Which complex of the mitochondrial electron transport chain does NOT pump protons across the inner mitochondrial membrane into the intermembrane space?
Answer and explanation
Correct answer: D. Complex II (Succinate dehydrogenase)
- Step 1: Complexes I, III, and IV pump protons from the matrix into the intermembrane space, generating the electrochemical gradient. Step 2. Complex II (succinate-Q reductase) transfers electrons from FADH2 to ubiquinone without translocating protons across the membrane. Answer: Complex II (Succinate dehydrogenase). Why not the others: Complexes I (4 H+), III (4 H+), and IV (2 H+) actively translocate protons.
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