In oxidative phosphorylation, what is the primary role of NADH and FADH2?

• A. They act as membrane channels that allow $H_{+}$ to diffuse back into the matrix to generate ATP without a proton gradient.
• B. They donate high-energy electrons to the electron transport chain, which helps drive proton pumping and ATP synthesis.
• C. They transport oxygen to complex IV to serve as the terminal electron acceptor in the electron transport chain.
• D. They directly catalyze the phosphorylation of ADP to ATP at ATP synthase by providing the active site for the reaction.

Answer: (B)

Verified step by step guidance

1. Understand the role of NADH and FADH2 in cellular respiration, specifically in oxidative phosphorylation, which occurs in the mitochondria.
2. Recognize that NADH and FADH2 are electron carriers that carry high-energy electrons derived from metabolic pathways like the citric acid cycle.
3. Know that these electrons are donated to the electron transport chain (ETC), a series of protein complexes embedded in the inner mitochondrial membrane.
4. Realize that the flow of electrons through the ETC provides the energy needed to pump protons (H\+ ions) from the mitochondrial matrix to the intermembrane space, creating a proton gradient.
5. Understand that this proton gradient drives ATP synthesis by ATP synthase, but NADH and FADH2 themselves do not directly catalyze ATP formation or transport oxygen.