Chapter 5 Study Guide

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University of Toronto Scarborough
Biological Sciences
Mark Fitzpatrick

Chapter 5: The Dynamic Cell Membrane 5.1 What is the Structure of a Biological Membrane? N Fluid Mosaic Model - a lipid pool, in which proteins and carbohydrates float N The lipids establish the physical integrity of the membrane and create an effective barrier to the rapid passage of hydrophilic materials N The proteins have functions, namely: moving materialsthrough the membrane and receiving chemical signals from the cells external environment N Carbohydrates are crucial for cell recognition of molecules Lipids N Main: phospholipid - has both hydrophilic and hydrophobic regions N Cholesterol isimportant for membrane integrity as it determines fluidity of the fatty acids in the membrane N The fatty acids of the phospholipids make the hydrophobic interior of the membrane somewhat fluid N Lateral movement is always happening; but rarely is there any flipping of phosphoplipids N The inner and outer halves of the bilayer may be quite different in the kinds of phospholipids they contain N Shorter-chain fatty acids, unsaturated fatty acids, and less cholesterol = more fluidity N Fluidity decreases at reduced temperatures; membrane functions may decline in organisms that cannot keep their bodies warm Proteins N Asymmetrically distributed N Proteins have both hydrophilic (have hydrophilic side chains - arginine, histidine, lysine, aspartic acid, glutamic acid, serine, threonine, asparagine, glutamine, tyrosine) and both hydrophobic (alanine, isoleucine, leucine, methionine, phenylalanine, tryptophan, valine) regions N Freeze fracturing - reveals proteins embedded in the bilayer o Freeze o Tissue is fractured via diamondglass knife N Two types of proteins; bond non-covalently o Integral - span the length of the membrane with extrusions o Peripheral - not embedded in the bilayer; polar interacting with polar regions of the membrane N Some proteins are covalently attached to fatty acids - resulting in a special type of proteins N Transmembrane proteins - integral proteins that have hydrophillic extrusions on both sides
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