In oxidative phosphorylation, what is the primary role of NADH in metabolism?

• A. It serves as the terminal electron acceptor and is reduced to form water.
• B. It donates high-energy electrons to the electron transport chain (e.g., Complex I), helping drive proton pumping and ATP synthesis.
• C. It directly phosphorylates ADP to ATP by transferring a phosphate group to ADP.
• D. It inhibits the electron transport chain by binding and blocking cytochrome c oxidase (Complex IV).

Answer: (B)

Verified step by step guidance

1. Understand the role of NADH in cellular metabolism, specifically in oxidative phosphorylation, which is the process by which cells generate ATP using energy from electrons transferred through the electron transport chain (ETC).
2. Recall that NADH is a reduced coenzyme that carries high-energy electrons derived from metabolic pathways such as glycolysis and the citric acid cycle.
3. Recognize that NADH donates these high-energy electrons to Complex I (NADH dehydrogenase) of the electron transport chain, initiating the flow of electrons through the ETC.
4. Understand that the electron transfer from NADH through the ETC drives proton pumping across the mitochondrial inner membrane, creating a proton gradient (proton motive force).
5. Know that this proton gradient is then used by ATP synthase to synthesize ATP from ADP and inorganic phosphate, linking NADH oxidation to ATP production.