Biology MCQ- Mitochondria and O2 consumption

[TytoAlba95]

Homework Statement

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Relevant Equations

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I don't get, how option A corresponds to time point I. Electron transport/flow is independent of the phosphorylation, isn't it? Though it is not independent the other way round, i.e. the setting up of proton gradient requires the electron flow.
I think the matching should have been:
I-E, II-D, III-E.
Options:
A-no effect, as discussed above
B-no effect
C- no effect
D- inhibits Complex III, so O2 consumption will decrease
E- Substrate of Complex II, so O2 consumption will increase

According to the key, (d) is the correct option.

 

[Ygggdrasil]

I don't get, how option A corresponds to time point I. Electron transport/flow is independent of the phosphorylation, isn't it? Though it is not independent the other way round, i.e. the setting up of proton gradient requires the electron flow.

No, both processes need to occur simultaneously. Proton flow requires ATP phosphorylation just as ATP phosphorylation requires proton flow. If protons could move across the membrane without ATP phosphorylation, ATP phosphorylation would not occur (As an analogy consider a hydroelectric dam. Water will not flow thorugh the dam if the turbine is not working. If the water had a way to flow around the turbine, the dam would not be efficient at producing energy).

 

[TytoAlba95]

Well, umm... when an uncoupler (thermogenin) dissipates the proton gradient it is said that the electron flow and ATP formation is uncoupled. ATP formation doesn't happen but the electron flow continues and a part of the energy which could not be channelled into ATP is converted into heat (happening in brown adipose tissue).

This was the basis of my concept that electron flow is independent of ATP formation.

 

[Ygggdrasil]

Well, umm... when an uncoupler (thermogenin) dissipates the proton gradient it is said that the electron flow and ATP formation is uncoupled. ATP formation doesn't happen but the electron flow continues and a part of the energy which could not be channelled into ATP is converted into heat (happening in brown adipose tissue).

This was the basis of my concept that electron flow is independent of ATP formation.

Yes, that is correct. However, in the absence of an uncoupler, ATP formation and proton flow are coupled and cannot occur independently.