Practice: Oxidative Phosphorylation 1 - Video Tutorials & Practice Problems
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Almost all of the oxygen consumed by cells is converted into water during electron transport. Pretty incredible if you think about it. Which of the following is only able to accept one electron at a time? That is a heme and you might remember that this is, the issue with the cytochromes. Cytochrome c in particular, a complex 3 can only accept 1 electron at a time. So, that's why we have the q cycle if you recall. The rest of these are capable of accepting more than 1 electron. So, antimycin blocks electron transfer between cytochromes b and c. Intact mitochondria were incubated with antimycin, NADH, and adequate oxygen. Which of the following will be found to be oxidized? So basically, the question is asking which of these is not going to be getting electrons? And if you recall, the order of the cytochromes during electron transport in complex 3, we have cytochrome b, and that gets electrons from ubiquinone or coenzyme q. Coenzyme q is the same thing as ubiquinone, and cytochrome b passes electrons onto cytochrome c which then passes electrons onto cytochrome cytochrome A. So, if this is not happening then cytochrome A will be reduced meaning it's going to be found in an oxidized form because this electron transfer between cytochrome B and C is being blocked. Now, reduced quinones are not formed during which of the following? Now, this is a tricky question and the answer is complex III and cytochrome c. There are no quinones, reduced during at complex 3 or cytochrome c. Quinones are oxidized at complex 3. Right? Ubiquinone drops off electrons there but it's not reduced there. However, complex 1 and and NADH will lead to reduced quinones. Right? Complex 2 and succinate will also relieve or rather lead to reduced quinones. Fatty acid oxidation, you might remember. This is going to generate FAD and that is going to or FADH 2 I should say. And that is going to pass electrons onto ubiquinone. Likewise, the oxidation of Glycerol 3 Phosphate. You might remember this is how NADH is going to get its, electrons in or one way that it can get its electrons into the mitochondria. Right? So it would pass them on to DHAP and it will become NAD plus by doing that. It will convert DHAP into Glycerol 3 Phosphate and that will be used to make FADH2 q or enzyme q or ubiquinone which, of course goes to complex 3. Sorry. My drawing got a little out of hand there but you get the idea. So, which of the following is not true of the proton motive force? That is that the the generation of the proton motor force requires succinate. That is not true. Right? Succinate will feed electrons via succinate dehydrogenase or complex 2. It will feed electrons into the electron transport chain that way. However, that's not the only entry point into the electron transport chain. Not only can electrons go, via NADH through complex 1 but as we just said in the previous question, fatty acid oxidation and the oxidation of Glycerol 3 phosphate are other ways for electrons to feed into the electron transport chain. Not to mention, the malate aspartate shuttle which will take NADH elect electrons from cytosolic NADH and bring them into the mitochondria to drop them off at complex 1. So the point is, there are many other pathways into the electron transport chain for electrons other than succinate dehydrogenase. With that, let's flip the page.