Question

The mitochondrial electron-transport chain contains four asymmetric membrane-spanning protein complexes. Which of the four complexes function as proton pumps?

1) Complex I
2) Complex II
3) Complex III
4) Complex IV

Answer 1

Complexes I, III, and IV in the mitochondrial electron-transport chain function as proton pumps, creating a proton gradient used for ATP synthesis.

Step-by-step explanation:

The student has asked which complexes in the mitochondrial electron-transport chain function as proton pumps. Within the mitochondria, complexes I, III, and IV act as proton pumps. These complexes help establish a hydrogen ion gradient by transporting protons (H+) across the inner mitochondrial membrane from the matrix to the intermembrane space. Specifically, complex I, or NADH dehydrogenase, uses the energy from electron transfer to pump four protons across the membrane.

Complex III, or cytochrome oxidoreductase, also pumps protons while passing electrons to cytochrome c. Finally, complex IV completes the process, enabling the electrons to continue their journey and pumping additional protons to fortify the gradient which will be utilized by ATP synthase to generate ATP.