plasma membrane -surrounded the cells -basic structure: -phospholipids -protein -carbohydrate...
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Plasma Membrane
- Surrounded the cells
- Basic structure: - Phospholipids - Protein- Carbohydrate- Cholesterol
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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 organellesExp.Mitochondrial membrane is 76 % proteinThe myelin membrane is 18 % protein
Lipid as phospholipids, predominantly phosphoglycerides, which have a glycerol backbone.
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- Phospholipids are amphipathic or amphiphilic,
head hydrophilic tails hydrophobic
- Hydrophilic pole water – loving polar
Hydrophobic pole water – hating non polar
• 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
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• Head Phosphatidyl-choline, Phosphatidylethanolamin, SphingomyelinPolar (no net electric charge )
Negative charge Phosphatidyl-serineInositol phospholipid smaller quantities cell signaling
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- 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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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
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- 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
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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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Carbohydrate components are oligosacharides:
Galactose, mannose, fructose
N.acethylneuraminic(sialic acid),N.acethylgalactosamine, N.acethyl glucosamine,
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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.
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•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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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.
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-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.