What are the essential components of the cell membrane?

The cell membrane, also known as the plasma membrane (PM) or cytoplasmic membrane, is found in all cells and separates the interior of the cell from the outside environment. The cell membrane regulates the transport of materials entering and exiting the cell. The cell membrane is formed of lipids, membrane proteins and carbohydrates.

The lipids contained in the membrane are phospholipids, a special type of lipid, that have a hydrophilic phosphate head and a hydrophobic tail consisting of two fatty acid chains. Because this type of membrane is made of two phospholipid layers, it is also called a bilipid membrane. 

Membrane proteins are common proteins that are part of, or interact with, cell membranes. They are embedded and dispersed in the compact bilipid structure. Based on their structure, there are main three types of membrane proteins: integral membrane protein that is permanently anchored or part of the membrane, peripheral membrane protein that is only temporarily attached to the lipid bilayer or to other integral proteins and acts as an enzyme , and lipid-anchored proteins.

Carbohydrates are the third major component of cell membranes. They are always found on the exterior surface of cells and are bound either to proteins (forming glycoproteins) or to lipids (forming glycolipids). Along with peripheral proteins, carbohydrates form specialized sites on the cell surface that allow cells to recognize each other.