Oxidative phosphorylation: cyanide: 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 · Oxidative phosphorylation: cyanide

Sample item

Cyanide causes rapid cellular hypoxia despite normal arterial oxygen content by inhibiting which electron-transport-chain complex?

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

The answer and the reasoning

D. Complex IV

Cyanide inhibits cytochrome c oxidase (complex IV), preventing reduction of oxygen to water. Cells cannot use delivered oxygen, producing severe lactic acidosis.

Option by option

  • A. Complex I

    Complex I transfers electrons from NADH to coenzyme Q.

  • B. Complex V

    Complex V is ATP synthase.

  • C. Complex II

    Complex II is succinate dehydrogenase.

  • D. Complex IV (correct)

    Correct. Complex IV is cytochrome c oxidase.

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.

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Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is D, Complex IV. Cyanide inhibits cytochrome c oxidase (complex IV), preventing reduction of oxygen to water.

Why is "Complex I" not the answer?

Complex I transfers electrons from NADH to coenzyme Q.

Why is "Complex V" not the answer?

Complex V is ATP synthase.

Why is "Complex II" not the answer?

Complex II is succinate dehydrogenase.

What concept does this question test?

It tests Oxidative phosphorylation: cyanide in Biochemistry. Cells cannot use delivered oxygen, producing severe lactic acidosis.

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 Oxidative phosphorylation: cyanide?

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.