Composition of Plasma membrane

Plasma membrane

The outer most boundary of the cell (animal cell) is called plasma membrane.

Composition

· It consists of 60% to 80% protein and 20% to 40% lipids; small quantity of carbohydrates is also present.

· Earlier, two models were proposed by scientists while second model was accepted and now plasma membrane on the principle of second one. These two models are as following;-

Unit membrane model

· According to this model, protein layer surrounds lipid bilayer from outer and inner side. this structure is known as unit membrane.

Later it was revealed that protein layer does not surround lipid bilayer.

Fluid mosaic model

· According to this model, protein layer does not surrounds lipid bilayer from outer and inner side but it is embedded in lipid layer.

Functions of plasma membrane

Selectively permeable membrane

· It is partially permeable, only selective particles pass through it.

· Lipid soluble particles pass through it very easily than others.

· Many small glucose, water and gas molecules (as they are neutral) easily pass through it.

· Charge bearing particles like ions have difficulty to pass through it.

· Passive transport helps the substances (which are not needed outside the cell) to enter inside the cell.

· Cell membrane also helps in active transport which requires energy.

Endocytosis

· Plasma membrane helps the cell to take in material, called endocytosis.

· It includes both eating (phagocytosis) and drinking (pinocytosis).