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Similar to cellmembrane ppt for biology for higher grades
cellmembrane ppt for biology for higher grades
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- 2. OUTLINES What iscell membrane? Chemical composition Structure of cell membrane Function of cell membrane Models of cell membrane 2
- 3. WHAT IS CELLMEMBRANE? 3
- 4. WHAT IS CELLMEMBRANE ? The cell membrane (also called the plasma membrane plasma membrane or plasmalemma plasmalemma) is a biological membrane separating the interior of a cell from the outside environment It appears in thin sections with the electron microscope as a triple-layered structure about 7.5–10 nanometers thick Term coined by C. Nageli and C. Cramer C. Nageli and C. Cramer in 1855, and Plasmalemma coined by J. Q. Plowe J. Q. Plowe in 1931 4
- 5. CELL MEMBRANE Thecell membrane is flexible and allows a unicellular organism to move 5
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- 7. CHEMICAL COMPOSITION CHEMICAL COMPOSITION 1.Lipids 1. Lipids -four major classes of lipids are commonly present in the plasma membrane: phospholipids (most abundant), spingolipids, glycolipids and sterols (e.g. cholesterol). All of them are amphipathic. Cholesterol is abundant in mammalian cell and is absent in prokaryotic cells 2. Proteins- 2. Proteins-plasma membrane contains about 50% protein. Amount and type is variable. Myelin cells contains about 25% protein internal membranes of chloroplast and mitochondria contains 50% protein. Proteins of plasma membranes are of two types ectoproteins ectoproteins and endoproteins endoproteins. Plasma membranes contains structural proteins, transport proteins and enzymes. Some of them acts as receptors. 7
- 8. CONT… (enzymes present inthe plasma membrane are Acetyl phosphatase, acid phosphatase acid phosphatase, ATPase, RNAase, maltase, lactase, phospholipase etc) 3. 3. Carbohydrates- Carbohydrates- they are present only in the plasma membrane and are present exterior (glycoproteins) or polar end of phospholipids at the external surface of plasma membrane 8
- 9. PHOSPHOLIPIDS Phospholipids (PL)molecule has a polar head and nonpolar tails The polar head is charged and hydrophilic (loves water) facing outward, contains a – PO4 group & glycerol The nonpolar tails are hydrophobic (hates water) facing inward contains 2 fatty acid chains that are nonpolar When PL placed in water form spherical bilayer 9
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- 11. MEMBRANE CHOLESTEROL Theamount of cholesterol may vary with the type of membrane Plasma membranes have nearly one cholesterol per phospholipid molecule 11
- 12. PROTEINS ARE CRITICALTO MEMBRANE FUNCTION 12
- 13. 13 Structure of cellmembrane
- 14. STRUCTURE OF THECELL MEMBRANE 14
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- 16. FUNCTION OF CELLMEMBRANE 16
- 17. FUNCTIONS OF PLASMA MEMBRANE Keepsa cell intact Protective barrier Regulate transport in & out of cell (selectively permeable) Small lipid-soluble molecules, e.g. oxygen and carbon dioxide can pass easily Water can freely cross the membrane 17
- 18. FUNCTIONS OF PLASMAMEMBRANE… Ions and large molecules cannot cross without assistance Allow cell recognition Provide anchoring sites for filaments of cytoskeleton Provide a binding site for enzymes Interlocking surfaces bind cells together (junctions) Contains the cytoplasm (fluid in cell) 18
- 19. MEMBRANE STRUCTURE Membranesconsist of a phospholipid bilayer combined with a variety of proteins in a fluid mosaic arrangement The surfaces of cell membranes are hydrophilic (water-loving); the interiors are hydrophobic 19
- 20. Models of plasmamembrane 20
- 21. DANIELLI AND DAVSONMODEL In 1935, Danielli and Davson Danielli and Davson studied triglyceride lipid bilayers over a water surface They found that they arranged themselves with the polar heads facing outward It always formed droplets (oil in water) and the surface tension was much higher than that of cells Called as Sandwich model Called as Sandwich model 21
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- 23. ROBERTSON'S MODEL In1965, Robertson Robertson noted the structure of membranes seen in the electron micrographs He saw no spaces for pores in the electron micrographs He hypothesized that the railroad track appearance came from the binding of osmium tetroxide to proteins and polar groups of lipids Proposed unit membrane hypothesis 23
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- 25. FLUID MOSAIC MODEL According to S. J. Singer and Garth Nicolson 1972 S. J. Singer and Garth Nicolson 1972, the biological membranes can be considered as a two- dimensional liquid where all lipid and protein molecules diffuse more or less freely Singer studied phospholipid bilayers and found that they can form a flattened surface on water, with no requirement for a protein coat It occurs in form of globular protein Widely accepted model Widely accepted model 25
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