MCQ- Mitochondria and O2 consumption

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Discussion Overview

The discussion revolves around the relationship between electron transport, ATP phosphorylation, and oxygen consumption in mitochondria, particularly in the context of a multiple-choice question (MCQ) regarding the effects of various options on these processes. The scope includes conceptual clarifications and technical explanations related to mitochondrial function and bioenergetics.

Discussion Character

  • Conceptual clarification
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant questions how option A corresponds to time point I, suggesting that electron transport is independent of phosphorylation, while acknowledging that establishing a proton gradient requires electron flow.
  • Another participant argues that both electron transport and ATP phosphorylation must occur simultaneously, using an analogy of a hydroelectric dam to illustrate the interdependence of these processes.
  • A participant introduces the concept of uncouplers, specifically thermogenin, stating that while ATP formation does not occur when the proton gradient is dissipated, electron flow continues, which supports their view that electron flow can be independent of ATP formation.
  • A later reply confirms the previous point about uncouplers but emphasizes that in the absence of uncouplers, ATP formation and proton flow are coupled and cannot occur independently.

Areas of Agreement / Disagreement

Participants express differing views on the independence of electron transport and ATP formation, with some asserting that they are coupled under normal conditions while others argue for their independence under specific circumstances, such as the presence of uncouplers. The discussion remains unresolved regarding the nature of this relationship.

Contextual Notes

There are limitations in the assumptions made about the independence and coupling of electron transport and ATP phosphorylation, as well as the specific conditions under which these processes operate. The discussion does not resolve the mathematical or conceptual nuances involved.

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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.
 
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SanjuktaGhosh said:
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).
 
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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.
 
SanjuktaGhosh said:
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.
 
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