In mitochondrial oxidative phosphorylation, does the electron transport chain (ETC) require oxygen to function as it normally does, and why?

• A. No; oxygen is only required by ATP synthase, not by the ETC complexes.
• B. No; the ETC can use NADH as the terminal electron acceptor in the absence of oxygen.
• C. Yes; oxygen is required because it directly phosphorylates ADP to form ATP at complex IV.
• D. Yes; oxygen is the terminal electron acceptor (reduced to water), allowing electron flow through complexes I–IV to continue.

Answer: (D)

Verified step by step guidance

1. Understand the role of the electron transport chain (ETC) in mitochondrial oxidative phosphorylation: it transfers electrons through complexes I to IV, creating a proton gradient used by ATP synthase to produce ATP.
2. Recognize that oxygen acts as the terminal electron acceptor in the ETC, meaning it accepts electrons at complex IV and is reduced to water.
3. Realize that without oxygen to accept electrons, the flow of electrons through the ETC would stop, halting proton pumping and the generation of the proton motive force.
4. Note that ATP synthase does not directly require oxygen; it uses the proton gradient established by the ETC to phosphorylate ADP to ATP.
5. Conclude that oxygen is essential for the ETC to function normally because it maintains electron flow by accepting electrons at the end of the chain, enabling continuous ATP production.