Current time: And so, of course, maybe the question we should really be asking is how many protons does it take, or how many protons need to flow through this ATP synthase to phosphorylate one molecule of ADP into ATP, and so, I'm actually gonna go ahead back to our ratios up here and write up here that if we knew how many protons were necessary to produce one molecule of ATP, we would be able to calculate essentially the ratio of ATP to NADH or FADH two.
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.
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.
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.
Now, recall that the basic premise here is that these reduced electron carriers donate electrons to the electron transport chain and in fact, specifically, NADH donates two electrons to protein complex number one, and FADH two donates two electrons to protein complex number two.
Now, the second important point is that as these electrons are kind of flowing down these proteins, for every two electrons that kind of flow by, it's actually been calculated that protein complex number one pumps four protons into the intermembrane space, protein complex three, it pumps, also, four protons, and protein complex number four pumps two protons.
Now, before I call it good, I wanna make one more last nitpicky point which is to realize that glycolysis, remember, takes place in the cytosol, so unlike the oxidation of pyruvate and the Krebs cycle, which take place in the mitochondria, the NADH that's produced in the glycolysis must actually be shuttled somehow into the inner mitochondrial membrane in order to donate its electrons into the electron transport chain.
The major energy provider of the cell. And so, if we add all of this up, we get 32 ATP.
And six NADH times two point five is going to yield 15. 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.
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 it turns out that depending on where the NADH is shuttled into the electron transport chain, so if we actually go back to our diagram here, some of the electrons from the NADH produced in glycolysis can be shuttled into the first electron, first protein complex, and some of them are actually shuttled into this third protein complex here.
Oxidative phosphorylation and chemiosmosis. But for a quite a while, it was difficult to nail down the exact number of ATP molecules that were produced in oxidative phosphorylation. On the other hand, FADH two enters in complex number two, so it only contributes to the total pumping of six protons and so, we can say that there are six protons that are pumped for every molecule of FADH two.
We get a metabolite and we activate this metabolite with a phosphate group. And two FADH two times one point five is going to yield three. Regulation of Krebs-TCA cycle. Calculating ATP produced in cellular respiration. Regulation of oxidative phosphorylation. Regulation of pyruvate dehydrogenase. And remember that this is exactly what it sounds like, we have a substrate, or a molecule, I'm just gonna say R. And you know, these all have specific names, but just for our purposes, it's important to recognize there are kind of just four main protein complexes, and in some textbooks, people will actually call ATP synthase, which I'm gonna go ahead and draw here in yellow as complex number five, so let me go ahead and label these, one through five, just so we remember that, so, these four represent the protein complexes that shuttle electrons and of course, five represents ATP synthase.
Oxidative phosphorylation questions. So, the body has actually come up with something called shuttle transport systems to shuttle this NADH into the mitochondria.