Cell Membrane

The cell membrane is the bounding layer of cytoplasm of the cell. This is also called as plasma membrane or cytoplasmic membrane. The cell membrane is a vital structure and critical barrier that separates the inside of the cell from the outer environment. Unlike the cell wall, it shrinks
under high osmotic pressure. The most widely accepted current model for cell membrane structure is the fluid mosaic model proposed by S Janathan Singer and Garth Nicholson.

Cell membrane is a composite, unit membrane which is tri laminar in nature and 7-8nm in thickness. Cell membrane is largely lipo protein in nature. It is composed of 20 - 30 percent phospholipids such as phosphatidyethanolamine, phosphatidyl-serine and phosphatidylcholine and 60 to 70 percent proteins. The phospholipids are amphipathic and form a lipid bylayer with hydrophobic groups ( fatty acids ) directing inward and hydrophilic groups
( glycerols ) directing outward. However in archaeobacteria the cell membrane is of mono lipid layer. The lipid matrix is fluid in nature and allow the componants to move around laterally. Of the total membrane proteins, about 70 - 80 percent proteins are embedded in the lipid matrix and are called as integral or intrinsic proteins. These integral proteins cannot be removed easily from the cell membrane about 20 - 30 percent of the total membrane proteins are loosely connected to the membrane and can be removed easily. These are called as peripheral or extrinsic proteins.