In oxidative phosphorylation, what directly provides the energy that powers ATP synthase to produce ATP?

• A. Direct transfer of phosphate from $N_A{D}_H$ to $ADP$
• B. The proton-motive force generated by the electrochemical gradient of $H^{+}$ across the inner mitochondrial membrane
• C. Energy released by splitting water into $O_2$ and $H^{+}$
• D. Substrate-level phosphorylation coupled to the oxidation of $F_A{D}_2$ by ATP synthase

Answer: (B)

Verified step by step guidance

1. Understand that ATP synthase is an enzyme complex located in the inner mitochondrial membrane responsible for synthesizing ATP from ADP and inorganic phosphate (Pi).
2. Recognize that ATP synthase is powered not by direct chemical energy from molecules like NADH or FADH2, but by a physical force generated across the membrane.
3. Identify that during oxidative phosphorylation, electron transport through complexes I-IV creates an electrochemical gradient of protons (H\(\textsuperscript{+}\)) across the inner mitochondrial membrane, known as the proton-motive force.
4. Know that this proton-motive force consists of both a difference in proton concentration (pH gradient) and an electrical potential difference across the membrane.
5. Conclude that the flow of protons back into the mitochondrial matrix through ATP synthase harnesses this proton-motive force to drive the conformational changes in ATP synthase necessary for ATP production.