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Lecture 9

BCH210 2014 Lecture 9.pdf

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University of Toronto St. George
Stavroula Andreopoulos

Lecture 10 Lipids and MembranesConsists of two items o 1 Lipid bilayerForms barrier from exterior outside of cell and cytosol inside of cell o 2 Membrane proteinsCan span lipid bilayer with hole through middleChannel allowing things to go in and out of membraneIntegral membrane proteinHave interaction with lipid bilayerPhospholipid Bilayerdifferent membranes lipid composition varies Protein to Lipid ratio varies o Myelinvery lipid rich75 lipids 25 protein o Plasmid Membrane like red blood cellsEqual amounts of lipids and proteinso Specialized membranemitochondria75 protein 25 lipidsProteins within membranes with particular functions varies o Eg Protein in membrane plasmid of liver cell may be different compared to proteins in a heart cell How is the lipid bilayer formedspontaneous assembly due to the chemical characteristics of the lipidsdriven by the hydrophobic effectother forces are also involved o van der waals attractive forces between nonpolar hydrophobic tails o polar head groups have electrostatic and hydrogen bonding capabilitiesLipid selfassembly Lipids spontaneously aggregate in water to bury their hydrophobic tails and expose their polar heads to water o Hydrophobic effect o Van der Waals packing The final structure in water depends on the shape of the individual lipid molecules Coneshaped lipids assemble in micelles At low concentrations fatty acids are either monomers OR form monolayersAbout a critical concentrationmicelles formPhospholipid assembly in water Cylindershaped lipids spontaneously form lipid bilayers in water Phospholipid assembly in waterPhospholipids form diverse bilayer structures in water Unilamellar vesicles tails are open and close to promote packing Multilamellar vesicles are not ideal to work with because of layers of water inside Zap with ultrasonic frequency to break them up Lipid Structuresliposome small aqueous compartment surrounded by a lipid bilayerionsmolecules can be trapped in the aqueous compartments of lipid vesiclesvesicles formed in a glycine solution will trap glycine molecules in each inner aqueous compartmentliposomes containing glycine are formed by sonication of phospholipids in the presence of glycine Components of PhospholipidsDifferent types o Glycerolphospholipids3 carbon unitHas a glycerol backboneTwo fatty acids attached joined by diester bondso In phospholipidsHave phosphate group where alcohol is joined by phosphoester bondComposed of glycerol backbone two fatty acyl chains phosphate and alcoholPhosphate vely charged and alcohol togetherForms head group of phospholipidFatty Acidshydrocarbon fatty acids are composed of a long hydrocarbon chain tail and a terminal carboxyl group headAcidcarboxyl parto Can lose a H o Negative charge anionicChainmethylene group with terminal methyl group o 12 carbonsC1carboxyl group carbonlast carbonDistance of carbons discussed fromcarbonMost fatty acids found in nature have an even number of carbon atoms o Odd numbers are rarespecialized in organsPrimitive bacteria algae
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