PLASMA MEMBRANE

PLASMA MEMBRANE
OCCURRENCE OF PLASMA MEMBRANE
Plasma membrane or the cell membrane is usually found in all types. it is the outer most boundaries of the animals cells and inner to cell wall in plant cells.
CHEMICAL COMPOSITION OF PLASMA MEMBRANE
Cell membrane is chemically composed of lipoproteins as lipids (20-40%) and proteins (60-80%). In addition there is small quantity of carbohydrates and cholesterol is also present.
lipids present are phospholipids and sterol, the cholesterol in the animals cell are sterol and in that of plant cell are phytosterol.

STRUCTURE AND MORPHOLOGY:
The most acceptable model for the membrane structure was proposed by singer and Nicholson in 1972, this model is called as the fluid Mosaic model.
Fluid part refers to the phospholipids molecules and mosaic part refers to the proteins.
THE LIPIDS BILAYER (FLUID)
The membrane is composed of a lipid bilayer in which the proteins are sandwiched in a mosaic pattern. The outer surface of the lipids layer is hydrophilic and is glycerol. The inner surface is hydrophobic and is composed of water- insoluble fatty acid tail.
ARRANGEMENT OF PROTEINS (MOSAIC)
The protein does not form a layer on lipids bilayer layer but are arranged in a mosaic pattern.
TYPES OF PROTEINS:
There are two types of proteins.
EXTRINSIC PROTEINS:
The proteins that lie on the outer surface of the lipid bilayer are called the extrinsic proteins or perpheral proteins most of which are present on the cytoplasmic side.
INTRINSIC PROTEINS:
The proteins that are completely buried in the lipid layer are called the intrinsic proteins.

THE GLYCOCALYX
Carbohydrates attached to the proteins forms glycoproteins, and carbohydrates attached to the lipids forms glycolipids. These carbohydrates form a layer on above the membrane called glycocalyx