Basic organization is a phospholipid bilayer

Proteins embedded

Oligosaccharide may be attached to proteins

Biological membranes are very thin structures composed of a bilayer of phospholipids with protein molecules embedded. The hydrophilic heads of the phospholipids face outwards, and the hydrophobic tails to the inside of the bilayer.

This diagram is a simple representation of the fluid-mosaic model showing some embedded proteins which traverse the membrane entirely. Because a membrane exhibits fluid-like properties, its molecules can migrate in the plane of the membrane.

Oligosaccharides (i.e. short chains of glucose and other sugars) may be bound to some of the intrinsic protein molecules and help determine the specificity of these glycoproteins as recognition sites for other molecules. These also anchor the polarity of intrinsic proteins in the membrane. In addition, glucose/lipid molecules may exist as glycolipids, and glucose/protein molecules as glycoproteins. The lipid cholesterol is also typically associated with membranes.