Oxidative phosphorylation occurs in

Question

BlackTom AI · Accepted Answer

Oxidative phosphorylation takes place across the inner mitochondrial membrane, where the electron transport chain and ATP synthase are embedded.

1. Relevant knowledge points and concepts
- Electron transport chain (ETC) complexes I–IV and ATP synthase are integral proteins of the inner mitochondrial membrane (IMM).
- ETC transfers electrons from NADH/FADH2 to O2, using the released energy to pump protons from the matrix into the intermembrane space, creating an electrochemical (proton) gradient.
- ATP synthase uses the proton-motive force (protons flowing back into the matrix through its channel) to synthesize ATP from ADP + Pi — this coupling of electron transport and ATP formation is oxidative phosphorylation.
- The IMM’s impermeability to protons except via specific proteins is essential for maintaining the gradient; cristae increase membrane surface area for more ETC complexes.

2. Step-by-step reasoning
- NADH/FADH2 donate electrons to ETC complexes located in the IMM.
- As electrons pass along the ETC, energy pumps protons from the matrix into the intermembrane space (creating a higher [H+] outside the matrix).
- This creates a proton gradient (chemical + electrical) across the IMM.
- Protons return through ATP synthase (an IMM protein), driving rotational catalysis that forms ATP — this full sequence is oxidative phosphorylation.

3. Intermediate steps (conceptual, not numerical)
- Electron donation → energy release → proton pumping → gradient formation → proton flow through ATP synthase → ATP formation.

4. Why the correct answer is correct
- All molecular machinery required for oxidative phosphorylation (ETC complexes and ATP synthase) is embedded in and functions across the inner mitochondrial membrane; therefore oxidative phosphorylation occurs there.

5. Why the other options are incorrect
- Cytoplasm/cytosol: glycolysis and some substrate-level phosphorylations occur here, but not oxidative phosphorylation.
- Ribosome: site of protein synthesis, not ATP production via electron transport.
- (Prokaryotic exception: in bacteria the plasma membrane performs analogous functions, but the question refers to eukaryotic mitochondria.)

6. Conclusion
- Therefore the correct answer is c. the inner mitochondrial membrane, which matches the provided answer.

Oxidative phosphorylation occurs in单项选择题

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