In oxidative phosphorylation, what is the primary purpose of the electron transport chain (ETC) in the inner mitochondrial membrane?

• A. To directly catalyze the phosphorylation of ADP to ATP by substrate-level phosphorylation
• B. To oxidize glucose to pyruvate in the mitochondrial matrix
• C. To use energy from electron transfer to pump protons (H${+}^{}$) across the inner mitochondrial membrane, generating a proton-motive force that drives ATP synthesis
• D. To transport ATP out of the mitochondrial matrix by moving it through Complex IV

Answer: (C)

Verified step by step guidance

1. Understand the role of the electron transport chain (ETC) in oxidative phosphorylation, which occurs in the inner mitochondrial membrane.
2. Recognize that the ETC consists of a series of protein complexes (Complexes I-IV) that transfer electrons derived from NADH and FADH2 to molecular oxygen.
3. Know that as electrons move through these complexes, energy is released and used to pump protons (H\+ ions) from the mitochondrial matrix into the intermembrane space, creating a proton gradient.
4. This proton gradient, also called the proton-motive force, stores potential energy across the inner mitochondrial membrane.
5. Finally, this proton-motive force drives ATP synthesis by allowing protons to flow back into the matrix through ATP synthase, which catalyzes the phosphorylation of ADP to ATP.