Non-shivering thermogenesis in brown adipose tissue is mediated by uncoupling protein 1 (thermogenin). Its mechanism of action is:

• A It inhibits complex I of the electron transport chain
• B It activates hormone-sensitive lipase through sympathetic stimulation
• C It hydrolyses ATP directly to release heat
• D It dissipates the proton gradient across the inner mitochondrial membrane, generating heat instead of ATP ✓

Explanation

UCP1 is a proton channel in the inner mitochondrial membrane of brown adipocytes. It allows protons pumped by the respiratory chain to flow back into the matrix bypassing ATP synthase, so oxidation proceeds uncoupled from phosphorylation and energy escapes as heat. It is activated by free fatty acids released under norepinephrine stimulation and inhibited by purine nucleotides such as GDP. It neither touches complex I nor acts downstream of lipase activation.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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