In oxidative phosphorylation, the movement of protons through ATP synthase occurs from the:

• A. Mitochondrial matrix into the cytosol
• B. Mitochondrial matrix into the intermembrane space
• C. Cytosol into the mitochondrial matrix
• D. Intermembrane space into the mitochondrial matrix

Answer: (D)

Verified step by step guidance

1. Understand the structure of the mitochondrion, which includes the outer membrane, intermembrane space, inner membrane, and the mitochondrial matrix.
2. Recall that during oxidative phosphorylation, the electron transport chain pumps protons (H\(\textsuperscript{+}\)) from the mitochondrial matrix into the intermembrane space, creating a proton gradient.
3. Recognize that ATP synthase uses this proton gradient to drive the synthesis of ATP by allowing protons to flow back down their concentration gradient.
4. Identify the direction of proton movement through ATP synthase: protons move from the intermembrane space (where their concentration is high) back into the mitochondrial matrix (where their concentration is low).
5. Conclude that the movement of protons through ATP synthase occurs from the intermembrane space into the mitochondrial matrix, which powers ATP production.