The Series of molecules through which electrons are transported from the donor molecule to the acceptor molecule by creating an electrochemical gradient that leads to the formation of ATP. The NADH 2 and FADH 2 are produced during glycolysis, connecting link reaction and Krebs cycle, they are oxidised with the help of various electron carriers and enzymes in this process. These carriers and enzymes are arranged on inner mitochondrial membrane in the form of various complexes as complex I, II, III, IV and V. NADH+H + is oxidised by NADH dehydrogenase (complex I) and it's electrons are transferred to ubiquinone present on inner membrane of mitochondria. Ubiquinone also receives reducing equivalents via FADH 2 (Complex II). FADH2 is generated during oxidation of succinate in the citric acid cycle. The reduced ubiquinone (ubiquinol) is then oxidised with the transfer of electrons to cytochrome-c via cytochrome-bc1 complex (complex III).The outer surface of the inner membrane has a small protein, cytochrome-c attached to it that acts as a mobile carrier for transfer of electrons between complex III and IV. Complex IV refers to cytochrome c oxidase complex containing cytochromes a and a3, along with two copper centres. When the electrons pass from one carrier to another via complex I to IV in the electron transport chain, they are coupled to ATP synthase (complex V). This coupling is necessary for the production of ATP from ADP and inorganic phosphate. The amount of ATP produced depends on the molecule, which has been oxidised.