Role of molecular oxygen in ETC -
Ans. is 'c' i.e., To act as last electron acceptor Structural organizations of components of ETCo 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 parts of any complex and are not fixed in the inner mitochondrial 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.Complex I (NADH - CoQ reductase) catalyzes the transfer of electron from NADH to coenzyme Q (CoQ).Complex II (Succinate - CoQ reductase or succinate dehydrogenase) transfers electrons from succinate to coenzyme Q.Complex III (CoQ - cytochrome C reductase), transfers electron from CoQ to cytochrome C.Complex IV (cytochrome C oxidase) transfers electrons from cytochrome C to O,.o Molecular is the last electron acceptor in ETC.o The flow of reducing equivalents (electrons) is in following sequence. Most of the substrate transfer their reducing equivalents to NAD to form NADH, reaction is catalyzed by dehydrogenases. Reduced NADH is oxidized by NADH dehydrogenase (NADH-CoQ reductase), an enzyme which contains FMN as a coenzyme and also a Fe-S protein. NADH transfers reducing equivalents to FMN which, intum, transfers reducing equivalents to FeS. FeS transfers reducing equivalents to coenzyme Q (CoQ). Further transfer is in sequence of Cyt b - Fe-S - Cvt C 1, - Cytc --> Cyt a - Cyt a3 - O2o Succinate transfer its reducing equivalents to FADH2 which transfer them to Fe-S. Fe-S transfer these reducing equivalents to coenzyme Q (CoQ). Further sequence is same.
Transfer of reducing equivalent to CoQ
Transfer of reducing equivalent from cytosol to mitochondria
To act as last electron acceptor
Generation of ATP
Respiratory Chain