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Biol130 - Unit6 Membranes Lecture Notes.pdf

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BIOL 130
Todd Holyoak

Unit 6Biological MembranesFluidityhow easily lipid molecules move within a membrane leafletIn all cells as the plasma membraneTightly packed tails more viscous membrane less fluidEncloses contents of the entire cellLoosely packed less viscous membrane more fluidIn eukaryotic cells used inAffected by length of fatty acids degree of saturationof double bondsMembrane bound organelles nuclear envelopeDouble membrane of mitochondria and chloroplastsTransition temperaturetemp at which membrane gels solidifiesAt and above room temp fluidFunctionsBelow room temp hydrophobic tails pack together and membrane gelsPermeable barrierTransport solutes moleculesMust be at fluid state for normal cell function Cant pass through but respond to signal to perform fcnStrategies for thisConversion of one energy form to anotherChange composition of membranesCompartmentalizationAlter phospholipids byArea for biochemical enzymatic activitiesDesaturate fatty acidsChange length of fatty acid chains Adjust amount of cholesterolMembrane phospholipids amphipathic with polar head group and hydrophobic tailCholesterolUnder warm temperature the more cholesterol the more viscous the membrane less fluidCan make up to 50 of plasma membrane lipid in some animal cellsRed Blood CellsModel to study plasma membraneAsymmetry of membrane lipidsBest understood plasma membranethe percent of total membrane lipids is not evenly facing inner cell cytosol and outer cell Inexpensive and lot availableextracellular spaceSimple no nucleus ER mitochondria or lysosomesOnly cholesterol is evenly distributed Preserved during membrane transportSugars facing inner vesicle forms vesicle fuses with plasma membrane and unfolds facing outerMembrane proteinsGive the membrane its functionTransporters Ex Na pump pump Na out of cells and K inAnchors Ex Integrins link intracellular actin filaments to extracellular matrix proteinsReceptors generate signals to perform cell function but does directly contact cellEnzymesProteins can associate with membranes in diff waysTransmembrane extend across bilayer as alpha helixs or beta sheets barrel can form poresMonolayer associated anchored to lipid by amphipathic alpha helixLipid linked attached to either side of bilayer by covalent attachment to lipid moleculeProtein attached proteins attached to the bilayer by weak noncovalent intera
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