According to the chemiosmotic theory, approximately how many protons pass through the F0-F1 ATPase to synthesise one molecule of ATP?

The correct option is 4.

Explanation

The Chemiosmotic Theory, proposed by Peter Mitchell, explains the mechanism of ATP synthesis in mitochondria and chloroplasts. It postulates that a proton gradient (proton motive force) generated across a membrane drives the formation of ATP via the enzyme complex ATP synthase (F₀-F₁ ATPase).

Detailed Analysis:

• The Electron Transport Chain (ETC) pumps protons (H⁺) from the mitochondrial matrix into the intermembrane space, creating an electrochemical gradient.
• These protons flow back into the matrix through the transmembrane F₀ channel of the ATP synthase. This flow provides the energy to rotate the F₁ subunit, which catalyzes the conversion of ADP and inorganic phosphate (Pi) into ATP.
• Stoichiometry: According to modern biochemical consensus regarding the P/O ratio (Phosphate/Oxygen ratio):
  • The oxidation of one NADH molecule results in the pumping of 10 protons across the membrane.
  • This process yields approximately 2.5 ATP molecules.
  • Consequently, the number of protons required to synthesize one molecule of ATP is calculated as 10 / 2.5 = 4 protons.
• Technically, 3 protons pass through the F₀ complex to drive the mechanical rotation for synthesis, while 1 proton is utilized for the active transport of substrates (ADP and Pi) across the membrane. Therefore, the total requirement is 4 H⁺.

Key Takeaway: Approximately 4 protons are required to synthesize one molecule of ATP during oxidative phosphorylation (3 protons for the ATP synthase mechanism and 1 proton for substrate transport).