Which feature most strongly contributes to membrane fluidity at moderate temperatures?

Which feature most strongly contributes to membrane fluidity at moderate temperatures?

• A. The degree of saturation of fatty acids in phospholipids
• B. The amount of cholesterol in the membrane
• C. The number of transmembrane proteins
• D. The height of the membrane

Answer: (A)

The level of fatty acid saturation in phospholipids is the key factor shaping membrane fluidity at moderate temperatures. When fatty acids are saturated, their straight tails pack tightly, making the membrane more viscous and less fluid. In contrast, unsaturated fatty acids have cis double bonds that insert kinks into the tails, preventing tight packing and creating space for molecules to move, which increases fluidity. This direct effect on how tightly lipids can pack and how freely they can move explains why saturation level most strongly influences fluidity under these conditions. Cholesterol can modulate fluidity, acting as a buffer across temperatures, but it doesn’t dictate fluidity as strongly as how saturated the fatty acids are. The number of transmembrane proteins and the height of the membrane don’t govern lipid mobility in the bilayer.

The level of fatty acid saturation in phospholipids is the key factor shaping membrane fluidity at moderate temperatures. When fatty acids are saturated, their straight tails pack tightly, making the membrane more viscous and less fluid. In contrast, unsaturated fatty acids have cis double bonds that insert kinks into the tails, preventing tight packing and creating space for molecules to move, which increases fluidity. This direct effect on how tightly lipids can pack and how freely they can move explains why saturation level most strongly influences fluidity under these conditions. Cholesterol can modulate fluidity, acting as a buffer across temperatures, but it doesn’t dictate fluidity as strongly as how saturated the fatty acids are. The number of transmembrane proteins and the height of the membrane don’t govern lipid mobility in the bilayer.