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University of Toronto St. George
Kenneth Yip

617624 Membrane structurePlasma membrane o Enclose cell define boundaries o Maintain essential differences between cytosolextracellular environment o Eukaryotic cellMembranes of membraneenclosed organelles eg ER golgi apparatus mitochondriamaintain characteristic differences between contents of each organellescytosol o Ion gradients across membranes established by activities of specialized membrane proteinsused to synthesize ATPdrive transmembrane movements of selected solutes o Nerve muscle cellProduce transmit e signalsReceptorsProteinssensors of external signalsallow cell to change behavior in response to environmental cues eg Signals from other cellsTransfer info across membrane o ALL MEMBRANES IN COMMONVery thin film of lipidprotein moleculesNoncovalent interactsDynamics fluidMove about in plane of membraneLipid arranged as continuous double layer about 5nm thick membrane proteins embeddedo 2D liquidconstituent molecules free to move laterally o 50 mass of membrane o Lipid bilayerBasic fluid structure of membraneRelatively impermeable barrier to passage of watersoluble molecules o All molecules are amphiphilicHydrophilicHydrophobico Most abundant membrane lipids PhospholipidsAmphiphilicbilayer 1 Polar head group2 hydrophobic hydrocarbon tails 14 24 COne tail with 1 cisdouble bondsunsaturated onesaturatedEach cisbond creates small kink in tail Composition Lengthsaturation of fatty acid tailshow phospholipid pack against one another tempfluidity of membrane vise versa2 types of preparation o Liposomes bilayers made in form of spherical vesicles o Black membrane planar bilayers formed across hole in partition between 2 aq environmentMeasure motion of liquid molecules o Construct lipid molecule Fluorescent dye small gold particle attached to polar head groupfollow diffusion o Modify lipid head group to carry spin labelNitroxyl group contains unpaired e spin creates paramagnetic signal detected by e spin resonance spectroscopyPhospholipid molecules in synthetic bilayer rarely migrate from monolayer leaflet on one side to other flipflop occurs 1 month except cholesterolReadily exchanges places within monolayerrise to rapid lateral diffusionaverage lipid molecule diffuses length of large bacterial cell in 1s Individual lipid molecules rotate rapidly about long axis Flexible hydrocarbon chains
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