Chapter 7

Chapter 7 - Plasma membrane controls traffic into and out...

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Plasma membrane controls traffic into and out of the cell it surrounds Selective permeability, most abundant lipids in membranes: phospholipids Phospholipids are amphipathic (both hydrophilic and hydrophobic region) Fluid mosaic model: membrane is a fluid structure with a mosaic of various proteins embedded in or attached to a double layer of phospholipids “Fluid” o Freeze-fracure: splits a membrane along the middle of the phospholipid bilayer, when membrane layers are viewed, interior of the bilayer appears cobblestoned, with proteins interspersed in a smooth matrix o Membrane is held together by hydrophobic interactions (weaker than covalent) o Lateral movement of phospholipids is rapid, proteins is slower o Unsaturated hydrocarbon tails: fluid to lower temperature because they cannot pack together as closely o Cholesterol hinders close packing of phospholipids, lowering the temperature required for membrane to solidify “Mosaic” o Integral proteins: penetrate hydrophobic core of lipid bilayer Many are transmembrane proteins which span membrane and others extend only partway through hydrophobic core Stretches of nonpolar amino acids coil into alpha helices o Peripheral proteins: not embedded in the lipid bilayer, appendages loosely bound to the surface of the protein Some are held in place by attachment to cytoskeleton, and others are attached to fibers of extracellular matrix o Transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, attachment to cytoskeleton and extracellular matrix Glycolipids- carbohydrates bonded to lipids Glycoproteins- carbohydrates bonded to proteins Synthesis of membranes
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o Synthesis of membrane proteins and lipids in endoplasmic reticulum,
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Chapter 7 - Plasma membrane controls traffic into and out...

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