Question

Which one of the following is not true regarding the release of energy during ATP synthesis through chemiosmosis? It involves:

• A. Breakdown of proton gradient
• B. Breakdown of electron gradient
• C. Movement of protons across the membrane to the stroma
• D. Reduction of NADP to NADPH₂ on the stroma side of the membrane

Answer 1

The Correct Option is B

To understand which statement is not true regarding the release of energy during ATP synthesis through chemiosmosis, we need to evaluate how chemiosmosis works in biological systems, specifically within the mitochondria and chloroplasts.

1. Chemiosmosis involves establishing a proton gradient across a membrane, typically the inner mitochondrial membrane or the thylakoid membrane in chloroplasts.
2. The proton gradient is crucial as it drives ATP synthesis by ATP synthase when protons move back across the membrane into the matrix (in mitochondria) or the stroma (in chloroplasts).
3. Breakdown of proton gradient: This statement is true. The proton gradient is utilized and 'broken down' as protons flow through ATP synthase, facilitating ATP production.
4. Breakdown of electron gradient: This is incorrect as there's no electron gradient that drives ATP synthesis. Rather, electrons are transferred through the electron transport chain, generating the proton gradient.
5. Movement of protons across the membrane to the stroma: This too is valid. Protons moving across the thylakoid membrane into the stroma release energy used to convert ADP into ATP.
6. Reduction of NADP to NADPH₂ on the stroma side of the membrane: In photosynthesis, this is true. Electrons reduce NADP⁺ to NADPH on the stroma side, but this process occurs after ATP synthesis and not during the release of energy through chemiosmosis.

Thus, the statement 'Breakdown of electron gradient' is not true regarding the energy release in ATP synthesis via chemiosmosis. It is the proton gradient, not an electron gradient, that facilitates this process.