In oxidative phosphorylation, the primary function of ATP synthase is to:

• A. Pump protons from the intermembrane space into the mitochondrial matrix to generate the proton gradient
• B. Oxidize $Q_{H^{+}}$ and reduce cytochrome $c$ in the electron transport chain
• C. Use the proton-motive force to catalyze $ADP+P_i\to ATP$
• D. Transfer electrons from $NADH$ to oxygen to form $H_{2}O$

Answer: (C)

Verified step by step guidance

1. Understand the role of ATP synthase in oxidative phosphorylation: ATP synthase is an enzyme complex located in the inner mitochondrial membrane that synthesizes ATP from ADP and inorganic phosphate (P_i).
2. Recognize that ATP synthase uses the proton-motive force, which is the electrochemical gradient of protons (H⁺) across the inner mitochondrial membrane, created by the electron transport chain pumping protons into the intermembrane space.
3. Recall that the proton gradient stores potential energy, and ATP synthase allows protons to flow back into the mitochondrial matrix through its channel, harnessing this energy to drive the phosphorylation of ADP to ATP.
4. Note that ATP synthase does not pump protons to create the gradient; instead, it uses the existing gradient to produce ATP. The pumping of protons is performed by complexes I, III, and IV of the electron transport chain.
5. Summarize that the primary function of ATP synthase is to catalyze the reaction: \(\text{ADP} + \text{P}_i \rightarrow \text{ATP}\), powered by the flow of protons down their electrochemical gradient.