Question

Which statement concerning ATP synthesis is true?

• A. ATP can be synthesized through substrate level phosphorylation, photophosphorylation and oxidative phosphorylation
• B. The proton-motive force is the establishment of proton gradients and electrochemical potentials across the inner membrane
• C. Proton-motive force is essential for back flow of $H^{+}$ from outer chamber of matrix of mitochondria through proton channel $\left(F_0\right)\text{of}{F}_0–F_1$ particle to produce ATP
• D. All of the above

Answer 1

The correct option is D All of the above

ATP is produced mainly by three processes.
(i) oxidative phosphorylation (mitochondria)
(ii) Substrate level phosphorylation
(iii) Photophosphorylation

The ATP synthase is a mitochondrial enzyme localized in the inner membrane, where it catalyses the synthesis of ATP from ADP and phosphate, driven by a flux of protons across a gradient generated by electron transfer from the proton chemically positive to the negative side.

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.

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 $\left(F_0\right)\text{of}{F}_0–F_1$ particle is responsible for the activation of ATPase which drives the synthesis of ATP from ADP and phosphate.

Thus, all the given statements are correct and the correct answer is option d.