Multiple choice

Which of the following membrane-bound complexes in mitochondria is not a proton pump?

  1. NADH dehydrogenase

  2. Succinate dehydrogenase

  3. Cytochrome bc1

  4. Cytochrome c oxidase
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Complex II (Succinate dehydrogenase) is the only ETC complex that does not pump protons. It oxidizes succinate to fumarate and passes electrons directly to ubiquinone (CoQ) without contributing to the proton gradient. Complexes I, III, and IV all pump protons.

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