Question

Which complex involved in electron transport and oxidative phosphorylation does not directly affect the pH of the mitochondiral intermembrane space?

A) Complex I

B) Complex II

C) Complex III

D) Complex IV

D) Complex IV

E) Complex V

Answer 1

Ans(B) : Complex II (Succinate dehydrogenase , an inner mitochondrial membrane - bound enzyme, is an integral component of complex II. It converts succinate to fumarate during krebs cycle. The two electrons released in the conversion of succinate to fumarate are transferred first to FAD, then to an iron - sulfur cluster & finally to coenzyme Q. Thus, coenzyme Q draws electrons into respiratory chain, not only from NADH , but also from FADH2. Complex II does not pump protons during transport of electrons across inner mitochondrial membrane in the intermembrane space, but transfers its electrons to complex III & thus, complex II does not directly affects the pH of intermembrane space, as it doen not pump protons.

- Whereas, complex I pumps four protons across inner mitochondrial membrane, during transport of each pair of electron from NADH to coenzyme Q.

- Complex III pumps 4 protons across inner mitochondrial membrane, during transport of each pair of electron from coenzyme Q to cytochrome c.

- Complex IV finally transfers electrons to oxygen & pumps 2 protons across inner mitochondrial membrane.

Hope this will help you☺