Which of the following situations does NOT result in a breakdown of the proton gradient across a biological membrane?

• A. Inhibition of ATP synthase activity
• B. Addition of an uncoupling agent such as dinitrophenol
• C. Disruption of the membrane structure by detergents
• D. Opening of ion channels that allow protons to freely diffuse

Answer: (A)

Verified step by step guidance

1. Understand that the proton gradient across a biological membrane is essential for processes like ATP synthesis, as it stores potential energy used by ATP synthase to produce ATP.
2. Recognize that a breakdown of the proton gradient means the gradient is dissipated or lost, which can happen if protons move freely across the membrane without driving ATP synthesis.
3. Analyze each situation: - Inhibition of ATP synthase activity means ATP synthase cannot use the proton gradient to make ATP, but it does not itself allow protons to cross the membrane freely, so the gradient remains intact. - Addition of an uncoupling agent like dinitrophenol allows protons to bypass ATP synthase, collapsing the gradient. - Disruption of the membrane structure by detergents breaks the membrane integrity, causing loss of the gradient. - Opening of ion channels that allow protons to freely diffuse also dissipates the gradient.
4. Conclude that only inhibition of ATP synthase activity does NOT cause the proton gradient to break down, because it blocks the use of the gradient but does not eliminate the gradient itself.
5. Summarize that the key difference is whether protons can freely cross the membrane independent of ATP synthase; if they can, the gradient breaks down, if not, the gradient remains.