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

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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

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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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•Membrane Protein

- Protein usually: 50%

-On the surface peripheral

-Within membrane integral

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

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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.