What is the composition of the plasma membrane?

The plasma membrane is a semi-permeable membrane, 6 nm to 10 nm in thickness. It is a 3-layered structure, with an inner lipid layer sandwiched between an outer and an inner protein layer. The plasma membrane is composed mainly of lipids, proteins and carbohydrates. Water makes up about 29% of the total weight.

• Lipid – The lipids in the plasma membrane include phospholipids, cholesterol and galactolipids. These lipid molecules consist of two parts – a glycerol head, which is hydrophilic, and two fatty acid tails, which are hydrophobic.
• Protein – Proteins are embedded into the membrane. 
• Carbohydrates – Carbohydrates occur in the form of glycoproteins and glycolipids and are confined exclusively to the extracellular side of the membrane