CELL STUCTURE

 

                                1.Cell Membrane - Structure

 Features:

Plasma membrane is a dynamic structure and its constituents are constantly renewed.

The thickness of membrane is about 7.5 nm

Semipermeable - allowing some substances to pass through while excluding others

Components:

                     Phospholipids

                     Cholesterol                40%                          

                     Proteins -------------- 55%

                    Carbohydrate -------- 5%

Arrangement of the components:

Explained by Fluid Mosaic Model proposed by Singer & Nicolson

           -  Phospholipids forms a fluid structure in which proteins and other components are    

              embedded to give a mosaic pattern.

          -   Fluidity helps the substances dissolved in lipid layer to move to different places in

               the membrane

 Lipid Bilayer:

           -  Made up of two layers of phospholipid molecules

           -  Each phospholipid molecule has a hydrophilic phosphate head and two hydrophobic

               fatty acid chains

           - These molecules are arranged in two layers in opposite direction

            - The inner and outer surfaces of the lipid bilayer are hydrophilic and the interior of

               the bilayer is hydrophobic 

  Proteins:

  Two types of proteins: Peripheral & integral or transmembrane proteins

   Peripheral proteins are attached to the outer and inner surfaces of membrane

   Integral proteins extends through the membrane from outside to inside

  Carbohydrates:

   Oligosaccharide molecules are attached to the surface of membrane.

   The molecules which are attached to membrane proteins are glycoproteins

   The molecules which are attached to phospholipid molecules are glycolipids

   These molecules form “Glycocalyx” surrounding the cell

  Significance of each component:

   Phospholipids - Maintains the membrane in fluid state & provides flexibility to the

                               membrane

  Cholesterol – Provides rigidity (stiffness) to the membrane

  Proteins – Critical components of membrane as it performs many functions

  Glycocalyx – Helps in cell to cell recognition

Functions of cell membrane:

1.      Forms a protective barrier surrounding the cells

2.      Semipermeability of the membrane differentiates the concentration of ECF from ICF

3.      which is responsible for development of biopotentials

4.      Links adjacent cells together by intercellular connections

5.      Provides anchoring sites for filaments of cytoskeleton

6.      Allow cell to cell recognition – Glycocalyx

7.      Provides a binding site for enzymes/hormones