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Main content
Current time:0:00Total duration:13:11
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Video transcript

so what I want to do in this video is give ourselves an overview of cellular respiration and it can be a pretty involved process and even the way I'm going to do it as messy as it looks it's going to be cleaner than actually what goes on inside of your cells and other organism cells because I'm going to show clearly from going from glucose and then see how we can produce ATP through glycolysis and the Krebs cycle and oxidative phosphorylation but in reality all sorts of molecules can jump in at different parts of the chain and then jump out at different parts of the chain to go along other pathways but I'll show kind of the traditional the traditional narrative so we're going to start off with for this and narrative we're going to start off with glucose we have a six carbon chain right over here and we have the process of glycolysis which is occurring in the cytosol the cytosol of our cell so if this is the cell right over here you could imagine well the glycolysis the glycolysis could be occurring right over there and that process of glycolysis is essentially splitting up this six carbon glucose molecule into two 3-carbon molecules and these three these three carbon molecules we go into detail into another in another video we call these pyruvate by ruvé eight and in the process of doing so and this is like you could say the point of glycolysis we're able to on a net basis produce two ATP's we actually produce four but we have to use two so on a net basis we produce two ATP's I'm going to keep a little table here to keep track so we produce two ATP's and we are also we're also in the process of that we reduce to nad molecules to NADH remember reduction is gaining of electrons and you see over here this is positively charged this is neutrally charged it essentially gains a hydride so this is reduction reduction and if we go all the way through the pathway all the way to oxidative phosphorylation the electron transport chain these NADH is these these the the reduced form of nad they can be then oxidized to provide and in doing so more energy is provided to provide to produce even more ATP's but we'll get to that so you're also going to get to nadh --is two na DHS get produced now at that point you could kind of think of it is a little bit of a decision point if there's no oxygen around or if you're the type of organism that doesn't want to continue for some reason with cellular respiration or doesn't know how this pyruvate can be used for fermentation and we have videos on fermentation lactic acid fermentation alcohol fermentation and fermentation is all about using the pyruvates to oxidize your NADH back into nad so it could be reused again for glycolysis so even though the NADH has energy that could be eventually converted to ATP and even though the pyruvates have energy that could eventually be converted into ATP when you do fermentation you kind of give up on that and you just view them as waste projects and you use the pyruvate to convert the NADH back into nad and then glycolysis can occur glycolysis can occur again but let's assume we're not going to go down the fermentation pathway and we're going to continue with traditional aerobic cellular respiration using oxygen well the next thing that's going to happen is that the carboxyl group and everything I'm going to show now it's going to happen for each of these pyruvate so you can imagine these things all happening twice so I'm going to multiply a bunch of things times two but what happens in the next step is this carboxyl group this carboxyl group is stripped off of the pyruvate and it essentially is going to be released as carbon dioxide so this is our carbon dioxide being released here and then the rest of our pyruvate which is essentially an acetyl group that latches on to coenzyme a and you'll hear a lot about coenzyme a sometimes they'll write just you know Co a like this sometimes we'll do Co a and then the sulfur connect bonded to the hydrogen and the reason why they'll draw the sulfur part is because the sulfur is what bonds with the acetyl group right over here but when so you have the carbon dioxide being released and then the acetyl group the acetyl group bonding with that sulfur and by doing that you form acetyl co a and acetyl co a just so you know you only see three letters here but this is actually a fairly involved molecule this is actually a picture of acetyl co a I know it's really small but hopefully you appreciate it's a more involved molecule that eatle group that we're talking about is just this part right over here and it's a coenzyme it's really acting to transfer that acetyl group and we'll see that in a second but it's also fun to look at these molecules because once again we see these patterns over and over again in biology or biochemistry acetyl co a you have an adenine right over here it's hard to see but you have a ribose and you also have two phosphate groups so this end of the acetyl co a is essentially is essentially an ADP but it's used as a coenzyme everything that I'm talking about this is all going to be facilitated by enzymes and the enzymes will have will have cofactors coenzymes if we're talking about organic cofactors that are going to help facilitate things along and as we see the acetyl group joins on to the coenzyme a forming acetyl co a but that's just a temporary attachment that the acetyl co is essentially going to transfer the acetyl group over to and now we're going to enter into into the citric acid cycle it's going to transfer these two carbons over to oxaloacetic acid to form citric acid so it's going to transfer these two carbons to this one two three four carbon molecule to form eight one two three four five six carbon molecule but before we go into the depths of the citric acid cycle I want to make sure that I don't lose track of my accounting because even that that step right over here where we decarboxylated the pyruvate we went from pyruvate to acetyl co a that also reduced some nad to NADH now this is going to happen once for each pyruvate but we're going to L the accounting we're going to say is for one glucose molecule so that for one glucose molecule is going to happen for each of the pyruvate so this is going to be times this is going to be times two so we're going to produce two na two NADH a--'s in this step going from pyruvate to acetyl co a now the bulk of I guess you could say the the catabolism of the carbons or the things that are eventually going to produce our our ATP's are going to happen in what we call the citric acid or the Krebs cycle it's called the citric acid cycle because when we transferred the acetyl group from the coenzyme a to the excel o acetic acid we formed citric acid and citric acid this is the thing that you have in lemons or orange juice it is it is this molecule right over here and the citric acid cycle and it's also called the Krebs cycle when you first learn it seems very very complex and some could argue that it is quite complex but I'm just going to give you an overview of what's going on the citric acid once again six-carbon it keeps getting broken down through multiple steps and I am really not showing all of the detail here all the way back to oxaloacetic acid where then it can accept and it can accept the two carbons again and just to be clear once the two carbons are released by the coenzyme a then it can that coenzyme a can be used again to decarboxylate some pyruvate so there's a bunch of cycles going on but the important takeaway is as we go through the citric acid cycle as we go from one intermediary to the next we keep reducing nad nad to NADH in fact we do this three times for each cycle of the citric acid cycle but remember we're going to do this for each for each acetyl co a for each pyruvate so all of this stuff is going to happen twice so for we're going to go through it twice for each original glucose molecule so here we have 1 2 3 nadh --is being produced but since we're going to go through it twice and we're going to be accounting for the original glucose molecule we could say that we have 6 na 6 na D H's 6 or you could say 6 nad is get reduced to NADH now you also in the process as you're breaking down going from going from the six carbon molecule to a four carbon molecule you're releasing carbon as carbon dioxide and you also have traditionally GDP being converted into gtp or sometimes adp converted to ATP but functionally it's equivalent to ATP either way so we could also say that we're going to directly remember going to do all of this stuff twice so we could say that to - I'll to say two ATP's to make it simple we could say gtp but I'll say two ATP's because once again this happens once in each cycle but we're going to do two cycles for each glucose and then we have this other enzyme right over here f ad that gets reduced to fadh2 but that stays covalently attached to the enzymes that are facilitating it so eventually that's being that's that's being used to reduce to reduce coenzyme q 2 q h2 so I'm just going to write the Q H 2 here but once again you're gonna get two of these so 2 2 Q 2 Q h2 q h2 s now let's think about what the net product over here is going to be and to think about it we should we should just will just and I'll do a little bit of a shorthand we'll go into more detail in future videos is these coenzymes the the nadh the the the qh - these are going to be oxidized during oxidative phosphorylation or and the electron transport chain to create a proton gradient across the inner membrane of mitochondria we're going to go into much more detail in the future but the that proton gradient is going to be used to produce more ATP and one way to think about it is each NADH each NADH is going to produce and I've seen a count it depends on the efficiency and where the NADH is actually going to be produced but it's going to produce anywhere between two and three ATP's the each Q each of the each of the reduced coenzyme q s so the Q H - that's going to each produce about one-and-a-half ATP's and people are still getting a good handle on exactly how this is happening it depends on the efficiency of the cell and what the cell is actually trying to do so using these using these ranges actually I'll say one and a half to two one and a half to two ATP's and these are these are our approximate numbers so let's think about let's think about what our total accounting is so if we just count up the ATP or the GTP's we're going to get to there to there so we're going to have for direct or very close to direct ATP's net being created and then how many NADH is we have to 4 and then we add 6 we have 10 NADH ten n/a DHS and then we have two of the coenzyme q 2 q h 2 s so that's going to be four ATP's this is going to be between this is going to be between 20 and 30 nadh --is sorry 20 and 30 ATP's 20 to 30 ATP's and then this is going to be 3 to 4 3 to 4 ATP's so if you add them all together if you add the low ends of the range you get let's see 20 plus 3 plus 4 this 27 ATP's twenty-seven ATP's and the high end of the range let's see you have 4 plus 30 plus 4 you have 38 38 ATP's and 38 ATP's is currently considered to be kind of a theoretical maximum but when we actually observe things in cells it looks like it comes around and around 29 to 30 ATP's and this once again it depends what the cells trying to do the type of cells and the type of efficiency but all of this is happening through cellular respiration and just to get a better sense of where all of this is occurring we're all disagreeing we said glycolysis is occurring in the cytosol the citric acid cycle this is occurring in the in the matrix of the mitochondria so this space right over here that is the citric acid cycle and that little magenta space that I've drawn so that's the matrix the video on mitochondria we go into much more detail on that and then the actual conversion of these coenzymes of you know the electron transport chain that's occurring across the membrane of the crista and the crista are these folds these kind of inner membrane folds of our mitochondria so it's occurring across that across those the membranes of those of of these actually the plural is Krista Krista is a is the singular of the Chris tied we'll go into more detail into that in other videos
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