disrupted,"},{"Start":"02:38.555 ","End":"02:43.648","Text":"it should not explain how the death molecule moves between cells."},{"Start":"02:43.648 ","End":"02:46.680","Text":"We cross out C. We\u0027re left with"},{"Start":"02:46.680 ","End":"02:50.090","Text":"the answer D. The death molecule passes through gap junctions."},{"Start":"02:50.090 ","End":"02:52.295","Text":"Gap junctions, as you can see here,"},{"Start":"02:52.295 ","End":"02:57.085","Text":"are actually the equivalent of plasmodesmata in animal cells."},{"Start":"02:57.085 ","End":"03:00.575","Text":"These are channels that allow adjacent cells to share water,"},{"Start":"03:00.575 ","End":"03:03.094","Text":"ions, and other molecules."},{"Start":"03:03.094 ","End":"03:07.490","Text":"It would make a lot of sense that if death molecule is shared between cells,"},{"Start":"03:07.490 ","End":"03:09.920","Text":"it must be passing through gap junctions,"},{"Start":"03:09.920 ","End":"03:12.720","Text":"which is indeed the correct answer."}],"ID":28133},{"Watched":false,"Name":"Exercise 8","Duration":"1m 51s","ChapterTopicVideoID":26990,"CourseChapterTopicPlaylistID":136374,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.410 ","End":"00:04.785","Text":"What is the structure that prokaryotes lack?"},{"Start":"00:04.785 ","End":"00:09.620","Text":"A, DNA or genetic material whatsoever; B,"},{"Start":"00:09.620 ","End":"00:12.320","Text":"a cell membrane; C,"},{"Start":"00:12.320 ","End":"00:14.210","Text":"a cell wall;"},{"Start":"00:14.210 ","End":"00:17.170","Text":"or D, a nucleus."},{"Start":"00:17.170 ","End":"00:21.015","Text":"Let\u0027s have a look at a prokaryote to understand better."},{"Start":"00:21.015 ","End":"00:23.715","Text":"We\u0027ve got our bacteria here,"},{"Start":"00:23.715 ","End":"00:29.295","Text":"and of course it has DNA as any other living organism must have."},{"Start":"00:29.295 ","End":"00:36.375","Text":"Therefore, we can cross out A. Prokaryotes do have DNA or genetic material."},{"Start":"00:36.375 ","End":"00:40.010","Text":"B, a cell membrane."},{"Start":"00:40.010 ","End":"00:43.985","Text":"We\u0027ve gotten here, it\u0027s orange here, the plasma membrane."},{"Start":"00:43.985 ","End":"00:46.265","Text":"All cells have a membrane,"},{"Start":"00:46.265 ","End":"00:49.430","Text":"which is a bi-layer of phospholipids."},{"Start":"00:49.430 ","End":"00:52.390","Text":"A cell membrane we can erase too."},{"Start":"00:52.390 ","End":"00:54.980","Text":"C, a cell wall."},{"Start":"00:54.980 ","End":"01:03.875","Text":"We\u0027ve got here this more pale yellow in-between the cell membrane and the yellow capsule."},{"Start":"01:03.875 ","End":"01:05.420","Text":"We\u0027ve got a cell wall."},{"Start":"01:05.420 ","End":"01:08.405","Text":"All prokaryotes have a cell wall."},{"Start":"01:08.405 ","End":"01:13.310","Text":"Some of them even have a capsule secreted outside of the cell wall."},{"Start":"01:13.310 ","End":"01:15.470","Text":"Therefore, since not only some,"},{"Start":"01:15.470 ","End":"01:18.080","Text":"but all prokaryotes have a cell wall,"},{"Start":"01:18.080 ","End":"01:24.215","Text":"we can cross out answer C. We\u0027re left with answer D. Let\u0027s check if that\u0027s right."},{"Start":"01:24.215 ","End":"01:26.660","Text":"The prokaryotes have a nucleus."},{"Start":"01:26.660 ","End":"01:28.249","Text":"What is a nucleus?"},{"Start":"01:28.249 ","End":"01:30.830","Text":"If we look at the eukaryotic cell,"},{"Start":"01:30.830 ","End":"01:36.214","Text":"we can see that the DNA is engulfed in a double membrane capsule called the nucleus."},{"Start":"01:36.214 ","End":"01:40.010","Text":"This nucleus is not present in the prokaryotic cell where"},{"Start":"01:40.010 ","End":"01:45.830","Text":"the DNA or the chromatin is not engulfed in any membraned structure."},{"Start":"01:45.830 ","End":"01:49.040","Text":"Our answer is D, a nucleus,"},{"Start":"01:49.040 ","End":"01:52.020","Text":"prokaryotes lack a nucleus."}],"ID":28134},{"Watched":false,"Name":"Exercise 9","Duration":"3m 6s","ChapterTopicVideoID":26991,"CourseChapterTopicPlaylistID":136374,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.440 ","End":"00:06.330","Text":"Which part of the cell makes the basic amino acid chain for proteins?"},{"Start":"00:06.330 ","End":"00:11.220","Text":"We know that the primary structure of any protein is a polypeptide,"},{"Start":"00:11.220 ","End":"00:15.510","Text":"which has actually many amino acids strung together."},{"Start":"00:15.510 ","End":"00:19.380","Text":"The question is, which part of the cell is the"},{"Start":"00:19.380 ","End":"00:24.150","Text":"one that connects these amino acids to each other in the right order?"},{"Start":"00:24.150 ","End":"00:27.810","Text":"Let\u0027s look at answer A, ribosomes."},{"Start":"00:27.810 ","End":"00:33.065","Text":"A ribosome is a cellular machine comprised of two sub-units,"},{"Start":"00:33.065 ","End":"00:34.460","Text":"the small sub-unit,"},{"Start":"00:34.460 ","End":"00:35.870","Text":"and the large sub-unit."},{"Start":"00:35.870 ","End":"00:43.310","Text":"These both together, the large sub-unit and the small sub-unit wrap the mRNA,"},{"Start":"00:43.310 ","End":"00:45.395","Text":"which carries the genetic code."},{"Start":"00:45.395 ","End":"00:49.163","Text":"The tRNA fits like a key into the lock."},{"Start":"00:49.163 ","End":"00:52.655","Text":"Each tRNA carries the right amino acid"},{"Start":"00:52.655 ","End":"00:57.170","Text":"that fits the genetic code of the three bases of mRNA."},{"Start":"00:57.170 ","End":"01:00.170","Text":"In this way, one after another,"},{"Start":"01:00.170 ","End":"01:06.050","Text":"the tRNA molecules bring the amino acids and the ribosomes connect them to each other,"},{"Start":"01:06.050 ","End":"01:09.010","Text":"forming the growing peptide chain."},{"Start":"01:09.010 ","End":"01:10.750","Text":"Have a closer look at this."},{"Start":"01:10.750 ","End":"01:13.525","Text":"If this is our two unit ribosome,"},{"Start":"01:13.525 ","End":"01:15.565","Text":"and we have the mRNA here,"},{"Start":"01:15.565 ","End":"01:18.970","Text":"each three bases fit like a key to"},{"Start":"01:18.970 ","End":"01:24.985","Text":"a lock of a tRNA molecule carrying a single amino acid."},{"Start":"01:24.985 ","End":"01:27.070","Text":"As they pass through here,"},{"Start":"01:27.070 ","End":"01:29.920","Text":"they anther amino acids onto the growing chain."},{"Start":"01:29.920 ","End":"01:32.365","Text":"Chain gets longer, and longer,"},{"Start":"01:32.365 ","End":"01:38.660","Text":"and longer still, eventually ending up with the primary structure of the protein."},{"Start":"01:38.660 ","End":"01:41.230","Text":"The ribosome seem to be correct,"},{"Start":"01:41.230 ","End":"01:43.120","Text":"but before we circle an answer,"},{"Start":"01:43.120 ","End":"01:45.115","Text":"we\u0027ll always look at the other answers too,"},{"Start":"01:45.115 ","End":"01:48.955","Text":"just to make sure that none of them are even better than the answer we already got."},{"Start":"01:48.955 ","End":"01:52.370","Text":"B is the endoplasmic reticulum."},{"Start":"01:52.370 ","End":"01:55.330","Text":"The endoplasmic reticulum is right here."},{"Start":"01:55.330 ","End":"01:58.270","Text":"It does carry ribosomes on the rough part,"},{"Start":"01:58.270 ","End":"02:01.090","Text":"but it itself is not what makes"},{"Start":"02:01.090 ","End":"02:06.320","Text":"the basic amino acid chain for the proteins. We can cross out b."},{"Start":"02:06.320 ","End":"02:08.315","Text":"Let us look at and just c,"},{"Start":"02:08.315 ","End":"02:11.500","Text":"the Golgi apparatus here in turquoise."},{"Start":"02:11.500 ","End":"02:14.785","Text":"Let\u0027s zoom in. What does the Golgi apparatus do?"},{"Start":"02:14.785 ","End":"02:17.590","Text":"It receives these membranous pecks from"},{"Start":"02:17.590 ","End":"02:21.760","Text":"the endoplasmic reticulum with the newly folded proteins."},{"Start":"02:21.760 ","End":"02:23.740","Text":"Here it finalizes the folding,"},{"Start":"02:23.740 ","End":"02:26.020","Text":"the secondary and tertiary structures,"},{"Start":"02:26.020 ","End":"02:30.850","Text":"and then packages them and sends them out to the right areas in the cell."},{"Start":"02:30.850 ","End":"02:34.450","Text":"The Golgi apparatus is important for the folding of the proteins,"},{"Start":"02:34.450 ","End":"02:37.520","Text":"but not for making the basic amino acid chain."},{"Start":"02:37.520 ","End":"02:40.460","Text":"We can cross out c, Golgi apparatus."},{"Start":"02:40.460 ","End":"02:44.495","Text":"Let\u0027s have a look at d, the centriole."},{"Start":"02:44.495 ","End":"02:48.290","Text":"Well, the centrioles are important in cell division of animal cells,"},{"Start":"02:48.290 ","End":"02:52.595","Text":"but they have nothing to do with building the amino acid chain for the proteins."},{"Start":"02:52.595 ","End":"02:55.475","Text":"Therefore, we can cross out d, centrioles."},{"Start":"02:55.475 ","End":"02:57.050","Text":"I\u0027ll get back to the ribosomes,"},{"Start":"02:57.050 ","End":"02:59.645","Text":"which actually does what we\u0027re asking for,"},{"Start":"02:59.645 ","End":"03:02.420","Text":"building the basic amino acid chain for proteins."},{"Start":"03:02.420 ","End":"03:06.820","Text":"The correct answer is a, ribosomes."}],"ID":28135}],"Thumbnail":null,"ID":136374},{"Name":"Cell Membranes","TopicPlaylistFirstVideoID":0,"Duration":null,"Videos":[{"Watched":false,"Name":"Cell Membranes- Introduction","Duration":"10m 39s","ChapterTopicVideoID":24918,"CourseChapterTopicPlaylistID":136375,"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. You\u0027re welcome to the introduction about cell membranes."},{"Start":"00:04.590 ","End":"00:06.270","Text":"By the end of this section,"},{"Start":"00:06.270 ","End":"00:10.500","Text":"you\u0027ll be able to understand the cell membrane fluid mosaic model,"},{"Start":"00:10.500 ","End":"00:15.720","Text":"describe phospholipid protein and carbohydrate functions in the membranes,"},{"Start":"00:15.720 ","End":"00:18.600","Text":"and discuss the membrane fluidity."},{"Start":"00:18.600 ","End":"00:22.380","Text":"The cell membrane is a biological structure that separates"},{"Start":"00:22.380 ","End":"00:25.679","Text":"the interior of all cells from the outside environment,"},{"Start":"00:25.679 ","End":"00:29.055","Text":"also known as the extracellular space."},{"Start":"00:29.055 ","End":"00:38.370","Text":"This is the intracellular space and this is the extracellular space."},{"Start":"00:38.560 ","End":"00:44.765","Text":"This protects the cell from its environment and helps maintain its inner composition."},{"Start":"00:44.765 ","End":"00:47.795","Text":"The cell membrane is built of a lipid bilayer."},{"Start":"00:47.795 ","End":"00:52.490","Text":"Here we see a double layer of phospholipids."},{"Start":"00:52.490 ","End":"00:55.850","Text":"Also is embedded with proteins."},{"Start":"00:55.850 ","End":"00:59.768","Text":"Different proteins cross right through it."},{"Start":"00:59.768 ","End":"01:05.380","Text":"Thus it controls the movement of substances in and out of the cells and organelles."},{"Start":"01:05.380 ","End":"01:09.470","Text":"It\u0027s selectively permeable to ions and organic molecules,"},{"Start":"01:09.470 ","End":"01:11.990","Text":"meaning that it\u0027s selected with the ions and"},{"Start":"01:11.990 ","End":"01:15.340","Text":"organic molecules it lets come in and out of the cell."},{"Start":"01:15.340 ","End":"01:18.680","Text":"The membrane also contains proteins that act as"},{"Start":"01:18.680 ","End":"01:23.585","Text":"extracellular input receivers and intracellular processing activators."},{"Start":"01:23.585 ","End":"01:29.405","Text":"That means that a hormone secreted faraway may reach the cell here."},{"Start":"01:29.405 ","End":"01:34.580","Text":"The cell receives this input using these proteins and"},{"Start":"01:34.580 ","End":"01:39.110","Text":"sends the message into the cell using other membrane proteins as activators,"},{"Start":"01:39.110 ","End":"01:41.675","Text":"starting a cellular process."},{"Start":"01:41.675 ","End":"01:45.350","Text":"The cell membrane also includes carbohydrates like"},{"Start":"01:45.350 ","End":"01:51.049","Text":"this glycoprotein that function in the identification in cell-cell recognition."},{"Start":"01:51.049 ","End":"01:53.855","Text":"Let\u0027s have a look at the phospholipids."},{"Start":"01:53.855 ","End":"01:57.595","Text":"These are the most abundant lipids in the plasma membrane."},{"Start":"01:57.595 ","End":"02:00.550","Text":"These are amphipathic molecules,"},{"Start":"02:00.550 ","End":"02:02.920","Text":"meaning that part of them are hydrophilic."},{"Start":"02:02.920 ","End":"02:06.070","Text":"Another side of this molecule is hydrophobic,"},{"Start":"02:06.070 ","End":"02:07.760","Text":"meaning it repels water."},{"Start":"02:07.760 ","End":"02:17.405","Text":"In this case, the head of the phospholipid is hydrophilic, meaning water-loving."},{"Start":"02:17.405 ","End":"02:24.160","Text":"The tails, which are either saturated or unsaturated fatty acids are hydrophobic,"},{"Start":"02:24.160 ","End":"02:30.325","Text":"meaning that they repel water."},{"Start":"02:30.325 ","End":"02:33.265","Text":"This is very important."},{"Start":"02:33.265 ","End":"02:36.430","Text":"The reason is that the membrane surfaces that face"},{"Start":"02:36.430 ","End":"02:41.485","Text":"the cell\u0027s interior and exterior are both hydrophilic, water-loving."},{"Start":"02:41.485 ","End":"02:45.935","Text":"Here we have an aqueous environment."},{"Start":"02:45.935 ","End":"02:49.130","Text":"Here we have an aqueous environment and"},{"Start":"02:49.130 ","End":"02:53.540","Text":"the hydrophilic heads are facing the aqueous environment."},{"Start":"02:53.540 ","End":"02:56.060","Text":"The cell membranes interior."},{"Start":"02:56.060 ","End":"03:01.880","Text":"This area here is hydrophobic and it does not interact with water."},{"Start":"03:01.880 ","End":"03:06.230","Text":"This is a very stable structure, and here\u0027s why."},{"Start":"03:06.230 ","End":"03:11.690","Text":"We know that if we drop oil into a cup of water and the oil is hydrophobic,"},{"Start":"03:11.690 ","End":"03:13.235","Text":"meaning it repels water,"},{"Start":"03:13.235 ","End":"03:16.025","Text":"the oil droplets won\u0027t mix with the water."},{"Start":"03:16.025 ","End":"03:17.905","Text":"They\u0027ll connect with each other."},{"Start":"03:17.905 ","End":"03:22.100","Text":"What happens if we drop phospholipids into the water?"},{"Start":"03:22.100 ","End":"03:23.825","Text":"In an aqueous solution,"},{"Start":"03:23.825 ","End":"03:26.900","Text":"phospholipids arrange themselves with their polar heads facing"},{"Start":"03:26.900 ","End":"03:30.515","Text":"outwards and your hydrophobic tails facing inwards,"},{"Start":"03:30.515 ","End":"03:32.885","Text":"and then this happens naturally."},{"Start":"03:32.885 ","End":"03:36.890","Text":"So here we can see that the hydrophobic tails are all facing"},{"Start":"03:36.890 ","End":"03:41.210","Text":"inwards and the hydrophilic heads are all facing outwards."},{"Start":"03:41.210 ","End":"03:44.870","Text":"This structure is called a micelle."},{"Start":"03:44.870 ","End":"03:48.410","Text":"This is actually a single-layer lipids sphere."},{"Start":"03:48.410 ","End":"03:51.185","Text":"These are very little spheres."},{"Start":"03:51.185 ","End":"03:54.410","Text":"If we drop phospholipids into a cup of water,"},{"Start":"03:54.410 ","End":"03:56.570","Text":"we might see another structure here."},{"Start":"03:56.570 ","End":"04:00.740","Text":"In this structure here we have a bilayer of the phospholipids."},{"Start":"04:00.740 ","End":"04:03.545","Text":"Here it\u0027s drawn more nicely."},{"Start":"04:03.545 ","End":"04:05.765","Text":"We have actually a sheet."},{"Start":"04:05.765 ","End":"04:09.230","Text":"Again, here is a hydrophilic, water-loving,"},{"Start":"04:09.230 ","End":"04:14.900","Text":"heads of the phospholipids face the water on either side of the bilayer."},{"Start":"04:14.900 ","End":"04:19.415","Text":"Only in the middle we have our hydrophobic area."},{"Start":"04:19.415 ","End":"04:23.975","Text":"If we just take a look here, we see that the heads are hydrophilic."},{"Start":"04:23.975 ","End":"04:25.805","Text":"They fit very well with"},{"Start":"04:25.805 ","End":"04:30.920","Text":"the aqueous environment and both ends and the middle is hydrophobic."},{"Start":"04:30.920 ","End":"04:34.400","Text":"This makes a barrier since any ions that are"},{"Start":"04:34.400 ","End":"04:38.300","Text":"hydrophilic cannot pass through the hydrophobic area."},{"Start":"04:38.300 ","End":"04:44.670","Text":"Now, what would happen if this bilayer just go in a circle?"},{"Start":"04:45.050 ","End":"04:49.025","Text":"Here we have an inner structure,"},{"Start":"04:49.025 ","End":"04:52.415","Text":"which is hydrophilic, water-loving,"},{"Start":"04:52.415 ","End":"04:55.565","Text":"an outward structure which is hydrophilic water-loving,"},{"Start":"04:55.565 ","End":"05:00.620","Text":"and an inner structure that\u0027s hydrophobic water-repelling."},{"Start":"05:00.620 ","End":"05:06.290","Text":"This is the lipid bilayer sphere that we know so well in a cell."},{"Start":"05:06.290 ","End":"05:08.180","Text":"This is exactly how it\u0027s arranged."},{"Start":"05:08.180 ","End":"05:11.780","Text":"This arrangement is very stable naturally."},{"Start":"05:11.780 ","End":"05:17.810","Text":"The fluid mosaic model is the proposed model for the dynamics of the cell membrane."},{"Start":"05:17.810 ","End":"05:22.460","Text":"Phospholipids are responsible for the plasma membranes\u0027 dynamic structure."},{"Start":"05:22.460 ","End":"05:25.355","Text":"We\u0027ll see what we mean by the dynamic structure."},{"Start":"05:25.355 ","End":"05:31.100","Text":"The membrane is actually a fluid mosaic of phospholipid molecules embedded with proteins,"},{"Start":"05:31.100 ","End":"05:34.025","Text":"carbohydrates, and cholesterol molecules."},{"Start":"05:34.025 ","End":"05:37.025","Text":"That means that we have here many molecules,"},{"Start":"05:37.025 ","End":"05:39.605","Text":"these phospholipids that are actually fluid."},{"Start":"05:39.605 ","End":"05:41.600","Text":"There\u0027s nothing holding it in place."},{"Start":"05:41.600 ","End":"05:44.950","Text":"Therefore this phospholipid may move to here,"},{"Start":"05:44.950 ","End":"05:46.400","Text":"and this one may move to here."},{"Start":"05:46.400 ","End":"05:48.275","Text":"They do move all the time."},{"Start":"05:48.275 ","End":"05:51.590","Text":"Very much like you might see in the structure of a soap bubble."},{"Start":"05:51.590 ","End":"05:53.180","Text":"If you look closer at the soap bubble,"},{"Start":"05:53.180 ","End":"05:55.910","Text":"you can see that the soap and the water are moving"},{"Start":"05:55.910 ","End":"06:00.935","Text":"around while the spherical structure is still maintained."},{"Start":"06:00.935 ","End":"06:03.665","Text":"Back-test cell membrane."},{"Start":"06:03.665 ","End":"06:08.360","Text":"Most of the lipids and some of the proteins can lose sight of it within the membrane."},{"Start":"06:08.360 ","End":"06:11.690","Text":"They\u0027re always moving around in a very fluid way."},{"Start":"06:11.690 ","End":"06:13.550","Text":"On the other hand, only in"},{"Start":"06:13.550 ","End":"06:18.095","Text":"rare occasions do the phospholipids flip-flop from side to side,"},{"Start":"06:18.095 ","End":"06:20.450","Text":"because that would mean that the hydrophilic,"},{"Start":"06:20.450 ","End":"06:24.750","Text":"water-loving head, will have to pass through the hydrophobic area."},{"Start":"06:24.880 ","End":"06:27.650","Text":"Of course, protein, lipid,"},{"Start":"06:27.650 ","End":"06:31.715","Text":"and carbohydrate proportions in the plasma membrane vary with cell type,"},{"Start":"06:31.715 ","End":"06:35.450","Text":"meaning that different cells have different proteins,"},{"Start":"06:35.450 ","End":"06:38.740","Text":"different lipids, and different cholesterol proportions."},{"Start":"06:38.740 ","End":"06:42.950","Text":"All the way it\u0027s explained that everything here is very dynamic and very fluid."},{"Start":"06:42.950 ","End":"06:47.585","Text":"Some of the membrane proteins are held in place by attachment to the cytoskeleton."},{"Start":"06:47.585 ","End":"06:50.390","Text":"That means that if we have an outer structure"},{"Start":"06:50.390 ","End":"06:53.480","Text":"or even a protein that we want to be kept in place,"},{"Start":"06:53.480 ","End":"06:57.545","Text":"it\u0027s anchored to the inner cytoskeleton of the cell,"},{"Start":"06:57.545 ","End":"07:04.190","Text":"like if you want to have a flagellum or anything that we want to keep its place,"},{"Start":"07:04.190 ","End":"07:07.890","Text":"it\u0027s going to be anchored here to the cytoskeleton."},{"Start":"07:08.050 ","End":"07:13.235","Text":"Of course, the rate of fluidity of the membrane is very important to maintain."},{"Start":"07:13.235 ","End":"07:15.080","Text":"If the membrane is too fluid,"},{"Start":"07:15.080 ","End":"07:17.194","Text":"the cell might lose its shape altogether."},{"Start":"07:17.194 ","End":"07:19.340","Text":"When a membrane is solidified,"},{"Start":"07:19.340 ","End":"07:21.505","Text":"it may become inactive."},{"Start":"07:21.505 ","End":"07:26.945","Text":"Membranes might solidify under certain temperatures if it gets too cold."},{"Start":"07:26.945 ","End":"07:32.600","Text":"Membranes are constructed of lipids with different kinds of fatty acid chains."},{"Start":"07:32.600 ","End":"07:36.395","Text":"Phospholipids with unsaturated fatty acids"},{"Start":"07:36.395 ","End":"07:40.265","Text":"are more fluid than those rich in saturated fatty acids."},{"Start":"07:40.265 ","End":"07:44.615","Text":"That\u0027s because the saturated fatty acids are very straight."},{"Start":"07:44.615 ","End":"07:49.869","Text":"They pack easily just like we could pack matches in a little box."},{"Start":"07:49.869 ","End":"07:52.965","Text":"Unsaturated tails are bent."},{"Start":"07:52.965 ","End":"07:54.740","Text":"Therefore there are a lot harder to pack."},{"Start":"07:54.740 ","End":"07:59.990","Text":"They prevent the packing and therefore they\u0027re fluid even in lower temperatures so"},{"Start":"07:59.990 ","End":"08:02.870","Text":"that every living organism has to maintain"},{"Start":"08:02.870 ","End":"08:06.095","Text":"the fluidity if its cells in an environment that it lives,"},{"Start":"08:06.095 ","End":"08:10.475","Text":"and membranes are built out of different phospholipids."},{"Start":"08:10.475 ","End":"08:15.770","Text":"In animal cells, steroid cholesterol is present between the phospholipids."},{"Start":"08:15.770 ","End":"08:20.480","Text":"This strongly affects the membrane fluidity at different temperatures."},{"Start":"08:20.480 ","End":"08:26.195","Text":"Here\u0027s how. So here we have the cholesterol in-between the phospholipids."},{"Start":"08:26.195 ","End":"08:28.535","Text":"At normal body temperature."},{"Start":"08:28.535 ","End":"08:33.785","Text":"The cholesterol makes the membrane less fluid by restraining phospholipids\u0027 movement."},{"Start":"08:33.785 ","End":"08:35.280","Text":"If it holds them together,"},{"Start":"08:35.280 ","End":"08:38.375","Text":"they are moving less and everything has less fluid."},{"Start":"08:38.375 ","End":"08:41.390","Text":"On the other hand, at lower temperatures,"},{"Start":"08:41.390 ","End":"08:44.105","Text":"and enters the close packing of phospholipids."},{"Start":"08:44.105 ","End":"08:47.000","Text":"It stands in between them and doesn\u0027t let them pack so well."},{"Start":"08:47.000 ","End":"08:51.125","Text":"This way it lowers the temperature required for the membrane to solidify."},{"Start":"08:51.125 ","End":"08:54.635","Text":"Meaning, at higher temperatures it restrains"},{"Start":"08:54.635 ","End":"08:59.225","Text":"the fluidity and at lower temperatures it restrains the solidity."},{"Start":"08:59.225 ","End":"09:04.380","Text":"Therefore, the cholesterol can be thought of as a temperature buffer for the membrane."},{"Start":"09:04.630 ","End":"09:07.970","Text":"After speaking with someone who had the phospholipids,"},{"Start":"09:07.970 ","End":"09:11.210","Text":"let\u0027s have a look at the membrane proteins and their function."},{"Start":"09:11.210 ","End":"09:14.390","Text":"Membrane proteins are categorized by the way they\u0027re"},{"Start":"09:14.390 ","End":"09:18.385","Text":"embedded in the fluid matrix of the lipid bilayer."},{"Start":"09:18.385 ","End":"09:21.890","Text":"Some associate with a single layer."},{"Start":"09:21.890 ","End":"09:25.520","Text":"It can be inner like that peripheral membrane protein or you can"},{"Start":"09:25.520 ","End":"09:29.270","Text":"find a protein that\u0027s connected to the outer layer of the phospholipid membrane."},{"Start":"09:29.270 ","End":"09:32.750","Text":"While others stretch from 1 side to the other,"},{"Start":"09:32.750 ","End":"09:34.745","Text":"and they\u0027re exposed on either side."},{"Start":"09:34.745 ","End":"09:40.055","Text":"Like this single-pass transmembrane protein or this multi-pass transmembrane protein,"},{"Start":"09:40.055 ","End":"09:42.515","Text":"it goes back and forth several times."},{"Start":"09:42.515 ","End":"09:45.890","Text":"These are proteins that stretch from side to side are"},{"Start":"09:45.890 ","End":"09:50.795","Text":"integral proteins because they are integrated in the membrane structure."},{"Start":"09:50.795 ","End":"09:53.075","Text":"One of the functions,"},{"Start":"09:53.075 ","End":"09:56.120","Text":"an example for a function of this protein"},{"Start":"09:56.120 ","End":"09:59.825","Text":"would be allowing the passage of hydrophilic substances,"},{"Start":"09:59.825 ","End":"10:03.725","Text":"which otherwise would not be able to pass the hydrophobic zone here,"},{"Start":"10:03.725 ","End":"10:06.770","Text":"this protein might let and pass by creating"},{"Start":"10:06.770 ","End":"10:11.825","Text":"a hydrophilic zone that crosses the hydrophobic membrane."},{"Start":"10:11.825 ","End":"10:17.285","Text":"Of course, different cell types vary in their composition of membrane proteins."},{"Start":"10:17.285 ","End":"10:22.430","Text":"In this section, we understood the cell membrane fluid mosaic model and"},{"Start":"10:22.430 ","End":"10:27.365","Text":"describe phospholipid protein and carbohydrate functions in membranes."},{"Start":"10:27.365 ","End":"10:31.070","Text":"We\u0027ve also discussed different aspects of membrane fluidity."},{"Start":"10:31.070 ","End":"10:32.625","Text":"In the coming sections,"},{"Start":"10:32.625 ","End":"10:37.770","Text":"we\u0027ll be speaking about transport across these membranes. I\u0027ll see you there."}],"ID":25831},{"Watched":false,"Name":"Passive Transport","Duration":"13m 15s","ChapterTopicVideoID":24919,"CourseChapterTopicPlaylistID":136375,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.050 ","End":"00:03.720","Text":"Hi, we\u0027re studying cell membranes."},{"Start":"00:03.720 ","End":"00:08.459","Text":"In this section, we\u0027ll be speaking about the passive transport through these membranes."},{"Start":"00:08.459 ","End":"00:10.140","Text":"By the end of this section,"},{"Start":"00:10.140 ","End":"00:14.330","Text":"you\u0027ll be able to understand the osmosis and diffusion processes."},{"Start":"00:14.330 ","End":"00:17.775","Text":"Explain why and how passive transport occurs,"},{"Start":"00:17.775 ","End":"00:22.455","Text":"and define tonicity and its relevance to passive transport."},{"Start":"00:22.455 ","End":"00:25.485","Text":"Let\u0027s define diffusion first."},{"Start":"00:25.485 ","End":"00:29.250","Text":"Diffusion is defined as the net movement of a substance from"},{"Start":"00:29.250 ","End":"00:33.600","Text":"a region of higher concentration to a region of lower concentration."},{"Start":"00:33.600 ","End":"00:35.500","Text":"If we look at this example here,"},{"Start":"00:35.500 ","End":"00:37.805","Text":"we have these pink molecules."},{"Start":"00:37.805 ","End":"00:40.760","Text":"There is a high concentration on the top side of"},{"Start":"00:40.760 ","End":"00:44.465","Text":"the rectangle and the low concentration on the lower side of the rectangle."},{"Start":"00:44.465 ","End":"00:47.360","Text":"We can expect then diffusion and net movement will be"},{"Start":"00:47.360 ","End":"00:51.470","Text":"from high concentration to low concentration."},{"Start":"00:51.470 ","End":"00:55.085","Text":"This movement in diffusion is random,"},{"Start":"00:55.085 ","End":"00:58.550","Text":"but even though each molecule moves randomly,"},{"Start":"00:58.550 ","End":"01:01.760","Text":"the diffusion of molecules may be directional in"},{"Start":"01:01.760 ","End":"01:05.150","Text":"case if there is a difference in concentrations."},{"Start":"01:05.150 ","End":"01:06.875","Text":"How does this occur?"},{"Start":"01:06.875 ","End":"01:10.340","Text":"Now, we have a high concentration of these molecules and all this half of"},{"Start":"01:10.340 ","End":"01:14.375","Text":"the rectangle and a low concentration or zero concentration here."},{"Start":"01:14.375 ","End":"01:20.350","Text":"Since the molecules are moving randomly to all the directions all the time,"},{"Start":"01:20.350 ","End":"01:24.255","Text":"eventually, molecules will be moving out of here."},{"Start":"01:24.255 ","End":"01:29.575","Text":"Since there are no molecules moving inwards or upwards from this end because it\u0027s empty,"},{"Start":"01:29.575 ","End":"01:33.080","Text":"so we\u0027re going to see molecules spread out."},{"Start":"01:37.110 ","End":"01:39.955","Text":"Once the molecules also reach here,"},{"Start":"01:39.955 ","End":"01:41.875","Text":"since here they also move randomly,"},{"Start":"01:41.875 ","End":"01:45.390","Text":"we\u0027ll have the same amount of molecules moving in this direction,"},{"Start":"01:45.390 ","End":"01:47.440","Text":"and then we have molecules moving in this direction."},{"Start":"01:47.440 ","End":"01:51.760","Text":"Therefore, as soon as there is no gradient in concentration,"},{"Start":"01:51.760 ","End":"01:54.265","Text":"we\u0027re going to see a net movement of zero."},{"Start":"01:54.265 ","End":"01:57.025","Text":"But as long as we have a really new concentration,"},{"Start":"01:57.025 ","End":"01:59.830","Text":"we\u0027re going to see that the substance has moved from"},{"Start":"01:59.830 ","End":"02:03.650","Text":"a region of high concentration to a region of low concentration."},{"Start":"02:03.650 ","End":"02:06.860","Text":"Of course, in that case, we\u0027re speaking about diffusion of"},{"Start":"02:06.860 ","End":"02:10.940","Text":"molecules and substances through the cell membrane."},{"Start":"02:10.940 ","End":"02:13.864","Text":"Here, we have two examples."},{"Start":"02:13.864 ","End":"02:16.160","Text":"When there\u0027s a high concentration inside"},{"Start":"02:16.160 ","End":"02:18.500","Text":"the cell and a low concentration outside of the cell,"},{"Start":"02:18.500 ","End":"02:20.150","Text":"the chemical driving force,"},{"Start":"02:20.150 ","End":"02:21.605","Text":"meaning the net diffusion,"},{"Start":"02:21.605 ","End":"02:23.630","Text":"will be outward, out of the cell."},{"Start":"02:23.630 ","End":"02:27.320","Text":"In this example, where molecules are highly concentrated outside"},{"Start":"02:27.320 ","End":"02:30.920","Text":"of the cell and have a very low concentration inside of the cell,"},{"Start":"02:30.920 ","End":"02:33.770","Text":"we can expect the net diffusion when the chemical"},{"Start":"02:33.770 ","End":"02:37.250","Text":"driving force to be driving these molecules into the cell."},{"Start":"02:37.250 ","End":"02:39.979","Text":"But what happen when they reach equilibrium?"},{"Start":"02:39.979 ","End":"02:45.505","Text":"At dynamic equilibrium molecules cross the membrane equally in both directions."},{"Start":"02:45.505 ","End":"02:49.460","Text":"Whether or not there\u0027s a high concentration and low concentration,"},{"Start":"02:49.460 ","End":"02:52.475","Text":"as long as we have an equilibrium between the concentrations,"},{"Start":"02:52.475 ","End":"02:56.890","Text":"molecules will be traveling out and in at the same rate,"},{"Start":"02:56.890 ","End":"02:59.350","Text":"and therefore, the net driving force will be zero."},{"Start":"02:59.350 ","End":"03:01.700","Text":"I\u0027m saying, goes from high concentration in and out."},{"Start":"03:01.700 ","End":"03:03.454","Text":"As long as we have an equilibrium,"},{"Start":"03:03.454 ","End":"03:06.980","Text":"we\u0027ll see the same rate of molecules"},{"Start":"03:06.980 ","End":"03:10.985","Text":"leaving the cell and the same rate of molecules entering the cell."},{"Start":"03:10.985 ","End":"03:16.205","Text":"Therefore again, the net will be zero."},{"Start":"03:16.205 ","End":"03:20.020","Text":"What are the factors that affect diffusion?"},{"Start":"03:20.020 ","End":"03:23.440","Text":"First of all, the extent of the concentration gradient."},{"Start":"03:23.440 ","End":"03:26.275","Text":"The stronger the concentration gradient will be,"},{"Start":"03:26.275 ","End":"03:29.890","Text":"the stronger the chemical driving force of diffusion will be."},{"Start":"03:29.890 ","End":"03:32.770","Text":"The mass of the molecules is very important too,"},{"Start":"03:32.770 ","End":"03:36.460","Text":"because bigger and heavier molecules"},{"Start":"03:36.460 ","End":"03:41.185","Text":"have a harder time moving through substances than fast little ones."},{"Start":"03:41.185 ","End":"03:44.905","Text":"The temperature is also very important because in higher temperatures,"},{"Start":"03:44.905 ","End":"03:46.960","Text":"all molecules are moving around faster,"},{"Start":"03:46.960 ","End":"03:50.635","Text":"and therefore, diffusion will be higher in higher temperatures."},{"Start":"03:50.635 ","End":"03:52.660","Text":"The solvent density, of course,"},{"Start":"03:52.660 ","End":"03:54.160","Text":"is an important factor too."},{"Start":"03:54.160 ","End":"03:56.350","Text":"As you mentioned with the mass of molecules,"},{"Start":"03:56.350 ","End":"03:59.620","Text":"molecules have a harder time moving through dense environments."},{"Start":"03:59.620 ","End":"04:02.750","Text":"Therefore, the more dense the environment will be,"},{"Start":"04:02.750 ","End":"04:04.850","Text":"the slower the diffusion will be."},{"Start":"04:04.850 ","End":"04:07.370","Text":"The solubility is also important because"},{"Start":"04:07.370 ","End":"04:11.240","Text":"highly soluble molecules won\u0027t easily pass through the substance."},{"Start":"04:11.240 ","End":"04:13.520","Text":"The distance, of course, is important because there\u0027s"},{"Start":"04:13.520 ","End":"04:16.225","Text":"longer distances will take more time to travel through."},{"Start":"04:16.225 ","End":"04:19.130","Text":"Let\u0027s have a look at passive transport now."},{"Start":"04:19.130 ","End":"04:21.784","Text":"When we speak about passive transport,"},{"Start":"04:21.784 ","End":"04:23.960","Text":"we\u0027re speaking about transport that does not"},{"Start":"04:23.960 ","End":"04:27.170","Text":"require the cell to exert energy for transport at all."},{"Start":"04:27.170 ","End":"04:29.585","Text":"That\u0027s why we call it passive transport, of course."},{"Start":"04:29.585 ","End":"04:31.110","Text":"In passive transport,"},{"Start":"04:31.110 ","End":"04:32.960","Text":"substances move from an area of"},{"Start":"04:32.960 ","End":"04:37.040","Text":"higher concentration along the gradient to areas of lower concentration,"},{"Start":"04:37.040 ","End":"04:39.935","Text":"just as we previously explained at diffusion."},{"Start":"04:39.935 ","End":"04:43.520","Text":"Non-polar and lipid-soluble material cross through"},{"Start":"04:43.520 ","End":"04:47.060","Text":"the membrane\u0027s hydrophobic lipid core easily. Why is that?"},{"Start":"04:47.060 ","End":"04:50.900","Text":"I want to remind you that the cell membrane is made of a double layer of phospholipids."},{"Start":"04:50.900 ","End":"04:53.990","Text":"Here\u0027s one layer, and here\u0027s the other layer."},{"Start":"04:53.990 ","End":"04:59.070","Text":"The phospholipid has a hydrophobic tail."},{"Start":"04:59.470 ","End":"05:10.260","Text":"This region here is the hydrophobic area here."},{"Start":"05:10.260 ","End":"05:15.590","Text":"Only non-polar and lipid soluble materials might cross through this hydrophobic region."},{"Start":"05:15.590 ","End":"05:25.235","Text":"While the other areas here are hydrophilic,"},{"Start":"05:25.235 ","End":"05:28.700","Text":"meaning water-loving, which is also a hydrophilic."},{"Start":"05:28.700 ","End":"05:31.865","Text":"Polar molecules, like hydrophilic molecules,"},{"Start":"05:31.865 ","End":"05:35.165","Text":"cannot readily pass through the plasma membrane in lipid core."},{"Start":"05:35.165 ","End":"05:37.490","Text":"How do they pass?"},{"Start":"05:37.490 ","End":"05:40.430","Text":"Ions and other polar molecules must"},{"Start":"05:40.430 ","End":"05:43.340","Text":"have special means of penetrating the plasma membranes."},{"Start":"05:43.340 ","End":"05:46.190","Text":"We\u0027ll now see what these special means are."},{"Start":"05:46.190 ","End":"05:50.345","Text":"I want to remind you, we\u0027re still speaking about passive transport here."},{"Start":"05:50.345 ","End":"05:54.980","Text":"When ions and other non-soluble materials have to pass to the cell,"},{"Start":"05:54.980 ","End":"05:57.965","Text":"we call this facilitated diffusion."},{"Start":"05:57.965 ","End":"06:00.560","Text":"These materials need to be aided by"},{"Start":"06:00.560 ","End":"06:04.270","Text":"membrane proteins in order to diffuse across the plasma membrane."},{"Start":"06:04.270 ","End":"06:07.640","Text":"Well, again, here we have the hydrophobic region and"},{"Start":"06:07.640 ","End":"06:11.015","Text":"all these ions are polar molecules can\u0027t pass through them,"},{"Start":"06:11.015 ","End":"06:14.885","Text":"so they need to be aided by these proteins that cross the whole membrane."},{"Start":"06:14.885 ","End":"06:20.675","Text":"These proteins allow polar ions to diffuse through the cell membrane\u0027s hydrophobic parts."},{"Start":"06:20.675 ","End":"06:25.775","Text":"Again, we\u0027re speaking here about diffusion, passive transport."},{"Start":"06:25.775 ","End":"06:32.690","Text":"Transport proteins include channel proteins like this one here, and carrier proteins."},{"Start":"06:32.690 ","End":"06:35.930","Text":"As you can see, the channel proteins are overwrite through while"},{"Start":"06:35.930 ","End":"06:37.340","Text":"the carrier proteins either change"},{"Start":"06:37.340 ","End":"06:40.310","Text":"their properties in order to let the molecules get through."},{"Start":"06:40.310 ","End":"06:46.130","Text":"Therefore, channel proteins transport much more quickly than carrier proteins do."},{"Start":"06:46.130 ","End":"06:49.460","Text":"Let\u0027s have a look at channel proteins first."},{"Start":"06:49.460 ","End":"06:52.910","Text":"Channel proteins are specific for the transported substance."},{"Start":"06:52.910 ","End":"06:58.175","Text":"For example, aquaporins allow water to pass through the membrane at a very high rate."},{"Start":"06:58.175 ","End":"07:02.975","Text":"Channel proteins are either open at all times or they\u0027re gated."},{"Start":"07:02.975 ","End":"07:06.170","Text":"We have channels that are always open like these channels"},{"Start":"07:06.170 ","End":"07:09.170","Text":"here and other channels that are gated,"},{"Start":"07:09.170 ","End":"07:10.940","Text":"like this ligand-gated channel,"},{"Start":"07:10.940 ","End":"07:15.005","Text":"which opens only when specific ligands bind to the protein."},{"Start":"07:15.005 ","End":"07:17.390","Text":"When the ligand is not bound to the protein,"},{"Start":"07:17.390 ","End":"07:19.160","Text":"the channel is closed."},{"Start":"07:19.160 ","End":"07:22.520","Text":"Voltage gated channels are activated by changes"},{"Start":"07:22.520 ","End":"07:25.805","Text":"in the electrical membrane potential near the channel."},{"Start":"07:25.805 ","End":"07:27.365","Text":"When the potential is right,"},{"Start":"07:27.365 ","End":"07:30.770","Text":"we\u0027ll see them open, otherwise, it\u0027ll be closed."},{"Start":"07:30.770 ","End":"07:33.935","Text":"We\u0027ll now move to speak about carrier proteins."},{"Start":"07:33.935 ","End":"07:37.520","Text":"These proteins bind a substance and undergo a change in"},{"Start":"07:37.520 ","End":"07:41.920","Text":"shape which translocates the substance through the plasma membrane."},{"Start":"07:41.920 ","End":"07:43.935","Text":"Here, we see an example."},{"Start":"07:43.935 ","End":"07:46.250","Text":"Amino acids, sugars, or small proteins,"},{"Start":"07:46.250 ","End":"07:47.735","Text":"whatever the molecule is,"},{"Start":"07:47.735 ","End":"07:51.635","Text":"a carrier protein has a binding site for the molecule."},{"Start":"07:51.635 ","End":"07:55.280","Text":"Here, we have a specific binding site for whatever the molecule is."},{"Start":"07:55.280 ","End":"07:58.355","Text":"The molecule then enters the binding site."},{"Start":"07:58.355 ","End":"08:04.640","Text":"The carrier protein changes shape that transports the molecule across the membrane."},{"Start":"08:04.640 ","End":"08:07.025","Text":"Again, we\u0027re speaking about passive transport,"},{"Start":"08:07.025 ","End":"08:08.630","Text":"it does not require energy,"},{"Start":"08:08.630 ","End":"08:10.790","Text":"it runs along the gradient."},{"Start":"08:10.790 ","End":"08:13.520","Text":"After that, the carrier protein resumes"},{"Start":"08:13.520 ","End":"08:17.375","Text":"its original shape and it\u0027s ready to bind to a new molecule."},{"Start":"08:17.375 ","End":"08:21.170","Text":"Carrier proteins may move the substance in both directions,"},{"Start":"08:21.170 ","End":"08:23.705","Text":"again, depending on the gradient."},{"Start":"08:23.705 ","End":"08:27.415","Text":"Typically, they\u0027re specific for a single substance."},{"Start":"08:27.415 ","End":"08:31.460","Text":"After speaking about diffusion and facilitated diffusion,"},{"Start":"08:31.460 ","End":"08:33.785","Text":"we can now speak about osmosis."},{"Start":"08:33.785 ","End":"08:35.360","Text":"Osmosis is defined,"},{"Start":"08:35.360 ","End":"08:36.890","Text":"the movement of water through"},{"Start":"08:36.890 ","End":"08:41.420","Text":"a semipermeable membrane according to the water\u0027s concentration gradient."},{"Start":"08:41.420 ","End":"08:43.970","Text":"Now, when we speak about the water\u0027s concentration,"},{"Start":"08:43.970 ","End":"08:46.970","Text":"let\u0027s just remember that in a solution, let\u0027s say,"},{"Start":"08:46.970 ","End":"08:53.100","Text":"we have a cup here and we have water,"},{"Start":"08:53.100 ","End":"08:55.760","Text":"and in the water, we have substance dissolve."},{"Start":"08:55.760 ","End":"09:00.580","Text":"Let\u0027s say it\u0027s salt or something, these ions here."},{"Start":"09:00.580 ","End":"09:02.524","Text":"When we look at the solution,"},{"Start":"09:02.524 ","End":"09:05.240","Text":"that solvent is the dissolving medium,"},{"Start":"09:05.240 ","End":"09:07.710","Text":"meaning the water here,"},{"Start":"09:08.350 ","End":"09:16.730","Text":"and the salt is the solute being dissolved in the solvent."},{"Start":"09:16.730 ","End":"09:19.160","Text":"When we define the concentration of a solution,"},{"Start":"09:19.160 ","End":"09:23.435","Text":"we always look at the solute and we say how much solute is in the solvent."},{"Start":"09:23.435 ","End":"09:26.480","Text":"Now, we\u0027re looking through the other side of the mirror."},{"Start":"09:26.480 ","End":"09:28.549","Text":"We\u0027re looking at the water\u0027s concentration,"},{"Start":"09:28.549 ","End":"09:29.795","Text":"which is like the opposite."},{"Start":"09:29.795 ","End":"09:32.515","Text":"Is there more solvent here or less solvent?"},{"Start":"09:32.515 ","End":"09:36.905","Text":"The higher concentration of solute or the higher concentration of the solution there is,"},{"Start":"09:36.905 ","End":"09:41.750","Text":"the less solvent we have per solute. Let\u0027s have a look here."},{"Start":"09:41.750 ","End":"09:44.840","Text":"Here, we have a high concentration of solution because we"},{"Start":"09:44.840 ","End":"09:48.604","Text":"have a lot of salt for only a few water molecules."},{"Start":"09:48.604 ","End":"09:50.780","Text":"Well, here we have a low concentration of"},{"Start":"09:50.780 ","End":"09:54.965","Text":"solution because we have a lot of water and only a bit of salt."},{"Start":"09:54.965 ","End":"09:57.410","Text":"But when we\u0027re looking at the water\u0027s concentration,"},{"Start":"09:57.410 ","End":"09:58.655","Text":"we\u0027re looking at the opposite."},{"Start":"09:58.655 ","End":"10:01.055","Text":"What\u0027s the concentration of the water?"},{"Start":"10:01.055 ","End":"10:02.720","Text":"Here, we have a lot of water."},{"Start":"10:02.720 ","End":"10:04.760","Text":"It says, if the water is highly concentrated,"},{"Start":"10:04.760 ","End":"10:07.070","Text":"and here we have only a little bit of water."},{"Start":"10:07.070 ","End":"10:11.700","Text":"It says, if the water has low concentration, and therefore,"},{"Start":"10:11.700 ","End":"10:15.545","Text":"the movement of water through the semipermeable membrane will be"},{"Start":"10:15.545 ","End":"10:21.530","Text":"from high concentration of water to the low concentration of water."},{"Start":"10:21.530 ","End":"10:25.520","Text":"Of course, this is inversely proportional to the solute\u0027s concentration and"},{"Start":"10:25.520 ","End":"10:30.355","Text":"as long as we\u0027re talking only about transport of water across the membrane."},{"Start":"10:30.355 ","End":"10:32.310","Text":"Just like in diffusion,"},{"Start":"10:32.310 ","End":"10:36.730","Text":"osmosis will stop if the water\u0027s concentration gradient goes to zero."},{"Start":"10:36.730 ","End":"10:39.530","Text":"When enough water will move into here and"},{"Start":"10:39.530 ","End":"10:43.475","Text":"the concentration will be equal on both sides inside and outside,"},{"Start":"10:43.475 ","End":"10:48.155","Text":"you\u0027re going to see a net moving to zero and then as soon as it stops effectively."},{"Start":"10:48.155 ","End":"10:50.630","Text":"But osmosis will also stop if"},{"Start":"10:50.630 ","End":"10:54.140","Text":"the water\u0027s hydrostatic pressure balances the somatic pressure."},{"Start":"10:54.140 ","End":"10:57.125","Text":"For example, if we\u0027re talking here about a plant cell,"},{"Start":"10:57.125 ","End":"10:59.375","Text":"which has a strong cell wall,"},{"Start":"10:59.375 ","End":"11:03.570","Text":"it will not allow the cell to expand and a lot of water enters the cell,"},{"Start":"11:03.570 ","End":"11:05.750","Text":"we\u0027re going to have hydrostatic pressure,"},{"Start":"11:05.750 ","End":"11:08.045","Text":"not allowing any more water to enter the cell"},{"Start":"11:08.045 ","End":"11:11.165","Text":"even if the concentration gradient is still there."},{"Start":"11:11.165 ","End":"11:14.420","Text":"The question of water entering a cell against"},{"Start":"11:14.420 ","End":"11:17.270","Text":"the hydrostatic pressure brings us straight to"},{"Start":"11:17.270 ","End":"11:20.735","Text":"the last thing we\u0027ll define in this section, tonicity."},{"Start":"11:20.735 ","End":"11:25.670","Text":"Tonicity is defined as the relative concentration of solutes dissolved in a solution,"},{"Start":"11:25.670 ","End":"11:29.450","Text":"which determine the direction and extent of osmosis."},{"Start":"11:29.450 ","End":"11:35.150","Text":"Osmolarity describes the solution\u0027s total solute concentration."},{"Start":"11:35.150 ","End":"11:37.579","Text":"An isotonic solutions,"},{"Start":"11:37.579 ","End":"11:42.320","Text":"the extracellular fluid has the same osmolarity as the cell cytoplasm."},{"Start":"11:42.320 ","End":"11:44.315","Text":"Hypotonic solutions,"},{"Start":"11:44.315 ","End":"11:50.105","Text":"the extracellular fluid has lower osmolarity than the fluid inside the cell."},{"Start":"11:50.105 ","End":"11:53.240","Text":"The opposite is hypertonic solutions where"},{"Start":"11:53.240 ","End":"11:58.295","Text":"the extracellular fluid has higher osmolarity within the cell\u0027s cytoplasm."},{"Start":"11:58.295 ","End":"12:00.620","Text":"That\u0027s interesting how this works."},{"Start":"12:00.620 ","End":"12:03.320","Text":"Isotonic solutions, we define as"},{"Start":"12:03.320 ","End":"12:08.135","Text":"the extracellular fluid has the same osmolarity as the cell\u0027s cytoplasm."},{"Start":"12:08.135 ","End":"12:14.180","Text":"Meaning, same amount of water will come into the cell and come out of the cell,"},{"Start":"12:14.180 ","End":"12:17.830","Text":"and we have here a normal shape blood cell."},{"Start":"12:17.830 ","End":"12:22.550","Text":"If we take this blood cell and place in a hypertonic solution"},{"Start":"12:22.550 ","End":"12:27.260","Text":"where the extracellular fluid has higher osmolarity than the cell\u0027s cytoplasm,"},{"Start":"12:27.260 ","End":"12:29.750","Text":"we\u0027re going to see a net movement of water out of"},{"Start":"12:29.750 ","End":"12:33.230","Text":"the cell and the blood cell will become shriveled."},{"Start":"12:33.230 ","End":"12:37.370","Text":"But what happens when we take this normal blood cell and place in"},{"Start":"12:37.370 ","End":"12:39.260","Text":"a hypotonic solution where"},{"Start":"12:39.260 ","End":"12:43.570","Text":"the extracellular fluid has lower osmolarity than the fluid inside the cell?"},{"Start":"12:43.570 ","End":"12:48.660","Text":"Now, water will be entering the cell and more water will enter the cell."},{"Start":"12:49.210 ","End":"12:53.180","Text":"Since blood cells are not plant cells,"},{"Start":"12:53.180 ","End":"12:57.410","Text":"they don\u0027t have the cell wall around them keeping them from expanding,"},{"Start":"12:57.410 ","End":"13:02.390","Text":"the cell will expand and expand until eventually, it\u0027ll just burst."},{"Start":"13:02.390 ","End":"13:06.920","Text":"In this section, we understood the osmosis and diffusion processes."},{"Start":"13:06.920 ","End":"13:10.175","Text":"We explained why and how passive transport occurs,"},{"Start":"13:10.175 ","End":"13:13.850","Text":"and we\u0027ve defined tonicity and its relevance to passive transport."},{"Start":"13:13.850 ","End":"13:16.320","Text":"See you in the next section."}],"ID":25832},{"Watched":false,"Name":"Active Transport","Duration":"2m 42s","ChapterTopicVideoID":24916,"CourseChapterTopicPlaylistID":136375,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.110 ","End":"00:03.165","Text":"Hi all, we\u0027re studying cell membranes"},{"Start":"00:03.165 ","End":"00:06.030","Text":"and in this section we\u0027ll be speaking about active transport."},{"Start":"00:06.030 ","End":"00:07.560","Text":"By the end of this section,"},{"Start":"00:07.560 ","End":"00:09.300","Text":"you\u0027ll be able to discriminate between"},{"Start":"00:09.300 ","End":"00:13.600","Text":"primary active transport and secondary active transport."},{"Start":"00:13.940 ","End":"00:20.115","Text":"In active transport, the solute is pumped across the membrane against its gradient."},{"Start":"00:20.115 ","End":"00:23.295","Text":"For this, the cell must expend energy."},{"Start":"00:23.295 ","End":"00:27.120","Text":"The active transport is performed by carrier proteins or pumps"},{"Start":"00:27.120 ","End":"00:31.560","Text":"rather than channel proteins like we\u0027ve seen in passive transport."},{"Start":"00:31.560 ","End":"00:34.980","Text":"This enable the cell to maintain internal concentrations of"},{"Start":"00:34.980 ","End":"00:40.350","Text":"small solutes that differ from concentrations in its own environment outside of the cell."},{"Start":"00:40.350 ","End":"00:44.955","Text":"There are 3 protein types or transporters we\u0027ll be speaking about."},{"Start":"00:44.955 ","End":"00:49.189","Text":"The uniporters carry 1 specific ion or molecule,"},{"Start":"00:49.189 ","End":"00:52.870","Text":"while cotransporters carry 2 of these molecules."},{"Start":"00:52.870 ","End":"00:56.570","Text":"A symporter carries 2 different ions or molecules,"},{"Start":"00:56.570 ","End":"00:59.030","Text":"but both in the same direction."},{"Start":"00:59.030 ","End":"01:03.785","Text":"An antiporter carries 2 different ions or molecules in different directions."},{"Start":"01:03.785 ","End":"01:06.305","Text":"Here we have 1 going in and 1 going up."},{"Start":"01:06.305 ","End":"01:12.105","Text":"Active transport is divided into primary active transport and secondary active transport."},{"Start":"01:12.105 ","End":"01:13.925","Text":"In primary active transport,"},{"Start":"01:13.925 ","End":"01:18.275","Text":"the ATP is used directly to actively transport ions across a membrane."},{"Start":"01:18.275 ","End":"01:22.595","Text":"Here we have a sodium potassium pump using energy from"},{"Start":"01:22.595 ","End":"01:27.945","Text":"ATP to pump out sodium and potassium ions against their gradient,"},{"Start":"01:27.945 ","End":"01:30.260","Text":"making a high concentration outside of"},{"Start":"01:30.260 ","End":"01:33.530","Text":"the cell and leaving a low concentration inside it."},{"Start":"01:33.530 ","End":"01:35.839","Text":"In secondary active transport,"},{"Start":"01:35.839 ","End":"01:38.720","Text":"we must use the ion concentrations that are built"},{"Start":"01:38.720 ","End":"01:42.215","Text":"outside of the plasma membrane by the primary active transport."},{"Start":"01:42.215 ","End":"01:45.320","Text":"This gradient is later used by symport to"},{"Start":"01:45.320 ","End":"01:48.440","Text":"transport other substances against their gradients."},{"Start":"01:48.440 ","End":"01:52.745","Text":"Here we can see, the same sodium potassium pump that we\u0027ve seen before."},{"Start":"01:52.745 ","End":"01:55.160","Text":"Now, we know there\u0027s a high concentration of sodium"},{"Start":"01:55.160 ","End":"01:57.560","Text":"outside the cell and a low concentration inside."},{"Start":"01:57.560 ","End":"02:00.200","Text":"Therefore, the chemical driving force pushes"},{"Start":"02:00.200 ","End":"02:03.585","Text":"sodium ion from outside of the cell inside of the cell."},{"Start":"02:03.585 ","End":"02:06.680","Text":"The energy from this flow of sodium ions into"},{"Start":"02:06.680 ","End":"02:11.179","Text":"the cell is used by the sodium glucose symport transporter."},{"Start":"02:11.179 ","End":"02:15.230","Text":"It loads glucose from extracellular fluid and then pumps it"},{"Start":"02:15.230 ","End":"02:20.030","Text":"inside using the energy from the sodium ion coming into the cell."},{"Start":"02:20.030 ","End":"02:23.645","Text":"While the glucose is transported against its own gradient."},{"Start":"02:23.645 ","End":"02:26.360","Text":"Even if there\u0027s a high concentration of glucose inside"},{"Start":"02:26.360 ","End":"02:29.110","Text":"the cell and a low concentration outside the cell,"},{"Start":"02:29.110 ","End":"02:33.680","Text":"the pump is going to use the energy from the flow of the sodium ions."},{"Start":"02:33.680 ","End":"02:36.035","Text":"We\u0027ve spoken about active transport,"},{"Start":"02:36.035 ","End":"02:37.640","Text":"and we now can discriminate between"},{"Start":"02:37.640 ","End":"02:42.870","Text":"primary active transport and secondary active transport. Thanks for listening."}],"ID":25829},{"Watched":false,"Name":"Bulk Transport","Duration":"4m 5s","ChapterTopicVideoID":24917,"CourseChapterTopicPlaylistID":136375,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.035","Text":"Hi, we\u0027re speaking about transport across cell membranes."},{"Start":"00:04.035 ","End":"00:07.470","Text":"In this section, we\u0027ll be speaking about bulk transport."},{"Start":"00:07.470 ","End":"00:09.060","Text":"By the end of the section,"},{"Start":"00:09.060 ","End":"00:13.365","Text":"you\u0027ll be able to describe endocytosis including phagocytosis,"},{"Start":"00:13.365 ","End":"00:17.100","Text":"pinocytosis, and receptor-mediated endocytosis."},{"Start":"00:17.100 ","End":"00:20.660","Text":"You will also understand the process of exocytosis."},{"Start":"00:20.660 ","End":"00:25.215","Text":"Let\u0027s start. What is endocytosis?"},{"Start":"00:25.215 ","End":"00:30.015","Text":"This is a type of active transport that moves particles into a cell."},{"Start":"00:30.015 ","End":"00:36.600","Text":"The plasma membrane of the cell invaginates forming a pocket around the target particles."},{"Start":"00:36.600 ","End":"00:39.035","Text":"The pocket then pinches off,"},{"Start":"00:39.035 ","End":"00:43.819","Text":"resulting in the particle being contained in a newly created intracellular vesicle."},{"Start":"00:43.819 ","End":"00:46.145","Text":"This is formed from the plasma membrane."},{"Start":"00:46.145 ","End":"00:48.150","Text":"Let\u0027s have a look at the plasma membrane here."},{"Start":"00:48.150 ","End":"00:50.150","Text":"We see that it\u0027s made of a double layer of"},{"Start":"00:50.150 ","End":"00:55.730","Text":"phospholipids as a cell invaginates around the substances that are swallowed,"},{"Start":"00:55.730 ","End":"00:57.490","Text":"just pinches into a bubble."},{"Start":"00:57.490 ","End":"00:59.900","Text":"This is a lot like blowing soap bubbles."},{"Start":"00:59.900 ","End":"01:05.635","Text":"The first type of endocytosis will mention is the phagocytosis, meaning cellular eating."},{"Start":"01:05.635 ","End":"01:08.915","Text":"This is when a cell engulfs the particle in a vacuole."},{"Start":"01:08.915 ","End":"01:13.700","Text":"The vacuole then fuses with a lysosome to digest its contents."},{"Start":"01:13.700 ","End":"01:18.235","Text":"We see here the pseudopodium which is a temporary arm-like structure,"},{"Start":"01:18.235 ","End":"01:21.240","Text":"the cell membrane just pushes out from both sides."},{"Start":"01:21.240 ","End":"01:23.495","Text":"It engulfs the food, or other particles."},{"Start":"01:23.495 ","End":"01:27.200","Text":"Again, it closes around itself and pinches off"},{"Start":"01:27.200 ","End":"01:31.340","Text":"in a vesicle which is actually very much like a soap bubble."},{"Start":"01:31.340 ","End":"01:40.290","Text":"We have here this vacuole with food inside and inside the cell,"},{"Start":"01:40.290 ","End":"01:46.220","Text":"we have these other vacuoles which are full of digestive enzymes called lysosomes."},{"Start":"01:46.220 ","End":"01:49.160","Text":"What happens is that the membranes,"},{"Start":"01:49.160 ","End":"01:51.530","Text":"again say it\u0027s like soap bubbles,"},{"Start":"01:51.530 ","End":"01:53.395","Text":"they can fuse with each other."},{"Start":"01:53.395 ","End":"01:59.160","Text":"Here we have our food and here we\u0027ve got the enzymes."},{"Start":"01:59.160 ","End":"02:03.225","Text":"They\u0027re going to take this food apart."},{"Start":"02:03.225 ","End":"02:14.710","Text":"We then have 1 vacuole full of enzymes and broken food particles"},{"Start":"02:15.070 ","End":"02:19.265","Text":"which the cell can now process for its own needs."},{"Start":"02:19.265 ","End":"02:22.925","Text":"In pinocytosis, meaning cellular drinking,"},{"Start":"02:22.925 ","End":"02:26.540","Text":"molecules dissolved in droplets are transferred into the cell,"},{"Start":"02:26.540 ","End":"02:31.445","Text":"while extracellular fluid is gulped into tiny vesicles."},{"Start":"02:31.445 ","End":"02:33.770","Text":"Here we have, it\u0027s coated with"},{"Start":"02:33.770 ","End":"02:37.460","Text":"these special proteins which shape the membrane into the pit."},{"Start":"02:37.460 ","End":"02:40.250","Text":"Then again pinches off and we have"},{"Start":"02:40.250 ","End":"02:45.110","Text":"a coated vesicle full of the solute that we wanted to swallow."},{"Start":"02:45.110 ","End":"02:49.550","Text":"Receptor-mediated endocytosis employs receptor proteins"},{"Start":"02:49.550 ","End":"02:52.325","Text":"facing outside the plasma membrane."},{"Start":"02:52.325 ","End":"02:56.765","Text":"These have a specific binding affinity for certain substances."},{"Start":"02:56.765 ","End":"03:00.680","Text":"Here we have the red receptor proteins and they"},{"Start":"03:00.680 ","End":"03:04.220","Text":"have very strong affinity to this purple triangular substance."},{"Start":"03:04.220 ","End":"03:10.160","Text":"When these receptor proteins connect with the purple substance in this example,"},{"Start":"03:10.160 ","End":"03:12.710","Text":"they send a message into the cell."},{"Start":"03:12.710 ","End":"03:17.225","Text":"Again to make this an imagination using these special coating proteins,"},{"Start":"03:17.225 ","End":"03:21.685","Text":"which coat the vesicles pinching off and into the cellular."},{"Start":"03:21.685 ","End":"03:26.540","Text":"Exocytosis is a type of active transport that moves particles out of the cell."},{"Start":"03:26.540 ","End":"03:29.450","Text":"Again, here we have a vesicle inside the cell."},{"Start":"03:29.450 ","End":"03:32.270","Text":"Again, we have a double layer of phospholipids."},{"Start":"03:32.270 ","End":"03:35.870","Text":"We have here the red substance that we want to get rid of."},{"Start":"03:35.870 ","End":"03:41.225","Text":"The vesicle moves towards the cell membrane and then fuses with it,"},{"Start":"03:41.225 ","End":"03:43.760","Text":"and the particles are let out while"},{"Start":"03:43.760 ","End":"03:48.150","Text":"the vesicle itself turns to be part of the cell membrane."},{"Start":"03:48.650 ","End":"03:51.705","Text":"We\u0027ve spoken in that bulk transport."},{"Start":"03:51.705 ","End":"03:55.580","Text":"You can now describe endocytosis including phagocytosis,"},{"Start":"03:55.580 ","End":"03:59.930","Text":"pinocytosis, and receptor-mediated endocytosis."},{"Start":"03:59.930 ","End":"04:06.180","Text":"You also understand the process of exocytosis. Thanks for listening."}],"ID":25830}],"Thumbnail":null,"ID":136375},{"Name":"Metabolism","TopicPlaylistFirstVideoID":0,"Duration":null,"Videos":[{"Watched":false,"Name":"Introduction to Metabolism","Duration":"2m 40s","ChapterTopicVideoID":24924,"CourseChapterTopicPlaylistID":136376,"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":"Hello. In this section, we\u0027re introducing metabolism."},{"Start":"00:03.750 ","End":"00:05.475","Text":"By the end of this section,"},{"Start":"00:05.475 ","End":"00:10.275","Text":"you\u0027ll be able to explain and describe the 2 major types of metabolic pathways."},{"Start":"00:10.275 ","End":"00:15.795","Text":"Also, you\u0027ll be able to discuss how chemical reactions play a role in energy transfer."},{"Start":"00:15.795 ","End":"00:20.595","Text":"Cell activities occur through step-wise biochemical reactions."},{"Start":"00:20.595 ","End":"00:23.865","Text":"Some reactions are spontaneous and release energy,"},{"Start":"00:23.865 ","End":"00:27.015","Text":"while others require energy to proceed."},{"Start":"00:27.015 ","End":"00:33.975","Text":"Cells must constantly produce more energy to refill the continuously used energy banks."},{"Start":"00:33.975 ","End":"00:37.980","Text":"Carbohydrate metabolism describes the process where"},{"Start":"00:37.980 ","End":"00:42.060","Text":"living things consume sugar as a major energy source."},{"Start":"00:42.060 ","End":"00:46.415","Text":"The following equation describes the breakdown of glucose."},{"Start":"00:46.415 ","End":"00:50.315","Text":"1 molecule of glucose and 6 molecules of oxygen,"},{"Start":"00:50.315 ","End":"00:53.149","Text":"turn to 6 molecules of carbon dioxide,"},{"Start":"00:53.149 ","End":"00:56.335","Text":"6 molecules of water and energy."},{"Start":"00:56.335 ","End":"01:02.794","Text":"Consumed carbohydrates are produced by photosynthesizing organisms, such as plants."},{"Start":"01:02.794 ","End":"01:05.990","Text":"Solar energy is required for synthesis of"},{"Start":"01:05.990 ","End":"01:10.025","Text":"glucose molecules during the photosynthesis reactions."},{"Start":"01:10.025 ","End":"01:14.330","Text":"The following equation describe the synthesis of glucose."},{"Start":"01:14.330 ","End":"01:18.080","Text":"6 molecules of carbon dioxide plus 6 molecules of water,"},{"Start":"01:18.080 ","End":"01:20.225","Text":"using an intake of energy,"},{"Start":"01:20.225 ","End":"01:25.635","Text":"produce 1 molecule of glucose and a byproduct of 6 molecules of oxygen."},{"Start":"01:25.635 ","End":"01:30.860","Text":"During photosynthesis, chemical energy is stored in the form of glucose."},{"Start":"01:30.860 ","End":"01:35.330","Text":"Let\u0027s explain anabolic and catabolic pathways."},{"Start":"01:35.330 ","End":"01:41.165","Text":"Anabolic pathway describe the synthesis of complex molecules from simpler ones."},{"Start":"01:41.165 ","End":"01:44.315","Text":"These pathways require an energy input."},{"Start":"01:44.315 ","End":"01:50.480","Text":"Catabolic pathways describe pathways that degrade complex molecules into simpler ones."},{"Start":"01:50.480 ","End":"01:55.100","Text":"These pathways release energy."},{"Start":"01:55.100 ","End":"02:00.995","Text":"In metabolic pathways, chemical reactions are facilitated by enzymes."},{"Start":"02:00.995 ","End":"02:05.150","Text":"These enzymes catalyze biological reactions that require energy,"},{"Start":"02:05.150 ","End":"02:07.895","Text":"as well as those that release energy."},{"Start":"02:07.895 ","End":"02:10.834","Text":"Here, we see the catabolism pathway."},{"Start":"02:10.834 ","End":"02:13.564","Text":"Degrading polymers into monomers."},{"Start":"02:13.564 ","End":"02:15.785","Text":"This releases energy."},{"Start":"02:15.785 ","End":"02:19.460","Text":"On the other hand, anabolism describes the synthesis of"},{"Start":"02:19.460 ","End":"02:24.360","Text":"polymers from monomers using an energy intake."},{"Start":"02:24.550 ","End":"02:31.265","Text":"In this section, we\u0027ve explained and described the 2 major types of metabolic pathways."},{"Start":"02:31.265 ","End":"02:36.605","Text":"Also, we\u0027ve discussed how chemical reactions play a role in energy transfer."},{"Start":"02:36.605 ","End":"02:40.500","Text":"Hope you enjoyed it. See you in the next section."}],"ID":25837},{"Watched":false,"Name":"Potential, Kinetic, Free, and Activation energy","Duration":"7m 34s","ChapterTopicVideoID":24920,"CourseChapterTopicPlaylistID":136376,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:01.700 ","End":"00:04.995","Text":"Hi, there. We\u0027re studying metabolism."},{"Start":"00:04.995 ","End":"00:07.500","Text":"In this section, we\u0027ll be discussing potential,"},{"Start":"00:07.500 ","End":"00:10.440","Text":"kinetic, free and activation energy."},{"Start":"00:10.440 ","End":"00:12.195","Text":"By the end of this section,"},{"Start":"00:12.195 ","End":"00:14.250","Text":"you\u0027ll be able to define energy,"},{"Start":"00:14.250 ","End":"00:17.625","Text":"explain the difference between kinetic and potential energy,"},{"Start":"00:17.625 ","End":"00:21.315","Text":"discuss the concepts of free energy and activation energy,"},{"Start":"00:21.315 ","End":"00:25.630","Text":"and describe endergonic and exergonic reactions."},{"Start":"00:25.700 ","End":"00:31.800","Text":"What is energy? Energy is defined as the ability to do work."},{"Start":"00:31.800 ","End":"00:34.425","Text":"As you can see from this illustration,"},{"Start":"00:34.425 ","End":"00:37.915","Text":"energy exists in many forms."},{"Start":"00:37.915 ","End":"00:40.940","Text":"Potential energy is the energy held by"},{"Start":"00:40.940 ","End":"00:44.480","Text":"an object because of its position relative to other objects."},{"Start":"00:44.480 ","End":"00:49.880","Text":"For example, this hammer held up high in the air is filled with potential energy."},{"Start":"00:49.880 ","End":"00:51.245","Text":"If we let go of it,"},{"Start":"00:51.245 ","End":"00:53.315","Text":"it\u0027ll fall and hit the nail."},{"Start":"00:53.315 ","End":"00:57.230","Text":"In this example here, pulling the string from the bow,"},{"Start":"00:57.230 ","End":"01:00.770","Text":"the elasticity of the bow here is filled with potential energy."},{"Start":"01:00.770 ","End":"01:03.035","Text":"What will happen when it\u0027s released?"},{"Start":"01:03.035 ","End":"01:05.825","Text":"This is what will happen. We\u0027ll get kinetic energy,"},{"Start":"01:05.825 ","End":"01:08.275","Text":"which is the energy within an object in motion."},{"Start":"01:08.275 ","End":"01:11.990","Text":"Here, we have the kinetic energy of the hammer coming down."},{"Start":"01:11.990 ","End":"01:15.230","Text":"Here, the potential energy from the bow was moved to"},{"Start":"01:15.230 ","End":"01:19.050","Text":"be kinetic energy in the arrow flying towards the target."},{"Start":"01:19.270 ","End":"01:23.840","Text":"Molecular bonds between atoms also have potential energy."},{"Start":"01:23.840 ","End":"01:26.555","Text":"This is stored as chemical energy."},{"Start":"01:26.555 ","End":"01:31.620","Text":"The chemical energy provides living cells energy from food."},{"Start":"01:31.750 ","End":"01:38.165","Text":"Breaking the molecular bonds with food molecules releases their potential energy."},{"Start":"01:38.165 ","End":"01:44.165","Text":"This energy may be harnessed to create other forms of energy or may be lost as heat."},{"Start":"01:44.165 ","End":"01:48.080","Text":"The sunlight charges the molecular energy known as"},{"Start":"01:48.080 ","End":"01:51.845","Text":"chemical energy within these molecular bonds here."},{"Start":"01:51.845 ","End":"01:55.610","Text":"Breaking these bonds in our body releases the potential energy,"},{"Start":"01:55.610 ","End":"01:57.920","Text":"it can be harnessed to use as mechanical energy."},{"Start":"01:57.920 ","End":"01:59.975","Text":"For example, if you want to ride a bike,"},{"Start":"01:59.975 ","End":"02:03.560","Text":"cars do a similar process by burning the fuel,"},{"Start":"02:03.560 ","End":"02:05.960","Text":"they release the chemical energy,"},{"Start":"02:05.960 ","End":"02:08.255","Text":"and use it as mechanical energy."},{"Start":"02:08.255 ","End":"02:11.750","Text":"Sometimes the energy is used as heat."},{"Start":"02:11.750 ","End":"02:15.600","Text":"For example, when we went to heat things with electricity."},{"Start":"02:15.670 ","End":"02:21.665","Text":"All energy transfers involved losing energy as heat, resulting in entropy."},{"Start":"02:21.665 ","End":"02:25.700","Text":"We see here that producers a large amount of energy,"},{"Start":"02:25.700 ","End":"02:29.020","Text":"but some of it is lost by the system as heat."},{"Start":"02:29.020 ","End":"02:31.110","Text":"The primary consumers,"},{"Start":"02:31.110 ","End":"02:34.820","Text":"the herbivores, get this amount of energy from the plants,"},{"Start":"02:34.820 ","End":"02:37.865","Text":"but a big part of it is lost by heat again,"},{"Start":"02:37.865 ","End":"02:42.050","Text":"and only a smaller amount is consumed by the secondary consumers,"},{"Start":"02:42.050 ","End":"02:43.960","Text":"which are small carnivores."},{"Start":"02:43.960 ","End":"02:47.445","Text":"Again, large part of this is lost in heat,"},{"Start":"02:47.445 ","End":"02:51.260","Text":"and what\u0027s left by the tertiary consumers is again,"},{"Start":"02:51.260 ","End":"02:55.415","Text":"lost in heat, and only a little bit of it is used for what they need."},{"Start":"02:55.415 ","End":"03:01.210","Text":"All chemical reactions involve a change in free energy called Gibbs free energy,"},{"Start":"03:01.210 ","End":"03:10.370","Text":"symbolized by Delta G. Delta G = Delta H minus T times Delta S. Let\u0027s define these now."},{"Start":"03:10.370 ","End":"03:12.800","Text":"T is the temperature in (K),"},{"Start":"03:12.800 ","End":"03:16.655","Text":"Delta S is the change in entropy which we have defined here."},{"Start":"03:16.655 ","End":"03:19.475","Text":"Delta H is the change in enthalpy."},{"Start":"03:19.475 ","End":"03:22.340","Text":"Enthalpy is a concept used in science and"},{"Start":"03:22.340 ","End":"03:26.270","Text":"engineering when both heat and work need to be calculated."},{"Start":"03:26.270 ","End":"03:29.135","Text":"When a substance changes at constant pressure,"},{"Start":"03:29.135 ","End":"03:34.105","Text":"enthalpy tells how much heat and work were added or removed from the substance."},{"Start":"03:34.105 ","End":"03:36.180","Text":"Enthalpy is similar to energy,"},{"Start":"03:36.180 ","End":"03:38.590","Text":"but not the same."},{"Start":"03:38.590 ","End":"03:42.830","Text":"Endergonic reactions and exergonic reactions."},{"Start":"03:42.830 ","End":"03:48.740","Text":"Reactions proceed spontaneously in the direction that lowers their Gibbs free energy."},{"Start":"03:48.740 ","End":"03:54.125","Text":"Reaction is deemed spontaneous if Delta G is negative."},{"Start":"03:54.125 ","End":"03:56.660","Text":"These reactions are exergonic reactions,"},{"Start":"03:56.660 ","End":"03:58.535","Text":"meaning they release energy."},{"Start":"03:58.535 ","End":"04:00.020","Text":"Now, let\u0027s have a look here."},{"Start":"04:00.020 ","End":"04:02.750","Text":"This is the reactants initial energy,"},{"Start":"04:02.750 ","End":"04:05.495","Text":"and this is the product energy."},{"Start":"04:05.495 ","End":"04:07.895","Text":"Since eventually, it\u0027s lower,"},{"Start":"04:07.895 ","End":"04:10.330","Text":"energy is released in the process."},{"Start":"04:10.330 ","End":"04:13.415","Text":"This could occur without adding energy into the system"},{"Start":"04:13.415 ","End":"04:17.255","Text":"since we have a Delta that\u0027s negative."},{"Start":"04:17.255 ","End":"04:22.625","Text":"An example for these processes would be catabolic processes."},{"Start":"04:22.625 ","End":"04:29.170","Text":"A reaction is non-spontaneous if the Delta G is positive or larger than 0,"},{"Start":"04:29.170 ","End":"04:32.914","Text":"these reactions are endergonic reactions."},{"Start":"04:32.914 ","End":"04:37.850","Text":"These are non-spontaneous reactions and they need an addition of free energy."},{"Start":"04:37.850 ","End":"04:41.795","Text":"Examples of these reactions would be anabolic processes."},{"Start":"04:41.795 ","End":"04:47.630","Text":"We see here that the reactant has a lower free Gibbs energy than the product."},{"Start":"04:47.630 ","End":"04:54.200","Text":"Therefore, energy must be supplied to get from this low energy to the high energy."},{"Start":"04:54.200 ","End":"04:59.740","Text":"But even exergonic reactions involve chemical bond breaking."},{"Start":"04:59.740 ","End":"05:05.315","Text":"A small amount of energy input is needed before the energy-releasing steps."},{"Start":"05:05.315 ","End":"05:10.415","Text":"The initial energy needed is called activation energy."},{"Start":"05:10.415 ","End":"05:13.000","Text":"Energy of activation."},{"Start":"05:13.000 ","End":"05:19.430","Text":"The transition state of the reaction exists at a higher energy state than the reactants,"},{"Start":"05:19.430 ","End":"05:23.810","Text":"and thus the activation energy is always positive."},{"Start":"05:23.810 ","End":"05:26.750","Text":"Activation energy is often provided as"},{"Start":"05:26.750 ","End":"05:31.265","Text":"a thermal energy that the reactant molecules absorbed from the surroundings."},{"Start":"05:31.265 ","End":"05:33.620","Text":"Let\u0027s look at this example here."},{"Start":"05:33.620 ","End":"05:35.450","Text":"We have here 2 molecules,"},{"Start":"05:35.450 ","End":"05:40.640","Text":"A which is bound to B and C which is bound to D. In the products we"},{"Start":"05:40.640 ","End":"05:46.025","Text":"see that A is bound to C and B is bound to D. In the transition state,"},{"Start":"05:46.025 ","End":"05:48.560","Text":"we must break these bonds between A and B,"},{"Start":"05:48.560 ","End":"05:54.050","Text":"and C and D. Breaking these bonds involves a higher free energy state."},{"Start":"05:54.050 ","End":"05:58.670","Text":"Therefore, the energy that needs to be added to the system in order to get to"},{"Start":"05:58.670 ","End":"06:04.955","Text":"the transition state before we can go down to the product state which is lowest 1."},{"Start":"06:04.955 ","End":"06:07.430","Text":"This is the energy releasing step,"},{"Start":"06:07.430 ","End":"06:10.190","Text":"and this is the activation energy step."},{"Start":"06:10.190 ","End":"06:14.765","Text":"The activation energy of a reaction determines the rate at which it will proceed."},{"Start":"06:14.765 ","End":"06:17.090","Text":"The lower the state will be,"},{"Start":"06:17.090 ","End":"06:21.455","Text":"the easier it will be for reactants to roll down to products."},{"Start":"06:21.455 ","End":"06:24.185","Text":"The higher the activation energy,"},{"Start":"06:24.185 ","End":"06:26.495","Text":"the slower the chemical reaction."},{"Start":"06:26.495 ","End":"06:29.390","Text":"Again, if the activation energy is high,"},{"Start":"06:29.390 ","End":"06:34.710","Text":"we\u0027re going to see a low rate of reactants rolling down to the product state."},{"Start":"06:34.720 ","End":"06:39.530","Text":"Important macromolecules in the body such as proteins, DNA,"},{"Start":"06:39.530 ","End":"06:44.630","Text":"and RNA, store considerable energy and their breakdown is exergonic."},{"Start":"06:44.630 ","End":"06:47.240","Text":"Why doesn\u0027t anybody just fall apart?"},{"Start":"06:47.240 ","End":"06:50.120","Text":"Well, if cellular temperatures alone provided"},{"Start":"06:50.120 ","End":"06:53.179","Text":"enough heat energy to overcome the activation barriers,"},{"Start":"06:53.179 ","End":"06:56.524","Text":"the cell\u0027s essential components will just disintegrate."},{"Start":"06:56.524 ","End":"07:00.860","Text":"Therefore, the structure of these molecules is more stable,"},{"Start":"07:00.860 ","End":"07:03.080","Text":"needing a high activation energy."},{"Start":"07:03.080 ","End":"07:08.000","Text":"Only when needed, enzymes are used to lower the activation energy."},{"Start":"07:08.000 ","End":"07:12.545","Text":"Then we can see the process rolling down."},{"Start":"07:12.545 ","End":"07:15.245","Text":"We\u0027ve introduced potential,"},{"Start":"07:15.245 ","End":"07:17.915","Text":"kinetic, free, and activation energy."},{"Start":"07:17.915 ","End":"07:20.075","Text":"In this section, we define energy,"},{"Start":"07:20.075 ","End":"07:23.465","Text":"we explain the difference between kinetic and potential energy."},{"Start":"07:23.465 ","End":"07:27.395","Text":"We discuss the concepts of free energy and activation energy,"},{"Start":"07:27.395 ","End":"07:31.084","Text":"and we describe endergonic and exergonic reactions."},{"Start":"07:31.084 ","End":"07:34.450","Text":"See you in the next section. Bye."}],"ID":25833},{"Watched":false,"Name":"The Laws of Thermodynamics","Duration":"3m 3s","ChapterTopicVideoID":24921,"CourseChapterTopicPlaylistID":136376,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.080 ","End":"00:04.245","Text":"Hi. In order to truly understand metabolism,"},{"Start":"00:04.245 ","End":"00:07.665","Text":"we must first know the laws of thermodynamics."},{"Start":"00:07.665 ","End":"00:09.450","Text":"By the end of this section,"},{"Start":"00:09.450 ","End":"00:12.360","Text":"you\u0027ll be able to discuss the concept of entropy and"},{"Start":"00:12.360 ","End":"00:16.560","Text":"explain the first and second laws of thermodynamics."},{"Start":"00:16.560 ","End":"00:20.370","Text":"Thermodynamics refers to the study of energy"},{"Start":"00:20.370 ","End":"00:24.730","Text":"and energy transfer involving physical matter."},{"Start":"00:24.800 ","End":"00:28.400","Text":"The matter and its environment relevant to a case of"},{"Start":"00:28.400 ","End":"00:31.925","Text":"energy transfer are classified as a system."},{"Start":"00:31.925 ","End":"00:36.100","Text":"Everything outside that system is the surroundings."},{"Start":"00:36.100 ","End":"00:41.270","Text":"In this case, our system is here inside the bottle and"},{"Start":"00:41.270 ","End":"00:46.490","Text":"the surroundings are outside the bottle. Same here."},{"Start":"00:46.490 ","End":"00:51.365","Text":"In open systems, the energy can transfer between the system and its surroundings."},{"Start":"00:51.365 ","End":"00:53.285","Text":"Energy can come out here."},{"Start":"00:53.285 ","End":"00:55.265","Text":"While in closed systems,"},{"Start":"00:55.265 ","End":"00:57.710","Text":"the energy cannot transfer to its surroundings."},{"Start":"00:57.710 ","End":"00:59.780","Text":"Here we have it closed up."},{"Start":"00:59.780 ","End":"01:03.275","Text":"Of course, biological organisms are open systems."},{"Start":"01:03.275 ","End":"01:09.760","Text":"Any biological organism transfers energy to its surroundings."},{"Start":"01:09.760 ","End":"01:14.470","Text":"This cat is hot now and the heat is going to the surroundings."},{"Start":"01:14.470 ","End":"01:20.434","Text":"The first law of thermodynamics states that energy cannot be created or destroyed,"},{"Start":"01:20.434 ","End":"01:22.220","Text":"but it can be transformed."},{"Start":"01:22.220 ","End":"01:24.665","Text":"For example, in photosynthesis,"},{"Start":"01:24.665 ","End":"01:29.675","Text":"light energy is transformed into chemical energy stored within organic molecules."},{"Start":"01:29.675 ","End":"01:33.050","Text":"We can get this chemical energy stored as sugar,"},{"Start":"01:33.050 ","End":"01:36.140","Text":"for example, and transform it into kinetic energy,"},{"Start":"01:36.140 ","End":"01:38.490","Text":"making our muscles work."},{"Start":"01:38.510 ","End":"01:43.985","Text":"Living cells, transform all chemical energy into ATP molecules."},{"Start":"01:43.985 ","End":"01:50.820","Text":"The energy in ATP molecules is easily accessible to perform any cellular work needed."},{"Start":"01:51.290 ","End":"01:57.640","Text":"The second law of thermodynamics states that no energy transfer is completely efficient."},{"Start":"01:57.640 ","End":"02:01.120","Text":"Some energy is always lost in an unusable form."},{"Start":"02:01.120 ","End":"02:06.220","Text":"Usually, the more energy that a system loses to its surroundings,"},{"Start":"02:06.220 ","End":"02:09.445","Text":"the more disordered this system becomes."},{"Start":"02:09.445 ","End":"02:15.700","Text":"Entropy is the term which tells us the randomness or disorder within a system."},{"Start":"02:15.700 ","End":"02:20.620","Text":"For example, here we have molecules in a solid state and in a liquid state."},{"Start":"02:20.620 ","End":"02:24.400","Text":"You can see that the entropy is higher in the liquid state."},{"Start":"02:24.400 ","End":"02:27.580","Text":"That means that higher entropy tells us of"},{"Start":"02:27.580 ","End":"02:31.205","Text":"a higher disorder and lower energy in the system."},{"Start":"02:31.205 ","End":"02:36.190","Text":"Molecules and chemical reactions have varying amounts of entropy."},{"Start":"02:36.190 ","End":"02:41.914","Text":"When a chemical reaction reaches a state of equilibrium, entropy increases."},{"Start":"02:41.914 ","End":"02:44.630","Text":"When molecules at a high concentration in"},{"Start":"02:44.630 ","End":"02:49.680","Text":"one place diffuse or spread out, energy also increases."},{"Start":"02:50.080 ","End":"02:53.750","Text":"In this section, we\u0027ve discussed the concept of entropy"},{"Start":"02:53.750 ","End":"02:57.140","Text":"and explained the first and second laws of thermodynamics."},{"Start":"02:57.140 ","End":"03:02.490","Text":"Now we can go on to understand metabolism better in the coming sections."}],"ID":25834},{"Watched":false,"Name":"ATP Adenosine Triphosphate","Duration":"4m 4s","ChapterTopicVideoID":24922,"CourseChapterTopicPlaylistID":136376,"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":"Hey there. We\u0027re studying metabolism and in"},{"Start":"00:03.480 ","End":"00:06.975","Text":"this section we\u0027ll be speaking about adenosine triphosphate,"},{"Start":"00:06.975 ","End":"00:10.470","Text":"or in its common abbreviation ATP."},{"Start":"00:10.470 ","End":"00:12.285","Text":"By the end of this section,"},{"Start":"00:12.285 ","End":"00:15.210","Text":"you\u0027ll be able to explain ATP\u0027s role as"},{"Start":"00:15.210 ","End":"00:22.120","Text":"the cellular energy currency and describe how energy releases through ATP hydrolysis."},{"Start":"00:22.430 ","End":"00:25.844","Text":"Adenosine triphosphate, or ATP,"},{"Start":"00:25.844 ","End":"00:28.920","Text":"is the primary energy currency of the cell."},{"Start":"00:28.920 ","End":"00:32.130","Text":"Therefore, most of the energy requiring"},{"Start":"00:32.130 ","End":"00:37.060","Text":"cellular reactions were found that ATP is what powers them."},{"Start":"00:37.060 ","End":"00:39.410","Text":"The adenosine is a nucleoside,"},{"Start":"00:39.410 ","End":"00:41.705","Text":"it\u0027s nitrogenous base is adenine,"},{"Start":"00:41.705 ","End":"00:43.610","Text":"and it has a 5-carbon sugar,"},{"Start":"00:43.610 ","End":"00:46.085","Text":"ribose here, this is pentose sugar."},{"Start":"00:46.085 ","End":"00:50.150","Text":"The phosphate groups in order of closest to farthest to the ribose sugar,"},{"Start":"00:50.150 ","End":"00:55.240","Text":"are Alpha, Beta and Gamma."},{"Start":"00:55.240 ","End":"01:00.690","Text":"Together these chemical groups constitute an energy powerhouse."},{"Start":"01:01.280 ","End":"01:03.870","Text":"How does this work?"},{"Start":"01:03.870 ","End":"01:06.620","Text":"Well, all 3 phosphate groups are negatively"},{"Start":"01:06.620 ","End":"01:10.380","Text":"charged and therefore they mutually repel each other."},{"Start":"01:10.880 ","End":"01:17.320","Text":"Connected and together is actually the chemical equivalent of a compressed spring."},{"Start":"01:17.320 ","End":"01:20.820","Text":"Both bonds that link the phosphates to each other,"},{"Start":"01:20.820 ","End":"01:25.045","Text":"here and here are equally high-energy bonds."},{"Start":"01:25.045 ","End":"01:28.899","Text":"These bonds may be broken by hydrolysis reactions."},{"Start":"01:28.899 ","End":"01:31.640","Text":"This releases the energy."},{"Start":"01:31.800 ","End":"01:36.790","Text":"If this is a charged battery here with the compressed springs,"},{"Start":"01:36.790 ","End":"01:39.640","Text":"when we let it go, we have the uncharged battery."},{"Start":"01:39.640 ","End":"01:42.595","Text":"How do we charge this battery again?"},{"Start":"01:42.595 ","End":"01:47.495","Text":"This is done through the ATP-ADP cycle."},{"Start":"01:47.495 ","End":"01:52.810","Text":"ATP hydrolyzes into ADP in the following reaction."},{"Start":"01:52.860 ","End":"01:55.398","Text":"The reactants are ATP,"},{"Start":"01:55.398 ","End":"01:59.830","Text":"and water for the hydrolysis and the products are ADP,"},{"Start":"01:59.830 ","End":"02:03.575","Text":"adenosine diphosphate with 2 phosphates only,"},{"Start":"02:03.575 ","End":"02:06.810","Text":"a free phosphate group here,"},{"Start":"02:06.810 ","End":"02:11.120","Text":"and free energy, which is released for cellular use."},{"Start":"02:11.120 ","End":"02:15.770","Text":"The ATP regeneration must require an input of free energy."},{"Start":"02:15.770 ","End":"02:20.240","Text":"Therefore we have ADP plus a free phosphate group"},{"Start":"02:20.240 ","End":"02:25.175","Text":"plus free energy and the products will be ATP plus water."},{"Start":"02:25.175 ","End":"02:27.230","Text":"Here we have the ATP,"},{"Start":"02:27.230 ","End":"02:30.945","Text":"adenosine triphosphate, 3 phosphates."},{"Start":"02:30.945 ","End":"02:35.390","Text":"Hydrolysis removes one of the phosphate groups, releasing the energy,"},{"Start":"02:35.390 ","End":"02:41.410","Text":"the bond between them and we get adenosine diphosphate with only 2 phosphate groups."},{"Start":"02:41.410 ","End":"02:43.655","Text":"In order to regenerate the ATP,"},{"Start":"02:43.655 ","End":"02:47.330","Text":"the cell must invest the energy it\u0027s absorbed from"},{"Start":"02:47.330 ","End":"02:51.710","Text":"food and another free phosphate group is added on."},{"Start":"02:51.710 ","End":"02:55.190","Text":"Again, we have here the loaded spring."},{"Start":"02:55.190 ","End":"02:59.455","Text":"What is done with this energy that\u0027s released?"},{"Start":"02:59.455 ","End":"03:02.825","Text":"In some reactions, the ATP causes"},{"Start":"03:02.825 ","End":"03:07.700","Text":"phosphorylation and that means that it transfers the phosphate on to another molecule."},{"Start":"03:07.700 ","End":"03:10.955","Text":"For example, here we have an inactive protein."},{"Start":"03:10.955 ","End":"03:14.425","Text":"While ATP hydrolyzed to ADP,"},{"Start":"03:14.425 ","End":"03:19.100","Text":"the other phosphate group is connected to this protein,"},{"Start":"03:19.100 ","End":"03:20.765","Text":"which is now active."},{"Start":"03:20.765 ","End":"03:23.725","Text":"This is processed by the enzyme kinase."},{"Start":"03:23.725 ","End":"03:28.940","Text":"The energy released from the bond between the 2 phosphate groups was now"},{"Start":"03:28.940 ","End":"03:35.500","Text":"invested in the bonding of the same phosphate group that was left here with the protein."},{"Start":"03:35.500 ","End":"03:39.980","Text":"Dephosphorylation is the removal of a phosphate group from the molecule."},{"Start":"03:39.980 ","End":"03:46.910","Text":"The ATP was dephosphorylized and this active protein was phosphorylized."},{"Start":"03:46.910 ","End":"03:48.770","Text":"Both reactions, of course,"},{"Start":"03:48.770 ","End":"03:50.855","Text":"are carried out by enzymes."},{"Start":"03:50.855 ","End":"03:54.140","Text":"We\u0027ve spoken about ATP and in this section we"},{"Start":"03:54.140 ","End":"03:57.695","Text":"explain ATP\u0027s role as a cellular energy currency."},{"Start":"03:57.695 ","End":"04:01.775","Text":"We\u0027ve described how energy releases through ATP hydrolysis."},{"Start":"04:01.775 ","End":"04:05.400","Text":"Thanks for listening. See you in the next section."}],"ID":25835},{"Watched":false,"Name":"Enzymes","Duration":"9m 46s","ChapterTopicVideoID":24923,"CourseChapterTopicPlaylistID":136376,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.470 ","End":"00:06.765","Text":"Hi, we\u0027re learning about metabolism and in this section we\u0027ll be speaking about enzymes."},{"Start":"00:06.765 ","End":"00:08.505","Text":"By the end of this section,"},{"Start":"00:08.505 ","End":"00:12.960","Text":"you\u0027ll be able to describe the role of enzymes and metabolic pathways,"},{"Start":"00:12.960 ","End":"00:16.275","Text":"explain how enzymes function as molecular catalysts"},{"Start":"00:16.275 ","End":"00:20.625","Text":"and discuss enzyme regulation by various factors."},{"Start":"00:20.625 ","End":"00:24.705","Text":"Enzymes are catalysts of chemical reactions."},{"Start":"00:24.705 ","End":"00:28.110","Text":"Almost all enzymes are proteins."},{"Start":"00:28.110 ","End":"00:32.540","Text":"The enzymes bind to the reactant molecule and break it down,"},{"Start":"00:32.540 ","End":"00:35.329","Text":"or they bind to several reactant molecules"},{"Start":"00:35.329 ","End":"00:38.540","Text":"and form chemical bonds between them more readily."},{"Start":"00:38.540 ","End":"00:44.600","Text":"The way they do this is not by changing the exergonic or endergonic nature of a reaction."},{"Start":"00:44.600 ","End":"00:50.435","Text":"What they do is that they reduce the activation energy of chemical reactions."},{"Start":"00:50.435 ","End":"00:54.350","Text":"We can look at it as a ball sitting in this position."},{"Start":"00:54.350 ","End":"00:56.600","Text":"The ball is high in free energy."},{"Start":"00:56.600 ","End":"01:01.670","Text":"It has potential energy and if we push it down the hill we gain this energy."},{"Start":"01:01.670 ","End":"01:05.405","Text":"This is a low-energy area and this is a higher energy area."},{"Start":"01:05.405 ","End":"01:09.695","Text":"Now the ball isn\u0027t falling because it has this bump to go over first."},{"Start":"01:09.695 ","End":"01:12.635","Text":"If we\u0027d first invest energy,"},{"Start":"01:12.635 ","End":"01:14.720","Text":"push the ball up to here,"},{"Start":"01:14.720 ","End":"01:17.450","Text":"we would get all of this energy."},{"Start":"01:17.450 ","End":"01:21.260","Text":"This is the activation energy."},{"Start":"01:21.260 ","End":"01:23.705","Text":"It\u0027s up here on this hill."},{"Start":"01:23.705 ","End":"01:26.705","Text":"This is all the energy that we\u0027d get."},{"Start":"01:26.705 ","End":"01:31.820","Text":"But the Delta is this total energy minus the activation energy,"},{"Start":"01:31.820 ","End":"01:34.700","Text":"which leaves us with the delta energy,"},{"Start":"01:34.700 ","End":"01:37.010","Text":"which is the energy that will actually be gaining since we\u0027d"},{"Start":"01:37.010 ","End":"01:40.295","Text":"invest energy here, the activation energy."},{"Start":"01:40.295 ","End":"01:42.200","Text":"Now, instead of thinking of a bowl,"},{"Start":"01:42.200 ","End":"01:44.495","Text":"let\u0027s think about chemical potential energy."},{"Start":"01:44.495 ","End":"01:47.130","Text":"Let\u0027s say we have here,"},{"Start":"01:47.360 ","End":"01:54.220","Text":"2 molecules of hydrogen"},{"Start":"01:55.150 ","End":"02:00.329","Text":"and also double molecule of oxygen."},{"Start":"02:01.760 ","End":"02:09.925","Text":"This is high-energy and if we turn them into water molecules,"},{"Start":"02:09.925 ","End":"02:12.900","Text":"the energy is lower."},{"Start":"02:13.280 ","End":"02:19.180","Text":"This is a chemically lower in energy, H_20."},{"Start":"02:19.180 ","End":"02:22.850","Text":"But in order to turn these into water,"},{"Start":"02:22.850 ","End":"02:25.670","Text":"we would first have to break these connections and breaking"},{"Start":"02:25.670 ","End":"02:29.186","Text":"these connections needs an investment of energy,"},{"Start":"02:29.186 ","End":"02:34.520","Text":"so we\u0027d have to invest energy and take it apart to be separate atoms here,"},{"Start":"02:34.520 ","End":"02:38.975","Text":"near the oxygens and then we gain all this energy."},{"Start":"02:38.975 ","End":"02:40.985","Text":"The Delta would be here."},{"Start":"02:40.985 ","End":"02:45.140","Text":"The enzymes, they can\u0027t change the Delta of the energy"},{"Start":"02:45.140 ","End":"02:47.990","Text":"because this is the amount of energy that we get"},{"Start":"02:47.990 ","End":"02:50.990","Text":"between this conformation and this conformation."},{"Start":"02:50.990 ","End":"02:55.880","Text":"What the enzymes can do is reduce the hill and we\u0027d have to invest"},{"Start":"02:55.880 ","End":"03:01.870","Text":"less energy to push them downhill make the hill lower."},{"Start":"03:02.320 ","End":"03:05.915","Text":"Let\u0027s see how enzymes actually do this."},{"Start":"03:05.915 ","End":"03:09.950","Text":"Enzymes bind the chemical reactants called the substrates."},{"Start":"03:09.950 ","End":"03:13.010","Text":"You\u0027ve got the enzyme and the substrate."},{"Start":"03:13.010 ","End":"03:19.640","Text":"The active site here is the location within the enzyme where the substrate binds type."},{"Start":"03:19.640 ","End":"03:25.324","Text":"Specificity, there is a specifically matched enzyme for each substrate."},{"Start":"03:25.324 ","End":"03:28.385","Text":"However, there is flexibility as well."},{"Start":"03:28.385 ","End":"03:31.475","Text":"We have here the enzyme substrate complex"},{"Start":"03:31.475 ","End":"03:35.330","Text":"with a specific substrate is now connected with the enzyme."},{"Start":"03:35.330 ","End":"03:41.185","Text":"Some reactions, a single reactant substrate breaks down into multiple products."},{"Start":"03:41.185 ","End":"03:46.795","Text":"You\u0027ve got a single substrate here and the enzyme breaks it down to multiple products."},{"Start":"03:46.795 ","End":"03:52.675","Text":"In other reactions, 2 substrates may come together to create 1 larger molecule,"},{"Start":"03:52.675 ","End":"03:55.675","Text":"head of the substrate and the enzyme fit together."},{"Start":"03:55.675 ","End":"03:58.390","Text":"There are 2 models explaining enzyme function."},{"Start":"03:58.390 ","End":"04:00.333","Text":"In the lock and key model,"},{"Start":"04:00.333 ","End":"04:05.305","Text":"the enzyme and the substrate fit together perfectly in 1 instantaneous step."},{"Start":"04:05.305 ","End":"04:10.465","Text":"You see that the substance is pictured to fit exactly into the enzyme."},{"Start":"04:10.465 ","End":"04:14.710","Text":"Of course, the enzymes and the substrates don\u0027t look like puzzle pieces,"},{"Start":"04:14.710 ","End":"04:18.200","Text":"but let\u0027s imagine that they fit each other perfectly."},{"Start":"04:18.200 ","End":"04:20.620","Text":"According to the induced fit model."},{"Start":"04:20.620 ","End":"04:26.305","Text":"The enzyme and the substrate interaction causes slight shifts in the enzyme structure."},{"Start":"04:26.305 ","End":"04:28.960","Text":"These confirm an ideal binding arrangement between"},{"Start":"04:28.960 ","End":"04:32.670","Text":"the enzyme and the substrate\u0027s transition state."},{"Start":"04:32.670 ","End":"04:37.000","Text":"You see here that the enzyme pictured here as again,"},{"Start":"04:37.000 ","End":"04:38.100","Text":"2 puzzle pieces,"},{"Start":"04:38.100 ","End":"04:40.060","Text":"they don\u0027t fit each other exactly."},{"Start":"04:40.060 ","End":"04:42.535","Text":"But as they connect each other,"},{"Start":"04:42.535 ","End":"04:45.850","Text":"they change the shape and this shape changing is"},{"Start":"04:45.850 ","End":"04:49.780","Text":"actually what induces the changes in the molecules."},{"Start":"04:49.780 ","End":"04:52.090","Text":"According to the induced fit model,"},{"Start":"04:52.090 ","End":"04:57.100","Text":"the ideal binding maximizes the enzyme\u0027s ability to catalyze this reaction."},{"Start":"04:57.100 ","End":"05:00.600","Text":"Enzymes promote the chemical reactions by;"},{"Start":"05:00.600 ","End":"05:04.730","Text":"1, bringing the substrates together in optimal orientation."},{"Start":"05:04.730 ","End":"05:09.740","Text":"For example, if we have glucose and fructose that we would like to connect and"},{"Start":"05:09.740 ","End":"05:12.169","Text":"then glycosidic bond to turn to sucrose"},{"Start":"05:12.169 ","End":"05:14.990","Text":"we\u0027d have to position these molecules in the right place."},{"Start":"05:14.990 ","End":"05:18.620","Text":"Only that way, the glycosidic bond will form."},{"Start":"05:18.620 ","End":"05:21.680","Text":"Enzymes also create an optimal environment"},{"Start":"05:21.680 ","End":"05:24.320","Text":"within the active site for the reaction to occur."},{"Start":"05:24.320 ","End":"05:28.040","Text":"If we needed a hydrophobic or hydrophilic environment,"},{"Start":"05:28.040 ","End":"05:30.380","Text":"this pocket in the active site will include"},{"Start":"05:30.380 ","End":"05:34.895","Text":"molecules that are perfectly fit for the chemical reactions that we need."},{"Start":"05:34.895 ","End":"05:38.330","Text":"Sometimes it might be also electromagnetic field or whatever"},{"Start":"05:38.330 ","End":"05:42.035","Text":"is needed to make this bond occur."},{"Start":"05:42.035 ","End":"05:45.860","Text":"Sometimes the enzymes themselves take part in a chemical reaction,"},{"Start":"05:45.860 ","End":"05:50.525","Text":"meaning the substrate atom is bind to the atoms of the enzyme itself."},{"Start":"05:50.525 ","End":"05:53.210","Text":"What\u0027s important is that enzymes always remain"},{"Start":"05:53.210 ","End":"05:56.375","Text":"ultimately unchanged by the reaction they catalyze."},{"Start":"05:56.375 ","End":"05:58.130","Text":"At the beginning of the reaction,"},{"Start":"05:58.130 ","End":"06:00.140","Text":"we\u0027ve had our enzyme looking like this."},{"Start":"06:00.140 ","End":"06:01.790","Text":"At the end of the reaction,"},{"Start":"06:01.790 ","End":"06:05.705","Text":"the enzyme is free and it\u0027s ready to do same action over and over."},{"Start":"06:05.705 ","End":"06:08.990","Text":"If the reaction needs an optimal environment, of course,"},{"Start":"06:08.990 ","End":"06:12.740","Text":"the enzymes are suited to function best within a certain pH and"},{"Start":"06:12.740 ","End":"06:17.650","Text":"temperature range where they can really give the right environment to the reaction."},{"Start":"06:17.650 ","End":"06:21.970","Text":"Metabolism is controlled through enzyme regulation,"},{"Start":"06:21.970 ","End":"06:25.690","Text":"meaning that cells control the enzyme activity and use them"},{"Start":"06:25.690 ","End":"06:30.190","Text":"to determine the rates at which various biochemical reactions will occur."},{"Start":"06:30.190 ","End":"06:34.315","Text":"How can cells regulate enzyme reactions?"},{"Start":"06:34.315 ","End":"06:40.045","Text":"Enzymes can be regulated in ways that either promote or reduce their activity."},{"Start":"06:40.045 ","End":"06:43.600","Text":"In competitive inhibition, competitive inhibitors"},{"Start":"06:43.600 ","End":"06:47.725","Text":"bind to the active site of an enzyme competing with the substrate."},{"Start":"06:47.725 ","End":"06:52.090","Text":"If the normal binding would be the substrate connected to the active site when"},{"Start":"06:52.090 ","End":"06:56.065","Text":"the competitive inhibitor is bound to the active site,"},{"Start":"06:56.065 ","End":"07:00.445","Text":"the substrate can connect and therefore the reaction will not occur."},{"Start":"07:00.445 ","End":"07:03.150","Text":"In non-competitive inhibition,"},{"Start":"07:03.150 ","End":"07:07.450","Text":"non-competitive inhibitors bind to another part of an enzyme."},{"Start":"07:07.450 ","End":"07:10.075","Text":"This is called the allosteric site."},{"Start":"07:10.075 ","End":"07:13.435","Text":"The binding of the inhibitor to the allosteric site"},{"Start":"07:13.435 ","End":"07:16.885","Text":"causes the enzyme to change its shape and therefore,"},{"Start":"07:16.885 ","End":"07:21.145","Text":"the active site is less effective and the substrate can\u0027t bind it."},{"Start":"07:21.145 ","End":"07:26.365","Text":"In many systems, they are allosteric activators as well as competitive inhibitors,"},{"Start":"07:26.365 ","End":"07:28.600","Text":"so it doesn\u0027t have to be this or this,"},{"Start":"07:28.600 ","End":"07:30.065","Text":"you can have both of them."},{"Start":"07:30.065 ","End":"07:32.950","Text":"Let\u0027s look into the allosteric inhibition here."},{"Start":"07:32.950 ","End":"07:35.680","Text":"Because there\u0027s also allosteric activation."},{"Start":"07:35.680 ","End":"07:40.585","Text":"Most allosterically regulated enzymes are made from polypeptides sub-units,"},{"Start":"07:40.585 ","End":"07:42.333","Text":"each with its own active site."},{"Start":"07:42.333 ","End":"07:49.535","Text":"The enzyme complex can be in 1 or 2 states, active or inactive."},{"Start":"07:49.535 ","End":"07:51.710","Text":"Here we have 2 forms."},{"Start":"07:51.710 ","End":"07:57.290","Text":"The binding of an activator stabilizes the active arrangement of the enzyme."},{"Start":"07:57.290 ","End":"08:00.830","Text":"When the activator binds to the allosteric site,"},{"Start":"08:00.830 ","End":"08:05.870","Text":"it stabilizes the active arrangement of the enzyme and now it can work."},{"Start":"08:05.870 ","End":"08:08.525","Text":"On the contrary, the binding of an inhibitor"},{"Start":"08:08.525 ","End":"08:11.885","Text":"stabilizes the inactive arrangement of the enzyme,"},{"Start":"08:11.885 ","End":"08:14.660","Text":"and therefore the enzyme will be inactive."},{"Start":"08:14.660 ","End":"08:18.110","Text":"Another kind of inhibition is the feedback inhibition."},{"Start":"08:18.110 ","End":"08:21.455","Text":"Here\u0027s an example of a negative feedback inhibition."},{"Start":"08:21.455 ","End":"08:25.550","Text":"The end product of a metabolic pathway blocks the production."},{"Start":"08:25.550 ","End":"08:31.850","Text":"We have here, this is the substrate and this is the first enzyme and it turns"},{"Start":"08:31.850 ","End":"08:37.940","Text":"the substrate to be say this purple rod and the purple rod connects with second enzyme,"},{"Start":"08:37.940 ","End":"08:42.410","Text":"which shapes it into this shape and the third enzyme turns it into the end product,"},{"Start":"08:42.410 ","End":"08:45.410","Text":"which is in this example, the green square."},{"Start":"08:45.410 ","End":"08:50.090","Text":"Now the green square itself can bind to an allosteric site,"},{"Start":"08:50.090 ","End":"08:53.780","Text":"an enzyme 1, making it inactive."},{"Start":"08:53.780 ","End":"08:56.060","Text":"Now, when the substrate reaches it,"},{"Start":"08:56.060 ","End":"08:59.120","Text":"it\u0027s not going to go through the metabolic pathway."},{"Start":"08:59.120 ","End":"09:01.880","Text":"This prevents the cell from wasting"},{"Start":"09:01.880 ","End":"09:05.675","Text":"chemical resources by synthesizing more product than is needed."},{"Start":"09:05.675 ","End":"09:11.555","Text":"In this example, we need to synthesize these red squares as much as we need them."},{"Start":"09:11.555 ","End":"09:13.025","Text":"Once we have enough of them,"},{"Start":"09:13.025 ","End":"09:16.435","Text":"we don\u0027t want the cell to synthesize more and more of them."},{"Start":"09:16.435 ","End":"09:22.520","Text":"The end-product itself of this pathway is the one that stops it from continuing."},{"Start":"09:22.520 ","End":"09:26.035","Text":"As soon as the green squares will finish,"},{"Start":"09:26.035 ","End":"09:29.640","Text":"then we\u0027re going to get this active confirmation again"},{"Start":"09:29.640 ","End":"09:33.605","Text":"and the cell will be able to again synthesize the product that it needs."},{"Start":"09:33.605 ","End":"09:38.435","Text":"In this section, we\u0027ve described the role of enzymes and metabolic pathways,"},{"Start":"09:38.435 ","End":"09:40.640","Text":"we explain how enzymes function as"},{"Start":"09:40.640 ","End":"09:46.590","Text":"molecular catalysts and we discussed enzyme regulation by various factors."}],"ID":25836},{"Watched":false,"Name":"Exercise 1","Duration":"4m 53s","ChapterTopicVideoID":26982,"CourseChapterTopicPlaylistID":136376,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:05.400","Text":"This question is about energy storage and long-term and short-term molecules."},{"Start":"00:05.400 ","End":"00:09.390","Text":"Energy is stored long-term in the bonds of 1 molecule,"},{"Start":"00:09.390 ","End":"00:12.810","Text":"and used short-term to perform work from another molecule."},{"Start":"00:12.810 ","End":"00:17.318","Text":"A, the energy is stored long-term bonds of ATP,"},{"Start":"00:17.318 ","End":"00:20.955","Text":"and use short-term to perform work from a carbohydrate molecule."},{"Start":"00:20.955 ","End":"00:24.180","Text":"B, energy is stored long-term in the bonds of"},{"Start":"00:24.180 ","End":"00:29.760","Text":"an anabolic molecule and use short-term to perform work from a catabolic molecule."},{"Start":"00:29.760 ","End":"00:34.574","Text":"C, energy is stored long-term in the bonds of carbohydrates,"},{"Start":"00:34.574 ","End":"00:38.520","Text":"and used short-term to perform work from an ATP molecule,"},{"Start":"00:38.520 ","End":"00:41.700","Text":"or D, energy is stored long-term in"},{"Start":"00:41.700 ","End":"00:47.630","Text":"a catabolic molecule and is used short-term to perform work from an anabolic molecule."},{"Start":"00:47.630 ","End":"00:49.865","Text":"Let\u0027s go over the answers one by one,"},{"Start":"00:49.865 ","End":"00:51.275","Text":"make some sense out of it."},{"Start":"00:51.275 ","End":"00:55.670","Text":"The first answer is talking about using energy stored long-term in"},{"Start":"00:55.670 ","End":"01:00.900","Text":"ATP molecules and short-term like carbohydrates."},{"Start":"01:01.120 ","End":"01:07.280","Text":"Plants absorb energy from the sunlight,"},{"Start":"01:07.280 ","End":"01:09.425","Text":"here in black, I guess."},{"Start":"01:09.425 ","End":"01:12.620","Text":"The solar energy coming from the sunlight is transformed to"},{"Start":"01:12.620 ","End":"01:18.574","Text":"chemical energy within the bonds of glucose molecules,"},{"Start":"01:18.574 ","End":"01:21.035","Text":"which is a sugar or carbohydrate."},{"Start":"01:21.035 ","End":"01:24.700","Text":"The sugar can stay as a monosaccharide or be stored as starch,"},{"Start":"01:24.700 ","End":"01:26.395","Text":"which is a polysaccharide."},{"Start":"01:26.395 ","End":"01:31.465","Text":"But in any case, the sugars are the way that plants store this energy."},{"Start":"01:31.465 ","End":"01:34.210","Text":"Now, who consumes this energy?"},{"Start":"01:34.210 ","End":"01:37.990","Text":"Plants do, and any other consumers, such as,"},{"Start":"01:37.990 ","End":"01:44.600","Text":"let\u0027s say this pig over here, little curly tail."},{"Start":"01:46.140 ","End":"01:49.270","Text":"The consumer, in this case, the pig,"},{"Start":"01:49.270 ","End":"01:53.030","Text":"eventually uses the energy stored in the carbohydrates."},{"Start":"01:53.030 ","End":"01:58.795","Text":"The mitochondria, the energy is used to produce ATP molecules,"},{"Start":"01:58.795 ","End":"02:03.815","Text":"which is then used by the cell to perform all the cellular activities it needs."},{"Start":"02:03.815 ","End":"02:06.205","Text":"We can look at it also this way."},{"Start":"02:06.205 ","End":"02:11.320","Text":"The ATP ADP cycle shows that the energy is absorbed from the food,"},{"Start":"02:11.320 ","End":"02:13.555","Text":"in this case, the carbohydrates."},{"Start":"02:13.555 ","End":"02:19.270","Text":"It\u0027s used to connect this phosphate group to the ADP adenine diphosphate,"},{"Start":"02:19.270 ","End":"02:21.130","Text":"which only has two phosphate groups."},{"Start":"02:21.130 ","End":"02:24.415","Text":"The energy is now stored in this chemical bond,"},{"Start":"02:24.415 ","End":"02:26.335","Text":"the third phosphate group."},{"Start":"02:26.335 ","End":"02:30.100","Text":"This energy is easily used by the cell in any short-term process"},{"Start":"02:30.100 ","End":"02:34.135","Text":"needing energy and the process of losing this third phosphate group,"},{"Start":"02:34.135 ","End":"02:36.003","Text":"the energy and the bond is released,"},{"Start":"02:36.003 ","End":"02:38.125","Text":"and used for any cellular processes."},{"Start":"02:38.125 ","End":"02:39.834","Text":"Now again, we\u0027re left with ADP,"},{"Start":"02:39.834 ","End":"02:42.400","Text":"which can again be charged by sugars,"},{"Start":"02:42.400 ","End":"02:44.900","Text":"or food, or anything consumed."},{"Start":"02:45.650 ","End":"02:48.370","Text":"Let\u0027s look at our answer again."},{"Start":"02:48.370 ","End":"02:52.480","Text":"The energy is not stored long-term in ATP and the ATP we said is"},{"Start":"02:52.480 ","End":"02:57.340","Text":"the short-term usage and is not used short-term in carbohydrates."},{"Start":"02:57.340 ","End":"02:59.230","Text":"Now, these are the long-term ones."},{"Start":"02:59.230 ","End":"03:01.540","Text":"We can already erase answer A,"},{"Start":"03:01.540 ","End":"03:03.625","Text":"I\u0027m going to look at answer B."},{"Start":"03:03.625 ","End":"03:06.055","Text":"An antibiotic molecule is used for"},{"Start":"03:06.055 ","End":"03:09.070","Text":"long-term and a catabolic molecule is used for short-term."},{"Start":"03:09.070 ","End":"03:11.095","Text":"What are these molecules?"},{"Start":"03:11.095 ","End":"03:15.715","Text":"Many of the organic molecules can be seen in 2 states."},{"Start":"03:15.715 ","End":"03:21.070","Text":"Polymers, which means many of the single building blocks attached to"},{"Start":"03:21.070 ","End":"03:27.190","Text":"a 1 long molecule or the monomers are the simple building blocks."},{"Start":"03:27.190 ","End":"03:32.735","Text":"In anabolism, monomers are connected to form polymers."},{"Start":"03:32.735 ","End":"03:35.435","Text":"This usually requires energy input."},{"Start":"03:35.435 ","End":"03:41.829","Text":"In catabolism, 1 polymer is taken apart to form many monomers."},{"Start":"03:41.829 ","End":"03:47.255","Text":"Two, cells tend to use polymers for longer storage than monomers,"},{"Start":"03:47.255 ","End":"03:49.010","Text":"but that isn\u0027t always true,"},{"Start":"03:49.010 ","End":"03:51.995","Text":"and monomers can also be used for long-term storage."},{"Start":"03:51.995 ","End":"03:56.210","Text":"In any case, we\u0027ve already seen that even the glucose molecules,"},{"Start":"03:56.210 ","End":"04:01.190","Text":"the monomers have taken apart the ATP prior to being consumed by the cell."},{"Start":"04:01.190 ","End":"04:04.285","Text":"We can cross that answer B."},{"Start":"04:04.285 ","End":"04:08.790","Text":"Answer C again, is a bit of carbohydrates and ATP."},{"Start":"04:08.790 ","End":"04:12.480","Text":"This time it tells us that the carbs are the long-term energy,"},{"Start":"04:12.480 ","End":"04:17.450","Text":"which seems right and the ATP is the short-term energy used by the cell."},{"Start":"04:17.450 ","End":"04:19.490","Text":"But before we circle this answer,"},{"Start":"04:19.490 ","End":"04:23.630","Text":"let\u0027s have a look at answered D. It\u0027s again talking about catabolic molecules,"},{"Start":"04:23.630 ","End":"04:24.940","Text":"and anabolic molecules,"},{"Start":"04:24.940 ","End":"04:27.350","Text":"and this time it gives us the opposite direction,"},{"Start":"04:27.350 ","End":"04:30.410","Text":"which is really even worse than the first option because"},{"Start":"04:30.410 ","End":"04:35.045","Text":"the polymers here are said to be used for short-term,"},{"Start":"04:35.045 ","End":"04:36.980","Text":"while the monomers for long-term,"},{"Start":"04:36.980 ","End":"04:38.945","Text":"which is absolutely not true."},{"Start":"04:38.945 ","End":"04:43.430","Text":"Therefore, we can get back to our ATP ADP cycle."},{"Start":"04:43.430 ","End":"04:45.845","Text":"Carbohydrates and ATP,"},{"Start":"04:45.845 ","End":"04:48.613","Text":"our carbohydrates are the long-term storage,"},{"Start":"04:48.613 ","End":"04:53.940","Text":"and the short-term molecule used for performing work in a cell is the ATP."}],"ID":28106},{"Watched":false,"Name":"Exercise 2","Duration":"2m 14s","ChapterTopicVideoID":26983,"CourseChapterTopicPlaylistID":136376,"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":"DNA replication involves the unwinding of 2 strands of parent DNA,"},{"Start":"00:05.610 ","End":"00:09.015","Text":"copying each strand to synthesize complimentary strands,"},{"Start":"00:09.015 ","End":"00:11.940","Text":"and releasing the parent and daughter DNA."},{"Start":"00:11.940 ","End":"00:15.615","Text":"Which of the following accurately describes this process?"},{"Start":"00:15.615 ","End":"00:18.540","Text":"A, this is an anabolic process."},{"Start":"00:18.540 ","End":"00:21.210","Text":"B, this is a catabolic process."},{"Start":"00:21.210 ","End":"00:24.824","Text":"C, this is both anabolic and catabolic,"},{"Start":"00:24.824 ","End":"00:27.450","Text":"or D, this is a metabolic process,"},{"Start":"00:27.450 ","End":"00:30.510","Text":"but is neither anabolic nor catabolic."},{"Start":"00:30.510 ","End":"00:33.330","Text":"Let\u0027s have a look at this process then."},{"Start":"00:33.330 ","End":"00:36.644","Text":"Here we\u0027ve got the parent DNA,"},{"Start":"00:36.644 ","End":"00:39.405","Text":"which is separated into 2 separate strands."},{"Start":"00:39.405 ","End":"00:45.530","Text":"Then each strand is used to synthesize the complimentary strand with single nucleotides."},{"Start":"00:45.530 ","End":"00:47.305","Text":"Here it goes,"},{"Start":"00:47.305 ","End":"00:50.048","Text":"one by one they are added to the strands,"},{"Start":"00:50.048 ","End":"00:54.220","Text":"from 5-prime to 3-prime until the complimentary strands are completed."},{"Start":"00:54.220 ","End":"01:00.530","Text":"Now we have 2 separate DNA strands replicated from the original parent molecule."},{"Start":"01:00.530 ","End":"01:02.630","Text":"What process is this?"},{"Start":"01:02.630 ","End":"01:04.145","Text":"Anabolic, catabolic?"},{"Start":"01:04.145 ","End":"01:07.685","Text":"Let\u0027s talk about anabolism and catabolism a little bit."},{"Start":"01:07.685 ","End":"01:12.140","Text":"Well, metabolism includes the 2 processes of anabolism and catabolism."},{"Start":"01:12.140 ","End":"01:13.623","Text":"While in anabolism,"},{"Start":"01:13.623 ","End":"01:15.245","Text":"monomers are single units,"},{"Start":"01:15.245 ","End":"01:19.145","Text":"building blocks are put together to form a single polymer."},{"Start":"01:19.145 ","End":"01:22.740","Text":"While in catabolism, 1 single polymer is"},{"Start":"01:22.740 ","End":"01:26.634","Text":"taken apart to many building blocks, the monomers."},{"Start":"01:26.634 ","End":"01:28.430","Text":"What did we have here?"},{"Start":"01:28.430 ","End":"01:32.870","Text":"We took many nucleotides and build 1 long DNA strand."},{"Start":"01:32.870 ","End":"01:36.605","Text":"Just taking many monomers and building a single polymer."},{"Start":"01:36.605 ","End":"01:38.625","Text":"Catabolism is out of question."},{"Start":"01:38.625 ","End":"01:39.929","Text":"Let\u0027s look at the answers here."},{"Start":"01:39.929 ","End":"01:43.170","Text":"B, catabolic process, you can erase."},{"Start":"01:43.170 ","End":"01:45.695","Text":"C, both anabolic and catabolic,"},{"Start":"01:45.695 ","End":"01:46.770","Text":"we know it\u0027s not catabolic,"},{"Start":"01:46.770 ","End":"01:48.665","Text":"so we can erase the whole answer here."},{"Start":"01:48.665 ","End":"01:50.780","Text":"D, this is a metabolic process,"},{"Start":"01:50.780 ","End":"01:53.239","Text":"but it\u0027s neither anabolic nor catabolic."},{"Start":"01:53.239 ","End":"01:56.105","Text":"Well, metabolism has to be 1 of them."},{"Start":"01:56.105 ","End":"02:00.740","Text":"We can\u0027t have metabolism that\u0027s neither anabolic nor catabolic."},{"Start":"02:00.740 ","End":"02:04.730","Text":"Therefore, we\u0027re left with the answer A, the anabolic process."},{"Start":"02:04.730 ","End":"02:06.875","Text":"As we said, monomers,"},{"Start":"02:06.875 ","End":"02:11.910","Text":"nucleotides were used to form 1 long DNA strand, a polymer."},{"Start":"02:11.910 ","End":"02:14.560","Text":"A is the correct answer."}],"ID":28107},{"Watched":false,"Name":"Exercise 3","Duration":"5m 13s","ChapterTopicVideoID":26984,"CourseChapterTopicPlaylistID":136376,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.260 ","End":"00:03.045","Text":"Consider a pendulum swinging."},{"Start":"00:03.045 ","End":"00:08.880","Text":"Which types of energy are associated with the pendulum in the following instances: One,"},{"Start":"00:08.880 ","End":"00:11.430","Text":"the moment at which it completes 1 cycle"},{"Start":"00:11.430 ","End":"00:14.865","Text":"just before it begins to fall back towards the other end."},{"Start":"00:14.865 ","End":"00:19.215","Text":"Two, the moment that it is in the middle between the 2 ends,"},{"Start":"00:19.215 ","End":"00:22.740","Text":"and three, just before it reaches the end of 1 cycle,"},{"Start":"00:22.740 ","End":"00:25.450","Text":"just before instant 1."},{"Start":"00:25.640 ","End":"00:28.769","Text":"This is a little complicated to imagine."},{"Start":"00:28.769 ","End":"00:32.145","Text":"Let\u0027s just draw it. What is a pendulum?"},{"Start":"00:32.145 ","End":"00:37.260","Text":"This is a weight hanging from a string tied to a center nail."},{"Start":"00:37.260 ","End":"00:39.525","Text":"When the weight is lifted in a curve,"},{"Start":"00:39.525 ","End":"00:42.570","Text":"it falls in a circular motion."},{"Start":"00:42.570 ","End":"00:44.845","Text":"It reaches the top again."},{"Start":"00:44.845 ","End":"00:48.080","Text":"Theoretically in an environment where there is no friction,"},{"Start":"00:48.080 ","End":"00:51.270","Text":"the pendulum can go forever."},{"Start":"00:51.280 ","End":"00:54.425","Text":"Why is this and how does this work?"},{"Start":"00:54.425 ","End":"00:57.805","Text":"Well, we\u0027ve mentioned several kinds of energy."},{"Start":"00:57.805 ","End":"01:00.755","Text":"Now, the first law of thermodynamics states"},{"Start":"01:00.755 ","End":"01:03.725","Text":"that energy can be transferred from one type to another,"},{"Start":"01:03.725 ","End":"01:05.540","Text":"but can never be lost."},{"Start":"01:05.540 ","End":"01:09.160","Text":"Let\u0027s have a look at kinetic and potential energies."},{"Start":"01:09.160 ","End":"01:13.265","Text":"When we take an object and raise it against gravity,"},{"Start":"01:13.265 ","End":"01:16.010","Text":"we\u0027re investing energy in this process."},{"Start":"01:16.010 ","End":"01:18.920","Text":"The energy is now invested in the object."},{"Start":"01:18.920 ","End":"01:21.345","Text":"The object has potential energy."},{"Start":"01:21.345 ","End":"01:23.175","Text":"If allowed to drop,"},{"Start":"01:23.175 ","End":"01:26.540","Text":"this energy will be transferred into kinetic energy,"},{"Start":"01:26.540 ","End":"01:29.060","Text":"which means the energy of movement."},{"Start":"01:29.060 ","End":"01:34.520","Text":"For example, investing energy by pulling and stretching the cord and"},{"Start":"01:34.520 ","End":"01:40.145","Text":"the bow transfers the energy to the tension in the cord and the bow."},{"Start":"01:40.145 ","End":"01:42.110","Text":"By releasing them,"},{"Start":"01:42.110 ","End":"01:47.245","Text":"the energy is now transferred to kinetic energy of the arrow flying through the air."},{"Start":"01:47.245 ","End":"01:52.325","Text":"Picking up the hammer up into the air invests energy against gravity."},{"Start":"01:52.325 ","End":"01:55.465","Text":"Therefore, the hammer now has potential energy."},{"Start":"01:55.465 ","End":"01:58.100","Text":"Letting go of the hammer, letting it drop,"},{"Start":"01:58.100 ","End":"02:03.180","Text":"now transfers this potential energy to be kinetic energy."},{"Start":"02:03.820 ","End":"02:07.385","Text":"Let\u0027s get back to a pendulum now."},{"Start":"02:07.385 ","End":"02:09.710","Text":"Here we have the pendulum."},{"Start":"02:09.710 ","End":"02:11.670","Text":"When we first take it into our hands,"},{"Start":"02:11.670 ","End":"02:13.625","Text":"the weight is at the bottom now,"},{"Start":"02:13.625 ","End":"02:15.065","Text":"no energy at all."},{"Start":"02:15.065 ","End":"02:19.285","Text":"Pulling it up to the top against gravity and investing all this energy in it,"},{"Start":"02:19.285 ","End":"02:21.950","Text":"now it gives it a lot of potential energy."},{"Start":"02:21.950 ","End":"02:23.735","Text":"When we release the pendulum,"},{"Start":"02:23.735 ","End":"02:25.175","Text":"it starts to fall."},{"Start":"02:25.175 ","End":"02:29.300","Text":"As it falls, the potential energy changes to kinetic energy."},{"Start":"02:29.300 ","End":"02:30.830","Text":"The more it falls,"},{"Start":"02:30.830 ","End":"02:32.680","Text":"the stronger the kinetic energy is,"},{"Start":"02:32.680 ","End":"02:35.185","Text":"and when it reaches the bottom point here,"},{"Start":"02:35.185 ","End":"02:38.570","Text":"there\u0027s no more potential energy, just kinetic energy."},{"Start":"02:38.570 ","End":"02:42.020","Text":"The kinetic energy that\u0027s left is just enough to pull"},{"Start":"02:42.020 ","End":"02:45.335","Text":"it up to the same point on the other side where it has been before."},{"Start":"02:45.335 ","End":"02:48.785","Text":"As the way it starts climbing up against gravity,"},{"Start":"02:48.785 ","End":"02:53.645","Text":"the kinetic energy is invested in it and turns it to be potential energy again."},{"Start":"02:53.645 ","End":"02:56.675","Text":"If we look at the top points here, here,"},{"Start":"02:56.675 ","End":"02:58.310","Text":"and here on both sides,"},{"Start":"02:58.310 ","End":"03:01.265","Text":"the pendulum has only potential energy."},{"Start":"03:01.265 ","End":"03:03.395","Text":"It\u0027s not at movement at all."},{"Start":"03:03.395 ","End":"03:07.355","Text":"The maximum point where they\u0027re going right or left,"},{"Start":"03:07.355 ","End":"03:09.530","Text":"here at the bottom, is the point where"},{"Start":"03:09.530 ","End":"03:14.405","Text":"the kinetic energy is the strongest and the potential energy is at 0."},{"Start":"03:14.405 ","End":"03:17.220","Text":"Any point here in-between,"},{"Start":"03:17.220 ","End":"03:19.980","Text":"whether we\u0027re going downhill or uphill,"},{"Start":"03:19.980 ","End":"03:22.625","Text":"whether we\u0027re going from right or from left,"},{"Start":"03:22.625 ","End":"03:26.795","Text":"we have a mixture of potential energy and kinetic energy."},{"Start":"03:26.795 ","End":"03:29.260","Text":"Let\u0027s see now what the question is now."},{"Start":"03:29.260 ","End":"03:34.099","Text":"Which types of energy are associated with the pendulum in the following instances?"},{"Start":"03:34.099 ","End":"03:37.240","Text":"At the moment at which it completes 1 cycle,"},{"Start":"03:37.240 ","End":"03:40.760","Text":"at point 1 after completing 1 cycle,"},{"Start":"03:40.760 ","End":"03:44.720","Text":"we\u0027re speaking about an instance where there is only potential energy."},{"Start":"03:44.720 ","End":"03:49.400","Text":"Therefore, a, saying that we have potential and kinetic is wrong, b,"},{"Start":"03:49.400 ","End":"03:51.254","Text":"telling us potential,"},{"Start":"03:51.254 ","End":"03:52.800","Text":"that can work, c,"},{"Start":"03:52.800 ","End":"03:54.600","Text":"potential, that could work, d,"},{"Start":"03:54.600 ","End":"03:57.525","Text":"potential and kinetic, that is wrong."},{"Start":"03:57.525 ","End":"03:59.880","Text":"Let\u0027s see the next one."},{"Start":"03:59.880 ","End":"04:04.550","Text":"Two, the moment that it is in the middle between the 2 ends."},{"Start":"04:04.550 ","End":"04:08.300","Text":"At this point, all the potential energy has already"},{"Start":"04:08.300 ","End":"04:12.365","Text":"been used and now it\u0027s all transferred to be kinetic energy."},{"Start":"04:12.365 ","End":"04:16.744","Text":"Let\u0027s see two, potential and kinetic."},{"Start":"04:16.744 ","End":"04:19.070","Text":"We\u0027re left only with b and c. Let\u0027s just look at them."},{"Start":"04:19.070 ","End":"04:23.165","Text":"Potential and kinetic. That\u0027s wrong."},{"Start":"04:23.165 ","End":"04:25.400","Text":"c tells us kinetic."},{"Start":"04:25.400 ","End":"04:28.430","Text":"That\u0027s true. Very good."},{"Start":"04:28.430 ","End":"04:30.155","Text":"We\u0027re going with c meantime."},{"Start":"04:30.155 ","End":"04:32.525","Text":"Let\u0027s just check the last one, three,"},{"Start":"04:32.525 ","End":"04:34.760","Text":"just before it reaches the end of 1 cycle,"},{"Start":"04:34.760 ","End":"04:37.040","Text":"just before instant 1."},{"Start":"04:37.040 ","End":"04:40.030","Text":"We\u0027re talking about the ball right here."},{"Start":"04:40.030 ","End":"04:46.105","Text":"The weight now in right before reaching point 1,"},{"Start":"04:46.105 ","End":"04:48.140","Text":"doesn\u0027t matter which side we\u0027re on,"},{"Start":"04:48.140 ","End":"04:50.140","Text":"we\u0027re on the uphill here, are going up,"},{"Start":"04:50.140 ","End":"04:51.575","Text":"and at this point,"},{"Start":"04:51.575 ","End":"04:55.445","Text":"almost all the kinetic energy is transferred"},{"Start":"04:55.445 ","End":"04:57.650","Text":"to potential energy and the ball is really"},{"Start":"04:57.650 ","End":"05:00.140","Text":"slowing down already now, but it\u0027s still going."},{"Start":"05:00.140 ","End":"05:01.820","Text":"It still has kinetic energy,"},{"Start":"05:01.820 ","End":"05:05.155","Text":"and already is loaded with a lot of potential energy."},{"Start":"05:05.155 ","End":"05:07.715","Text":"Number 3, potential and kinetic."},{"Start":"05:07.715 ","End":"05:11.460","Text":"That is the right one. We can now cross out all the wrong answers,"},{"Start":"05:11.460 ","End":"05:13.970","Text":"and circle answer c."}],"ID":28108},{"Watched":false,"Name":"Exercise 4","Duration":"5m 10s","ChapterTopicVideoID":26985,"CourseChapterTopicPlaylistID":136376,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.230 ","End":"00:03.600","Text":"Which of the following comparisons or contrasts"},{"Start":"00:03.600 ","End":"00:07.200","Text":"between endergonic and exergonic reactions is false?"},{"Start":"00:07.200 ","End":"00:12.765","Text":"A, endergonic reactions have a positive change in Gibbs free energy,"},{"Start":"00:12.765 ","End":"00:16.425","Text":"while exergonic reactions have a negative change in free energy."},{"Start":"00:16.425 ","End":"00:23.520","Text":"B, endergonic reactions consume energy and exergonic reactions release energy."},{"Start":"00:23.520 ","End":"00:27.870","Text":"C, both endergonic and exergonic reactions"},{"Start":"00:27.870 ","End":"00:32.220","Text":"require a small amount of energy to overcome an activation barrier."},{"Start":"00:32.220 ","End":"00:36.260","Text":"Or D, endergonic reactions take place slowly,"},{"Start":"00:36.260 ","End":"00:39.380","Text":"and exergonic reactions take place quickly."},{"Start":"00:39.380 ","End":"00:45.450","Text":"Let\u0027s have a look at these answers one by one and see which one of them is false."},{"Start":"00:46.540 ","End":"00:50.030","Text":"Endergonic reactions are reactions where"},{"Start":"00:50.030 ","End":"00:55.745","Text":"the free energy of the reactants is lower than the free energy of the product."},{"Start":"00:55.745 ","End":"01:03.590","Text":"This is the change in energy or the Delta in G. Energy must be supplied to this reaction."},{"Start":"01:03.590 ","End":"01:07.850","Text":"On the other hand, exergonic reactions are reactions"},{"Start":"01:07.850 ","End":"01:11.975","Text":"where the reactant\u0027s free energy is higher than the product\u0027s free energy."},{"Start":"01:11.975 ","End":"01:15.605","Text":"Therefore, the change in free energy is negative."},{"Start":"01:15.605 ","End":"01:18.620","Text":"Energy is released in these reactions."},{"Start":"01:18.620 ","End":"01:20.675","Text":"Let\u0027s have a look at answer A,"},{"Start":"01:20.675 ","End":"01:24.230","Text":"endergonic reactions have a positive change in free energy."},{"Start":"01:24.230 ","End":"01:29.240","Text":"Let\u0027s see here we have endergonic reactions and a positive change in free energy,"},{"Start":"01:29.240 ","End":"01:32.825","Text":"and exergonic reactions have a negative change in energy."},{"Start":"01:32.825 ","End":"01:36.125","Text":"This is correct and since we\u0027re looking for the false statement,"},{"Start":"01:36.125 ","End":"01:40.235","Text":"we can mark off A as not the right answer for us."},{"Start":"01:40.235 ","End":"01:46.250","Text":"B, endergonic reactions consume energy and exergonic reactions release energy."},{"Start":"01:46.250 ","End":"01:48.845","Text":"Let\u0027s see here endergonic reactions."},{"Start":"01:48.845 ","End":"01:51.650","Text":"They consume energy since the product is in"},{"Start":"01:51.650 ","End":"01:56.635","Text":"a higher energy state than the reactant. That is true."},{"Start":"01:56.635 ","End":"01:59.960","Text":"Exergonic reactions release energy since"},{"Start":"01:59.960 ","End":"02:03.290","Text":"the products are on a lower level of free energy than the reactants."},{"Start":"02:03.290 ","End":"02:05.975","Text":"When the reactants change to be the products,"},{"Start":"02:05.975 ","End":"02:07.625","Text":"there is a release of free energy,"},{"Start":"02:07.625 ","End":"02:10.400","Text":"so B is also correct."},{"Start":"02:10.400 ","End":"02:13.835","Text":"Therefore, it\u0027s not the full statement that we\u0027re looking for."},{"Start":"02:13.835 ","End":"02:18.095","Text":"C, both endergonic and exergonic reactions"},{"Start":"02:18.095 ","End":"02:23.090","Text":"require a small amount of energy to overcome an activation barrier."},{"Start":"02:23.090 ","End":"02:26.180","Text":"Well, we already saw that the endergonic reactions"},{"Start":"02:26.180 ","End":"02:29.315","Text":"need a supply of energy to overcome this barrier."},{"Start":"02:29.315 ","End":"02:34.340","Text":"The reactant will not change to be the product without an investment of energy."},{"Start":"02:34.340 ","End":"02:37.265","Text":"But what about the exergonic reaction?"},{"Start":"02:37.265 ","End":"02:42.020","Text":"We might have expected the reactant to change spontaneously straight to the product,"},{"Start":"02:42.020 ","End":"02:44.150","Text":"releasing energy on the way."},{"Start":"02:44.150 ","End":"02:46.010","Text":"But this doesn\u0027t happen."},{"Start":"02:46.010 ","End":"02:49.520","Text":"This is because the reactant\u0027s state is stable."},{"Start":"02:49.520 ","End":"02:53.915","Text":"In order to change from the reactant to the product,"},{"Start":"02:53.915 ","End":"02:58.550","Text":"the reactants have to undergo a change to the transition state."},{"Start":"02:58.550 ","End":"03:04.550","Text":"For example, if we have here the first molecule comprised of the A and B atoms,"},{"Start":"03:04.550 ","End":"03:08.000","Text":"and the second molecule comprise of the C and D atoms."},{"Start":"03:08.000 ","End":"03:11.730","Text":"In order to change them so that atom A will connect with C and"},{"Start":"03:11.730 ","End":"03:15.968","Text":"atom B will be connected with D in the final molecules of the products,"},{"Start":"03:15.968 ","End":"03:20.255","Text":"we first need to separate atom A from atom B and atom C from atom"},{"Start":"03:20.255 ","End":"03:25.160","Text":"D. Since this stable state is in a lower energy than the transition state,"},{"Start":"03:25.160 ","End":"03:28.175","Text":"it requires an investment of some energy."},{"Start":"03:28.175 ","End":"03:30.530","Text":"Once this energy barrier is passed,"},{"Start":"03:30.530 ","End":"03:34.040","Text":"you can expect a spontaneous change to the products."},{"Start":"03:34.040 ","End":"03:39.060","Text":"This investment in energy is called the energy of activation."},{"Start":"03:39.550 ","End":"03:43.775","Text":"Yes, it\u0027s true that both endergonic and exergonic reactions"},{"Start":"03:43.775 ","End":"03:48.785","Text":"require at least a small amount of energy to overcome an activation barrier."},{"Start":"03:48.785 ","End":"03:53.855","Text":"Since we\u0027re looking for the false statement this statement is also not false."},{"Start":"03:53.855 ","End":"03:56.225","Text":"Well, let\u0027s have a look at answer D now."},{"Start":"03:56.225 ","End":"04:01.270","Text":"Endergonic reactions take place slowly and exergonic reactions take place quickly,"},{"Start":"04:01.270 ","End":"04:04.550","Text":"so endergonic reactions needed an investment of energy."},{"Start":"04:04.550 ","End":"04:09.260","Text":"We might expect these reactions to take place slower than exergonic reactions."},{"Start":"04:09.260 ","End":"04:15.199","Text":"But since both endergonic and exergonic reactions require an investment in energy,"},{"Start":"04:15.199 ","End":"04:21.005","Text":"we can expect them to take place slowly in general in a natural environment."},{"Start":"04:21.005 ","End":"04:25.370","Text":"What helps these reactions speed up?"},{"Start":"04:25.370 ","End":"04:29.390","Text":"Living organisms use an enzyme to do this."},{"Start":"04:29.390 ","End":"04:32.090","Text":"The enzymes cannot change the difference"},{"Start":"04:32.090 ","End":"04:35.305","Text":"in energy between the reactants and the products."},{"Start":"04:35.305 ","End":"04:40.280","Text":"What the enzymes can do is lower the energy of activation required to"},{"Start":"04:40.280 ","End":"04:45.845","Text":"move from reactants to transitions state and thus speeding up the process."},{"Start":"04:45.845 ","End":"04:50.525","Text":"When we speak about endergonic reactions that require an investment in energy,"},{"Start":"04:50.525 ","End":"04:52.730","Text":"the enzymes can supply this energy,"},{"Start":"04:52.730 ","End":"04:55.085","Text":"usually using an ATP molecule."},{"Start":"04:55.085 ","End":"04:57.830","Text":"It really might speed up reactions is not"},{"Start":"04:57.830 ","End":"05:00.694","Text":"whether the reaction is endergonic or exergonic,"},{"Start":"05:00.694 ","End":"05:04.595","Text":"but rather whether the enzyme is activated or not."},{"Start":"05:04.595 ","End":"05:06.920","Text":"Since we\u0027re looking for the false answer,"},{"Start":"05:06.920 ","End":"05:10.990","Text":"we can circle answer D as a correct answer."}],"ID":28109},{"Watched":false,"Name":"Exercise 5","Duration":"4m 21s","ChapterTopicVideoID":26986,"CourseChapterTopicPlaylistID":136376,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.500","Text":"Hi, in this question we\u0027re asked to find the best way to judge"},{"Start":"00:04.500 ","End":"00:09.330","Text":"the relative activation energies between 2 given chemical reactions."},{"Start":"00:09.330 ","End":"00:11.220","Text":"The first answer, a,"},{"Start":"00:11.220 ","End":"00:16.635","Text":"is to compare the change in Gibbs free energy values between the 2 reactions."},{"Start":"00:16.635 ","End":"00:19.695","Text":"Answer b is to compare the reaction rates."},{"Start":"00:19.695 ","End":"00:23.640","Text":"C, compare their ideal environmental conditions."},{"Start":"00:23.640 ","End":"00:28.470","Text":"Or d, compare the spontaneity between the 2 reactions."},{"Start":"00:28.470 ","End":"00:30.600","Text":"In order to find the best answer,"},{"Start":"00:30.600 ","End":"00:34.080","Text":"let\u0027s have a closer look at activation energies."},{"Start":"00:34.080 ","End":"00:36.860","Text":"An exergonic chemical reactions,"},{"Start":"00:36.860 ","End":"00:41.078","Text":"the reactants are in a higher energy state than the products,"},{"Start":"00:41.078 ","End":"00:46.044","Text":"and therefore during the change of the reactants to the products energy is released."},{"Start":"00:46.044 ","End":"00:49.805","Text":"Why doesn\u0027t this reaction occurs spontaneously all the time?"},{"Start":"00:49.805 ","End":"00:53.840","Text":"1 of the reactants stay as reactants in a stable state."},{"Start":"00:53.840 ","End":"00:57.545","Text":"The answer is, the activation energy."},{"Start":"00:57.545 ","End":"01:01.115","Text":"In order for the reactants to change the products,"},{"Start":"01:01.115 ","End":"01:05.450","Text":"in this example, a molecule comprised of atoms A and B,"},{"Start":"01:05.450 ","End":"01:09.050","Text":"and another molecule comprised of atoms C and D needs to"},{"Start":"01:09.050 ","End":"01:12.995","Text":"change to be 2 molecules where now atoms A and C are connected,"},{"Start":"01:12.995 ","End":"01:14.900","Text":"and atoms B and D are connected."},{"Start":"01:14.900 ","End":"01:19.175","Text":"Even though the products are in a lower energy state than the reactants,"},{"Start":"01:19.175 ","End":"01:22.835","Text":"meaning that the products are favorable energy wise."},{"Start":"01:22.835 ","End":"01:26.270","Text":"In order for the reactants to change to be the products,"},{"Start":"01:26.270 ","End":"01:31.490","Text":"first the connection between atom A and B and the connection between atoms"},{"Start":"01:31.490 ","End":"01:36.905","Text":"C and D needs to be taken apart in order to reach the transition state."},{"Start":"01:36.905 ","End":"01:40.610","Text":"From now, spontaneously we can expect atoms A and"},{"Start":"01:40.610 ","End":"01:44.375","Text":"C to connect with each other and atoms B and D to connect with each other,"},{"Start":"01:44.375 ","End":"01:46.235","Text":"since this is more favorable."},{"Start":"01:46.235 ","End":"01:49.385","Text":"But in order to reach this transition state,"},{"Start":"01:49.385 ","End":"01:51.984","Text":"an energy input is required,"},{"Start":"01:51.984 ","End":"01:56.125","Text":"that\u0027s because the transition state is higher in energy than the reactants."},{"Start":"01:56.125 ","End":"01:58.970","Text":"This is less favorable energy-wise,"},{"Start":"01:58.970 ","End":"02:04.020","Text":"and therefore it requires a positive investment in energy."},{"Start":"02:04.990 ","End":"02:07.535","Text":"The reactants are stable."},{"Start":"02:07.535 ","End":"02:09.988","Text":"They don\u0027t change straight to the products,"},{"Start":"02:09.988 ","End":"02:13.370","Text":"because they first require an investment of energy."},{"Start":"02:13.370 ","End":"02:16.565","Text":"This is called the activation energy."},{"Start":"02:16.565 ","End":"02:20.960","Text":"EA stands for energy for activation."},{"Start":"02:20.960 ","End":"02:23.359","Text":"Now, we\u0027re asked to compare"},{"Start":"02:23.359 ","End":"02:27.875","Text":"the relative activation energies between 2 given chemical reactions."},{"Start":"02:27.875 ","End":"02:31.730","Text":"The energy of activation is what stops"},{"Start":"02:31.730 ","End":"02:34.870","Text":"the reactants from changing spontaneously to products,"},{"Start":"02:34.870 ","End":"02:37.870","Text":"and the lower this activation energy is,"},{"Start":"02:37.870 ","End":"02:42.735","Text":"we can expect the rate of reactants changing the products to be higher."},{"Start":"02:42.735 ","End":"02:47.770","Text":"The smaller the energy of activation is in the process,"},{"Start":"02:47.770 ","End":"02:50.360","Text":"we can expect the process to become faster."},{"Start":"02:50.360 ","End":"02:56.105","Text":"That\u0027s because we need to invest less energy which might happen spontaneously slower,"},{"Start":"02:56.105 ","End":"02:58.325","Text":"and that is exactly how enzymes work."},{"Start":"02:58.325 ","End":"03:02.150","Text":"Enzymes speed up chemical reactions not by changing"},{"Start":"03:02.150 ","End":"03:08.459","Text":"the energy difference which stays the same between the reactants, and the products."},{"Start":"03:10.840 ","End":"03:17.210","Text":"What the enzymes can do is to change the activation energy and make it lower,"},{"Start":"03:17.210 ","End":"03:20.695","Text":"and this is what speeds up the chemical reaction."},{"Start":"03:20.695 ","End":"03:22.505","Text":"If you\u0027re asked to judge"},{"Start":"03:22.505 ","End":"03:25.985","Text":"the relative activation energies between 2 given chemical reactions,"},{"Start":"03:25.985 ","End":"03:27.775","Text":"how would we find them?"},{"Start":"03:27.775 ","End":"03:30.500","Text":"Well, by comparing the change in energy values"},{"Start":"03:30.500 ","End":"03:33.050","Text":"between the 2 reactions, we won\u0027t find a thing."},{"Start":"03:33.050 ","End":"03:36.665","Text":"We can see here that this reaction is a lot faster than this one,"},{"Start":"03:36.665 ","End":"03:39.410","Text":"although the change in energy is the same in both of them,"},{"Start":"03:39.410 ","End":"03:41.718","Text":"so a is wrong."},{"Start":"03:41.718 ","End":"03:44.375","Text":"Also comparing their ideal environmental conditions"},{"Start":"03:44.375 ","End":"03:47.900","Text":"won\u0027t give us any knowledge about the activation energies."},{"Start":"03:47.900 ","End":"03:52.475","Text":"Answer d offers us to compare the spontaneity between the 2 reactions,"},{"Start":"03:52.475 ","End":"03:54.425","Text":"which is also incorrect."},{"Start":"03:54.425 ","End":"03:56.540","Text":"From what we\u0027ve seen about enzymes,"},{"Start":"03:56.540 ","End":"04:02.335","Text":"we know that compare the reaction rates can tell us all about the energy of activation."},{"Start":"04:02.335 ","End":"04:05.160","Text":"The faster the reaction rates will find,"},{"Start":"04:05.160 ","End":"04:10.790","Text":"the chemical reaction with higher rates can tell us that the activation energy is lower."},{"Start":"04:10.790 ","End":"04:13.399","Text":"Therefore, answer b is correct."},{"Start":"04:13.399 ","End":"04:16.400","Text":"The best way to judge the relative activation energies"},{"Start":"04:16.400 ","End":"04:21.510","Text":"between 2 given chemical reactions is by comparing the reaction rates."}],"ID":28110},{"Watched":false,"Name":"Exercise 6","Duration":"3m 55s","ChapterTopicVideoID":26987,"CourseChapterTopicPlaylistID":136376,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.320 ","End":"00:06.090","Text":"Which of the following is not an example of an energy transformation?"},{"Start":"00:06.090 ","End":"00:08.805","Text":"A, turning on a light switch."},{"Start":"00:08.805 ","End":"00:11.565","Text":"B, solar panels at work."},{"Start":"00:11.565 ","End":"00:14.790","Text":"C, formation of static electricity,"},{"Start":"00:14.790 ","End":"00:17.115","Text":"or D, none of the above."},{"Start":"00:17.115 ","End":"00:19.170","Text":"In order to answer this question,"},{"Start":"00:19.170 ","End":"00:22.905","Text":"let\u0027s first explain what energy transformation is."},{"Start":"00:22.905 ","End":"00:26.549","Text":"Energy exists in many forms: Kinetic,"},{"Start":"00:26.549 ","End":"00:29.205","Text":"potential, mechanical and so on."},{"Start":"00:29.205 ","End":"00:34.500","Text":"The law of conservation of energy states that in an isolated system,"},{"Start":"00:34.500 ","End":"00:37.140","Text":"energy might change between the different types,"},{"Start":"00:37.140 ","End":"00:40.545","Text":"but may not be gained or lost."},{"Start":"00:40.545 ","End":"00:43.700","Text":"For example, the sunlight energy,"},{"Start":"00:43.700 ","End":"00:47.675","Text":"the solar energy is converted to chemical energy by plants."},{"Start":"00:47.675 ","End":"00:52.625","Text":"The chemical energy that we consume is converted to mechanical energy by our muscles."},{"Start":"00:52.625 ","End":"00:56.860","Text":"Electrical energy in our homes is transformed to thermal energy for cooking,"},{"Start":"00:56.860 ","End":"01:00.050","Text":"and the chemical energy stored in the bonds of gasoline or"},{"Start":"01:00.050 ","End":"01:05.645","Text":"other flammable fluids may be transformed to mechanical energy by motors."},{"Start":"01:05.645 ","End":"01:08.185","Text":"Let\u0027s have a look at the answers here."},{"Start":"01:08.185 ","End":"01:10.940","Text":"A, turning on a light switch."},{"Start":"01:10.940 ","End":"01:13.640","Text":"What happens when you turn on a light switch?"},{"Start":"01:13.640 ","End":"01:16.460","Text":"Here we have a simple electric circuit."},{"Start":"01:16.460 ","End":"01:18.590","Text":"The battery gives us the power,"},{"Start":"01:18.590 ","End":"01:21.650","Text":"but in order for the electrons to flow along the circuit,"},{"Start":"01:21.650 ","End":"01:24.310","Text":"the circuit must be closed."},{"Start":"01:24.310 ","End":"01:27.425","Text":"Therefore, by switching on and closing the circuit,"},{"Start":"01:27.425 ","End":"01:31.505","Text":"we now allow the current of electrons to run through the system."},{"Start":"01:31.505 ","End":"01:34.460","Text":"This electromagnetic energy running through"},{"Start":"01:34.460 ","End":"01:38.405","Text":"the wire is transformed by the light bulb to light energy."},{"Start":"01:38.405 ","End":"01:43.565","Text":"But the transfer of energy is from the battery through the wires to the lamp."},{"Start":"01:43.565 ","End":"01:45.470","Text":"Switching on the circuit,"},{"Start":"01:45.470 ","End":"01:46.760","Text":"closing the circuit,"},{"Start":"01:46.760 ","End":"01:49.685","Text":"did not provide the system with the energy."},{"Start":"01:49.685 ","End":"01:52.865","Text":"The energy was provided by the battery."},{"Start":"01:52.865 ","End":"01:57.545","Text":"Therefore, this is not a good example of energy transformation."},{"Start":"01:57.545 ","End":"01:59.255","Text":"But before we mark this answer,"},{"Start":"01:59.255 ","End":"02:01.300","Text":"let\u0027s have a look at the other options."},{"Start":"02:01.300 ","End":"02:04.685","Text":"Answer B gives an example of solar panels at work."},{"Start":"02:04.685 ","End":"02:06.920","Text":"How do solar panels work then?"},{"Start":"02:06.920 ","End":"02:14.310","Text":"Solar panels use sunlight to separate the electric charges in the panels,"},{"Start":"02:14.310 ","End":"02:18.020","Text":"sending the negative electrons to 1 part of the panel,"},{"Start":"02:18.020 ","End":"02:21.320","Text":"therefore forming an electric current along the wire."},{"Start":"02:21.320 ","End":"02:26.750","Text":"Here we have a transformation of solar energy to electric energy."},{"Start":"02:26.750 ","End":"02:30.430","Text":"This is an example of energy transformation."},{"Start":"02:30.430 ","End":"02:33.890","Text":"Since the question is about which 1 is not a good example,"},{"Start":"02:33.890 ","End":"02:36.055","Text":"B can be crossed out."},{"Start":"02:36.055 ","End":"02:38.205","Text":"Let\u0027s have a look at example C,"},{"Start":"02:38.205 ","End":"02:40.935","Text":"the formation of static electricity."},{"Start":"02:40.935 ","End":"02:44.735","Text":"In this example of a formation of static electricity,"},{"Start":"02:44.735 ","End":"02:48.800","Text":"a glass rod is being rubbed on a silk cloth."},{"Start":"02:48.800 ","End":"02:53.300","Text":"This mechanical energy of rubbing the glass rod back and forth on"},{"Start":"02:53.300 ","End":"03:00.070","Text":"the silk causes electrons to leave the glass rod and connect to the silk."},{"Start":"03:00.070 ","End":"03:04.685","Text":"Now, the silk has a negative charge and the rod has a positive charge."},{"Start":"03:04.685 ","End":"03:06.845","Text":"If we bring them close to each other,"},{"Start":"03:06.845 ","End":"03:11.195","Text":"the electrons will move back quickly to the rod, forming a spark."},{"Start":"03:11.195 ","End":"03:17.210","Text":"Here the mechanical energy is being transformed to electric charge."},{"Start":"03:17.210 ","End":"03:20.420","Text":"Again, this is not a good answer because we\u0027re looking for"},{"Start":"03:20.420 ","End":"03:23.735","Text":"an answer that\u0027s not an example of energy transformation."},{"Start":"03:23.735 ","End":"03:26.465","Text":"Well, here there\u0027s clearly a transformation between"},{"Start":"03:26.465 ","End":"03:29.710","Text":"mechanical energy and electric energy."},{"Start":"03:29.710 ","End":"03:31.890","Text":"We are back to example A."},{"Start":"03:31.890 ","End":"03:34.100","Text":"While turning on the light switch does allow"},{"Start":"03:34.100 ","End":"03:37.820","Text":"a transformation of energy between the battery and the lamp,"},{"Start":"03:37.820 ","End":"03:40.535","Text":"the energy that\u0027s used by our finger to switch on"},{"Start":"03:40.535 ","End":"03:44.000","Text":"the lamp does not provide the energy for the light,"},{"Start":"03:44.000 ","End":"03:48.050","Text":"and therefore is not a good example of energy transformation."},{"Start":"03:48.050 ","End":"03:50.555","Text":"Since A is true,"},{"Start":"03:50.555 ","End":"03:52.655","Text":"D can be crossed out also,"},{"Start":"03:52.655 ","End":"03:55.320","Text":"and we\u0027ve marked our answer."}],"ID":28111},{"Watched":false,"Name":"Exercise 7","Duration":"3m 29s","ChapterTopicVideoID":26988,"CourseChapterTopicPlaylistID":136376,"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 each of the 3 systems,"},{"Start":"00:02.370 ","End":"00:04.200","Text":"determine the state of entropy,"},{"Start":"00:04.200 ","End":"00:08.989","Text":"low or high, when comparing the first and second."},{"Start":"00:08.989 ","End":"00:14.900","Text":"1, the instant that a perfume bottle is spread compared with 30 seconds later."},{"Start":"00:14.900 ","End":"00:18.864","Text":"2, a 50 year old car compared with a brand new car,"},{"Start":"00:18.864 ","End":"00:22.890","Text":"and 3, a living organism compared with a dead organism."},{"Start":"00:22.890 ","End":"00:24.975","Text":"What is entropy?"},{"Start":"00:24.975 ","End":"00:34.335","Text":"Entropy is a scientific measurement for disorder or randomness."},{"Start":"00:34.335 ","End":"00:40.310","Text":"The second law of thermodynamics tells us that entropy or the disorder will"},{"Start":"00:40.310 ","End":"00:43.070","Text":"always grow spontaneously unless we"},{"Start":"00:43.070 ","End":"00:46.400","Text":"put in specific energy into putting things back into order."},{"Start":"00:46.400 ","End":"00:49.925","Text":"Think of a house or a child\u0027s room."},{"Start":"00:49.925 ","End":"00:51.965","Text":"The room will get messy."},{"Start":"00:51.965 ","End":"00:53.810","Text":"Things will get out of the closet,"},{"Start":"00:53.810 ","End":"00:55.760","Text":"toys will get spread out on the floor."},{"Start":"00:55.760 ","End":"00:59.210","Text":"Unless you make a specific effort to put things back away,"},{"Start":"00:59.210 ","End":"01:03.065","Text":"the randomness or the disorder will always grow."},{"Start":"01:03.065 ","End":"01:07.400","Text":"The same thing happens in the environment, in the world."},{"Start":"01:07.400 ","End":"01:12.620","Text":"Let\u0027s have a look now at the 3 systems that we\u0027re asked to compare."},{"Start":"01:12.620 ","End":"01:15.620","Text":"The incident that a perfume is sprayed compared with"},{"Start":"01:15.620 ","End":"01:19.820","Text":"30 seconds later when a perfume can be smelled through the whole house."},{"Start":"01:19.820 ","End":"01:22.997","Text":"At the very beginning, right when it\u0027s sprayed,"},{"Start":"01:22.997 ","End":"01:26.150","Text":"the perfume is all condensed in 1 small cloud."},{"Start":"01:26.150 ","End":"01:27.860","Text":"But very soon,"},{"Start":"01:27.860 ","End":"01:32.570","Text":"the disorder takes over and it spreads throughout the whole house in a random way."},{"Start":"01:32.570 ","End":"01:35.405","Text":"Comparing the incidence of spraying the perfume bottle"},{"Start":"01:35.405 ","End":"01:37.873","Text":"to 30 seconds later will tell us that first,"},{"Start":"01:37.873 ","End":"01:41.435","Text":"there\u0027s low entropy because there\u0027s a lot of order."},{"Start":"01:41.435 ","End":"01:44.000","Text":"After, it gets to be more disordered."},{"Start":"01:44.000 ","End":"01:48.620","Text":"This would be low. Let\u0027s have a look at the second example."},{"Start":"01:48.620 ","End":"01:52.055","Text":"A 50 year old car compared with a brand new car."},{"Start":"01:52.055 ","End":"01:54.140","Text":"Well, during those 50 years,"},{"Start":"01:54.140 ","End":"01:55.565","Text":"the car got rusty,"},{"Start":"01:55.565 ","End":"01:57.035","Text":"parts got degraded,"},{"Start":"01:57.035 ","End":"02:00.839","Text":"there in less order than the new car that was just assembled now."},{"Start":"02:00.839 ","End":"02:06.470","Text":"Therefore, comparing the old disordered car to the new ordered and neat car,"},{"Start":"02:06.470 ","End":"02:10.055","Text":"you can say that here the entropy is a lot higher."},{"Start":"02:10.055 ","End":"02:12.635","Text":"Let\u0027s have a look at the third example,"},{"Start":"02:12.635 ","End":"02:15.845","Text":"living organism versus dead organism."},{"Start":"02:15.845 ","End":"02:18.905","Text":"Well, as long as organisms are alive,"},{"Start":"02:18.905 ","End":"02:20.855","Text":"the cells maintain order."},{"Start":"02:20.855 ","End":"02:25.205","Text":"They push out the chemicals that are unwanted and they bring in chemicals in her wanted."},{"Start":"02:25.205 ","End":"02:27.125","Text":"They perform different processes,"},{"Start":"02:27.125 ","End":"02:29.780","Text":"cellular processes keeping order and shape,"},{"Start":"02:29.780 ","End":"02:32.735","Text":"and the whole way the organism is built."},{"Start":"02:32.735 ","End":"02:34.475","Text":"As soon as the organism dies,"},{"Start":"02:34.475 ","End":"02:35.990","Text":"things start falling apart,"},{"Start":"02:35.990 ","End":"02:39.205","Text":"and now we\u0027re in a higher disorder."},{"Start":"02:39.205 ","End":"02:45.965","Text":"Again, the perfume at the beginning is highly ordered and afterwards is disordered."},{"Start":"02:45.965 ","End":"02:49.505","Text":"We have a low state of entropy at the beginning."},{"Start":"02:49.505 ","End":"02:54.695","Text":"The old car is in the highest state of entropy compared to the new car."},{"Start":"02:54.695 ","End":"03:03.365","Text":"The living organism is in a low state of entropy compared to the old rotting apple."},{"Start":"03:03.365 ","End":"03:05.135","Text":"Let\u0027s look at the answers now."},{"Start":"03:05.135 ","End":"03:07.955","Text":"We said low, high, and low."},{"Start":"03:07.955 ","End":"03:11.510","Text":"Low, high, and low is the first answer which is true."},{"Start":"03:11.510 ","End":"03:14.030","Text":"Second answer is low,"},{"Start":"03:14.030 ","End":"03:15.800","Text":"high, and high, in which we can cross out."},{"Start":"03:15.800 ","End":"03:19.220","Text":"Third answer high, low,"},{"Start":"03:19.220 ","End":"03:22.070","Text":"and high, which is the opposite of the right answer."},{"Start":"03:22.070 ","End":"03:23.945","Text":"The fourth answer, D, high,"},{"Start":"03:23.945 ","End":"03:25.790","Text":"low, and low, which is also wrong."},{"Start":"03:25.790 ","End":"03:29.940","Text":"We can mark answer a as a correct answer."}],"ID":28112},{"Watched":false,"Name":"Exercise 8","Duration":"5m 5s","ChapterTopicVideoID":26978,"CourseChapterTopicPlaylistID":136376,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:05.160","Text":"This question is about the energy released by the hydrolysis of ATP."},{"Start":"00:05.160 ","End":"00:12.135","Text":"Answer A is at this energy is primarily stored between the alpha and beta phosphates."},{"Start":"00:12.135 ","End":"00:19.635","Text":"B, is that the energy that\u0027s released is equal to minus 57 kilocalories per mole."},{"Start":"00:19.635 ","End":"00:24.780","Text":"C is that this energy is harnessed as heat energy by the cell to perform work."},{"Start":"00:24.780 ","End":"00:28.140","Text":"The answer D tells us that the energy"},{"Start":"00:28.140 ","End":"00:31.995","Text":"released is providing energy to a coupled reactions."},{"Start":"00:31.995 ","End":"00:34.124","Text":"Let\u0027s have a look at the ATP,"},{"Start":"00:34.124 ","End":"00:37.800","Text":"also known as adenosine triphosphate."},{"Start":"00:37.800 ","End":"00:45.545","Text":"Adenosine triphosphate is a nucleic acid with the sugar as ribose here."},{"Start":"00:45.545 ","End":"00:48.455","Text":"The nitrogenous bases adenine,"},{"Start":"00:48.455 ","End":"00:51.185","Text":"and it has 3 phosphate groups,"},{"Start":"00:51.185 ","End":"00:53.420","Text":"alpha, beta, and gamma."},{"Start":"00:53.420 ","End":"00:59.205","Text":"That\u0027s why it\u0027s called a triphosphate because tri means 3."},{"Start":"00:59.205 ","End":"01:03.905","Text":"The hydrolysis of 1 of the phosphate groups releases energy."},{"Start":"01:03.905 ","End":"01:06.245","Text":"This is used for cellular work."},{"Start":"01:06.245 ","End":"01:08.720","Text":"Now we\u0027re left with ADP,"},{"Start":"01:08.720 ","End":"01:14.860","Text":"adenosine diphosphate because di means 2."},{"Start":"01:14.860 ","End":"01:19.670","Text":"During cellular respiration, energy is absorbed from food."},{"Start":"01:19.670 ","End":"01:24.425","Text":"This energy is invested and connecting another phosphate group."},{"Start":"01:24.425 ","End":"01:29.405","Text":"Now again we have ATP, adenosine triphosphate."},{"Start":"01:29.405 ","End":"01:34.110","Text":"This energy is used afterwards for cellular work."},{"Start":"01:34.420 ","End":"01:37.955","Text":"We can look at it as a battery."},{"Start":"01:37.955 ","End":"01:40.055","Text":"The battery is charged,"},{"Start":"01:40.055 ","End":"01:42.020","Text":"it has 3 phosphate groups,"},{"Start":"01:42.020 ","End":"01:43.700","Text":"and the battery is used,"},{"Start":"01:43.700 ","End":"01:45.050","Text":"it has only 2."},{"Start":"01:45.050 ","End":"01:48.320","Text":"Releasing the phosphate group also releases the energy."},{"Start":"01:48.320 ","End":"01:50.360","Text":"Where was this energy?"},{"Start":"01:50.360 ","End":"01:53.960","Text":"The energy was invested in connecting the phosphate group."},{"Start":"01:53.960 ","End":"01:57.815","Text":"The ATP is higher in energy than the ADP."},{"Start":"01:57.815 ","End":"01:59.390","Text":"That means that chemically,"},{"Start":"01:59.390 ","End":"02:01.415","Text":"this is a favorite state."},{"Start":"02:01.415 ","End":"02:05.825","Text":"Connecting the third phosphate group needs an investment of energy."},{"Start":"02:05.825 ","End":"02:07.805","Text":"When a phosphate group is released,"},{"Start":"02:07.805 ","End":"02:09.800","Text":"the energy is released with it."},{"Start":"02:09.800 ","End":"02:14.210","Text":"The amount of energy that\u0027s invested and connecting the gamma,"},{"Start":"02:14.210 ","End":"02:16.070","Text":"the third phosphate group,"},{"Start":"02:16.070 ","End":"02:22.340","Text":"is 7.3 kilo calories per mole."},{"Start":"02:22.340 ","End":"02:26.180","Text":"Therefore, the hydrolysis of ATP to ADP."},{"Start":"02:26.180 ","End":"02:29.825","Text":"This is the amount of energy that is freed to use by the cell,"},{"Start":"02:29.825 ","End":"02:36.425","Text":"7.3 kilo calories per mole."},{"Start":"02:36.425 ","End":"02:42.890","Text":"If we do look at the delta at the difference in free energy,"},{"Start":"02:42.890 ","End":"02:52.695","Text":"and this whole process is equal to minus 7.3 kilo calories per mole."},{"Start":"02:52.695 ","End":"02:56.820","Text":"That\u0027s because this is the energy that\u0027s released."},{"Start":"02:57.110 ","End":"02:59.540","Text":"Let\u0027s have a look at the answers now."},{"Start":"02:59.540 ","End":"03:02.780","Text":"A the energy that\u0027s released by hydrolysis of"},{"Start":"03:02.780 ","End":"03:06.950","Text":"ATP is primarily stored between the alpha and beta phosphates."},{"Start":"03:06.950 ","End":"03:11.675","Text":"We can see that it\u0027s stored between the beta and gamma phosphates."},{"Start":"03:11.675 ","End":"03:16.430","Text":"If we\u0027d ask about hydrolysis of ADP and then as in diphosphate,"},{"Start":"03:16.430 ","End":"03:21.005","Text":"we could say that the energy was stored between the alpha and the beta phosphates."},{"Start":"03:21.005 ","End":"03:24.005","Text":"But since we\u0027re talking about hydrolysis of ATP,"},{"Start":"03:24.005 ","End":"03:29.425","Text":"Adenosine triphosphate, we\u0027re talking about this energy here between beta and gamma."},{"Start":"03:29.425 ","End":"03:33.205","Text":"Therefore, answer a is wrong. Let\u0027s have a look at b."},{"Start":"03:33.205 ","End":"03:39.055","Text":"The energy released by hydrolysis of ADP is equal to minus 37 kilocalories per mole."},{"Start":"03:39.055 ","End":"03:42.010","Text":"Well, even if we didn\u0027t remember this number by heart and"},{"Start":"03:42.010 ","End":"03:45.175","Text":"we remember there was a 7 we might get mixed up here."},{"Start":"03:45.175 ","End":"03:48.310","Text":"But since they tell us that the energy that\u0027s"},{"Start":"03:48.310 ","End":"03:51.490","Text":"released is equal to minus 57 kilocalories per mole."},{"Start":"03:51.490 ","End":"03:55.914","Text":"We can already know that it\u0027s wrong because the energy that\u0027s released is positive."},{"Start":"03:55.914 ","End":"03:59.020","Text":"It\u0027s 7.3 kilocalories per mole."},{"Start":"03:59.020 ","End":"04:01.330","Text":"Overall in the process,"},{"Start":"04:01.330 ","End":"04:04.270","Text":"we do have a minus that\u0027s because the energy difference"},{"Start":"04:04.270 ","End":"04:08.200","Text":"between the high energize adenosine triphosphate,"},{"Start":"04:08.200 ","End":"04:14.000","Text":"ATP, and the low energized ADP."},{"Start":"04:14.000 ","End":"04:19.210","Text":"This is an overall minus of 7.3."},{"Start":"04:19.210 ","End":"04:22.220","Text":"But since we\u0027re talking about the energy that\u0027s released,"},{"Start":"04:22.220 ","End":"04:24.860","Text":"this is positive energy that\u0027s released and"},{"Start":"04:24.860 ","End":"04:28.590","Text":"it\u0027s used by the cell to perform it\u0027s reactions."},{"Start":"04:28.640 ","End":"04:32.220","Text":"A and B are both wrong and we can now go on to answer"},{"Start":"04:32.220 ","End":"04:36.860","Text":"C the energy is harnessed as heat energy by the cell to perform work."},{"Start":"04:36.860 ","End":"04:41.750","Text":"Well, the cells use the energy from the ATP to perform cellular work,"},{"Start":"04:41.750 ","End":"04:43.430","Text":"but it\u0027s not converted to heat."},{"Start":"04:43.430 ","End":"04:48.490","Text":"It\u0027s used straight as chemical energy is converted as chemical energy from the ATP,"},{"Start":"04:48.490 ","End":"04:51.695","Text":"to chemical energy used by the protein."},{"Start":"04:51.695 ","End":"04:55.790","Text":"Therefore, C is wrong and D is right."},{"Start":"04:55.790 ","End":"04:58.989","Text":"The energy released by hydrolysis of ATP"},{"Start":"04:58.989 ","End":"05:02.960","Text":"is providing energy to coupled chemical reactions."},{"Start":"05:02.960 ","End":"05:05.430","Text":"That is a correct answer."}],"ID":28113},{"Watched":false,"Name":"Exercise 9","Duration":"2m 56s","ChapterTopicVideoID":26979,"CourseChapterTopicPlaylistID":136376,"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":"Which of the following molecules is likely to have the most potential energy?"},{"Start":"00:05.595 ","End":"00:08.415","Text":"A. Sucrose. B,."},{"Start":"00:08.415 ","End":"00:11.745","Text":"ATP. C. Glucose,"},{"Start":"00:11.745 ","End":"00:14.355","Text":"or d, ADP."},{"Start":"00:14.355 ","End":"00:17.010","Text":"Let\u0027s have a look at these molecules."},{"Start":"00:17.010 ","End":"00:21.120","Text":"ATP and ADP are 2 nucleic acids that"},{"Start":"00:21.120 ","End":"00:25.110","Text":"differ from each other by the number of phosphate groups connected to them,"},{"Start":"00:25.110 ","End":"00:28.740","Text":"while sucrose and glucose are both sugars."},{"Start":"00:28.740 ","End":"00:31.620","Text":"Let\u0027s have a look first at the ATP and ADP and"},{"Start":"00:31.620 ","End":"00:34.945","Text":"try to find which 1 of them has the most potential energy."},{"Start":"00:34.945 ","End":"00:42.315","Text":"We know that the ADP-ATP cycle uses these 2 molecules and recycles them."},{"Start":"00:42.315 ","End":"00:46.130","Text":"The ATP has 2 high charge bonds between"},{"Start":"00:46.130 ","End":"00:51.170","Text":"the Alpha and Beta phosphate groups and between the Beta and Gamma groups."},{"Start":"00:51.170 ","End":"00:53.375","Text":"This is a full charged battery."},{"Start":"00:53.375 ","End":"00:58.430","Text":"The ATP is used by the cell to perform energy consuming work."},{"Start":"00:58.430 ","End":"01:00.845","Text":"I have here the energy."},{"Start":"01:00.845 ","End":"01:03.530","Text":"The energy is released by taking apart"},{"Start":"01:03.530 ","End":"01:07.880","Text":"the third phosphate group and releasing the energy that was stored in this bond."},{"Start":"01:07.880 ","End":"01:10.405","Text":"We\u0027re now left with ADP."},{"Start":"01:10.405 ","End":"01:14.505","Text":"Adenosine diphosphate, and di means 2,"},{"Start":"01:14.505 ","End":"01:16.485","Text":"and tri means 3."},{"Start":"01:16.485 ","End":"01:18.750","Text":"During consumption of food,"},{"Start":"01:18.750 ","End":"01:24.350","Text":"energy from food is used to bond the third phosphate group,"},{"Start":"01:24.350 ","End":"01:27.080","Text":"again, making the adenosine triphosphate,"},{"Start":"01:27.080 ","End":"01:29.885","Text":"and this is the ATP-ADP cycle."},{"Start":"01:29.885 ","End":"01:35.394","Text":"We already know that the ATP is higher in energy than the ADP."},{"Start":"01:35.394 ","End":"01:39.470","Text":"Now let\u0027s see the difference between sucrose and glucose."},{"Start":"01:39.470 ","End":"01:42.245","Text":"Glucose and sucrose are both sugars."},{"Start":"01:42.245 ","End":"01:44.285","Text":"Glucose is a monosaccharide,"},{"Start":"01:44.285 ","End":"01:48.665","Text":"meaning that it\u0027s a single sugar unit while sucrose is a disaccharide,"},{"Start":"01:48.665 ","End":"01:50.360","Text":"a double sugar unit."},{"Start":"01:50.360 ","End":"01:53.555","Text":"Sucrose is made of glucose and fructose,"},{"Start":"01:53.555 ","End":"01:55.895","Text":"which are connected by glycosidic bond."},{"Start":"01:55.895 ","End":"01:58.760","Text":"Therefore, the sucrose has an energy that equals to"},{"Start":"01:58.760 ","End":"02:02.119","Text":"the amount of energy in glucose and in fructose combined,"},{"Start":"02:02.119 ","End":"02:04.370","Text":"including the glycosidic bond."},{"Start":"02:04.370 ","End":"02:09.350","Text":"Therefore, it\u0027s obvious that sucrose has more energy than glucose."},{"Start":"02:09.350 ","End":"02:16.500","Text":"Now we have to decide which of these has more energy, sucrose or ATP?"},{"Start":"02:17.410 ","End":"02:21.335","Text":"Well, since we know that in cellular respiration,"},{"Start":"02:21.335 ","End":"02:27.080","Text":"glucose has taken a part and over 30 ATP molecules are extracted from it,"},{"Start":"02:27.080 ","End":"02:33.250","Text":"we can understand that glucose has at least 30 times the energy as ATP does."},{"Start":"02:33.250 ","End":"02:36.500","Text":"Sucrose has more energy than glucose."},{"Start":"02:36.500 ","End":"02:39.725","Text":"You can say that sucrose is our number 1 energy molecule,"},{"Start":"02:39.725 ","End":"02:42.860","Text":"glucose will be our number 2 energy molecule,"},{"Start":"02:42.860 ","End":"02:46.115","Text":"ATP will be a number 3 energy molecule,"},{"Start":"02:46.115 ","End":"02:48.380","Text":"and ADP has the least energy."},{"Start":"02:48.380 ","End":"02:51.110","Text":"We can cross out b, c,"},{"Start":"02:51.110 ","End":"02:53.855","Text":"and d, and mark a,"},{"Start":"02:53.855 ","End":"02:56.760","Text":"sucrose, as a correct answer."}],"ID":28114},{"Watched":false,"Name":"Exercise 10","Duration":"3m 27s","ChapterTopicVideoID":26980,"CourseChapterTopicPlaylistID":136376,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.080 ","End":"00:06.105","Text":"Here we ask about enzymes and we need to find which answer is not true by enzymes."},{"Start":"00:06.105 ","End":"00:11.145","Text":"A, they increase the difference in energy of reactions."},{"Start":"00:11.145 ","End":"00:14.730","Text":"B, they\u0027re usually made of amino acids."},{"Start":"00:14.730 ","End":"00:20.535","Text":"C, they lower the activation energy of chemical reactions or D,"},{"Start":"00:20.535 ","End":"00:26.025","Text":"each 1 is specific to the particular substrate or substrates to which it binds."},{"Start":"00:26.025 ","End":"00:29.610","Text":"In this case, since we have 2 answers speaking about"},{"Start":"00:29.610 ","End":"00:33.225","Text":"the energy and another 2 answers which are more general,"},{"Start":"00:33.225 ","End":"00:37.200","Text":"I\u0027d like to start with answers B and D and then proceed to A and"},{"Start":"00:37.200 ","End":"00:42.415","Text":"C. Answer B states that they\u0027re usually made of amino acids."},{"Start":"00:42.415 ","End":"00:46.970","Text":"Since enzymes are almost always proteins and the primary structure of"},{"Start":"00:46.970 ","End":"00:51.830","Text":"proteins is actually a poly-peptide long chain of amino acids,"},{"Start":"00:51.830 ","End":"00:54.150","Text":"answer B is correct,"},{"Start":"00:54.150 ","End":"00:56.540","Text":"and since we\u0027re looking for a statement that is not true,"},{"Start":"00:56.540 ","End":"00:59.430","Text":"we can cross out answer B."},{"Start":"00:59.470 ","End":"01:05.705","Text":"Let\u0027s have a look at answer D. Enzymes are specific to particular substrates."},{"Start":"01:05.705 ","End":"01:08.720","Text":"While a human cell has approximately"},{"Start":"01:08.720 ","End":"01:14.210","Text":"1,300 different enzymes to perform the different cellular processes of metabolism."},{"Start":"01:14.210 ","End":"01:18.245","Text":"That just comes to show how specific enzymes are to the substrates."},{"Start":"01:18.245 ","End":"01:23.305","Text":"Yes, each enzyme is specific to a substrate or a group of substrates,"},{"Start":"01:23.305 ","End":"01:26.855","Text":"and it can work only with that group of substrates."},{"Start":"01:26.855 ","End":"01:30.305","Text":"Cross out answer D, which is true."},{"Start":"01:30.305 ","End":"01:32.870","Text":"Let\u0027s pick about energy now."},{"Start":"01:32.870 ","End":"01:36.080","Text":"Exergonic processes, the free energy of"},{"Start":"01:36.080 ","End":"01:39.679","Text":"the reactants is higher than the free energy of the products,"},{"Start":"01:39.679 ","End":"01:44.315","Text":"meaning that there\u0027s a release of energy and the energy difference is negative."},{"Start":"01:44.315 ","End":"01:48.155","Text":"1 of the reactants turn straight into the products in that case."},{"Start":"01:48.155 ","End":"01:51.500","Text":"The answer is that there is an activation energy."},{"Start":"01:51.500 ","End":"01:54.335","Text":"The first has to be invested in the reactants."},{"Start":"01:54.335 ","End":"01:56.245","Text":"Why is this?"},{"Start":"01:56.245 ","End":"02:01.280","Text":"Well, let\u0027s say that the reactants are 2 molecules made out of"},{"Start":"02:01.280 ","End":"02:06.035","Text":"atoms A and B and C and D. The products,"},{"Start":"02:06.035 ","End":"02:09.050","Text":"although energetically they\u0027re more chemically favorable."},{"Start":"02:09.050 ","End":"02:10.880","Text":"Or A and C connected in,"},{"Start":"02:10.880 ","End":"02:16.490","Text":"B and D connected to each other can\u0027t do that before going through the transition state,"},{"Start":"02:16.490 ","End":"02:20.810","Text":"taking apart the connections between atoms A and B and atom C and"},{"Start":"02:20.810 ","End":"02:25.115","Text":"D. This is unfavorable chemically, energetically,"},{"Start":"02:25.115 ","End":"02:29.630","Text":"and therefore, we have to invest the energy of activation in order to"},{"Start":"02:29.630 ","End":"02:34.699","Text":"first take apart these molecules before we can reach the more favorable products."},{"Start":"02:34.699 ","End":"02:37.670","Text":"How can we speed up this process?"},{"Start":"02:37.670 ","End":"02:41.480","Text":"The answer is that we cannot change the chemical properties and"},{"Start":"02:41.480 ","End":"02:45.065","Text":"the energetic properties between the reactants and the products,"},{"Start":"02:45.065 ","End":"02:49.230","Text":"these will always stay the same."},{"Start":"02:51.880 ","End":"02:58.183","Text":"What we can do is lower the amount of energy we need in order to activate this process,"},{"Start":"02:58.183 ","End":"03:00.230","Text":"and that is what the enzymes do."},{"Start":"03:00.230 ","End":"03:02.675","Text":"They lower the activation energy,"},{"Start":"03:02.675 ","End":"03:04.910","Text":"allowing the process to start by"},{"Start":"03:04.910 ","End":"03:08.555","Text":"investing a lower amount of energy, which happens faster."},{"Start":"03:08.555 ","End":"03:11.900","Text":"Therefore, since we\u0027re looking for the statements that are not true,"},{"Start":"03:11.900 ","End":"03:13.730","Text":"we can cross out that they lower"},{"Start":"03:13.730 ","End":"03:17.180","Text":"the activation energy of chemical reactions and these are the same,"},{"Start":"03:17.180 ","End":"03:19.650","Text":"and we\u0027re looking for something that it\u0027s not true."},{"Start":"03:19.650 ","End":"03:20.750","Text":"We can mark answer A;"},{"Start":"03:20.750 ","End":"03:24.335","Text":"they increase the difference in Gibbs free energy of reaction,"},{"Start":"03:24.335 ","End":"03:27.810","Text":"which is the statement that is not true."}],"ID":28115},{"Watched":false,"Name":"Exercise 11","Duration":"3m 34s","ChapterTopicVideoID":26981,"CourseChapterTopicPlaylistID":136376,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.410 ","End":"00:05.383","Text":"An allosteric inhibitor does which of the following?"},{"Start":"00:05.383 ","End":"00:08.430","Text":"A, it binds to an enzyme away from"},{"Start":"00:08.430 ","End":"00:11.835","Text":"the active site and changes the conformation of the active site,"},{"Start":"00:11.835 ","End":"00:15.717","Text":"increasing its affinity for substrate binding."},{"Start":"00:15.717 ","End":"00:17.985","Text":"B, allosteric inhibitor,"},{"Start":"00:17.985 ","End":"00:22.260","Text":"binds to the active site and blocks it from binding to the substrate."},{"Start":"00:22.260 ","End":"00:28.303","Text":"C, an allosteric inhibitor binds to an enzyme away from the active site,"},{"Start":"00:28.303 ","End":"00:30.800","Text":"and changes the conformation of the active site,"},{"Start":"00:30.800 ","End":"00:33.545","Text":"decreasing its affinity for the substrate."},{"Start":"00:33.545 ","End":"00:36.360","Text":"D, an allosteric inhibitor,"},{"Start":"00:36.360 ","End":"00:40.220","Text":"binds directly to the active site and mimics the substrate."},{"Start":"00:40.220 ","End":"00:42.335","Text":"In order to answer this question,"},{"Start":"00:42.335 ","End":"00:45.215","Text":"let\u0027s have a little look at enzyme inhibition."},{"Start":"00:45.215 ","End":"00:49.880","Text":"A normal binding, we have the enzyme which has an active site."},{"Start":"00:49.880 ","End":"00:51.995","Text":"When a substrate binds with the enzyme,"},{"Start":"00:51.995 ","End":"00:54.395","Text":"we get the enzyme-substrate complex,"},{"Start":"00:54.395 ","End":"00:57.500","Text":"which allows the enzyme to perform its task."},{"Start":"00:57.500 ","End":"01:00.275","Text":"There are 2 types of enzyme inhibition,"},{"Start":"01:00.275 ","End":"01:03.948","Text":"competitive inhibition and non-competitive inhibition."},{"Start":"01:03.948 ","End":"01:09.619","Text":"In competitive inhibition, the inhibitor mimics the substrate."},{"Start":"01:09.619 ","End":"01:11.900","Text":"It binds to the active site of an enzyme,"},{"Start":"01:11.900 ","End":"01:15.605","Text":"and thus the substrate unable to bind to the enzyme,"},{"Start":"01:15.605 ","End":"01:18.410","Text":"and the enzyme does not perform its work on it."},{"Start":"01:18.410 ","End":"01:20.656","Text":"In non-competitive inhibition,"},{"Start":"01:20.656 ","End":"01:23.930","Text":"the inhibitor does not connect to the active site."},{"Start":"01:23.930 ","End":"01:27.365","Text":"Instead it connects to a different site called the Allosteric site."},{"Start":"01:27.365 ","End":"01:30.350","Text":"Connecting to this site changes the conformation of"},{"Start":"01:30.350 ","End":"01:33.800","Text":"the enzyme and the active site turns to be inactive."},{"Start":"01:33.800 ","End":"01:36.050","Text":"In this illustration, we can see that it\u0027s shape had"},{"Start":"01:36.050 ","End":"01:39.020","Text":"changed and the enzyme can perform its task."},{"Start":"01:39.020 ","End":"01:42.859","Text":"Another use for the allosteric site was at the activator."},{"Start":"01:42.859 ","End":"01:45.110","Text":"When the activator connects to the enzyme,"},{"Start":"01:45.110 ","End":"01:46.724","Text":"it changes its conformation."},{"Start":"01:46.724 ","End":"01:49.040","Text":"The substrate may now connect to the enzyme,"},{"Start":"01:49.040 ","End":"01:52.790","Text":"forming the enzyme-substrate complex and the enzyme could do its work."},{"Start":"01:52.790 ","End":"01:54.710","Text":"In normal binding,"},{"Start":"01:54.710 ","End":"01:56.540","Text":"the substrate can bind to the active site."},{"Start":"01:56.540 ","End":"01:58.340","Text":"In competitive inhibition,"},{"Start":"01:58.340 ","End":"02:02.080","Text":"a molecule binds to the active site blocking the substrate."},{"Start":"02:02.080 ","End":"02:04.493","Text":"In non-competitive inhibition,"},{"Start":"02:04.493 ","End":"02:08.420","Text":"an inhibitor connects to the allosteric site, changing the conformation,"},{"Start":"02:08.420 ","End":"02:10.929","Text":"not allowing the substrate to bind to it now,"},{"Start":"02:10.929 ","End":"02:15.575","Text":"changing the conformation of the active site and the substrate cannot connect to it."},{"Start":"02:15.575 ","End":"02:17.525","Text":"In an allosteric activation,"},{"Start":"02:17.525 ","End":"02:20.248","Text":"an activator binds to the allosteric site,"},{"Start":"02:20.248 ","End":"02:23.345","Text":"and changes the active site to fit to the substrate."},{"Start":"02:23.345 ","End":"02:25.550","Text":"Let\u0027s have a look at the answers again."},{"Start":"02:25.550 ","End":"02:30.889","Text":"Answer a says that allosteric inhibitors bind to an enzyme away from the active site,"},{"Start":"02:30.889 ","End":"02:32.735","Text":"so far so good,"},{"Start":"02:32.735 ","End":"02:35.278","Text":"and changes the conformation of the active site,"},{"Start":"02:35.278 ","End":"02:38.990","Text":"that sounds good too, increasing its affinity for substrate binding."},{"Start":"02:38.990 ","End":"02:41.584","Text":"Well, that\u0027s wrong. That should be decreasing"},{"Start":"02:41.584 ","End":"02:45.230","Text":"because only the activator increases the affinity for substrate binding."},{"Start":"02:45.230 ","End":"02:49.095","Text":"So answer a is wrong. Let\u0027s have a look at b."},{"Start":"02:49.095 ","End":"02:51.230","Text":"An allosteric inhibitor binds to"},{"Start":"02:51.230 ","End":"02:54.230","Text":"the active site and blocks it from binding to the substrate."},{"Start":"02:54.230 ","End":"02:56.465","Text":"Well, that\u0027s a competitive inhibitor,"},{"Start":"02:56.465 ","End":"02:58.280","Text":"not an allosteric inhibitor."},{"Start":"02:58.280 ","End":"03:00.175","Text":"So answer b is wrong too."},{"Start":"03:00.175 ","End":"03:03.350","Text":"Answers c, an allosteric inhibitor binds"},{"Start":"03:03.350 ","End":"03:06.425","Text":"to an enzyme away from the active site, that\u0027s good."},{"Start":"03:06.425 ","End":"03:08.855","Text":"It changes the conformation of the active site,"},{"Start":"03:08.855 ","End":"03:12.665","Text":"that\u0027s good too, decreasing its affinity for the substrate."},{"Start":"03:12.665 ","End":"03:14.240","Text":"So this answer seems right."},{"Start":"03:14.240 ","End":"03:17.360","Text":"Let\u0027s just have a look at answering d before we mark our final answer."},{"Start":"03:17.360 ","End":"03:22.370","Text":"D, an allosteric inhibitor binds directly to the active site and mimics the substrate."},{"Start":"03:22.370 ","End":"03:24.105","Text":"This looks a lot like answer b."},{"Start":"03:24.105 ","End":"03:25.755","Text":"This is the wrong inhibition,"},{"Start":"03:25.755 ","End":"03:27.240","Text":"this is competitive inhibition,"},{"Start":"03:27.240 ","End":"03:30.120","Text":"and not allosteric or noncompetitive inhibition."},{"Start":"03:30.120 ","End":"03:31.770","Text":"So answer d is wrong too,"},{"Start":"03:31.770 ","End":"03:34.330","Text":"and we can mark answer is c."}],"ID":28116}],"Thumbnail":null,"ID":136376},{"Name":"Respiration","TopicPlaylistFirstVideoID":0,"Duration":null,"Videos":[{"Watched":false,"Name":"Introduction to Respiration","Duration":"8m 21s","ChapterTopicVideoID":24932,"CourseChapterTopicPlaylistID":136378,"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. In order to introduce respiration,"},{"Start":"00:03.570 ","End":"00:06.030","Text":"we\u0027ll be speaking about redox reactions"},{"Start":"00:06.030 ","End":"00:09.510","Text":"and the way that molecules can be used to store energy."},{"Start":"00:09.510 ","End":"00:11.430","Text":"By the end of this section,"},{"Start":"00:11.430 ","End":"00:15.390","Text":"you\u0027ll be able to discuss the importance of electrons in a transfer of energy in"},{"Start":"00:15.390 ","End":"00:21.375","Text":"living systems and explain how ATP is used by cells as an energy source."},{"Start":"00:21.375 ","End":"00:27.630","Text":"Energy production within a cell involves many coordinated chemical pathways."},{"Start":"00:27.630 ","End":"00:32.870","Text":"In oxidation, an electron is stripped from an atom in a substance."},{"Start":"00:32.870 ","End":"00:38.095","Text":"For example, here we have compound A and it loses electrons,"},{"Start":"00:38.095 ","End":"00:40.410","Text":"A is now oxidized."},{"Start":"00:40.410 ","End":"00:44.475","Text":"In reduction, an electron is added to a substance,"},{"Start":"00:44.475 ","End":"00:47.850","Text":"substance B hasn\u0027t been reduced."},{"Start":"00:47.850 ","End":"00:50.820","Text":"Since these reactions need to be coupled,"},{"Start":"00:50.820 ","End":"00:54.275","Text":"the electrons need to come from somewhere and need to end up somewhere."},{"Start":"00:54.275 ","End":"00:56.765","Text":"Oxidation and reduction reactions are called"},{"Start":"00:56.765 ","End":"01:01.430","Text":"oxidation-reduction reactions or in short, redox reactions."},{"Start":"01:01.430 ","End":"01:07.955","Text":"Since in this example substance A is given the electrons and reducing substance B,"},{"Start":"01:07.955 ","End":"01:09.970","Text":"we call this reducing agent."},{"Start":"01:09.970 ","End":"01:15.860","Text":"Since substance B is taking the electrons from substance A and making it oxidized,"},{"Start":"01:15.860 ","End":"01:19.385","Text":"we call substance B the oxidizing agent."},{"Start":"01:19.385 ","End":"01:22.790","Text":"You won\u0027t be surprised to hear that oxygen is one"},{"Start":"01:22.790 ","End":"01:26.270","Text":"of the most ubiquitous oxidizing agents in nature."},{"Start":"01:26.270 ","End":"01:31.555","Text":"Oxidation results in a decrease in potential energy in the oxidized compound,"},{"Start":"01:31.555 ","End":"01:34.595","Text":"therefore, this energy must be released."},{"Start":"01:34.595 ","End":"01:39.020","Text":"In combustion reactions where sugar is oxidized by oxygen,"},{"Start":"01:39.020 ","End":"01:42.230","Text":"we have a big burst of energy that\u0027s released right away."},{"Start":"01:42.230 ","End":"01:44.030","Text":"None of this is stored."},{"Start":"01:44.030 ","End":"01:45.800","Text":"On the other hand in the cell,"},{"Start":"01:45.800 ","End":"01:50.270","Text":"the transfer of energy in a step-wise manner allows the cell to use"},{"Start":"01:50.270 ","End":"01:55.490","Text":"the energy in small packages rather than a single destructive burst as in combustion."},{"Start":"01:55.490 ","End":"01:57.470","Text":"How is this done?"},{"Start":"01:57.470 ","End":"01:59.915","Text":"This is done using electron carriers."},{"Start":"01:59.915 ","End":"02:04.430","Text":"These are molecules that carry high-energy electrons between compounds."},{"Start":"02:04.430 ","End":"02:08.900","Text":"For example, nicotinamide adenine dinucleotide"},{"Start":"02:08.900 ","End":"02:14.030","Text":"or in short NAD is derived from vitamin B3, niacin."},{"Start":"02:14.030 ","End":"02:16.430","Text":"NAD plus here,"},{"Start":"02:16.430 ","End":"02:19.250","Text":"is the oxidized form of the molecule."},{"Start":"02:19.250 ","End":"02:26.315","Text":"NADH is reduced form of the molecule after it has accepted 2 electrons and a proton."},{"Start":"02:26.315 ","End":"02:31.255","Text":"NADH can now donate these electrons to another molecule."},{"Start":"02:31.255 ","End":"02:33.675","Text":"Reduced again to NAD plus,"},{"Start":"02:33.675 ","End":"02:37.105","Text":"it can accept electrons from an organic molecule."},{"Start":"02:37.105 ","End":"02:39.859","Text":"ATP in living systems."},{"Start":"02:39.859 ","End":"02:46.255","Text":"In living systems, a cell must store energy safely and release it for use only as needed."},{"Start":"02:46.255 ","End":"02:52.460","Text":"Adenosine triphosphate or ATP is the energy currency of the cell."},{"Start":"02:52.460 ","End":"02:57.865","Text":"When ATP breaks down its terminal phosphate group, energy is released."},{"Start":"02:57.865 ","End":"03:03.065","Text":"Later, the released phosphate is bound to another molecule and activates it."},{"Start":"03:03.065 ","End":"03:05.840","Text":"Here we see the adenosine triphosphate,"},{"Start":"03:05.840 ","End":"03:07.685","Text":"which is like a charged battery,"},{"Start":"03:07.685 ","End":"03:11.570","Text":"and after it loses 1 of the phosphate groups,"},{"Start":"03:11.570 ","End":"03:17.750","Text":"we have your adenosine diphosphate and we have the free energy that we\u0027ve used."},{"Start":"03:17.750 ","End":"03:20.060","Text":"Now this battery is empty again."},{"Start":"03:20.060 ","End":"03:23.060","Text":"Of course, that cell is going to recharge it."},{"Start":"03:23.060 ","End":"03:26.780","Text":"We have here our ATP-ADP cycle."},{"Start":"03:26.780 ","End":"03:30.365","Text":"Adenosine monophosphate, AMP,"},{"Start":"03:30.365 ","End":"03:36.680","Text":"is the adenine molecule bonded to a ribose molecule into a single phosphate group."},{"Start":"03:36.680 ","End":"03:39.530","Text":"Here we have the adenosine, which is the sugar,"},{"Start":"03:39.530 ","End":"03:42.095","Text":"and we have the adenine molecule,"},{"Start":"03:42.095 ","End":"03:44.290","Text":"and a phosphate group."},{"Start":"03:44.290 ","End":"03:49.550","Text":"The ribose is a 5-carbon sugar. The numbers are here."},{"Start":"03:49.550 ","End":"03:51.440","Text":"This is 1, 2,"},{"Start":"03:51.440 ","End":"03:54.440","Text":"3, 4, and 5."},{"Start":"03:54.440 ","End":"03:56.820","Text":"Notice this is an oxygen."},{"Start":"03:56.860 ","End":"04:03.430","Text":"The addition of a second phosphate group forms adenosine diphosphate, ADP."},{"Start":"04:03.430 ","End":"04:09.935","Text":"Addition of a third phosphate group forms adenosine triphosphate, ATP."},{"Start":"04:09.935 ","End":"04:14.270","Text":"The phosphate groups are negatively charged and they repel each other."},{"Start":"04:14.270 ","End":"04:19.555","Text":"Therefore, ADP and ATP molecules are inherently unstable."},{"Start":"04:19.555 ","End":"04:23.450","Text":"That means that adding of these 3 phosphate groups that repel each"},{"Start":"04:23.450 ","End":"04:27.448","Text":"other is like winding a spring and holding it shut tight."},{"Start":"04:27.448 ","End":"04:28.835","Text":"As soon as we let them go,"},{"Start":"04:28.835 ","End":"04:31.280","Text":"they will release energy and come apart."},{"Start":"04:31.280 ","End":"04:36.680","Text":"Dephosphorylation is the removal of phosphate groups and this of course releases energy."},{"Start":"04:36.680 ","End":"04:38.630","Text":"Let\u0027s see how this works."},{"Start":"04:38.630 ","End":"04:44.780","Text":"Hydrolysis reactions involve breaking complex macromolecules apart using water."},{"Start":"04:44.780 ","End":"04:47.825","Text":"Here we have ATP,"},{"Start":"04:47.825 ","End":"04:51.950","Text":"adenosine triphosphate with 3 phosphate groups."},{"Start":"04:51.950 ","End":"04:57.275","Text":"Hydrolysis using a water molecule takes 1 of them apart."},{"Start":"04:57.275 ","End":"05:04.770","Text":"The hydrolysis of ATP produces ADP which means diphosphate, 2 of them,"},{"Start":"05:04.770 ","End":"05:08.375","Text":"and inorganic phosphate ion, here it is,"},{"Start":"05:08.375 ","End":"05:10.700","Text":"and release of free energy,"},{"Start":"05:10.700 ","End":"05:13.250","Text":"which was in this chemical bond."},{"Start":"05:13.250 ","End":"05:17.135","Text":"ATP is continuously broken down into ADP,"},{"Start":"05:17.135 ","End":"05:19.475","Text":"releasing a lot of energy for the cell."},{"Start":"05:19.475 ","End":"05:24.240","Text":"ADP is continuously regenerated into ATP."},{"Start":"05:24.770 ","End":"05:28.310","Text":"In this reaction, water is regenerated when"},{"Start":"05:28.310 ","End":"05:31.970","Text":"a third phosphate is added to the ADP molecule forming"},{"Start":"05:31.970 ","End":"05:41.090","Text":"ATP and we\u0027re going to get an extra molecule of water."},{"Start":"05:41.090 ","End":"05:47.020","Text":"Where does the energy come from to add the phosphate group on?"},{"Start":"05:47.020 ","End":"05:51.470","Text":"Energy for regenerating ATP comes from the breakdown of glucose,"},{"Start":"05:51.470 ","End":"05:56.185","Text":"fructose or galactose or sugars consumed by the cell."},{"Start":"05:56.185 ","End":"05:58.430","Text":"ATP is a direct language,"},{"Start":"05:58.430 ","End":"06:01.130","Text":"meaning glucose catabolism and the multitude of"},{"Start":"06:01.130 ","End":"06:05.045","Text":"endergonic pathways that power living cells."},{"Start":"06:05.045 ","End":"06:08.915","Text":"How is the energy from ATP used in the cell?"},{"Start":"06:08.915 ","End":"06:11.515","Text":"This is done by phosphorylation."},{"Start":"06:11.515 ","End":"06:15.770","Text":"ATP forms an intermediate complex with a substrate and"},{"Start":"06:15.770 ","End":"06:20.975","Text":"enzyme and transfer as its third phosphate group with its energy to the substrate."},{"Start":"06:20.975 ","End":"06:25.520","Text":"Phosphorylation refers to the addition of a phosphate group."},{"Start":"06:25.520 ","End":"06:29.539","Text":"This is illustrated by the following generic reaction."},{"Start":"06:29.539 ","End":"06:32.780","Text":"While A and B represent 2 different substrates,"},{"Start":"06:32.780 ","End":"06:35.885","Text":"the phosphorylated complex A now,"},{"Start":"06:35.885 ","End":"06:41.345","Text":"uses another enzyme called phosphatase which cuts off this phosphate group,"},{"Start":"06:41.345 ","End":"06:45.440","Text":"releasing energy and changing it to a substance B."},{"Start":"06:45.440 ","End":"06:49.535","Text":"But how is ATP generated in the cell?"},{"Start":"06:49.535 ","End":"06:55.565","Text":"ATP is generated through 2 mechanisms during the breakdown of glucose, sugar."},{"Start":"06:55.565 ","End":"07:01.385","Text":"Few ATP molecules are generated by chemical reactions and catabolic pathways such as"},{"Start":"07:01.385 ","End":"07:04.430","Text":"substrate-level phosphorylation where ATP is"},{"Start":"07:04.430 ","End":"07:08.380","Text":"produced by the direct transfer of a phosphate to ADP."},{"Start":"07:08.380 ","End":"07:11.750","Text":"This is transferred from another phosphorylated compound,"},{"Start":"07:11.750 ","End":"07:16.215","Text":"for example, in glycolysis or respiration,"},{"Start":"07:16.215 ","End":"07:19.670","Text":"we see here how the substrate,"},{"Start":"07:19.670 ","End":"07:25.415","Text":"which is PEP, donates its phosphate group to ADP and here we get ADP."},{"Start":"07:25.415 ","End":"07:32.365","Text":"But the real bulk of ATP production occurs by oxidative phosphorylation."},{"Start":"07:32.365 ","End":"07:35.225","Text":"This process takes place in mitochondria,"},{"Start":"07:35.225 ","End":"07:40.265","Text":"eukaryotic cells or in the plasma membrane of a prokaryotic cell,"},{"Start":"07:40.265 ","End":"07:42.725","Text":"also known as chemiosmosis."},{"Start":"07:42.725 ","End":"07:46.375","Text":"This is the main ATP production in cellular metabolism."},{"Start":"07:46.375 ","End":"07:52.805","Text":"Oxidative phosphorylation generates 90 percent of the ATP made during glucose catabolism."},{"Start":"07:52.805 ","End":"07:54.905","Text":"It\u0027s also used in the light reactions of"},{"Start":"07:54.905 ","End":"07:58.190","Text":"photosynthesis to harness the energy of the sunlight."},{"Start":"07:58.190 ","End":"08:00.440","Text":"This process involves oxygen."},{"Start":"08:00.440 ","End":"08:02.270","Text":"In the following sections,"},{"Start":"08:02.270 ","End":"08:06.524","Text":"we\u0027ll be going into the really fine details of oxidative phosphorylation,"},{"Start":"08:06.524 ","End":"08:10.220","Text":"and we\u0027ll understand exactly how ATP is generated in this process."},{"Start":"08:10.220 ","End":"08:14.840","Text":"In the meantime, we\u0027ve discussed the importance of electrons in the transfer of energy in"},{"Start":"08:14.840 ","End":"08:22.410","Text":"living systems and explained how ATP is used by cells as an energy source. See you soon."}],"ID":25845},{"Watched":false,"Name":"Glycolysis","Duration":"8m ","ChapterTopicVideoID":24931,"CourseChapterTopicPlaylistID":136378,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.020 ","End":"00:04.185","Text":"Hi, we\u0027re studying Cellular Respiration."},{"Start":"00:04.185 ","End":"00:06.750","Text":"In this section, we\u0027ll be speaking about the first step"},{"Start":"00:06.750 ","End":"00:09.780","Text":"in this process called Glycolysis."},{"Start":"00:09.780 ","End":"00:11.580","Text":"By the end of this section,"},{"Start":"00:11.580 ","End":"00:15.150","Text":"you\u0027ll be able to describe the overall result of glycolysis in"},{"Start":"00:15.150 ","End":"00:18.690","Text":"terms of molecules produced during the chemical breakdown of glucose."},{"Start":"00:18.690 ","End":"00:22.140","Text":"You will also be able to define the output of glycolysis in"},{"Start":"00:22.140 ","End":"00:26.895","Text":"terms of ATP molecules and NADH molecules produced."},{"Start":"00:26.895 ","End":"00:31.020","Text":"Glycolysis literally means glyco,"},{"Start":"00:31.020 ","End":"00:32.670","Text":"which is sugar, and lysis,"},{"Start":"00:32.670 ","End":"00:34.260","Text":"which is taken apart."},{"Start":"00:34.260 ","End":"00:40.105","Text":"Nearly all the energy used by living cells comes from the breakdown of glucose."},{"Start":"00:40.105 ","End":"00:45.380","Text":"Almost all living organisms carry out glycolysis as part of their metabolism."},{"Start":"00:45.380 ","End":"00:49.520","Text":"Glycolysis is independent of the presence of oxygen."},{"Start":"00:49.520 ","End":"00:52.535","Text":"Although we know that cellular respiration,"},{"Start":"00:52.535 ","End":"00:53.810","Text":"at least in eukaryotes,"},{"Start":"00:53.810 ","End":"00:58.400","Text":"includes oxygen as the final acceptor of electrons."},{"Start":"00:58.400 ","End":"01:02.180","Text":"This first step glycolysis does not involve oxygen at all,"},{"Start":"01:02.180 ","End":"01:03.770","Text":"and therefore it\u0027s also performed by"},{"Start":"01:03.770 ","End":"01:07.775","Text":"many other organisms that don\u0027t use oxygen in their respiration."},{"Start":"01:07.775 ","End":"01:12.995","Text":"Glycolysis takes place in the cytoplasm of both prokaryotic and eukaryotic cells."},{"Start":"01:12.995 ","End":"01:19.385","Text":"While in eukaryotes, the rest of the respiration takes place in the mitochondria."},{"Start":"01:19.385 ","End":"01:22.465","Text":"How does glucose enter the cell?"},{"Start":"01:22.465 ","End":"01:25.250","Text":"Glucose may enter the cell in 2 ways."},{"Start":"01:25.250 ","End":"01:27.830","Text":"The first way is by GLUT proteins,"},{"Start":"01:27.830 ","End":"01:31.670","Text":"which is an abbreviation for glucose transporter proteins."},{"Start":"01:31.670 ","End":"01:34.785","Text":"These facilitate the glucose diffusion."},{"Start":"01:34.785 ","End":"01:39.785","Text":"If you remember, diffusion means that molecules are moving along their own gradient."},{"Start":"01:39.785 ","End":"01:44.965","Text":"If you have a high concentration of glucose molecules outside of the cell,"},{"Start":"01:44.965 ","End":"01:47.785","Text":"and a low concentration inside,"},{"Start":"01:47.785 ","End":"01:51.305","Text":"glucose will diffuse along this gradient."},{"Start":"01:51.305 ","End":"01:54.770","Text":"Since glucose can pass freely through the membrane,"},{"Start":"01:54.770 ","End":"01:58.025","Text":"it needs these transporter proteins to take them in."},{"Start":"01:58.025 ","End":"02:03.800","Text":"The GLUT1 specifically binds to the glucose and then changes this conformation."},{"Start":"02:03.800 ","End":"02:06.020","Text":"Let\u0027s the glucose into the cell."},{"Start":"02:06.020 ","End":"02:11.930","Text":"This form of transport along the gradient does not require the cell to use any energy."},{"Start":"02:11.930 ","End":"02:15.260","Text":"But what will happen in case there\u0027s a high concentration of"},{"Start":"02:15.260 ","End":"02:19.325","Text":"glucose inside the cell and a very low concentration outside?"},{"Start":"02:19.325 ","End":"02:24.395","Text":"Now glucose intake cannot be done along with gradient without energy."},{"Start":"02:24.395 ","End":"02:28.685","Text":"Therefore, the cell also has secondary active transport"},{"Start":"02:28.685 ","End":"02:33.490","Text":"as a way of taking in glucose from outside against the gradient."},{"Start":"02:33.490 ","End":"02:36.410","Text":"Secondary active transport requires"},{"Start":"02:36.410 ","End":"02:39.380","Text":"primary active transport to do something else before that,"},{"Start":"02:39.380 ","End":"02:44.030","Text":"secondary active transport is always coupled with primary active transport."},{"Start":"02:44.030 ","End":"02:49.820","Text":"In this case, the glucose pump is paired with a sodium-potassium pump."},{"Start":"02:49.820 ","End":"02:53.780","Text":"The sodium-potassium pump uses energy derived from"},{"Start":"02:53.780 ","End":"03:00.200","Text":"ATP molecules to actively pump potassium into the cell and sodium out of the cell."},{"Start":"03:00.200 ","End":"03:02.465","Text":"Since this process uses energy,"},{"Start":"03:02.465 ","End":"03:06.965","Text":"the cell can create a concentration of sodium molecules out of the cell,"},{"Start":"03:06.965 ","End":"03:11.180","Text":"and a low concentration of sodium molecules inside the cell."},{"Start":"03:11.180 ","End":"03:14.360","Text":"This causes a chemical driving force of"},{"Start":"03:14.360 ","End":"03:19.280","Text":"the sodium ions moving from outside of the cell, inside the cell."},{"Start":"03:19.280 ","End":"03:23.690","Text":"The energy of the flow of sodium ions into the cell is used by"},{"Start":"03:23.690 ","End":"03:25.730","Text":"the glucose pump to pump along"},{"Start":"03:25.730 ","End":"03:29.965","Text":"glucose molecules along into the cell with it against the gradient."},{"Start":"03:29.965 ","End":"03:36.575","Text":"As we said, glycolysis involves of the lysis of taking apart glyco of sugars."},{"Start":"03:36.575 ","End":"03:40.950","Text":"Glycolysis, glucose, which is a 6-carbon molecule,"},{"Start":"03:40.950 ","End":"03:44.284","Text":"is split into 2 molecules of pyruvate,"},{"Start":"03:44.284 ","End":"03:48.425","Text":"which each include a backbone of 3 carbon atoms."},{"Start":"03:48.425 ","End":"03:51.900","Text":"We have here 6 carbons 1,"},{"Start":"03:51.900 ","End":"03:54.255","Text":"2, 3,"},{"Start":"03:54.255 ","End":"03:57.565","Text":"4, 5, and 6."},{"Start":"03:57.565 ","End":"04:00.755","Text":"Notice that the ring is closed with an oxygen atom."},{"Start":"04:00.755 ","End":"04:07.445","Text":"These 6 carbon atoms find themselves in 2 pyruvate atoms at the end of the process."},{"Start":"04:07.445 ","End":"04:10.280","Text":"Glycolysis includes 2 phases."},{"Start":"04:10.280 ","End":"04:13.295","Text":"The first phase is the energy investment phase,"},{"Start":"04:13.295 ","End":"04:16.580","Text":"and the second phase is the energy payoff phase."},{"Start":"04:16.580 ","End":"04:18.530","Text":"In the energy investment phase,"},{"Start":"04:18.530 ","End":"04:22.730","Text":"2 ATP molecules are used for glucose phosphorylation."},{"Start":"04:22.730 ","End":"04:26.090","Text":"The phosphorylating glucose is then split into 2,"},{"Start":"04:26.090 ","End":"04:29.285","Text":"3 carbon molecules, still phosphorylated."},{"Start":"04:29.285 ","End":"04:32.395","Text":"At this point, they are very high in energy."},{"Start":"04:32.395 ","End":"04:37.550","Text":"We take the glucose and we charge it with energy and bring it to an unstable state."},{"Start":"04:37.550 ","End":"04:38.990","Text":"From this unstable state,"},{"Start":"04:38.990 ","End":"04:41.960","Text":"it can now tumble down to a much lower energy state."},{"Start":"04:41.960 ","End":"04:44.750","Text":"This is the energy payoff phase."},{"Start":"04:44.750 ","End":"04:49.380","Text":"Here, phosphorylation without ATP investment is achieved."},{"Start":"04:49.380 ","End":"04:57.535","Text":"ADP molecules,4 of them to be exact are phosphorylated to form 4 ATP molecules."},{"Start":"04:57.535 ","End":"05:01.985","Text":"Also, 2 NADH molecules are reduced to NADH,"},{"Start":"05:01.985 ","End":"05:08.470","Text":"and we now have 4 ATPs and 2 NADH molecules which are charged with energy."},{"Start":"05:08.470 ","End":"05:10.055","Text":"As for the glucose,"},{"Start":"05:10.055 ","End":"05:15.115","Text":"it ends up as 2 pyruvate molecules and also 2 molecules of water."},{"Start":"05:15.115 ","End":"05:20.614","Text":"If we look at the net, we put in 1 molecule of glucose and got 2 molecules of pyruvate,"},{"Start":"05:20.614 ","End":"05:22.870","Text":"2 molecules of water as a byproduct too."},{"Start":"05:22.870 ","End":"05:25.415","Text":"We have 4 ATP molecules formed,"},{"Start":"05:25.415 ","End":"05:29.780","Text":"but we invested 2 at the beginning here in the energy investment phase."},{"Start":"05:29.780 ","End":"05:33.365","Text":"Therefore, the net product is 2 ATP molecules,"},{"Start":"05:33.365 ","End":"05:36.650","Text":"and we also have 2 NADH molecules."},{"Start":"05:36.650 ","End":"05:40.070","Text":"Can now see the whole process we have here are"},{"Start":"05:40.070 ","End":"05:43.685","Text":"6 carbon molecule of glucose being split into 2,"},{"Start":"05:43.685 ","End":"05:45.935","Text":"3-carbon molecules of pyruvate."},{"Start":"05:45.935 ","End":"05:51.394","Text":"Their net product is 2 ATP molecules and 2 NADH molecules."},{"Start":"05:51.394 ","End":"05:53.645","Text":"In order to continue this process,"},{"Start":"05:53.645 ","End":"05:56.980","Text":"the cell must have a continuous intake of glucose."},{"Start":"05:56.980 ","End":"06:03.500","Text":"We also have to have ADP molecules available to accept the extra phosphate group."},{"Start":"06:03.500 ","End":"06:10.570","Text":"We also need to have available NAD^+ molecules to be reduced to NADH."},{"Start":"06:10.570 ","End":"06:15.515","Text":"ATP is easy because ATP is used all over the cell for energy."},{"Start":"06:15.515 ","End":"06:24.140","Text":"We get the energy and we recycle the ADP and the phosphate groups."},{"Start":"06:24.140 ","End":"06:26.630","Text":"ADP will always be available for this."},{"Start":"06:26.630 ","End":"06:28.645","Text":"What about NADH?"},{"Start":"06:28.645 ","End":"06:30.995","Text":"If the NADH is not available."},{"Start":"06:30.995 ","End":"06:34.145","Text":"The second half of glycolysis will slow down or stop."},{"Start":"06:34.145 ","End":"06:36.710","Text":"If oxygen is available in the system,"},{"Start":"06:36.710 ","End":"06:40.805","Text":"the NADH will later be oxidated for ATP production."},{"Start":"06:40.805 ","End":"06:45.350","Text":"We have here, the NADH will be oxidized to NAD"},{"Start":"06:45.350 ","End":"06:51.050","Text":"plus and the output will be ATP formation,"},{"Start":"06:51.050 ","End":"06:54.980","Text":"and the energy will be used for the ATP as we\u0027re going to see in the next sections."},{"Start":"06:54.980 ","End":"06:59.630","Text":"But what happens in environments that don\u0027t have oxygen at all?"},{"Start":"06:59.630 ","End":"07:05.480","Text":"Here, fermentation can provide the oxidation of NADH to NAD^+."},{"Start":"07:05.480 ","End":"07:10.430","Text":"We know that certain yeasts and certain bacteria may use fermentation."},{"Start":"07:10.430 ","End":"07:13.060","Text":"We might use them to make wine or bread in the fermentation."},{"Start":"07:13.060 ","End":"07:15.320","Text":"We\u0027re going to also see that in the next sections."},{"Start":"07:15.320 ","End":"07:22.290","Text":"We\u0027ve got here an option for fermentation."},{"Start":"07:24.940 ","End":"07:27.440","Text":"We\u0027ve spoken about glycolysis,"},{"Start":"07:27.440 ","End":"07:30.245","Text":"the first step of cellular respiration."},{"Start":"07:30.245 ","End":"07:33.559","Text":"In this section, we describe the overall results of glycolysis"},{"Start":"07:33.559 ","End":"07:37.370","Text":"in terms of molecules produced during the chemical breakdown of glucose."},{"Start":"07:37.370 ","End":"07:43.260","Text":"Remember, we have 2 pyruvates."},{"Start":"07:46.300 ","End":"07:53.540","Text":"We\u0027ve also defined the output of glycolysis in terms of ATP and NADH molecules produced."},{"Start":"07:53.540 ","End":"07:57.215","Text":"We\u0027ve got net of 2 of each of them."},{"Start":"07:57.215 ","End":"08:00.570","Text":"I\u0027ll see you in the next sections, goodbye."}],"ID":25844},{"Watched":false,"Name":"Oxidation of Pyruvate and the Citric Acid Cycle","Duration":"7m 9s","ChapterTopicVideoID":24934,"CourseChapterTopicPlaylistID":136378,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.320 ","End":"00:04.230","Text":"Hi. We\u0027re studying cellular respiration."},{"Start":"00:04.230 ","End":"00:07.800","Text":"After speaking about glycolysis in previous sections,"},{"Start":"00:07.800 ","End":"00:10.035","Text":"we\u0027ll now be speaking about the next steps,"},{"Start":"00:10.035 ","End":"00:11.940","Text":"which are oxidation of pyruvate,"},{"Start":"00:11.940 ","End":"00:14.040","Text":"and the citric acid cycle."},{"Start":"00:14.040 ","End":"00:17.970","Text":"By the end of this section you\u0027ll be able to describe how pyruvate,"},{"Start":"00:17.970 ","End":"00:22.590","Text":"the product of glycolysis is prepared for entry into the citric acid cycle."},{"Start":"00:22.590 ","End":"00:26.190","Text":"You\u0027ll also be able to explain how a circular pathway,"},{"Start":"00:26.190 ","End":"00:29.490","Text":"such as the citric acid cycle fundamentally differs"},{"Start":"00:29.490 ","End":"00:33.540","Text":"from a linear biochemical pathway, such as glycolysis."},{"Start":"00:33.540 ","End":"00:38.880","Text":"Let\u0027s have an overview of the stages of cellular respiration."},{"Start":"00:38.880 ","End":"00:44.050","Text":"The gathering of energy from glucose is done by 3 stages."},{"Start":"00:44.050 ","End":"00:48.935","Text":"The first step we mentioned in previous sections in glycolysis."},{"Start":"00:48.935 ","End":"00:53.390","Text":"In this step glucose is broken down into 2 molecules of pyruvate."},{"Start":"00:53.390 ","End":"00:56.005","Text":"Glucose is broken into pyruvate."},{"Start":"00:56.005 ","End":"01:01.060","Text":"The next step the citric acid cycle completes the breakdown of glucose."},{"Start":"01:01.060 ","End":"01:05.660","Text":"The final energy harvesting is completed in the oxidative phosphorylation."},{"Start":"01:05.660 ","End":"01:09.205","Text":"This accounts for most of the ATP synthesis."},{"Start":"01:09.205 ","End":"01:11.865","Text":"As we can see in the illustration,"},{"Start":"01:11.865 ","End":"01:16.325","Text":"the glycolysis is performed in the cytosol while the following steps,"},{"Start":"01:16.325 ","End":"01:22.220","Text":"the citric acid cycle and oxidative phosphorylation occur in the mitochondrion."},{"Start":"01:22.220 ","End":"01:25.896","Text":"For the entire process of cellular respiration,"},{"Start":"01:25.896 ","End":"01:31.825","Text":"between 30 and 32 ATP molecules are harvested from each glucose processed."},{"Start":"01:31.825 ","End":"01:33.655","Text":"How is this achieved?"},{"Start":"01:33.655 ","End":"01:37.990","Text":"Well, during glycolysis we have a net of 4 minus"},{"Start":"01:37.990 ","End":"01:43.030","Text":"2 equals 2 ATP molecules produced during Krebs cycle,"},{"Start":"01:43.030 ","End":"01:45.235","Text":"another name for the citric acid cycle,"},{"Start":"01:45.235 ","End":"01:48.125","Text":"another 2 ATP molecules are produced."},{"Start":"01:48.125 ","End":"01:54.970","Text":"But, during these 2 processes many NADH and FADH_2 molecules are reduced,"},{"Start":"01:54.970 ","End":"01:57.789","Text":"carrying their electrons to the next process,"},{"Start":"01:57.789 ","End":"02:00.430","Text":"the oxidative phosphorylation where"},{"Start":"02:00.430 ","End":"02:04.940","Text":"the electrons are used to produce many more ATP molecules."},{"Start":"02:04.940 ","End":"02:08.495","Text":"This step, the oxidative phosphorylation yields"},{"Start":"02:08.495 ","End":"02:12.140","Text":"different numbers of ATP molecules in different organisms and therefore,"},{"Start":"02:12.140 ","End":"02:15.305","Text":"in different textbooks you\u0027ll find different numbers for these."},{"Start":"02:15.305 ","End":"02:20.225","Text":"I suggest that you look specifically at your own textbook to get the numbers right."},{"Start":"02:20.225 ","End":"02:26.945","Text":"The total net ATP yield is usually between 30 and 32 ATP molecules."},{"Start":"02:26.945 ","End":"02:32.570","Text":"As previously mentioned, glycolysis occurs whether or not oxygen is present."},{"Start":"02:32.570 ","End":"02:34.340","Text":"We\u0027ve also mentioned that in"},{"Start":"02:34.340 ","End":"02:39.245","Text":"anaerobic environments where oxygen is not present a fermentation occurs."},{"Start":"02:39.245 ","End":"02:44.270","Text":"But, if oxygen is available aerobic respiration will go forward."},{"Start":"02:44.270 ","End":"02:47.930","Text":"In eukaryotic cells the pyruvate molecules are transported"},{"Start":"02:47.930 ","End":"02:52.175","Text":"into the mitochondria where the oxidation of glucose is completed."},{"Start":"02:52.175 ","End":"02:55.640","Text":"Here we can see the steps of the oxidation of pyruvate."},{"Start":"02:55.640 ","End":"03:01.805","Text":"In the first step a carboxyl group is removed from the pyruvate releasing carbon dioxide."},{"Start":"03:01.805 ","End":"03:05.120","Text":"The pyruvate, which is a 3-carbon molecule"},{"Start":"03:05.120 ","End":"03:10.550","Text":"loses its first carbon molecule and is now left with only 2 of them."},{"Start":"03:10.550 ","End":"03:15.350","Text":"In the second step, NAD plus is reduced to NADH."},{"Start":"03:15.350 ","End":"03:20.770","Text":"This occurs by using coenzyme A or in short CoA."},{"Start":"03:20.770 ","End":"03:27.200","Text":"Now, an acetyl group is transferred to coenzyme A resulting in acetyl CoA."},{"Start":"03:27.200 ","End":"03:32.425","Text":"Now we have a 2-carbon molecule connected with the CoA."},{"Start":"03:32.425 ","End":"03:35.430","Text":"In short, in the oxidation of pyruvate,"},{"Start":"03:35.430 ","End":"03:41.060","Text":"pyruvate is transformed into acetyl coenzyme A or in short, acetyl CoA."},{"Start":"03:41.060 ","End":"03:46.800","Text":"The major function of this step is to deliver the acetyl group to the next stage."},{"Start":"03:46.840 ","End":"03:51.055","Text":"Let\u0027s have a look at the pyruvate oxidation again."},{"Start":"03:51.055 ","End":"03:57.305","Text":"A multienzyme complex converts pyruvate into acetyl CoA by a 3-step process."},{"Start":"03:57.305 ","End":"03:59.728","Text":"The first one is the oxidation of pyruvate,"},{"Start":"03:59.728 ","End":"04:02.000","Text":"and release of carbon dioxide."},{"Start":"04:02.000 ","End":"04:05.210","Text":"Again, we lose the first carbon molecule to"},{"Start":"04:05.210 ","End":"04:10.130","Text":"carbon dioxide and are left with a 2-carbon molecule."},{"Start":"04:10.130 ","End":"04:12.080","Text":"In the second step,"},{"Start":"04:12.080 ","End":"04:16.175","Text":"NAD plus is reduced to NADH."},{"Start":"04:16.175 ","End":"04:20.960","Text":"The NADH will be carrying electrons to the next steps."},{"Start":"04:20.960 ","End":"04:24.110","Text":"Finally, the production of acetyl CoA from"},{"Start":"04:24.110 ","End":"04:27.695","Text":"a coenzyme A and the remaining 2 carbon fragment occurs."},{"Start":"04:27.695 ","End":"04:30.860","Text":"Here we have the product, acetyl CoA."},{"Start":"04:30.860 ","End":"04:34.040","Text":"Let\u0027s have a look now at the citric acid cycle,"},{"Start":"04:34.040 ","End":"04:36.290","Text":"also known as Krebs cycle."},{"Start":"04:36.290 ","End":"04:41.370","Text":"This cycle completes the breakdown of pyruvate to carbon dioxide."},{"Start":"04:41.370 ","End":"04:44.685","Text":"It generates 1 ATP molecule,"},{"Start":"04:44.685 ","End":"04:47.115","Text":"reduces 3 NADH molecules,"},{"Start":"04:47.115 ","End":"04:51.885","Text":"and 1 FADH_2 for each cycle using 1 pyruvate molecule."},{"Start":"04:51.885 ","End":"04:57.510","Text":"Since we know that for each glucose molecule we get 2 pyruvate molecules,"},{"Start":"04:57.510 ","End":"05:00.660","Text":"we may multiply these numbers by 2."},{"Start":"05:00.880 ","End":"05:08.770","Text":"The citric acid cycle itself consists of 8 different steps catalyzed by specific enzymes."},{"Start":"05:08.770 ","End":"05:11.960","Text":"In the first part of the citric acid cycle,"},{"Start":"05:11.960 ","End":"05:17.705","Text":"the acetyl group of acetyl CoA is combined with oxaloacetate forming citrate,"},{"Start":"05:17.705 ","End":"05:21.335","Text":"also known as citric acid thus the name."},{"Start":"05:21.335 ","End":"05:23.600","Text":"Notice that the coenzyme A is stripped from"},{"Start":"05:23.600 ","End":"05:27.965","Text":"the acetyl CoA and is recycled for the steps to happen again."},{"Start":"05:27.965 ","End":"05:31.220","Text":"The steps eventually decompose the citrate to"},{"Start":"05:31.220 ","End":"05:34.865","Text":"oxaloacetate again making the process a cycle."},{"Start":"05:34.865 ","End":"05:39.530","Text":"On the way you see we lose another 2 molecules of carbon dioxide"},{"Start":"05:39.530 ","End":"05:44.705","Text":"totally decomposing the 2 carbon molecules that enter the cycle."},{"Start":"05:44.705 ","End":"05:51.430","Text":"The reduced NADH and FADH_2 molecules carry electrons to the electron transport chain."},{"Start":"05:51.430 ","End":"05:53.250","Text":"Here we have the NADH,"},{"Start":"05:53.250 ","End":"05:55.985","Text":"the FADH_2, and the NADH."},{"Start":"05:55.985 ","End":"05:59.525","Text":"Notice that also ATP is formed in the process."},{"Start":"05:59.525 ","End":"06:02.995","Text":"The process generates 1 ATP molecule,"},{"Start":"06:02.995 ","End":"06:06.785","Text":"3 NADH, and 1 FADH_2 per cycle."},{"Start":"06:06.785 ","End":"06:12.080","Text":"Again, since per each glucose we have 2 acetyl CoA molecules entering,"},{"Start":"06:12.080 ","End":"06:14.240","Text":"so per each glucose molecule,"},{"Start":"06:14.240 ","End":"06:15.575","Text":"we have 2 ATPs,"},{"Start":"06:15.575 ","End":"06:20.225","Text":"6 NADH, and 2 FADH_2 molecules reduced per cycle."},{"Start":"06:20.225 ","End":"06:22.550","Text":"The citric acid cycle is considered as"},{"Start":"06:22.550 ","End":"06:27.275","Text":"an aerobic pathway even though you can see here it doesn\u0027t consume any oxygen."},{"Start":"06:27.275 ","End":"06:30.605","Text":"Following glycolysis and a citric acid cycle,"},{"Start":"06:30.605 ","End":"06:36.805","Text":"the NADH and FADH_2 that are reduced account for most of the energy extracted from food."},{"Start":"06:36.805 ","End":"06:42.485","Text":"NADH and FADH_2 donate the electrons to the electron transport chain,"},{"Start":"06:42.485 ","End":"06:47.165","Text":"which powers the ATP synthesis via oxidative phosphorylation,"},{"Start":"06:47.165 ","End":"06:50.015","Text":"which we\u0027re going to meet in the next section."},{"Start":"06:50.015 ","End":"06:53.224","Text":"In this section we described how pyruvate,"},{"Start":"06:53.224 ","End":"06:57.605","Text":"the product of glycolysis is prepared for entry into the citric acid cycle."},{"Start":"06:57.605 ","End":"07:00.185","Text":"We\u0027ve also explained how a circular pathway,"},{"Start":"07:00.185 ","End":"07:02.090","Text":"such as the citric acid cycle,"},{"Start":"07:02.090 ","End":"07:07.430","Text":"fundamentally differs from a linear biochemical pathway such as glycolysis."},{"Start":"07:07.430 ","End":"07:10.410","Text":"See you in the next section."}],"ID":25847},{"Watched":false,"Name":"Oxidative Phosphorylation","Duration":"8m 55s","ChapterTopicVideoID":24935,"CourseChapterTopicPlaylistID":136378,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:03.495","Text":"Hey there. We\u0027re studying respiration."},{"Start":"00:03.495 ","End":"00:07.290","Text":"In this section, we\u0027ll be learning about oxidative phosphorylation."},{"Start":"00:07.290 ","End":"00:11.700","Text":"By the end of this section you\u0027ll be able to describe how electrons move through"},{"Start":"00:11.700 ","End":"00:14.490","Text":"the electron transport chain and what happens"},{"Start":"00:14.490 ","End":"00:17.940","Text":"to the energy levels of these electrons during the process."},{"Start":"00:17.940 ","End":"00:21.075","Text":"You\u0027ll also be able to explain how a proton gradient is"},{"Start":"00:21.075 ","End":"00:24.990","Text":"established and maintained by the electron transport chain."},{"Start":"00:24.990 ","End":"00:30.200","Text":"Glycolysis in the citric acid cycle produce several ATP molecules"},{"Start":"00:30.200 ","End":"00:35.759","Text":"along with reduced NADH and FADH_2 electron carriers."},{"Start":"00:35.900 ","End":"00:42.150","Text":"In glycolysis we have a net of 2 ATP molecules and we also have"},{"Start":"00:42.150 ","End":"00:49.130","Text":"2 reduced NADH molecules and pyruvate oxidation together with the citric acid cycle,"},{"Start":"00:49.130 ","End":"00:52.429","Text":"again, only 2 ATP molecules are actually produced."},{"Start":"00:52.429 ","End":"00:59.329","Text":"While we have 8 NADH reduced molecules and 2 FADH_2 induced molecules."},{"Start":"00:59.329 ","End":"01:03.965","Text":"What happens with all these electron carriers and where is the bulk energy produced?"},{"Start":"01:03.965 ","End":"01:06.905","Text":"The answer is the oxidative phosphorylation,"},{"Start":"01:06.905 ","End":"01:10.085","Text":"where the NADH and FADH_2 electron carriers"},{"Start":"01:10.085 ","End":"01:13.760","Text":"are used in the oxidative phosphorylation process."},{"Start":"01:13.760 ","End":"01:17.390","Text":"This process is responsible for most of the energy extracted from"},{"Start":"01:17.390 ","End":"01:22.414","Text":"food that\u0027s between 26 and 28 ATP molecules."},{"Start":"01:22.414 ","End":"01:27.170","Text":"The first part, the electron transport chain is where hydrogen ions also"},{"Start":"01:27.170 ","End":"01:31.910","Text":"known as protons accumulate in the intermembrane space as a mitochondria."},{"Start":"01:31.910 ","End":"01:35.250","Text":"In the second part, the chemiosmosis."},{"Start":"01:35.250 ","End":"01:38.305","Text":"The protons move down the concentration gradient,"},{"Start":"01:38.305 ","End":"01:41.550","Text":"so we have a high concentration here in the intermembrane space,"},{"Start":"01:41.550 ","End":"01:45.815","Text":"and they pass through the protein complex ATP synthase,"},{"Start":"01:45.815 ","End":"01:51.949","Text":"thereby phosphorylating ADP molecules into high-energy ATP molecules."},{"Start":"01:51.949 ","End":"01:55.100","Text":"In eukaryotes, the electron transport chain"},{"Start":"01:55.100 ","End":"01:57.815","Text":"is present in the inner mitochondrial membrane."},{"Start":"01:57.815 ","End":"02:01.405","Text":"We have here the outer membrane and we have the inner membrane"},{"Start":"02:01.405 ","End":"02:06.735","Text":"here and this is where this whole thing happens actually, the process."},{"Start":"02:06.735 ","End":"02:11.068","Text":"The inside of the inner membrane is called the matrix,"},{"Start":"02:11.068 ","End":"02:15.970","Text":"and we have the matrix, and in-between the 2 membranes we have the intermembrane space."},{"Start":"02:15.970 ","End":"02:19.100","Text":"In prokaryotes, a similar process occurs within"},{"Start":"02:19.100 ","End":"02:23.405","Text":"the plasma membrane but in this section we won\u0027t be mentioning prokaryotes anymore."},{"Start":"02:23.405 ","End":"02:25.790","Text":"The electron transport chain is composed of"},{"Start":"02:25.790 ","End":"02:31.860","Text":"4 protein complexes labeled 1 through 4 and accessory electron carriers,"},{"Start":"02:32.170 ","End":"02:35.570","Text":"1, 2, 3, 4 and carriers."},{"Start":"02:35.570 ","End":"02:39.920","Text":"The electrons drop in free energy as they go down the chain and"},{"Start":"02:39.920 ","End":"02:44.585","Text":"finally they are passed to oxygen forming water. How does this happen?"},{"Start":"02:44.585 ","End":"02:48.640","Text":"The oxygen is the final electron acceptor in electron transport chain."},{"Start":"02:48.640 ","End":"02:53.750","Text":"The electrons are used to reduce an oxygen molecule to oxygen ions."},{"Start":"02:53.750 ","End":"02:57.820","Text":"The extra electrons on the oxygen ions attract hydrogen ions"},{"Start":"02:57.820 ","End":"03:02.765","Text":"also known as protons from the surrounding medium and water is formed."},{"Start":"03:02.765 ","End":"03:09.440","Text":"The electron comes from the NADH or FADH_2, the electron carriers."},{"Start":"03:09.440 ","End":"03:13.070","Text":"These are the least electronegative in the process and as they go"},{"Start":"03:13.070 ","End":"03:17.360","Text":"along between these different acceptors they go down in their free energy."},{"Start":"03:17.360 ","End":"03:20.210","Text":"Finally, the electrons are accepted by the oxygen,"},{"Start":"03:20.210 ","End":"03:22.040","Text":"the final electron acceptor,"},{"Start":"03:22.040 ","End":"03:23.885","Text":"and water is formed."},{"Start":"03:23.885 ","End":"03:27.830","Text":"This whole process breaks the large free energy drop from food to"},{"Start":"03:27.830 ","End":"03:32.360","Text":"water into smaller steps that release energy in controllable amounts."},{"Start":"03:32.360 ","End":"03:37.275","Text":"We have here this whole drop, an energy."},{"Start":"03:37.275 ","End":"03:39.300","Text":"In combustion, for example,"},{"Start":"03:39.300 ","End":"03:41.615","Text":"this drop is all done in 1 step."},{"Start":"03:41.615 ","End":"03:43.430","Text":"All the energy is released as heat,"},{"Start":"03:43.430 ","End":"03:45.640","Text":"it cannot be used for anything else."},{"Start":"03:45.640 ","End":"03:48.320","Text":"In a minute we\u0027ll see how the cell uses"},{"Start":"03:48.320 ","End":"03:52.040","Text":"these steps to harness the energy to what it needs."},{"Start":"03:52.040 ","End":"03:56.885","Text":"The electron transport chain generates no ATP directly."},{"Start":"03:56.885 ","End":"04:01.945","Text":"How is so much ATP generated in the oxidative phosphorylation?"},{"Start":"04:01.945 ","End":"04:06.775","Text":"This is due to the proton motive force caused by the electron transport chain."},{"Start":"04:06.775 ","End":"04:10.000","Text":"While the electrons are being carried from protein to protein,"},{"Start":"04:10.000 ","End":"04:15.070","Text":"certain electron carriers accept and release protons along with the electrons."},{"Start":"04:15.070 ","End":"04:18.080","Text":"You\u0027ll notice here that the protons are accepted on"},{"Start":"04:18.080 ","End":"04:21.400","Text":"1 side of the membrane and released on the other side."},{"Start":"04:21.400 ","End":"04:26.260","Text":"In this illustration, I just want to note that this is the opposite direction."},{"Start":"04:26.260 ","End":"04:32.200","Text":"Here we had the electrons going down this way and here we have them going up."},{"Start":"04:32.200 ","End":"04:35.300","Text":"This is the mitochondrial matrix,"},{"Start":"04:35.300 ","End":"04:37.605","Text":"inside the inner membrane,"},{"Start":"04:37.605 ","End":"04:39.510","Text":"this is the inner membrane itself,"},{"Start":"04:39.510 ","End":"04:42.010","Text":"and here we have the intermembrane space between"},{"Start":"04:42.010 ","End":"04:45.050","Text":"the inner membrane and the outer membrane."},{"Start":"04:45.050 ","End":"04:47.840","Text":"All this is inside the mitochondria again."},{"Start":"04:47.840 ","End":"04:53.440","Text":"You\u0027ll see that the protons are taken in on the inside,"},{"Start":"04:53.440 ","End":"04:59.115","Text":"on the matrix, this causes many protons to accumulate in the intermembrane space."},{"Start":"04:59.115 ","End":"05:04.750","Text":"Again, we have here the matrix and the intermembrane space between"},{"Start":"05:04.750 ","End":"05:11.050","Text":"the inner membrane and the outer membrane here and we have here a lot of protons here."},{"Start":"05:11.050 ","End":"05:13.360","Text":"The proton gradient is referred to as"},{"Start":"05:13.360 ","End":"05:17.380","Text":"a proton motive force highlighting its capacity to do work."},{"Start":"05:17.380 ","End":"05:21.370","Text":"The energy stored in a proton gradient across the membrane couples"},{"Start":"05:21.370 ","End":"05:26.230","Text":"relax actions of the electron transport chain to ATP synthesis."},{"Start":"05:26.230 ","End":"05:28.345","Text":"How is this done?"},{"Start":"05:28.345 ","End":"05:32.485","Text":"The energy coupling mechanism is called chemiosmosis."},{"Start":"05:32.485 ","End":"05:37.130","Text":"As we mentioned, protons accumulate in the intermembrane space."},{"Start":"05:37.130 ","End":"05:40.270","Text":"Here, the protons then flow down"},{"Start":"05:40.270 ","End":"05:45.370","Text":"the concentration gradient passing through the protein complex, ATP synthase."},{"Start":"05:45.370 ","End":"05:50.430","Text":"All these protons that accumulate here in the intermembrane space are now"},{"Start":"05:50.430 ","End":"05:56.200","Text":"flowing back along the gradient into the mitochondrial matrix."},{"Start":"05:56.200 ","End":"06:01.435","Text":"As they flow they pass through the ATP synthase which is actually"},{"Start":"06:01.435 ","End":"06:07.220","Text":"a miniscule water wheel just like you know from any old flour mill."},{"Start":"06:07.220 ","End":"06:09.815","Text":"The flow of the water turns the wheel,"},{"Start":"06:09.815 ","End":"06:11.360","Text":"that\u0027s very easy to understand,"},{"Start":"06:11.360 ","End":"06:16.190","Text":"it\u0027s all mechanic, but this is the same thing that happens inside ourselves."},{"Start":"06:16.190 ","End":"06:20.225","Text":"The protons flow from the intermembrane space"},{"Start":"06:20.225 ","End":"06:24.590","Text":"into the mitochondrial matrix and they actually turn the wheel."},{"Start":"06:24.590 ","End":"06:26.555","Text":"We have here a rotor,"},{"Start":"06:26.555 ","End":"06:28.520","Text":"the knob, and the rod,"},{"Start":"06:28.520 ","End":"06:33.214","Text":"the whole thing is a miniscule machine inside ourselves."},{"Start":"06:33.214 ","End":"06:43.505","Text":"This energy of turning the catalytic knob around is used to phosphorylate ADP into ATP."},{"Start":"06:43.505 ","End":"06:48.335","Text":"The ADP is a low energy and the ATP is a high-energy molecule."},{"Start":"06:48.335 ","End":"06:52.370","Text":"The energy from this turning and twisting is now invested in"},{"Start":"06:52.370 ","End":"06:57.380","Text":"the ATP molecules which can now be used by the cell for any other use."},{"Start":"06:57.380 ","End":"07:04.140","Text":"The use of energy in a chemical gradient to drive cellular work is called chemiosmosis."},{"Start":"07:04.360 ","End":"07:09.305","Text":"For an energetic overview of oxidative phosphorylation."},{"Start":"07:09.305 ","End":"07:11.920","Text":"The number of hydrogen ions that can be pumped"},{"Start":"07:11.920 ","End":"07:14.754","Text":"through the membrane varies between species."},{"Start":"07:14.754 ","End":"07:19.090","Text":"For example, fewer ATP molecules are generated when"},{"Start":"07:19.090 ","End":"07:24.145","Text":"FADH plus acts as electron transporter more than NAD plus."},{"Start":"07:24.145 ","End":"07:28.990","Text":"Therefore, the final number of ATP molecules that are"},{"Start":"07:28.990 ","End":"07:34.300","Text":"produced varies between species and they actually also varies between textbooks."},{"Start":"07:34.300 ","End":"07:37.870","Text":"I would advise each of you to check with his own textbook to make sure"},{"Start":"07:37.870 ","End":"07:41.935","Text":"that he has the right number of ATP molecules."},{"Start":"07:41.935 ","End":"07:46.060","Text":"About 34 percent of the energy in a glucose molecule is actually"},{"Start":"07:46.060 ","End":"07:51.950","Text":"transferred to ATP during cellular respiration while the rest is lost as heat."},{"Start":"07:51.950 ","End":"07:56.850","Text":"During glycolysis we have a net of 2 ATP molecules,"},{"Start":"07:56.850 ","End":"08:00.740","Text":"I\u0027m going to remind you that there are actually 4 but since we invest 2,"},{"Start":"08:00.740 ","End":"08:04.085","Text":"so we get a net of 2 of them."},{"Start":"08:04.085 ","End":"08:06.159","Text":"In a citric acid cycle,"},{"Start":"08:06.159 ","End":"08:09.825","Text":"another 2 ATP molecules are produced and in the third step,"},{"Start":"08:09.825 ","End":"08:16.145","Text":"oxidative phosphorylation, that\u0027s the big money time we get between 26 and 28 molecules."},{"Start":"08:16.145 ","End":"08:23.790","Text":"That means that altogether we have between 26 plus 4 which is 30 and"},{"Start":"08:23.790 ","End":"08:33.340","Text":"28 plus 4 which is 32 ATP molecules."},{"Start":"08:34.280 ","End":"08:37.880","Text":"In this section, we described how electrons move through"},{"Start":"08:37.880 ","End":"08:40.180","Text":"the electron transport chain and we also"},{"Start":"08:40.180 ","End":"08:43.670","Text":"described what happens to their energy levels during this process."},{"Start":"08:43.670 ","End":"08:47.510","Text":"We explained how a proton gradient is established and maintained by"},{"Start":"08:47.510 ","End":"08:51.730","Text":"the electron transport chain and later used to produce ATP."},{"Start":"08:51.730 ","End":"08:54.400","Text":"See you in the next section."}],"ID":25848},{"Watched":false,"Name":"Metabolism without Oxygen","Duration":"6m 50s","ChapterTopicVideoID":24933,"CourseChapterTopicPlaylistID":136378,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.330","Text":"Hi. We\u0027re studying cellular respiration."},{"Start":"00:04.330 ","End":"00:08.095","Text":"In this section, I\u0027ll be discussing metabolism without oxygen."},{"Start":"00:08.095 ","End":"00:09.730","Text":"By the end of this section,"},{"Start":"00:09.730 ","End":"00:12.340","Text":"you\u0027ll be able to discuss the fundamental difference"},{"Start":"00:12.340 ","End":"00:15.610","Text":"between aerobic cellular respiration and fermentation."},{"Start":"00:15.610 ","End":"00:20.110","Text":"You\u0027ll also be able to describe the 2 main types of fermentation."},{"Start":"00:20.110 ","End":"00:23.110","Text":"Most cellular respiration depends on"},{"Start":"00:23.110 ","End":"00:28.630","Text":"a strong electronegativity of oxygen to pull electrons down the transport chain."},{"Start":"00:28.630 ","End":"00:31.375","Text":"But without presence of oxygen,"},{"Start":"00:31.375 ","End":"00:36.205","Text":"the electron transport chain will cease to operate. Let\u0027s have a look at that."},{"Start":"00:36.205 ","End":"00:38.335","Text":"In all cellular respiration,"},{"Start":"00:38.335 ","End":"00:42.730","Text":"glucose first enters the cell and then undergoes glycolysis."},{"Start":"00:42.730 ","End":"00:48.065","Text":"In glycolysis, glucose is turned into 2 pyruvate molecules."},{"Start":"00:48.065 ","End":"00:50.395","Text":"The product of glycolysis is"},{"Start":"00:50.395 ","End":"00:56.700","Text":"2 ATP charged molecules and 2 NADH charged or reduced molecules."},{"Start":"00:56.700 ","End":"01:02.840","Text":"ATP is always used in the cell and therefore it\u0027s recycled to ADP plus a phosphate group."},{"Start":"01:02.840 ","End":"01:05.870","Text":"But the NADH, which is an electron acceptor,"},{"Start":"01:05.870 ","End":"01:07.010","Text":"is used afterward,"},{"Start":"01:07.010 ","End":"01:11.465","Text":"the oxidative phosphorylation giving its electrons to oxygen,"},{"Start":"01:11.465 ","End":"01:14.870","Text":"and therefore it\u0027s recycled to NAD plus."},{"Start":"01:14.870 ","End":"01:19.460","Text":"But what happens when there\u0027s no oxygen present in anaerobic conditions?"},{"Start":"01:19.460 ","End":"01:22.880","Text":"How does NADH get recycled and oxidated"},{"Start":"01:22.880 ","End":"01:26.870","Text":"back to NAD plus to let glycolysis continue flowing?"},{"Start":"01:26.870 ","End":"01:29.570","Text":"Again, when oxygen is present,"},{"Start":"01:29.570 ","End":"01:35.240","Text":"the NADH is oxidated back to"},{"Start":"01:35.240 ","End":"01:41.510","Text":"be NAD plus available for another random glycolysis."},{"Start":"01:41.510 ","End":"01:44.900","Text":"But what happens in an anaerobic environment?"},{"Start":"01:44.900 ","End":"01:46.685","Text":"When there\u0027s no oxygen,"},{"Start":"01:46.685 ","End":"01:48.590","Text":"we have to use a different process,"},{"Start":"01:48.590 ","End":"01:51.130","Text":"a process of fermentation."},{"Start":"01:51.130 ","End":"01:56.735","Text":"Here, ATP production by glycolysis is coupled with anaerobic respiration,"},{"Start":"01:56.735 ","End":"01:58.685","Text":"also known as fermentation."},{"Start":"01:58.685 ","End":"02:02.030","Text":"In fermentation, organic molecules are used as"},{"Start":"02:02.030 ","End":"02:05.375","Text":"the final electron acceptors instead of oxygen."},{"Start":"02:05.375 ","End":"02:11.870","Text":"Some bacteria and archaea reduce carbon dioxide to methane to oxidase NADH."},{"Start":"02:11.870 ","End":"02:16.235","Text":"Others use sulfate to regenerate NAD plus from NADH."},{"Start":"02:16.235 ","End":"02:17.590","Text":"But in this section,"},{"Start":"02:17.590 ","End":"02:25.205","Text":"we\u0027ll be speaking about the 2 main types of fermentation creating ethanol or lactic acid."},{"Start":"02:25.205 ","End":"02:28.925","Text":"Let\u0027s have a look at lactic acid fermentation."},{"Start":"02:28.925 ","End":"02:31.955","Text":"This type of fermentation is used by bacteria,"},{"Start":"02:31.955 ","End":"02:36.070","Text":"fungi, and animal cells under anaerobic circumstances."},{"Start":"02:36.070 ","End":"02:42.120","Text":"We, humans, use these bacteria in the process of making cheese and yogurt out of milk."},{"Start":"02:42.120 ","End":"02:45.790","Text":"But some of our own cells also use this fermentation."},{"Start":"02:45.790 ","End":"02:49.370","Text":"For example, our red blood cells don\u0027t include mitochondria,"},{"Start":"02:49.370 ","End":"02:52.505","Text":"and therefore they cannot metabolize with oxygen."},{"Start":"02:52.505 ","End":"02:58.040","Text":"Skeletal muscles also use lactic acid fermentation when oxygen supply is insufficient,"},{"Start":"02:58.040 ","End":"03:00.095","Text":"like in long runs."},{"Start":"03:00.095 ","End":"03:02.350","Text":"In this fermentation,"},{"Start":"03:02.350 ","End":"03:06.215","Text":"pyruvate is reduced by NADH forming NAD plus."},{"Start":"03:06.215 ","End":"03:10.820","Text":"The lactate is the end product and we have no release of carbon dioxide."},{"Start":"03:10.820 ","End":"03:15.915","Text":"NADH is oxidated to NAD plus,"},{"Start":"03:15.915 ","End":"03:22.980","Text":"pyruvate is reduced to lactate or lactic acid."},{"Start":"03:22.980 ","End":"03:25.940","Text":"This is the end product that we like to eat in the yogurt."},{"Start":"03:25.940 ","End":"03:29.600","Text":"We have no release of carbon dioxide because the 3-carbon structure of"},{"Start":"03:29.600 ","End":"03:34.865","Text":"the pyruvate is now the 3-carbon structure and the lactate or lactic acid."},{"Start":"03:34.865 ","End":"03:42.110","Text":"Here we have the pyruvic acid or pyruvate plus NADH and on the other side,"},{"Start":"03:42.110 ","End":"03:45.310","Text":"we have the lactic acid and NAD plus."},{"Start":"03:45.310 ","End":"03:48.140","Text":"This reaction can proceed in either direction."},{"Start":"03:48.140 ","End":"03:55.295","Text":"But the reaction from left to right is inhibited by acidic conditions."},{"Start":"03:55.295 ","End":"03:58.205","Text":"When lactic acid is built up in our muscles,"},{"Start":"03:58.205 ","End":"04:00.920","Text":"it\u0027s eventually moved and brought to the liver,"},{"Start":"04:00.920 ","End":"04:05.075","Text":"there in which we convert it into pyruvic acid or pyruvate,"},{"Start":"04:05.075 ","End":"04:07.880","Text":"and further catabolized for energy."},{"Start":"04:07.880 ","End":"04:11.645","Text":"The second type of fermentation is alcohol fermentation."},{"Start":"04:11.645 ","End":"04:16.610","Text":"Here, the pyruvate is converted to ethanol in 2 steps."},{"Start":"04:16.610 ","End":"04:21.500","Text":"The first step is the release of carbon dioxide from pyruvate."},{"Start":"04:21.500 ","End":"04:25.045","Text":"If pyruvate has 3 carbon skeleton,"},{"Start":"04:25.045 ","End":"04:27.750","Text":"and when we take 1 of them out to form the carbon dioxide,"},{"Start":"04:27.750 ","End":"04:29.420","Text":"we\u0027re left with 2 carbons."},{"Start":"04:29.420 ","End":"04:32.030","Text":"This is called acetaldehyde."},{"Start":"04:32.030 ","End":"04:36.365","Text":"The second step is the production of NAD plus and ethanol."},{"Start":"04:36.365 ","End":"04:39.980","Text":"NADH is again oxidized to NAD plus."},{"Start":"04:39.980 ","End":"04:44.815","Text":"Now we\u0027ve got 2 ethanol molecules here from each glucose."},{"Start":"04:44.815 ","End":"04:51.220","Text":"The NAD plus is again recycled and used in glycolysis to produce ATP."},{"Start":"04:51.220 ","End":"04:56.120","Text":"We use alcohol fermentation by yeast and brewing beer,"},{"Start":"04:56.120 ","End":"04:58.355","Text":"winemaking, and baking."},{"Start":"04:58.355 ","End":"05:01.550","Text":"When we want our dough to arise, we put yeast in."},{"Start":"05:01.550 ","End":"05:04.645","Text":"The glucose is then consumed by the yeast."},{"Start":"05:04.645 ","End":"05:10.845","Text":"The carbon dioxide makes bubbles, and dough rises."},{"Start":"05:10.845 ","End":"05:18.959","Text":"In brewing, we enjoy also the bubbles from the carbon dioxide and also the alcohol."},{"Start":"05:20.560 ","End":"05:24.890","Text":"In winemaking, sometimes we enjoy the ethanol itself,"},{"Start":"05:24.890 ","End":"05:26.480","Text":"and sometimes in bubbly wine,"},{"Start":"05:26.480 ","End":"05:29.135","Text":"we enjoy carbon dioxide as well."},{"Start":"05:29.135 ","End":"05:33.550","Text":"Let\u0027s compare fermentation with aerobic respiration."},{"Start":"05:33.550 ","End":"05:37.205","Text":"Both of them oxidize glucose by glycolysis,"},{"Start":"05:37.205 ","End":"05:39.830","Text":"ending with 2 ATP molecules."},{"Start":"05:39.830 ","End":"05:41.840","Text":"In both processes,"},{"Start":"05:41.840 ","End":"05:45.065","Text":"NAD plus is the electron acceptor."},{"Start":"05:45.065 ","End":"05:51.050","Text":"But there are different ways of oxidizing the NADH to NAD plus."},{"Start":"05:51.050 ","End":"05:55.835","Text":"In fermentation, an organic molecule is the final electron acceptor,"},{"Start":"05:55.835 ","End":"05:59.585","Text":"whether we get ethanol or lactate."},{"Start":"05:59.585 ","End":"06:03.110","Text":"While in cellular respiration using oxygen,"},{"Start":"06:03.110 ","End":"06:05.465","Text":"the electron transport chain is the acceptor."},{"Start":"06:05.465 ","End":"06:08.270","Text":"Finally, in the end, reaching the oxygen."},{"Start":"06:08.270 ","End":"06:14.935","Text":"Cellular respiration with oxygen produces 32 ATP molecules per glucose molecule,"},{"Start":"06:14.935 ","End":"06:19.504","Text":"but fermentation produces only 2 ATP molecules."},{"Start":"06:19.504 ","End":"06:23.210","Text":"Pyruvate is the junction and the metabolic road that"},{"Start":"06:23.210 ","End":"06:26.420","Text":"leads to 2 alternative catabolic routes."},{"Start":"06:26.420 ","End":"06:28.310","Text":"When oxygen is present,"},{"Start":"06:28.310 ","End":"06:30.890","Text":"we go to oxidative phosphorylation."},{"Start":"06:30.890 ","End":"06:32.780","Text":"We know oxygen is present,"},{"Start":"06:32.780 ","End":"06:36.305","Text":"or in other organisms that only use anaerobic respiration,"},{"Start":"06:36.305 ","End":"06:38.480","Text":"we go to fermentation."},{"Start":"06:38.480 ","End":"06:41.690","Text":"In this section, we\u0027ve discussed the fundamental difference"},{"Start":"06:41.690 ","End":"06:44.975","Text":"between aerobic cellular respiration and fermentation."},{"Start":"06:44.975 ","End":"06:48.035","Text":"We\u0027ve described the 2 main types of fermentation."},{"Start":"06:48.035 ","End":"06:51.690","Text":"See you soon in the next section. Bye."}],"ID":25846},{"Watched":false,"Name":"Connections of Carbohydrate, Protein, and Lipid Metabolic Pathways","Duration":"6m 16s","ChapterTopicVideoID":24930,"CourseChapterTopicPlaylistID":136378,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.470 ","End":"00:03.705","Text":"Hi. We\u0027re studying respiration."},{"Start":"00:03.705 ","End":"00:07.200","Text":"In this section, we\u0027ll be speaking about the connections of carbohydrate,"},{"Start":"00:07.200 ","End":"00:10.185","Text":"protein, and lipid metabolic pathways."},{"Start":"00:10.185 ","End":"00:11.910","Text":"By the end of this section,"},{"Start":"00:11.910 ","End":"00:15.765","Text":"you\u0027ll be able to discuss the ways in which carbohydrate metabolic pathways,"},{"Start":"00:15.765 ","End":"00:18.225","Text":"glycolysis, and the citric acid cycle"},{"Start":"00:18.225 ","End":"00:22.305","Text":"interrelate with protein and lipid metabolic pathways."},{"Start":"00:22.305 ","End":"00:28.395","Text":"Also, you\u0027ll be able to explain why metabolic pathways are not considered closed systems."},{"Start":"00:28.395 ","End":"00:34.260","Text":"As you know, organisms also consume organic compounds other than glucose for food."},{"Start":"00:34.260 ","End":"00:36.450","Text":"These include other sugars,"},{"Start":"00:36.450 ","End":"00:40.309","Text":"and whether they\u0027re single or are chain like starches,"},{"Start":"00:40.309 ","End":"00:44.435","Text":"proteins and fats or lipids."},{"Start":"00:44.435 ","End":"00:49.025","Text":"Catabolic pathways for carbohydrates, proteins,"},{"Start":"00:49.025 ","End":"00:54.305","Text":"and lipids enter glycolysis and the citric acid cycle pathways."},{"Start":"00:54.305 ","End":"00:59.914","Text":"For example, carbohydrates entering glycolysis, proteins,"},{"Start":"00:59.914 ","End":"01:03.640","Text":"which are actually long chains of amino acids are taken apart to"},{"Start":"01:03.640 ","End":"01:09.379","Text":"a single acids and each amino acid enters the metabolic pathway where it belongs."},{"Start":"01:09.379 ","End":"01:16.460","Text":"Some amino acids may enter in glycolysis while some enter in the pyruvate oxidation,"},{"Start":"01:16.460 ","End":"01:21.260","Text":"while yet others enter straight into the citric acid cycle."},{"Start":"01:21.260 ","End":"01:24.580","Text":"Along with these, fatty acids,"},{"Start":"01:24.580 ","End":"01:28.390","Text":"lipids, enter the citric acid cycle straightaway."},{"Start":"01:28.390 ","End":"01:31.630","Text":"Substances enter from other pathways and"},{"Start":"01:31.630 ","End":"01:34.675","Text":"intermediates leave for other pathways or in other words,"},{"Start":"01:34.675 ","End":"01:40.194","Text":"many of the substances in 1 pathway serve as reactants in other pathways."},{"Start":"01:40.194 ","End":"01:42.820","Text":"The pathways are actually all interlocked,"},{"Start":"01:42.820 ","End":"01:45.445","Text":"therefore, they\u0027re not closed systems."},{"Start":"01:45.445 ","End":"01:49.915","Text":"Let\u0027s see now how other sugars are connected to glucose metabolism."},{"Start":"01:49.915 ","End":"01:53.995","Text":"Catabolism of fructose, galactose, or glucose,"},{"Start":"01:53.995 ","End":"01:55.630","Text":"produces the same number of"},{"Start":"01:55.630 ","End":"02:00.880","Text":"ATP molecules but these are all monosaccharides or single sugars."},{"Start":"02:00.880 ","End":"02:06.285","Text":"Let\u0027s have a look at a longer chain sugar like glycogen."},{"Start":"02:06.285 ","End":"02:09.580","Text":"This is an energy storage molecule in animals."},{"Start":"02:09.580 ","End":"02:13.749","Text":"We can see it\u0027s made out of many chain glucose molecules."},{"Start":"02:13.749 ","End":"02:16.870","Text":"The liver stores glucose as glycogen."},{"Start":"02:16.870 ","End":"02:23.080","Text":"That means that surplus glucose is stored as glycogen in both liver and muscle cells."},{"Start":"02:23.080 ","End":"02:28.405","Text":"When we eat a lot of sugar and the extra sugar is not needed at the moment in the body,"},{"Start":"02:28.405 ","End":"02:30.580","Text":"it\u0027s stored as glycogen."},{"Start":"02:30.580 ","End":"02:35.005","Text":"Those long chains like storing food for the winter."},{"Start":"02:35.005 ","End":"02:38.110","Text":"Later on when we need sugar that we don\u0027t have in our blood,"},{"Start":"02:38.110 ","End":"02:42.995","Text":"the glycogen is taken apart in glycogenolysis."},{"Start":"02:42.995 ","End":"02:47.600","Text":"Now, we have free glucose to serve for energy in the muscles."},{"Start":"02:47.600 ","End":"02:54.065","Text":"The glycogen storage allows ATP to be produced for a longer time period during exercise."},{"Start":"02:54.065 ","End":"02:56.060","Text":"Now we have the glucose,"},{"Start":"02:56.060 ","End":"02:58.505","Text":"and since we have the glucose as a single units,"},{"Start":"02:58.505 ","End":"03:01.460","Text":"we\u0027re back to their regular pathway."},{"Start":"03:01.460 ","End":"03:04.370","Text":"Here we can see again the long chains,"},{"Start":"03:04.370 ","End":"03:08.030","Text":"many glucose molecules and when we take them apart,"},{"Start":"03:08.030 ","End":"03:12.965","Text":"they can enter the pathway in glycolysis and go on."},{"Start":"03:12.965 ","End":"03:18.605","Text":"All carbohydrates are actually sugars and they enter the pathway as we know it."},{"Start":"03:18.605 ","End":"03:22.880","Text":"Let\u0027s see now the connections of proteins to glucose metabolism."},{"Start":"03:22.880 ","End":"03:27.245","Text":"Proteins are hydrolyzed by a variety of enzymes in cells."},{"Start":"03:27.245 ","End":"03:31.655","Text":"Again, the proteins are actually long chains of amino acids."},{"Start":"03:31.655 ","End":"03:36.305","Text":"Most of the time the amino acids are recycled into synthesis of new proteins."},{"Start":"03:36.305 ","End":"03:41.060","Text":"So when we eat proteins many times they\u0027re just taken apart to the amino acids,"},{"Start":"03:41.060 ","End":"03:45.125","Text":"and then we use them again to rebuild the proteins that we need in our cell."},{"Start":"03:45.125 ","End":"03:48.230","Text":"But some amino acids might be shunted into"},{"Start":"03:48.230 ","End":"03:51.845","Text":"the pathways of glucose metabolism. Where does this happen?"},{"Start":"03:51.845 ","End":"03:56.075","Text":"As I mentioned earlier, it can happen also in glycolysis,"},{"Start":"03:56.075 ","End":"03:57.980","Text":"depending on the amino acids,"},{"Start":"03:57.980 ","End":"04:00.515","Text":"some of them may go into acetyl-CoA,"},{"Start":"04:00.515 ","End":"04:04.475","Text":"or some may enter the citric acid cycle right away."},{"Start":"04:04.475 ","End":"04:07.309","Text":"Prior to entering these pathways,"},{"Start":"04:07.309 ","End":"04:10.760","Text":"each amino acid must have its amino group removed."},{"Start":"04:10.760 ","End":"04:13.010","Text":"This is the amino group here."},{"Start":"04:13.010 ","End":"04:16.160","Text":"The amino group, this nitrogenous waste,"},{"Start":"04:16.160 ","End":"04:18.865","Text":"eventually leaves the body in the urine."},{"Start":"04:18.865 ","End":"04:21.660","Text":"What about lipids, fats?"},{"Start":"04:21.660 ","End":"04:26.480","Text":"Cholesterol and triglycerides are connected to the glucose pathway as well."},{"Start":"04:26.480 ","End":"04:31.730","Text":"Just a reminder, cholesterol contributes to cell membrane flexibility and"},{"Start":"04:31.730 ","End":"04:37.760","Text":"also serves as a precursor of steroid hormones such as estrogen or testosterone."},{"Start":"04:37.760 ","End":"04:42.380","Text":"Triglycerides are a form of long-term energy storage in animals."},{"Start":"04:42.380 ","End":"04:44.330","Text":"We\u0027ll now see why."},{"Start":"04:44.330 ","End":"04:49.565","Text":"The fatty acids are broken down by Beta oxidation and yield acetyl-CoA,"},{"Start":"04:49.565 ","End":"04:53.000","Text":"NADH, and FADH_2,"},{"Start":"04:53.000 ","End":"04:55.909","Text":"both are electron carriers."},{"Start":"04:55.909 ","End":"05:03.140","Text":"Now as you remember, the acetyl-CoA is a molecule based on double carbon backbone."},{"Start":"05:03.140 ","End":"05:07.280","Text":"Each glucose molecule produces only 2 of them."},{"Start":"05:07.280 ","End":"05:12.000","Text":"How many of these can be produced from each fatty acid chain?"},{"Start":"05:13.010 ","End":"05:15.245","Text":"We have a lot of them,"},{"Start":"05:15.245 ","End":"05:17.795","Text":"really, a lot of them enter the pathway here."},{"Start":"05:17.795 ","End":"05:21.500","Text":"I\u0027m not going to count them here and of course,"},{"Start":"05:21.500 ","End":"05:24.490","Text":"these chains can be longer too."},{"Start":"05:24.490 ","End":"05:28.940","Text":"Glycerol enters here in glycolysis,"},{"Start":"05:28.940 ","End":"05:34.105","Text":"but the fatty acids themselves are broken into these sets of 2,"},{"Start":"05:34.105 ","End":"05:37.925","Text":"and eventually come into the pathway as acetyl-CoA."},{"Start":"05:37.925 ","End":"05:42.260","Text":"That\u0027s why it\u0027s not surprising that 1 gram of fat produces more"},{"Start":"05:42.260 ","End":"05:47.375","Text":"than twice as much ATP as an oxidized gram of carbohydrates."},{"Start":"05:47.375 ","End":"05:50.495","Text":"We now understand how different carbohydrates,"},{"Start":"05:50.495 ","End":"05:55.170","Text":"lipids, and proteins enter the metabolic pathways."},{"Start":"05:55.240 ","End":"05:57.980","Text":"In this section, we discussed the way in which"},{"Start":"05:57.980 ","End":"06:00.890","Text":"carbohydrate metabolic pathways, glycolysis,"},{"Start":"06:00.890 ","End":"06:06.140","Text":"and the citric acid cycle are interrelated with protein and lipid metabolic pathways."},{"Start":"06:06.140 ","End":"06:09.590","Text":"We also explain why metabolic pathways are not considered"},{"Start":"06:09.590 ","End":"06:14.360","Text":"closed systems rather intertwined systems all connected to each other."},{"Start":"06:14.360 ","End":"06:17.010","Text":"See you in the next section."}],"ID":25843},{"Watched":false,"Name":"Regulation of Cellular Respiration","Duration":"10m 51s","ChapterTopicVideoID":24936,"CourseChapterTopicPlaylistID":136378,"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":"Hi, now that we\u0027ve spoken all about cellular respiration,"},{"Start":"00:03.660 ","End":"00:07.334","Text":"let\u0027s speak a little bit about how this process is regulated."},{"Start":"00:07.334 ","End":"00:09.180","Text":"By the end of this section,"},{"Start":"00:09.180 ","End":"00:12.300","Text":"you\u0027ll be able to describe how feedback inhibition effects"},{"Start":"00:12.300 ","End":"00:15.480","Text":"the production of an intermediate or product in a pathway,"},{"Start":"00:15.480 ","End":"00:21.135","Text":"and then identify the main mechanisms that regulate the rate of cellular respiration."},{"Start":"00:21.135 ","End":"00:26.580","Text":"Regulatory mechanisms include reactions that are catalyzed by 1 enzyme."},{"Start":"00:26.580 ","End":"00:29.630","Text":"Here we have an enzyme that can either take"},{"Start":"00:29.630 ","End":"00:32.855","Text":"this single molecule and take it apart into 2 products,"},{"Start":"00:32.855 ","End":"00:34.820","Text":"or do the exact opposite by taking"},{"Start":"00:34.820 ","End":"00:38.705","Text":"the 2 products and turning them to be 1 whole molecule."},{"Start":"00:38.705 ","End":"00:43.549","Text":"Reactions like this can go to equilibrium, stalling the reaction."},{"Start":"00:43.549 ","End":"00:47.765","Text":"For example, if we start out with 4 of these molecules,"},{"Start":"00:47.765 ","End":"00:51.740","Text":"so eventually they would be taken apart by the enzyme,"},{"Start":"00:51.740 ","End":"00:54.395","Text":"and we would get all these products,"},{"Start":"00:54.395 ","End":"00:55.849","Text":"8 pieces of products."},{"Start":"00:55.849 ","End":"00:57.710","Text":"But as these accumulate,"},{"Start":"00:57.710 ","End":"01:00.170","Text":"the opposite effect is going to happen and they\u0027re going to"},{"Start":"01:00.170 ","End":"01:03.244","Text":"be again put together single molecules,"},{"Start":"01:03.244 ","End":"01:06.770","Text":"which will again go through the enzyme and taken apart."},{"Start":"01:06.770 ","End":"01:11.420","Text":"Eventually will reach the equilibrium and the reaction will be stalled."},{"Start":"01:11.420 ","End":"01:14.906","Text":"When will this process that\u0027s stalled continue?"},{"Start":"01:14.906 ","End":"01:18.725","Text":"Only if 1 of the ends is being used by another process."},{"Start":"01:18.725 ","End":"01:22.010","Text":"For example, if the products are used and now"},{"Start":"01:22.010 ","End":"01:24.200","Text":"the whole molecule is are going to again be"},{"Start":"01:24.200 ","End":"01:26.750","Text":"taken apart and are going to be used and again,"},{"Start":"01:26.750 ","End":"01:28.130","Text":"the passing will continue going."},{"Start":"01:28.130 ","End":"01:30.860","Text":"The second type of reaction,"},{"Start":"01:30.860 ","End":"01:33.965","Text":"is reactions that are catalyzed by 2 different enzymes,"},{"Start":"01:33.965 ","End":"01:36.260","Text":"each specific for a given direction."},{"Start":"01:36.260 ","End":"01:38.780","Text":"This example, we start with the whole substrate,"},{"Start":"01:38.780 ","End":"01:42.050","Text":"which is taken apart by the first enzyme in to the product,"},{"Start":"01:42.050 ","End":"01:46.520","Text":"which are 2 pieces and the second enzyme which takes these 2 pieces as"},{"Start":"01:46.520 ","End":"01:52.585","Text":"the substrate and puts them together as a product of 1 single molecule."},{"Start":"01:52.585 ","End":"01:57.290","Text":"In these reactions, the control over the reaction rate increases."},{"Start":"01:57.290 ","End":"02:00.844","Text":"This is why. If we inhibit 1 of these enzymes,"},{"Start":"02:00.844 ","End":"02:02.615","Text":"we can control the rate."},{"Start":"02:02.615 ","End":"02:07.220","Text":"Now all the molecules that are taken apart will be put together again,"},{"Start":"02:07.220 ","End":"02:10.250","Text":"and we\u0027re going to have an accumulation of the whole product."},{"Start":"02:10.250 ","End":"02:11.855","Text":"We don\u0027t have to wait for an equilibrium,"},{"Start":"02:11.855 ","End":"02:14.780","Text":"we can really push all the molecules to 1 side."},{"Start":"02:14.780 ","End":"02:19.580","Text":"On the other hand, if we take this inhibition off and inhibit the other enzyme,"},{"Start":"02:19.580 ","End":"02:23.780","Text":"we can now move all of these molecules to the second state being taken apart."},{"Start":"02:23.780 ","End":"02:26.555","Text":"How does this inhibition work?"},{"Start":"02:26.555 ","End":"02:30.050","Text":"Well, reactions of the pathway are controlled by"},{"Start":"02:30.050 ","End":"02:33.785","Text":"attachment of a molecule to an allosteric site on the protein."},{"Start":"02:33.785 ","End":"02:38.545","Text":"Now, allosteric site is a site here or here,"},{"Start":"02:38.545 ","End":"02:43.085","Text":"which is not the active site where the substrate will connect to."},{"Start":"02:43.085 ","End":"02:47.660","Text":"The allosteric site changes the conformation of the enzyme."},{"Start":"02:47.660 ","End":"02:50.765","Text":"The most commonly used are ATP,"},{"Start":"02:50.765 ","End":"02:55.580","Text":"ADP, AMP, NAD plus, and NADH."},{"Start":"02:55.580 ","End":"02:57.710","Text":"These may increase or decrease"},{"Start":"02:57.710 ","End":"03:01.295","Text":"the enzyme activity depending on the prevailing conditions."},{"Start":"03:01.295 ","End":"03:04.370","Text":"1 example here, we have an activator."},{"Start":"03:04.370 ","End":"03:07.925","Text":"The activator connects to the allosteric site of the protein,"},{"Start":"03:07.925 ","End":"03:09.905","Text":"opening the active site,"},{"Start":"03:09.905 ","End":"03:15.460","Text":"allowing the substrate to connect and allowing the enzyme to produce the products."},{"Start":"03:15.460 ","End":"03:17.480","Text":"In the second example,"},{"Start":"03:17.480 ","End":"03:24.109","Text":"the enzyme itself is active only when phosphorylated using ATP or ADP."},{"Start":"03:24.109 ","End":"03:27.470","Text":"Once phosphorylated, the active site is open again,"},{"Start":"03:27.470 ","End":"03:31.835","Text":"allowing the substrate to connect to the enzyme and the enzyme is active."},{"Start":"03:31.835 ","End":"03:36.335","Text":"Metabolism is commonly controlled by feedback inhibition."},{"Start":"03:36.335 ","End":"03:40.985","Text":"Here we have an example of feedback inhibition where we have a molecular pathway here."},{"Start":"03:40.985 ","End":"03:42.785","Text":"We have 3 enzymes."},{"Start":"03:42.785 ","End":"03:48.215","Text":"The first enzyme takes the substrate and it turns it into the intermediate substrate A."},{"Start":"03:48.215 ","End":"03:53.930","Text":"The second enzyme changes the substrate now into a second intermediate substrate B."},{"Start":"03:53.930 ","End":"03:57.185","Text":"While, a third enzyme changes it into the end-product."},{"Start":"03:57.185 ","End":"04:01.475","Text":"In this example, the end-product itself when accumulating in the cell"},{"Start":"04:01.475 ","End":"04:06.650","Text":"connects to an allosteric site on the first enzyme, changing its conformation."},{"Start":"04:06.650 ","End":"04:09.200","Text":"Now the substrate cannot connect."},{"Start":"04:09.200 ","End":"04:13.639","Text":"Once the process will stop and the end product will get used up."},{"Start":"04:13.639 ","End":"04:16.580","Text":"It won\u0027t attach itself anymore to the allosteric site and"},{"Start":"04:16.580 ","End":"04:20.470","Text":"the enzyme will again allow the process to continue."},{"Start":"04:20.470 ","End":"04:22.530","Text":"In cellular respiration,"},{"Start":"04:22.530 ","End":"04:24.440","Text":"the end product is ATP."},{"Start":"04:24.440 ","End":"04:29.240","Text":"If ATP concentrations begin to drop, respiration speeds up."},{"Start":"04:29.240 ","End":"04:32.135","Text":"On the contrary, when there\u0027s plenty of ATP,"},{"Start":"04:32.135 ","End":"04:34.490","Text":"the respiration slows down again."},{"Start":"04:34.490 ","End":"04:38.450","Text":"Controlling catabolism is based mainly on regulating the activity of"},{"Start":"04:38.450 ","End":"04:42.875","Text":"specific enzymes at strategic points in a catabolic pathway."},{"Start":"04:42.875 ","End":"04:46.835","Text":"Various mechanisms are used to control cellular respiration,"},{"Start":"04:46.835 ","End":"04:49.624","Text":"including the intake of glucose."},{"Start":"04:49.624 ","End":"04:54.170","Text":"The cell\u0027s access to glucose can be regulated by GLUT proteins,"},{"Start":"04:54.170 ","End":"04:56.600","Text":"which are in glucose transporters."},{"Start":"04:56.600 ","End":"04:58.625","Text":"Here we have our cell."},{"Start":"04:58.625 ","End":"05:02.255","Text":"The glucose is outside of the cell and cannot come in."},{"Start":"05:02.255 ","End":"05:05.030","Text":"The GLUT4 transporter is connected to"},{"Start":"05:05.030 ","End":"05:08.980","Text":"this vesicle which is now unfused with the membrane."},{"Start":"05:08.980 ","End":"05:11.360","Text":"In the presence of insulin,"},{"Start":"05:11.360 ","End":"05:15.815","Text":"these red balls, GLUT4 vesicles fuse with the plasma membrane."},{"Start":"05:15.815 ","End":"05:20.255","Text":"The insulin causes the vesicle to fuse with the membrane."},{"Start":"05:20.255 ","End":"05:22.190","Text":"Now that it\u0027s fused with the membrane,"},{"Start":"05:22.190 ","End":"05:25.293","Text":"the GLUT transporter allows the glucose to enter the cell."},{"Start":"05:25.293 ","End":"05:28.265","Text":"The regulation doesn\u0027t stop there."},{"Start":"05:28.265 ","End":"05:30.710","Text":"Glycolysis, the citric acid cycle,"},{"Start":"05:30.710 ","End":"05:32.510","Text":"and the electron transport chain,"},{"Start":"05:32.510 ","End":"05:36.565","Text":"all 3 are non-reversible reactions are regulated too."},{"Start":"05:36.565 ","End":"05:39.230","Text":"Whether a particular enzyme activity is released"},{"Start":"05:39.230 ","End":"05:42.410","Text":"depends upon the energy needed by the cell."},{"Start":"05:42.410 ","End":"05:45.695","Text":"Let\u0027s zoom into the glycolysis now."},{"Start":"05:45.695 ","End":"05:50.945","Text":"The glycolysis is the process where glucose is converted into pyruvate."},{"Start":"05:50.945 ","End":"05:53.629","Text":"1 molecule of glucose enters the process"},{"Start":"05:53.629 ","End":"05:57.170","Text":"and you get 2 pyruvate molecules at the end of it."},{"Start":"05:57.170 ","End":"06:04.100","Text":"In this process, the free energy released is used to form 2 ATP and 2 NADH molecules."},{"Start":"06:04.100 ","End":"06:08.615","Text":"These 2 ATP molecules are actually 4 ATP molecules that are formed,"},{"Start":"06:08.615 ","End":"06:11.600","Text":"but initially we invest 2 in the process,"},{"Start":"06:11.600 ","End":"06:14.420","Text":"so we get a net of 2 ATP molecules."},{"Start":"06:14.420 ","End":"06:18.200","Text":"This is a sequence of 10 enzyme-catalyzed reactions."},{"Start":"06:18.200 ","End":"06:21.860","Text":"Let\u0027s start by looking at the energy investment phase."},{"Start":"06:21.860 ","End":"06:25.985","Text":"Here we can see the different steps of the energy investment phase."},{"Start":"06:25.985 ","End":"06:29.375","Text":"We can see the 2 ATP molecules invested."},{"Start":"06:29.375 ","End":"06:33.685","Text":"In blue, we have the enzymes involved in the process."},{"Start":"06:33.685 ","End":"06:38.875","Text":"Here we have the substrate and the intermediate substrates, the next steps."},{"Start":"06:38.875 ","End":"06:41.230","Text":"Let\u0027s zoom in here."},{"Start":"06:41.230 ","End":"06:47.230","Text":"The first step, and we see here that the glucose is phosphorylated by"},{"Start":"06:47.230 ","End":"06:53.980","Text":"the hexokinase to be glucose-6-phosphate using 1 ATP molecule."},{"Start":"06:53.980 ","End":"06:56.739","Text":"As we said, the hexokinase catalyzes"},{"Start":"06:56.739 ","End":"07:00.940","Text":"the phosphorylation of glucose to glucose-6 phosphate."},{"Start":"07:00.940 ","End":"07:03.340","Text":"When hexokinase is inhibited,"},{"Start":"07:03.340 ","End":"07:08.275","Text":"glucose accumulates in the cell and eventually diffuses out of the cell."},{"Start":"07:08.275 ","End":"07:10.840","Text":"This is the first enzyme in the pathway."},{"Start":"07:10.840 ","End":"07:14.184","Text":"We can see here how am I regulating first enzyme."},{"Start":"07:14.184 ","End":"07:18.405","Text":"We can actually change the whole process of the pathway."},{"Start":"07:18.405 ","End":"07:22.024","Text":"Glucose-6 phosphate, this 1 here,"},{"Start":"07:22.024 ","End":"07:24.050","Text":"accumulates when a later enzyme,"},{"Start":"07:24.050 ","End":"07:26.810","Text":"phosphofructokinase, is inhibited."},{"Start":"07:26.810 ","End":"07:32.720","Text":"Now let\u0027s see the regulation of this enzyme, the phosphofructokinase."},{"Start":"07:32.720 ","End":"07:38.420","Text":"Phosphofructokinase is the main enzyme control in glycolysis."},{"Start":"07:38.420 ","End":"07:45.995","Text":"It catalyzes the phosphorylation of fructose 6-phosphate to fructose 1,6-bisphosphate."},{"Start":"07:45.995 ","End":"07:48.535","Text":"Here we\u0027ve got that intermediate,"},{"Start":"07:48.535 ","End":"07:52.370","Text":"fructose-6 phosphate and a phosphofructokinase."},{"Start":"07:52.370 ","End":"07:58.250","Text":"This enzyme uses ATP to phosphorylate it to fructose 1,6-bisphosphate."},{"Start":"07:58.250 ","End":"08:02.710","Text":"We see here the 2 phosphate groups now."},{"Start":"08:02.710 ","End":"08:06.320","Text":"Phosphofructokinase activity depends on"},{"Start":"08:06.320 ","End":"08:10.685","Text":"ATP concentrations in the cell. Let\u0027s have a look here."},{"Start":"08:10.685 ","End":"08:15.320","Text":"In the x-axis, we have fructose-6 phosphate concentration,"},{"Start":"08:15.320 ","End":"08:17.840","Text":"which is our substrate for the enzyme."},{"Start":"08:17.840 ","End":"08:19.970","Text":"Of course, a higher concentration of"},{"Start":"08:19.970 ","End":"08:23.540","Text":"the substrate will mean a higher activity of the enzyme."},{"Start":"08:23.540 ","End":"08:26.525","Text":"Now here, more substrate to work on."},{"Start":"08:26.525 ","End":"08:32.975","Text":"But notice now that the enzyme activity is dependent also on the ATP concentration."},{"Start":"08:32.975 ","End":"08:35.270","Text":"When there\u0027s a low ATP concentration,"},{"Start":"08:35.270 ","End":"08:37.460","Text":"meaning the cell needs ATP now,"},{"Start":"08:37.460 ","End":"08:41.345","Text":"the phosphofructokinase works a lot faster."},{"Start":"08:41.345 ","End":"08:45.230","Text":"You can see here the activity is a lot faster for the same concentration"},{"Start":"08:45.230 ","End":"08:49.355","Text":"of substrate when there\u0027s a high ATP concentration in the cell."},{"Start":"08:49.355 ","End":"08:54.725","Text":"Meaning that affectively high levels of ATP inhibit the enzymes activity."},{"Start":"08:54.725 ","End":"08:59.420","Text":"The last step in glycolysis is catalyzed by pyruvate kinase."},{"Start":"08:59.420 ","End":"09:02.000","Text":"Here we have to get the pyruvate and the end and"},{"Start":"09:02.000 ","End":"09:05.580","Text":"the enzyme that gives it to us is the pyruvate kinase."},{"Start":"09:05.680 ","End":"09:09.615","Text":"Here is pyruvate kinase and the end-product, the pyruvate."},{"Start":"09:09.615 ","End":"09:12.140","Text":"If no more energy is needed in the cell,"},{"Start":"09:12.140 ","End":"09:19.200","Text":"so this enzyme is inhibited and pyruvate is not formed and the whole process stops."},{"Start":"09:19.300 ","End":"09:23.135","Text":"The next step is the citric acid cycle."},{"Start":"09:23.135 ","End":"09:27.020","Text":"Here we have a close-up look and we can see here the products in"},{"Start":"09:27.020 ","End":"09:32.255","Text":"the intermediate substrates and the enzymes that are actually doing the work here."},{"Start":"09:32.255 ","End":"09:35.990","Text":"The regulation of the citric acid cycle is controlled through"},{"Start":"09:35.990 ","End":"09:38.630","Text":"the isocitrate dehydrogenase and"},{"Start":"09:38.630 ","End":"09:44.585","Text":"the Alpha-ketoglutarate dehydrogenase enzymes that make the first 2 molecules of NADH."},{"Start":"09:44.585 ","End":"09:51.640","Text":"Here we have the isocitrate dehydrogenase and the Alpha ketoglutarate dehydrogenase."},{"Start":"09:51.640 ","End":"09:56.690","Text":"When adequate ATP and NADH levels are available for the cell,"},{"Start":"09:56.690 ","End":"10:01.685","Text":"the rates of the reactions of these 2 enzymes decrease."},{"Start":"10:01.685 ","End":"10:06.034","Text":"When more ATP is needed, the rate increases."},{"Start":"10:06.034 ","End":"10:09.500","Text":"Let\u0027s have a look now at the electron transport chain."},{"Start":"10:09.500 ","End":"10:13.530","Text":"Here, also known as oxidative phosphorylation."},{"Start":"10:13.740 ","End":"10:16.205","Text":"Here\u0027s a zoom in."},{"Start":"10:16.205 ","End":"10:19.130","Text":"Here feedback inhibition does not"},{"Start":"10:19.130 ","End":"10:22.280","Text":"affect specific enzymes in the electron transport chain,"},{"Start":"10:22.280 ","End":"10:24.215","Text":"like we\u0027ve seen in the other steps."},{"Start":"10:24.215 ","End":"10:29.030","Text":"Rather, the relative concentrations of ADP and ATP in the cell trigger"},{"Start":"10:29.030 ","End":"10:34.620","Text":"the entire electron transport chain to slow down or speed up."},{"Start":"10:35.940 ","End":"10:39.980","Text":"In this section, we described how feedback inhibition affects"},{"Start":"10:39.980 ","End":"10:43.460","Text":"the production of an intermediate or a product in the pathway,"},{"Start":"10:43.460 ","End":"10:48.700","Text":"and we identified the main mechanisms that regulate the rate of cellular respiration."},{"Start":"10:48.700 ","End":"10:51.670","Text":"See you in the next section."}],"ID":25849},{"Watched":false,"Name":"Exercise 1","Duration":"2m 39s","ChapterTopicVideoID":27021,"CourseChapterTopicPlaylistID":136378,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:01.800","Text":"In this question, we\u0027re asked,"},{"Start":"00:01.800 ","End":"00:05.490","Text":"what the energy currency is used by cells."},{"Start":"00:05.490 ","End":"00:08.325","Text":"The answers are ATP,"},{"Start":"00:08.325 ","End":"00:13.350","Text":"ADP, AMP, or adenosine."},{"Start":"00:13.350 ","End":"00:16.094","Text":"Let\u0027s have a look at these molecules."},{"Start":"00:16.094 ","End":"00:19.530","Text":"Adenine is a double ringed organic molecule"},{"Start":"00:19.530 ","End":"00:22.724","Text":"from the family of organic molecules known as purines."},{"Start":"00:22.724 ","End":"00:27.345","Text":"When combined with a pentose or 5-carboned based sugar,"},{"Start":"00:27.345 ","End":"00:31.319","Text":"like a ribose, it\u0027s known as adenosine."},{"Start":"00:31.319 ","End":"00:36.240","Text":"Adenosine usually comes with 1 or more phosphate groups."},{"Start":"00:36.240 ","End":"00:44.020","Text":"With 1 phosphate group is known as adenosine monophosphate or AMP."},{"Start":"00:44.020 ","End":"00:48.020","Text":"When adenosine comes with 1 phosphate group connected to it,"},{"Start":"00:48.020 ","End":"00:53.430","Text":"it\u0027s known as adenosine monophosphate,"},{"Start":"00:53.430 ","End":"00:56.655","Text":"or in short, AMP."},{"Start":"00:56.655 ","End":"00:59.130","Text":"When connected to 2 phosphate groups,"},{"Start":"00:59.130 ","End":"01:04.571","Text":"it\u0027s known as adenosine diphosphate,"},{"Start":"01:04.571 ","End":"01:10.080","Text":"meaning adenosine with 2 phosphates or ADP."},{"Start":"01:10.080 ","End":"01:12.600","Text":"When connected to 3 phosphate groups,"},{"Start":"01:12.600 ","End":"01:17.550","Text":"it\u0027s known as adenosine triphosphate,"},{"Start":"01:17.550 ","End":"01:20.505","Text":"also known as ATP."},{"Start":"01:20.505 ","End":"01:25.055","Text":"Adenosine is 1 of the 4 nucleic acids making the DNA structure,"},{"Start":"01:25.055 ","End":"01:29.070","Text":"but it\u0027s also used by the cell for energy currency."},{"Start":"01:33.200 ","End":"01:36.890","Text":"The chemical bonds between the adenosine and"},{"Start":"01:36.890 ","End":"01:40.040","Text":"the phosphate groups have a lot of energy stored in them."},{"Start":"01:40.040 ","End":"01:42.955","Text":"Adenosine triphosphate, ATP,"},{"Start":"01:42.955 ","End":"01:50.074","Text":"has a large amount of energy stored in these 3 chemical connections."},{"Start":"01:50.074 ","End":"01:53.990","Text":"The cell uses ATP as an energy currency."},{"Start":"01:53.990 ","End":"01:57.800","Text":"Many cellular chemical reactions that consume energy use"},{"Start":"01:57.800 ","End":"02:02.530","Text":"highly energized ATP molecules as an energy source."},{"Start":"02:02.530 ","End":"02:05.870","Text":"During the consumption of the energy from the ATP,"},{"Start":"02:05.870 ","End":"02:10.940","Text":"1 of the phosphate groups is disconnected from the ATP, leaving only 2."},{"Start":"02:10.940 ","End":"02:15.180","Text":"Now it\u0027s adenosine diphosphate or ADP,"},{"Start":"02:15.490 ","End":"02:18.670","Text":"what can be seen as an uncharged battery."},{"Start":"02:18.670 ","End":"02:21.740","Text":"Later, the low-energy ADP molecules are"},{"Start":"02:21.740 ","End":"02:25.370","Text":"newly charged with energy by connecting a new phosphate group,"},{"Start":"02:25.370 ","End":"02:28.880","Text":"and resulting in a new charged ATP molecule."},{"Start":"02:28.880 ","End":"02:30.975","Text":"If we look in our answers here,"},{"Start":"02:30.975 ","End":"02:32.460","Text":"ATP seems to be right."},{"Start":"02:32.460 ","End":"02:34.875","Text":"We can cross out ADP and AMP,"},{"Start":"02:34.875 ","End":"02:39.550","Text":"and adenosine, and mark ATP as our correct answer."}],"ID":28147},{"Watched":false,"Name":"Exercise 2","Duration":"2m 42s","ChapterTopicVideoID":27022,"CourseChapterTopicPlaylistID":136378,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:03.975","Text":"During the second half of glycolysis, what occurs?"},{"Start":"00:03.975 ","End":"00:06.990","Text":"A, ATP is used up."},{"Start":"00:06.990 ","End":"00:10.005","Text":"B, sucrose is split in 2."},{"Start":"00:10.005 ","End":"00:16.890","Text":"C, ATP is produced and D, glucose becomes fructose."},{"Start":"00:16.890 ","End":"00:20.595","Text":"Now, let\u0027s have a look at glycolysis."},{"Start":"00:20.595 ","End":"00:23.145","Text":"Glycolysis is made of 2 words, glyco,"},{"Start":"00:23.145 ","End":"00:27.315","Text":"meaning sugar and lysis, meaning taking apart."},{"Start":"00:27.315 ","End":"00:30.390","Text":"During glycolysis, sugar is taken apart."},{"Start":"00:30.390 ","End":"00:36.975","Text":"Specifically, glycolysis splits glucose into 2 molecules of a 3-carbon sugar, pyruvate."},{"Start":"00:36.975 ","End":"00:39.840","Text":"We started out with 1 6-carbon sugar,"},{"Start":"00:39.840 ","End":"00:44.945","Text":"the glucose, and end up with 2 3-carbon sugars, pyruvate."},{"Start":"00:44.945 ","End":"00:46.820","Text":"As we\u0027re informed in the question,"},{"Start":"00:46.820 ","End":"00:49.250","Text":"glycolysis has 2 phases and we\u0027re asked"},{"Start":"00:49.250 ","End":"00:52.085","Text":"what happens during the second phase of glycolysis?"},{"Start":"00:52.085 ","End":"00:54.935","Text":"In the first phase, the energy investment phase,"},{"Start":"00:54.935 ","End":"00:59.030","Text":"2 ATP molecules are used to phosphorylate the glucose."},{"Start":"00:59.030 ","End":"01:02.135","Text":"The second phase is the energy payoff phase."},{"Start":"01:02.135 ","End":"01:08.300","Text":"Here there is phosphorylation without ATP investment and it produces 2 NADH molecules and"},{"Start":"01:08.300 ","End":"01:14.705","Text":"4 ATP molecules per each glucose molecule entering the glycolysis process."},{"Start":"01:14.705 ","End":"01:20.450","Text":"Here we have an output of 4 ATP molecules formed and"},{"Start":"01:20.450 ","End":"01:28.590","Text":"another 2 NADH molecules getting us a net of 4 minus 2 molecules,"},{"Start":"01:28.590 ","End":"01:32.090","Text":"giving us a net of 2 ATP molecules."},{"Start":"01:32.090 ","End":"01:35.960","Text":"If we want to check now and see what happens during the second half of glycolysis."},{"Start":"01:35.960 ","End":"01:39.770","Text":"You could say that ATP and NADH molecules are formed."},{"Start":"01:39.770 ","End":"01:43.460","Text":"In the question we\u0027re also asked about sucrose and glucose."},{"Start":"01:43.460 ","End":"01:47.909","Text":"We are also asked about another 2 sugars, sucrose and fructose."},{"Start":"01:47.909 ","End":"01:50.075","Text":"Let\u0027s have a look at these sugars."},{"Start":"01:50.075 ","End":"01:54.290","Text":"Sucrose is actually a double sugar made out"},{"Start":"01:54.290 ","End":"01:57.950","Text":"of glucose and fructose connected by a glycosidic bond."},{"Start":"01:57.950 ","End":"02:03.890","Text":"With this molecule, when a sucrose is taken apart in hydrolysis using a water molecule,"},{"Start":"02:03.890 ","End":"02:06.280","Text":"we get glucose and fructose."},{"Start":"02:06.280 ","End":"02:09.110","Text":"We can already cross out sucrose is split in 2"},{"Start":"02:09.110 ","End":"02:12.155","Text":"because we know that glucose is split into 2 and that\u0027s the whole process,"},{"Start":"02:12.155 ","End":"02:13.400","Text":"not just a second phase."},{"Start":"02:13.400 ","End":"02:17.120","Text":"We also know that glucose does not become fructose,"},{"Start":"02:17.120 ","End":"02:20.629","Text":"rather glucose produces 2 pyruvate molecules."},{"Start":"02:20.629 ","End":"02:23.045","Text":"Let\u0027s have a look at the other 2 answers now."},{"Start":"02:23.045 ","End":"02:25.805","Text":"During the second half of glycolysis, what occurs?"},{"Start":"02:25.805 ","End":"02:28.535","Text":"Answer A states that ATP is used up."},{"Start":"02:28.535 ","End":"02:34.595","Text":"But we know that an investment of ATP occurs in the first phase. We can erase that."},{"Start":"02:34.595 ","End":"02:38.765","Text":"C is the correct answer that ATP and C,"},{"Start":"02:38.765 ","End":"02:42.150","Text":"ATP is produced is our correct answer."}],"ID":28148},{"Watched":false,"Name":"Exercise 3","Duration":"3m 28s","ChapterTopicVideoID":27023,"CourseChapterTopicPlaylistID":136378,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.380","Text":"In this question, we\u0027re asked if a reducing chemical reaction,"},{"Start":"00:04.380 ","End":"00:07.835","Text":"A, reduces the compound to a simpler form,"},{"Start":"00:07.835 ","End":"00:11.940","Text":"B, add an electron to the substrate, C,"},{"Start":"00:11.940 ","End":"00:14.355","Text":"removes the hydrogen atom from the substrate,"},{"Start":"00:14.355 ","End":"00:17.280","Text":"or D, is a catabolic reaction."},{"Start":"00:17.280 ","End":"00:19.544","Text":"Since we\u0027re asked about reduction,"},{"Start":"00:19.544 ","End":"00:21.945","Text":"let\u0027s have a short review of oxidation and reduction,"},{"Start":"00:21.945 ","End":"00:24.810","Text":"also known as redox."},{"Start":"00:24.810 ","End":"00:26.808","Text":"In oxidation reactions,"},{"Start":"00:26.808 ","End":"00:29.990","Text":"electrons are stripped from out of the atoms of a substrate,"},{"Start":"00:29.990 ","End":"00:32.960","Text":"leading to an oxidized molecule."},{"Start":"00:32.960 ","End":"00:35.750","Text":"On the contrary, the reduction reaction is"},{"Start":"00:35.750 ","End":"00:38.975","Text":"where an electron is added to another substance."},{"Start":"00:38.975 ","End":"00:42.590","Text":"Oxidation and reduction are coupled so"},{"Start":"00:42.590 ","End":"00:46.100","Text":"that the reducing agent loses its electrons and gets"},{"Start":"00:46.100 ","End":"00:54.510","Text":"oxidized and the oxidizing agent pulls the electrons from the substrate in the oxidation."},{"Start":"00:54.510 ","End":"00:58.790","Text":"It might be a little bit confusing but let\u0027s remember it like this."},{"Start":"00:58.790 ","End":"01:01.460","Text":"In reduction, electrons are gained."},{"Start":"01:01.460 ","End":"01:03.635","Text":"These electrons must come from somewhere."},{"Start":"01:03.635 ","End":"01:08.480","Text":"Therefore, we need a reducing agent to donate its own electrons to the reduction."},{"Start":"01:08.480 ","End":"01:10.438","Text":"On the other hand, in oxidation,"},{"Start":"01:10.438 ","End":"01:12.650","Text":"the substrate must lose its molecules."},{"Start":"01:12.650 ","End":"01:16.520","Text":"Therefore, we have an oxidizing agent that pulls the electrons strong"},{"Start":"01:16.520 ","End":"01:21.200","Text":"enough so they leave the substrate of the oxidation."},{"Start":"01:21.200 ","End":"01:22.805","Text":"Now that we\u0027ve got this straight,"},{"Start":"01:22.805 ","End":"01:24.635","Text":"we know that in oxidation,"},{"Start":"01:24.635 ","End":"01:27.530","Text":"you lose your electrons and in reduction,"},{"Start":"01:27.530 ","End":"01:29.255","Text":"you gain your electrons."},{"Start":"01:29.255 ","End":"01:33.785","Text":"Reduction and oxidation have nothing to do with reducing compounds to simpler form."},{"Start":"01:33.785 ","End":"01:38.870","Text":"Answer B, a reducing chemical reaction adds an electron to the substrate,"},{"Start":"01:38.870 ","End":"01:42.125","Text":"that looks true, but before we choose our correct answer,"},{"Start":"01:42.125 ","End":"01:44.840","Text":"we should always have a look at the other answers first."},{"Start":"01:44.840 ","End":"01:46.040","Text":"Answer C tells us that"},{"Start":"01:46.040 ","End":"01:50.315","Text":"a reducing chemical reaction removes a hydrogen atom from the substrate."},{"Start":"01:50.315 ","End":"01:51.900","Text":"Well, true."},{"Start":"01:51.900 ","End":"01:53.225","Text":"In many redox reactions,"},{"Start":"01:53.225 ","End":"01:55.385","Text":"in order to balance the electric charge,"},{"Start":"01:55.385 ","End":"01:59.270","Text":"hydrogen atoms are gained or lost by the substrate."},{"Start":"01:59.270 ","End":"02:02.600","Text":"But since hydrogen ions have a positive charge,"},{"Start":"02:02.600 ","End":"02:04.310","Text":"we find that many times,"},{"Start":"02:04.310 ","End":"02:06.290","Text":"in reduction reactions,"},{"Start":"02:06.290 ","End":"02:09.800","Text":"hydrogen ions are gained."},{"Start":"02:09.800 ","End":"02:13.370","Text":"Together with the electrons that are gained,"},{"Start":"02:13.370 ","End":"02:17.875","Text":"we get perfect balance and we\u0027ll just get this."},{"Start":"02:17.875 ","End":"02:23.780","Text":"We\u0027ll just get a molecule that looks like this with no electric charge whatsoever."},{"Start":"02:23.780 ","End":"02:27.316","Text":"C, remove the hydrogen atom from the substrate, no."},{"Start":"02:27.316 ","End":"02:30.155","Text":"That might happen in oxidation but not in reduction."},{"Start":"02:30.155 ","End":"02:35.750","Text":"Let\u0027s have a look at answer D. A reducing chemical reaction is a catabolic reaction."},{"Start":"02:35.750 ","End":"02:40.880","Text":"Metabolic processes are divided into 2, anabolism and catabolism."},{"Start":"02:40.880 ","End":"02:44.120","Text":"While anabolism usually involves building polymers out"},{"Start":"02:44.120 ","End":"02:47.660","Text":"of single monomers and requires an input of energy,"},{"Start":"02:47.660 ","End":"02:51.800","Text":"catabolism releases energy while breaking down larger molecules."},{"Start":"02:51.800 ","End":"02:55.835","Text":"These metabolic processes work together in all living organisms."},{"Start":"02:55.835 ","End":"02:59.195","Text":"Now let\u0027s have a look. In oxidation reactions,"},{"Start":"02:59.195 ","End":"03:02.119","Text":"the electrons leave the molecule."},{"Start":"03:02.119 ","End":"03:04.040","Text":"This releases energy."},{"Start":"03:04.040 ","End":"03:05.980","Text":"This might be an example."},{"Start":"03:05.980 ","End":"03:09.155","Text":"Oxidation maybe an example of catabolism."},{"Start":"03:09.155 ","End":"03:12.515","Text":"On the contrary, reduction requires energy input."},{"Start":"03:12.515 ","End":"03:18.215","Text":"This is an endergonic reaction and an example of anabolism."},{"Start":"03:18.215 ","End":"03:24.485","Text":"Therefore, answer D can also be crossed out and we now may mark our correct answer B."},{"Start":"03:24.485 ","End":"03:29.099","Text":"A reducing chemical reaction adds an electron to the substrate."}],"ID":28149},{"Watched":false,"Name":"Exercise 4","Duration":"1m 55s","ChapterTopicVideoID":27024,"CourseChapterTopicPlaylistID":136378,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:02.640","Text":"Here we\u0027re asked, what is removed from"},{"Start":"00:02.640 ","End":"00:05.958","Text":"pyruvate during its conversion into an acetyl group?"},{"Start":"00:05.958 ","End":"00:07.665","Text":"Wait, hold your horses."},{"Start":"00:07.665 ","End":"00:11.115","Text":"When did we learn about pyruvate and acetyl groups?"},{"Start":"00:11.115 ","End":"00:16.965","Text":"To answer that, let\u0027s have a short overview about the stages of cellular respiration."},{"Start":"00:16.965 ","End":"00:19.740","Text":"The breakdown of glucose in order to harvest"},{"Start":"00:19.740 ","End":"00:22.875","Text":"the chemical energy is performed in 3 main stages."},{"Start":"00:22.875 ","End":"00:26.700","Text":"In glycolysis, glucose is broken into 2 molecules of pyruvate."},{"Start":"00:26.700 ","End":"00:30.360","Text":"The pyruvate is then converted into an acetyl-CoA group,"},{"Start":"00:30.360 ","End":"00:35.445","Text":"which enters the citric acid cycle where the complete breakdown of glucose is performed."},{"Start":"00:35.445 ","End":"00:38.990","Text":"Electrons carried by NADH and FADH2 from"},{"Start":"00:38.990 ","End":"00:42.995","Text":"these processes are carried over to the oxidative phosphorylation,"},{"Start":"00:42.995 ","End":"00:46.970","Text":"where they\u0027re used to synthesize many ATP molecules."},{"Start":"00:46.970 ","End":"00:49.670","Text":"Let\u0027s have a look at the pyruvate."},{"Start":"00:49.670 ","End":"00:55.040","Text":"We\u0027re asked about this stage where pyruvate is converted to acetyl-CoA."},{"Start":"00:55.040 ","End":"00:59.015","Text":"Here we see the pyruvate molecule and we can see at this part of it,"},{"Start":"00:59.015 ","End":"01:02.665","Text":"the carbon with 2 oxygen molecules."},{"Start":"01:02.665 ","End":"01:07.580","Text":"Here we can see how the carbon atom with 2 other oxygen atoms are"},{"Start":"01:07.580 ","End":"01:12.385","Text":"removed from the pyruvate, extracting carbon dioxide."},{"Start":"01:12.385 ","End":"01:17.420","Text":"Here we can see how, in the process of converting pyruvate into acetyl-CoA,"},{"Start":"01:17.420 ","End":"01:21.290","Text":"1 carbon atom and 2 oxygen molecules are"},{"Start":"01:21.290 ","End":"01:26.780","Text":"removed from the molecule and they leave in the form of carbon dioxide."},{"Start":"01:26.780 ","End":"01:32.405","Text":"If we\u0027re asked what is removed from pyruvate during its conversion into an acetyl group,"},{"Start":"01:32.405 ","End":"01:35.495","Text":"well, we might think that oxygen is right."},{"Start":"01:35.495 ","End":"01:37.670","Text":"But since we have carbon dioxide,"},{"Start":"01:37.670 ","End":"01:40.460","Text":"we can cross out oxygen, ATP."},{"Start":"01:40.460 ","End":"01:43.010","Text":"Well, it\u0027s true that oxygen is stripped off in"},{"Start":"01:43.010 ","End":"01:47.180","Text":"a pyruvate but an even more correct answer would be carbon dioxide."},{"Start":"01:47.180 ","End":"01:50.435","Text":"Therefore, we can cross out oxygen, ATP,"},{"Start":"01:50.435 ","End":"01:52.115","Text":"and mark answer D,"},{"Start":"01:52.115 ","End":"01:55.620","Text":"carbon dioxide as the correct answer."}],"ID":28150},{"Watched":false,"Name":"Exercise 5","Duration":"4m 15s","ChapterTopicVideoID":27019,"CourseChapterTopicPlaylistID":136378,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.140 ","End":"00:03.539","Text":"Here we\u0027re asked what the role is of the electrons"},{"Start":"00:03.539 ","End":"00:07.270","Text":"added to NAD^+ in anaerobic respiration."},{"Start":"00:07.700 ","End":"00:11.370","Text":"NAD^+ this molecule, or also known its full name as"},{"Start":"00:11.370 ","End":"00:14.550","Text":"nicotinamide adenine dinucleotide is"},{"Start":"00:14.550 ","End":"00:18.645","Text":"a molecule that\u0027s very important in many metabolic processes of the cell."},{"Start":"00:18.645 ","End":"00:21.420","Text":"We can see by saying that it\u0027s a dinucleotide,"},{"Start":"00:21.420 ","End":"00:23.940","Text":"meaning it\u0027s a double nucleotide and has"},{"Start":"00:23.940 ","End":"00:27.815","Text":"2 nucleotides that are connected by their phosphate groups."},{"Start":"00:27.815 ","End":"00:34.970","Text":"On one side, we have the adenine already known to you in the DNA structure,"},{"Start":"00:34.970 ","End":"00:39.140","Text":"on the other side we have the nicotinamide, this one here."},{"Start":"00:39.140 ","End":"00:43.945","Text":"That\u0027s why this molecule is known as NAD^+."},{"Start":"00:43.945 ","End":"00:46.460","Text":"This molecule has another form too."},{"Start":"00:46.460 ","End":"00:51.245","Text":"Adding a hydrogen ion and 2 electrons gives us the oxidized form."},{"Start":"00:51.245 ","End":"00:54.320","Text":"As you can see, we have here the extra hydrogen atom,"},{"Start":"00:54.320 ","End":"00:58.830","Text":"which is missing here and the positive charge has gone too."},{"Start":"00:58.830 ","End":"01:01.655","Text":"This is the reduced form,"},{"Start":"01:01.655 ","End":"01:04.400","Text":"and this is the oxidized form."},{"Start":"01:04.400 ","End":"01:07.650","Text":"Since this molecule can carry 2 electrons,"},{"Start":"01:07.650 ","End":"01:09.515","Text":"it\u0027s used as an electron carrier,"},{"Start":"01:09.515 ","End":"01:12.740","Text":"a coenzyme in several metabolic processes of the cell."},{"Start":"01:12.740 ","End":"01:16.325","Text":"In aerobic respiration it\u0027s produced in several steps."},{"Start":"01:16.325 ","End":"01:18.515","Text":"The first one is glycolysis,"},{"Start":"01:18.515 ","End":"01:21.995","Text":"where glucose is processed to 2 molecules of pyruvate."},{"Start":"01:21.995 ","End":"01:26.545","Text":"You can see here that NAD^+ is oxidized to NADH."},{"Start":"01:26.545 ","End":"01:29.930","Text":"In the next step where pyruvate is changed to acetyl-CoA,"},{"Start":"01:29.930 ","End":"01:36.740","Text":"more molecules of NAD^+ are charged with electrons oxidizing the molecule to NADH."},{"Start":"01:36.740 ","End":"01:38.990","Text":"Finally, in the citric acid cycle,"},{"Start":"01:38.990 ","End":"01:43.340","Text":"several molecules of NAD^+ are oxidized to NADH."},{"Start":"01:43.340 ","End":"01:46.925","Text":"Where are all of these NADH molecules carrying the electrons to?"},{"Start":"01:46.925 ","End":"01:48.515","Text":"All the NADH molecules,"},{"Start":"01:48.515 ","End":"01:49.925","Text":"from the glycolysis,"},{"Start":"01:49.925 ","End":"01:52.280","Text":"from the pyruvate oxidation and from"},{"Start":"01:52.280 ","End":"01:56.720","Text":"the citric acid cycle eventually lead to the oxidative phosphorylation,"},{"Start":"01:56.720 ","End":"02:00.005","Text":"where the electrons are moved to the electron transport system,"},{"Start":"02:00.005 ","End":"02:03.295","Text":"causing chemiosmosis and forming ATP."},{"Start":"02:03.295 ","End":"02:07.760","Text":"As the electrons are moved from the NADH to the electron transport,"},{"Start":"02:07.760 ","End":"02:11.515","Text":"protons are pumped to the intermembrane space of the mitochondrion."},{"Start":"02:11.515 ","End":"02:17.750","Text":"The flow of all of these ions back through the membrane passes through the ATP synthase,"},{"Start":"02:17.750 ","End":"02:20.600","Text":"which works pretty much like a molecular water wheel,"},{"Start":"02:20.600 ","End":"02:24.560","Text":"producing highly energized ATP molecules."},{"Start":"02:24.560 ","End":"02:28.710","Text":"This process is also known as chemiosmosis."},{"Start":"02:28.900 ","End":"02:31.565","Text":"Let\u0027s have a look at our answers now."},{"Start":"02:31.565 ","End":"02:36.310","Text":"Answer a states that the electrons become part of a fermentation pathway."},{"Start":"02:36.310 ","End":"02:39.620","Text":"Well, true in the fermentation pathway,"},{"Start":"02:39.620 ","End":"02:45.385","Text":"NADH needs to be recycled back to NAD^+ in order to let glycolysis continue working."},{"Start":"02:45.385 ","End":"02:47.090","Text":"In the fermentation process,"},{"Start":"02:47.090 ","End":"02:51.830","Text":"these electrons are eventually used in fermentation of both lactate or ethanol."},{"Start":"02:51.830 ","End":"02:55.860","Text":"But in our question we were asked about aerobic respiration and"},{"Start":"02:55.860 ","End":"03:00.230","Text":"these two processes are anaerobic processes."},{"Start":"03:00.230 ","End":"03:03.920","Text":"Answer a would be wrong not because it doesn\u0027t happen,"},{"Start":"03:03.920 ","End":"03:06.095","Text":"but because we\u0027re asked about aerobic processes."},{"Start":"03:06.095 ","End":"03:09.665","Text":"Answer b states that they go to another pathway for ATP production,"},{"Start":"03:09.665 ","End":"03:11.765","Text":"which is pretty much what we saw here."},{"Start":"03:11.765 ","End":"03:15.110","Text":"Yes, there eventually taken to the electron transport chain and"},{"Start":"03:15.110 ","End":"03:19.040","Text":"the oxidative phosphorylation and used to produce ATP."},{"Start":"03:19.040 ","End":"03:22.295","Text":"But before we mark our correct answer as b,"},{"Start":"03:22.295 ","End":"03:24.050","Text":"let\u0027s have a look at answers c and d,"},{"Start":"03:24.050 ","End":"03:25.850","Text":"and just make sure that they\u0027re not even more correct."},{"Start":"03:25.850 ","End":"03:27.740","Text":"Let\u0027s have a look at answers c and d"},{"Start":"03:27.740 ","End":"03:30.250","Text":"and make sure that we\u0027re not missing anything even better."},{"Start":"03:30.250 ","End":"03:33.320","Text":"Answer c states that they energize the entry"},{"Start":"03:33.320 ","End":"03:36.170","Text":"of the acetyl group into the citric acid cycle,"},{"Start":"03:36.170 ","End":"03:38.810","Text":"which we already know is not true."},{"Start":"03:38.810 ","End":"03:42.460","Text":"Answer d states that they\u0027re converted to NADP."},{"Start":"03:42.460 ","End":"03:44.920","Text":"Well, it\u0027s a bit tricky."},{"Start":"03:45.220 ","End":"03:55.380","Text":"NAD^+ with another 2 electron and hydrogen ion give us NADH."},{"Start":"03:55.380 ","End":"04:00.095","Text":"NADP is a different electron carrier that we know from different processes."},{"Start":"04:00.095 ","End":"04:02.720","Text":"NADP is wrong also."},{"Start":"04:02.720 ","End":"04:05.585","Text":"Now we can mark answer b as a correct answer."},{"Start":"04:05.585 ","End":"04:08.090","Text":"The role of the electrons added to NAD^+ in"},{"Start":"04:08.090 ","End":"04:11.330","Text":"aerobic respiration is that they go to another pathway,"},{"Start":"04:11.330 ","End":"04:15.900","Text":"the electron transport pathway for ATP production."}],"ID":28151},{"Watched":false,"Name":"Exercise 6","Duration":"3m 17s","ChapterTopicVideoID":27020,"CourseChapterTopicPlaylistID":136378,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.110 ","End":"00:06.135","Text":"How many NADH molecules are produced on each turn of the citric acid cycle?"},{"Start":"00:06.135 ","End":"00:11.490","Text":"Let\u0027s have a look at the NADH molecule, nicotinamide adenine dinucleotide."},{"Start":"00:11.490 ","End":"00:14.100","Text":"Dinucleotide tells us that there are 2 nucleotides"},{"Start":"00:14.100 ","End":"00:16.725","Text":"here connected by their phosphate groups,"},{"Start":"00:16.725 ","End":"00:20.835","Text":"adenine tells us that 1 of the nucleotides is adenine"},{"Start":"00:20.835 ","End":"00:24.975","Text":"already familiar to us because it\u0027s part of the DNA structure."},{"Start":"00:24.975 ","End":"00:27.735","Text":"Our other nucleotide is the nicotinamide,"},{"Start":"00:27.735 ","End":"00:31.260","Text":"and here we can see that it has a positive electric charge."},{"Start":"00:31.260 ","End":"00:33.610","Text":"But this molecule,"},{"Start":"00:33.680 ","End":"00:37.140","Text":"NAD+, has another form,"},{"Start":"00:37.140 ","End":"00:39.105","Text":"while this is the reduced form,"},{"Start":"00:39.105 ","End":"00:41.765","Text":"adding 2 electrons in this molecule,"},{"Start":"00:41.765 ","End":"00:46.910","Text":"and the hydrogen atom gives us NADH."},{"Start":"00:46.910 ","End":"00:52.165","Text":"This means that this molecule can carry 2 electrons and its oxidized form,"},{"Start":"00:52.165 ","End":"00:56.900","Text":"and the NADH can carry these electrons to whatever process it might need."},{"Start":"00:56.900 ","End":"00:58.640","Text":"In cellular respiration,"},{"Start":"00:58.640 ","End":"01:02.060","Text":"NADH molecules are produced in glycolysis,"},{"Start":"01:02.060 ","End":"01:04.265","Text":"and the pyruvate oxidation,"},{"Start":"01:04.265 ","End":"01:06.400","Text":"and in the citric acid cycle."},{"Start":"01:06.400 ","End":"01:10.640","Text":"They are all moved eventually to the oxidative phosphorylation where"},{"Start":"01:10.640 ","End":"01:15.680","Text":"the electrons are used to pump protons in the electron transport system."},{"Start":"01:15.680 ","End":"01:21.340","Text":"Eventually, this flow of protons will produce highly energized molecules of ATP."},{"Start":"01:21.340 ","End":"01:24.550","Text":"We\u0027re asked here specifically about the citric acid cycle,"},{"Start":"01:24.550 ","End":"01:25.760","Text":"and we need to say"},{"Start":"01:25.760 ","End":"01:29.480","Text":"how many NADH molecules are actually produced on each turn of the cycle."},{"Start":"01:29.480 ","End":"01:31.550","Text":"Now, this might be a bit tricky because"},{"Start":"01:31.550 ","End":"01:34.045","Text":"ins some of your textbooks you\u0027ll see different numbers,"},{"Start":"01:34.045 ","End":"01:36.920","Text":"and that\u0027s because in the first step of cellular respiration,"},{"Start":"01:36.920 ","End":"01:40.460","Text":"glycolysis, 1 molecule of glucose is used to form"},{"Start":"01:40.460 ","End":"01:46.059","Text":"2 pyruvate molecules which enters the citric acid cycle as acetyl-CoA."},{"Start":"01:46.059 ","End":"01:51.825","Text":"In many of our textbooks we\u0027ll see that in glycolysis we have 2 molecules of NADH,"},{"Start":"01:51.825 ","End":"01:53.845","Text":"and here in the pyruvate oxidation,"},{"Start":"01:53.845 ","End":"01:55.835","Text":"and the citric acid cycle together,"},{"Start":"01:55.835 ","End":"01:58.370","Text":"we\u0027ll have 8 molecules of NADH,"},{"Start":"01:58.370 ","End":"02:01.915","Text":"and 2 molecules of FADH_2,"},{"Start":"02:01.915 ","End":"02:04.250","Text":"but this is not accurate because we\u0027re talking"},{"Start":"02:04.250 ","End":"02:07.085","Text":"here about the double cycle of the citric acid."},{"Start":"02:07.085 ","End":"02:12.110","Text":"Because we\u0027re talking here about 2 molecules of pyruvate entering the citric acid cycle,"},{"Start":"02:12.110 ","End":"02:17.540","Text":"meaning that basically would speak about only 1/2 a molecule of glucose,"},{"Start":"02:17.540 ","End":"02:20.825","Text":"which will be 2 times 1/2 a molecule of glucose,"},{"Start":"02:20.825 ","End":"02:23.180","Text":"gives us 1 pyruvate molecule,"},{"Start":"02:23.180 ","End":"02:26.210","Text":"and during the citric acid cycle once,"},{"Start":"02:26.210 ","End":"02:28.040","Text":"which changes just to 1 also,"},{"Start":"02:28.040 ","End":"02:31.635","Text":"which gives us actually 4 NADH molecules,"},{"Start":"02:31.635 ","End":"02:34.445","Text":"and only 1 FADH2."},{"Start":"02:34.445 ","End":"02:37.160","Text":"But that\u0027s not the end of it because 1 of"},{"Start":"02:37.160 ","End":"02:42.515","Text":"these 4 NADH molecules is not produced in the citric acid cycle itself,"},{"Start":"02:42.515 ","End":"02:45.455","Text":"rather in the pyruvate oxidation."},{"Start":"02:45.455 ","End":"02:48.495","Text":"We\u0027re left with the answer 3,"},{"Start":"02:48.495 ","End":"02:51.485","Text":"and if we have a look at the citric acid cycle,"},{"Start":"02:51.485 ","End":"02:56.205","Text":"we can see that indeed here we have here 2 NADH molecule is formed,"},{"Start":"02:56.205 ","End":"03:02.250","Text":"and another 1 in this part of the second altogether giving us 3 NADH."},{"Start":"03:03.560 ","End":"03:06.915","Text":"We can cross out answers A,"},{"Start":"03:06.915 ","End":"03:08.550","Text":"B, and D,"},{"Start":"03:08.550 ","End":"03:14.590","Text":"and circle the correct answer C. There are 3 NADH molecules that are produced,"},{"Start":"03:14.590 ","End":"03:18.330","Text":"and 1 single turn of the citric acid cycle."}],"ID":28152}],"Thumbnail":null,"ID":136378},{"Name":"Photosynthesis","TopicPlaylistFirstVideoID":0,"Duration":null,"Videos":[{"Watched":false,"Name":"Introduction to Photosynthesis","Duration":"8m 6s","ChapterTopicVideoID":24926,"CourseChapterTopicPlaylistID":136377,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.545","Text":"Hi. In this section we\u0027re going to introduce photosynthesis."},{"Start":"00:04.545 ","End":"00:06.210","Text":"By the end of this section,"},{"Start":"00:06.210 ","End":"00:11.175","Text":"you\u0027ll be able to explain the significance of photosynthesis to all living organisms,"},{"Start":"00:11.175 ","End":"00:15.210","Text":"identify the substrates and products of photosynthesis and"},{"Start":"00:15.210 ","End":"00:20.205","Text":"describe the main structures and molecular processes involved in photosynthesis."},{"Start":"00:20.205 ","End":"00:23.745","Text":"Photosynthesis is essential to all life."},{"Start":"00:23.745 ","End":"00:28.650","Text":"This is the only process that convert sunlight energy into chemical compounds."},{"Start":"00:28.650 ","End":"00:32.820","Text":"In photosynthesis, sunlight is used to energize electrons."},{"Start":"00:32.820 ","End":"00:36.205","Text":"This energy is then stored as sugar molecules."},{"Start":"00:36.205 ","End":"00:39.335","Text":"Even coal and petroleum products used today"},{"Start":"00:39.335 ","End":"00:41.420","Text":"release sunlight energy that was captured by"},{"Start":"00:41.420 ","End":"00:45.005","Text":"photosynthesis more than 300 million years ago."},{"Start":"00:45.005 ","End":"00:47.045","Text":"Photoautotrophs"},{"Start":"00:47.045 ","End":"00:56.230","Text":"meaning light,"},{"Start":"00:56.230 ","End":"01:02.525","Text":"self, feeders are organisms that feed themselves,"},{"Start":"01:02.525 ","End":"01:06.935","Text":"meaning they produce their own energy using light as an energy source."},{"Start":"01:06.935 ","End":"01:14.060","Text":"Photoautotrophs; light self feeders include plants, algae, and cyanobacteria."},{"Start":"01:14.060 ","End":"01:18.380","Text":"These are the only organisms that are capable of performing photosynthesis."},{"Start":"01:18.380 ","End":"01:20.495","Text":"How do we get our energy?"},{"Start":"01:20.495 ","End":"01:22.730","Text":"We are heterotrophs."},{"Start":"01:22.730 ","End":"01:25.640","Text":"These include all other organisms that"},{"Start":"01:25.640 ","End":"01:28.594","Text":"rely on the sugars produced by photosynthetic organisms."},{"Start":"01:28.594 ","End":"01:33.440","Text":"For example, this calorie on the energy produced by the grasses here."},{"Start":"01:33.440 ","End":"01:38.165","Text":"The lion relies on the energy he gets from the cow,"},{"Start":"01:38.165 ","End":"01:39.875","Text":"relying on the energy from the grass."},{"Start":"01:39.875 ","End":"01:43.015","Text":"The mushrooms also rely on the energy for this rotting wood."},{"Start":"01:43.015 ","End":"01:48.275","Text":"The wood got its energy from the plant and the tree that perform photosynthesis."},{"Start":"01:48.275 ","End":"01:53.840","Text":"Also people eating a cheeseburger rely on the energy from the plants, from the wheat,"},{"Start":"01:53.840 ","End":"01:56.985","Text":"cucumbers, onion, tomato,"},{"Start":"01:56.985 ","End":"01:59.645","Text":"lettuce, even the sesame, that\u0027s all."},{"Start":"01:59.645 ","End":"02:02.555","Text":"Those are all plants that get their energy from photosynthesis."},{"Start":"02:02.555 ","End":"02:05.375","Text":"We\u0027ll even have here the meat, coming from the cow,"},{"Start":"02:05.375 ","End":"02:07.940","Text":"the cheese and the cheeseburger also comes from the cow"},{"Start":"02:07.940 ","End":"02:10.615","Text":"which gets its energy from photosynthesis."},{"Start":"02:10.615 ","End":"02:15.170","Text":"All of the living world relies on the energy from the sun."},{"Start":"02:15.170 ","End":"02:20.935","Text":"This energy is captured by the photoautotrophs and converted to sugar."},{"Start":"02:20.935 ","End":"02:23.085","Text":"Well, not all of life,"},{"Start":"02:23.085 ","End":"02:24.330","Text":"but almost all of life,"},{"Start":"02:24.330 ","End":"02:26.735","Text":"we do have some rare groups of bacteria;"},{"Start":"02:26.735 ","End":"02:30.215","Text":"chemoautotrophs, which are chemical self-feeders,"},{"Start":"02:30.215 ","End":"02:35.180","Text":"and they synthesize sugars by extracting energy from inorganic chemical compounds."},{"Start":"02:35.180 ","End":"02:39.185","Text":"We find these in deep sea where there are volcanic vents,"},{"Start":"02:39.185 ","End":"02:42.740","Text":"where all kinds of chemicals is seeping through the crust of the Earth."},{"Start":"02:42.740 ","End":"02:47.930","Text":"Other chemoautotrophs are germs which oxidate ammonia to nitrite."},{"Start":"02:47.930 ","End":"02:50.365","Text":"We use these in your sewage plants."},{"Start":"02:50.365 ","End":"02:53.900","Text":"Let\u0027s have a brief look at the process itself."},{"Start":"02:53.900 ","End":"02:59.255","Text":"Photosynthesis requires specific wavelengths of visible sunlight for energy,"},{"Start":"02:59.255 ","End":"03:02.750","Text":"carbon dioxide for fixation and water."},{"Start":"03:02.750 ","End":"03:04.310","Text":"We\u0027ve got the sunlight,"},{"Start":"03:04.310 ","End":"03:05.930","Text":"carbon dioxide, and the water,"},{"Start":"03:05.930 ","End":"03:08.120","Text":"all coming into the process."},{"Start":"03:08.120 ","End":"03:12.245","Text":"Photosynthesis produces simple carbohydrate molecules."},{"Start":"03:12.245 ","End":"03:15.360","Text":"These are also called the sugars."},{"Start":"03:15.360 ","End":"03:19.060","Text":"We have here the sugar is being produced."},{"Start":"03:19.060 ","End":"03:25.264","Text":"The sugar molecules contain the energized carbon that all living things need to survive."},{"Start":"03:25.264 ","End":"03:30.625","Text":"Photosynthesis also has a very important by-product; the oxygen."},{"Start":"03:30.625 ","End":"03:34.215","Text":"The law of conservation of mass tells us that"},{"Start":"03:34.215 ","End":"03:37.760","Text":"any atoms entering the process will also have to exit it."},{"Start":"03:37.760 ","End":"03:40.820","Text":"No atoms will be lost or formed."},{"Start":"03:40.820 ","End":"03:42.635","Text":"Let\u0027s have a look at this process here."},{"Start":"03:42.635 ","End":"03:46.715","Text":"We\u0027ve got 6 carbon dioxide molecules, 12 water molecules."},{"Start":"03:46.715 ","End":"03:48.980","Text":"Using the light energy in the photosynthesis,"},{"Start":"03:48.980 ","End":"03:51.485","Text":"we produce 1 molecule of glucose,"},{"Start":"03:51.485 ","End":"03:53.645","Text":"6 molecules of oxygen,"},{"Start":"03:53.645 ","End":"03:55.309","Text":"and 6 water molecules."},{"Start":"03:55.309 ","End":"03:56.780","Text":"Let\u0027s count up here."},{"Start":"03:56.780 ","End":"03:59.885","Text":"We\u0027ve got here 6 carbons,"},{"Start":"03:59.885 ","End":"04:03.485","Text":"and up here the 6 carbons when they come out."},{"Start":"04:03.485 ","End":"04:06.125","Text":"Let\u0027s see now the oxygen here."},{"Start":"04:06.125 ","End":"04:07.940","Text":"We\u0027ve got here 6 times 2,"},{"Start":"04:07.940 ","End":"04:12.305","Text":"so that\u0027s 12 over here, another 12 here."},{"Start":"04:12.305 ","End":"04:13.880","Text":"Let\u0027s see now on the way out,"},{"Start":"04:13.880 ","End":"04:15.240","Text":"6 of them are here."},{"Start":"04:15.240 ","End":"04:19.535","Text":"6 times 2 is 12,"},{"Start":"04:19.535 ","End":"04:22.490","Text":"and we got another 6 here, altogether that\u0027s 24."},{"Start":"04:22.490 ","End":"04:24.425","Text":"The oxygen is accounted for."},{"Start":"04:24.425 ","End":"04:26.375","Text":"Let\u0027s look at the hydrogen now."},{"Start":"04:26.375 ","End":"04:29.270","Text":"That\u0027s 12 times 2,"},{"Start":"04:29.270 ","End":"04:31.055","Text":"24 of them,"},{"Start":"04:31.055 ","End":"04:33.995","Text":"and here we\u0027ve got 12,"},{"Start":"04:33.995 ","End":"04:35.930","Text":"another 6 times 2 is 12."},{"Start":"04:35.930 ","End":"04:38.225","Text":"We\u0027ve accounted for all the atoms."},{"Start":"04:38.225 ","End":"04:40.595","Text":"We know the equation is all right."},{"Start":"04:40.595 ","End":"04:42.560","Text":"Another way to look at it would be here,"},{"Start":"04:42.560 ","End":"04:44.270","Text":"we can look at the reactants and the products,"},{"Start":"04:44.270 ","End":"04:48.095","Text":"and here we can see that all the atoms are accounted for."},{"Start":"04:48.095 ","End":"04:54.200","Text":"Essentially, if we look at the overall chemical alteration during photosynthesis,"},{"Start":"04:54.200 ","End":"04:57.650","Text":"we find is the reverse process of cellular respiration,"},{"Start":"04:57.650 ","End":"05:00.515","Text":"where the reactants are glucose, water,"},{"Start":"05:00.515 ","End":"05:05.435","Text":"and oxygen, and the products are carbon dioxide and water."},{"Start":"05:05.435 ","End":"05:09.680","Text":"Let\u0027s have a look now at the basic photosynthetic structures."},{"Start":"05:09.680 ","End":"05:12.125","Text":"All autotrophic eukaryotes,"},{"Start":"05:12.125 ","End":"05:17.645","Text":"photosynthesis takes place inside a special organelle called the chloroplast."},{"Start":"05:17.645 ","End":"05:22.415","Text":"In plants, a process generally takes place in leaves."},{"Start":"05:22.415 ","End":"05:26.274","Text":"Leaves have an inner layer called the mesophyll."},{"Start":"05:26.274 ","End":"05:31.915","Text":"Each mesophyll cell contains between 30 and 40 chloroplasts."},{"Start":"05:31.915 ","End":"05:35.090","Text":"The gas exchange of carbon dioxide coming out"},{"Start":"05:35.090 ","End":"05:38.390","Text":"and oxygen coming in occurs through the stomata."},{"Start":"05:38.390 ","End":"05:41.750","Text":"These are openings on the outer layer of the leaf."},{"Start":"05:41.750 ","End":"05:44.825","Text":"Let\u0027s have a look at the chloroplast itself."},{"Start":"05:44.825 ","End":"05:48.245","Text":"The chloroplast has a double membrane layer here,"},{"Start":"05:48.245 ","End":"05:50.585","Text":"inner and outer membrane."},{"Start":"05:50.585 ","End":"05:54.140","Text":"Between them, we have the intermembrane space."},{"Start":"05:54.140 ","End":"06:00.200","Text":"The chloroplast has ribosomes of its own and even its own DNA."},{"Start":"06:00.200 ","End":"06:04.980","Text":"In the inside, it consists of stacked structures; the thylakoids."},{"Start":"06:04.980 ","End":"06:07.800","Text":"The thylakoid being a membrane structure and"},{"Start":"06:07.800 ","End":"06:12.065","Text":"closes an internal space called the thylakoid lumen."},{"Start":"06:12.065 ","End":"06:15.635","Text":"Each stack of thylakoids is called a granum."},{"Start":"06:15.635 ","End":"06:20.455","Text":"The liquid-filled space out of the granum is called the stroma."},{"Start":"06:20.455 ","End":"06:22.670","Text":"Let\u0027s have another look at this."},{"Start":"06:22.670 ","End":"06:24.650","Text":"You\u0027ve got the chloroplast here,"},{"Start":"06:24.650 ","End":"06:26.870","Text":"it\u0027s made of a double membrane layer."},{"Start":"06:26.870 ","End":"06:29.720","Text":"We have the outer membrane and the inner membrane."},{"Start":"06:29.720 ","End":"06:32.509","Text":"Between them, we have the intermembrane space."},{"Start":"06:32.509 ","End":"06:37.415","Text":"The stacked structures inside of the thylakoids each pile is 1 granum."},{"Start":"06:37.415 ","End":"06:39.440","Text":"The liquid enclosed inside"},{"Start":"06:39.440 ","End":"06:43.685","Text":"the inner membrane but outside of the thylakoids is the stroma,"},{"Start":"06:43.685 ","End":"06:47.135","Text":"and inside the thylakoids we have the lumen."},{"Start":"06:47.135 ","End":"06:49.455","Text":"Chlorophyll is the green pigment."},{"Start":"06:49.455 ","End":"06:52.635","Text":"It resides in the thylakoid membranes of themselves."},{"Start":"06:52.635 ","End":"06:55.769","Text":"The chlorophyll; the green pigment are the thylakoid"},{"Start":"06:55.769 ","End":"06:59.435","Text":"inside the chloroplast is what gives plants their green color."},{"Start":"06:59.435 ","End":"07:03.754","Text":"Photosynthesis is divided into 2 sequential stages."},{"Start":"07:03.754 ","End":"07:05.885","Text":"The first stage, the photo stage,"},{"Start":"07:05.885 ","End":"07:08.675","Text":"includes the light-dependent reactions."},{"Start":"07:08.675 ","End":"07:13.537","Text":"Here sunlight energy is absorbed and converted into stored chemical energy."},{"Start":"07:13.537 ","End":"07:15.170","Text":"We see the sunlight coming in."},{"Start":"07:15.170 ","End":"07:19.255","Text":"This all happens in the thylakoid and we see the chemical energy,"},{"Start":"07:19.255 ","End":"07:21.694","Text":"NADPH, reduced molecules,"},{"Start":"07:21.694 ","End":"07:25.655","Text":"and ATP, highly energetic molecules."},{"Start":"07:25.655 ","End":"07:28.535","Text":"The second stage, the synthesis stage,"},{"Start":"07:28.535 ","End":"07:31.189","Text":"includes all the light-independent reactions,"},{"Start":"07:31.189 ","End":"07:33.590","Text":"also called Calvin cycle."},{"Start":"07:33.590 ","End":"07:36.620","Text":"Here the chemical energy that was produced in"},{"Start":"07:36.620 ","End":"07:42.410","Text":"the light-dependent reactions drives the assembly of sugar molecules from carbon dioxide."},{"Start":"07:42.410 ","End":"07:44.680","Text":"You have the carbon dioxide entering the cycle,"},{"Start":"07:44.680 ","End":"07:47.910","Text":"and we have the sugar molecules coming out."},{"Start":"07:47.980 ","End":"07:50.915","Text":"We\u0027ve introduced photosynthesis."},{"Start":"07:50.915 ","End":"07:53.450","Text":"In this section, we\u0027ve explained the significance of"},{"Start":"07:53.450 ","End":"07:56.165","Text":"photosynthesis to all living organisms."},{"Start":"07:56.165 ","End":"07:59.908","Text":"We\u0027ve identified the substrates and products of photosynthesis,"},{"Start":"07:59.908 ","End":"08:04.775","Text":"and described the main structures and molecular processes involved in photosynthesis."},{"Start":"08:04.775 ","End":"08:07.410","Text":"See you in the next section."}],"ID":25839},{"Watched":false,"Name":"The Light-Dependent Reactions of Photosynthesis","Duration":"8m 34s","ChapterTopicVideoID":24928,"CourseChapterTopicPlaylistID":136377,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:01.980","Text":"Hi. As you know,"},{"Start":"00:01.980 ","End":"00:05.010","Text":"photosynthesis is divided into 2 stages."},{"Start":"00:05.010 ","End":"00:08.595","Text":"The first stage includes the light-dependent reactions,"},{"Start":"00:08.595 ","End":"00:12.240","Text":"and the second stage includes the light independent reactions."},{"Start":"00:12.240 ","End":"00:17.025","Text":"In this section, we\u0027ll be introducing the light-dependent reactions of photosynthesis."},{"Start":"00:17.025 ","End":"00:18.525","Text":"By the end of this section,"},{"Start":"00:18.525 ","End":"00:22.245","Text":"you\u0027ll be able to define short and long wavelengths of light,"},{"Start":"00:22.245 ","End":"00:25.170","Text":"explain how plants absorb energy from sunlight,"},{"Start":"00:25.170 ","End":"00:29.910","Text":"and describe where photosynthesis takes place within a plant."},{"Start":"00:29.910 ","End":"00:32.040","Text":"In the light-dependent reactions,"},{"Start":"00:32.040 ","End":"00:35.625","Text":"ADP molecules are phosphorylated."},{"Start":"00:35.625 ","End":"00:38.990","Text":"We have an input of an ADP molecule and"},{"Start":"00:38.990 ","End":"00:44.275","Text":"another phosphate group and output of a phosphorylated ATP molecule."},{"Start":"00:44.275 ","End":"00:49.130","Text":"NADP plus, an electron acceptor is reduced."},{"Start":"00:49.130 ","End":"00:56.405","Text":"Here we see the NADP plus coming into the reaction and an output of reduced NADPH."},{"Start":"00:56.405 ","End":"00:59.030","Text":"A water molecule is split."},{"Start":"00:59.030 ","End":"01:02.195","Text":"If we\u0027d have, let\u0027s say, 2 water molecules,"},{"Start":"01:02.195 ","End":"01:10.195","Text":"we\u0027d get 4 hydrogen ions and oxygen."},{"Start":"01:10.195 ","End":"01:13.430","Text":"The oxygen is released from the plant."},{"Start":"01:13.430 ","End":"01:17.975","Text":"This whole process works under light energy."},{"Start":"01:17.975 ","End":"01:20.990","Text":"But what is light energy?"},{"Start":"01:20.990 ","End":"01:25.519","Text":"Solar radiation travels in the form of waves."},{"Start":"01:25.519 ","End":"01:29.645","Text":"Each light wave is characterized by its wavelength."},{"Start":"01:29.645 ","End":"01:34.625","Text":"Wavelength is defined as the distance between 2 consecutive points."},{"Start":"01:34.625 ","End":"01:37.070","Text":"Here we have our wave,"},{"Start":"01:37.070 ","End":"01:42.440","Text":"and if we take the same point and 2 consecutive crests,"},{"Start":"01:42.440 ","End":"01:44.315","Text":"that gives us a wavelength."},{"Start":"01:44.315 ","End":"01:48.095","Text":"The sun emits solar energy in a wide spectrum"},{"Start":"01:48.095 ","End":"01:53.105","Text":"from very shortwave Gamma rays to very long radio waves."},{"Start":"01:53.105 ","End":"01:56.900","Text":"This spectrum is called the electromagnetic spectrum."},{"Start":"01:56.900 ","End":"02:00.320","Text":"As I mentioned, Gamma rays are very short,"},{"Start":"02:00.320 ","End":"02:03.130","Text":"while radio waves can be hundreds of meters long."},{"Start":"02:03.130 ","End":"02:06.935","Text":"The short tight waves carry the most energy."},{"Start":"02:06.935 ","End":"02:08.840","Text":"The longer the wavelength,"},{"Start":"02:08.840 ","End":"02:10.774","Text":"the less energy it carries."},{"Start":"02:10.774 ","End":"02:13.430","Text":"For example, the higher energy waves,"},{"Start":"02:13.430 ","End":"02:16.070","Text":"such as x-rays or ultraviolet rays,"},{"Start":"02:16.070 ","End":"02:18.950","Text":"can penetrate tissues and damage cells."},{"Start":"02:18.950 ","End":"02:23.075","Text":"Of this very wide spectrum of electromagnetic wavelengths,"},{"Start":"02:23.075 ","End":"02:26.755","Text":"a very narrow range is visible to the human eye."},{"Start":"02:26.755 ","End":"02:29.430","Text":"We call this the visible light."},{"Start":"02:29.430 ","End":"02:33.905","Text":"The shorter wavelengths are interpreted by our brain as purple,"},{"Start":"02:33.905 ","End":"02:39.210","Text":"violet, blue, green, yellow, orange, and red."},{"Start":"02:39.520 ","End":"02:44.030","Text":"Waves shorter than this violet are ultraviolet."},{"Start":"02:44.030 ","End":"02:47.375","Text":"Many insects can see ultraviolet wavelengths too."},{"Start":"02:47.375 ","End":"02:51.530","Text":"Waves longer than the red that we can see are infrared."},{"Start":"02:51.530 ","End":"02:54.175","Text":"How is this slight absorbed?"},{"Start":"02:54.175 ","End":"02:58.340","Text":"Organic pigments, whether in the human retina in the eye or"},{"Start":"02:58.340 ","End":"03:00.470","Text":"the chloroplast thylakoid in plants"},{"Start":"03:00.470 ","End":"03:03.275","Text":"have a narrow range of energy levels they can absorb,"},{"Start":"03:03.275 ","End":"03:07.030","Text":"between 400 and 700 nanometers."},{"Start":"03:07.030 ","End":"03:10.430","Text":"The light energy initiates the process of"},{"Start":"03:10.430 ","End":"03:15.655","Text":"photosynthesis when pigments absorb specific wavelengths of visible light."},{"Start":"03:15.655 ","End":"03:19.320","Text":"When pigments in our eyes absorb specific wavelengths,"},{"Start":"03:19.320 ","End":"03:22.565","Text":"this initiates the process of seeing."},{"Start":"03:22.565 ","End":"03:25.505","Text":"But when the light energy is absorbed by pigments in the plant,"},{"Start":"03:25.505 ","End":"03:27.920","Text":"it initiates the process of photosynthesis."},{"Start":"03:27.920 ","End":"03:31.040","Text":"The pigments absorb only specific wavelengths of"},{"Start":"03:31.040 ","End":"03:35.090","Text":"visible light and reflect or transmit the rest."},{"Start":"03:35.090 ","End":"03:36.860","Text":"We call these colors."},{"Start":"03:36.860 ","End":"03:40.670","Text":"For example, if you take a blue piece of paper,"},{"Start":"03:40.670 ","End":"03:45.635","Text":"put it in the sun, this blue piece of paper absorbs all the wavelengths,"},{"Start":"03:45.635 ","End":"03:47.960","Text":"except for the blue wavelength."},{"Start":"03:47.960 ","End":"03:51.255","Text":"Here, around 450 nanometers."},{"Start":"03:51.255 ","End":"03:53.490","Text":"This slide is reflected,"},{"Start":"03:53.490 ","End":"03:57.460","Text":"it\u0027s absorbed by the pigments in our eyes and we see it as blue."},{"Start":"03:57.460 ","End":"04:01.720","Text":"If you take a black paper and put it in the sun,"},{"Start":"04:01.720 ","End":"04:04.075","Text":"it absorbs all the wavelengths."},{"Start":"04:04.075 ","End":"04:06.145","Text":"That\u0027s why it looks dark to us."},{"Start":"04:06.145 ","End":"04:10.855","Text":"If you take a white piece of paper and put it in the sun,"},{"Start":"04:10.855 ","End":"04:12.950","Text":"it doesn\u0027t absorb any wavelengths,"},{"Start":"04:12.950 ","End":"04:15.025","Text":"it reflects all the rest of them."},{"Start":"04:15.025 ","End":"04:18.415","Text":"That\u0027s why if you take the black paper and the white paper and put them in the sun,"},{"Start":"04:18.415 ","End":"04:19.855","Text":"leave them for a few minutes,"},{"Start":"04:19.855 ","End":"04:22.300","Text":"you\u0027ll feel that the black paper heated up"},{"Start":"04:22.300 ","End":"04:25.060","Text":"very quickly while the white paper stayed cool."},{"Start":"04:25.060 ","End":"04:27.130","Text":"That\u0027s because the black paper absorbed"},{"Start":"04:27.130 ","End":"04:31.180","Text":"all the solar energy while the white paper reflected everything."},{"Start":"04:31.180 ","End":"04:34.225","Text":"If we take a look at this plant here,"},{"Start":"04:34.225 ","End":"04:39.920","Text":"the green leaves and say a beautiful red flower."},{"Start":"04:39.920 ","End":"04:42.830","Text":"The red flower actually absorbs"},{"Start":"04:42.830 ","End":"04:47.525","Text":"all the other wavelengths and reflects the long red wavelengths."},{"Start":"04:47.525 ","End":"04:54.440","Text":"The green leaves absorb red and blue-violet wavelengths and reflect the rest.,"},{"Start":"04:54.440 ","End":"04:56.945","Text":"and that\u0027s why they look green to us."},{"Start":"04:56.945 ","End":"05:01.220","Text":"Chlorophylls and carotenoids are the 2 major classes"},{"Start":"05:01.220 ","End":"05:05.450","Text":"of photosynthetic pigments found in plants and algae."},{"Start":"05:05.450 ","End":"05:10.085","Text":"Chlorophyll A and chlorophyll B gives leaves their green color."},{"Start":"05:10.085 ","End":"05:16.115","Text":"As you can see, they absorb blue-violet light and red-orange light."},{"Start":"05:16.115 ","End":"05:19.195","Text":"That\u0027s why they reflect the green light."},{"Start":"05:19.195 ","End":"05:22.700","Text":"Carotenoids function as photosynthetic pigments that are"},{"Start":"05:22.700 ","End":"05:26.630","Text":"very efficient molecules for the disposal of excess energy."},{"Start":"05:26.630 ","End":"05:31.700","Text":"For example, Beta carotene is responsible for the orange color of carrots."},{"Start":"05:31.700 ","End":"05:35.630","Text":"Many photosynthetic organisms have a mixture of pigments."},{"Start":"05:35.630 ","End":"05:40.325","Text":"This way they can absorb energy from a wider range of wavelengths."},{"Start":"05:40.325 ","End":"05:44.975","Text":"Each type of pigment can be identified by its absorption spectrum."},{"Start":"05:44.975 ","End":"05:48.830","Text":"The absorption spectrum of chlorophyll A suggests that"},{"Start":"05:48.830 ","End":"05:53.090","Text":"violet-blue and red light are best for photosynthesis."},{"Start":"05:53.090 ","End":"05:55.865","Text":"By measuring the oxygen release,"},{"Start":"05:55.865 ","End":"05:57.980","Text":"we can make an action spectrum."},{"Start":"05:57.980 ","End":"06:01.130","Text":"This spectrum profiles the relative effectiveness of"},{"Start":"06:01.130 ","End":"06:04.945","Text":"different wavelengths of radiation in driving a process."},{"Start":"06:04.945 ","End":"06:10.110","Text":"The chlorophyll A absorbs red in the violet-blue area"},{"Start":"06:10.110 ","End":"06:15.200","Text":"and in the the orange-red area and leaves out this greenish-yellow area."},{"Start":"06:15.200 ","End":"06:17.210","Text":"That\u0027s why plants look to us green."},{"Start":"06:17.210 ","End":"06:22.400","Text":"If we measure the oxygen while shining on light and different wavelengths on the plant,"},{"Start":"06:22.400 ","End":"06:25.370","Text":"we can see that there\u0027s high oxygen release in these areas,"},{"Start":"06:25.370 ","End":"06:27.485","Text":"and low oxygen release in these areas,"},{"Start":"06:27.485 ","End":"06:31.220","Text":"meaning that the plants don\u0027t absorb this light energy."},{"Start":"06:31.220 ","End":"06:33.215","Text":"They absorb light energy well,"},{"Start":"06:33.215 ","End":"06:35.150","Text":"in this area and in this area,"},{"Start":"06:35.150 ","End":"06:36.855","Text":"and that\u0027s because of the pigments,"},{"Start":"06:36.855 ","End":"06:38.360","Text":"the chlorophyll A,"},{"Start":"06:38.360 ","End":"06:41.225","Text":"which has high absorption in both these areas."},{"Start":"06:41.225 ","End":"06:45.445","Text":"Let\u0027s try to understand how the light-dependent reactions work."},{"Start":"06:45.445 ","End":"06:49.540","Text":"Solar energy is converted into chemical energy in the form of"},{"Start":"06:49.540 ","End":"06:54.190","Text":"reduced NADPH and phosphorylated ATP."},{"Start":"06:54.190 ","End":"07:01.105","Text":"Again, we have the NADP plus coming into the reaction and exiting reduced NADPH."},{"Start":"07:01.105 ","End":"07:06.475","Text":"We have the ADP coming into the reaction and exiting phosphorylated as ATP."},{"Start":"07:06.475 ","End":"07:10.990","Text":"These 2 molecules are high in energy while these 2 molecules are low in energy."},{"Start":"07:10.990 ","End":"07:14.500","Text":"This is a battery charger for these molecules."},{"Start":"07:14.500 ","End":"07:18.850","Text":"The conversion takes place in a photosystem complex."},{"Start":"07:18.850 ","End":"07:22.360","Text":"This is located within the thylakoid membrane."},{"Start":"07:22.360 ","End":"07:26.355","Text":"Inside the cell of the leaf,"},{"Start":"07:26.355 ","End":"07:28.820","Text":"we have this organelle called the chloroplast."},{"Start":"07:28.820 ","End":"07:33.875","Text":"In the chloroplast we have these membrane-bound structures called thylakoids."},{"Start":"07:33.875 ","End":"07:36.005","Text":"Within the membrane of the thylakoid,"},{"Start":"07:36.005 ","End":"07:38.045","Text":"we have our photosystem complex."},{"Start":"07:38.045 ","End":"07:40.895","Text":"Let\u0027s have a look here, this is the thylakoid membrane,"},{"Start":"07:40.895 ","End":"07:43.205","Text":"this is the inner part of the thylakoid,"},{"Start":"07:43.205 ","End":"07:45.695","Text":"and this is the outer part called the stroma."},{"Start":"07:45.695 ","End":"07:48.200","Text":"It\u0027s within the chloroplast, of course."},{"Start":"07:48.200 ","End":"07:50.675","Text":"Here\u0027s our photosystem."},{"Start":"07:50.675 ","End":"07:52.695","Text":"There are 2 photosystems."},{"Start":"07:52.695 ","End":"07:56.580","Text":"Photosystem II or as abbreviated PS II,"},{"Start":"07:56.580 ","End":"08:03.430","Text":"is also called P680 because it\u0027s best at absorbing a wavelength of 680 nanometers."},{"Start":"08:03.430 ","End":"08:07.450","Text":"Photosystem I, abbreviated as PS I,"},{"Start":"08:07.450 ","End":"08:10.775","Text":"is best at absorbing a wavelength of 700 nanometers."},{"Start":"08:10.775 ","End":"08:12.500","Text":"It\u0027s called P700."},{"Start":"08:12.500 ","End":"08:14.960","Text":"If you\u0027re curious to find out what actually"},{"Start":"08:14.960 ","End":"08:17.855","Text":"happens with the light energy in these photosystems,"},{"Start":"08:17.855 ","End":"08:20.910","Text":"you\u0027ll have to listen to the next section too."},{"Start":"08:21.920 ","End":"08:26.150","Text":"In this section, we\u0027ve described short and long wavelengths of light."},{"Start":"08:26.150 ","End":"08:30.110","Text":"We\u0027ve explained how plants absorb energy from sunlight and defined"},{"Start":"08:30.110 ","End":"08:35.100","Text":"where photosynthesis takes place within a plant. See you soon."}],"ID":25841},{"Watched":false,"Name":"Linear Electron Flow","Duration":"9m 26s","ChapterTopicVideoID":24927,"CourseChapterTopicPlaylistID":136377,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:01.495","Text":"Hi. In this section,"},{"Start":"00:01.495 ","End":"00:05.850","Text":"we\u0027ll talk about the linear electron flow on the photosynthesis."},{"Start":"00:05.850 ","End":"00:07.860","Text":"By the end of this section,"},{"Start":"00:07.860 ","End":"00:12.270","Text":"you\u0027ll be able to describe the linear electron flow of photosynthesis."},{"Start":"00:12.270 ","End":"00:16.980","Text":"The overall function of the light-dependent reactions in photosynthesis is to convert"},{"Start":"00:16.980 ","End":"00:22.545","Text":"solar energy into chemical energy in the form of reduced NADPH molecules,"},{"Start":"00:22.545 ","End":"00:28.095","Text":"and phosphorylated ATP molecules to molecules high in energy."},{"Start":"00:28.095 ","End":"00:34.340","Text":"There are 2 possible routes for electron flow, cyclic and linear."},{"Start":"00:34.340 ","End":"00:39.950","Text":"The linear electron flow includes both photosystems II and I and"},{"Start":"00:39.950 ","End":"00:46.310","Text":"produces ATP and NADPH with a byproduct, oxygen."},{"Start":"00:46.310 ","End":"00:52.745","Text":"The cyclic electron flow includes only a photosystem I and produces only ATP."},{"Start":"00:52.745 ","End":"00:55.580","Text":"Here we\u0027ll learn only about the linear electron flow."},{"Start":"00:55.580 ","End":"00:59.075","Text":"The cyclic electron flow will get its own section."},{"Start":"00:59.075 ","End":"01:02.045","Text":"Let\u0027s see the photosystem structure."},{"Start":"01:02.045 ","End":"01:06.200","Text":"Each photosystem is serviced by a light harvesting complex"},{"Start":"01:06.200 ","End":"01:11.070","Text":"which captures energy from sunlight and they\u0027ve exit to the reaction center."},{"Start":"01:11.150 ","End":"01:14.890","Text":"This conflicts includes several antenna proteins"},{"Start":"01:14.890 ","End":"01:17.500","Text":"to which the chlorophyll molecules are bound."},{"Start":"01:17.500 ","End":"01:19.600","Text":"The antenna proteins surround"},{"Start":"01:19.600 ","End":"01:24.100","Text":"the reaction center where the actual photo-chemistry takes place."},{"Start":"01:24.100 ","End":"01:31.450","Text":"The photosystem contains a mixture of between 300-400 chlorophyll A and B molecules,"},{"Start":"01:31.450 ","End":"01:35.125","Text":"as well as other pigments like carotenoids."},{"Start":"01:35.125 ","End":"01:40.240","Text":"The absorption of a single photon or distinct quantity or a packet of light by"},{"Start":"01:40.240 ","End":"01:45.235","Text":"any of the chlorophylls pushes an electron and that molecule into an excited state."},{"Start":"01:45.235 ","End":"01:50.245","Text":"At this point, light energy is converted into an excited electron."},{"Start":"01:50.245 ","End":"01:53.110","Text":"The energy is then transferred from chlorophyll to"},{"Start":"01:53.110 ","End":"01:57.485","Text":"chlorophyll until eventually it is delivered to the reaction center."},{"Start":"01:57.485 ","End":"02:00.500","Text":"We have here the energy coming from the photon,"},{"Start":"02:00.500 ","End":"02:03.755","Text":"the light energy that excites an electron."},{"Start":"02:03.755 ","End":"02:08.810","Text":"The electron itself does not move between the molecules rather, the energy."},{"Start":"02:08.810 ","End":"02:12.590","Text":"When the electron drops down to a less energetic state,"},{"Start":"02:12.590 ","End":"02:16.525","Text":"the energy is released and excites an electron and another molecule."},{"Start":"02:16.525 ","End":"02:19.400","Text":"That way, the energy is moved from molecule to"},{"Start":"02:19.400 ","End":"02:23.015","Text":"molecule until it reaches the reaction center, chlorophyll."},{"Start":"02:23.015 ","End":"02:28.160","Text":"The reaction center contains a pair of chlorophyll a molecules that upon"},{"Start":"02:28.160 ","End":"02:34.255","Text":"excitation undergo oxidation and gives up an electron in the process of photo act."},{"Start":"02:34.255 ","End":"02:37.805","Text":"At this point the electron itself leave the chlorophyll."},{"Start":"02:37.805 ","End":"02:41.180","Text":"Again, we have the photon light energy,"},{"Start":"02:41.180 ","End":"02:44.240","Text":"which moves from chlorophyll to chlorophyll as energy."},{"Start":"02:44.240 ","End":"02:47.600","Text":"When it reaches the special pair of chlorophyll a molecules,"},{"Start":"02:47.600 ","End":"02:52.415","Text":"the electron itself leaves a chlorophyll. Where does it go?"},{"Start":"02:52.415 ","End":"02:56.450","Text":"Well, photosystem II and photosystem I are"},{"Start":"02:56.450 ","End":"03:00.635","Text":"2 major components of the photosynthetic electron transport chain."},{"Start":"03:00.635 ","End":"03:04.090","Text":"The electron is transported through a chain."},{"Start":"03:04.090 ","End":"03:06.860","Text":"In this chain, the electron energy is"},{"Start":"03:06.860 ","End":"03:10.745","Text":"used to transfer protons across the thylakoid membrane."},{"Start":"03:10.745 ","End":"03:16.240","Text":"You see in the protons accumulating in the thylakoid space."},{"Start":"03:16.240 ","End":"03:23.465","Text":"The buildup of hydrogen ions inside the thylakoid lumen creates a concentration gradient."},{"Start":"03:23.465 ","End":"03:27.260","Text":"The hydrogen ions passively diffuse according to"},{"Start":"03:27.260 ","End":"03:31.370","Text":"their concentration gradient from the thylakoid lumen to the stroma."},{"Start":"03:31.370 ","End":"03:38.375","Text":"Remind you, the stroma is the interspace of the chloroplast inside the inner membrane,"},{"Start":"03:38.375 ","End":"03:40.490","Text":"but outside of the thylakoids."},{"Start":"03:40.490 ","End":"03:46.275","Text":"The hydrogen ions leaving the thylakoid space, the lumen,"},{"Start":"03:46.275 ","End":"03:55.745","Text":"to the stroma, passed through ATP synthase in a process defined as chemiosmosis."},{"Start":"03:55.745 ","End":"03:59.315","Text":"This is very much like water flowing in a mill."},{"Start":"03:59.315 ","End":"04:02.660","Text":"The hydrogen ions cause the ATP synthase to"},{"Start":"04:02.660 ","End":"04:07.340","Text":"spin and catalyze phosphorylation of ADP to ATP."},{"Start":"04:07.340 ","End":"04:12.935","Text":"Very much like this wheel here turning energy from the water flowing through it."},{"Start":"04:12.935 ","End":"04:18.905","Text":"This is actually a miniscule machine with a knob and a rotor deck turnaround."},{"Start":"04:18.905 ","End":"04:23.075","Text":"What facilitates this turn is the flow of the hydrogen ions,"},{"Start":"04:23.075 ","End":"04:24.395","Text":"just like we have here,"},{"Start":"04:24.395 ","End":"04:26.640","Text":"the flow of the water."},{"Start":"04:26.890 ","End":"04:34.895","Text":"The flow of the hydrogen ions actually is used to energize these ADP molecules,"},{"Start":"04:34.895 ","End":"04:42.810","Text":"to phosphorylate them and now we have high-energy molecules, ATP, adenosine triphosphate."},{"Start":"04:42.810 ","End":"04:45.380","Text":"Before that we had adenosine diphosphate,"},{"Start":"04:45.380 ","End":"04:51.095","Text":"which means 2 and here we have 3 phosphates."},{"Start":"04:51.095 ","End":"04:54.245","Text":"This is termed chemiosmosis,"},{"Start":"04:54.245 ","End":"04:59.610","Text":"when we use energy in a chemical gradient to drive cellular work."},{"Start":"05:00.100 ","End":"05:03.155","Text":"Again, we have the thylakoid lumen,"},{"Start":"05:03.155 ","End":"05:06.830","Text":"which we have a high concentration of these protons,"},{"Start":"05:06.830 ","End":"05:10.235","Text":"the hydrogen ions and we have here the stroma,"},{"Start":"05:10.235 ","End":"05:13.445","Text":"which is the space outside of the thylakoids,"},{"Start":"05:13.445 ","End":"05:19.610","Text":"but inside the chloroplast and these flowing right through here are what energize"},{"Start":"05:19.610 ","End":"05:22.130","Text":"this rotor to turn and turn and turn and"},{"Start":"05:22.130 ","End":"05:26.840","Text":"this kinetic energy is used to phosphorylate the ADP into ATP."},{"Start":"05:26.840 ","End":"05:31.400","Text":"Now we have these high energized molecules."},{"Start":"05:31.400 ","End":"05:36.574","Text":"The energy from the sunlight is harnessed to energize an electron."},{"Start":"05:36.574 ","End":"05:40.385","Text":"The electron is then moved through the electron transport chain."},{"Start":"05:40.385 ","End":"05:42.380","Text":"As it moves from molecule to molecule,"},{"Start":"05:42.380 ","End":"05:46.265","Text":"it goes from higher energy to lower energy eventually,"},{"Start":"05:46.265 ","End":"05:48.350","Text":"it reaches photosystem I."},{"Start":"05:48.350 ","End":"05:54.980","Text":"When photosystem I is oxidized it again uses light to energize the electron."},{"Start":"05:54.980 ","End":"06:02.245","Text":"The high energy electron is eventually used to reduce NADP plus to NADPH."},{"Start":"06:02.245 ","End":"06:04.335","Text":"In subsequent steps,"},{"Start":"06:04.335 ","End":"06:09.965","Text":"the electron is carried by NADPH to the Calvin cycle together with the ATP."},{"Start":"06:09.965 ","End":"06:15.515","Text":"These are the positive on the carbon from long-term storage in the form of carbohydrates."},{"Start":"06:15.515 ","End":"06:21.995","Text":"But if electrons are constantly being sent out through photosystem II towards photosystem"},{"Start":"06:21.995 ","End":"06:28.730","Text":"I and ending up in NADPH where does photosystem II receive new electrons over time?"},{"Start":"06:28.730 ","End":"06:33.560","Text":"The answer is that the missing electrons is replaced by extracting"},{"Start":"06:33.560 ","End":"06:38.845","Text":"a low-energy electron from water in a process known as photolysis."},{"Start":"06:38.845 ","End":"06:42.150","Text":"Photolysis again is made out of 2 words photo,"},{"Start":"06:42.150 ","End":"06:44.290","Text":"meaning light, and lysis,"},{"Start":"06:44.290 ","End":"06:46.265","Text":"meaning taking something apart."},{"Start":"06:46.265 ","End":"06:51.230","Text":"So photolysis is using light to take this molecule apart."},{"Start":"06:51.230 ","End":"06:54.335","Text":"The molecule is a water molecule."},{"Start":"06:54.335 ","End":"07:00.635","Text":"Photolysis is splitting 1 water molecule and that releases 2 electrons,"},{"Start":"07:00.635 ","End":"07:04.375","Text":"2 hydrogen atoms, and 1 atom of oxygen."},{"Start":"07:04.375 ","End":"07:10.475","Text":"Each 2 water molecules produced 1 diatomic oxygen gas molecule."},{"Start":"07:10.475 ","End":"07:13.210","Text":"What happens to all this oxygen?"},{"Start":"07:13.210 ","End":"07:16.535","Text":"Well, a map 10 percent of it is used by the plant,"},{"Start":"07:16.535 ","End":"07:18.800","Text":"but the remainder escapes to the atmosphere."},{"Start":"07:18.800 ","End":"07:20.450","Text":"If you\u0027ve ever asked yourself,"},{"Start":"07:20.450 ","End":"07:22.970","Text":"where does the oxygen that you breathe comes from?"},{"Start":"07:22.970 ","End":"07:24.940","Text":"Well, this is the answer."},{"Start":"07:24.940 ","End":"07:29.400","Text":"If we were to compare the chemiosmosis between chloroplasts and"},{"Start":"07:29.400 ","End":"07:35.665","Text":"mitochondria we would find that both generate ATP by similar chemiosmosis."},{"Start":"07:35.665 ","End":"07:38.375","Text":"In both, an electron transport chain,"},{"Start":"07:38.375 ","End":"07:40.925","Text":"pumps protons across the membrane,"},{"Start":"07:40.925 ","End":"07:43.910","Text":"causing a strong gradient of protons."},{"Start":"07:43.910 ","End":"07:47.225","Text":"This flow of protons is then harnessed via"},{"Start":"07:47.225 ","End":"07:52.024","Text":"ATP synthase to generate high-energy ATP molecules."},{"Start":"07:52.024 ","End":"07:56.465","Text":"But the chloroplasts and mitochondria use different sources of energy,"},{"Start":"07:56.465 ","End":"08:00.305","Text":"while mitochondria use chemical energy from consume molecules,"},{"Start":"08:00.305 ","End":"08:03.935","Text":"chloroplasts generate ATP using light energy."},{"Start":"08:03.935 ","End":"08:07.855","Text":"Also notice that the protons direction of movement is different."},{"Start":"08:07.855 ","End":"08:12.114","Text":"In mitochondria the protons are pumped at the intermembrane space"},{"Start":"08:12.114 ","End":"08:17.035","Text":"and drive ATP synthesis as they diffuse back into the mitochondrial matrix."},{"Start":"08:17.035 ","End":"08:18.970","Text":"Here we have the mitochondrion."},{"Start":"08:18.970 ","End":"08:22.059","Text":"We have here the inner space is called the matrix."},{"Start":"08:22.059 ","End":"08:28.615","Text":"We have a double membrane here and the protons are pumped into the intermembrane space."},{"Start":"08:28.615 ","End":"08:34.000","Text":"The protons are pumped out of the matrix to the intermembrane space."},{"Start":"08:34.000 ","End":"08:38.005","Text":"They diffuse back through ATP synthase generating ATP."},{"Start":"08:38.005 ","End":"08:42.895","Text":"In chloroplasts, you\u0027ll notice that the protons go in opposite directions."},{"Start":"08:42.895 ","End":"08:45.730","Text":"Here the interspace is called the stroma."},{"Start":"08:45.730 ","End":"08:50.735","Text":"Inside the stroma we have the thylakoids, another membranous structure."},{"Start":"08:50.735 ","End":"08:53.690","Text":"In the chloroplasts, the protons are pumped into"},{"Start":"08:53.690 ","End":"08:57.769","Text":"the thylakoid space and they diffuse up back into the stroma."},{"Start":"08:57.769 ","End":"08:59.915","Text":"So here and in the chloroplasts,"},{"Start":"08:59.915 ","End":"09:04.940","Text":"the protons are pumped into the innermost space and they diffuse back to the stroma,"},{"Start":"09:04.940 ","End":"09:11.040","Text":"the main space, while here the pump to the outermost space and then diffuse back in."},{"Start":"09:12.190 ","End":"09:15.890","Text":"With a nice deep breath of oxygen coming from"},{"Start":"09:15.890 ","End":"09:20.390","Text":"photosynthesis we\u0027ve finished another section"},{"Start":"09:20.390 ","End":"09:24.200","Text":"and we described the linear electron flow of photosynthesis."},{"Start":"09:24.200 ","End":"09:26.880","Text":"See you in the next section."}],"ID":25840},{"Watched":false,"Name":"Cyclic Electron Flow","Duration":"4m 8s","ChapterTopicVideoID":24925,"CourseChapterTopicPlaylistID":136377,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:01.800","Text":"Hi. In this section,"},{"Start":"00:01.800 ","End":"00:06.465","Text":"we\u0027ll be speaking about the cyclic electron flow of photosynthesis."},{"Start":"00:06.465 ","End":"00:08.205","Text":"By the end of this section,"},{"Start":"00:08.205 ","End":"00:13.485","Text":"you\u0027ll be able to describe the process and products of this path of photosynthesis."},{"Start":"00:13.485 ","End":"00:18.690","Text":"Let\u0027s have a look at this mechanical analogy of the linear electron flow."},{"Start":"00:18.690 ","End":"00:23.010","Text":"The electron is released from a water molecule in photolysis,"},{"Start":"00:23.010 ","End":"00:29.154","Text":"separating the oxygen from the,"},{"Start":"00:29.154 ","End":"00:30.825","Text":"we have here 2 molecules of water."},{"Start":"00:30.825 ","End":"00:36.600","Text":"We have here 1 molecule of oxygen, 4 hydrogens."},{"Start":"00:36.600 ","End":"00:42.330","Text":"The electron is excited using energy from the sunlight, the photon."},{"Start":"00:42.330 ","End":"00:46.010","Text":"The electron is excited to high level of energy."},{"Start":"00:46.010 ","End":"00:50.645","Text":"The energy is then released gradually through the electron transport chain."},{"Start":"00:50.645 ","End":"00:52.895","Text":"When it reaches the next photosystem,"},{"Start":"00:52.895 ","End":"00:54.995","Text":"photosystem I, again,"},{"Start":"00:54.995 ","End":"00:58.670","Text":"a photon is used to excite the electron which is"},{"Start":"00:58.670 ","End":"01:03.295","Text":"eventually used to reduce NADP plus to NADPH."},{"Start":"01:03.295 ","End":"01:06.830","Text":"The cyclic electron flow is thought to have evolved"},{"Start":"01:06.830 ","End":"01:11.374","Text":"before the linear electron flow in photosynthesizing bacteria."},{"Start":"01:11.374 ","End":"01:16.010","Text":"In this process, the electron is not released from water."},{"Start":"01:16.010 ","End":"01:19.145","Text":"It also does not end up in the NADPH."},{"Start":"01:19.145 ","End":"01:22.065","Text":"Rather, it\u0027s recycled."},{"Start":"01:22.065 ","End":"01:24.890","Text":"How is this done?"},{"Start":"01:24.890 ","End":"01:29.150","Text":"The electrons are shuttled back to the cytochrome complex"},{"Start":"01:29.150 ","End":"01:33.200","Text":"using ferredoxin that is an iron containing protein,"},{"Start":"01:33.200 ","End":"01:35.315","Text":"which is an electron carrier."},{"Start":"01:35.315 ","End":"01:39.260","Text":"They then return to the photosystem reaction center via"},{"Start":"01:39.260 ","End":"01:43.235","Text":"plastocyanin which is a copper containing protein,"},{"Start":"01:43.235 ","End":"01:45.250","Text":"an electron carrier,"},{"Start":"01:45.250 ","End":"01:49.575","Text":"and the way they pass through the cytochrome complex."},{"Start":"01:49.575 ","End":"01:54.260","Text":"The cyclic electron flow produces neither NADPH as"},{"Start":"01:54.260 ","End":"01:58.610","Text":"an end product nor oxygen as a byproduct of photolysis."},{"Start":"01:58.610 ","End":"02:02.795","Text":"The reason is that the electron is recycled all the time."},{"Start":"02:02.795 ","End":"02:05.870","Text":"We don\u0027t need to get new electrons from water molecules and we"},{"Start":"02:05.870 ","End":"02:09.380","Text":"don\u0027t have to use them in the end for reducing any other molecule."},{"Start":"02:09.380 ","End":"02:12.410","Text":"How is the ATP produced in this process?"},{"Start":"02:12.410 ","End":"02:15.770","Text":"The ATP is produced through chemiosmosis just as"},{"Start":"02:15.770 ","End":"02:19.280","Text":"we have seen in the non-cyclic photophosphorylation."},{"Start":"02:19.280 ","End":"02:24.530","Text":"In other words, the excited electron that\u0027s excited in the photosystem I by"},{"Start":"02:24.530 ","End":"02:31.855","Text":"the light energy is moved by the ferredoxin to the cytochrome complex also known as b6f."},{"Start":"02:31.855 ","End":"02:34.730","Text":"Here, the electron is passed via"},{"Start":"02:34.730 ","End":"02:40.790","Text":"the electron transport chain and the energy is used to pump protons into the lumen."},{"Start":"02:40.790 ","End":"02:44.030","Text":"Again, this is inside the chloroplast."},{"Start":"02:44.030 ","End":"02:46.055","Text":"The stroma is the inner area of"},{"Start":"02:46.055 ","End":"02:50.105","Text":"the chloroplast and the lumen is the inside of the thylakoid."},{"Start":"02:50.105 ","End":"02:52.690","Text":"Here we have the thylakoid membrane."},{"Start":"02:52.690 ","End":"02:56.030","Text":"What we get here as a strong gradient of"},{"Start":"02:56.030 ","End":"03:00.470","Text":"these protons here which will eventually flow out with great force."},{"Start":"03:00.470 ","End":"03:04.435","Text":"This flow is used to turn on molecular wheel."},{"Start":"03:04.435 ","End":"03:07.670","Text":"In this illustration, the protons are coming from top to bottom."},{"Start":"03:07.670 ","End":"03:09.575","Text":"While in our illustration here,"},{"Start":"03:09.575 ","End":"03:12.560","Text":"they\u0027re coming from bottom to top so just don\u0027t get confused with that."},{"Start":"03:12.560 ","End":"03:16.610","Text":"This is the same water wheel and it\u0027s using the energy from the flow of"},{"Start":"03:16.610 ","End":"03:22.460","Text":"protons to phosphorylate ADP to highly energetic ATP molecules."},{"Start":"03:22.460 ","End":"03:27.980","Text":"The cyclic electron flow does not occur under normal conditions in plants,"},{"Start":"03:27.980 ","End":"03:31.550","Text":"but the chloroplasts may shift to this process when"},{"Start":"03:31.550 ","End":"03:35.370","Text":"the ATP supply drops but there\u0027s plenty of NADPH."},{"Start":"03:35.370 ","End":"03:39.040","Text":"Right now the plant needs to make a lot of ATP without making NADPH."},{"Start":"03:39.040 ","End":"03:46.190","Text":"Then it may shift to the cyclic electron flow producing only ATP without producing NADPH."},{"Start":"03:46.190 ","End":"03:49.115","Text":"This way, the cell can balance its needs."},{"Start":"03:49.115 ","End":"03:53.690","Text":"Chloroplasts also may shift to this process when light intensity is low."},{"Start":"03:53.690 ","End":"03:55.760","Text":"That is because in lower frequencies,"},{"Start":"03:55.760 ","End":"03:58.525","Text":"only photosystem I can function."},{"Start":"03:58.525 ","End":"04:03.350","Text":"We\u0027ve spoken about the 6th electron flow and we described the process"},{"Start":"04:03.350 ","End":"04:08.550","Text":"and the products of this path in photosynthesis. See you later."}],"ID":25838},{"Watched":false,"Name":"Using Light Energy to Make Organic Molecules","Duration":"8m 37s","ChapterTopicVideoID":24929,"CourseChapterTopicPlaylistID":136377,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:01.010 ","End":"00:07.289","Text":"In this section I\u0027ll explain how the light energy is converted into organic molecules."},{"Start":"00:07.289 ","End":"00:09.240","Text":"By the end of this section,"},{"Start":"00:09.240 ","End":"00:14.610","Text":"you\u0027ll be able to describe the Calvin cycle and define carbon fixation."},{"Start":"00:14.610 ","End":"00:19.020","Text":"Previously, we have learned that the solar energy is used to"},{"Start":"00:19.020 ","End":"00:23.190","Text":"learn ATP and NADPH molecules with energy."},{"Start":"00:23.190 ","End":"00:26.310","Text":"These molecules from the light-dependent reactions are"},{"Start":"00:26.310 ","End":"00:28.950","Text":"used in the process of carbohydrate building,"},{"Start":"00:28.950 ","End":"00:31.560","Text":"also known as carbon fixation."},{"Start":"00:31.560 ","End":"00:35.880","Text":"Then ask yourself, why doesn\u0027t the cell just use the ATP"},{"Start":"00:35.880 ","End":"00:39.585","Text":"and NADPH process from the light-dependent reactions?"},{"Start":"00:39.585 ","End":"00:43.840","Text":"Why does it need to be used to create sugar?"},{"Start":"00:43.900 ","End":"00:47.825","Text":"The answer lies in the stability of these molecules."},{"Start":"00:47.825 ","End":"00:53.255","Text":"While the lifespans of ATP and NADPH last for the range of several seconds."},{"Start":"00:53.255 ","End":"00:58.535","Text":"Carbohydrates and other forms of reduced carbon can survive almost indefinitely."},{"Start":"00:58.535 ","End":"01:01.310","Text":"Where does that carbon come from?"},{"Start":"01:01.310 ","End":"01:03.290","Text":"The carbon atoms used for building"},{"Start":"01:03.290 ","End":"01:07.070","Text":"the carbohydrates are supplied by carbon dioxide molecules."},{"Start":"01:07.070 ","End":"01:13.280","Text":"In plants, carbon dioxide enters then leaves through stomata to mesophyll cells."},{"Start":"01:13.280 ","End":"01:18.005","Text":"The carbon dioxide enters through these openings the stomata,"},{"Start":"01:18.005 ","End":"01:20.060","Text":"it reaches the mesophyll cells,"},{"Start":"01:20.060 ","End":"01:24.340","Text":"and in the mesophyll cells are these organelles called the chloroplasts."},{"Start":"01:24.340 ","End":"01:30.425","Text":"The inner space and the chloroplast is called the stroma."},{"Start":"01:30.425 ","End":"01:35.140","Text":"We have these coin shaped thylakoids, which we\u0027ll soon see."},{"Start":"01:35.140 ","End":"01:38.420","Text":"Eventually, the carbon dioxide diffuses into"},{"Start":"01:38.420 ","End":"01:42.810","Text":"the stroma of the chloroplast and enters the Calvin cycle."},{"Start":"01:43.060 ","End":"01:46.475","Text":"What is that Calvin cycle we\u0027re talking about?"},{"Start":"01:46.475 ","End":"01:50.960","Text":"The Calvin cycle, also known as the Calvin-Benson cycle by its discovers,"},{"Start":"01:50.960 ","End":"01:58.850","Text":"is an antibiotic process that builds sugar from smaller molecules by using ATP and NADPH."},{"Start":"01:58.850 ","End":"02:06.235","Text":"In other words, the energy from ATP and NADPH molecules is invested in sugars."},{"Start":"02:06.235 ","End":"02:11.120","Text":"The carbon arrives at carbon dioxide and exits as a sugar."},{"Start":"02:11.120 ","End":"02:15.560","Text":"Glyceraldehyde 3-phosphate, also known as G3P."},{"Start":"02:15.560 ","End":"02:18.665","Text":"For the net synthesis of 1 G3P molecule,"},{"Start":"02:18.665 ","End":"02:20.600","Text":"the cycle has to rule 3 times,"},{"Start":"02:20.600 ","End":"02:23.165","Text":"fixing 3 molecules of carbon dioxide."},{"Start":"02:23.165 ","End":"02:25.100","Text":"Let\u0027s see why that is."},{"Start":"02:25.100 ","End":"02:30.480","Text":"Well, each carbon dioxide molecule has 1 carbon atom,"},{"Start":"02:31.100 ","End":"02:36.630","Text":"while each G3P molecule has 3 carbons."},{"Start":"02:36.630 ","End":"02:42.440","Text":"We\u0027ll need 3 carbon dioxide molecules to form this 1, G3P sugar."},{"Start":"02:42.440 ","End":"02:47.870","Text":"Let\u0027s look at the number of carbon atoms and the different molecules in the Calvin cycle."},{"Start":"02:47.870 ","End":"02:51.195","Text":"In the first phase, the carbon fixation,"},{"Start":"02:51.195 ","End":"02:58.670","Text":"3 molecules of carbon dioxide are fused with 3 molecules that are 5-carbon backbone."},{"Start":"02:58.670 ","End":"03:01.555","Text":"That gives us 3,"},{"Start":"03:01.555 ","End":"03:05.885","Text":"6 carbon molecules which are unstable,"},{"Start":"03:05.885 ","End":"03:09.250","Text":"and it quickly turned to 6, 3 carbon molecules."},{"Start":"03:09.250 ","End":"03:10.965","Text":"After the reduction,"},{"Start":"03:10.965 ","End":"03:14.270","Text":"1 of these 3 carbon molecules eventually leaves"},{"Start":"03:14.270 ","End":"03:18.950","Text":"the cycle and 5 of them are regenerated to be the carbon dioxide acceptor."},{"Start":"03:18.950 ","End":"03:23.225","Text":"We have here 5 times 3 carbon backbone molecule,"},{"Start":"03:23.225 ","End":"03:24.795","Text":"which are turned into 3,"},{"Start":"03:24.795 ","End":"03:29.675","Text":"5 carbon molecules, which will again except 3 carbon dioxide molecules."},{"Start":"03:29.675 ","End":"03:31.640","Text":"Let\u0027s see how that works now."},{"Start":"03:31.640 ","End":"03:35.180","Text":"Let\u0027s have a look at this process in further detail."},{"Start":"03:35.180 ","End":"03:39.470","Text":"The first phase of the Calvin cycle is the carbon fixation."},{"Start":"03:39.470 ","End":"03:42.510","Text":"This phase is catalyzed by Ribulose-1,"},{"Start":"03:42.510 ","End":"03:48.040","Text":"5-bisphosphate carboxylase-oxygenase, known as short as RuBisCO."},{"Start":"03:48.040 ","End":"03:51.380","Text":"This enzyme is the most abundant enzyme on earth."},{"Start":"03:51.380 ","End":"03:53.450","Text":"This happens in the stroma."},{"Start":"03:53.450 ","End":"03:58.865","Text":"Stroma is the inner space in the chloroplast."},{"Start":"03:58.865 ","End":"04:05.675","Text":"What happens here? We have 3 molecules of ribulose bisphosphate."},{"Start":"04:05.675 ","End":"04:12.755","Text":"Bisphosphate means it has 2 phosphates and this is again a 5-carbon backbone molecule."},{"Start":"04:12.755 ","End":"04:15.435","Text":"We have 3 of them, and the RuBisCO,"},{"Start":"04:15.435 ","End":"04:18.870","Text":"this enzyme connects this 1 carbon from"},{"Start":"04:18.870 ","End":"04:24.530","Text":"the carbon dioxide onto each of these ribulose bisphosphate molecules."},{"Start":"04:24.530 ","End":"04:29.915","Text":"Then we have a 6 carbon molecule with 1 phosphate group on either side."},{"Start":"04:29.915 ","End":"04:37.350","Text":"Again, this 6 carbon molecule is quickly broken into 2,"},{"Start":"04:37.350 ","End":"04:41.060","Text":"3 carbon molecules with 1 phosphate on the side."},{"Start":"04:41.060 ","End":"04:49.675","Text":"This is called phosphoglyceric also known as 3-phosphoglyceric acid or 3-PGA."},{"Start":"04:49.675 ","End":"04:53.475","Text":"We start again with 3 carbon dioxide molecules,"},{"Start":"04:53.475 ","End":"04:56.495","Text":"3 ribulose bisphosphate molecules,"},{"Start":"04:56.495 ","End":"05:01.265","Text":"and we end up with 6 phosphatidic acid molecules."},{"Start":"05:01.265 ","End":"05:03.845","Text":"What happens in the next step?"},{"Start":"05:03.845 ","End":"05:06.455","Text":"In the second phase, the reduction phase,"},{"Start":"05:06.455 ","End":"05:13.135","Text":"the energy stored in ATP and NADPH molecules are used to convert the 3-PGA,"},{"Start":"05:13.135 ","End":"05:16.110","Text":"There is 1-3 phosphoglycerate into"},{"Start":"05:16.110 ","End":"05:21.740","Text":"6 molecules of glyceraldehyde 3-phosphate known as G3P."},{"Start":"05:21.740 ","End":"05:28.145","Text":"Again, we have here the 3-PGA,"},{"Start":"05:28.145 ","End":"05:33.495","Text":"and it\u0027s converted into G3P."},{"Start":"05:33.495 ","End":"05:36.800","Text":"Let\u0027s just cancel carbon atoms and make sure that we\u0027re still even."},{"Start":"05:36.800 ","End":"05:39.755","Text":"We have here 6, 3 carbon backbone molecules,"},{"Start":"05:39.755 ","End":"05:41.630","Text":"and we end up again with 6,"},{"Start":"05:41.630 ","End":"05:44.554","Text":"3 carbon backbone molecules."},{"Start":"05:44.554 ","End":"05:50.840","Text":"The energy is invested from the ATP and the NADPH is used to"},{"Start":"05:50.840 ","End":"05:58.150","Text":"reduce the 3 bisphosphoglycerate in here into G3P."},{"Start":"05:58.150 ","End":"06:04.265","Text":"The G3p here is actually the end-product of the Calvin cycle."},{"Start":"06:04.265 ","End":"06:08.290","Text":"The G3P is actually a 3-carbon sugar."},{"Start":"06:08.290 ","End":"06:11.120","Text":"It\u0027s used to make other monosaccharides,"},{"Start":"06:11.120 ","End":"06:12.890","Text":"such as glucose, for example."},{"Start":"06:12.890 ","End":"06:15.035","Text":"Glucose we know is a 6-carbon sugar."},{"Start":"06:15.035 ","End":"06:20.975","Text":"So it takes 2 G3P molecules to form 1 glucose molecule."},{"Start":"06:20.975 ","End":"06:24.065","Text":"But this isn\u0027t at the end of the Calvin cycle."},{"Start":"06:24.065 ","End":"06:26.465","Text":"Again, we\u0027re speaking about a cycle here."},{"Start":"06:26.465 ","End":"06:29.825","Text":"What does the last step of the Calvin cycle?"},{"Start":"06:29.825 ","End":"06:35.165","Text":"This is the reduction of ribulose bisphosphate."},{"Start":"06:35.165 ","End":"06:38.540","Text":"Each 6 G3P molecules,"},{"Start":"06:38.540 ","End":"06:41.045","Text":"only 1 is exported as sugar,"},{"Start":"06:41.045 ","End":"06:43.585","Text":"while the other 5 stay in the cycle."},{"Start":"06:43.585 ","End":"06:46.160","Text":"ATP is again invested in them."},{"Start":"06:46.160 ","End":"06:48.875","Text":"We see here the extra phosphate group."},{"Start":"06:48.875 ","End":"06:52.960","Text":"These 5 times 3 carbon molecules,"},{"Start":"06:52.960 ","End":"06:59.900","Text":"5 times 3 gives us 15 carbon molecules are eventually used to form 3,"},{"Start":"06:59.900 ","End":"07:03.585","Text":"5-carbon molecules, 3 times 5,"},{"Start":"07:03.585 ","End":"07:05.835","Text":"which again 15,"},{"Start":"07:05.835 ","End":"07:08.525","Text":"so we keep the same amount of carbon atoms."},{"Start":"07:08.525 ","End":"07:11.165","Text":"We get the extra phosphate group from ATP,"},{"Start":"07:11.165 ","End":"07:15.500","Text":"and we end up with 3 ribulose bisphosphate molecules ready"},{"Start":"07:15.500 ","End":"07:20.210","Text":"to accept 3 new carbon dioxide molecules entering the cycle."},{"Start":"07:20.210 ","End":"07:23.180","Text":"If we take a look at the whole process of photosynthesis,"},{"Start":"07:23.180 ","End":"07:26.345","Text":"we see that the ATP and the NADPH"},{"Start":"07:26.345 ","End":"07:30.725","Text":"from the light-dependent reactions are used in the Calvin cycle."},{"Start":"07:30.725 ","End":"07:34.460","Text":"Energy stored in the ATP and NADPH is"},{"Start":"07:34.460 ","End":"07:38.570","Text":"download it in the sugar molecules exiting the process."},{"Start":"07:38.570 ","End":"07:42.380","Text":"The ADP and NADP plus from"},{"Start":"07:42.380 ","End":"07:44.810","Text":"the light independent reactions are"},{"Start":"07:44.810 ","End":"07:47.945","Text":"sent back to be recycled in the light-dependent reactions."},{"Start":"07:47.945 ","End":"07:50.644","Text":"Actually, we can look at them as batteries."},{"Start":"07:50.644 ","End":"07:53.105","Text":"These are charged batteries full of energy."},{"Start":"07:53.105 ","End":"07:55.400","Text":"The energy is used in accounting cycle."},{"Start":"07:55.400 ","End":"07:57.500","Text":"Now, these empty batteries are"},{"Start":"07:57.500 ","End":"08:00.709","Text":"sent back to the charge and the light-dependent reactions."},{"Start":"08:00.709 ","End":"08:06.515","Text":"The light-dependent reactions, H2O water undergoes photolysis,"},{"Start":"08:06.515 ","End":"08:12.170","Text":"being taken apart by light to extract the electrons used for the electron carriers."},{"Start":"08:12.170 ","End":"08:14.570","Text":"That leaves us with oxygen."},{"Start":"08:14.570 ","End":"08:18.965","Text":"Carbon dioxide entering the process leaves us sugar."},{"Start":"08:18.965 ","End":"08:23.420","Text":"We now understand the full process of photosynthesis."},{"Start":"08:23.420 ","End":"08:27.545","Text":"We\u0027ve spoken about using light energy to make organic molecules,"},{"Start":"08:27.545 ","End":"08:32.480","Text":"and in this section we described the Calvin cycle and define the carbon fixation."},{"Start":"08:32.480 ","End":"08:34.370","Text":"In the following section,"},{"Start":"08:34.370 ","End":"08:38.400","Text":"we\u0027ll see alternative mechanisms for carbon fixation."}],"ID":25842},{"Watched":false,"Name":"Exercise 1","Duration":"2m 56s","ChapterTopicVideoID":27001,"CourseChapterTopicPlaylistID":136377,"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":"Which of the following components is not used by"},{"Start":"00:03.000 ","End":"00:07.920","Text":"both plants and cyanobacteria to carry out photosynthesis?"},{"Start":"00:07.920 ","End":"00:11.925","Text":"A, Chloroplasts, B, chlorophyll,"},{"Start":"00:11.925 ","End":"00:14.325","Text":"C, carbon dioxide,"},{"Start":"00:14.325 ","End":"00:17.695","Text":"or D, water. Let\u0027s start with A."},{"Start":"00:17.695 ","End":"00:19.250","Text":"What are chloroplasts?"},{"Start":"00:19.250 ","End":"00:24.785","Text":"Chloroplasts are the organelle within the plant cells that perform photosynthesis."},{"Start":"00:24.785 ","End":"00:26.810","Text":"Plants have chloroplasts."},{"Start":"00:26.810 ","End":"00:29.285","Text":"The cyanobacteria have chloroplasts."},{"Start":"00:29.285 ","End":"00:32.010","Text":"Cyanobacteria by the name \"bacteria.\""},{"Start":"00:32.010 ","End":"00:35.210","Text":"As we know, prokaryotes don\u0027t have organelles at all."},{"Start":"00:35.210 ","End":"00:40.700","Text":"Cyanobacteria carry out photosynthesis on their own without an organelle."},{"Start":"00:40.700 ","End":"00:45.890","Text":"In fact, a cyanobacterium itself resembles a whole chloroplast."},{"Start":"00:45.890 ","End":"00:48.740","Text":"You can see here the thylakoid membrane inside,"},{"Start":"00:48.740 ","End":"00:52.710","Text":"its own DNA, just like the chloroplast has."},{"Start":"00:53.600 ","End":"00:58.520","Text":"The endosymbiotic theory states that the chloroplasts present"},{"Start":"00:58.520 ","End":"01:03.260","Text":"today in plants and algae cells originated as cyanobacteria."},{"Start":"01:03.260 ","End":"01:09.500","Text":"The cyanobacterium was engulfed with a eukaryotic cell but not digested,"},{"Start":"01:09.500 ","End":"01:14.750","Text":"resulting in symbiosis where the cell provides defense and nutrients to the organelle,"},{"Start":"01:14.750 ","End":"01:16.280","Text":"now called a chloroplast,"},{"Start":"01:16.280 ","End":"01:19.165","Text":"and the chloroplast provides sugar."},{"Start":"01:19.165 ","End":"01:23.450","Text":"The question we\u0027re asked if cyanobacteria use chloroplasts."},{"Start":"01:23.450 ","End":"01:24.830","Text":"Of course, the answer is no."},{"Start":"01:24.830 ","End":"01:26.565","Text":"But before we select this answer,"},{"Start":"01:26.565 ","End":"01:28.825","Text":"let\u0027s just have a look at the other answers."},{"Start":"01:28.825 ","End":"01:31.129","Text":"B asks about chlorophyll."},{"Start":"01:31.129 ","End":"01:32.899","Text":"Let\u0027s have a look at the chlorophyll."},{"Start":"01:32.899 ","End":"01:34.190","Text":"What is chlorophyll?"},{"Start":"01:34.190 ","End":"01:39.025","Text":"The chlorophyll is the pigment and the heart of light reactions of photosynthesis."},{"Start":"01:39.025 ","End":"01:41.750","Text":"This pigment absorbs the light energy and"},{"Start":"01:41.750 ","End":"01:45.560","Text":"transforms it into chemical energy by exciting an electron."},{"Start":"01:45.560 ","End":"01:49.820","Text":"The chlorophyll is present in both plants and cyanobacteria in"},{"Start":"01:49.820 ","End":"01:53.750","Text":"photosynthesis since this reaction occurs in both of them."},{"Start":"01:53.750 ","End":"01:55.010","Text":"We can cross that chlorophyll."},{"Start":"01:55.010 ","End":"01:56.720","Text":"Let\u0027s have a look at carbon dioxide."},{"Start":"01:56.720 ","End":"02:01.925","Text":"Carbon dioxide is the source of carbon molecules fixed in the Calvin cycle to sugar."},{"Start":"02:01.925 ","End":"02:07.690","Text":"In this diagram, we can see how carbon molecules from carbon dioxide are fixed to G3P,"},{"Start":"02:07.690 ","End":"02:09.280","Text":"which to them,"},{"Start":"02:09.280 ","End":"02:12.335","Text":"give us 1 glucose molecule."},{"Start":"02:12.335 ","End":"02:15.710","Text":"Therefore, we can cross out carbon dioxide since again,"},{"Start":"02:15.710 ","End":"02:18.965","Text":"the chloroplasts resembles 1 cyanobacterium"},{"Start":"02:18.965 ","End":"02:21.635","Text":"and the photosynthesis is performed in both of them,"},{"Start":"02:21.635 ","End":"02:24.395","Text":"fixing carbon from carbon dioxide into sugar."},{"Start":"02:24.395 ","End":"02:25.850","Text":"The last answer is water."},{"Start":"02:25.850 ","End":"02:27.640","Text":"Again, if we\u0027re looking at our diagram,"},{"Start":"02:27.640 ","End":"02:30.035","Text":"that water is consumed by the light reactions."},{"Start":"02:30.035 ","End":"02:32.075","Text":"Here we can see how water,"},{"Start":"02:32.075 ","End":"02:35.495","Text":"H2O, is separated into its components,"},{"Start":"02:35.495 ","End":"02:37.935","Text":"oxygen and hydrogen in"},{"Start":"02:37.935 ","End":"02:42.200","Text":"photolysis in order to free 1 electron for the electron transfer chain."},{"Start":"02:42.200 ","End":"02:45.335","Text":"Again, since this occurs in both plants and cyanobacteria,"},{"Start":"02:45.335 ","End":"02:47.375","Text":"we can cross out the answer water."},{"Start":"02:47.375 ","End":"02:50.075","Text":"We can now go back to the first answer, chloroplasts."},{"Start":"02:50.075 ","End":"02:51.350","Text":"This is the correct answer."},{"Start":"02:51.350 ","End":"02:54.005","Text":"It\u0027s not used by both plants and cyanobacteria,"},{"Start":"02:54.005 ","End":"02:56.550","Text":"but only by plants."}],"ID":28117},{"Watched":false,"Name":"Exercise 2","Duration":"2m 58s","ChapterTopicVideoID":27002,"CourseChapterTopicPlaylistID":136377,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:04.335","Text":"Here we\u0027re asked what the 2 main products of photosynthesis are."},{"Start":"00:04.335 ","End":"00:06.240","Text":"The answers are: a,"},{"Start":"00:06.240 ","End":"00:08.970","Text":"oxygen and carbon dioxide, b,"},{"Start":"00:08.970 ","End":"00:11.670","Text":"chlorophyll and oxygen, c,"},{"Start":"00:11.670 ","End":"00:14.055","Text":"carbohydrates and oxygen, or,"},{"Start":"00:14.055 ","End":"00:17.265","Text":"d, carbohydrates and carbon dioxide."},{"Start":"00:17.265 ","End":"00:20.220","Text":"Let\u0027s have a quick look at photosynthesis,"},{"Start":"00:20.220 ","End":"00:23.640","Text":"a small overview that\u0027ll help us answer this question."},{"Start":"00:23.640 ","End":"00:27.210","Text":"The 2 stages of photosynthesis are"},{"Start":"00:27.210 ","End":"00:31.035","Text":"the light-dependent reactions and the light-independent reactions,"},{"Start":"00:31.035 ","End":"00:33.030","Text":"otherwise known as the Calvin cycle."},{"Start":"00:33.030 ","End":"00:34.985","Text":"In the light-dependent reactions,"},{"Start":"00:34.985 ","End":"00:37.985","Text":"energy from the sunlight excites electrons,"},{"Start":"00:37.985 ","End":"00:41.030","Text":"which are then transferred in a pathway that allows"},{"Start":"00:41.030 ","End":"00:46.190","Text":"this energy to be used to generate ATP and NADPH."},{"Start":"00:46.190 ","End":"00:49.430","Text":"In this process, new electrons are needed all the time."},{"Start":"00:49.430 ","End":"00:53.825","Text":"Water molecules are taken apart in what we call photolysis,"},{"Start":"00:53.825 ","End":"00:58.520","Text":"the electrons are extracted and the water molecule made out of oxygen and"},{"Start":"00:58.520 ","End":"01:04.369","Text":"hydrogen is taken apart to protons and oxygen molecules."},{"Start":"01:04.369 ","End":"01:14.135","Text":"Every 2 water molecules are taken apart essentially to 4 protons and 1 oxygen molecule,"},{"Start":"01:14.135 ","End":"01:16.370","Text":"which is then freed to the atmosphere."},{"Start":"01:16.370 ","End":"01:22.235","Text":"This oxygen here is a byproduct of photolysis in the first part of light reactions."},{"Start":"01:22.235 ","End":"01:27.200","Text":"The second set of reactions in photosynthesis is called the light-independent reactions."},{"Start":"01:27.200 ","End":"01:30.290","Text":"In this stage, the ATP molecule and the"},{"Start":"01:30.290 ","End":"01:35.740","Text":"NADPH carrying these electrons are transferred to the Calvin cycle,"},{"Start":"01:35.740 ","End":"01:37.799","Text":"where in a series of processes,"},{"Start":"01:37.799 ","End":"01:44.180","Text":"the carbon atom from atmospheric carbon dioxide is fixed eventually to form sugars,"},{"Start":"01:44.180 ","End":"01:47.380","Text":"otherwise known as carbohydrates."},{"Start":"01:47.380 ","End":"01:51.890","Text":"We\u0027re asked what the 2 main products of photosynthesis are and we know that"},{"Start":"01:51.890 ","End":"01:54.395","Text":"the first important product is sugar or"},{"Start":"01:54.395 ","End":"01:58.205","Text":"carbohydrates and the byproduct of this process is oxygen,"},{"Start":"01:58.205 ","End":"02:01.175","Text":"which is essential to most life forms today."},{"Start":"02:01.175 ","End":"02:03.200","Text":"Now let\u0027s have a look at the answers."},{"Start":"02:03.200 ","End":"02:05.480","Text":"a, oxygen and carbon dioxide."},{"Start":"02:05.480 ","End":"02:06.950","Text":"Well, oxygen is right,"},{"Start":"02:06.950 ","End":"02:10.282","Text":"but carbon dioxide is not a product of photosynthesis,"},{"Start":"02:10.282 ","End":"02:14.090","Text":"so we can cross that a. b, chlorophyll and oxygen."},{"Start":"02:14.090 ","End":"02:18.050","Text":"Chlorophyll is the pigment which absorbs the light in"},{"Start":"02:18.050 ","End":"02:22.190","Text":"the light-dependent reactions so this is obviously wrong."},{"Start":"02:22.190 ","End":"02:23.540","Text":"Oxygen, again, is right,"},{"Start":"02:23.540 ","End":"02:25.735","Text":"but we have oxygen here."},{"Start":"02:25.735 ","End":"02:27.885","Text":"Oxygen is right, of course,"},{"Start":"02:27.885 ","End":"02:30.570","Text":"but we need both products to be right,"},{"Start":"02:30.570 ","End":"02:32.445","Text":"so we\u0027ll cross that answer b."},{"Start":"02:32.445 ","End":"02:35.415","Text":"Answer c, carbohydrates,"},{"Start":"02:35.415 ","End":"02:39.460","Text":"yes, and oxygen, yes."},{"Start":"02:39.460 ","End":"02:43.210","Text":"Let\u0027s just have a look at the last option before we decide on our answer."},{"Start":"02:43.210 ","End":"02:45.355","Text":"d, carbohydrates,"},{"Start":"02:45.355 ","End":"02:49.410","Text":"which is true, and carbon dioxide, no."},{"Start":"02:49.410 ","End":"02:52.534","Text":"You can now cross out d, and c,"},{"Start":"02:52.534 ","End":"02:56.675","Text":"carbohydrates and oxygen are the 2 main products of photosynthesis."},{"Start":"02:56.675 ","End":"02:58.950","Text":"This is the correct answer."}],"ID":28118},{"Watched":false,"Name":"Exercise 3","Duration":"3m 7s","ChapterTopicVideoID":27003,"CourseChapterTopicPlaylistID":136377,"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":"Here we\u0027re asked, in which compartment of the plant cell"},{"Start":"00:03.765 ","End":"00:08.565","Text":"the light-independent reactions of photosynthesis take place?"},{"Start":"00:08.565 ","End":"00:12.090","Text":"We always have to make sure that we read the question correctly."},{"Start":"00:12.090 ","End":"00:17.925","Text":"The light-independent reactions are the reactions that don\u0027t need light to work."},{"Start":"00:17.925 ","End":"00:20.340","Text":"This is the second stage of photosynthesis,"},{"Start":"00:20.340 ","End":"00:21.810","Text":"where carbon atoms from"},{"Start":"00:21.810 ","End":"00:27.860","Text":"atmospheric carbon dioxide molecules are fixed to form sugar molecules."},{"Start":"00:27.860 ","End":"00:31.100","Text":"The answers are: the thylakoid,"},{"Start":"00:31.100 ","End":"00:36.680","Text":"the stroma, the outer membrane, or the mesophyll."},{"Start":"00:36.680 ","End":"00:38.600","Text":"By this time, I hope you all know that"},{"Start":"00:38.600 ","End":"00:42.395","Text":"photosynthesis occurs in the organelle named the chloroplast."},{"Start":"00:42.395 ","End":"00:45.320","Text":"The chloroplast appears in mesophyll cells,"},{"Start":"00:45.320 ","End":"00:50.780","Text":"an area here of parenchyma between 2 layers of epidermal cells."},{"Start":"00:50.780 ","End":"00:55.685","Text":"Since we now know that the mesophyll is not a compartment of the plant cell at all,"},{"Start":"00:55.685 ","End":"00:58.175","Text":"rather a compartment of the leaf,"},{"Start":"00:58.175 ","End":"01:03.110","Text":"we can already cross that answer d. Let\u0027s have a look at the remaining 3 answers."},{"Start":"01:03.110 ","End":"01:05.659","Text":"The thylakoid, the stroma,"},{"Start":"01:05.659 ","End":"01:09.545","Text":"and the outer membrane are all components of the chloroplast."},{"Start":"01:09.545 ","End":"01:15.739","Text":"The chloroplast is wrapped by 2 membranes called the inner and the outer membranes."},{"Start":"01:15.739 ","End":"01:18.199","Text":"This is a double layer of membrane,"},{"Start":"01:18.199 ","End":"01:22.370","Text":"while each membrane itself is a bilayer of phospholipids."},{"Start":"01:22.370 ","End":"01:27.979","Text":"Therefore, the chloroplast has an intermembrane space between these 2 membranes."},{"Start":"01:27.979 ","End":"01:33.184","Text":"The matrix contained inside the inner membrane is called the stroma."},{"Start":"01:33.184 ","End":"01:36.110","Text":"Within the stroma, a membranous structure that"},{"Start":"01:36.110 ","End":"01:39.445","Text":"looks like stacked coins is called the thylakoid."},{"Start":"01:39.445 ","End":"01:41.870","Text":"The thylakoid is full of the green pigment,"},{"Start":"01:41.870 ","End":"01:44.555","Text":"which is what gives the chloroplasts its green color,"},{"Start":"01:44.555 ","End":"01:47.045","Text":"which is what gives leaves their green color,"},{"Start":"01:47.045 ","End":"01:49.730","Text":"which is what gives plants their green color."},{"Start":"01:49.730 ","End":"01:52.069","Text":"Each pile of thylakoids is called the granum."},{"Start":"01:52.069 ","End":"01:54.559","Text":"Light-dependent reactions occur here,"},{"Start":"01:54.559 ","End":"01:59.990","Text":"as those green pigments absorb the light and the energy is used to excite electrons."},{"Start":"01:59.990 ","End":"02:06.200","Text":"Eventually, this high energy is used to form ATP molecules, high energy molecules."},{"Start":"02:06.200 ","End":"02:10.655","Text":"They\u0027re later moved to the Calvin cycle, the light-independent reactions."},{"Start":"02:10.655 ","End":"02:15.545","Text":"The electron is also carried by an NADPH molecule, originally,"},{"Start":"02:15.545 ","End":"02:18.290","Text":"NADP+ to the Calvin cycle,"},{"Start":"02:18.290 ","End":"02:21.755","Text":"where it\u0027s used to fix carbon from carbon dioxide to sugars."},{"Start":"02:21.755 ","End":"02:26.720","Text":"The light-dependent reactions occur within the thylakoid and throughout its membrane,"},{"Start":"02:26.720 ","End":"02:30.050","Text":"where the electron transport chain moves the electrons from"},{"Start":"02:30.050 ","End":"02:33.770","Text":"protein to protein as it pumps protons in."},{"Start":"02:33.770 ","End":"02:37.490","Text":"The thylakoid is where the light-dependent reactions occur,"},{"Start":"02:37.490 ","End":"02:39.995","Text":"not where the light-independent reactions occur,"},{"Start":"02:39.995 ","End":"02:42.560","Text":"and therefore, we can cross out answer a."},{"Start":"02:42.560 ","End":"02:45.575","Text":"The ATP and NADPH molecules, as we said,"},{"Start":"02:45.575 ","End":"02:50.045","Text":"are used in the Calvin cycle to fix the carbon to sugar."},{"Start":"02:50.045 ","End":"02:51.800","Text":"Where does this occur?"},{"Start":"02:51.800 ","End":"02:54.785","Text":"In the stroma, the inner matrix,"},{"Start":"02:54.785 ","End":"02:56.720","Text":"or around the outer membrane?"},{"Start":"02:56.720 ","End":"02:59.390","Text":"The answer is they occur in the stroma."},{"Start":"02:59.390 ","End":"03:03.320","Text":"It will not let the ATP and NADPH molecules cross it."},{"Start":"03:03.320 ","End":"03:07.470","Text":"We can select our correct answer, the stroma."}],"ID":28119},{"Watched":false,"Name":"Exercise 4","Duration":"2m 8s","ChapterTopicVideoID":27004,"CourseChapterTopicPlaylistID":136377,"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":"Which statement about thylakoids in eukaryotes is not correct?"},{"Start":"00:05.565 ","End":"00:10.275","Text":"a, thylakoids are assembled in stacks; b,"},{"Start":"00:10.275 ","End":"00:15.150","Text":"the space surrounding thylakoids is called the stroma; c,"},{"Start":"00:15.150 ","End":"00:18.420","Text":"thylakoids are comprised of a double membrane;"},{"Start":"00:18.420 ","End":"00:21.765","Text":"or d, thylakoids contain chlorophyll."},{"Start":"00:21.765 ","End":"00:23.850","Text":"Let\u0027s have a look at these answers."},{"Start":"00:23.850 ","End":"00:26.730","Text":"Answer a states that thylakoids,"},{"Start":"00:26.730 ","End":"00:28.379","Text":"they\u0027re assembled in stacks."},{"Start":"00:28.379 ","End":"00:31.305","Text":"Let\u0027s have a look at this diagram of the chloroplast."},{"Start":"00:31.305 ","End":"00:33.690","Text":"Here we can see the thylakoid membrane;"},{"Start":"00:33.690 ","End":"00:37.385","Text":"a membranous structure that resembles stacked coins."},{"Start":"00:37.385 ","End":"00:39.965","Text":"Each stack is called a granum."},{"Start":"00:39.965 ","End":"00:42.530","Text":"Thylakoids are assembled in stacks,"},{"Start":"00:42.530 ","End":"00:45.980","Text":"and since we\u0027re asked about the statement that is not correct,"},{"Start":"00:45.980 ","End":"00:49.570","Text":"we can cross out answer a, which is correct."},{"Start":"00:49.570 ","End":"00:55.490","Text":"Answer b says that the space surrounding thylakoids is called stroma, and indeed,"},{"Start":"00:55.490 ","End":"01:01.295","Text":"this matrix within the inner membrane of the chloroplast is called the stroma."},{"Start":"01:01.295 ","End":"01:03.470","Text":"Therefore, since it\u0027s correct,"},{"Start":"01:03.470 ","End":"01:05.495","Text":"we can also cross out answer b."},{"Start":"01:05.495 ","End":"01:09.875","Text":"Answer c states that thylakoids are comprised of a double membrane."},{"Start":"01:09.875 ","End":"01:13.415","Text":"True that the chloroplast itself has a double membrane;"},{"Start":"01:13.415 ","End":"01:17.585","Text":"an inner and an outer membrane with an intermembrane space."},{"Start":"01:17.585 ","End":"01:20.885","Text":"But thylakoids themselves, as we can see here,"},{"Start":"01:20.885 ","End":"01:22.880","Text":"have only 1 layer."},{"Start":"01:22.880 ","End":"01:28.675","Text":"Of course, each layer of membrane is made of a bi-layer of phospholipids."},{"Start":"01:28.675 ","End":"01:32.750","Text":"Thylakoids are comprised of a double membrane, is incorrect."},{"Start":"01:32.750 ","End":"01:35.495","Text":"But before we choose answer c,"},{"Start":"01:35.495 ","End":"01:37.235","Text":"let\u0027s just have a look at answer d,"},{"Start":"01:37.235 ","End":"01:39.994","Text":"stating that thylakoids contain chlorophyll."},{"Start":"01:39.994 ","End":"01:44.285","Text":"Chlorophyll is the green pigment contained in the thylakoid membrane."},{"Start":"01:44.285 ","End":"01:47.195","Text":"This gives the thylakoids their green color,"},{"Start":"01:47.195 ","End":"01:49.355","Text":"which gives the chloroplast its green color,"},{"Start":"01:49.355 ","End":"01:51.820","Text":"which gives plants their green colors."},{"Start":"01:51.820 ","End":"01:54.080","Text":"Answer d is true,"},{"Start":"01:54.080 ","End":"01:56.465","Text":"and since we\u0027re looking for a false statement,"},{"Start":"01:56.465 ","End":"02:00.725","Text":"we can cross out answer d. c is the correct answer."},{"Start":"02:00.725 ","End":"02:03.500","Text":"Thylakoids are not comprised of a double membrane."},{"Start":"02:03.500 ","End":"02:08.640","Text":"They have only 1, while the chloroplast itself does have a double membrane."}],"ID":28120},{"Watched":false,"Name":"Exercise 5","Duration":"3m 56s","ChapterTopicVideoID":27005,"CourseChapterTopicPlaylistID":136377,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.410 ","End":"00:03.540","Text":"Hi. In this question,"},{"Start":"00:03.540 ","End":"00:07.800","Text":"we\u0027re asked to predict the end result in a hypothetical scenario where"},{"Start":"00:07.800 ","End":"00:11.610","Text":"a chloroplasts light independent enzymes developed"},{"Start":"00:11.610 ","End":"00:15.870","Text":"a mutation that prevented them from activating in response to light."},{"Start":"00:15.870 ","End":"00:19.485","Text":"The first answer is an accumulation of G3P."},{"Start":"00:19.485 ","End":"00:24.045","Text":"The second option is that ATP and NADPH would accumulate."},{"Start":"00:24.045 ","End":"00:27.045","Text":"The third answer is water accumulation,"},{"Start":"00:27.045 ","End":"00:31.230","Text":"and the fourth answer is carbon dioxide depletion."},{"Start":"00:31.230 ","End":"00:35.600","Text":"In order to understand this question better and find the answer to it,"},{"Start":"00:35.600 ","End":"00:39.025","Text":"let\u0027s quickly review the 2 parts of photosynthesis."},{"Start":"00:39.025 ","End":"00:40.895","Text":"In the first part of photosynthesis,"},{"Start":"00:40.895 ","End":"00:43.715","Text":"known also as the light-dependent reactions,"},{"Start":"00:43.715 ","End":"00:46.535","Text":"solar energy is converted to chemical energy,"},{"Start":"00:46.535 ","End":"00:50.795","Text":"creating energy rich ADP molecules and another phosphate group"},{"Start":"00:50.795 ","End":"00:55.445","Text":"and charging NADP plus molecules with electrons."},{"Start":"00:55.445 ","End":"00:57.515","Text":"In order to get these electrons,"},{"Start":"00:57.515 ","End":"00:59.270","Text":"water molecules are taken apart leaving"},{"Start":"00:59.270 ","End":"01:02.830","Text":"oxygen as a by-product of the light-dependent reactions."},{"Start":"01:02.830 ","End":"01:04.610","Text":"The second set of reactions,"},{"Start":"01:04.610 ","End":"01:08.510","Text":"the light-independent reactions, also known as the Calvin cycle."},{"Start":"01:08.510 ","End":"01:13.220","Text":"The ATP molecules and the NADPH molecules are used to"},{"Start":"01:13.220 ","End":"01:18.590","Text":"fix carbon from atmospheric carbon dioxide molecules to sugars."},{"Start":"01:18.590 ","End":"01:22.655","Text":"In this process, the ATP molecules lose a phosphate group,"},{"Start":"01:22.655 ","End":"01:26.090","Text":"and we now have ADP molecules with 2 phosphate groups"},{"Start":"01:26.090 ","End":"01:29.795","Text":"only instead of 3 and an extra phosphate group,"},{"Start":"01:29.795 ","End":"01:32.765","Text":"which will again be recycled in the light reactions."},{"Start":"01:32.765 ","End":"01:37.790","Text":"The NADPH loses its electrons and also a hydrogen atom,"},{"Start":"01:37.790 ","End":"01:40.392","Text":"and we get NADP plus."},{"Start":"01:40.392 ","End":"01:43.160","Text":"Again, recycled in the light reactions."},{"Start":"01:43.160 ","End":"01:45.650","Text":"In our hypothetical scenario,"},{"Start":"01:45.650 ","End":"01:49.475","Text":"this part, the light-independent reaction is not working."},{"Start":"01:49.475 ","End":"01:51.790","Text":"Therefore, what will happen?"},{"Start":"01:51.790 ","End":"01:55.610","Text":"I could assume that the ATP and NADPH formed in"},{"Start":"01:55.610 ","End":"01:58.400","Text":"the light-dependent reactions would not be used by"},{"Start":"01:58.400 ","End":"02:02.750","Text":"the Calvin cycle and would not be returned to be recycled."},{"Start":"02:02.750 ","End":"02:04.190","Text":"It will just accumulate. We would get"},{"Start":"02:04.190 ","End":"02:10.260","Text":"more and more and more ATP and more and more NADPH,"},{"Start":"02:10.260 ","End":"02:12.480","Text":"which would not be used at all anywhere."},{"Start":"02:12.480 ","End":"02:14.030","Text":"Let\u0027s have a look at our answers now."},{"Start":"02:14.030 ","End":"02:19.325","Text":"Answer a tells us that we would get an accumulation of G3P but wait, what is G3P?"},{"Start":"02:19.325 ","End":"02:21.920","Text":"We don\u0027t have G3P in this diagram at all."},{"Start":"02:21.920 ","End":"02:25.100","Text":"Let\u0027s zoom into the Calvin cycle,"},{"Start":"02:25.100 ","End":"02:27.140","Text":"where we see the carbon is fixed,"},{"Start":"02:27.140 ","End":"02:29.330","Text":"goes through a series of reactions,"},{"Start":"02:29.330 ","End":"02:31.550","Text":"eventually ending up in G3P,"},{"Start":"02:31.550 ","End":"02:33.775","Text":"which is a 3-carbon molecule."},{"Start":"02:33.775 ","End":"02:37.680","Text":"This 3-carbon molecule, if we use 2 of them,"},{"Start":"02:37.680 ","End":"02:43.625","Text":"can be used to form 1 glucose molecule which needs 6 carbons."},{"Start":"02:43.625 ","End":"02:50.075","Text":"Other G3P molecules are used in the Calvin cycle again in order to fix new carbon atoms."},{"Start":"02:50.075 ","End":"02:52.340","Text":"Since we\u0027re talking about a scenario where"},{"Start":"02:52.340 ","End":"02:56.495","Text":"the enzymes in the Calvin cycle don\u0027t work at all in response to light,"},{"Start":"02:56.495 ","End":"02:59.450","Text":"we would not expect a buildup of G3P."},{"Start":"02:59.450 ","End":"03:03.470","Text":"We could cross out answer a and get back to our big diagram,"},{"Start":"03:03.470 ","End":"03:08.435","Text":"where our answer b tells us that ATP and NADPH would accumulate,"},{"Start":"03:08.435 ","End":"03:10.855","Text":"which is in fact what we predicted right now."},{"Start":"03:10.855 ","End":"03:12.980","Text":"Let\u0027s leave this answer aside and just have a look at"},{"Start":"03:12.980 ","End":"03:15.740","Text":"the other answers before choosing our correct answer."},{"Start":"03:15.740 ","End":"03:21.380","Text":"Answer c says that water would accumulate but since in our theoretical scenario,"},{"Start":"03:21.380 ","End":"03:25.100","Text":"the light-dependent reactions are continuing to work."},{"Start":"03:25.100 ","End":"03:27.530","Text":"We would not expect water to accumulate."},{"Start":"03:27.530 ","End":"03:32.025","Text":"It would continuously be taken apart to get more electrons."},{"Start":"03:32.025 ","End":"03:35.030","Text":"Water would not accumulate and we can cross out answer c. Answer d"},{"Start":"03:35.030 ","End":"03:41.300","Text":"states that we would expect a carbon dioxide depletion but since again,"},{"Start":"03:41.300 ","End":"03:43.565","Text":"this whole reaction here is not working,"},{"Start":"03:43.565 ","End":"03:46.955","Text":"there\u0027s no reason that carbon dioxide would be used at all."},{"Start":"03:46.955 ","End":"03:50.960","Text":"In fact, we wouldn\u0027t expect to see any drop in levels of carbon dioxide."},{"Start":"03:50.960 ","End":"03:56.460","Text":"We could cross our answer d and mark answer b as our correct answer."}],"ID":28121},{"Watched":false,"Name":"Exercise 6","Duration":"10m 9s","ChapterTopicVideoID":27006,"CourseChapterTopicPlaylistID":136377,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:07.260","Text":"What is true about both NADPH and G3P molecules produced during photosynthesis?"},{"Start":"00:07.260 ","End":"00:11.910","Text":"A, they are both end products of photosynthesis, B,"},{"Start":"00:11.910 ","End":"00:15.675","Text":"they are both substrates for photosynthesis, C,"},{"Start":"00:15.675 ","End":"00:19.230","Text":"they are both produced from carbon dioxide or D,"},{"Start":"00:19.230 ","End":"00:22.485","Text":"they both store energy in chemical bonds."},{"Start":"00:22.485 ","End":"00:25.605","Text":"Let\u0027s have a look at these answers before we start."},{"Start":"00:25.605 ","End":"00:29.130","Text":"What are NADPH and G3P molecules?"},{"Start":"00:29.130 ","End":"00:31.770","Text":"Let\u0027s have an overview of photosynthesis."},{"Start":"00:31.770 ","End":"00:35.462","Text":"Photosynthesis is divided into 2 main stages."},{"Start":"00:35.462 ","End":"00:38.645","Text":"In the first stage, the light-dependent reactions,"},{"Start":"00:38.645 ","End":"00:41.690","Text":"solar energy is converted to chemical energy to"},{"Start":"00:41.690 ","End":"00:45.740","Text":"produce the highly energized ATP molecules and"},{"Start":"00:45.740 ","End":"00:49.370","Text":"the electron carrier NADPH are used in a series of"},{"Start":"00:49.370 ","End":"00:53.360","Text":"reactions to take apart carbon dioxide molecules,"},{"Start":"00:53.360 ","End":"00:57.985","Text":"which is made of a carbon atom connected to 2 oxygen atoms."},{"Start":"00:57.985 ","End":"01:03.077","Text":"These carbons are taken away from the carbon dioxide molecule"},{"Start":"01:03.077 ","End":"01:08.165","Text":"and eventually they\u0027re fixed to form glucose, sugar."},{"Start":"01:08.165 ","End":"01:10.700","Text":"This is called carbon fixation."},{"Start":"01:10.700 ","End":"01:13.955","Text":"We can already see the NADPH that we\u0027ve been asked about."},{"Start":"01:13.955 ","End":"01:17.720","Text":"It\u0027s an electron carrier carrying electrons from"},{"Start":"01:17.720 ","End":"01:22.265","Text":"the light reactions to the Calvin cycle. What is G3P?"},{"Start":"01:22.265 ","End":"01:26.840","Text":"To see the G3P let\u0027s have a closer look at the Calvin cycle."},{"Start":"01:26.840 ","End":"01:32.660","Text":"Here\u0027s a G3P, glyceraldehyde-3-phosphate."},{"Start":"01:32.660 ","End":"01:36.530","Text":"When a carbon atom is taken from the carbon dioxide it\u0027s fixed onto"},{"Start":"01:36.530 ","End":"01:40.790","Text":"a 5 carbon molecule to get a 6 carbon molecule,"},{"Start":"01:40.790 ","End":"01:47.310","Text":"1,2,3,4,5,6, which is then taken apart to 2,3 carbon molecules."},{"Start":"01:47.310 ","End":"01:51.180","Text":"They get phosphorylated as you can see and it goes on."},{"Start":"01:51.180 ","End":"01:55.655","Text":"The end product for the Calvin cycle was glyceraldehyde-3-phosphate."},{"Start":"01:55.655 ","End":"01:59.180","Text":"The G3P, a 3-carbon molecule can either be"},{"Start":"01:59.180 ","End":"02:03.135","Text":"used to produce glucose or other organic compounds."},{"Start":"02:03.135 ","End":"02:09.755","Text":"But 5 out of 6 G3P molecules that are produced are not used to make glucose,"},{"Start":"02:09.755 ","End":"02:13.100","Text":"rather they stay in the Calvin cycle to reproduce"},{"Start":"02:13.100 ","End":"02:18.300","Text":"that 5 carbon molecule used again to fix the 1 carbon atom,"},{"Start":"02:18.300 ","End":"02:21.485","Text":"and so the cycle continues."},{"Start":"02:21.485 ","End":"02:23.705","Text":"Where is the G3P here?"},{"Start":"02:23.705 ","End":"02:26.428","Text":"The G3P is produced in the Calvin cycle."},{"Start":"02:26.428 ","End":"02:28.015","Text":"Then some of it,"},{"Start":"02:28.015 ","End":"02:33.020","Text":"1 out of 6 are exported to produce sugar or other organic molecules"},{"Start":"02:33.020 ","End":"02:38.720","Text":"while 5 out of 6 of these remain in the Calvin cycle and are reused."},{"Start":"02:38.720 ","End":"02:41.080","Text":"Now, let\u0027s have a look at our answers."},{"Start":"02:41.080 ","End":"02:46.190","Text":"A, they are both end products of photosynthesis. Let\u0027s have a look at that."},{"Start":"02:46.190 ","End":"02:50.865","Text":"G3P is indeed an end product."},{"Start":"02:50.865 ","End":"02:58.835","Text":"The NADPH even though it might be one of the end products of the light reactions,"},{"Start":"02:58.835 ","End":"03:01.835","Text":"it\u0027s certainly not the end product of photosynthesis,"},{"Start":"03:01.835 ","End":"03:09.065","Text":"which is G3P or glucose or any other organic compounds produced from G3P and therefore,"},{"Start":"03:09.065 ","End":"03:11.150","Text":"we can cross out answer A."},{"Start":"03:11.150 ","End":"03:17.135","Text":"B, they\u0027re both substrates for photosynthesis. Lets have a look."},{"Start":"03:17.135 ","End":"03:24.420","Text":"NADPH and G3P."},{"Start":"03:24.560 ","End":"03:27.650","Text":"The NADPH is it a substrate?"},{"Start":"03:27.650 ","End":"03:31.924","Text":"It\u0027s produced, but it\u0027s also used in Calvin cycle as a substrate."},{"Start":"03:31.924 ","End":"03:35.140","Text":"Is our G3P a substrate."},{"Start":"03:35.140 ","End":"03:37.940","Text":"Well, even though G3P is the end product,"},{"Start":"03:37.940 ","End":"03:41.330","Text":"it\u0027s also continuously used in the Calvin cycle,"},{"Start":"03:41.330 ","End":"03:43.730","Text":"so yes, it is a substrate."},{"Start":"03:43.730 ","End":"03:45.760","Text":"Answer B looks correct."},{"Start":"03:45.760 ","End":"03:49.970","Text":"Before we mark answer B as our answer let\u0027s just have a look at answer C and"},{"Start":"03:49.970 ","End":"03:55.130","Text":"D. Answer C states that they are both produced from carbon dioxide."},{"Start":"03:55.130 ","End":"03:58.230","Text":"Well, we\u0027ve seen that G3P,"},{"Start":"03:58.230 ","End":"04:03.119","Text":"a 3-carbon molecule is produced from the carbons extracted from carbon dioxide."},{"Start":"04:03.119 ","End":"04:06.600","Text":"For G3P that would be correct,"},{"Start":"04:06.600 ","End":"04:09.480","Text":"but what about NADPH?"},{"Start":"04:09.480 ","End":"04:12.680","Text":"The NADPH molecule is produced in"},{"Start":"04:12.680 ","End":"04:18.043","Text":"the light reactions and it does not use carbon dioxide. This will be wrong."},{"Start":"04:18.043 ","End":"04:23.975","Text":"We can cross out answer C. Answer D says that they both store energy in chemical bonds."},{"Start":"04:23.975 ","End":"04:29.090","Text":"Sugar and G3P for that matter sure do store energy in their chemical bonds."},{"Start":"04:29.090 ","End":"04:33.050","Text":"When they\u0027re taken apart these chemical bonds give their energy in"},{"Start":"04:33.050 ","End":"04:37.775","Text":"the mitochondria to produce ATP in all their eukaryotic cells."},{"Start":"04:37.775 ","End":"04:42.680","Text":"That would be correct for G3P."},{"Start":"04:42.680 ","End":"04:44.695","Text":"What about NADPH?"},{"Start":"04:44.695 ","End":"04:47.288","Text":"NADPH is an electron carrier."},{"Start":"04:47.288 ","End":"04:51.875","Text":"It carries 2 excited electrons in a higher energy state."},{"Start":"04:51.875 ","End":"04:54.590","Text":"; Later on these electrons are handed over to"},{"Start":"04:54.590 ","End":"04:59.045","Text":"different atoms where they reside in a lower energetic state."},{"Start":"04:59.045 ","End":"05:02.990","Text":"The energy stored in NADPH is not in the chemical bonds,"},{"Start":"05:02.990 ","End":"05:06.004","Text":"rather in the excited state of its electrons."},{"Start":"05:06.004 ","End":"05:09.590","Text":"They both store energy in chemical bonds is"},{"Start":"05:09.590 ","End":"05:14.510","Text":"a wrong answer and we can now proceed to mark answer B as a correct answer."},{"Start":"05:14.510 ","End":"05:17.810","Text":"NADPH and G3P molecules that are produced during"},{"Start":"05:17.810 ","End":"05:22.565","Text":"photosynthesis are both also substrates for photosynthesis."},{"Start":"05:22.565 ","End":"05:24.200","Text":"This is the correct answer."},{"Start":"05:24.200 ","End":"05:24.201","Text":"NADPH is an electron carrier."},{"Start":"05:24.201 ","End":"05:24.202","Text":"It carries 2 excited electrons in a higher energy state and then later on these electrons"},{"Start":"05:24.202 ","End":"05:24.203","Text":"are handed over to"},{"Start":"05:24.203 ","End":"05:24.204","Text":"different atoms where they"},{"Start":"05:24.204 ","End":"05:24.205","Text":"reside in a lower energetic state."},{"Start":"05:24.205 ","End":"05:24.206","Text":"The energy stored in NADPH is not in the chemical bonds rather in"},{"Start":"05:24.206 ","End":"05:24.207","Text":"the excited state of its electrons."},{"Start":"05:24.207 ","End":"05:24.208","Text":"They both energy in the chemical bonds is the wrong answer and we can now proceed"},{"Start":"05:24.208 ","End":"05:24.209","Text":"to mark answer B"},{"Start":"05:24.209 ","End":"05:24.210","Text":"as a correct answer."},{"Start":"05:24.210 ","End":"05:24.211","Text":"NADPH and G3P molecules that are produced during photosynthesis"},{"Start":"05:24.211 ","End":"05:24.212","Text":"are both substrates of photosynthesis."},{"Start":"05:24.212 ","End":"05:25.200","Text":"This is the correct answer."}],"ID":28122},{"Watched":false,"Name":"Exercise 7","Duration":"3m 39s","ChapterTopicVideoID":27007,"CourseChapterTopicPlaylistID":136377,"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":"Which of the following structures is not a component of a photosystem?"},{"Start":"00:05.010 ","End":"00:08.070","Text":"A, ATP synthase."},{"Start":"00:08.070 ","End":"00:10.830","Text":"B, antenna pigment."},{"Start":"00:10.830 ","End":"00:13.259","Text":"C, reaction center."},{"Start":"00:13.259 ","End":"00:16.275","Text":"Or d, primary electron acceptor."},{"Start":"00:16.275 ","End":"00:18.255","Text":"In order to answer this question,"},{"Start":"00:18.255 ","End":"00:20.580","Text":"let\u0027s have a look at the light-dependent reactions of"},{"Start":"00:20.580 ","End":"00:24.210","Text":"photosynthesis that includes 2 photosystems,"},{"Start":"00:24.210 ","End":"00:27.690","Text":"photosystem 2 and photosystem 1."},{"Start":"00:27.690 ","End":"00:30.990","Text":"Photosystem 2 absorbs energy from sunlight."},{"Start":"00:30.990 ","End":"00:35.390","Text":"The energy from this excited electron passes from pigment, to pigment,"},{"Start":"00:35.390 ","End":"00:37.895","Text":"to pigment, to pigment like a volleyball,"},{"Start":"00:37.895 ","End":"00:40.355","Text":"until it reaches the reaction center."},{"Start":"00:40.355 ","End":"00:45.575","Text":"Here the excited electron is accepted by the primary electron acceptor,"},{"Start":"00:45.575 ","End":"00:51.785","Text":"moving through the electron transport chain while pumping protons through the membrane."},{"Start":"00:51.785 ","End":"00:53.930","Text":"When reaching photosystem 1."},{"Start":"00:53.930 ","End":"00:56.090","Text":"Again, energy absorbed from"},{"Start":"00:56.090 ","End":"00:59.300","Text":"the light is bounced from pigment, to pigment, to pigment,"},{"Start":"00:59.300 ","End":"01:02.480","Text":"to pigment until it reaches the reaction center where"},{"Start":"01:02.480 ","End":"01:06.530","Text":"the electron is again accepted by the primary electron acceptor,"},{"Start":"01:06.530 ","End":"01:10.430","Text":"eventually accepted by an NADP plus electron carrier,"},{"Start":"01:10.430 ","End":"01:13.100","Text":"reducing it to NADPH."},{"Start":"01:13.100 ","End":"01:19.645","Text":"Now the 2 electrons together with a proton are needed to reduce NADP plus to NADPH."},{"Start":"01:19.645 ","End":"01:23.030","Text":"Then now, high concentration of protons within"},{"Start":"01:23.030 ","End":"01:27.365","Text":"the membrane pushes its way out through ATP synthase."},{"Start":"01:27.365 ","End":"01:30.620","Text":"The energy from this flow of protons is used to add"},{"Start":"01:30.620 ","End":"01:34.970","Text":"a third phosphate group to ADP with 2 phosphate groups,"},{"Start":"01:34.970 ","End":"01:39.035","Text":"turning it now to a highly energized ATP molecule."},{"Start":"01:39.035 ","End":"01:46.205","Text":"The NADPH electron carriers and the ATP molecules will now move on to the Calvin cycle,"},{"Start":"01:46.205 ","End":"01:49.785","Text":"the light independent reactions in order to form sugar."},{"Start":"01:49.785 ","End":"01:52.370","Text":"Let\u0027s have a look at these structures now and see which"},{"Start":"01:52.370 ","End":"01:54.830","Text":"of them is not a component of a photosystem."},{"Start":"01:54.830 ","End":"01:56.780","Text":"The first answer, ATP synthase,"},{"Start":"01:56.780 ","End":"01:58.145","Text":"as we can see here,"},{"Start":"01:58.145 ","End":"02:00.305","Text":"is actually, as we noted,"},{"Start":"02:00.305 ","End":"02:04.100","Text":"very much like a water wheel using the flow of protons"},{"Start":"02:04.100 ","End":"02:08.090","Text":"to produce highly energized ATP molecules."},{"Start":"02:08.090 ","End":"02:12.715","Text":"This is not part of photosystem 2 or photosystem 1."},{"Start":"02:12.715 ","End":"02:16.040","Text":"Therefore, ATP synthase looks like a good candidate for"},{"Start":"02:16.040 ","End":"02:20.585","Text":"the right answer of a structure that is not a component of a photosystem."},{"Start":"02:20.585 ","End":"02:22.655","Text":"But before we choose this answer,"},{"Start":"02:22.655 ","End":"02:24.470","Text":"let\u0027s have a look at the other options."},{"Start":"02:24.470 ","End":"02:26.030","Text":"What\u0027s an antenna pigment?"},{"Start":"02:26.030 ","End":"02:31.354","Text":"As you recall, we spoke about the light energy exciting electrons and pigment molecules."},{"Start":"02:31.354 ","End":"02:35.045","Text":"As the excited electron returns to its low energy state,"},{"Start":"02:35.045 ","End":"02:37.894","Text":"the energy is used to excite another electron,"},{"Start":"02:37.894 ","End":"02:42.095","Text":"which in turn sends energy to excite another electron,"},{"Start":"02:42.095 ","End":"02:45.980","Text":"and as it returns, it uses the energy to excite another electron."},{"Start":"02:45.980 ","End":"02:50.825","Text":"All these pigments are also known as antenna pigments."},{"Start":"02:50.825 ","End":"02:53.390","Text":"Their job is to absorb the photon from"},{"Start":"02:53.390 ","End":"02:56.645","Text":"the sunlight and move it all to the reaction center."},{"Start":"02:56.645 ","End":"03:01.190","Text":"The antenna pigment is part of photosystem and you can cross it out."},{"Start":"03:01.190 ","End":"03:05.090","Text":"This energy is eventually moved to the reaction center,"},{"Start":"03:05.090 ","End":"03:08.455","Text":"which is also part of the photosystem and therefore can be crossed out as well."},{"Start":"03:08.455 ","End":"03:10.535","Text":"Contrary to the antenna pigments,"},{"Start":"03:10.535 ","End":"03:13.025","Text":"which mood energy from 1 another,"},{"Start":"03:13.025 ","End":"03:15.979","Text":"the electron from the reaction center, chlorophyll,"},{"Start":"03:15.979 ","End":"03:20.405","Text":"does not return to its steady state in the same chlorophyll, rather,"},{"Start":"03:20.405 ","End":"03:23.270","Text":"it moves on to the primary electron acceptor"},{"Start":"03:23.270 ","End":"03:26.960","Text":"where it will continue its way through the electron transport chain."},{"Start":"03:26.960 ","End":"03:31.550","Text":"The primary electron acceptor is also part of the photosystem,"},{"Start":"03:31.550 ","End":"03:35.765","Text":"whether it\u0027s photosystem 2 or photosystem 1 and we can cross it out."},{"Start":"03:35.765 ","End":"03:40.719","Text":"Our correct answer would be A, ATP synthase."}],"ID":28123},{"Watched":false,"Name":"Exercise 8","Duration":"2m 11s","ChapterTopicVideoID":26998,"CourseChapterTopicPlaylistID":136377,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:06.775","Text":"From which component of the light-dependent reaction does NADPH form most directly?"},{"Start":"00:06.775 ","End":"00:10.075","Text":"A, photosystem II."},{"Start":"00:10.075 ","End":"00:13.080","Text":"B, photosystem I."},{"Start":"00:13.080 ","End":"00:15.930","Text":"C, cytochrome complex."},{"Start":"00:15.930 ","End":"00:18.735","Text":"Or d, ATP synthase."},{"Start":"00:18.735 ","End":"00:22.905","Text":"Let\u0027s have a look at these 4 components and their place in the light-dependent reactions."},{"Start":"00:22.905 ","End":"00:26.220","Text":"The light-dependent reactions include these components,"},{"Start":"00:26.220 ","End":"00:29.505","Text":"photosystem II and photosystem I."},{"Start":"00:29.505 ","End":"00:33.180","Text":"The electron transport chain that connects between them"},{"Start":"00:33.180 ","End":"00:37.350","Text":"including the cytochrome complex,1 of the many proteins that"},{"Start":"00:37.350 ","End":"00:40.665","Text":"passes the electrons between the photosystems and"},{"Start":"00:40.665 ","End":"00:44.180","Text":"ATP synthase which harnesses the energy from the flow of"},{"Start":"00:44.180 ","End":"00:46.490","Text":"protons in order to energize"},{"Start":"00:46.490 ","End":"00:52.385","Text":"ADP molecules to ATP molecules by adding another phosphate group."},{"Start":"00:52.385 ","End":"00:54.800","Text":"NADPH, an electron carrier,"},{"Start":"00:54.800 ","End":"00:58.490","Text":"is formed after electrons stripped from water molecules by"},{"Start":"00:58.490 ","End":"01:02.900","Text":"photolysis are carried through both photosystems and"},{"Start":"01:02.900 ","End":"01:07.250","Text":"the electron transport chain and eventually are used to reduce NADP"},{"Start":"01:07.250 ","End":"01:11.840","Text":"plus molecules to NADPH molecules carrying 2 electrons."},{"Start":"01:11.840 ","End":"01:14.010","Text":"Let\u0027s have a look at the answers now."},{"Start":"01:14.010 ","End":"01:18.080","Text":"Photosystem II is involved in producing NADPH,"},{"Start":"01:18.080 ","End":"01:20.465","Text":"but photosystem I, since you\u0027re asked,"},{"Start":"01:20.465 ","End":"01:24.200","Text":"is even more directly connected to it since this reaction"},{"Start":"01:24.200 ","End":"01:28.640","Text":"takes place at the end of the process of photosystem I."},{"Start":"01:28.640 ","End":"01:31.145","Text":"We can really cross out photosystem II."},{"Start":"01:31.145 ","End":"01:35.210","Text":"Let\u0027s have a look at answers c and d to see if any of them are more"},{"Start":"01:35.210 ","End":"01:39.360","Text":"closely related to NADPH production than photosystem I."},{"Start":"01:39.360 ","End":"01:42.200","Text":"C, the cytochrome complex is part of"},{"Start":"01:42.200 ","End":"01:45.695","Text":"the electron transport chain as we mentioned earlier and therefore,"},{"Start":"01:45.695 ","End":"01:47.735","Text":"it is not more closely related to"},{"Start":"01:47.735 ","End":"01:51.875","Text":"NADPH formation than photosystem I and it can be crossed out."},{"Start":"01:51.875 ","End":"01:55.430","Text":"D, regarding ATP synthase is not connected at"},{"Start":"01:55.430 ","End":"01:59.715","Text":"all to NADPH production rather to the production of ATP."},{"Start":"01:59.715 ","End":"02:02.170","Text":"ATP synthase, answer d,"},{"Start":"02:02.170 ","End":"02:05.645","Text":"is also wrong and we can now mark the correct answer b,"},{"Start":"02:05.645 ","End":"02:11.700","Text":"photosystem I as the component that forms NADPH most directly."}],"ID":28124},{"Watched":false,"Name":"Exercise 9","Duration":"4m 50s","ChapterTopicVideoID":26999,"CourseChapterTopicPlaylistID":136377,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:02.940","Text":"Which molecule must enter the Calvin cycle"},{"Start":"00:02.940 ","End":"00:07.290","Text":"continually for the light-independent reactions to take place?"},{"Start":"00:07.290 ","End":"00:09.165","Text":"A, RuBisCO,"},{"Start":"00:09.165 ","End":"00:11.160","Text":"b, RuBP,"},{"Start":"00:11.160 ","End":"00:16.245","Text":"c, 3-PGA or d, carbon dioxide?"},{"Start":"00:16.245 ","End":"00:17.865","Text":"In order to answer this question,"},{"Start":"00:17.865 ","End":"00:19.725","Text":"let\u0027s have a look at the Calvin cycle,"},{"Start":"00:19.725 ","End":"00:22.920","Text":"also known as the light-independent reactions since"},{"Start":"00:22.920 ","End":"00:26.550","Text":"these reactions don\u0027t directly use the sunlight to energize them."},{"Start":"00:26.550 ","End":"00:29.850","Text":"In this figure, we can see an overview of the Calvin cycle,"},{"Start":"00:29.850 ","End":"00:35.280","Text":"where carbon atoms are stripped from carbon dioxide and fixed to organic molecules,"},{"Start":"00:35.280 ","End":"00:38.850","Text":"eventually leaving the cycle as G3P."},{"Start":"00:38.850 ","End":"00:42.390","Text":"Two of these molecules can form 1 molecule of glucose."},{"Start":"00:42.390 ","End":"00:45.950","Text":"All the G3P molecules continue in the Calvin cycle and are"},{"Start":"00:45.950 ","End":"00:50.675","Text":"used again to fix carbon from new carbon dioxide molecules."},{"Start":"00:50.675 ","End":"00:54.020","Text":"We can see where the carbon dioxide is involved in"},{"Start":"00:54.020 ","End":"00:57.215","Text":"this process but in order to see the other molecules,"},{"Start":"00:57.215 ","End":"00:59.615","Text":"let\u0027s zoom in to the Calvin cycle."},{"Start":"00:59.615 ","End":"01:03.275","Text":"Again, we see here the input of carbon dioxide molecules."},{"Start":"01:03.275 ","End":"01:09.740","Text":"The carbon atoms are stripped from carbon dioxide and fixed onto a 5-carbon molecule,"},{"Start":"01:09.740 ","End":"01:11.780","Text":"forming a 6-carbon molecule,"},{"Start":"01:11.780 ","End":"01:15.755","Text":"eventually forming G3P, a 3-carbon molecule,"},{"Start":"01:15.755 ","End":"01:17.840","Text":"which to them can form glucose,"},{"Start":"01:17.840 ","End":"01:21.110","Text":"which is a 6-carbon molecule and then recycled to once"},{"Start":"01:21.110 ","End":"01:25.160","Text":"again fix the carbon atoms from the carbon dioxide molecules."},{"Start":"01:25.160 ","End":"01:28.995","Text":"Here, we can see RuBisCO from answer a,"},{"Start":"01:28.995 ","End":"01:31.215","Text":"RuBP from answer b,"},{"Start":"01:31.215 ","End":"01:36.485","Text":"and 3-PGA from answer c. Since we are looking at this process by order,"},{"Start":"01:36.485 ","End":"01:39.380","Text":"let\u0027s have a look at these 3 molecules by their order in"},{"Start":"01:39.380 ","End":"01:42.545","Text":"the process rather than by their order in the question."},{"Start":"01:42.545 ","End":"01:45.680","Text":"The first molecule is 3-PGA,"},{"Start":"01:45.680 ","End":"01:47.415","Text":"or in it\u0027s long form,"},{"Start":"01:47.415 ","End":"01:52.710","Text":"3-phosphoglycerate or 3-phosphoglyceric acid which gives us"},{"Start":"01:52.710 ","End":"01:58.780","Text":"the phosphoglyceric acid or in its long form, 3-phosphoglyceric acid."},{"Start":"02:02.630 ","End":"02:04.860","Text":"This, as we can see,"},{"Start":"02:04.860 ","End":"02:06.620","Text":"is a 3-carbon molecule."},{"Start":"02:06.620 ","End":"02:12.125","Text":"It\u0027s formed after the 1 carbon from carbon dioxide is fixed onto a 5-carbon molecule,"},{"Start":"02:12.125 ","End":"02:16.975","Text":"forming a 6-carbon molecule with 2 phosphate groups from each side."},{"Start":"02:16.975 ","End":"02:20.900","Text":"This 6-carbon molecule is less stable and is quickly taken apart"},{"Start":"02:20.900 ","End":"02:25.130","Text":"to 2 3-carbon molecules with 1 phosphate group on each side."},{"Start":"02:25.130 ","End":"02:27.390","Text":"This is a 3-PGA."},{"Start":"02:27.390 ","End":"02:29.075","Text":"As we go around our cycle,"},{"Start":"02:29.075 ","End":"02:32.490","Text":"we\u0027ll meet the next answer, RuBP."},{"Start":"02:39.860 ","End":"02:45.690","Text":"Known as ribulose1, 5 bisphosphate RUBP."},{"Start":"02:45.690 ","End":"02:47.625","Text":"This, as mentioned earlier,"},{"Start":"02:47.625 ","End":"02:54.045","Text":"is a molecule with a backbone of 5 carbon atoms and it has 2 phosphate groups."},{"Start":"02:54.045 ","End":"03:00.190","Text":"Therefore, bi, meaning 2 bisphosphate and it\u0027s to this molecule"},{"Start":"03:00.190 ","End":"03:03.070","Text":"that the 1 carbon atoms stripped from"},{"Start":"03:03.070 ","End":"03:08.150","Text":"carbon dioxide is fixed onto using the enzyme RuBisCo"},{"Start":"03:16.310 ","End":"03:19.350","Text":"or its full form, ribulose1,"},{"Start":"03:19.350 ","End":"03:23.640","Text":"5 bisphosphate carboxylase oxygenase, RuBisCo."},{"Start":"03:23.640 ","End":"03:25.065","Text":"This enzyme, as said,"},{"Start":"03:25.065 ","End":"03:29.785","Text":"fixes the 6th carbon molecule onto the ribulose1, 5 bisphosphate."},{"Start":"03:29.785 ","End":"03:31.895","Text":"Now that we\u0027ve seen all these molecules,"},{"Start":"03:31.895 ","End":"03:33.485","Text":"let\u0027s start answering the question."},{"Start":"03:33.485 ","End":"03:35.750","Text":"Which molecule must enter the Calvin cycle"},{"Start":"03:35.750 ","End":"03:39.660","Text":"continually for the light-independent reactions take place?"},{"Start":"03:44.120 ","End":"03:47.285","Text":"Answer a, RuBisCo is an enzyme."},{"Start":"03:47.285 ","End":"03:49.700","Text":"Since enzymes by definition are not"},{"Start":"03:49.700 ","End":"03:53.450","Text":"altered during the processes that they catalyze, RuBisCo,"},{"Start":"03:53.450 ","End":"03:55.340","Text":"at least in the short-term,"},{"Start":"03:55.340 ","End":"04:00.560","Text":"should not run out and does not need to be continually fed to this process."},{"Start":"04:00.560 ","End":"04:02.539","Text":"We could cross that answer a."},{"Start":"04:02.539 ","End":"04:05.220","Text":"Answer b, ribulose1,"},{"Start":"04:05.220 ","End":"04:09.200","Text":"5 phosphate is actually made in the process itself."},{"Start":"04:09.200 ","End":"04:12.200","Text":"Therefore, it too does not need to be continually"},{"Start":"04:12.200 ","End":"04:15.410","Text":"supplied from outer sources to this process."},{"Start":"04:15.410 ","End":"04:19.445","Text":"Answer c, 3-PGA, the phosphoglyceric acid"},{"Start":"04:19.445 ","End":"04:23.785","Text":"is also formed in the process itself and does not need to be supplied."},{"Start":"04:23.785 ","End":"04:28.160","Text":"At this point, we can cross out answers a, b,"},{"Start":"04:28.160 ","End":"04:30.220","Text":"and c. Our answer d,"},{"Start":"04:30.220 ","End":"04:33.950","Text":"carbon dioxide is continually fed into the Calvin cycle."},{"Start":"04:33.950 ","End":"04:37.084","Text":"If we were to stop the input of carbon dioxide,"},{"Start":"04:37.084 ","End":"04:40.310","Text":"the Calvin cycle would not be able to continue and therefore,"},{"Start":"04:40.310 ","End":"04:44.900","Text":"our correct answer is answer d. Carbon dioxide is the molecule"},{"Start":"04:44.900 ","End":"04:50.790","Text":"which must continually enter the Calvin cycle for the reactions to take place."}],"ID":28125},{"Watched":false,"Name":"Exercise 10","Duration":"3m 13s","ChapterTopicVideoID":27000,"CourseChapterTopicPlaylistID":136377,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:02.070","Text":"Hey. In this question,"},{"Start":"00:02.070 ","End":"00:06.510","Text":"we\u0027re asked about an experiment with plants grown under different colored lights."},{"Start":"00:06.510 ","End":"00:09.615","Text":"Of course, in order for the experiment to be valid,"},{"Start":"00:09.615 ","End":"00:12.390","Text":"we must be speaking about the same plant species"},{"Start":"00:12.390 ","End":"00:15.660","Text":"run under the light for the same amount of time."},{"Start":"00:15.660 ","End":"00:19.575","Text":"The only difference is that Plant A is grown under a blue light,"},{"Start":"00:19.575 ","End":"00:25.065","Text":"Plant B is grown under a green light and Plant C is grown under an orange light."},{"Start":"00:25.065 ","End":"00:27.320","Text":"In this question, we\u0027re asked,"},{"Start":"00:27.320 ","End":"00:30.095","Text":"assuming the plants use only chlorophyll A,"},{"Start":"00:30.095 ","End":"00:33.485","Text":"B and carotenoids for photosynthesis."},{"Start":"00:33.485 ","End":"00:39.185","Text":"We are asked to predict the order of the plants from most growth to least growth."},{"Start":"00:39.185 ","End":"00:41.209","Text":"In order to answer this question,"},{"Start":"00:41.209 ","End":"00:46.985","Text":"we\u0027ll need to take a quick look at the absorption spectrum of these 3 pigments."},{"Start":"00:46.985 ","End":"00:49.115","Text":"As we can see here,"},{"Start":"00:49.115 ","End":"00:56.405","Text":"chlorophyll A absorbs both around blue-violet and around orange red."},{"Start":"00:56.405 ","End":"01:00.710","Text":"Though the absorbance is higher around the blue violet color."},{"Start":"01:00.710 ","End":"01:04.895","Text":"Chlorophyll A absorbs the most light from the blue wavelengths"},{"Start":"01:04.895 ","End":"01:10.465","Text":"and a little bit of the orange somewhere there between the yellow and the red."},{"Start":"01:10.465 ","End":"01:18.170","Text":"Carotenoids absorb only around the blue wavelengths and don\u0027t absorb it all in the green,"},{"Start":"01:18.170 ","End":"01:20.330","Text":"yellow, orange, or red."},{"Start":"01:20.330 ","End":"01:22.670","Text":"By looking at the absorption spectrum,"},{"Start":"01:22.670 ","End":"01:26.070","Text":"we can see right away that neither chlorophyll A,"},{"Start":"01:26.070 ","End":"01:30.005","Text":"nor chlorophyll B or carotenoids absorb green light,"},{"Start":"01:30.005 ","End":"01:33.020","Text":"and therefore we can predict that Plant B,"},{"Start":"01:33.020 ","End":"01:35.945","Text":"that\u0027s grown under the green light and therefore,"},{"Start":"01:35.945 ","End":"01:38.960","Text":"we can easily assume that the plant that will grow the"},{"Start":"01:38.960 ","End":"01:43.265","Text":"least will be Plant B that\u0027s grown under the green light."},{"Start":"01:43.265 ","End":"01:50.700","Text":"You can see here that the answer is B and D. We can observe the other answers B and"},{"Start":"01:50.700 ","End":"01:58.250","Text":"D state that the least grown plant will be Plant C. We can cross out answers B and D,"},{"Start":"01:58.250 ","End":"02:04.955","Text":"and we will remain with answers A and C that both give us B as the least grown plant."},{"Start":"02:04.955 ","End":"02:07.760","Text":"Our question is, who will grow faster?"},{"Start":"02:07.760 ","End":"02:13.115","Text":"Plant A under blue light or Plant C under orange light?"},{"Start":"02:13.115 ","End":"02:17.030","Text":"Answer A states that Plant A under blue light will grow"},{"Start":"02:17.030 ","End":"02:21.380","Text":"more than Plant C under red light and answer C states the opposite,"},{"Start":"02:21.380 ","End":"02:25.460","Text":"the plant grown under the red light will grow more than the plant that\u0027s in a blue light."},{"Start":"02:25.460 ","End":"02:30.785","Text":"Now, let\u0027s have another look at the absorption spectrum of the different pigments."},{"Start":"02:30.785 ","End":"02:32.600","Text":"As we noted before,"},{"Start":"02:32.600 ","End":"02:35.525","Text":"carotenoids only absorb blue purple light,"},{"Start":"02:35.525 ","End":"02:38.240","Text":"not at all, the orange area."},{"Start":"02:38.240 ","End":"02:42.380","Text":"We can see that both chlorophyll A and chlorophyll B absorb"},{"Start":"02:42.380 ","End":"02:47.750","Text":"more energy from light and wavelengths that look blue to our eyes,"},{"Start":"02:47.750 ","End":"02:51.095","Text":"then the wavelength that look orange to our eyes."},{"Start":"02:51.095 ","End":"02:54.245","Text":"Therefore, we can assume that the plant that\u0027s grown under blue light"},{"Start":"02:54.245 ","End":"02:57.850","Text":"will grow more than the plant that\u0027s grown on the orange light."},{"Start":"02:57.850 ","End":"03:00.730","Text":"The correct answer would not be answer C,"},{"Start":"03:00.730 ","End":"03:03.485","Text":"light plant will grow faster than the blue light plant,"},{"Start":"03:03.485 ","End":"03:06.985","Text":"we can cross that out and you can mark A as our right answer."},{"Start":"03:06.985 ","End":"03:12.940","Text":"Blue light, then orange light and last, green light."}],"ID":28126}],"Thumbnail":null,"ID":136377},{"Name":"Cell Communication","TopicPlaylistFirstVideoID":0,"Duration":null,"Videos":[{"Watched":false,"Name":"Cell communication intro","Duration":"1m 9s","ChapterTopicVideoID":27012,"CourseChapterTopicPlaylistID":261601,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:06.730","Text":"Hi. In this section we\u0027ll be introducing the concept of cell communication."},{"Start":"00:06.830 ","End":"00:10.050","Text":"As we all know, in the human society,"},{"Start":"00:10.050 ","End":"00:14.865","Text":"social organization is dependent on communication between the individuals."},{"Start":"00:14.865 ","End":"00:16.650","Text":"As is with people,"},{"Start":"00:16.650 ","End":"00:21.330","Text":"it is vital for individual cells to be able to interact with their environment."},{"Start":"00:21.330 ","End":"00:26.400","Text":"Cells developed communication mechanisms that can both receive and transfer"},{"Start":"00:26.400 ","End":"00:31.740","Text":"messages and produce changes within the cell in response to such messages."},{"Start":"00:31.740 ","End":"00:36.890","Text":"Multicellular organisms, cells send and receive chemical messages"},{"Start":"00:36.890 ","End":"00:43.175","Text":"constantly to coordinate the actions of distant organs, tissues, and cells."},{"Start":"00:43.175 ","End":"00:46.775","Text":"The ability to send messages quickly and efficiently"},{"Start":"00:46.775 ","End":"00:51.395","Text":"enables cells to coordinate and fine tune their functions."},{"Start":"00:51.395 ","End":"00:54.500","Text":"The efficient and relatively error-free function of"},{"Start":"00:54.500 ","End":"00:59.570","Text":"communication systems is vital for all life as we know it."},{"Start":"00:59.570 ","End":"01:01.685","Text":"In the following sections,"},{"Start":"01:01.685 ","End":"01:04.520","Text":"we\u0027ll learn all about cell communication in"},{"Start":"01:04.520 ","End":"01:09.750","Text":"both single-cell and multicellular organisms. I\u0027ll see you there."}],"ID":28136},{"Watched":false,"Name":"Methods of intracellular signaling","Duration":"8m 58s","ChapterTopicVideoID":27013,"CourseChapterTopicPlaylistID":261601,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:02.820","Text":"Hi, we\u0027re learning all about cell communication,"},{"Start":"00:02.820 ","End":"00:06.975","Text":"and in this section we\u0027ll be speaking about the methods of intracellular signaling."},{"Start":"00:06.975 ","End":"00:09.390","Text":"Intra meaning within,"},{"Start":"00:09.390 ","End":"00:12.585","Text":"in contrast to intercellular,"},{"Start":"00:12.585 ","End":"00:15.195","Text":"which inter means in between."},{"Start":"00:15.195 ","End":"00:18.885","Text":"Here we\u0027re speaking about the methods of intracellular signaling,"},{"Start":"00:18.885 ","End":"00:21.945","Text":"meaning the signaling within the cell."},{"Start":"00:21.945 ","End":"00:26.490","Text":"As we\u0027ve learned, there are 3 main steps in cellular signaling."},{"Start":"00:26.490 ","End":"00:31.695","Text":"The first step of reception is where the signaling molecule is received by the cell."},{"Start":"00:31.695 ","End":"00:36.090","Text":"The message is then moved through a protein pathway called transduction,"},{"Start":"00:36.090 ","End":"00:38.895","Text":"eventually leading to the cellular response."},{"Start":"00:38.895 ","End":"00:41.870","Text":"The induction of the signaling pathway depends on"},{"Start":"00:41.870 ","End":"00:45.260","Text":"modification of cellular components by enzymes."},{"Start":"00:45.260 ","End":"00:46.625","Text":"As you can see here,"},{"Start":"00:46.625 ","End":"00:50.525","Text":"there are numerous enzymatic modifications that can occur in this pathway."},{"Start":"00:50.525 ","End":"00:54.725","Text":"Each modification has to affect the next component downstream."},{"Start":"00:54.725 ","End":"00:56.390","Text":"Here in this example,"},{"Start":"00:56.390 ","End":"00:59.195","Text":"we have binding of the signaling molecule,"},{"Start":"00:59.195 ","End":"01:02.255","Text":"the epinephrine to the G-protein-coupled receptor."},{"Start":"01:02.255 ","End":"01:04.590","Text":"Epinephrine is also known as adrenaline."},{"Start":"01:04.590 ","End":"01:08.720","Text":"This hormone is involved in the flight or fight"},{"Start":"01:08.720 ","End":"01:13.460","Text":"response and it affects many pathways that could help in this situation."},{"Start":"01:13.460 ","End":"01:15.230","Text":"In this specific example,"},{"Start":"01:15.230 ","End":"01:18.440","Text":"the epinephrine is bound to a G-protein-coupled receptor,"},{"Start":"01:18.440 ","End":"01:21.270","Text":"also known as GPCR."},{"Start":"01:22.840 ","End":"01:26.475","Text":"GPC and R here."},{"Start":"01:26.475 ","End":"01:29.270","Text":"This receptor molecule, the GPCR,"},{"Start":"01:29.270 ","End":"01:32.640","Text":"goes right through the cellular membrane."},{"Start":"01:32.710 ","End":"01:36.680","Text":"On the outside it can connect to the signaling molecule,"},{"Start":"01:36.680 ","End":"01:40.670","Text":"the epinephrine, and on the inside it\u0027s connected to a G-protein."},{"Start":"01:40.670 ","End":"01:42.770","Text":"That\u0027s why it\u0027s a G-protein-coupled receptor."},{"Start":"01:42.770 ","End":"01:48.290","Text":"The G-protein is bound to a GMP molecule,"},{"Start":"01:48.290 ","End":"01:50.480","Text":"a guanine monophosphate, similar to"},{"Start":"01:50.480 ","End":"01:54.260","Text":"the ATP molecule that we know the cell uses as an energy source."},{"Start":"01:54.260 ","End":"01:57.805","Text":"Stripping 2 phosphate groups gives us the AMP."},{"Start":"01:57.805 ","End":"01:59.570","Text":"Instead of adenine triphosphate,"},{"Start":"01:59.570 ","End":"02:01.895","Text":"we get adenine monophosphate."},{"Start":"02:01.895 ","End":"02:03.550","Text":"Tri meaning 3,"},{"Start":"02:03.550 ","End":"02:05.805","Text":"and mono meaning 1."},{"Start":"02:05.805 ","End":"02:09.400","Text":"GMP is guanine monophosphate,"},{"Start":"02:09.400 ","End":"02:12.190","Text":"which means 1 phosphate group with"},{"Start":"02:12.190 ","End":"02:16.150","Text":"a G protein-coupled receptor can add 2 phosphate groups,"},{"Start":"02:16.150 ","End":"02:18.805","Text":"turning it to GTP."},{"Start":"02:18.805 ","End":"02:23.410","Text":"Now the inactive G protein that was bound to a GMP is bound to"},{"Start":"02:23.410 ","End":"02:28.885","Text":"a highly energized GTP molecule and it is now active leading to the next step,"},{"Start":"02:28.885 ","End":"02:30.020","Text":"leading to the next step,"},{"Start":"02:30.020 ","End":"02:31.243","Text":"leading to the next step,"},{"Start":"02:31.243 ","End":"02:32.373","Text":"leading to the next step,"},{"Start":"02:32.373 ","End":"02:38.710","Text":"leading to the next step and getting us a response of converting glycogen to glucose."},{"Start":"02:38.710 ","End":"02:42.250","Text":"Glycogen is a long-term energy storage form of glucose,"},{"Start":"02:42.250 ","End":"02:44.620","Text":"where many glucose molecules are attached to each other,"},{"Start":"02:44.620 ","End":"02:46.495","Text":"and although good for storage,"},{"Start":"02:46.495 ","End":"02:48.245","Text":"they cannot be accessed easily."},{"Start":"02:48.245 ","End":"02:50.885","Text":"So in this response to fight or flight,"},{"Start":"02:50.885 ","End":"02:53.795","Text":"the glycogen is now taken apart to glucose,"},{"Start":"02:53.795 ","End":"02:57.605","Text":"which could be used right away for the energy that the cell needs."},{"Start":"02:57.605 ","End":"02:59.525","Text":"We\u0027ve mentioned phosphorylation."},{"Start":"02:59.525 ","End":"03:02.975","Text":"Phosphorylation means the addition of a phosphate group to a molecule."},{"Start":"03:02.975 ","End":"03:07.339","Text":"We\u0027ve just seen the example of a G-protein bound to GMP,"},{"Start":"03:07.339 ","End":"03:09.845","Text":"which can be phosphorylated to GDP,"},{"Start":"03:09.845 ","End":"03:13.505","Text":"which means diphosphate or GTP, which means triphosphate."},{"Start":"03:13.505 ","End":"03:16.715","Text":"Di is 2 and tri is 3."},{"Start":"03:16.715 ","End":"03:19.010","Text":"Mono of course is 1."},{"Start":"03:19.010 ","End":"03:22.080","Text":"Again, we\u0027ve got our GPCR here,"},{"Start":"03:22.080 ","End":"03:24.545","Text":"and we\u0027ve got the inactive G-protein."},{"Start":"03:24.545 ","End":"03:28.835","Text":"Once the epinephrine is bound to the GPCR molecule,"},{"Start":"03:28.835 ","End":"03:30.935","Text":"we\u0027ve activated a G-protein,"},{"Start":"03:30.935 ","End":"03:38.210","Text":"activated all the transduction chain and eventually leading to a cellular response."},{"Start":"03:38.210 ","End":"03:41.165","Text":"Phosphates are also often added to serine,"},{"Start":"03:41.165 ","End":"03:44.285","Text":"threonine and tyrosine residues of proteins."},{"Start":"03:44.285 ","End":"03:47.977","Text":"As you remember, proteins are made of long chains of amino acids,"},{"Start":"03:47.977 ","End":"03:52.010","Text":"and the residues or the R groups of each amino acid is what"},{"Start":"03:52.010 ","End":"03:56.330","Text":"gives the amino acid its own chemical characteristics."},{"Start":"03:56.330 ","End":"03:59.690","Text":"Phosphates can be added to serine,"},{"Start":"03:59.690 ","End":"04:02.750","Text":"threonine or tyrosine residues of proteins."},{"Start":"04:02.750 ","End":"04:06.010","Text":"Then we\u0027ve got a charged phosphate group and"},{"Start":"04:06.010 ","End":"04:09.170","Text":"this changes the whole way that the protein works."},{"Start":"04:09.170 ","End":"04:13.805","Text":"The family of proteins that phosphorylate other proteins are called kinases."},{"Start":"04:13.805 ","End":"04:16.400","Text":"Each kinase is of course unique to"},{"Start":"04:16.400 ","End":"04:19.960","Text":"the certain protein or molecule that it phosphorylates."},{"Start":"04:19.960 ","End":"04:24.500","Text":"The phosphorylation itself can change the way the protein works,"},{"Start":"04:24.500 ","End":"04:27.815","Text":"either activating it or inactivating it."},{"Start":"04:27.815 ","End":"04:31.310","Text":"In order to reverse the effect and remove the phosphate group,"},{"Start":"04:31.310 ","End":"04:35.945","Text":"dephosphorylation is done by specific phosphatase enzymes,"},{"Start":"04:35.945 ","End":"04:38.750","Text":"which take the phosphate group off,"},{"Start":"04:38.750 ","End":"04:41.360","Text":"which can remove the phosphate group."},{"Start":"04:41.360 ","End":"04:43.850","Text":"Another group of important molecules for"},{"Start":"04:43.850 ","End":"04:47.405","Text":"intracellular signaling are the second messengers."},{"Start":"04:47.405 ","End":"04:49.850","Text":"These are small molecules that propagate"},{"Start":"04:49.850 ","End":"04:53.345","Text":"a signal after it has been initiated in the receptor."},{"Start":"04:53.345 ","End":"04:56.675","Text":"They help to spread the signal throughout the cytoplasm by"},{"Start":"04:56.675 ","End":"05:00.049","Text":"altering the behavior of different cellular proteins."},{"Start":"05:00.049 ","End":"05:05.060","Text":"Calcium ions and cyclic AMP are common second messengers."},{"Start":"05:05.060 ","End":"05:07.565","Text":"Let\u0027s speak first about the calcium ions."},{"Start":"05:07.565 ","End":"05:13.565","Text":"The concentration of calcium ions in the cytosol is normally very low inside the cell,"},{"Start":"05:13.565 ","End":"05:15.875","Text":"much lower than outside the cell."},{"Start":"05:15.875 ","End":"05:19.690","Text":"But still there are areas where it\u0027s concentrated inside the cell too,"},{"Start":"05:19.690 ","End":"05:21.785","Text":"and it\u0027s not let into the cytosol."},{"Start":"05:21.785 ","End":"05:23.240","Text":"A signal relayed by"},{"Start":"05:23.240 ","End":"05:28.235","Text":"a signal transduction pathway may trigger an increase in calcium in the cytosol."},{"Start":"05:28.235 ","End":"05:30.710","Text":"In a minute we\u0027ll see how that works."},{"Start":"05:30.710 ","End":"05:34.985","Text":"Many times,"},{"Start":"05:34.985 ","End":"05:40.730","Text":"pathways leading to the release of calcium involve inositol triphosphate known as IP3,"},{"Start":"05:40.730 ","End":"05:43.835","Text":"and diacylglycerol, known as DAG,"},{"Start":"05:43.835 ","End":"05:45.815","Text":"as additional second messengers."},{"Start":"05:45.815 ","End":"05:51.545","Text":"These 2 are produced by cleavage of a certain phospholipid and a plasma membrane."},{"Start":"05:51.545 ","End":"05:57.050","Text":"We\u0027ve got here our G-protein-coupled receptor the GPCR here,"},{"Start":"05:57.050 ","End":"06:00.725","Text":"phosphorylating the GMP to GTP,"},{"Start":"06:00.725 ","End":"06:03.195","Text":"thereby activating the G-protein."},{"Start":"06:03.195 ","End":"06:06.860","Text":"The activated G-protein activates phospholipase C,"},{"Start":"06:06.860 ","End":"06:08.585","Text":"which cleaves these molecules,"},{"Start":"06:08.585 ","End":"06:10.580","Text":"DAG and the IP3."},{"Start":"06:10.580 ","End":"06:16.520","Text":"In this example, although there\u0027s a low concentration of calcium ions in the cytosol,"},{"Start":"06:16.520 ","End":"06:21.860","Text":"they are concentrated very highly inside the endoplasmic reticulum lumen."},{"Start":"06:21.860 ","End":"06:25.040","Text":"The way for the calcium ions to leave"},{"Start":"06:25.040 ","End":"06:29.975","Text":"the endoplasmic reticulum into the cytoplasm is through these calcium channels."},{"Start":"06:29.975 ","End":"06:33.965","Text":"But the calcium channels are gated means that they have a gate that\u0027s closed."},{"Start":"06:33.965 ","End":"06:36.185","Text":"The molecule that activates,"},{"Start":"06:36.185 ","End":"06:39.590","Text":"the molecule that opens these gates is the IP3."},{"Start":"06:39.590 ","End":"06:45.200","Text":"So the message here that was sent used IP3 as a second messenger,"},{"Start":"06:45.200 ","End":"06:47.600","Text":"which now opens the calcium channels."},{"Start":"06:47.600 ","End":"06:51.199","Text":"These calcium ions activate various proteins,"},{"Start":"06:51.199 ","End":"06:54.455","Text":"leading to various cellular responses."},{"Start":"06:54.455 ","End":"06:57.110","Text":"We\u0027ve spoken about the calcium ions."},{"Start":"06:57.110 ","End":"06:59.420","Text":"Let\u0027s speak now about the cyclic AMP,"},{"Start":"06:59.420 ","End":"07:02.015","Text":"which is another widely used second messenger."},{"Start":"07:02.015 ","End":"07:07.115","Text":"Adenylyl cyclase, an enzyme in the plasma membrane converts ATP,"},{"Start":"07:07.115 ","End":"07:09.590","Text":"which is this highly energized molecule to"},{"Start":"07:09.590 ","End":"07:13.010","Text":"cyclic AMP in response to an extracellular signal."},{"Start":"07:13.010 ","End":"07:15.215","Text":"This is the adenylyl cyclase,"},{"Start":"07:15.215 ","End":"07:21.575","Text":"it clears off 2 of the phosphate groups"},{"Start":"07:21.575 ","End":"07:25.235","Text":"and makes this connection turning it to be a cyclic molecule."},{"Start":"07:25.235 ","End":"07:30.995","Text":"Other components of cyclic AMP pathways are G-proteins and protein kinases,"},{"Start":"07:30.995 ","End":"07:32.450","Text":"like the ones we just saw."},{"Start":"07:32.450 ","End":"07:34.639","Text":"Let\u0027s see an example for these pathways."},{"Start":"07:34.639 ","End":"07:36.755","Text":"So here again we have our GPCR."},{"Start":"07:36.755 ","End":"07:39.340","Text":"We can see it goes right through the membrane."},{"Start":"07:39.340 ","End":"07:42.260","Text":"On the outer area, it can connect to the first messenger,"},{"Start":"07:42.260 ","End":"07:45.905","Text":"which is the signaling molecule coming from outside of the cell."},{"Start":"07:45.905 ","End":"07:50.060","Text":"It activates the G-protein by phosphorylating the GMP to GTP."},{"Start":"07:50.060 ","End":"07:54.320","Text":"In this example, the G-protein activates the adenylyl cyclase."},{"Start":"07:54.320 ","End":"07:57.890","Text":"The adenylyl cyclase, as you\u0027ve just seen here,"},{"Start":"07:57.890 ","End":"08:02.015","Text":"converts the ATP to cAMP,"},{"Start":"08:02.015 ","End":"08:03.775","Text":"which is the second messenger."},{"Start":"08:03.775 ","End":"08:07.850","Text":"Cyclic AMP frequently activates protein kinase A,"},{"Start":"08:07.850 ","End":"08:10.235","Text":"which phosphorylates various other proteins."},{"Start":"08:10.235 ","End":"08:14.119","Text":"Now that we\u0027ve got a large number of cyclic AMP molecules in a cell,"},{"Start":"08:14.119 ","End":"08:16.985","Text":"they activate protein kinases,"},{"Start":"08:16.985 ","End":"08:21.230","Text":"which phosphorylate any other proteins needed for the cellular responses."},{"Start":"08:21.230 ","End":"08:22.970","Text":"Parallel to this system,"},{"Start":"08:22.970 ","End":"08:28.249","Text":"the same cells also have G-protein systems that inhibit the adenylyl cyclase,"},{"Start":"08:28.249 ","End":"08:31.055","Text":"and this provides regulation for the cell metabolism."},{"Start":"08:31.055 ","End":"08:35.990","Text":"So if we have a different G-protein-coupled receptor that inhibits the adenylyl cyclase,"},{"Start":"08:35.990 ","End":"08:38.750","Text":"it can shut off this whole pathway."},{"Start":"08:38.750 ","End":"08:40.850","Text":"With a different messenger, when we need to,"},{"Start":"08:40.850 ","End":"08:42.545","Text":"we can shut down this pathway,"},{"Start":"08:42.545 ","End":"08:44.480","Text":"or using the original messenger,"},{"Start":"08:44.480 ","End":"08:45.970","Text":"we can activate it again."},{"Start":"08:45.970 ","End":"08:49.640","Text":"Here we have a wonderful system for regulation of cell metabolism."},{"Start":"08:49.640 ","End":"08:53.659","Text":"Thanks for listening to this video about methods of the intracellular signaling."},{"Start":"08:53.659 ","End":"08:55.550","Text":"In the next video I\u0027ll be speaking about"},{"Start":"08:55.550 ","End":"08:59.490","Text":"the cellular responses to the signaling. I\u0027ll see you there."}],"ID":28137},{"Watched":false,"Name":"Propagation of The Signal","Duration":"5m 49s","ChapterTopicVideoID":27014,"CourseChapterTopicPlaylistID":261601,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:02.835","Text":"Hi, we\u0027re studying cell communication."},{"Start":"00:02.835 ","End":"00:06.120","Text":"Previously, we discussed the signaling molecules."},{"Start":"00:06.120 ","End":"00:10.395","Text":"In this section, we\u0027ll speak about the propagation of the signal itself in the cell."},{"Start":"00:10.395 ","End":"00:13.155","Text":"How did the signal transduction work?"},{"Start":"00:13.155 ","End":"00:16.169","Text":"Once a ligand binds to the receptor,"},{"Start":"00:16.169 ","End":"00:20.145","Text":"the signal that was transmitted through the membrane and into the cytoplasm."},{"Start":"00:20.145 ","End":"00:23.310","Text":"When a ligand binds to that cell surface receptor here,"},{"Start":"00:23.310 ","End":"00:26.580","Text":"it affects the receptors intracellular domain."},{"Start":"00:26.580 ","End":"00:32.939","Text":"This leads to the activation of the intracellular domain or its associated proteins."},{"Start":"00:32.939 ","End":"00:37.575","Text":"Eventually, the molecular message will be received at the target protein,"},{"Start":"00:37.575 ","End":"00:40.420","Text":"which will activate the cellular response."},{"Start":"00:40.420 ","End":"00:43.340","Text":"Some cases with a signaling molecule can come through"},{"Start":"00:43.340 ","End":"00:47.105","Text":"the membrane and bind directly with intracellularly receptors."},{"Start":"00:47.105 ","End":"00:49.940","Text":"They can interact with other cellular components and activate"},{"Start":"00:49.940 ","End":"00:53.645","Text":"the response without using transduction molecules."},{"Start":"00:53.645 ","End":"00:57.200","Text":"Let\u0027s now discuss several types of receptors."},{"Start":"00:57.200 ","End":"00:59.720","Text":"Dimerization is where 2 molecules of"},{"Start":"00:59.720 ","End":"01:05.005","Text":"a similar composition come together to form a single polymer known as a dimer."},{"Start":"01:05.005 ","End":"01:07.320","Text":"Here you\u0027ve got 2 receptors,"},{"Start":"01:07.320 ","End":"01:11.240","Text":"the same composition and if a ligand binds to each of them,"},{"Start":"01:11.240 ","End":"01:13.100","Text":"don\u0027t connect and form a dimer."},{"Start":"01:13.100 ","End":"01:17.450","Text":"The receptors intracellular domains close and activate each other."},{"Start":"01:17.450 ","End":"01:20.590","Text":"Now the intracellular domains are activated."},{"Start":"01:20.590 ","End":"01:24.965","Text":"In this example, the activated tyrosine kinase regions"},{"Start":"01:24.965 ","End":"01:28.565","Text":"are fully activated by ATP phosphorylation."},{"Start":"01:28.565 ","End":"01:32.405","Text":"In this example, the activation of the intracellular region"},{"Start":"01:32.405 ","End":"01:36.800","Text":"of this dimer activates 2 separate cellular responses."},{"Start":"01:36.800 ","End":"01:42.045","Text":"An example for signal transduction using dimerization would be in the nucleus,"},{"Start":"01:42.045 ","End":"01:44.690","Text":"where hormone receptors acting as transcription"},{"Start":"01:44.690 ","End":"01:49.055","Text":"factors form dimers that improve binding to DNA."},{"Start":"01:49.055 ","End":"01:51.230","Text":"The transduction of the message or"},{"Start":"01:51.230 ","End":"01:53.900","Text":"the signaling pathway is initiated"},{"Start":"01:53.900 ","End":"01:57.100","Text":"by the binding of the signaling molecule to the receptor."},{"Start":"01:57.100 ","End":"02:00.890","Text":"The signaling pathway, also known as the signaling cascade,"},{"Start":"02:00.890 ","End":"02:05.135","Text":"is when the intracellular components set off a chain of events."},{"Start":"02:05.135 ","End":"02:08.285","Text":"The binding of the signaling molecule to the receptor"},{"Start":"02:08.285 ","End":"02:11.885","Text":"triggers the first step in a chain of molecular interactions."},{"Start":"02:11.885 ","End":"02:14.180","Text":"The binding of the signaling molecule to"},{"Start":"02:14.180 ","End":"02:20.345","Text":"the receptor triggers the first step in the chain of molecular interactions."},{"Start":"02:20.345 ","End":"02:23.195","Text":"The receptor activates another protein,"},{"Start":"02:23.195 ","End":"02:26.780","Text":"which activates another, which activates another, and so on."},{"Start":"02:26.780 ","End":"02:29.795","Text":"Until the protein producing the response itself,"},{"Start":"02:29.795 ","End":"02:33.590","Text":"until the target protein and that produces the response is activated."},{"Start":"02:33.590 ","End":"02:36.455","Text":"The events in the cascade occur in a series,"},{"Start":"02:36.455 ","End":"02:38.960","Text":"much like a current flow in the river."},{"Start":"02:38.960 ","End":"02:43.655","Text":"Interactions that occur before a certain point or undefined as upstream events,"},{"Start":"02:43.655 ","End":"02:47.705","Text":"while events after that point are called downstream events."},{"Start":"02:47.705 ","End":"02:51.860","Text":"You see here that signaling molecule initiates the pathway."},{"Start":"02:51.860 ","End":"02:54.530","Text":"Since the events occur subsequently,"},{"Start":"02:54.530 ","End":"03:00.455","Text":"we can refer to them as upstream happening earlier or downstream happening later."},{"Start":"03:00.455 ","End":"03:03.230","Text":"Of course, cellular response is also very."},{"Start":"03:03.230 ","End":"03:06.155","Text":"For example, we can get altered metabolism,"},{"Start":"03:06.155 ","End":"03:09.230","Text":"altered cytoskeleton, altered gene expression,"},{"Start":"03:09.230 ","End":"03:15.610","Text":"cell division, altered gene expression or cell division or any other cellular response."},{"Start":"03:15.610 ","End":"03:18.200","Text":"The signal integration signals from"},{"Start":"03:18.200 ","End":"03:23.570","Text":"different cell surface receptors may merge to activate the same response in the cell."},{"Start":"03:23.570 ","End":"03:26.750","Text":"For example, we can have a response that will only be"},{"Start":"03:26.750 ","End":"03:31.730","Text":"activated when 2 different signal molecules are present."},{"Start":"03:31.730 ","End":"03:34.740","Text":"Only when this one and this one are present in order to"},{"Start":"03:34.740 ","End":"03:37.925","Text":"activate the pathway that will initiate the response."},{"Start":"03:37.925 ","End":"03:42.245","Text":"In other cases,"},{"Start":"03:42.245 ","End":"03:47.180","Text":"either one of the signaling molecules may they activate the response on its own."},{"Start":"03:47.180 ","End":"03:53.585","Text":"As stated, the cellular effects are very variable."},{"Start":"03:53.585 ","End":"04:02.075","Text":"The effects of extracellular signals can be amplified by enzymatic cascades."},{"Start":"04:02.075 ","End":"04:06.185","Text":"In this example, we can see a single response."},{"Start":"04:06.185 ","End":"04:12.320","Text":"This example we see the classic model of really molecules leading to a single response."},{"Start":"04:12.320 ","End":"04:17.030","Text":"But many cellular proteins can affect several different downstream events."},{"Start":"04:17.030 ","End":"04:21.740","Text":"This leads to a single pathway that branches off towards different endpoints."},{"Start":"04:21.740 ","End":"04:24.120","Text":"Like in this example,"},{"Start":"04:27.530 ","End":"04:31.935","Text":"where 1 protein leads to 2 different responses."},{"Start":"04:31.935 ","End":"04:36.180","Text":"As stated earlier, signals from"},{"Start":"04:36.180 ","End":"04:46.235","Text":"different cell surface receptors"},{"Start":"04:46.235 ","End":"04:49.385","Text":"can merge to activate or inhibit the response."},{"Start":"04:49.385 ","End":"04:54.109","Text":"In this case, we have here 2 different receptors and we see that eventually"},{"Start":"04:54.109 ","End":"04:58.310","Text":"this protein can be affected by either of"},{"Start":"04:58.310 ","End":"05:03.155","Text":"the pathways either activating or inhibiting the response."},{"Start":"05:03.155 ","End":"05:07.745","Text":"Some ligands can initiate different signals in different cell types."},{"Start":"05:07.745 ","End":"05:10.010","Text":"We have here the same ligand that reaches"},{"Start":"05:10.010 ","End":"05:13.930","Text":"different cell types and eventually we get different responses."},{"Start":"05:13.930 ","End":"05:18.200","Text":"These examples are just the tip of the iceberg of the great variation"},{"Start":"05:18.200 ","End":"05:25.885","Text":"and possibilities in cell-signaling."},{"Start":"05:25.885 ","End":"05:28.975","Text":"Come listen to the next Section 2."},{"Start":"05:28.975 ","End":"05:32.825","Text":"Thanks for joining me."},{"Start":"05:32.825 ","End":"05:34.820","Text":"I hope you\u0027ll come to the next section."},{"Start":"05:34.820 ","End":"05:36.350","Text":"Thanks for joining me."},{"Start":"05:36.350 ","End":"05:41.565","Text":"See you later. Thanks for joining me."},{"Start":"05:41.565 ","End":"05:44.210","Text":"In the coming sections, we\u0027ll be speaking about different methods of"},{"Start":"05:44.210 ","End":"05:49.080","Text":"signaling and different cellular responses. See you there."}],"ID":28138},{"Watched":false,"Name":"Response to the signal","Duration":"7m 9s","ChapterTopicVideoID":27015,"CourseChapterTopicPlaylistID":261601,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:03.240","Text":"Hi, we\u0027re studying cell communication."},{"Start":"00:03.240 ","End":"00:07.590","Text":"Signaling directly affects the cell\u0027s DNA and protein producing machinery."},{"Start":"00:07.590 ","End":"00:09.255","Text":"Just as a quick reminder,"},{"Start":"00:09.255 ","End":"00:12.630","Text":"the 3 steps of cellular signaling are number 1,"},{"Start":"00:12.630 ","End":"00:14.205","Text":"reception of the signal."},{"Start":"00:14.205 ","End":"00:15.975","Text":"Usually number 1,"},{"Start":"00:15.975 ","End":"00:18.555","Text":"the reception of the signal, number 2,"},{"Start":"00:18.555 ","End":"00:21.675","Text":"transduction and number 3 response,"},{"Start":"00:21.675 ","End":"00:23.400","Text":"which will be speaking about today."},{"Start":"00:23.400 ","End":"00:28.155","Text":"The signaling and directly affects the cell\u0027s DNA and protein producing machinery."},{"Start":"00:28.155 ","End":"00:30.690","Text":"The results of signaling pathways that are extremely"},{"Start":"00:30.690 ","End":"00:33.420","Text":"varied and depend on the type of cell involved,"},{"Start":"00:33.420 ","End":"00:36.390","Text":"as well as the external and internal conditions."},{"Start":"00:36.390 ","End":"00:41.345","Text":"The output response defines the cell\u0027s reaction to an extracellular signal."},{"Start":"00:41.345 ","End":"00:47.660","Text":"A signal transduction pathway leads to regulation of one or more cellular activities."},{"Start":"00:47.660 ","End":"00:52.265","Text":"The response may occur in a cell\u0027s nucleus or in the cytoplasm."},{"Start":"00:52.265 ","End":"00:55.340","Text":"In this example we can see that the transduction and"},{"Start":"00:55.340 ","End":"01:01.610","Text":"its phosphorylation cascade eventually lead to a response inside the cell\u0027s nucleus."},{"Start":"01:01.610 ","End":"01:05.420","Text":"Many of the signaling pathways manipulate transcription or translation"},{"Start":"01:05.420 ","End":"01:09.514","Text":"of mRNA and therefore the synthesis of cellular proteins."},{"Start":"01:09.514 ","End":"01:12.110","Text":"In this case, again, the transduction that led to"},{"Start":"01:12.110 ","End":"01:14.755","Text":"the response inside the cell\u0027s nucleus,"},{"Start":"01:14.755 ","End":"01:18.230","Text":"and the response here was activating transcription factors,"},{"Start":"01:18.230 ","End":"01:22.655","Text":"which lead to the production of mRNA and eventually proteins."},{"Start":"01:22.655 ","End":"01:24.440","Text":"Other pathways may change"},{"Start":"01:24.440 ","End":"01:28.310","Text":"the enzyme\u0027s activity rather than in production like we\u0027ve just seen."},{"Start":"01:28.310 ","End":"01:31.400","Text":"For example, the binding of epinephrine to receptors on"},{"Start":"01:31.400 ","End":"01:36.335","Text":"muscle cells eventually activates the enzyme glycogen phosphorylase."},{"Start":"01:36.335 ","End":"01:40.040","Text":"For example, epinephrine binding leads to an increase in"},{"Start":"01:40.040 ","End":"01:45.175","Text":"glycogen degradation the glucose by activating the glycogen phosphorylase enzyme."},{"Start":"01:45.175 ","End":"01:46.760","Text":"That was pretty fast,"},{"Start":"01:46.760 ","End":"01:48.260","Text":"but let\u0027s take a look at it now."},{"Start":"01:48.260 ","End":"01:51.755","Text":"The epinephrine binds to the receptor and the muscle cell,"},{"Start":"01:51.755 ","End":"01:55.925","Text":"eventually leading to the activation of glycogen phosphorylase."},{"Start":"01:55.925 ","End":"01:58.640","Text":"This enzyme takes apart glycogen,"},{"Start":"01:58.640 ","End":"02:02.090","Text":"which is made of many glucose molecules connected to each other."},{"Start":"02:02.090 ","End":"02:05.170","Text":"The degrades them to single glucose molecules."},{"Start":"02:05.170 ","End":"02:07.970","Text":"In this manner, muscle cells obtained already"},{"Start":"02:07.970 ","End":"02:11.240","Text":"pool of glucose during fight or flight response."},{"Start":"02:11.240 ","End":"02:16.445","Text":"Cell-signaling pathways also play a major role in cell division."},{"Start":"02:16.445 ","End":"02:21.830","Text":"Cells may divide upon receiving external stimulating signals from other cells."},{"Start":"02:21.830 ","End":"02:26.860","Text":"The ligands that promote cell growth are called growth factors."},{"Start":"02:26.860 ","End":"02:31.845","Text":"Most growth factors bind to cell surface receptors tyrosine kinases,"},{"Start":"02:31.845 ","End":"02:34.535","Text":"also known as RTKs."},{"Start":"02:34.535 ","End":"02:41.540","Text":"Activation of specific RTKs initiates a signaling pathway leading to cell division."},{"Start":"02:41.540 ","End":"02:45.100","Text":"There are 4 aspects of signal regulation."},{"Start":"02:45.100 ","End":"02:50.105","Text":"The first is the amplification of the signal and therefore the response."},{"Start":"02:50.105 ","End":"02:55.190","Text":"The cell\u0027s response for a received signal is amplified by the enzyme cascades."},{"Start":"02:55.190 ","End":"02:59.075","Text":"That means that the number of products increases with every step."},{"Start":"02:59.075 ","End":"03:02.525","Text":"In this example, the hormone connects to the receptor,"},{"Start":"03:02.525 ","End":"03:05.600","Text":"leading to the activation of several G proteins."},{"Start":"03:05.600 ","End":"03:09.440","Text":"Each one of these G proteins activates several enzymes."},{"Start":"03:09.440 ","End":"03:13.640","Text":"These enzymes each create several molecules of cyclic AMP."},{"Start":"03:13.640 ","End":"03:15.500","Text":"This already large number of"},{"Start":"03:15.500 ","End":"03:20.495","Text":"cyclic AMP molecules activates many more protein kinase enzymes."},{"Start":"03:20.495 ","End":"03:25.730","Text":"We see that a single molecule can be amplified to a very strong signal."},{"Start":"03:25.730 ","End":"03:30.590","Text":"The second aspect of signal regulation is the specificity of the response."},{"Start":"03:30.590 ","End":"03:35.360","Text":"Different cell types have different groups of reception and transduction proteins."},{"Start":"03:35.360 ","End":"03:40.220","Text":"This allows different cells detect and respond to a dissimilar signals."},{"Start":"03:40.220 ","End":"03:42.830","Text":"It also allows identical signals to cause"},{"Start":"03:42.830 ","End":"03:46.765","Text":"different effects in cells with different proteins and pathways."},{"Start":"03:46.765 ","End":"03:49.640","Text":"As we can see here, this signaling molecule,"},{"Start":"03:49.640 ","End":"03:51.485","Text":"which reaches a specific receptor,"},{"Start":"03:51.485 ","End":"03:53.900","Text":"activates 1 pathway and when it"},{"Start":"03:53.900 ","End":"03:57.170","Text":"reaches a different receptor activates a different pathway."},{"Start":"03:57.170 ","End":"04:02.750","Text":"The pathway branching and crosstalk further helps the cell coordinate incoming signals."},{"Start":"04:02.750 ","End":"04:04.475","Text":"In this cell for example,"},{"Start":"04:04.475 ","End":"04:11.330","Text":"we have 2 different signals that talk with each other and coordinate a specific response."},{"Start":"04:11.330 ","End":"04:14.360","Text":"Also as a pathway proteins are different in the cells,"},{"Start":"04:14.360 ","End":"04:18.260","Text":"we may get several different responses to the same signal."},{"Start":"04:18.260 ","End":"04:21.830","Text":"The third aspect is the overall efficiency of the response."},{"Start":"04:21.830 ","End":"04:24.965","Text":"This is enhanced by the scaffolding proteins."},{"Start":"04:24.965 ","End":"04:27.800","Text":"The third aspect is the overall efficiency of"},{"Start":"04:27.800 ","End":"04:31.910","Text":"the response and it\u0027s enhanced by scaffolding proteins."},{"Start":"04:31.910 ","End":"04:38.285","Text":"Scaffolding proteins are large relay proteins and they connect to other relay proteins."},{"Start":"04:38.285 ","End":"04:43.310","Text":"As we see here, the scaffolding protein is connected to 3 different protein kinases."},{"Start":"04:43.310 ","End":"04:46.925","Text":"This allows to increase the signal transduction efficiency"},{"Start":"04:46.925 ","End":"04:51.020","Text":"by bringing together different proteins that are involved in the same pathway."},{"Start":"04:51.020 ","End":"04:54.155","Text":"Now they can work together more efficiently."},{"Start":"04:54.155 ","End":"04:59.230","Text":"Sometimes scaffolding proteins also helping activating relevant relay proteins,"},{"Start":"04:59.230 ","End":"05:02.660","Text":"so we might have proteins like these that are inactive when they\u0027re"},{"Start":"05:02.660 ","End":"05:06.995","Text":"not connected to the scaffolding protein, which activates them."},{"Start":"05:06.995 ","End":"05:10.775","Text":"Fourth aspect is the termination of the signal."},{"Start":"05:10.775 ","End":"05:13.935","Text":"Determination of a signal at the right time is crucial."},{"Start":"05:13.935 ","End":"05:18.785","Text":"One method of stopping the signal is to degrade the ligand or to remove it."},{"Start":"05:18.785 ","End":"05:22.145","Text":"The unbound receptors revert to an inactive state."},{"Start":"05:22.145 ","End":"05:27.605","Text":"The pathway is stopped and eventually the cellular response is discontinued."},{"Start":"05:27.605 ","End":"05:29.450","Text":"But inside the cell,"},{"Start":"05:29.450 ","End":"05:31.070","Text":"different enzymes can reverse"},{"Start":"05:31.070 ","End":"05:34.925","Text":"the cellular modifications that results from signaling cascades."},{"Start":"05:34.925 ","End":"05:40.715","Text":"For example, phosphatase causes dephosphorylation of proteins by kinases."},{"Start":"05:40.715 ","End":"05:47.330","Text":"For example here, this inactive protein that was previously phosphorylated by a kinase,"},{"Start":"05:47.330 ","End":"05:50.675","Text":"is now dephosphorylated by the phosphatase,"},{"Start":"05:50.675 ","End":"05:54.680","Text":"removing the phosphate group and inactivating the protein."},{"Start":"05:54.680 ","End":"05:59.285","Text":"The inactivation can be by terminating the signal and waiting for the response to stop,"},{"Start":"05:59.285 ","End":"06:03.425","Text":"or by actively reversing the result of the signaling cascades."},{"Start":"06:03.425 ","End":"06:04.820","Text":"Last but not least,"},{"Start":"06:04.820 ","End":"06:06.515","Text":"we\u0027ll talk about apoptosis,"},{"Start":"06:06.515 ","End":"06:09.095","Text":"which is also known as programmed cell death."},{"Start":"06:09.095 ","End":"06:12.470","Text":"Here we have the receptor for death signaling molecule,"},{"Start":"06:12.470 ","End":"06:14.255","Text":"and when this is accepted,"},{"Start":"06:14.255 ","End":"06:17.885","Text":"it results in a cascade leading to apoptosis."},{"Start":"06:17.885 ","End":"06:20.870","Text":"We are components of the seller chopped up and wrapped into"},{"Start":"06:20.870 ","End":"06:24.365","Text":"vesicles that are digested by scavenger cells."},{"Start":"06:24.365 ","End":"06:28.490","Text":"Why couldn\u0027t we just let the cell die without going through apoptosis?"},{"Start":"06:28.490 ","End":"06:31.700","Text":"That\u0027s because apoptosis prevents enzymes from"},{"Start":"06:31.700 ","End":"06:35.045","Text":"leaking out of a dying cell and damaging neighboring cells,"},{"Start":"06:35.045 ","End":"06:38.630","Text":"which might have happened if we had not taken care of this carefully."},{"Start":"06:38.630 ","End":"06:42.260","Text":"Apoptosis also contributes to the appropriate formation of"},{"Start":"06:42.260 ","End":"06:47.090","Text":"various organisms structures during embryonic development and maturation."},{"Start":"06:47.090 ","End":"06:51.260","Text":"In this example, we can see how in the embryonic development of our hands,"},{"Start":"06:51.260 ","End":"06:54.680","Text":"apoptosis allows the digits to divine between each other."},{"Start":"06:54.680 ","End":"06:59.450","Text":"In this example, tissues are removed when a tadpole matures to an adult frog,"},{"Start":"06:59.450 ","End":"07:01.070","Text":"the whole tail is removed."},{"Start":"07:01.070 ","End":"07:04.670","Text":"Thanks for listening to this video and the next video we\u0027ll speak about"},{"Start":"07:04.670 ","End":"07:09.510","Text":"communication between the unicellular organisms. I\u0027ll see you there."}],"ID":28139},{"Watched":false,"Name":"Signaling in single celled organisms","Duration":"2m 31s","ChapterTopicVideoID":27016,"CourseChapterTopicPlaylistID":261601,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:03.900","Text":"Hi. We\u0027re studying cell communication."},{"Start":"00:03.900 ","End":"00:08.445","Text":"In this section, we\u0027ll be studying in single-celled organisms."},{"Start":"00:08.445 ","End":"00:13.290","Text":"Single-celled organisms can respond to their environment and signal to each other."},{"Start":"00:13.290 ","End":"00:16.530","Text":"They use components and processes similar to"},{"Start":"00:16.530 ","End":"00:20.940","Text":"those of cell-surface receptors in multicellular organisms."},{"Start":"00:20.940 ","End":"00:27.060","Text":"We\u0027ll now give examples from yeast cells and from bacterial cells."},{"Start":"00:27.060 ","End":"00:32.310","Text":"During reproduction, budding yeast secrete a signaling mating factor."},{"Start":"00:32.310 ","End":"00:37.100","Text":"This factor binds to cell-surface receptors in other yeast cells."},{"Start":"00:37.100 ","End":"00:40.670","Text":"It initiates a cell signaling cascade that includes"},{"Start":"00:40.670 ","End":"00:45.590","Text":"protein kinases and GTP-binding proteins that work like G proteins."},{"Start":"00:45.590 ","End":"00:47.990","Text":"Signaling enables bacteria to monitor"},{"Start":"00:47.990 ","End":"00:51.200","Text":"extracellular conditions and communicate with each other."},{"Start":"00:51.200 ","End":"00:54.649","Text":"Autoinducers are molecules secreted by bacteria"},{"Start":"00:54.649 ","End":"00:58.880","Text":"that only in high concentrations promote the cellular response."},{"Start":"00:58.880 ","End":"01:01.565","Text":"This is known as quorum sensing."},{"Start":"01:01.565 ","End":"01:03.560","Text":"Here we have an example."},{"Start":"01:03.560 ","End":"01:05.480","Text":"When there\u0027s a low density of cells,"},{"Start":"01:05.480 ","End":"01:08.600","Text":"the autoinducers diffuse away from the cell."},{"Start":"01:08.600 ","End":"01:12.185","Text":"On the other hand, when a cell density is high,"},{"Start":"01:12.185 ","End":"01:16.170","Text":"more autoinducers, here in red, are present."},{"Start":"01:16.170 ","End":"01:20.435","Text":"They bind to receptors that regulate the transcription of certain genes."},{"Start":"01:20.435 ","End":"01:23.510","Text":"The genes responsible for the production of autoinducers"},{"Start":"01:23.510 ","End":"01:26.405","Text":"are expressed resulting in a positive feedback loop."},{"Start":"01:26.405 ","End":"01:28.310","Text":"Some species of bacteria"},{"Start":"01:28.310 ","End":"01:32.645","Text":"exchange chemical signals to coordinate the creation of biofilms."},{"Start":"01:32.645 ","End":"01:35.990","Text":"Biofilms are collective of one or more types of"},{"Start":"01:35.990 ","End":"01:39.485","Text":"microorganisms that can grow on many different surfaces."},{"Start":"01:39.485 ","End":"01:45.305","Text":"In the first stage, free-floating planktonic bacteria adhere to the surface."},{"Start":"01:45.305 ","End":"01:50.120","Text":"In a second stage, the sessile bacteria that are connected to the surface begin to"},{"Start":"01:50.120 ","End":"01:55.160","Text":"secrete EPS, extracellular polymeric substances."},{"Start":"01:55.160 ","End":"02:00.020","Text":"These substances surround and cement"},{"Start":"02:00.020 ","End":"02:04.895","Text":"the cells together improving their ability to scavenge both water and nutrients,"},{"Start":"02:04.895 ","End":"02:07.730","Text":"and also may serve as a defense from outer threats"},{"Start":"02:07.730 ","End":"02:11.080","Text":"such as physical scraping or antibiotics."},{"Start":"02:11.080 ","End":"02:14.255","Text":"In third stage, the biofilm develops."},{"Start":"02:14.255 ","End":"02:18.950","Text":"Several species of bacteria may participate in creating of the biofilm."},{"Start":"02:18.950 ","End":"02:22.130","Text":"In the fourth stage, planktonic bacteria is released to"},{"Start":"02:22.130 ","End":"02:25.760","Text":"the mature biofilm and looks for a new surface to which to connect to."},{"Start":"02:25.760 ","End":"02:29.450","Text":"one common example of a biofilm is dental plaque."},{"Start":"02:29.450 ","End":"02:32.100","Text":"Thanks for listening to this section."}],"ID":28140},{"Watched":false,"Name":"Signaling Molecules and Cellular Receptors","Duration":"10m 35s","ChapterTopicVideoID":27017,"CourseChapterTopicPlaylistID":261601,"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":"Hi, we\u0027re studying Cell Communication."},{"Start":"00:04.095 ","End":"00:09.705","Text":"In this section, we\u0027ll be learning about signaling molecules and cellular receptors."},{"Start":"00:09.705 ","End":"00:11.505","Text":"By the end of this section,"},{"Start":"00:11.505 ","End":"00:14.984","Text":"you\u0027ll be able to define the 3 stages of cell signaling,"},{"Start":"00:14.984 ","End":"00:20.715","Text":"describe 4 different types of signaling mechanisms found in multicellular organisms,"},{"Start":"00:20.715 ","End":"00:25.680","Text":"and compare internal receptors with cell surface receptors."},{"Start":"00:25.680 ","End":"00:31.215","Text":"The 3 stages of cell signaling are first reception."},{"Start":"00:31.215 ","End":"00:36.655","Text":"This is when the signaling molecule binds the receptor protein on the target cell,"},{"Start":"00:36.655 ","End":"00:41.645","Text":"you\u0027ve got the signaling molecule here bound to the receptor."},{"Start":"00:41.645 ","End":"00:45.050","Text":"The second stage is transduction."},{"Start":"00:45.050 ","End":"00:49.190","Text":"The binding of the signaling molecule to the receptor modifies"},{"Start":"00:49.190 ","End":"00:53.330","Text":"the structure of the receptor and starts a signal transduction pathway,"},{"Start":"00:53.330 ","End":"00:58.085","Text":"as we can see here using several other molecules in the cell."},{"Start":"00:58.085 ","End":"01:03.755","Text":"Eventually, the pathway will lead to the activation of a cellular response,"},{"Start":"01:03.755 ","End":"01:07.160","Text":"which is the third stage of cellular signaling when a target cell"},{"Start":"01:07.160 ","End":"01:11.125","Text":"response to the transduced signal and a specific way."},{"Start":"01:11.125 ","End":"01:16.735","Text":"The many forms of signaling can be divided into 4 categories."},{"Start":"01:16.735 ","End":"01:20.540","Text":"The first category is the autocrine signaling,"},{"Start":"01:20.540 ","End":"01:24.125","Text":"this type of signaling is produced by signaling cells"},{"Start":"01:24.125 ","End":"01:27.920","Text":"that can also bind to the ligand that\u0027s released themselves."},{"Start":"01:27.920 ","End":"01:32.990","Text":"The signaling and target cell can be the same or a similar cell."},{"Start":"01:32.990 ","End":"01:36.815","Text":"For example, if a cell is infected with a virus,"},{"Start":"01:36.815 ","End":"01:42.935","Text":"it can signal itself to undergo program cell death killing the virus in the process."},{"Start":"01:42.935 ","End":"01:44.960","Text":"Here we see the cell secreting"},{"Start":"01:44.960 ","End":"01:49.670","Text":"the signaling molecules which eventually meet the receptors and its own membrane,"},{"Start":"01:49.670 ","End":"01:52.295","Text":"activating its own response."},{"Start":"01:52.295 ","End":"01:55.625","Text":"The second form of signaling is paracrine signaling."},{"Start":"01:55.625 ","End":"02:00.110","Text":"These are signals that act locally between cells that are close together."},{"Start":"02:00.110 ","End":"02:04.885","Text":"The signals move by diffusion through the extracellular matrix."},{"Start":"02:04.885 ","End":"02:08.420","Text":"These signals usually elicit quick responses in"},{"Start":"02:08.420 ","End":"02:12.605","Text":"the receiving cell that lasts only a very short period of time."},{"Start":"02:12.605 ","End":"02:16.220","Text":"We see here the signaling cell and the cells close"},{"Start":"02:16.220 ","End":"02:19.630","Text":"by which are receiving the signal and responding to it."},{"Start":"02:19.630 ","End":"02:22.160","Text":"Other cells in the same vicinity don\u0027t"},{"Start":"02:22.160 ","End":"02:25.670","Text":"respond because they have different types of receptors."},{"Start":"02:25.670 ","End":"02:31.460","Text":"Ligand molecules are quickly degraded by enzymes or removed by neighboring cells."},{"Start":"02:31.460 ","End":"02:34.610","Text":"In this case, ligand molecules are quickly"},{"Start":"02:34.610 ","End":"02:38.410","Text":"degraded by enzymes or removed by neighboring cells."},{"Start":"02:38.410 ","End":"02:41.610","Text":"The third form is the endocrine signaling."},{"Start":"02:41.610 ","End":"02:46.655","Text":"Here the signaling cells are along distance from the receiving cells."},{"Start":"02:46.655 ","End":"02:51.125","Text":"In this case, the signaling chemicals are called hormones."},{"Start":"02:51.125 ","End":"02:53.960","Text":"Specialized cells release the hormones which"},{"Start":"02:53.960 ","End":"02:57.050","Text":"travel to target cells via the circulatory system."},{"Start":"02:57.050 ","End":"03:02.950","Text":"You can see the arteries carrying blood also carrying the hormones secreted faraway."},{"Start":"03:02.950 ","End":"03:07.880","Text":"Eventually, the hormones get to the target cells who respond to them."},{"Start":"03:07.880 ","End":"03:11.210","Text":"The main difference between the 3 categories mentioned is"},{"Start":"03:11.210 ","End":"03:14.780","Text":"the distance that the signal travels to reach the target cell."},{"Start":"03:14.780 ","End":"03:17.720","Text":"A forth and different category from the first"},{"Start":"03:17.720 ","End":"03:22.820","Text":"3 is a direct signaling across gap junctions."},{"Start":"03:22.820 ","End":"03:25.730","Text":"Animal cells and plant cells use"},{"Start":"03:25.730 ","End":"03:30.020","Text":"cell junctions that connect the cytoplasm of adjacent cells."},{"Start":"03:30.020 ","End":"03:33.895","Text":"Gap junctions in animals and plasmodesmata in"},{"Start":"03:33.895 ","End":"03:38.785","Text":"plants are connections between the plasma membranes of neighboring cells."},{"Start":"03:38.785 ","End":"03:45.120","Text":"Signaling substances into the cytosol can pass freely between adjacent cells."},{"Start":"03:45.120 ","End":"03:48.440","Text":"This allows intracellular mediators such as"},{"Start":"03:48.440 ","End":"03:52.835","Text":"calcium ions or other ions to diffuse between the 2 cells."},{"Start":"03:52.835 ","End":"03:55.925","Text":"Specificity of channels ensures that the cells remain"},{"Start":"03:55.925 ","End":"03:59.510","Text":"independent but can quickly and easily transmit signals,"},{"Start":"03:59.510 ","End":"04:03.140","Text":"that means that these gap junctions don\u0027t allow any ions to pass"},{"Start":"04:03.140 ","End":"04:08.000","Text":"freely only specific ions pass in the right time."},{"Start":"04:08.000 ","End":"04:11.900","Text":"Direct signaling allows a whole group of cells to"},{"Start":"04:11.900 ","End":"04:16.145","Text":"coordinate the response to a signal that only 1 of them may have received."},{"Start":"04:16.145 ","End":"04:19.895","Text":"Now let\u0027s talk about different types of receptors."},{"Start":"04:19.895 ","End":"04:24.995","Text":"Receptors are proteins in the target cell that bind to ligands."},{"Start":"04:24.995 ","End":"04:27.215","Text":"There are 2 types."},{"Start":"04:27.215 ","End":"04:29.944","Text":"The first is internal receptors,"},{"Start":"04:29.944 ","End":"04:36.275","Text":"here also known as intracellular or cytoplasmic receptors."},{"Start":"04:36.275 ","End":"04:39.860","Text":"They are found in the cytoplasm or the nucleus of the cell,"},{"Start":"04:39.860 ","End":"04:43.475","Text":"meaning they are on the inside of the cell and not on the outside."},{"Start":"04:43.475 ","End":"04:46.760","Text":"So how does a similarly molecule enter the cell?"},{"Start":"04:46.760 ","End":"04:49.820","Text":"The internal receptors usually respond to"},{"Start":"04:49.820 ","End":"04:54.400","Text":"hydrophobic ligand molecules that can travel across the plasma membrane."},{"Start":"04:54.400 ","End":"05:00.560","Text":"In many cases, these internal receptors act as regulators of mRNA synthesis,"},{"Start":"05:00.560 ","End":"05:04.310","Text":"known as transcription to mediate gene expression."},{"Start":"05:04.310 ","End":"05:07.320","Text":"Here we see the intracellular receptor,"},{"Start":"05:07.320 ","End":"05:10.065","Text":"it can be in the cytoplasm or the nucleus."},{"Start":"05:10.065 ","End":"05:15.695","Text":"The signaling molecule passes through the plasma membrane because it\u0027s hydrophobic."},{"Start":"05:15.695 ","End":"05:19.585","Text":"When it binds to the intracellular receptor it becomes active,"},{"Start":"05:19.585 ","End":"05:24.815","Text":"and can now bind to the DNA to mediate the expression of specific genes."},{"Start":"05:24.815 ","End":"05:28.744","Text":"The second type of receptors are cell surface receptors,"},{"Start":"05:28.744 ","End":"05:31.204","Text":"also known as membrane receptors."},{"Start":"05:31.204 ","End":"05:37.805","Text":"These are cell surface membrane anchored proteins that bind to external ligand molecules,"},{"Start":"05:37.805 ","End":"05:42.260","Text":"meaning that now the signaling molecules are external to the cell."},{"Start":"05:42.260 ","End":"05:46.385","Text":"The cell surface receptors start a signal transduction,"},{"Start":"05:46.385 ","End":"05:49.640","Text":"where the extracellular signal from the outside is"},{"Start":"05:49.640 ","End":"05:53.365","Text":"converted into an intracellular signal on the inside."},{"Start":"05:53.365 ","End":"05:57.635","Text":"The ligands meaning the signal molecules themselves,"},{"Start":"05:57.635 ","End":"06:00.550","Text":"don\u0027t have to enter the cell that they affect."},{"Start":"06:00.550 ","End":"06:04.580","Text":"The receptors of course are specific to individual cell types,"},{"Start":"06:04.580 ","End":"06:09.925","Text":"meaning that the extracellular signal molecules will only activate the correct cells."},{"Start":"06:09.925 ","End":"06:16.400","Text":"A malfunction in any of these proteins can have severe consequences on the cells health."},{"Start":"06:16.400 ","End":"06:18.320","Text":"In the following minutes,"},{"Start":"06:18.320 ","End":"06:21.685","Text":"we\u0027ll talk all about the cell surface receptors."},{"Start":"06:21.685 ","End":"06:25.365","Text":"There are 3 components of the cell surface receptors."},{"Start":"06:25.365 ","End":"06:31.700","Text":"The first 1 is the external ligand binding domain also called the extracellular domain,"},{"Start":"06:31.700 ","End":"06:35.570","Text":"this is the part of the protein that faces the outside."},{"Start":"06:35.570 ","End":"06:38.900","Text":"The second part is the transmembrane domain,"},{"Start":"06:38.900 ","End":"06:41.705","Text":"this is the part that\u0027s anchored in the membrane."},{"Start":"06:41.705 ","End":"06:46.250","Text":"The third part is the intracellular domain inside the cell."},{"Start":"06:46.250 ","End":"06:49.415","Text":"The size and extent of each of these domains"},{"Start":"06:49.415 ","End":"06:53.360","Text":"varies widely depending on the type of receptor."},{"Start":"06:53.360 ","End":"06:57.920","Text":"There are 3 main types of cell surface receptors."},{"Start":"06:57.920 ","End":"07:02.395","Text":"The first group is the group of ion channel receptors."},{"Start":"07:02.395 ","End":"07:08.465","Text":"These receptors act as gates that open and close when the receptor changes shape."},{"Start":"07:08.465 ","End":"07:11.510","Text":"When a signal molecule binds to the receptor,"},{"Start":"07:11.510 ","End":"07:15.020","Text":"the gate opens and lets specific ions pass through."},{"Start":"07:15.020 ","End":"07:19.280","Text":"We see here the ligand-gated ion channel receptor it\u0027s closed"},{"Start":"07:19.280 ","End":"07:23.450","Text":"now because the signaling molecule the ligand isn\u0027t bounded,"},{"Start":"07:23.450 ","End":"07:27.170","Text":"therefore the ions remain outside the cell."},{"Start":"07:27.170 ","End":"07:30.440","Text":"In the second stage here we can see that now that"},{"Start":"07:30.440 ","End":"07:33.965","Text":"the ligand is bound to the receptor it changes its shape."},{"Start":"07:33.965 ","End":"07:39.865","Text":"The ions are now free to come in eventually causing a cellular response."},{"Start":"07:39.865 ","End":"07:42.770","Text":"In the third stage here when the ligand is removed,"},{"Start":"07:42.770 ","End":"07:47.210","Text":"the channel is closed again and the ions again cannot enter the cell."},{"Start":"07:47.210 ","End":"07:50.450","Text":"The second type of cell surface receptors is"},{"Start":"07:50.450 ","End":"07:55.615","Text":"the G-protein-coupled receptor also known as the GPCR."},{"Start":"07:55.615 ","End":"08:01.715","Text":"These are cell surface transmembrane receptors that work with the help of a G protein."},{"Start":"08:01.715 ","End":"08:07.285","Text":"When the receptor is activated the G-proteins bind energy rich GTP,"},{"Start":"08:07.285 ","End":"08:10.835","Text":"then the energy loaded G proteins interact with"},{"Start":"08:10.835 ","End":"08:14.695","Text":"either an ion channel or an enzyme in the membrane."},{"Start":"08:14.695 ","End":"08:19.300","Text":"GPCR systems are very common and varied in their functions."},{"Start":"08:19.300 ","End":"08:22.340","Text":"Here we see that G-protein-coupled receptors or"},{"Start":"08:22.340 ","End":"08:28.330","Text":"the GPCR we see the G-protein here loaded with a low-energy GDP,"},{"Start":"08:28.330 ","End":"08:31.205","Text":"also we see an inactive enzyme."},{"Start":"08:31.205 ","End":"08:34.903","Text":"Once the signaling molecule binds to the receptor,"},{"Start":"08:34.903 ","End":"08:36.680","Text":"the receptor is activated,"},{"Start":"08:36.680 ","End":"08:43.025","Text":"then switches the low-energy GDP from the G-protein to a high-energy GTP."},{"Start":"08:43.025 ","End":"08:46.310","Text":"The energy loaded G-protein now activates"},{"Start":"08:46.310 ","End":"08:49.910","Text":"this enzyme here or opens an ion channel in other cases,"},{"Start":"08:49.910 ","End":"08:52.475","Text":"eventually leading to cellular responses."},{"Start":"08:52.475 ","End":"08:54.455","Text":"In activating the enzyme,"},{"Start":"08:54.455 ","End":"08:58.315","Text":"the GDP lost it\u0027s extra phosphate group and its energy,"},{"Start":"08:58.315 ","End":"09:02.660","Text":"and is now back to its initial state loaded with low-energy GDP"},{"Start":"09:02.660 ","End":"09:07.640","Text":"waiting for new activator to activate it and load a new GTP molecule onto it."},{"Start":"09:07.640 ","End":"09:12.829","Text":"The third type of cell surface receptors is the enzyme-linked receptors."},{"Start":"09:12.829 ","End":"09:17.495","Text":"These are cell surface receptors that are associated with an enzyme."},{"Start":"09:17.495 ","End":"09:21.250","Text":"When a ligand binds to the extracellular domain,"},{"Start":"09:21.250 ","End":"09:25.970","Text":"a signal is transferred through the membrane activating the enzyme."},{"Start":"09:25.970 ","End":"09:31.750","Text":"The enzyme then transfers phosphate groups from ATP to another protein,"},{"Start":"09:31.750 ","End":"09:36.605","Text":"this can trigger multiple signal transduction pathways at once."},{"Start":"09:36.605 ","End":"09:39.454","Text":"Let\u0027s have a look at the illustration here then."},{"Start":"09:39.454 ","End":"09:42.220","Text":"We have here the enzyme-linked receptors also known as"},{"Start":"09:42.220 ","End":"09:47.365","Text":"RTKs here they\u0027re in the state of inactive monomers."},{"Start":"09:47.365 ","End":"09:50.810","Text":"In the second stage, the signaling molecules bind to"},{"Start":"09:50.810 ","End":"09:57.395","Text":"the ligand binding sites causing the 2 monomers to attach now forming a dimer."},{"Start":"09:57.395 ","End":"10:04.325","Text":"This activated receptor now uses ATP to phosphorylate the tyrosine groups."},{"Start":"10:04.325 ","End":"10:07.460","Text":"We can see here how this can trigger"},{"Start":"10:07.460 ","End":"10:13.580","Text":"multiple signal transduction pathways at once by binding to several proteins."},{"Start":"10:13.580 ","End":"10:21.245","Text":"Abnormal functions of RTKs is associated with many types of cancers."},{"Start":"10:21.245 ","End":"10:25.145","Text":"In this section, we\u0027ve defined the 3 stages of cell signaling."},{"Start":"10:25.145 ","End":"10:28.730","Text":"We\u0027ve described 4 different types of signaling mechanisms,"},{"Start":"10:28.730 ","End":"10:33.050","Text":"and we compare the internal receptors with cell surface receptors."},{"Start":"10:33.050 ","End":"10:35.640","Text":"See you in the next section."}],"ID":28141},{"Watched":false,"Name":"Signaling Molecules","Duration":"3m 42s","ChapterTopicVideoID":27018,"CourseChapterTopicPlaylistID":261601,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:03.780","Text":"Hi, we\u0027re studying cell communication."},{"Start":"00:03.780 ","End":"00:07.305","Text":"In this section we\u0027ll be speaking about signaling molecules."},{"Start":"00:07.305 ","End":"00:09.660","Text":"Ligands are substances that combine to"},{"Start":"00:09.660 ","End":"00:13.695","Text":"a biological molecule such as a protein to form a complex."},{"Start":"00:13.695 ","End":"00:19.245","Text":"Ligands act as chemical signals that travel to target cells to coordinate responses."},{"Start":"00:19.245 ","End":"00:21.930","Text":"They\u0027re produced by the signaling cells and"},{"Start":"00:21.930 ","End":"00:24.615","Text":"they bind to the receptors on the target cells."},{"Start":"00:24.615 ","End":"00:27.255","Text":"The types of ligands are incredibly varied."},{"Start":"00:27.255 ","End":"00:30.435","Text":"They range from ions to small proteins."},{"Start":"00:30.435 ","End":"00:33.840","Text":"Small hydrophobic ligands are not soluble in water,"},{"Start":"00:33.840 ","End":"00:37.675","Text":"therefore, they must bind to carrier proteins while in the bloodstream."},{"Start":"00:37.675 ","End":"00:39.150","Text":"They can directly diffuse through"},{"Start":"00:39.150 ","End":"00:42.240","Text":"the plasma membrane and interact with internal receptors."},{"Start":"00:42.240 ","End":"00:45.170","Text":"You see the inner part of the plasma membrane is also"},{"Start":"00:45.170 ","End":"00:49.120","Text":"hydrophobic and therefore these ligands can pass easily right through them."},{"Start":"00:49.120 ","End":"00:52.325","Text":"Here we have the exterior, outside of the cell,"},{"Start":"00:52.325 ","End":"00:56.195","Text":"and here we have the interior in a cell."},{"Start":"00:56.195 ","End":"00:59.240","Text":"The ligand being hydrophobic can pass"},{"Start":"00:59.240 ","End":"01:03.480","Text":"easily through the hydrophobic region of the cell membrane."},{"Start":"01:03.950 ","End":"01:07.595","Text":"Here are some examples of hydrophobic ligands."},{"Start":"01:07.595 ","End":"01:12.019","Text":"A good example for small hydrophobic ligands would be different steroids."},{"Start":"01:12.019 ","End":"01:14.600","Text":"You can see that many of these steroids have"},{"Start":"01:14.600 ","End":"01:19.745","Text":"a similar carbon rings skeleton with different functional groups attached."},{"Start":"01:19.745 ","End":"01:24.230","Text":"You may be especially familiar with the female estradiol secreted from"},{"Start":"01:24.230 ","End":"01:30.230","Text":"the ovaries and the male testosterone secreted from the testicles."},{"Start":"01:30.230 ","End":"01:33.980","Text":"These hormones are secreted by the gonads and they\u0027re carried to"},{"Start":"01:33.980 ","End":"01:38.015","Text":"the rest of the body by the bloodstream affecting cells throughout all the body."},{"Start":"01:38.015 ","End":"01:41.270","Text":"On the other hand, water-soluble ligands can go"},{"Start":"01:41.270 ","End":"01:44.449","Text":"right through the bloodstream without using carrier proteins."},{"Start":"01:44.449 ","End":"01:48.305","Text":"Water-soluble ligands are a very diverse group."},{"Start":"01:48.305 ","End":"01:50.900","Text":"They include small molecules, peptides,"},{"Start":"01:50.900 ","End":"01:55.355","Text":"and proteins such as insulin which regulates glucose uptake,"},{"Start":"01:55.355 ","End":"01:58.955","Text":"oxytocin which stimulates smooth muscle contractions,"},{"Start":"01:58.955 ","End":"02:02.915","Text":"and the erythropoietin which acts in the development of red blood cells."},{"Start":"02:02.915 ","End":"02:05.010","Text":"These are polar molecules and although they\u0027re"},{"Start":"02:05.010 ","End":"02:07.460","Text":"soluble in the bloodstream they cannot pass through"},{"Start":"02:07.460 ","End":"02:12.650","Text":"the plasma membrane unaided since the plasma membrane includes the hydrophobic area."},{"Start":"02:12.650 ","End":"02:15.745","Text":"Some are too large to pass through the membrane at all."},{"Start":"02:15.745 ","End":"02:21.605","Text":"Therefore, they mostly bind to the extracellular domain of cell-surface receptors."},{"Start":"02:21.605 ","End":"02:23.585","Text":"There are many other ligands."},{"Start":"02:23.585 ","End":"02:28.190","Text":"One example would be nitric oxide, abbreviated NO."},{"Start":"02:28.190 ","End":"02:31.190","Text":"This is a gas that also acts as a ligand."},{"Start":"02:31.190 ","End":"02:35.563","Text":"It\u0027s able to diffuse directly across the plasma membrane."},{"Start":"02:35.563 ","End":"02:40.175","Text":"It interact with receptors in smooth muscles and induces relaxation of the tissue."},{"Start":"02:40.175 ","End":"02:45.005","Text":"Smooth muscles are found around hollow organs in the body such as the stomach,"},{"Start":"02:45.005 ","End":"02:47.480","Text":"the uterus, or blood vessels."},{"Start":"02:47.480 ","End":"02:53.720","Text":"Causing smooth muscles to relax can have a big effect on the blood pressure, for example."},{"Start":"02:53.720 ","End":"02:56.450","Text":"Controlling smooth muscles around blood vessels can"},{"Start":"02:56.450 ","End":"02:59.335","Text":"have a strong effect on blood pressure, for example."},{"Start":"02:59.335 ","End":"03:02.060","Text":"Nitric oxide interacts with receptors in"},{"Start":"03:02.060 ","End":"03:05.245","Text":"smooth muscles and induces relaxation of the tissue."},{"Start":"03:05.245 ","End":"03:10.685","Text":"Since smooth muscles surround hollow organs in the body such as the stomach,"},{"Start":"03:10.685 ","End":"03:13.150","Text":"the uterus, and blood vessels,"},{"Start":"03:13.150 ","End":"03:16.990","Text":"we can see one example of an effect of nitric oxide of"},{"Start":"03:16.990 ","End":"03:21.490","Text":"relaxing the muscles around blood vessels thus lowering blood pressure."},{"Start":"03:21.490 ","End":"03:24.730","Text":"Since nitric oxide has a very short half-life,"},{"Start":"03:24.730 ","End":"03:26.335","Text":"a matter of seconds,"},{"Start":"03:26.335 ","End":"03:29.185","Text":"it functions over a very short distances."},{"Start":"03:29.185 ","End":"03:31.120","Text":"NO affects are targeted by"},{"Start":"03:31.120 ","End":"03:35.800","Text":"prescription medications for erectile dysfunction such as Viagra."},{"Start":"03:35.800 ","End":"03:39.925","Text":"In this section, we\u0027ve spoken about signaling molecules."},{"Start":"03:39.925 ","End":"03:42.470","Text":"See you in the next section soon."}],"ID":28142},{"Watched":false,"Name":"Exercise 1","Duration":"5m 9s","ChapterTopicVideoID":27010,"CourseChapterTopicPlaylistID":261601,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:02.220","Text":"In this question, we\u0027re asked,"},{"Start":"00:02.220 ","End":"00:07.995","Text":"what property prevents the ligands of cell surface receptors from entering the cell?"},{"Start":"00:07.995 ","End":"00:10.350","Text":"The answers are either A,"},{"Start":"00:10.350 ","End":"00:13.755","Text":"the molecules bind to the extracellular domain."},{"Start":"00:13.755 ","End":"00:17.310","Text":"B, the molecules are hydrophilic and"},{"Start":"00:17.310 ","End":"00:21.465","Text":"cannot penetrate the hydrophobic interior of the plasma membrane."},{"Start":"00:21.465 ","End":"00:24.450","Text":"C, the molecules are attached to"},{"Start":"00:24.450 ","End":"00:28.290","Text":"transport proteins that deliver them through the bloodstream to target cells."},{"Start":"00:28.290 ","End":"00:31.955","Text":"Or D, The ligands are able to penetrate the membrane"},{"Start":"00:31.955 ","End":"00:36.140","Text":"and directly influence gene expression upon receptor binding."},{"Start":"00:36.140 ","End":"00:38.495","Text":"In order to answer this question,"},{"Start":"00:38.495 ","End":"00:42.905","Text":"let\u0027s quickly review the different types of ligand receptors."},{"Start":"00:42.905 ","End":"00:45.125","Text":"Some receptors are internal,"},{"Start":"00:45.125 ","End":"00:47.450","Text":"meaning we find them in the cell,"},{"Start":"00:47.450 ","End":"00:51.020","Text":"either in the cytoplasm or in the nucleus."},{"Start":"00:51.020 ","End":"00:56.420","Text":"In this case, the signaling molecule known as the ligand makes its way through"},{"Start":"00:56.420 ","End":"01:01.550","Text":"the cell membrane and binds to the receptor inside the cell itself."},{"Start":"01:01.550 ","End":"01:03.035","Text":"But in many cases,"},{"Start":"01:03.035 ","End":"01:06.305","Text":"the ligand can\u0027t make its way through the cell membrane."},{"Start":"01:06.305 ","End":"01:08.480","Text":"For this reason, in order to bind with"},{"Start":"01:08.480 ","End":"01:11.375","Text":"ligands that cannot make their way through the cell membrane,"},{"Start":"01:11.375 ","End":"01:15.170","Text":"the cells use several types of cell surface receptors."},{"Start":"01:15.170 ","End":"01:19.610","Text":"Different types of receptors can either open a gated channel,"},{"Start":"01:19.610 ","End":"01:22.445","Text":"can activate enzymes and specifically,"},{"Start":"01:22.445 ","End":"01:26.134","Text":"many of these receptors are G protein-coupled receptors,"},{"Start":"01:26.134 ","End":"01:31.160","Text":"known as GPCR, activating G proteins inside the cell."},{"Start":"01:31.160 ","End":"01:33.620","Text":"In any case, what would be the reason for"},{"Start":"01:33.620 ","End":"01:37.675","Text":"the ligand not being able to make its way through the cell membrane?"},{"Start":"01:37.675 ","End":"01:41.270","Text":"If you listen closely, this is actually the question that we\u0027re being asked."},{"Start":"01:41.270 ","End":"01:43.490","Text":"What is the property that prevents the ligands of"},{"Start":"01:43.490 ","End":"01:46.895","Text":"cell surface receptors from entering the cell?"},{"Start":"01:46.895 ","End":"01:49.535","Text":"Let\u0027s have a look at the cell membrane."},{"Start":"01:49.535 ","End":"01:53.809","Text":"The cell membrane is built of this molecule, the phospholipid."},{"Start":"01:53.809 ","End":"01:56.810","Text":"Here we have the same molecule, the phospholipid,"},{"Start":"01:56.810 ","End":"02:00.350","Text":"2 different reviews illustrated in 2 ways."},{"Start":"02:00.350 ","End":"02:04.130","Text":"The structural formula or this space-filling model."},{"Start":"02:04.130 ","End":"02:10.760","Text":"In any case, we can see that it has a hydrophilic head and 2 hydrophobic tails."},{"Start":"02:10.760 ","End":"02:15.980","Text":"Well, hydrophilic means water-loving and accounts for the fact that this part of"},{"Start":"02:15.980 ","End":"02:19.430","Text":"the molecule is polar and therefore easily forms"},{"Start":"02:19.430 ","End":"02:22.384","Text":"hydrogen bonds with the polar water molecules."},{"Start":"02:22.384 ","End":"02:24.530","Text":"On the other hand, the hydrophobic tails are"},{"Start":"02:24.530 ","End":"02:28.625","Text":"non-polar and therefore they\u0027re repelled by the water molecules."},{"Start":"02:28.625 ","End":"02:31.720","Text":"The cell membrane is built of a bilayer,"},{"Start":"02:31.720 ","End":"02:35.160","Text":"2 layers of these phospholipid molecules."},{"Start":"02:35.160 ","End":"02:41.555","Text":"While the hydrophilic heads face the outside of the cell and the inside of the cell,"},{"Start":"02:41.555 ","End":"02:44.119","Text":"both regions surrounded by water molecules,"},{"Start":"02:44.119 ","End":"02:47.795","Text":"the inside of the membrane includes the hydrophobic tails,"},{"Start":"02:47.795 ","End":"02:54.500","Text":"creating a hydrophobic region where hydrophilic molecules cannot get through."},{"Start":"02:54.500 ","End":"02:58.880","Text":"Therefore, a hydrophobic molecule would easily make"},{"Start":"02:58.880 ","End":"03:03.350","Text":"its way through the hydrophobic region and reach the inside of the cell,"},{"Start":"03:03.350 ","End":"03:04.985","Text":"whereas the hydrophilic,"},{"Start":"03:04.985 ","End":"03:09.334","Text":"water-loving ligand, would easily pass through the bloodstream."},{"Start":"03:09.334 ","End":"03:15.820","Text":"It would not be able to easily pass the hydrophobic region of the hydrophobic tails."},{"Start":"03:15.820 ","End":"03:22.580","Text":"For this reason, it would need to connect to an extracellular cell surface receptor."},{"Start":"03:22.580 ","End":"03:24.860","Text":"Now let\u0027s have a look at our answers."},{"Start":"03:24.860 ","End":"03:29.150","Text":"Answer A states that the molecules bind to the extracellular domain."},{"Start":"03:29.150 ","End":"03:31.250","Text":"Well, that is true,"},{"Start":"03:31.250 ","End":"03:34.100","Text":"but it\u0027s not the reason that they can\u0027t penetrate the membrane."},{"Start":"03:34.100 ","End":"03:37.640","Text":"We could cross out answer A that\u0027s irrelevant to the question."},{"Start":"03:37.640 ","End":"03:39.590","Text":"Let\u0027s have a look at answer B."},{"Start":"03:39.590 ","End":"03:43.310","Text":"The molecules are hydrophilic and cannot penetrate"},{"Start":"03:43.310 ","End":"03:47.215","Text":"the hydrophobic interior of the plasma membrane."},{"Start":"03:47.215 ","End":"03:49.880","Text":"That sounds true. That\u0027s what we explained."},{"Start":"03:49.880 ","End":"03:52.160","Text":"But before we choose the correct answer,"},{"Start":"03:52.160 ","End":"03:55.655","Text":"let\u0027s have a look at the other answers to make sure that there\u0027s nothing even better."},{"Start":"03:55.655 ","End":"03:58.370","Text":"Answer C states that the molecules are attached to"},{"Start":"03:58.370 ","End":"04:02.270","Text":"transport proteins that deliver them through the bloodstream to target cells."},{"Start":"04:02.270 ","End":"04:07.220","Text":"Since these hydrophilic molecules are polar and they easily dissolve in water."},{"Start":"04:07.220 ","End":"04:08.645","Text":"As a rule of thumb,"},{"Start":"04:08.645 ","End":"04:12.755","Text":"usually they don\u0027t need transport proteins to deliver them through the bloodstream,"},{"Start":"04:12.755 ","End":"04:14.600","Text":"as opposed to a hydrophobic signaling"},{"Start":"04:14.600 ","End":"04:17.645","Text":"molecules that could not dissolve in the bloodstream."},{"Start":"04:17.645 ","End":"04:21.290","Text":"In any case even such signaling molecules that are"},{"Start":"04:21.290 ","End":"04:25.100","Text":"hydrophobic and need to be carried by transport proteins,"},{"Start":"04:25.100 ","End":"04:29.405","Text":"are released by these transport proteins when they reach the cell surface."},{"Start":"04:29.405 ","End":"04:32.525","Text":"Answer C is wrong in any case and we can cross it out."},{"Start":"04:32.525 ","End":"04:35.960","Text":"Answer D states that the ligands are able to penetrate"},{"Start":"04:35.960 ","End":"04:40.210","Text":"the membrane and directly influence gene expression upon receptor binding."},{"Start":"04:40.210 ","End":"04:41.945","Text":"That as we\u0027ve seen,"},{"Start":"04:41.945 ","End":"04:46.880","Text":"is true only for signaling molecules that bind to intracellular receptors and"},{"Start":"04:46.880 ","End":"04:52.235","Text":"not to those who bind to cell surface receptors that were asked about in this question."},{"Start":"04:52.235 ","End":"04:54.710","Text":"Answer D is wrong too."},{"Start":"04:54.710 ","End":"04:58.280","Text":"We can mark answer B as a correct answer."},{"Start":"04:58.280 ","End":"05:00.620","Text":"The property that prevents the ligands of"},{"Start":"05:00.620 ","End":"05:05.375","Text":"cell surface receptors from entering the cell is that the molecules are hydrophilic."},{"Start":"05:05.375 ","End":"05:09.900","Text":"They cannot penetrate the hydrophobic interior of the plasma membrane."}],"ID":28143},{"Watched":false,"Name":"Exercise 2","Duration":"2m 31s","ChapterTopicVideoID":27011,"CourseChapterTopicPlaylistID":261601,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:02.715","Text":"In this question, we\u0027re asked if the secretion of"},{"Start":"00:02.715 ","End":"00:06.945","Text":"hormones by the pituitary gland is an example of a,"},{"Start":"00:06.945 ","End":"00:10.950","Text":"autocrine signaling, b, paracrine signaling,"},{"Start":"00:10.950 ","End":"00:13.545","Text":"c, endocrine signaling,"},{"Start":"00:13.545 ","End":"00:17.010","Text":"or d, direct signaling across gap junctions."},{"Start":"00:17.010 ","End":"00:19.530","Text":"Let\u0027s have a look at the different methods of signaling."},{"Start":"00:19.530 ","End":"00:25.680","Text":"In autocrine signaling cells signal to themselves or to similar cells right next to them."},{"Start":"00:25.680 ","End":"00:30.320","Text":"As we can see, the cell is secreting the signal molecule which is binding to"},{"Start":"00:30.320 ","End":"00:35.540","Text":"a receptor on its own membrane causing a response in the same cell."},{"Start":"00:35.540 ","End":"00:39.425","Text":"Therefore, it\u0027s autocrine signaling, auto meaning self."},{"Start":"00:39.425 ","End":"00:42.485","Text":"On the other hand, in paracrine signaling,"},{"Start":"00:42.485 ","End":"00:46.295","Text":"cell may signals to a group of local cells that are close together."},{"Start":"00:46.295 ","End":"00:50.180","Text":"The signals move by diffusion through the extracellular matrix."},{"Start":"00:50.180 ","End":"00:59.330","Text":"This signaling although usually rather quick is a bit slower than autocrine signaling."},{"Start":"00:59.330 ","End":"01:00.755","Text":"In endocrine signaling,"},{"Start":"01:00.755 ","End":"01:04.220","Text":"cells that are at a great distance from the target cells signal"},{"Start":"01:04.220 ","End":"01:07.920","Text":"by secreting a special signaling molecule called a hormone."},{"Start":"01:07.920 ","End":"01:10.790","Text":"The hormones flow through the bloodstream and get to"},{"Start":"01:10.790 ","End":"01:14.165","Text":"the whole body where they eventually reach the target cells."},{"Start":"01:14.165 ","End":"01:17.090","Text":"This being long-distance signaling is usually"},{"Start":"01:17.090 ","End":"01:19.895","Text":"slower than autocrine and paracrine signaling."},{"Start":"01:19.895 ","End":"01:21.635","Text":"It also lasts for longer,"},{"Start":"01:21.635 ","End":"01:26.345","Text":"as it takes longer for the signaling hormones to clear from the bloodstream."},{"Start":"01:26.345 ","End":"01:30.110","Text":"The fastest signaling is direct similar across gap junctions."},{"Start":"01:30.110 ","End":"01:32.780","Text":"Both animal cells and plant cells have"},{"Start":"01:32.780 ","End":"01:36.050","Text":"special connections between adjacent cells and animal cells."},{"Start":"01:36.050 ","End":"01:37.550","Text":"They\u0027re called gap junctions,"},{"Start":"01:37.550 ","End":"01:40.355","Text":"and in plant cells, they\u0027re called plasmodesmata."},{"Start":"01:40.355 ","End":"01:45.500","Text":"Here the signaling substances in the cytosol can pass freely between the adjacent cells."},{"Start":"01:45.500 ","End":"01:49.040","Text":"Let\u0027s clear all this explanation here and get to our question."},{"Start":"01:49.040 ","End":"01:53.230","Text":"The secretion of hormones by the pituitary gland is an example of?"},{"Start":"01:53.230 ","End":"01:56.310","Text":"The pituitary gland is here, it\u0027s in the brain."},{"Start":"01:56.310 ","End":"02:00.500","Text":"It signals to many different parts of the body by secreting hormones to"},{"Start":"02:00.500 ","End":"02:03.140","Text":"the bloodstream and since this is not an example"},{"Start":"02:03.140 ","End":"02:06.065","Text":"of autocrine signaling from one cell to itself."},{"Start":"02:06.065 ","End":"02:08.385","Text":"Paracrine signaling, signaling between"},{"Start":"02:08.385 ","End":"02:15.650","Text":"a group of cells in close proximity or direct signaling across gap junctions,"},{"Start":"02:15.650 ","End":"02:17.750","Text":"we can cross out answers a, b,"},{"Start":"02:17.750 ","End":"02:22.340","Text":"and d. The pituitary gland is a good example for endocrine signaling."},{"Start":"02:22.340 ","End":"02:26.015","Text":"Answer\u0027s c, by secreting hormones from one part of the body,"},{"Start":"02:26.015 ","End":"02:31.410","Text":"the brain, through the bloodstream to many target cells all across the body."}],"ID":28144},{"Watched":false,"Name":"Exercise 3","Duration":"6m 27s","ChapterTopicVideoID":27008,"CourseChapterTopicPlaylistID":261601,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:06.615","Text":"Why are ion channels necessary to transport ions into or out of a cell?"},{"Start":"00:06.615 ","End":"00:11.325","Text":"A, ions are too large to diffuse through the membrane."},{"Start":"00:11.325 ","End":"00:14.775","Text":"B, ions are charged particles,"},{"Start":"00:14.775 ","End":"00:18.840","Text":"and cannot diffuse through the hydrophobic interior of the membrane."},{"Start":"00:18.840 ","End":"00:23.250","Text":"C, ions do not need ion channels to move through the membrane."},{"Start":"00:23.250 ","End":"00:28.459","Text":"Or D, ions bind the carrier proteins in the bloodstream,"},{"Start":"00:28.459 ","End":"00:32.270","Text":"which must be removed before transport into the cell."},{"Start":"00:32.270 ","End":"00:34.880","Text":"In order to answer this question,"},{"Start":"00:34.880 ","End":"00:38.495","Text":"let\u0027s speak about hydrophobic and hydrophilic molecules."},{"Start":"00:38.495 ","End":"00:43.805","Text":"These are water molecules made of 1 oxygen atom and 2 hydrogen atoms."},{"Start":"00:43.805 ","End":"00:45.680","Text":"Here are 3 water molecules."},{"Start":"00:45.680 ","End":"00:49.595","Text":"Each molecule is made out of 1 oxygen atom,"},{"Start":"00:49.595 ","End":"00:51.440","Text":"and 2 hydrogen atoms."},{"Start":"00:51.440 ","End":"00:55.550","Text":"The atoms in the molecule are connected by covalent bonds,"},{"Start":"00:55.550 ","End":"00:59.750","Text":"meaning the electrons in this molecule are shared between the atoms."},{"Start":"00:59.750 ","End":"01:02.660","Text":"But since the electronegativity of"},{"Start":"01:02.660 ","End":"01:07.045","Text":"oxygen is stronger than the electronegativity of hydrogen atoms,"},{"Start":"01:07.045 ","End":"01:09.050","Text":"the electrons are found around"},{"Start":"01:09.050 ","End":"01:13.235","Text":"the oxygen atom more time than they are around the hydrogen atom."},{"Start":"01:13.235 ","End":"01:16.415","Text":"For this reason, the water molecule is polar."},{"Start":"01:16.415 ","End":"01:19.490","Text":"Meaning that 1 end, the oxygen end,"},{"Start":"01:19.490 ","End":"01:23.225","Text":"has a Delta of negative electric charge."},{"Start":"01:23.225 ","End":"01:24.770","Text":"While the pole,"},{"Start":"01:24.770 ","End":"01:27.080","Text":"or the side where the hydrogen atoms are,"},{"Start":"01:27.080 ","End":"01:31.565","Text":"has a Delta of a positive electric charge."},{"Start":"01:31.565 ","End":"01:34.670","Text":"Therefore, we could say that each of these water molecules is"},{"Start":"01:34.670 ","End":"01:38.900","Text":"polar with a negative charge on the oxygen side,"},{"Start":"01:38.900 ","End":"01:41.810","Text":"and a positive charge on the hydrogen side."},{"Start":"01:41.810 ","End":"01:44.480","Text":"As we know, negative electric charges and"},{"Start":"01:44.480 ","End":"01:47.885","Text":"positive electric charges are attracted to each other."},{"Start":"01:47.885 ","End":"01:52.280","Text":"These attractions form loose bonds called hydrogen bonds."},{"Start":"01:52.280 ","End":"01:55.205","Text":"Hydrogen bonds continuously form between"},{"Start":"01:55.205 ","End":"01:58.745","Text":"oxygen molecules and hydrogen molecules in water."},{"Start":"01:58.745 ","End":"02:00.080","Text":"Since the water is fluid,"},{"Start":"02:00.080 ","End":"02:02.255","Text":"and the molecules keep on moving between each other,"},{"Start":"02:02.255 ","End":"02:06.860","Text":"the hydrogen bonds are formed and degraded constantly."},{"Start":"02:06.860 ","End":"02:08.855","Text":"But not only does the polarity of water"},{"Start":"02:08.855 ","End":"02:11.900","Text":"affect the bonds between water molecules themselves,"},{"Start":"02:11.900 ","End":"02:13.895","Text":"water molecules being polar,"},{"Start":"02:13.895 ","End":"02:16.170","Text":"having 1 negative pole,"},{"Start":"02:16.170 ","End":"02:22.565","Text":"and when the positive pole are easily attracted to any negative or positive atom."},{"Start":"02:22.565 ","End":"02:24.500","Text":"This way, table salt,"},{"Start":"02:24.500 ","End":"02:27.835","Text":"or NaCl, is dissolved in water."},{"Start":"02:27.835 ","End":"02:33.440","Text":"As you can see, the negative chlorine ion attracts the positive sodium atom,"},{"Start":"02:33.440 ","End":"02:36.710","Text":"attract the negatively charged oxygen atoms."},{"Start":"02:36.710 ","End":"02:39.020","Text":"In this way, the salt is dissolved in"},{"Start":"02:39.020 ","End":"02:42.260","Text":"the water as the ions are disconnected from 1 another,"},{"Start":"02:42.260 ","End":"02:45.800","Text":"and form bonds with a different poles of the water molecules."},{"Start":"02:45.800 ","End":"02:47.885","Text":"In this way, any positively,"},{"Start":"02:47.885 ","End":"02:50.810","Text":"or negatively, or polar molecules,"},{"Start":"02:50.810 ","End":"02:52.370","Text":"will dissolve in water."},{"Start":"02:52.370 ","End":"02:57.380","Text":"Therefore, they\u0027re named hydrophilic molecules, water-loving molecules."},{"Start":"02:57.380 ","End":"03:01.535","Text":"On the other hand, if we put in molecules that are not charged at all,"},{"Start":"03:01.535 ","End":"03:06.170","Text":"the water molecules will form hydrogen bonds only with each other."},{"Start":"03:06.170 ","End":"03:09.500","Text":"The uncharged molecules will eventually be pushed"},{"Start":"03:09.500 ","End":"03:12.815","Text":"away as the water molecules form the bonds with each other."},{"Start":"03:12.815 ","End":"03:15.875","Text":"That\u0027s what happens when you pour oil into a cup of water."},{"Start":"03:15.875 ","End":"03:17.510","Text":"The oil being hydrophobic,"},{"Start":"03:17.510 ","End":"03:20.105","Text":"or water repelling molecules,"},{"Start":"03:20.105 ","End":"03:23.020","Text":"are not dissolved by the polar water molecules."},{"Start":"03:23.020 ","End":"03:27.050","Text":"Our next step of understanding the transport of ions into and out of the cell,"},{"Start":"03:27.050 ","End":"03:31.350","Text":"will require us to have a close look at the cell membrane."},{"Start":"03:31.490 ","End":"03:35.794","Text":"The Cell membrane is composed of a bi-layer of this molecule."},{"Start":"03:35.794 ","End":"03:38.450","Text":"The phospholipid has a hydrophilic head."},{"Start":"03:38.450 ","End":"03:42.920","Text":"As you can see, it has a phosphate group which is charged, and polar."},{"Start":"03:42.920 ","End":"03:46.610","Text":"Therefore, the head of this molecule is hydrophilic,"},{"Start":"03:46.610 ","End":"03:51.115","Text":"water-loving, attracted to water, soluble in water."},{"Start":"03:51.115 ","End":"03:55.655","Text":"On the other hand, the 2 tails made of fatty acids,"},{"Start":"03:55.655 ","End":"03:58.415","Text":"like oil are hydrophobic."},{"Start":"03:58.415 ","End":"04:01.255","Text":"Meaning that they cannot dissolve in water."},{"Start":"04:01.255 ","End":"04:05.195","Text":"Here, we have our phospholipid in a space filling model."},{"Start":"04:05.195 ","End":"04:07.685","Text":"We have here the hydrophilic head,"},{"Start":"04:07.685 ","End":"04:11.425","Text":"and the 2 hydrophobic water repelling tails."},{"Start":"04:11.425 ","End":"04:15.060","Text":"The cell membrane, the bi-layer is organized,"},{"Start":"04:15.060 ","End":"04:19.985","Text":"so that the hydrophilic water-loving heads are facing the outside of the cell,"},{"Start":"04:19.985 ","End":"04:23.570","Text":"the watery area, which is also watery area."},{"Start":"04:23.570 ","End":"04:27.590","Text":"On the other hand, the interior of the membrane composes the fatty acids,"},{"Start":"04:27.590 ","End":"04:29.735","Text":"repels water, and is hydrophobic."},{"Start":"04:29.735 ","End":"04:31.595","Text":"If we look at the membrane,"},{"Start":"04:31.595 ","End":"04:33.980","Text":"any molecule soluble in water,"},{"Start":"04:33.980 ","End":"04:37.580","Text":"hydrophilic which can easily reach the cell membrane,"},{"Start":"04:37.580 ","End":"04:41.030","Text":"will not be able to pass the hydrophobic interior of"},{"Start":"04:41.030 ","End":"04:45.710","Text":"the cell membrane to reach the watery area on the inside of the cell."},{"Start":"04:45.710 ","End":"04:51.550","Text":"Therefore, the net transport molecules that could take them through this membrane."},{"Start":"04:51.550 ","End":"04:54.150","Text":"Now, let\u0027s have a look at our answers again."},{"Start":"04:54.150 ","End":"04:58.235","Text":"A, ions are too large to diffuse through the membrane."},{"Start":"04:58.235 ","End":"05:00.110","Text":"No, they\u0027re not too large."},{"Start":"05:00.110 ","End":"05:01.490","Text":"They could easily fit."},{"Start":"05:01.490 ","End":"05:04.540","Text":"As we just mentioned, the problem is not their size,"},{"Start":"05:04.540 ","End":"05:06.980","Text":"rather their electric charge."},{"Start":"05:06.980 ","End":"05:09.020","Text":"We can cross out answer A."},{"Start":"05:09.020 ","End":"05:12.500","Text":"Let\u0027s have a look at answer B. Ions are charged particles,"},{"Start":"05:12.500 ","End":"05:18.035","Text":"and cannot diffuse through the hydrophobic interior of the membrane. That sounds right."},{"Start":"05:18.035 ","End":"05:20.240","Text":"But before we choose our correct answer,"},{"Start":"05:20.240 ","End":"05:23.980","Text":"let\u0027s have a look at the other answers and make sure that none of them are even better."},{"Start":"05:23.980 ","End":"05:25.635","Text":"Answer C states that,"},{"Start":"05:25.635 ","End":"05:28.745","Text":"ions do not need ion channels to move through the membrane."},{"Start":"05:28.745 ","End":"05:30.980","Text":"We\u0027ve just explained why they do need,"},{"Start":"05:30.980 ","End":"05:35.660","Text":"because of course they\u0027re hydrophilic and the interior is hydrophobic."},{"Start":"05:35.660 ","End":"05:38.575","Text":"They can not mix and they cannot pass in between."},{"Start":"05:38.575 ","End":"05:42.670","Text":"We can cross out answer C. Answer D states that,"},{"Start":"05:42.670 ","End":"05:45.455","Text":"ions bind the carrier proteins in the bloodstream,"},{"Start":"05:45.455 ","End":"05:48.545","Text":"which must be removed before transport into the cell."},{"Start":"05:48.545 ","End":"05:53.480","Text":"It\u0027s true that some molecules are carried in the bloodstream by carrier proteins."},{"Start":"05:53.480 ","End":"05:57.215","Text":"Since ions are hydrophilic, water-loving,"},{"Start":"05:57.215 ","End":"05:59.720","Text":"you can usually expect ions to be dissolved in"},{"Start":"05:59.720 ","End":"06:03.410","Text":"the bloodstream with no use of carrier proteins at all."},{"Start":"06:03.410 ","End":"06:07.980","Text":"At any case, that would be irrelevant for transport into the cell."},{"Start":"06:07.980 ","End":"06:10.560","Text":"We can cross out answer D,"},{"Start":"06:10.560 ","End":"06:12.675","Text":"and choose a correct answer,"},{"Start":"06:12.675 ","End":"06:18.050","Text":"answer B. Ion channels are necessarily to transport ions into and out of a cell,"},{"Start":"06:18.050 ","End":"06:20.165","Text":"because the ions are charged particles."},{"Start":"06:20.165 ","End":"06:26.970","Text":"They cannot diffuse through the hydrophobic water repelling interior of the membrane."}],"ID":28145},{"Watched":false,"Name":"Exercise 4","Duration":"3m 24s","ChapterTopicVideoID":27009,"CourseChapterTopicPlaylistID":261601,"HasSubtitles":true,"ThumbnailPath":null,"UploadDate":null,"DurationForVideoObject":null,"Description":null,"MetaTitle":null,"MetaDescription":null,"Canonical":null,"VideoComments":[],"Subtitles":[{"Start":"00:00.000 ","End":"00:02.220","Text":"Hi. In this question,"},{"Start":"00:02.220 ","End":"00:04.290","Text":"we\u0027re asked about the difference of speed"},{"Start":"00:04.290 ","End":"00:07.185","Text":"between endocrine signaling and paracrine signaling."},{"Start":"00:07.185 ","End":"00:09.045","Text":"Let\u0027s have a look at the question."},{"Start":"00:09.045 ","End":"00:14.220","Text":"Endocrine signals are transmitted more slowly than paracrine signals."},{"Start":"00:14.220 ","End":"00:16.490","Text":"Because an endocrine signaling."},{"Start":"00:16.490 ","End":"00:23.037","Text":"A, the ligands are transported through the bloodstream and travel greater distances."},{"Start":"00:23.037 ","End":"00:25.830","Text":"B, endocrine signaling is slower because"},{"Start":"00:25.830 ","End":"00:29.940","Text":"an endocrine signaling the target and the signaling cells are close together."},{"Start":"00:29.940 ","End":"00:36.075","Text":"C, endocrine signals are slower than paracrine signals because an endocrine signals,"},{"Start":"00:36.075 ","End":"00:38.460","Text":"the ligands are degraded rapidly."},{"Start":"00:38.460 ","End":"00:41.250","Text":"Or d, the endocrine signals are"},{"Start":"00:41.250 ","End":"00:46.415","Text":"slower because the ligands don\u0027t bind to carrier proteins during transport."},{"Start":"00:46.415 ","End":"00:50.150","Text":"A quick reminder about endocrine signaling and paracrine signaling."},{"Start":"00:50.150 ","End":"00:54.950","Text":"Endocrine signaling is a long distance signaling by chemicals called hormones."},{"Start":"00:54.950 ","End":"01:00.380","Text":"The hormones are released by specialized cells placed in specific organs in the body."},{"Start":"01:00.380 ","End":"01:02.210","Text":"The hormones then travel through"},{"Start":"01:02.210 ","End":"01:06.290","Text":"the bloodstream to various target cells all over the body."},{"Start":"01:06.290 ","End":"01:08.955","Text":"On the other hand, in paracrine signaling,"},{"Start":"01:08.955 ","End":"01:12.710","Text":"the signals act locally between cells that are close together."},{"Start":"01:12.710 ","End":"01:17.270","Text":"The signals move by diffusion through the extracellular matrix."},{"Start":"01:17.270 ","End":"01:18.950","Text":"In paracrine signaling,"},{"Start":"01:18.950 ","End":"01:22.415","Text":"the response is usually very fast in the receiving cell,"},{"Start":"01:22.415 ","End":"01:25.295","Text":"it only lasts a short period of time."},{"Start":"01:25.295 ","End":"01:30.605","Text":"The ligand molecules are quickly degraded by enzymes or avoided by neighboring cells."},{"Start":"01:30.605 ","End":"01:33.185","Text":"Now let\u0027s have a look at our answers."},{"Start":"01:33.185 ","End":"01:36.590","Text":"A, in endocrine signaling the ligands and"},{"Start":"01:36.590 ","End":"01:40.460","Text":"transported through the bloodstream and travel greater distances."},{"Start":"01:40.460 ","End":"01:41.970","Text":"Yes, that\u0027s true."},{"Start":"01:41.970 ","End":"01:44.750","Text":"That would cause a signal to be much slower than"},{"Start":"01:44.750 ","End":"01:49.955","Text":"paracrine signalins that are transmitted by adjacent cells."},{"Start":"01:49.955 ","End":"01:51.820","Text":"This answer looks right,"},{"Start":"01:51.820 ","End":"01:53.400","Text":"but before choosing a,"},{"Start":"01:53.400 ","End":"01:54.665","Text":"is a correct answer."},{"Start":"01:54.665 ","End":"01:57.260","Text":"Let\u0027s have a look at answers b, c,"},{"Start":"01:57.260 ","End":"02:00.880","Text":"and d, and make sure that none of them are even better than this 1."},{"Start":"02:00.880 ","End":"02:03.740","Text":"Answer b states that an endocrine"},{"Start":"02:03.740 ","End":"02:07.295","Text":"signaling the target and signaling cells are close together."},{"Start":"02:07.295 ","End":"02:10.505","Text":"That is not true. Endocrine signaling."},{"Start":"02:10.505 ","End":"02:14.585","Text":"The signaling cells can be in the brain or in the ovaries and testes,"},{"Start":"02:14.585 ","End":"02:17.375","Text":"or in any other specialized secreting gland."},{"Start":"02:17.375 ","End":"02:21.440","Text":"The hormones travel through the bloodstream to anywhere else in the body."},{"Start":"02:21.440 ","End":"02:25.310","Text":"The hormones then travel through the bloodstream to the whole body,"},{"Start":"02:25.310 ","End":"02:28.475","Text":"affecting cells in various places throughout the body,"},{"Start":"02:28.475 ","End":"02:31.685","Text":"so b is wrong. We can cross out b."},{"Start":"02:31.685 ","End":"02:37.070","Text":"Let\u0027s have a look at answer c. In endocrine signaling the ligands are degraded rapidly."},{"Start":"02:37.070 ","End":"02:39.530","Text":"Well, this again like answer b,"},{"Start":"02:39.530 ","End":"02:41.300","Text":"is true for paracrine signaling,"},{"Start":"02:41.300 ","End":"02:42.970","Text":"not for endocrine signaling,"},{"Start":"02:42.970 ","End":"02:48.190","Text":"which is usually a long-term signal. C is wrong also."},{"Start":"02:48.190 ","End":"02:53.405","Text":"We can cross out answer c. Answer d it says the endocrine signals"},{"Start":"02:53.405 ","End":"02:58.325","Text":"are slower because the ligands don\u0027t bind to carrier proteins during transport,"},{"Start":"02:58.325 ","End":"03:03.010","Text":"which is not necessarily true and also would not slow down the signal."},{"Start":"03:03.010 ","End":"03:07.535","Text":"We can cross that answer d and select a as a correct answer."},{"Start":"03:07.535 ","End":"03:10.610","Text":"Endocrine signals are transmitted more slowly"},{"Start":"03:10.610 ","End":"03:13.580","Text":"than paracrine signals because an endocrine signaling,"},{"Start":"03:13.580 ","End":"03:15.140","Text":"the ligands are transported through"},{"Start":"03:15.140 ","End":"03:18.980","Text":"the bloodstream and they need to travel a greater distance"},{"Start":"03:18.980 ","End":"03:21.470","Text":"than in paracrine signals that are"},{"Start":"03:21.470 ","End":"03:25.530","Text":"local signals between cells that are close to each other."}],"ID":28146}],"Thumbnail":null,"ID":261601}]

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