Next lesson. Current timeTotal duration Google Classroom Facebook Twitter. Video transcript - [Instructor] Alright, so, if we were gonna go on the ambitious task of tallying up how much ATP was produced in one cycle of cellular respiration or, just to be super clear here, I mean how much ATP was produced per the oxidation or breakdown of one molecule of glucose in cellular respiration?
We might start off by just getting ourselves organized and reminding ourselves that there are two kind of main ways that we produce ATP in cellular respiration so, the first minor contribution comes from something called substrate level phosphorylation. And remember that this is exactly what it sounds like, we have a substrate, or a molecule, I'm just gonna say R.
And remember that in the context of cellular respiration, this is usually, we think of this as a kind of metabolite, an intermediate metabolite of glucose, so somewhere along glucose is oxidation. We get a metabolite and we activate this metabolite with a phosphate group. And from this phosphate group, we can actually donate it directly to ADP to produce ATP, and of course our molecule also gets modified in the process, usually gaining a hydroxy group, but the details aren't entirely important except to realize that this phosphorylation is occurring at the level of a substrate.
This is in contrast, of course, to oxidative phosphorylation, which is where we get the bulk of our ATP. And this oxidative refers to the fact that this process requires oxygen and in fact, the importance of oxygen here is that this oxygen is reduced by electron carrier molecules and something called the electron transport chain so, remember that we have a electron carrier molecules called NADH and FADH two that are produced at various stages of cellular respiration, glycolysis, the oxidation of pyruvate, the Krebs Cycle, and it's basically storing up all of that energy from the glucose molecule and it's gonna donate it into the electron transport chain, and of course the final electron acceptor is oxygen, which is then reduced to water.
But the important here is that this flow of electrons is able to power something, essentially fuel something called ATP synthase which is an enzyme that is in the mitochondrial membrane that produces the bulk of our ATP.
Now, the next point I want to make here is that it's actually been possible for us to calculate the exact number of ATP produced in substrate level phosphorylation and we've also nailed down the amount of NADH and FADH two molecules that are produced in this process as well. But for a quite a while, it was difficult to nail down the exact number of ATP molecules that were produced in oxidative phosphorylation. And for this reason, actually, and I'll get back to kind of why we're unable to, you know, kind of nail down a number here but for this reason, you might often see quite a range of predictions for how much ATP's actually produced in one cycle of cellular respiration, just to give you an idea of that, you know, when I look at some textbooks, you can see a range of anywhere from 30 to 38 molecules of ATP that are predicted to be produced for the oxidation of one molecule of glucose.
So, of course, to get back to this kind of elusive calculation of ATP, researchers have done controlled studies in which they basically take a known amount of NADH or FADH two and they have mitochondria available in the lab, and they basically allow the mitochondria to oxidatively phosphorylate these molecules and essentially measure how much ATP is produced, but kind of to their surprise at first, they found that for NADH, for one molecule of NADH, they calculated, there was not a whole number of ATP produced, in fact, they found that there was somewhere between two to three ATP molecules produced for every one NADH molecule.
Now, for the longest time, researchers kind of looked at these results and said, "You know, whole numbers are a lot easier to deal with, "and so, why don't we just assume, "for the sake of assumption, "that we can kind of round up, "and we'll say that for every one molecule of NADH, "let's say that we have three molecules of ATP produced.
In addition to generating ATP by oxidative phosphorylation in prokaryotic cells, proton motive force is also used for functions such as transporting materials across membranes and rotating flagella. Also, some bacteria use different carriers in their electron transport chain than others and the carriers may vary in the number of protons they transport across the membrane. In eukaryotic cells, unlike prokaryotes, NADH generated in the cytoplasm during glycolysis must be transported across the mitochondrial membrane before it can transfer electrons to the electron transport chain and this requires energy.
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