Effects of sterols on Membrane Fluidity

Cholesterol's Dual Effect on Membranes

• Cholesterol has two different effects on the cell membrane:
  • It increases the melting temperature of the membrane.
  • It prevents the membrane from becoming solid at lower temperatures.

How Cholesterol Works

• Cholesterol is rigid. It packs itself between the fatty acid chains of phospholipids.

• By packing the phospholipids together more tightly, it increases the melting temperature of the membrane.

• When the temperature drops, cholesterol prevents the fatty acid chains from packing in as tightly, which stops the membrane from becoming solid at lower temperatures.

Cholesterol as a Fluidity Buffer

• Cholesterol acts as a fluidity buffer in membranes.

  • It prevents the membrane from becoming too fluid.
  • It prevents the membrane from becoming too solid.

• Cholesterol protects us from membranes solidifying as we go into hypothermia.

• At a certain low temperature, cholesterol can no longer prevent solidification, and the entire membrane becomes solid, preventing proteins from moving around.

Cholesterol and Membrane Permeability

• Cholesterol decreases the permeability of membranes.

• It ensures that there is enough packing in the membrane to prevent lipids from separating and allowing small molecules or ions to slip through.

• Cholesterol is found in lipid rafts.