Structure of model membrane

model membrane

1. STRUCTURE OF MODEL MEMBRANE Presented by- Sapana Prajapati Class-M.sc sem-1 CBO-403 Department of life sciences, H.N.G.U.,Patan

2. CONTENTS What is plasma membrane? Fluid mosaic model Sandwich model Unit membrane model Chemical composition

3. WHAT IS PLASMA MEMBRANE? The outer most limit of a cell is composed of living or non-living materials or both it is called as Plasma membrane. Plasma membrane also called cytoplasmic membrane,cell membrane or plasmalemma . This outer boundary of the cell is also called the plasma membrane .It is composed of four different types of molecules

4. Cont.. Phospholipids Cholesterol Proteins Carbohydrates Many scientists gave various theories and models to explain its structure. The names of some important models are given below : Fluid mosaic model- Singer and Nicolson.(1972) Sandwich model - Danielli and Davson .(1930) Unit membrane model – Robertson.(1959)

5. FLUID MOSAIC MODEL This model is proposed by Singer and Nicolson (1972).it also shows two layers of lipids and proteins each. But according to it the protein layers have two types of molecules.some molecules enter deeply layers and are called intrinsic proteins. They cannot be easily separated.

6. Cont.. second type of protein molecules which do not enter deeply into the lipid layers but remain attached to their surface only,are called extrinsic proteins. They are easily separable. Its viscosity or fluidity like oil.

7. Cont..

8. SANDWICH MODEL The Davson-Danielli model was a model of the Plasma membrane of a cell,proposed in 1935 by Hugh Davson and James Danielli . The model describes a Phospholipid bilayer that lies between two layers of globular proteins. Davson-Danielli model was the first attempt to describe membrane structure in terms of molecules and to relate the structure to biological and chemical properties.

9. Cont… According to bimolecular model of Danielli and Davson,plasma membrane .The polar (hydrophilic) heads of phospholipids are oriented towards the protein layers forming a hydrophilic zone. The nonpolar (hydrophobic)tails of phospholipids are oriented in between polar heads forming a hydrophobic zone. They theorised a phospholipid bilayer surrounded by two layers of proteins,on the inner and outer surfaces.

10. Cont… This may be thought of as a ‘Protein Sandwich model’.

11. UNIT MEMBRANE MODEL The unit membrane model proposed by Robertson (1959) is most accepted and widely used one. According to this model,plasma membrane is a trilamellar struture having a thickness of about 75 A°. The outer layers on both the sides are made up of protein.They are osmophilic in nature and each one measures a thickness of about 20A°.

12. Cont… A layer of lipid is present between two layers of protein.This lipid layer is hydrophobic in nature and measures a thickness of about 35A°. Actually the lipid layer is composed of two phospholipid layers which are so closely arranged that they appear to be a singal layer when viewed from the top.

13. Cont…

14. CHEMICAL COMPOSITION Chemically the plasma membrane consists of lipids and proteins but a small amount of carbohydrates has also been reported from certain cell membranes. LIPID : The lipids constitute 20 to 40 percent of the total dry weight in plasma membrane. The main lipid constituents are phospholipid and cholesterol.Other important lipids are glycolipids,glycophosphatides .

15. Cont… The glycolipids of plasma membrane are compounds containing sugar and lipid and fatty acid like palmitic,stearic,oleic acid etc. Protein : The proteins which constitute the plasma membrane are 60 to 80 percent of the total dry weight. Membrane proteins can function as enzymes to speed up chemical reactions,act as receptors for specific molecules or transport materials across the cell membrane.

16. Cont… The proteins are made up of number of amino acids united by peptide linkages. Glycoprotein on the outside may be responsible for adherence of cells. This protein have two most important functions: The help in movement of molecules of substances across the membrane. They help in different enzymatic activities of the membrane.

17. Cont… Carbohydrates : The presence of carbohydrates in plasma membrane was suggested by Bell (1962). The most common carbohydrates are hexose,hexosamine,fucose,and sialic acid.

18. REFERENCES Cell biology, Genetics, Molecular Biology, Evolution and Ecology by : P. S. Verma, V. K. Agarwal . https://en.m.wikipedia.org Home.earthlink.net/~

19. Thank You