What is the electron transport chain and oxidative phosphorylation?

The electron transport chain (ETC) is a series of protein complexes (I, II, III, IV) and mobile carriers in the inner mitochondrial membrane that transfer electrons from NADH and FADH2 to oxygen. This electron flow drives proton pumping across the membrane, creating an electrochemical gradient. ATP synthase uses this gradient to synthesize ATP from ADP and Pi (oxidative phosphorylation). Each NADH yields approximately 2.5 ATP, each FADH2 yields approximately 1.5 ATP. The process is the major ATP source in aerobic organisms, producing approximately 30-32 ATP per glucose (including glycolysis and TCA cycle).