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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.
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