A newborn exposed to cold maintains body temperature without shivering. Brown adipose tissue in this infant expresses a protein in the inner mitochondrial membrane that allows protons to re-enter the matrix without passing through ATP synthase. The immediate consequence of activating this protein is:

• A Inhibition of the electron transport chain due to a high proton motive force
• B Reversal of ATP synthase, pumping protons out of the matrix
• C Complete arrest of oxygen consumption
• D Increased heat production with continued electron transport but reduced ATP synthesis ✓

Explanation

Thermogenin (uncoupling protein 1) provides a proton leak across the inner membrane, dissipating the proton gradient as heat. Electron transport and oxygen consumption continue or even accelerate because the gradient stays low, but the energy is released as heat instead of being captured as ATP. Option A is wrong because the gradient falls, it does not build up. Complete arrest of respiration, as seen with oligomycin acting on a coupled chain, does not happen when uncouplers relieve back-pressure on the chain.

Reference: Lehninger Principles of Biochemistry, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.