<P> Most eukaryotic cells have mitochondria , which produce ATP from products of the citric acid cycle , fatty acid oxidation , and amino acid oxidation . At the mitochondrial inner membrane , electrons from NADH and FADH2 pass through the electron transport chain to oxygen , which is reduced to water . The electron transport chain comprises an enzymatic series of electron donors and acceptors . Each electron donor will pass electrons to a more electronegative acceptor , which in turn donates these electrons to another acceptor , a process that continues down the series until electrons are passed to oxygen , the most electronegative and terminal electron acceptor in the chain . Passage of electrons between donor and acceptor releases energy , which is used to generate a proton gradient across the mitochondrial membrane by actively `` pumping '' protons into the intermembrane space , producing a thermodynamic state that has the potential to do work . The entire process is called oxidative phosphorylation , since ADP is phosphorylated to ATP using the energy of hydrogen oxidation in many steps . </P>
where does the electron transport chain pumps protons
mitochondrial membrane