Mitochondrial Respiration Inhibitors Matching

Mitochondrial respiration inhibitors play crucial roles in studying electron transport chain (ETC) and ATP synthesis mechanisms. The correct matching for this GATE Biotechnology 2025 question identifies FCCP as a proton uncoupler, cyanide as a Complex IV blocker, oligomycin A as an ATP synthase inhibitor, and butyl malonate as a succinate uptake blocker.

Correct Answer

Option (A) P-2; Q-1; R-4; S-3 provides the accurate matching of inhibitors to their functions in mitochondrial respiration.

Inhibitor Functions Breakdown

P. FCCP (2. Makes the membrane permeable to protons):
FCCP acts as a proton ionophore, shuttling protons across the inner mitochondrial membrane and dissipating the proton motive force without halting electron transport. This uncoupling stimulates oxygen consumption while abolishing ATP synthesis.

Q. Cyanide (1. Inhibits cytochrome c oxidase):
Cyanide binds irreversibly to the heme a3-CuB binuclear center of Complex IV (cytochrome c oxidase), preventing electron transfer to oxygen and halting the ETC at its final step.

Q. Cyanide (1. Inhibits cytochrome c oxidase):
Cyanide binds irreversibly to the heme a3-CuB binuclear center of Complex IV (cytochrome c oxidase), preventing electron transfer to oxygen and halting the ETC at its final step.

R. Oligomycin A (4. Inhibits ATP synthase):
Oligomycin A blocks the FO subunit proton channel of ATP synthase (Complex V), preventing proton flow through F1FO-ATP synthase and inhibiting ATP production while maintaining the proton gradient.

S. Butyl malonate (3. Blocks mitochondrial uptake of succinate):
Butyl malonate competitively inhibits the dicarboxylate carrier, preventing succinate transport from cytosol into the mitochondrial matrix and thus blocking Complex II substrate supply.

Why Other Options Fail

• Option (B) P-2; Q-3; R-1; S-4: Incorrectly assigns cyanide to succinate uptake block (Q-3) instead of Complex IV inhibition and mismatches oligomycin with Complex IV.

• Option (C) P-2; Q-4; R-3; S-1: Wrongly pairs cyanide with ATP synthase inhibition (Q-4) and butyl malonate with Complex IV blockage.

• Option (D) P-3; Q-1; R-2; S-4: Misplaces FCCP as succinate uptake blocker (P-3) and oligomycin as proton permeabilizer.