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Chapter 8 . LipidsChapter 8Lipids. . . . . . . . . . . . . . . . . . . . . . . .Chapter OutlineLipids: Compounds composed largely of reduced carbons and exhibiting low water solubility. Lipids may be completely hydrophobic or, if they contain polar groups, amphipathicFatty acids: Carboxyl head group and hydrocarbon tailTypically even number of carbons (14 to 24)Saturated fatty acids lack carbon-carbon double bondsUnsaturated fatty acids contain one or more double bonds in cis configurationMonosaturated: Single carbon-carbon double bondPolyunsaturated: cis Double bonds separated by methylene carbon (-CH2-)Nomenclature:Systematic: e.g., octadecanoic acid: 18-carbons longCommon names: Stearic acidShort hand notation: 18:0 -18 carbons long with no double bonds18:1(9) -18 carbons long with one double bond starting at carbon 9Essential fatty acids: Linoleic and -linolenic acid: Plant fatty acids required in diets of animals: used to synthesize arachidonic acid -precursor to eicosanoids (prostaglandins)Triacylglycerols (triacylglycerides): Fats and oilsGlycerol esterified with three fatty acidsSaponification: Alkali hydrolysis of triacylglycerols: Products: Glycerol and free fatty acids (Salt of free fatty acids -soap)Glycerophospholipids: A class of phospholipids1,2 Diacylglycerol with phosphate ester at carbon 3Stereospecific numbering system: Number glycerol carbons based on (R,S) system: C1 is carbon that would lead to S-configuration if its priority was increasedPhosphatidic acid: sn-Glycerol-3-phospate with fatty acids esterified to C1 and C2Phosphatidic acid precursor of glycerophospholipidsC1 fatty acid typically saturatedC2 fatty aid typically unsaturatedGlycerophospholipids: Polar group esterified to phosphate of phosphatidic acidEthanolamine: PhosphatidylethanolamineCholine: PhosphatidylethanolamineGlycerolSerineInositolDiphosphatidyl glycerol (cardiolipin)Ether glycerophospholipidsEther linkage at carbon 1111
Chapter 8 . LipidsAlkyl group esterified to carbon 2Plasmalogens: Ether glycerophospholipids with cis--unsaturated alkyl group at CSphingolipids: Backbone of sphingosine: 18-carbon amino alcohol with C-C trans double bondCeramide: sphingosine with fatty acid in amide linkageSphingomyelins: Alcohol esterified to phosphoceramideCholineEthanolamineGlycosphingolipids: Ceramide with sugars in -glycosidic linkageCerebroside: Sugar is glucose or galactoseSulfatide: Sugar is galactose with sulfate esterified at carbon 3 of galactoseGangliosides: Ceramide with three or more sugars including sialic acidWaxes: Esters of long-chain alcohol and long-chain fatty acidTerpenes: Class of lipids formed from 2-methyl-1,3-butadiene (isoprene)Monoterpene: Two isoprene units: 10 carbonsSesquiterpenes: Three isoprene units: 15 carbonsDiterpenes: Four isoprenes: two monoterpenes: 20 carbons