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

• A. It serves as the terminal electron acceptor by combining with electrons and protons to form water.
• B. It transports oxygen from the cytosol into the mitochondrial intermembrane space for reduction by Complex IV.
• C. It donates high-energy electrons to Complex I of the electron transport chain, helping drive proton pumping across the inner mitochondrial membrane.
• D. It directly phosphorylates ADP to ATP by transferring a phosphate group to ADP in the mitochondrial matrix.

Answer: (C)

Verified step by step guidance

1. Understand the context of oxidative phosphorylation, which is the process in cellular respiration where ATP is produced using energy derived from electrons transferred through the electron transport chain (ETC).
2. Recognize that NADH is a key electron carrier molecule generated during earlier stages of cellular respiration (glycolysis, pyruvate oxidation, and the citric acid cycle).
3. Identify the role of NADH in donating electrons: NADH transfers its high-energy electrons to Complex I (NADH dehydrogenase) of the ETC, initiating the electron flow through the chain.
4. Know that the electrons donated by NADH help drive proton pumping from the mitochondrial matrix to the intermembrane space, creating a proton gradient essential for ATP synthesis.
5. Clarify that NADH does not serve as the terminal electron acceptor, does not transport oxygen, and does not directly phosphorylate ADP; instead, its primary role is to donate electrons to Complex I to facilitate proton pumping and ATP production.