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Structure of model membrane

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gohil sanjay bhagvanji

The document discusses several models that describe the structure of the plasma membrane: 1) The fluid mosaic model proposed in 1972 depicts a bilayer of phospholipids with intrinsic and extrinsic proteins embedded within, giving the membrane a fluid-like quality. 2) The sandwich model from 1930 depicts phospholipids sandwiched between two layers of globular proteins. 3) The unit membrane model from 1959, which is most widely accepted, depicts a trilamellar structure with an inner and outer protein layer surrounding a thin hydrophobic phospholipid bilayer. The plasma membrane is composed primarily of phospholipids, cholesterol, proteins, and some carbohydrates. Its role is to envelop and protect the cell while

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STRUCTURE OF MODEL MEMBRANE Presented by-Sapana Prajapati Class-M.sc sem-1 CBO-403 Department of life sciences, H.N.G.U.,Patan
CONTENTS • What is plasma membrane? • Fluid mosaic model • Sandwich model • Unit membrane model • Chemical composition
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
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 : i. Fluid mosaic model- Singer and Nicolson.(1972) ii. Sandwich model -Danielli and Davson.(1930) iii. Unit membrane model – Robertson.(1959)
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.
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.
Cont..
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.
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.
Cont… • This may be thought of as a ‘Protein Sandwich model’.
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°.
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.
Cont…
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.
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.
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: 1) The help in movement of molecules of substances across the membrane. 2) They help in different enzymatic activities of the membrane.
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.
REFERENCES • Cell biology, Genetics, Molecular Biology, Evolution and Ecology by : P. S. Verma, V. K. Agarwal. • https://en.m.wikipedia.org • Home.earthlink.net/~
Structure of model membrane

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Structure of 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 : i. Fluid mosaic model- Singer and Nicolson.(1972) ii. Sandwich model -Danielli and Davson.(1930) iii. 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.
  • 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.
  • 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: 1) The help in movement of molecules of substances across the membrane. 2) 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/~