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BIOL*1090 Notes

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BIOL 1090
Marc Coppolino

BIOLOGYMembrane Fluidity RecallMembrane fluidity is determined by Saturatedstraightnature of lipids in the membrane Unsaturatedkinked o unsaturated lipids fluidity o saturated lipids fluiditytemperature o warming increases fluidityliquid crystal o cooling decreases fluiditygel Membrane fluidity is crucial to cell functionbalance between ordered rigid structure and disordered structure allows o mechanical support and flexibility Note o dynamic interactions between membrane componentsMembranesexample proteins can come together reversibly are spaceo membrane assembly and modification filling Membrane fluidity must be maintained quitein response to changes in temperature not in birds or mammals lipid packed composition can be changed by o desaturation of lipids enzymatic reaction produces double bonds to fluidity o exchange of lipid chains saturated to unsaturated to fluidityexample Listeria monocytogenes changes the lipid content of its plasma membrane while growing at 10C and can therefore survive at relatively cold temperaturescholestrol regulates membrane fluidity o alters packing and flexibility of lipids o has a litigating effect on membranesif added to a liquid crystal membrane fluidityif added to a crystalline gel membrane fluidity o influences metabolism of lipidsDynamic Properties of the Plasma Membranelipids move easily laterally within leafletslipid movement between leaflets is slow and difficult o hydrophilic head group would have to pass through hydrophobic tail regionmembrane proteins can diffuse within bilayer o movement of proteins is restricted some are fixed o rapid movement is spatially limited o longrange diffusion is slow o biochemical modification can dramatically alter a proteins mobility in the membrane part of chemical transductionLipid Rafts Membrane Microdomainslipid rafts small areas of the PM that are rich in certain types of lipids ex cholestrolrelatively rigid some membrane proteins accumulate in rafts usually specific regulatory proteins o may form functional compartment naturefunction of rafts is controversial lab results dont always correspond to clinical trials and some results do not even corroborate their existenceLipid Raft within a MembraneMovement Across Membranes Lipid bilayers do not allow many compounds to pass through them freely Four basic mechanisms of transport existA Simple Diffusion O CO HO 222 very small uncharged molecules and waterflow is down concentration gradienttoB Diffusion through a Channel K Na Clsmall charged molecules ions o makes them hydrophilic with a shell of water that is impossible to shedflow is down concentration gradientto ion channels formed by integral membrane proteins that line aqueous pore o selective to one type of ion usually and gated can be open or closed o example voltagegated K channel100 000 000 K ions per second speed of molecular activity 1kmhrPatch clamping measures voltage of channels and can determine how many channels are in one area
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