Question

During the oxidation of $FAD{H}_2$, _________ is not involved.

• A. complex I
• B. complex II
• C. complex III
• D. complex IV

Answer 1

The correct option is A complex I

During the oxidation of $FAD{H}_2$, complex I is not involved. During the oxidation of $FAD{H}_2$, complex II, III and IV are involved.

$FAD{H}_2$ undergoes oxidation and releases electrons to the iron-sulfur protein of complex II. From complex II, electrons are transferred to ubiquinone. The ubiquinone gets reduced to form ubiquinol. The electrons from ubiquinol are transferred to the cytochrome b and cytochrome c1 of complex III. The electrons are then further transferred to cytochrome c. Cytochrome c is a small protein attached to the outer surface of the inner membrane of mitochondria and acts as a mobile carrier for the transfer of electrons between complex III and IV. In complex IV, the electrons pass through cytochromes a and $a_3$. From complex IV, electrons pass to oxygen.
Oxygen is the final acceptor of the electrons which combines with $H^{+}$ to form water.