In oxidative phosphorylation, what is the primary function of NADH and FADH$2_{}$?

• A. They transport oxygen from the lungs to mitochondria to serve as the final electron acceptor.
• B. They act as terminal electron acceptors by combining with electrons and protons to form water at Complex IV.
• C. They donate high-energy electrons to the electron transport chain (e.g., Complex I for NADH and Complex II for FADH$2_{}$), helping drive proton pumping and ATP synthesis.
• D. They directly catalyze the phosphorylation of ADP to ATP by transferring a phosphate group to ADP.

Answer: (C)

Verified step by step guidance

1. Understand the role of NADH and FADH\_2 in cellular respiration, specifically in oxidative phosphorylation within the mitochondria.
2. Recall that NADH and FADH\_2 are electron carriers that carry high-energy electrons derived from metabolic pathways like the Krebs cycle.
3. Recognize that these carriers donate their electrons to the electron transport chain (ETC), with NADH donating to Complex I and FADH\_2 donating to Complex II.
4. Know that the donated electrons move through the ETC, which drives proton pumping across the mitochondrial inner membrane, creating a proton gradient.
5. Understand that this proton gradient powers ATP synthase to produce ATP, but NADH and FADH\_2 themselves do not directly phosphorylate ADP to ATP.