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Membrane Structures.docx

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Jane Mitchell

Readings pg 617624Membrane StructurePlasma membrane encloses cell defines boundaries maintains differences bw cytosol and extracellular environment o Contains protein sensors receptors allows cell to change behaviour according to environment transfer info also accepts signals from surrounding cellsInside eukaryotic cells membranes of endoplasmic reticulum Golgi apparatus mitochondria and other membrane enclosed organelles maintain the characteristic differences bw contents of each organelle and cytosolIon gradients drive transmembrane movement of solutes or transmit electrical signals in nerve and muscle cellsAll membranes have thin lipid layer and protein molecules which are held together by noncovalent interactionsThe lipid bilayer 5nm thick Provides basic structure for all cell membranesAll lipids are amphiphilicMajor lipids in cell membrane o Phospholipids have polar head 2 hydrophobic HC tails fatty acidsOne tail has one or more cisdouble bonds unsaturated other has single bond saturated Cis double bonds create a kink in tail o phsophoglycerides have 3 carbon glycerol backbone2 long chain fatty acids are linked together through ester bonds to adjacent carbon atoms of glycerol and third C atom attached to phosphate groupBy combining diff fatty acids and head grpsphosphoglyceridesphosphatidylethanolamine phosphatidylserine phosphatidylcholine o Sphingomyelin built from sphingosine long acyl chain with an amino grp NH and 2 hydroxyl grps OH at one end of moleculeA fatty acid tail is attached to NH and phosphocholine attached to terminal hydroxyl grp leaving one hydroxyl grp free which contributes to polar properties of adjacent head grp as it can form hydrogen bonds with head grp of neighbouring lipid with a water molecule or with a membrane proteinSpphingomyelin sphingosine o Cholesterol polar head grp rigid steroid ring structure nonplar HC tail and glycolipids also in lipid bilayerFormation of hydrophobic or hydrophilic grps increases free energy o Lipid molecules have hydrophobic in interior and hydrophilic exterior can do this in 2 waysCan form spherical micelles cone shaped
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