What happens to Q in Complex II of the ETC?

In Complex II of the electron transport chain (ETC), the role of coenzyme Q (ubiquinone, often denoted as Q) is crucial in the transfer of electrons from succinate to the electron transport chain. Complex II catalyzes the oxidation of succinate to fumarate, an intermediate in the citric acid cycle, while simultaneously reducing Q to QH2 (ubiquinol).

When succinate is oxidized, electrons are transferred to FAD, reducing it to FADH2. This reduced FADH2 then explicitly transfers its electrons to Q, resulting in the conversion of Q to QH2. This process allows QH2 to carry the electrons to the next complex in the ETC, Complex III.

This conversion is significant as it forms an integral part of oxidative phosphorylation, allowing the flow of electrons down the electron transport chain, contributing to the proton gradient required for ATP synthesis. Understanding this step is critical as it highlights the importance of Q in the respiratory process and the energy conversion happening within mitochondria. Thus, the correct answer that describes the behavior of Q in Complex II of the ETC is its conversion to QH2.