The ETC consists of four main protein complexes (Complex I, II, III, and IV) and ATP synthase. Electrons are passed through these complexes via a series of redox reactions, releasing energy to pump protons from the mitochondrial matrix to the intermembrane space. This creates an electrochemical gradient, known as the proton motive force. ATP synthase utilizes this gradient to synthesize ATP from ADP and inorganic phosphate.
