What is the function of Complex II in the ETC?

The function of Complex II in the electron transport chain (ETC) primarily involves the acceptance of electrons from succinate, which is derived from the citric acid cycle. These electrons are transferred to an FAD group within Complex II, which becomes reduced to FADH2 during this process. This step is crucial as it allows Complex II to play a key role in linking the citric acid cycle to the electron transport chain.

Unlike other complexes in the ETC, Complex II does not directly pump protons across the mitochondrial membrane. Instead, it contributes to the overall electron flow by transferring these electrons to ubiquinone (coenzyme Q), which subsequently becomes reduced to ubiquinol (QH2). This process is vital for maintaining the electron transport chain's function and facilitating ATP production via oxidative phosphorylation.

Understanding this mechanism is critical for comprehending how metabolic pathways are interconnected and how energy is produced in cellular respiration.