Why is "Oligomycin blocks complex IV and DNP bypasses it" not the answer?

Complex IV inhibitors such as cyanide would not be bypassed by DNP.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Oxidative phosphorylation: oligomycin and DNP?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry questions on this site to test what stuck.

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Oxidative phosphorylation MCQ (B11-BIO1-7)

Q: What is the answer to this Biochemistry question?

The best answer is B, Oligomycin blocks the Fo proton channel of ATP synthase, and DNP dissipates the proton gradient so respiration resumes without ATP synthesis. Electron transport is coupled to ATP synthesis through the proton gradient, so blocking proton re-entry through ATP synthase builds a gradient that halts respiration.

Q: What concept does this question test?

It tests Oxidative phosphorylation: oligomycin and DNP in Biochemistry. An uncoupler such as DNP carries protons across the membrane, removing the back-pressure so oxygen consumption rises while ATP production falls and heat is released.

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Biochemistry · Oxidative phosphorylation: oligomycin and DNP

Sample item

In an oxygen electrode, isolated mitochondria oxidising succinate with ADP and phosphate consume oxygen briskly. Oligomycin stops oxygen consumption. Adding 2,4-dinitrophenol then restores rapid oxygen consumption. What is the interpretation?

ADNP inhibits ATP synthase and oligomycin dissipates the gradientBOligomycin blocks the Fo proton channel of ATP synthase, and DNP dissipates the proton gradient so respiration resumes without ATP synthesisCOligomycin blocks the adenine nucleotide translocase, and DNP regenerates ADPDOligomycin blocks complex IV and DNP bypasses it

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

B. Oligomycin blocks the Fo proton channel of ATP synthase, and DNP dissipates the proton gradient so respiration resumes without ATP synthesis

Electron transport is coupled to ATP synthesis through the proton gradient, so blocking proton re-entry through ATP synthase builds a gradient that halts respiration. An uncoupler such as DNP carries protons across the membrane, removing the back-pressure so oxygen consumption rises while ATP production falls and heat is released.

Option by option

A. DNP inhibits ATP synthase and oligomycin dissipates the gradient
The roles are reversed here; DNP is the uncoupler and oligomycin the ATP synthase inhibitor.
B. Oligomycin blocks the Fo proton channel of ATP synthase, and DNP dissipates the proton gradient so respiration resumes without ATP synthesis (correct)
Correct. Respiratory control is relieved by the uncoupler despite blocked ATP synthase.
C. Oligomycin blocks the adenine nucleotide translocase, and DNP regenerates ADP
Translocase inhibition is the action of atractyloside, and DNP does not generate ADP.
D. Oligomycin blocks complex IV and DNP bypasses it
Complex IV inhibitors such as cyanide would not be bypassed by DNP.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Oxidative phosphorylation: oligomycin and DNP: practice question

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The answer and the reasoning

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