cell membrane

1. CELL MEMBRANE
1 By
Harshraj S Shinde
K. K. Wagh College of Agricultural Biotechnology, Nashik

2. OUTLINES
 What is cell membrane?
 Chemical composition
 Structure of cell membrane
 Function of cell membrane
 Models of cell membrane
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3. WHAT IS CELL MEMBRANE?
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4. WHAT IS CELL MEMBRANE ?
 The cell membrane (also called the plasma membraneplasma membrane or plasmalemmaplasmalemma) 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. CramerC. Nageli and C. Cramer in 1855, and Plasmalemma coined
by J. Q. PloweJ. Q. Plowe in 1931
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5. CELL MEMBRANE
 The cell membrane is flexible
and allows a unicellular
organism to move
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6. CHEMICAL COMPOSITIONCHEMICAL COMPOSITION
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7. CHEMICAL COMPOSITIONCHEMICAL COMPOSITION
1. Lipids1. 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 ectoproteinsectoproteins
and endoproteinsendoproteins. Plasma membranes contains structural proteins,
transport proteins and enzymes. Some of them acts as receptors.
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8. CONT…
(enzymes present in the plasma membrane are Acetyl
phosphatase, acid phosphataseacid 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
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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
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10. PHOSPHOLIPIDS….
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11. MEMBRANE CHOLESTEROL
 The amount of cholesterol
may vary with the type of
membrane
 Plasma membranes have
nearly one cholesterol per
phospholipid molecule
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12. PROTEINS ARE CRITICAL TO
MEMBRANE FUNCTION
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13. 13
Structure of cell membrane

14. STRUCTURE OF THE CELL
MEMBRANE
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15. MEMBRANE COMPONENTS
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16. FUNCTION OF CELL MEMBRANE
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17. FUNCTIONS OF PLASMA
MEMBRANE
Keeps a 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
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18. FUNCTIONS OF PLASMA MEMBRANE…
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)
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19. MEMBRANE STRUCTURE
 Membranes consist 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
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20. Models of plasma membrane
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21. DANIELLI AND DAVSON MODEL
 In 1935, Danielli and DavsonDanielli 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 modelCalled as Sandwich model
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22. DANIELLI AND DAVSON
MODEL
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23. ROBERTSON'S MODEL
 In 1965, RobertsonRobertson 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
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24. ROBERTSON'S MODEL
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25. FLUID MOSAIC MODEL
 According to S. J. Singer and Garth Nicolson 1972S. 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 modelWidely accepted model
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26. FLUID MOSAIC MODEL…..
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27. VIDEO
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28. Reference book
Cell Biology,
Genetics,
Molecular Biology,
Evolution and Ecology
S.CHAND
P.S. VERMA
V.K.AGARWAL

29. THANK YOU.THANK YOU.
Questions
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