Question

Which is a necessary component of oxidative phosphorylation?

		A. The transfer of a phosphate group from a phosphorylated substrate to ADP to produce ATP
		B. The transfer of a phosphate group from ATP to a substrate
		C. The excitation of chlorophyll by sunlight to donate an electron to an electron transport system
		D. An initial electron donor, bacterial cytochromes and a final electron acceptor.

Answer 1

The correct answer is D. An initial electron donor, bacterial cytochromes, and a final electron acceptor.

Explanation: Oxidative phosphorylation is the synthesis of ATP from ADP and P_i using a large amount of free energy released when the oxidation of NADH and FADH₂ takes place. Electrons are transferred along the electron transport chain from NADH/FADH₂ (initial electron donor) to O₂ (final electron acceptor) through a series of electron carriers (iron-sulfur clusters, coenzyme Q, cytochromes, and copper ions) present on the inner mitochondrial membrane.

According to the chemiosmotic hypothesis, electron transport chain releases free energy and that energy is conserved by pumping protons out of the mitochondrial matrix into the intermitochondrial space. This creates an electrochemical proton gradient across the inner membrane and this gradient drives proton back through ATP synthase, which uses the energy of proton flow to generate ATP from ADP and P_i . Therefore electron transport chain and oxidative phosphorylation are coupled.

On the other hand, the transfer of a phosphate group from a phosphorylated substrate to ADP to produce ATP is known as substrate-level phosphorylation.

Therefore, the correct answer is D. An initial electron donor, bacterial cytochromes, and a final electron acceptor.