Presentation on cdell membrane (4).pptx

cell membrane and its components are discussed.

1. Cell membrane By Akansha Singh M.Sc. previous Bareilly collage Bareilly..

2. Outlines What is cell membrane Chemical compositions Structure of cell membrane Models of cell membrane Functions of cell membrane

3. What is cell membrane ? The cell membrane ( also called the plasma membrane or plasmalemma )is a biological membrane separating the interior cell from the outside environment. It appears in thin sections with the electron microscope as a triple layered structure about 7.5 nanometers thick The term cell membrane was coined by C.Nageli and Cramer in 1855. In1895 , Charles Overton suggested that plasma membrane is composed of lipids. In 1925 , E. Gorter and G.Grendel proposed that plasma membrane is composed of Phospholipid bilayer.

4. Chemical composition Lipids- four major classes of lipids are commonly present in the plasma membrane: Phospholipid ( most abundant) , spingolipids , glycolipid and sterols (eg.Cholesterol).All of them are amphipathic . Cholesterol is abundant in mammalian cell and is absent in prokaryotic cells. Proteins- plasma membrane contains about 50% protein. Amount and type is variable. Carbohydrates- they are present only in the plasma membrane and are present exterior ( glycoproteins) or polar end of Phospholipid at the external surface of plasma membrane.

5. Phospholipids Phospholipid molecule has a polar head and non polar tails. The polar head is charged and Hydrophilic (water Loving) facing outward ,contains a PO4 group and glycerol. The non polar tails are Hydrophobic ( hates water) facing inward contains 2 fatty acid chains that are non polar.

6. Membrane Cholesterol The amount of Cholesterol may vary with the type of membrane. Plasma membranes have nearly one Cholesterol per Phospholipid molecule.

7. Membrane components

8. Membrane protein Transmembrane protein : These extend through the lipid bilayer projecting out on either side of membrane Peripheral protein : These are present on both outer and inner surfaces of lipid bilayer and are loosely connected to it either by covalent or non covalent interactions.

9. Models of cell membrane 1.Sandwich model 1. In 1935 , Danielli and Davson Studied triglycerides lipid bilayer over a water surface. 2. They found that they arranged themselves with the polar heads facing outward. 3. It always formed droplets ( oil in water) and the surface tension was much higher than of cell . Drawback: It can’t explain the actual process of transportation.

10. Unit membrane model Robertson (1959) described trilaminar structure of PM consisting of two parallel outer dense layer which corresponds to the two protein layer and a middle light colour layer of 30-35A thickness corresponding to the hydrocarbon chains of the lipids. He demonstrate that the bio membranes present inside the cells and around various cell organelles exhibits trilaminar structure.

11. Unit membrane model

12. Fluid mosaic model Given by Singer and Nicolson in 1972. According to this model ,biological membranes are quasi fluid structure . Plasma membrane is Formed of “ protein iceberg’s in a sea of lipids. Lipid molecules show 2 types of movement- 1. Transition movements – Molecules of one lipid layer can change position in the same layer. 2. Flip flop Movement- Here molecules of 2 lipid bilayer interchange their position..

13. Proteins are globular and are of two types . 1. Extrinsic / Peripheral protein- These are 30% of total proteins . They act as permeases. They are loosely attached so can be easily separated ex- ATPase, Acetylcholine asterase. 2. Integral / Intrinsic protein- These are 70% of total plasma protein. These are partially or fully embedded in lipid bilayer so can’t be separated. .

14. Functions of cell membrane Regulation of the passage of material. Maintenance of differential distribution of ions. Response to environment. Contact with neighboring cells. Cell recognition. Communication between neighboring cells. Cellular Adhesion . Protection. Excretion.

15. Thank you….