In oxidative phosphorylation, ATP synthase plays a direct role in which process?

• A. Pumping protons from the intermembrane space into the mitochondrial matrix to build the proton gradient
• B. Reducing molecular oxygen to water at the terminal step of the electron transport chain
• C. Synthesizing ATP from ADP and inorganic phosphate (Pi) using the proton-motive force across the inner mitochondrial membrane
• D. Transferring electrons from NADH to ubiquinone (coenzyme Q) to initiate the electron transport chain

Answer: (C)

Verified step by step guidance

1. Understand the role of ATP synthase in oxidative phosphorylation, which is the process by which cells generate ATP using energy derived from the electron transport chain.
2. Recall that the electron transport chain creates a proton gradient by pumping protons (H\(\textsuperscript{+}\)) from the mitochondrial matrix into the intermembrane space, establishing a proton-motive force.
3. Recognize that ATP synthase uses this proton-motive force to allow protons to flow back into the mitochondrial matrix through its channel, harnessing the energy released during this flow.
4. Identify that the energy from proton flow through ATP synthase drives the enzymatic synthesis of ATP from ADP and inorganic phosphate (Pi), which is the direct role of ATP synthase.
5. Distinguish this function from other processes such as proton pumping, electron transfer, or oxygen reduction, which are carried out by other complexes in the electron transport chain.