NCERT Class 11 Science — Chapter 2: Respiration in Plants

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

Official previous-year question

Verified 1 Aug 2026.

Options

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Solution

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).

Your note

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The correct option is 4.

Explanation

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⁺.