Exam Review - Chapter 19

The topology of an integral membrane protein can

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Unformatted text preview: ectional areas of the head group and acyl side chain are similar o Hydrophobic portion is excluded from water and interact with each other o Hydrophilic head groups interact with water at each surface of the bilayer o Structure is relatively unstable because in contact with water, so folds into itself to form the vesicle Vesicle: hollow sphere formed from the bilayer sheet folding onto itself o forms a separate aqueous compartment o bilayer is 3 nm thick o hydrocarbon core is made from –CH2 and –CH3 gropus of the fatty acyl groups very nonpolar and impermeable to polar solutes o membrane components are asymmetric and variable – lipid composition and disposition across the bilayer changes membrane composition is necessary for dictating function Integral membrane proteins: proteins firmly associated in the lipid bilayer and are removable by agents that interfere with hydrophobic interactions Peripheral membrane proteins: associated with the membrane through electrostatic interactions and hydrogen bonding with the hydrophilic domains of integral proteins and with the polar head groups of membrane lipids Amphitropic proteins: proteins found in the cytosol and in association with membranes o Results from a protein’s noncovalent interaction with a membrane protein or lipid o Sometimes lipids are covalently attached to the amphitropic protein Reversible association exists through phosphorylation Membrane protein topology can be determined with reagents (localization of protein domains relative to the bilayer) Membrane proteins span the lipid bilayer Glycophorin: the erythrocyte glycoprotein Amino- terminal domain is on the outer surface and is cleaved by trypsin Carboxyl- terminus protrudes inside the cell, and cannot act with impermeant reagents Glycophorin is asymmetric functional asymmetry All the molecules of a given ion pump, have same orientation and pump ions in same direction Its amino- terminal is always on the outside Integral proteins have firm attachment to membranes as a result of hydrophobic interactions between membrane lipids and hydrophobic regions of protein Bacteriorhodopsin: a light- driven proton pump o Has seven hydrophobic domains that cross the lipid bilayer seven times o Composed of alpha helices Annular lipids:...
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