The metabolic pathway through which the electron passes from one carrier to another inside the inner mitochondrial membrane is called ETC or mitochondrial respiratory chain. An electron transport chain is a series of coenzymes and cytochromes that take part in the passage of electrons from a chemical to its ultimate acceptor. Inner mitochondrial membrane possesses five electron carriers i.e. complex I, complex II, complex III, complex IV and complex V. Complex I to IV are involved in the electron transport - NADG-UQ Reductase, Succinate UQ complex, UQH2-cytochrome c reductase complex, Cytochrome c oxidase complex. Complex V is connected with ATP synthesis. In ETS, the electrons from NADH produced during the citric acid cycle are oxidized by NADH dehydrogenase and are transferred to ubiquinone located within the inner membrane. The ubiquinone also receives electrons from FADH2 which are transferred to cytochrome c via cytochrome bc1complex. When the electrons pass from one carrier to another via electron transport chain, they produce ATP from ADP and inorganic phosphate. The number of ATP molecules synthesized depends upon electron donor. Oxidation of one molecule of NADH gives rise to 3 molecules of ATP, while oxidation of one molecule of FAD produces two molecules of ATP.