Question

Which of the following complexes involved in electron transport and oxidative phosphorylation does NOT directly impact the pH of mitochondrial intermembrane space?

A) Complex I

B) Complex II

C) Complex III

D) Complex IV

E) Complex V

Answer 1

Protein complexes such as Complex I-IV are involved in the electron transport chain.

They are involved in moving electrons from NADH and FADH2 to molecular oxygen.

Answer: Complexes involved in electron transport and oxidative phosphorylation does NOT directly impact the pH of mitochondrial intermembrane space are Complex 1, 3 and 4

The explanation is follows:

• The respiratory chain in the inner mitochondrial membrane carries out oxidative phosphorylation.
• Three enzyme complexes are responsible for the electron transport: NADH-ubiquinone oxidoreductase complex (complex I), ubiquinone-cytochrome c oxidoreductase complex (complex III), and cytochrome c oxidase (complex IV).
• Respiratory inhibitors block the electron transport chain. Pesticide rotenone blocks complex I, Antimycin A blocks complex III, Cyanide, carbon monoxide, and azide block complex IV.
• The protons are pumped from the mitochondrial matrix to the IMS by these respiratory complexes. As a result, an electrochemical gradient is generated, which is combined by forces due to a H+ gradient (pH gradient) and a voltage gradient (membrane potential).
• The pH in the IMS is about 0.7 unit lower than the one in the matrix and the membrane potential of the IMS side becomes more positively charged than the matrix side. This electrochemical gradient from the IMS to the matrix is used to drive the synthesis of ATP in the mitochondria.