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.