Which molecule mediates heat production in brown adipose tissue during cold exposure?

• A. Cytochrome c oxidase
• B. UCP1 uncouples oxidative phosphorylation to generate heat.
• C. Actin
• D. Myosin

Answer: (B)

Non-shivering thermogenesis in brown adipose tissue is driven by a mitochondrial protein that uncouples respiration from ATP production. When cold exposure occurs, sympathetic signaling activates brown fat, and the key player is UCP1. Located in the inner mitochondrial membrane, UCP1 creates a controlled proton leak so protons re-enter the matrix without driving ATP synthase. The energy from substrate oxidation is then released as heat instead of being captured as ATP, warming the body.

Cytochrome c oxidase is part of the electron transport chain and helps move electrons and pump protons to support ATP production, but it doesn’t directly induce the regulated heat generation that brown fat needs. Actin and myosin are contractile proteins involved in muscle movement, not in the thermogenic process of brown fat. Thus, UCP1 is the molecule that mediates heat production during cold exposure.