CHapter 5 (Fall2010)

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Department
Biological Sciences
Course
BIOA01H3
Professor
Mary Olaveson
Semester
Fall

Description
BIOA01FALL2010 CHAPTER 5 The Dynamic Cell Membrane 51 Structure of a Biological MembraneThe lipids in biological membranes are usually phospholipidsThe phospholipid has hydrophilic and hydrophobic regionsHydrophilic the phosphorus containing head which is charged and therefore associates with the polar water moleculesHydrophobic the long nonpolar tails made up of fatty acids which associate with nonpolar moleculesPhospholipids can differ in terms of fatty acid chain length degree of unsaturation and the polar phosphate containing group presentUp to 25 of the lipid content of a membrane may be cholesterol situated next to an unsaturated fatty acidThe bilayer stabilizes the entire membrane structure but leaves it flexibleThe fatty acids of the phospholipids make the hydrophobic interior somewhat fluidpermits some molecules to move laterallyShorterchain fatty acids unsaturated fatty acids and less cholesterol results in more fluid membranesBecause molecules move more slowly and fluidity decreases at reduced temperature membrane function may decline in organisms that cannot keep their bodies warmSome organisms simply change their membranes under cold conditions replacing saturated with unsaturated fatty acids and using fatty acids with shorter tails ex Hibernating animal bacteria plantsProteins in the phospholipid bilayer have both hydrophilllic and hydrophobic regionsHydrophilic stretches of amino acids with hydrophilic side chainsthese regions domains interact with water sticking out into the aquous extracellular environment or cytoplasmHydrophobic stretches of amino acids with hydrophobic side chains give other regions of the protein a non polar characterthese domains interact with the fatty acid chains in the interior of the phospholipid bylayer away from waterProteins and lipids are independent of one another in the bilayer and interact only noncavalentlyIntegral membrane proteins have hydrophobic domains and penetrate the phospholipid bilayerhave long hydrophobic alpha helical regions that span the core of the bilayer their hydrophilllic ends protrude into the aquous environment on either side of the membranePeripheral membrane proteins lack hydrophoibic domains and are not embedded in the bilayer polar or charged regions that interact with exposed parts of the integral proteins or with the polar heads of the phospholipidsTransmembrane proteins integral membrane proteins that protrude on both sides of the membrane known as transmembrane proteins show different faces on the 2 membrane surfaces such proteins have certain specific domains on the outside of the membrane and others within the membrane and still others on the inside of the membranePeripheral membrane proteins are localized on either side of the membrane but not both
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