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Chapter 12 Lipids.docx

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University of Toronto St. George

Chapter 12 Lipids Lipids are essential components of all living organisms Much greater variation than proteins and carbohydratesWater insoluble highly soluble in nonpolar solvents Can be strictly hydrophobic small number not usually biological or more often amphipathic with both polar and nonpolar regions Classes of lipidsalmost all biological lipids are amphipathicFatty acids have a general formula of RCOOH where R is a hydrocarbon chainMore complex lipids can have fatty acids as componentso Triayclglycerols fats and oils can function as storage molecules for metabolic energy and provide thermal insulation and padding o Waxes in cell walls exoskeleton and skin serve a protective roleo Sphingolipidso GlycerophospholipidsPhospholipids Glycosphingolipidshave sphingosine and carbohydrate Isoprenebased 5C lipids include steroids lipid vitamins and terpenes called isoprenoidso Steroid hormonesregulation Fatty acidsmore than 100 different fatty acids Differ based on length of hydrocarbons Most have a pKa of4550therefore ionized at physiological pH Form of detergent long hydrophobic tails Concentration of free fatty acid is low in cellsbecause if high could disrupt membranes Joined to other molecules by an ester linkage ie glycerolRCO moiety contributed by the acid is the acyl group eg esters of linoleate are called linoleoyl estersMost common are C12 to C20 with even number since fatty acids are synthesized by sequential addition of 2 carbon unitsC1 is the carboxyl carbon and then numbered sequentially Relative abundance of particular fatty acids varies with the organism or type of organ food source Saturated fatty acids 12Clauric acid found in oil from plant 14Cmyristic acid oil from nutmeg 16Cpamitic acid from palm oil 18Cstearic acid from tallow 20Carachidic acid from peanutsUnsaturated fatty acids 161palmitoleic acid 181oleic acid 182linoleic acid 183 linolenic acid 204arachidonic acid x Position of double bond indicated withPosition of double bond is almost always cis causing a bend or kink in the fatty acid chainSaturated chainspack tightly and form more rigid organized aggregates eg membranes therefore solids at RT Unsaturated chainsbend and pack in a less ordered way with greater potential for motion ie produce flexible fluid aggregates therefore liquid at RTLength of the tail and degree of unsaturation affects the melting point
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