Cell membranes are not a uniform fluid mosaic: cholesterol and sphingolipids can locally pack into more ordered 'raft' microdomains that act as organizing platforms for membrane proteins.
raft forms when lipid + cholesterol collide with P ~ nucleation * (1/fluidity)
- Phospholipids — the bulk bilayer lipids diffusing laterally in the plasma membrane.
- Cholesterol molecules — rigid sterol molecules that pack tightly against saturated lipid tails.
- Raft nucleation rate — probability that a lipid-cholesterol encounter locks into an ordered microdomain.
- Membrane fluidity — overall lateral mobility of the bilayer — higher fluidity makes stable raft nucleation harder.
Lipid rafts concentrate signaling receptors and GPI-anchored proteins, so disrupting them with cholesterol-depleting drugs (like methyl-beta-cyclodextrin) is a standard tool for probing raft-dependent signaling.