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BIOC 2580 Lipid Readings

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BIOC 2580
Peter Dawson

LIPIDS: Fatty Acids  Biological lipids are insoluble in water  Fats and oils are stored forms of energy in organisms  Phospholipids and sterols are major structural elements of biological membranes  Other lipids play crucial roles such as: o Enzyme cofactors o Electron carriers o Light-absorbing pigments o Hydrophobic anchors for proteins o Chaperones to help membrane proteins fold o Emulsifying agents in digestive tract o Hormones o Intracellular messengers Storage Lipids  Fats and oils are derivatives of fatty acids  Fatty acids are hydrocarbon derivatives at about the same low oxidation state (highly reduced) as the hydrocarbons in fossil fuels  Cellular oxidation of fatty acids is highly exergonic  Two types of fatty acid: o Triacylglycerol o Waxes Fatty Acids are Hydrocarbon Derivatives  Fatty acids are carboxylic acids with hydrocarbon chains ranging from 4 to 36 carbons long  Unbranched=fully saturated (no double bonds)  Most commonly occurring fatty acid have even numbers of carbon atoms in an unbranched chain of 12 to 24 carbons o Even number of carbons results from the mode of synthesis of these compounds which involves successive condensations of two-carbon units (Acetate)  In most monounsaturated fatty acids the double bond is between C9 and C10  Double bonds of polyunsaturated fatty acids are generally C12 and C15 o The double bonds are almost never conjugated but are separated by methylene group o In unsaturated fatty acids, double bonds are in cis o Trans fatty acids are produced by fermentation  Polyunsaturated fatty acids (PUFAs) o Double bond between third and fourth carbon (omega-3) from methyl end are important in human nutrition o An imbalance of omega-3 and omega-6 PUFAs is associated with an increased risk of cardiovascular disease o Humans can synthesize EPA and DHA important in cellular function  Physical properties are determined by the length and degree of unsaturation of the hydrocarbon chain  Nonpolar hydrocarbon chain accounts for the poor solubility of fatty acids in water  The longer the fatty acyl chain and the fewer the double bonds, the lower the solubility in water  Carboxylic acid group is polar (and ionized in neutral pH) and accounts for the slight solubility of short-chain fatty acids in water  Melting points are strongly influenced by the length and degree of unsaturation of the hydrocarbon chain  At room temperature: o Saturated fatty acids are waxy o Unsaturated fatty acids are oily liquids  The difference in melting points is due to different degrees of packing of the fatty acid molecules  In fully saturated compounds: o Free rotation around each carbon-carbon bond gives hydrocarbon chain great flexibility o Most stable conformation is the fully exten
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