Q. 33 The movement of protons through the 𝐅𝟎 𝐅𝟏-ATPase during mitochondrial respiration is required for
____
(A) the increase in pH of mitochondrial matrix.
(B) changing the conformation of FoF1
-ATPase to expel the ATP.
(C) importing Pi
from inter membrane space.
(D) decreasing the affinity of ADP to FoF1
-ATPase.

Protons flow through the Fo portion of FoF1-ATPase during mitochondrial respiration to drive ATP synthesis via conformational changes. This process harnesses the proton motive force from the electron transport chain. The correct answer is option (B).

Correct Answer

Option (B) changing the conformation of FoF1-ATPase to expel the ATP.​

Proton translocation through the Fo subunit rotates the c-ring, which turns the γ subunit in F1. This rotation induces sequential conformational changes in the β subunits—loose, tight, and open states—releasing newly formed ATP into the mitochondrial matrix. Without this proton-driven rotation, ATP remains bound in the tight conformation.​

Option Analysis

• (A) the increase in pH of mitochondrial matrix. Incorrect. Proton entry from the intermembrane space (high H⁺) into the matrix (low H⁺) decreases matrix pH by raising H⁺ concentration, not increasing it.​

• (B) changing the conformation of FoF1-ATPase to expel the ATP. Correct, as explained above. The binding change mechanism relies on proton-powered rotation for ATP release.​

• (C) importing Pi from inter membrane space. Incorrect. Phosphate (Pi) enters the matrix via the phosphate carrier (PiC) using H⁺/Pi symport from the intermembrane space, independent of FoF1-ATPase.​

• (D) decreasing the affinity of ADP to FoF1-ATPase. Incorrect. Proton movement increases ADP/Pi affinity in the loose conformation for ATP formation; it does not decrease ADP binding.​

Mechanism Overview

The FoF1-ATPase (Complex V) synthesizes ATP using ~3-4 protons per ATP via oxidative phosphorylation.​

• Protons enter Fo from intermembrane space, rotating c-ring (~10 c-subunits).

• Rotation drives γ subunit spin in F1, cycling β subunits: open (expels ATP) → loose (binds ADP+Pi) → tight (forms ATP).

• This rotary catalysis couples respiration to ATP production.​