TBR: Oxidative Phosphorylation Question

[justadream]

TBR Bio Book II page 229 #2



The passage talks about how oligomyocin inhibits the ATP-ase needed to make ATP in oxidative phosphorylation. It says oligomyocin basically shuts down oxidative phosphorylation and that the cells will shut down the ETC.



I have two questions:

1) Why does oligomyocin stop the ETC? When you lack oxygen, it’s clear why the ETC stops. But when you have an inhibitor of something that happens after the ETC (i.e., generation of ATP by ATP-ase), why does that affect the ETC? I expected the ETC to continue pumping H+ but with no ATP generation. Maybe it’s some type of negative feedback?



2) More generally, if a cell continues ETC but no gradient is established (for example, if an uncoupling agent allows H+ to freely move across membranes), does the cell technically still count as doing “aerobic respiration”? In such a scenario, you would still make 2 net ATP from the Citric Acid Cycle’s substrate phosphorylation.

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[sxld_cu]

I have never looked at TBR review books, but I'll take a shot at this one. Here's my train of thought... (not sure if it's right or not, so would love to hear other people's thoughts too

Oligomycin inhibits ATP synthase by blocking the proton channel
In order for oxidative phosphorylation to occur, the proton gradient needs to be maintained, and the transport of protons back into the mitochondrial matrix through ATPase generates ATP from ADP
When oligomycin is present, H+ cannot pass back into the matrix so an excess of H+ remains in the intermembrane space (I guess some H+ manage to pass through via proton leak and mitochondrial uncoupling but let's presume that's negligible)
In oxidative phosphorylation, NADH donates its electrons to the ETC and the ETC uses this energy released by the electrons to transport H+ into the intermembrane space
If there is an excess of H+ already in the intermembrane space, I'm guessing that this functions to deter electron transport because more electron transport would mean even more H+ (kind of like an extension of Le Chatelier's principle in a biological context)