Lipid domains

Biological membranes are not just homogeneous combination of proteins and lipids. Within  them are discrete  domains  in that  certain  lipids and proteins  cluster together  to  form  functional  and structural units.  For instance, the clustering together of sphingomyelin, glycosphingolipids and cholesterol in the outer leaflet of the bilayer with another lipids in the inner leaflet provides increase to lipid rafts. Several lipid modifled proteins can associate with lipid rafts and these structures have been implicated in many cellular processes, involving cell signaling and the transport of lipids and proteins from the Golgi to the plasma membrane.

                              Figure:  The fluid mosaic model of membrane structure.