A characteristic of complex III is that it A) transports electrons from cytochrome c to complex IV. B) is reduced by FADH₂. C) uses the Q cycle mechanism to oxidize ubiquinone. D) participates in electron transfer when the donor is NADH but not when the donor is succinate (or FADH₂).

Question

Quizplus · Accepted Answer

Complex III (also known as cytochrome bc1 complex or ubiquinol-cytochrome c reductase) uses the Q cycle mechanism to oxidize ubiquinone. This mechanism involves the transfer of electrons to ubiquinone from two molecules of cyt c, with one electron passing through a high-potential chain and the other electron passing through a low-potential chain. This generates a proton gradient across the inner mitochondrial membrane, which drives ATP synthesis by complex V (ATP synthase). Complex III transports electrons from ubiquinol to cytochrome c, which in turn transfers them to complex IV (cytochrome c oxidase).

A Characteristic of Complex III Is That It