When membrane fluidity is in the cold, what maintains it?

When membrane fluidity is in the cold, what maintains it?

• A. cholesterol alone
• B. increased membrane proteins
• C. unsaturation of lipids only
• D. cholesterol and increasing phospholipid unsaturation

Answer: (D)

Membrane fluidity is adjusted by cells to keep membranes workable at different temperatures, a process called homeoviscous adaptation. In the cold, maintaining fluidity relies on two coordinated strategies. First, increasing phospholipid unsaturation introduces kinks in fatty acid chains, preventing tight packing and helping the membrane stay more fluid. Second, cholesterol sits between fatty acid tails and acts as a buffer: it prevents membranes from becoming too rigid when cold, while also limiting excessive fluidity at higher temperatures. Together, cholesterol and greater unsaturation of phospholipids best preserve membrane fluidity in the cold. Increased membrane proteins don’t directly adjust lipid packing, so they don’t fulfill the same role, and unsaturation alone lacks the stabilizing buffering effect cholesterol provides.

Membrane fluidity is adjusted by cells to keep membranes workable at different temperatures, a process called homeoviscous adaptation. In the cold, maintaining fluidity relies on two coordinated strategies. First, increasing phospholipid unsaturation introduces kinks in fatty acid chains, preventing tight packing and helping the membrane stay more fluid. Second, cholesterol sits between fatty acid tails and acts as a buffer: it prevents membranes from becoming too rigid when cold, while also limiting excessive fluidity at higher temperatures. Together, cholesterol and greater unsaturation of phospholipids best preserve membrane fluidity in the cold. Increased membrane proteins don’t directly adjust lipid packing, so they don’t fulfill the same role, and unsaturation alone lacks the stabilizing buffering effect cholesterol provides.