In mitochondrial oxidative phosphorylation, the final electron acceptor of the electron transport chain (ETC) is which molecule?

• A. Molecular oxygen ($O_2$), which is reduced to water
• B. Coenzyme Q (ubiquinone), which carries electrons from Complex I/II to Complex III
• C. NAD$+$, which is reduced to NADH
• D. Cytochrome $c$, which carries electrons between Complex III and Complex IV

Answer: (A)

Verified step by step guidance

1. Understand the role of the electron transport chain (ETC) in mitochondrial oxidative phosphorylation: it transfers electrons through a series of complexes to ultimately produce ATP.
2. Identify the flow of electrons: electrons are passed from NADH and FADH2 to Complex I and II, then to Coenzyme Q (ubiquinone), which transfers electrons to Complex III.
3. Recognize that Cytochrome c carries electrons from Complex III to Complex IV in the ETC.
4. Recall that Complex IV (cytochrome c oxidase) transfers electrons to the final electron acceptor, which is essential for maintaining the flow of electrons through the chain.
5. Know that the final electron acceptor in the ETC is molecular oxygen (O\_2), which accepts electrons and is reduced to form water (H\_2O), allowing the ETC to continue functioning.