Plasma Membrane -Surrounded the cells -Basic structure: -Phospholipids -Protein -Carbohydrate -Cholesterol

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3 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

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General architecture All membranes contain lipid and protein, with vary ratio every cell and organelles Exp. Mitochondrial membrane is 76 % protein The myelin membrane is 18 % protein Lipid as phospholipids, predominantly phosphoglycerides, which have a glycerol backbone. 5

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

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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 9

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

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14 - 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

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17 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

18 - 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

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Cholesterol and glycolipid Membrane contain large amount of cholesterol  up to one molecule for every phospholipids molecule Cholesterol molecule enhance the permeability barrier properties in molecule lipid bilayer 21

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Membrane Protein - Protein usually: 50% -On the surface  peripheral -Within membrane  integral 23

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26 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 in inner mitochondrial membrane,chloroplast lamellae, etc.-Increase the hydrophilic character of lipids and proteins. -Stabilize the membrane protein.

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

29 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.

30 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.

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

37 Membrane Organization -Integral protein bind asymetrically to the li- pid bilayer. -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.

38 -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.