In oxidative phosphorylation, which enzyme directly phosphorylates ADP to form ATP using the proton-motive force across the inner mitochondrial membrane?

• A. NADH dehydrogenase (Complex I)
• B. Cytochrome c oxidase (Complex IV)
• C. Succinate dehydrogenase (Complex II)
• D. ATP synthase (Complex V)

Answer: (D)

Verified step by step guidance

1. Understand the process of oxidative phosphorylation, which occurs in the inner mitochondrial membrane and involves the generation of ATP using energy derived from the electron transport chain.
2. Recognize that the electron transport chain consists of multiple complexes (I, II, III, IV) that transfer electrons and pump protons to create a proton gradient (proton-motive force) across the inner mitochondrial membrane.
3. Identify that the proton-motive force is used by a specific enzyme to synthesize ATP from ADP and inorganic phosphate (Pi).
4. Recall that NADH dehydrogenase (Complex I), succinate dehydrogenase (Complex II), and cytochrome c oxidase (Complex IV) are involved in electron transport and proton pumping but do not directly catalyze ATP formation.
5. Conclude that ATP synthase (Complex V) is the enzyme that directly uses the proton-motive force to phosphorylate ADP to ATP, completing oxidative phosphorylation.