Lect 02 F10 - THE LIPID BILAYER Universal basis for...

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THE LIPID BILAYER Universal basis for membrane structure Two main constituents are lipids and associated proteins
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2) Diffusion barrier: Polar molecules cannot move freely across membrane The self-assembly properties of lipids lead spontaneously to the formation of sealed compartments. Two consequences: ENERGETICALLY FAVORED ENERGETICALLY UNFAVORED 1) Will quickly re-seal if damaged. Vesicles can FUSE
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Three major types of membrane lipid molecules Each type is amphipathic
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The parts of a phospholipid molecule: Phosphatidylcholine. two sites of glycerol link to fatty acid residues the third site links to a phosphate group. -phosphate links to another organic substance
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Four major PHOSPHOLIPIDS in mammalian plasma membranes. derived from glycerol derived from sphingosine Head groups vary: size, charge, shape
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The composition of the lipid bilayer varies dramatically and affects its physical and functional properties Membrane fluidity- extent to which lipid molecules can move in the plane of the membrane Phase transition- as temperature decreases bilayer changes state from liquid to solid. The more “fluid” the membrane, the lower the phase transition temperature.
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The length and saturation of fatty acid tails affects fluidity Tails typically contain between 14-24 carbon atoms Saturated-no cis double bonds Unsaturated-one of more double bonds introduces kink in tail. Kinky fatty acid tails do not pack as tightly and so increase membrane fluidity at a given temperature.
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makes lipid bilayer more fluid at low temperatures enhances permeability barrier properties of lipid bilayer by sealing non-polar part of the bilayers Cholesterol is an essential component of membranes Cholesterol orients in bilayer such that rigid steroid rings interact with regions of hydrocarbon chains closest to polar head groups.
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Lipid rafts-an important concept in membrane research. Current data suggests not all lipids are uniformly distributed in membrane.
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This note was uploaded on 11/10/2010 for the course CBNS 101 taught by Professor - during the Spring '08 term at UC Riverside.

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Lect 02 F10 - THE LIPID BILAYER Universal basis for...

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