Role of molecular oxygen in ETC ?

Ans. is 'c' i.e., To act as last electron acceptor Structural organizations of components of ETC 3 Components of respiratory chain do not function as discrete carriers of reducing equivalent but are organized into four complexes each of which acts as a specific oxidoreductase. Coenzyme Q and cytochrome C are not pas of any complex and are not fixed in the inner mitochondria! membrane. The other components are fixed in the membrane. These components are arranged in order of increasing redox potential. Therefore, reducing equivalents (electrons) flow in one direction, I ---> II --> III --> IV, only because redox couple with low redox potential is better electron donor where as the one with high redox potential is electron acceptor. Thus, reducing equivalents (electrons) flow through the chain from the components of more negative redox potential to the components of more positive redox potential. i) Complex I (NADH - CoQ reductase) catalyzes the transfer of electron from NADH to coenzyme Q (CoQ). ii) Complex II (Succinate - CoQ reductase or succinate dehydrogenase) transfers electrons from succinate to coenzyme Q. iii) Complex III (CoQ - cytochrome C reductase), transfers electron from CoQ to cytochrome C. iv) Complex IV (cytochrome C oxidase) transfers electrons from cytochrome C to 02.