Membranes of cold-adapted fish contain a higher proportion of unsaturated fatty acids than the membranes of close relatives living in warm water. What advantage does this provide?

Core Concept

Membrane fluidity depends on how closely neighboring phospholipid tails pack. Straight saturated chains align tightly, so van der Waals attractions lock them into a gel-like state as temperature drops. A cis double bond introduces a rigid kink that disrupts this orderly packing, lowering the transition temperature and keeping the bilayer fluid and functional in the cold. Cold-adapted fish therefore maintain a higher fraction of unsaturated tails, a pattern documented across species. Cholesterol plays a related buffering role in many animal membranes.