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Lipid Review for Intro to Biochem This is the review on Bennett's section on Lipids for Introduction to Biochemistry from 2010.

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Gabriel Guillet

BIOCHEMISTRY REVIEW IILIPIDS Lipids are substances of biological origin that are soluble in organic solvents such as chloroform and methanol but only sparingly soluble if at all in waterthere are mainly two kinds of lipids 1 storage lipids and 2 structural membrane lipidsStorage Lipidscellular oxidation of fatty acids to carbon dioxide and water is highly energetic analogous to the controlled rapid burning of fossil fuels in internal combustion engines fatty acids are a source of cellular energy thus represent a source of stored energyFATTY ACIDScarboxylic acids with long chain hydrocarbon side groups and are aliphatic chains do not contain aromatic ringspolar head and nonpolar tailshighly reduced same oxidation state as fossil fuelsrarely do they appear in nature FREELY they are usually esterifiedVarying Lengths and Bondsthe hydrocarbon side chains range from 4 to 36 carbons most fatty acids have even number of 12 24 carbon atoms in unbranched chain they are predominantlybiosynthesized by C unitsthe successive condensation of two carbon acetate units 2fatty acids 14 and 20 carbon atoms are uncommon in animals the predominant fatty acids are 1618 carbon atomspalmitic oleic lineolic acnd stearic acids In Different Species KingdomsPLANTS AND ANIMALS alipathic chains in plant and animal lipids can be unbranced and fully saturated contain no double bondsex stearic acidHowever over half are unsaturated contain double bonds ex oleic acid andpolyunsaturatedpolyunsaturated fatty acids PUFAs contain two or more double bonds in SOME plants unusual fatty acids such as oils and waxes produced by plantsBACTERIAL FATTY ACIDS rarely polyunsaturated and commonly are branched hydroxylated or containcyclopropane ringsNomenclature and StandardsSTANDARD NOMENCLATURE first carbon position to the carboxyl carbon with carbon next to it is assigned the alpha positionfor PUFAS number 1 is assigned to the methyl carbon at the end of the chainThe carbon is defined as omega carbons position of the double bonds are indicated relateive to the omega carbon position of double bonds58111417 number of carbonsnumber of double bondsdeltaExample EPA205 deltaSATURATED FATTY ACIDSare highly flexiblecan assume a wide range of conformations there is relatively free rotation about each of their CC bondsdespite its flexibility the fully extended conformation has minimum energy given the least amount of steric interference between neighbouring groupsfully saturated fatty acids in extended form pack into nearly crystallize arrays stabilized by multiple hydrophobic interactions Symbol Common Name Systematic Name Structure 120 Lauric acid Dodecanoic acid CHCHCOOH 3210140 Myristic acid Tetradecanoic acid CHCHCOOH 3212160 Palmitic Acid Hexadecanoic acid CHCHCOOH 3214180Stearic Acid Octadecanoic acid CHCHCOOH 3216200 Arachidic acid Eicosanoic acid CHCHCOOH 3218220 Behenic Acid Docosanoic acid CHCHCOOH 3220240 Lignoceric acid Tetracosanoic acid CHCHCOOH 3222 POLYUNSATURATED FATTY ACIDSflexibility is restrictedfatty acid double bonds are almost always in cis configuration resulting in a 30degree bend in the hydrocarbon chain that interferes with their efficient packing in space the cis double bond restricts rotation introducing a rigid bend in the hydrocarbon tail others free to rotatethe reduced van der Waals interactions cause fatty acid melting points to decrease with degree of unsaturation rarely triple bonds occur in fatty acids or compounds of biological origindouble bonds in PUFAS are almost never conjugatedin PUFAS the double bonds tend to occur at every third carbon atom toward methyl terminus of hte molecule thth first double bond usually between 9 and 10 carbon Symbol Common Name Systematic Name Structure 161 n7 Palmitoleic acid 9hexadecenoic acid CHCHCHCHCHCOOH 32527181 n9 Oleic acid 9octadecenoid acid CHCHCHCHCHCOOH 32727182n6 Linoleic acid 912octadecadienoic acid183 n3 Alphalinoleic acid 91215octadecatrienoic acid183n6 Gammalinolenic 6912octadecatrienoic acid acid204n6 Arachidonic acid 581114Eicosatetraenoic acid
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