In oxidative phosphorylation, what two processes are coupled throughout the electron transport chain (ETC) to drive ATP synthesis?

• A. ATP hydrolysis by ATP synthase and direct phosphorylation of oxygen to form water
• B. Electron transfer through ETC complexes and proton translocation across the inner mitochondrial membrane to build the proton-motive force
• C. FADH2 oxidation in Complex II and carbon fixation via the Calvin cycle
• D. NADH oxidation in the cytosol and substrate-level phosphorylation in the mitochondrial matrix

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the key components involved in oxidative phosphorylation, which primarily include the electron transport chain (ETC) complexes and ATP synthase located in the inner mitochondrial membrane.
2. Step 2: Recognize that the ETC facilitates electron transfer from electron donors like NADH and FADH2 through a series of protein complexes (Complexes I-IV), which is coupled to the pumping of protons (H+) from the mitochondrial matrix to the intermembrane space.
3. Step 3: Identify that this proton translocation creates an electrochemical gradient known as the proton-motive force, which stores potential energy across the inner mitochondrial membrane.
4. Step 4: Understand that ATP synthase uses the energy stored in the proton-motive force to drive the synthesis of ATP from ADP and inorganic phosphate (Pi) as protons flow back into the matrix through the enzyme.
5. Step 5: Conclude that the two coupled processes throughout the ETC are (1) electron transfer through the ETC complexes and (2) proton translocation across the inner mitochondrial membrane, which together drive ATP synthesis by ATP synthase.