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Plasma Membrane

Plasma Membrane. Surrounded the cells Basic structure: Phospholipids Protein Carbohydrate Cholesterol. Membrane Function: - To control the intracellular milieu -The enzymes catalyze reactions -As cytoskeleton fibers  cell shape -A passageway for molecules - Protein as a receptor

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Plasma Membrane

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  1. Plasma Membrane • Surrounded the cells • Basic structure: • Phospholipids • Protein • Carbohydrate • Cholesterol

  2. Membrane Function: -To control the intracellular milieu -The enzymes catalyze reactions -As cytoskeleton fibers  cell shape -A passageway for molecules - Protein as a receptor -Enclose the cell  separate the cells -Cell binds to each other  tissue

  3. General architectureAll membranes contain lipid and protein, with vary ratio every cell and organellesExp.Mitochondrial membrane is 76 % proteinThe myelin membrane is 18 % proteinLipid as phospholipids, predominantly phosphoglycerides, which have a glycerol backbone.

  4. - Phospholipids are amphipathic or amphiphilic, • head hydrophilic • tails  hydrophobic • - Hydrophilic pole  water – loving  polar • Hydrophobic pole  water – hating  non polar

  5. Phospholipids predominate in the plasma membrane of many mammalian cell The tail groups: Fattyacyl chains have usually 16, 18 or 20 number of carbon atoms  Saturated  straight chain Unsaturated fattyacyl chain normally have one double bond, but some have 2, 3, or 4  Unsaturated  a rigid kink Differences in length and saturation  affect the fluidity

  6. Head • Phosphatidyl-choline, • Phosphatidylethanolamin, Sphingomyelin • Polar (no net electric charge ) • Negative charge  Phosphatidyl-serine • Inositol phospholipid  smaller quantities •  cell signaling

  7. Shape and Amphipathic nature of the lipid molecule : • Bilayer or micelles  spontaneously in aqueous solution  lipid molecule surrounded on all sides by water  shape of lipid molecule

  8. Fluidity The fluidity depends on: Composition of the lipid Temperature - Cis-double bonds  kinks in hydrocarbon chain  difficult to pack together  fluid in lower temperature

  9. - At normal temperature  fluid • Lower temperature: • unsaturated  fluid state, • saturated  gel like state. • - Heat: gel like  fluid like • - Van der Waals interaction  fluidity. • - The lipid molecules can migrate: • lateral diffusion, flexion, rotation • and very rarely flip-flop

  10. Cholesterol and glycolipidMembrane contain large amount of cholesterol  up to one molecule for every phospholipids molecule Cholesterol molecule enhance the permeability barrier properties in molecule lipid bilayer

  11. Membrane Protein- Protein usually: 50%-On the surface  peripheral -Within membrane  integral

  12. Glycoproteins and Glycolipid -Carbohydrates found in many membranes: covalently bound either to protein  glyco protein; or to lipid  glycolipid. -Abundant in the plasma membrane of eukaryo tic cells,but are abscent ininner mitochondrial membrane,chloroplast lamellae, etc .-Increase the hydrophilic character of lipids and proteins. -Stabilize the membrane protein.

  13. Carbohydrate components are oligosacharides: Galactose, mannose, fructose N.acethylneuraminic(sialic acid), N.acethylgalactosamine, N.acethyl glucosamine,

  14. Glycolipids :located in the cell surface membrane. -Blood group antigens  immune reaction  glycoproteins or glycolipids  blood group A, B, AB and O. -Antigenic determinant  genetically deter- mined -All people have enzymes that synthesizes the O antigen. -The O antigen is a chain of fructose, galactose, glucose and N.acethylglucosamine.

  15. The A antigen is similar to O, except that the A antigen contains an N-acetylgalactosamine attached to the outer galactose residue; • the B antigen is also similar to O, except for an extra galactose residue attached to the outer galactose. • All people have the enzymes that synthesize the O antigen. People with type A blood also have the enzyme that adds the extra N-acetylgalactosamine; those with type B blood have the enzyme that adds the extra galactose. • People with type AB blood synthesize A and B antigens; those with type O make only the O antigen.

  16. Erythrocyt have an usual plasma membrane that is tightly anchored to the cytosceleton.

  17. Membrane Organization -Integral protein bind asymetrically to the li- pidbilayer. -Integral protein  single, specific orientation  to cytosolic and exoplasmic faces. -The two membrane leaflet have different lipid composition. -Glycolipid are always found in exoplasmic leaflet. -Integral proteins and lipids are mobile -Some protein interact with cytoskeletal compound.

  18. -In specialized plasma membrane intestinal epithelial cells  apical and basolateral region  different function. -Microvilli  extensions of the cell surface. -Glycocalyx  a loose network , in the outer membrane surface oligosaccharide  glycoproteins or glycolipids.

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