Bioenergetics: practice question

A Biochemistry question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Biochemistry · Bioenergetics

Sample item

Cyanide toxicity causes cellular hypoxia by inhibiting which part of the electron transport chain?

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

The answer and the reasoning

C. Cytochrome c oxidase (complex IV)

Cyanide inhibits cytochrome c oxidase in complex IV, preventing oxygen from accepting electrons and abruptly halting oxidative phosphorylation despite adequate oxygen delivery in the blood.

Option by option

  • A. Cytosolic lactate dehydrogenase

    Lactate dehydrogenase is cytosolic and not the cyanide target.

  • B. ATP synthase directly

    ATP synthase is affected secondarily by loss of the proton gradient.

  • C. Cytochrome c oxidase (complex IV) (correct)

    Correct: complex IV inhibition blocks final electron transfer to oxygen.

  • D. Succinate dehydrogenase only

    Succinate dehydrogenase is complex II and is not cyanide's principal target.

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.

More Biochemistry questions

Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is C, Cytochrome c oxidase (complex IV). Cyanide inhibits cytochrome c oxidase in complex IV, preventing oxygen from accepting electrons and abruptly halting oxidative phosphorylation despite adequate oxygen delivery in the blood.

Why is "Cytosolic lactate dehydrogenase" not the answer?

Lactate dehydrogenase is cytosolic and not the cyanide target.

Why is "ATP synthase directly" not the answer?

ATP synthase is affected secondarily by loss of the proton gradient.

Why is "Succinate dehydrogenase only" not the answer?

Succinate dehydrogenase is complex II and is not cyanide's principal target.

What concept does this question test?

It tests Bioenergetics in Biochemistry. The correct option holds because: Correct: complex IV inhibition blocks final electron transfer to oxygen.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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 Bioenergetics?

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.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.