Protons pumped during oxidative phosphorylation accumulate where?

Protons pumped during oxidative phosphorylation accumulate where?

• A. Mitochondrial matrix
• B. Intermembrane space of the mitochondria
• C. Cytosol
• D. Nucleus

Answer: (B)

During oxidative phosphorylation, the electron transport chain pumps protons across the inner mitochondrial membrane from the matrix into the intermembrane space. Because protons can't cross back easily through the membrane, they accumulate in the intermembrane space, creating a proton gradient (proton-motive force). This stored energy drives ATP synthesis as protons flow back into the matrix through ATP synthase. The cytosol and nucleus aren’t involved in this proton-pumping step, and the matrix is the source region from which protons are moved, not where they accumulate.

During oxidative phosphorylation, the electron transport chain pumps protons across the inner mitochondrial membrane from the matrix into the intermembrane space. Because protons can't cross back easily through the membrane, they accumulate in the intermembrane space, creating a proton gradient (proton-motive force). This stored energy drives ATP synthesis as protons flow back into the matrix through ATP synthase. The cytosol and nucleus aren’t involved in this proton-pumping step, and the matrix is the source region from which protons are moved, not where they accumulate.