THE CELL MEMBRANE The boundary of the cell is called the cell membrane . It is also called Plasma membrane.

The cell membrane-Structure The cell membrane is made up of Phospholipids Proteins Cholesterol Carbohydrates

Cell membrane -structure 75% of the membrane contains phospholipids What are phospholipids? Lipid molecule with a phosphate group in it is called phospholipids. One of the three fatty acid in a lipid molecule is replaced by a phosphate group to form a phospholipid molecule.

Structure of cell membrane Usually Lipids are Non- polar molecules, which do not mix with water. But in a phospholipid molecule , the phosphate group is polar ,ie, it has an attraction for water molecules. The polar phosphate head is HYDROPHILIC The non polar end is HYDROPHOBIC

Structure of cell membrane Scientists Proposed a theory to explain the arrangement of molecules in the cell membrane. Two scientists named Singer and Nicholson proposed THE FLUID MOSAIC MODEL of the cell membrane in 1972. They said the cell membrane is made up of two layers of phospholipids.

The fluid Mosaic Model Of the cell membrane

Fluid Mosaic model Large number of PROTEINS are present in the cell membrane . They “float about “ in the phospholipid bilayer. There are two types of proteins in the membrane . INTRINSIC proteins and EXTRINSIC proteins.

PROTEINS in the membrane INTRINSIC proteins are completely inside in the lipid bilayer. Extrinsic proteins are found only on the outer surface or on the inner surface of the membrane.

FLUID MOSAIC MODEL Membrane also contains CHLESTEROL. It increases the rigidity and stability of the membrane.

Fluid mosaic model On the outer layer of the membrane there are GLYCOLIPID molecules. They are combinations of lipids and carbohydrates.

On the surface of the membrane there are GLYCOPROTEINS also. They are combinations of carbohydrates and proteins

FUNCTIONS of the cell membrane Cell membrane forms a boundary around the cell contents. It protects the contents of the cell. It is semipermeable. It allows and regulates the movement of molecules into and out of the cell.