Membrane Domains

The lipid bilayer of the cell membrane contains distinct clusters of lipids and proteins, called domains.

These domains often concentrate proteins and specific lipid molecules to increase their interactions and provide different environments in distinct portions of the membrane.

For example, an intestinal epithelial cell has apical and basolateral domains that differ in their protein and lipid composition. The apical domain lines the intestinal cavity and contains proteins involved in ion uptake and sugar metabolism.

In contrast, the basolateral domain contains proteins that interact with neighboring cells and the basement membrane and help in cell-cell communication and adhesion.

Proteins are inhibited from entering into another domain by cell-cell junctions, also known as tight junctions.

Specific membrane lipids including sphingolipids and cholesterol form microdomains known as lipid rafts. The saturated chains of sphingolipids and cholesterol are more closely packed than the phospholipids with unsaturated fatty acid tails, leading to the formation of denser and distinct lipid rafts in the membrane.