Essential fatty acids nomenclature

The most common dietary fatty acids are the saturated long-chain fatty acids palmitate (C16) and stearate (C18), the monounsaturated fatty acid oleate (C18 l), and the polyunsaturated essential fatty acid, linoleate (C18 2) (To review fatty acid nomenclature, consult Chapter 5). Animal fat contains principally saturated and monounsaturated long-chain fatty acids, whereas vegetable oils contain linoleate and some longer-chain and polyunsaturated fatty acids. They also contain smaller amounts of branched-chain and odd-chain-length fatty acids. Medium-chain-length fatty acids are present principally in dairy fat (e.g., milk and butter), maternal milk, and vegetable oils. 

Figure 35.8 Eicosapentaenoic add (EPA). A C20 5 poiy-unsaturated fatty acid, i.e. it has 20 carbon atoms and five cis-unsaturated bonds at C5, C8, Cll, C14 and C17. Nomenclature NB There is an alternative system for identifying the carbon atoms of fatty acids which is popular with nutritionists and uses Greek letters. The carboxylic acid group is ignored and the next carbon is a-, then P-, y-, etc. until the last caibon which is the last letter of the Greek alphabet, CD-. The system then counts backwards from ffl, so we have 1, 2, 3, etc. Thus EPA, which is an essential fatty add found in fish oU, is classified as a 3 fatty add. (Chemists (who claim to be the prima donnas of chemical nomenclature) pr er to label the last carbon n , so chemists refer to nl, n2, n3, etc.)...

Figure 1 Fatty-acid structure and nomenclature. (A) Chemical formula and carbon atom numbering system for a 16-carbon saturated fatty acid (16 0). (B) Schematic representation of 16 0. (C) A monounsaturated fatty add, 18 1n-9, showing the double bond nine carbon atoms from the methyl end (carbon 18). (D) The essential n-6 fatty acid 18 2n-6, where the first double bond is found six carbon atoms from the methyl end. The two double bonds are separated by a methylene (-CH2-) group. (E) The essential n-3 fatty acid 18 3n-3, where the first double bond is found three carbon atoms from the methyl end. (F) Phytanic acid, a dietary / -methyl-branched-chain fatty acid (3,7,11,15-tetramethyl 16 0). The melhyl group on carbon 3 prevents this fatty acid from degradation by /3-oxidation. (G) Pristanic acid (2,6,10,14-tetramethyl 15 0) is the product of phytanic acid o-oxidation, in which a single carbon (carbon 1) is lost. The methyl group on carbon 2 does not preclude subsequent degradation by /3-oxidation.

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