Describe the Q cycle in Complex III and its significance in proton pumping.

• A. The Q cycle removes protons from the mitochondrial matrix without electron transfer.
• B. The Q cycle acts as the final electron acceptor, forming water.
• C. The Q cycle directly synthesizes ATP from ADP and inorganic phosphate.
• D. The Q cycle involves the transfer of electrons from ubiquinone to cytochrome c, resulting in the pumping of 4 protons into the intermembrane space.

Answer: (D)