Question

Which statement correctly describes how the mitochondrial uncoupling agent valinomycin inhibits oxidative phosphorylation without collapsing the proton (H+) gradient across the inner mitochondrial membrane?

a. Valinomycin carries Kt into the mitochondrial matrix, reducing the electrical component of the electrochemical gradient across the inner mitochondrial membrane.
b. Valinomycin carries Ht into the mitochondrial matrix, decreasing the mitochondrial membrane potential without generating ATP.
c. Valinomycin is a complex I inhibitor that prevents NADH oxidation and the pumping of H+ into the intermembrane space.
d. Valinomycin is an ATP synthase inhibitor that prevents H+ from moving down its concentration gradient into the matrix.

Answer 1

a. Valinomycin carries Kt into the mitochondrial matrix, reducing the electrical component of the electrochemical gradient across the inner mitochondrial membrane.

Step-by-step explanation:

Oxidative phosphorylation is a process by which cells generate ATP (the energy coin of the cells) by coupling an electrochemical potential gradient across the inner mitochondrial membrane created by the electron transport chain to phosphorylation of ADP. Moreover, an ionophore is a molecule that reversibly binds ions. Ionophores are often involved in the movement of ions across the cell membrane. Valinomycin is an ionophore that mediates the transport of potassium (K+) ions down a concentration gradient, which is capable of disrupting the gradient across the membrane by modifying the K+ gradient. Valinomycin binds to K+ ions and enables them to pass more rapidly across the mitochondrial inner membrane, thereby neutralizing the excess of negative charge inside the mitochondrial matrix and thus slowing ATP synthesis.