Q. What are the fundamental constituents of the cell membrane?

The cell membrane is formed of lipids, carbohydrates and proteins.

The membrane lipids are phospholipids, a special kind of lipid to which one extremity a phosphate group is bound thus assigning electrical charge to this region of the molecule Since phospholipids have one electrically charged extremity and a long neutral organic chain they can organize themselves in two layers of associated molecules the hydrophilic portion (polar) of each layer faces outwards in contact with water (a polar molecule too) of the extracellular and the intracellular space and the hydrophobic chains (non polar) face inwards isolated from the water. Because this type of membrane is made of two phospolipid layers it is also known as a bilipid membrane.

Membrane proteins are embed and dispersed in the compact bilipid structure. Carbohydrates appear in the outer surface of the membrane associated to some of those proteins under the form of bound to phospholipids forming glycolipids or glycoproteins. The membrane carbohydrates form the glycocalix of the membrane.

This description (with further explanations) is known as the fluid mosaic model as regards the structure of the cell membrane.