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Lipids: Fatty Acids, Triglycerides and Phospholipids

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University of Guelph
BIOC 2580
E P Wijekoon

BIOC 2580 Final Exam Notes 1. Lipids Fatty Acids Functions • Building blocks for complex lipids • Central intermediates in metabolism Structure • Carboxylic acids with hydrocarbon chains (4-36carbons) • Most abundant fatty acids have even # of C atoms Nomenclature • Can number carbons 1,2,3… starting with carboxylic acid • Can label in Greek α, β… starting at carbon to which the carboxylic acid group is bonded • Can identify C positions relative to terminal methyl carbon called ω Hydrophobicity • Aggregate spontaneously when mixed in water to form complexes  Nature of aggregate depends on chemistry of lipid and environmental conditions (temp, presence of other solutes • Miscelles: smallest and simplest of lipid aggregates  Diameters 3 – few hundred nm  Cause cloudy appearance Typical Saturated Fatty Acids Unsaturated Fatty Acids • Have one of more double bonds • Polyunsaturate fatty acids (PUFA): double bond separated by methylene carbon  Bond pattern: double- single- single- double • Unsaturated double bonds naturally occur in cis conformation • Trans uncommon  Process of partial hydrogenation of oils (make them harder) can isomerize double bonds Trans Fatty Acids • Trans double bond allows fatty acid to adopt extended conformation • Pack more regularly than cis bonds • Higher melting point Nomenclature • Positions of double bonds specified relative to carboxyl carbon (C-1)  Superscript following Δ • Can specify double bonds relative to ω carbon rd th  Used for fatty acids between 3 and 4 C atoms from methylene C or between C6 and C7 from methyl group Properties • Determined by length and degree if unsaturation of hydrocarbon chain • Unsaturation lowers melting point/increases fluidity:  Saturated FA tightly packed – van der Waals interactions  Unsaturated FA have kinks from cis double bonds – weaker interactions • Water solubility decreases with:  Longer hydrocarbon chain  Fewer double bonds Esters and Anhydrides • Esters: carboxylic acids combined with alcohols • Anhydrides: carboxylic acids combined with acids • Both formed by condensation reactions  Bonds can be hydrolyzed • Free fatty acids never stay very long in cells  Usually converted to esters or anhydrides Triacylglycerols (TAGs, triglycerides) Structure • 3 fatty acids linked to glycerol molecule via ester linkages • “acyl” – acid derivative Function/Properties • Most important storage form of fats • Highly hydrophobic – carboxylic acids tied up in esters (less polar) • Melting point depends on length and degree of saturation of FA constituents  Higher the percentage of longer chain saturated FAs the higher the melting temp Phosphate Derivatives
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