Question

In mitochondrion, the proton gradient required for ATP synthesis develops across

• A. Inner membrane
• B. Inter membrane space
• C. Outer membrane
• D. $F_0-F_1$ particles

Answer 1

The correct option is A Inner membrane

The inner mitochondrial membrane is permeable to water but impermeable to protons except at the points where the respiratory chain and ATP synthase are located. The respiratory chain is oriented in such a way that the electrons move in an inward direction and protons flow in an outward direction. Reduced NAD released from Krebs cycle when enter in the electron transport system transports three pairs of protons across the inner mitochondrial membrane to the intermembrane space. Similarly, FADH 2 also transports pairs of protons into the intermembrane space. The unidirectional flow of protons towards the outer side results in the accumulation of protons in the intermembrane space. The pH of the outer surface of inner mitochondrial membrane lowers considerably due to the concentration of net positive charge. Thus a pH gradient is generated across the inner mitochondrial membrane. The pH gradient and the proton concentration gradient across the inner membrane built a proton motive force. This force drives protons across the membrane towards the mitochondrial matrix. The return flow of proton down their electrochemical gradient through the enzymatic complex is responsible for the activation of ATPase which drives the synthesis of ATP from ADP and phosphate.

Thus, the correct answer is option A.