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

• A. It transports oxygen from the lungs to tissues to support aerobic respiration.
• B. It directly phosphorylates ADP to ATP by transferring a phosphate group to ADP.
• C. It donates high-energy electrons to Complex I of the electron transport chain, helping drive proton pumping and ATP synthesis.
• D. It functions as the terminal electron acceptor, being reduced to water at Complex IV.

Answer: (C)

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 high-energy electron carrier produced during glycolysis, the citric acid cycle, and other metabolic pathways. Its main function is to donate electrons to the ETC to facilitate ATP production.
3. Identify that NADH donates electrons specifically to Complex I (NADH dehydrogenase) of the ETC. This donation initiates a series of redox reactions that result in the pumping of protons across the mitochondrial inner membrane, creating a proton gradient.
4. Recognize that the proton gradient generated by electron transfer through the ETC drives ATP synthesis by ATP synthase, which phosphorylates ADP to ATP using the energy stored in the gradient.
5. Clarify common misconceptions: NADH does not transport oxygen, does not directly phosphorylate ADP, and is not the terminal electron acceptor (which is oxygen at Complex IV). Its primary role is electron donation to Complex I to power proton pumping and ATP synthesis.