The First Half of the Q Cycle Results in Which

Question

The first half of the Q cycle results in which of the following? A) transfer of 4 protons to the intermembrane space B) a semiquinone radical (UQ∙^-) in the Qnsite C) 2 molecules of reduced cytochrome c D) return of one UQH2to the coenzyme Q pool E) none of the above

Accepted Answer

The first half of the Q cycle results in the generation of a semiquinone radical (UQ∙^-) in the Q_n site. This occurs when a ubiquinone (UQ) molecule accepts two electrons from the oxidized cytochrome b (n) and two protons from the matrix to form a semiquinone radical in the Q-binding site (Q_{) of cytochrome b. The semiquinone radical then moves to the Q-binding site (Q}) of the cytochrome c1, which is the first half of the Q cycle.