What is the function of Complex III in the ETC?

Complex III, also known as the cytochrome bc1 complex, plays a crucial role in the electron transport chain (ETC) by transferring electrons from ubiquinol (QH2) to cytochrome c. This process is significant because it is a critical step in the generation of a proton gradient across the mitochondrial membrane, which is used by ATP synthase to produce ATP.

The way Complex III operates involves the following steps: it accepts electrons from QH2, which has been previously reduced from coenzyme Q (ubiquinone) during earlier stages of the electron transport chain. After this transfer, the electrons are passed through a series of iron-sulfur (Fe/S) clusters and heme groups within the Complex. This transfer facilitates not only the flow of electrons but also the pumping of protons from the mitochondrial matrix into the intermembrane space, which helps create the electrochemical gradient essential for ATP synthesis.

This understanding of Complex III’s function underscores its importance in cellular respiration and energy production, as it effectively links the reduction of electron carriers to the generation of a proton motive force, ultimately leading to ATP generation through oxidative phosphorylation.