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FATTY ACIDS Fatty Acids ……… DEFINITION • Fatty acid: a long, unbranched chain carboxylic acid, most commonly of 12 - 20 carbons, derived from hydrolysis of animal fats, vegetable oils, or phosphodiacylglycerols of biological membranes. • Denovo synthesis occurs from acetyl coA (lipogenesis) • Fatty acids - are components of triacylglycerols, glycerophospholipids, sphingolipids • Fatty acids differ from one another in: (1) Length of the hydrocarbon tails (2) Degree of unsaturation (double bond) (3) Position of the double bonds in the chain Prentice Hall c2002 Chapter 9 7 Fig 9.2 • Long Chain Fatty Acids are typically even numbered • SATURATED no C-C double bonds • UNSATURATED - at least one C-C double bond • Monounsaturated - only one C-C double bond • Polyunsaturated - two or more C-C double bonds • Omega-3, omega-6 and omega-9 Fig. 9.3 Structures of three C18 fatty acids (a) Stearate (octadecanoate) (b) Oleate (cis-D9octadecenoate) (c) Linolenate (all-cis-D9,12,15octadecatrienoate) • The cis double bonds produce kinks in the tails of unsaturated fatty acids Prentice Hall c2002 Chapter 9 10 Fatty Acids Unsaturated Saturated Carbon Atoms/ Double Bonds 12:0 14:0 16:0 18:0 20:0 16:1 18:1 18:2 18:3 20:4 Common Name lauric acid myristic acid palmitic acid stearic acid arachidic acid palmitoleic acid oleic acid linoleic acid linolenic acid arachidonic acid mp (°C) 44 58 63 71 77 -0.5 16 -5 -11 -49 Fatty Acids • Among the fatty acids most abundant in plants and animals – nearly all have an even number of carbon atoms, most between 12 and 20, in an unbranched chain – the three most abundant are palmitic (16:0), stearic acid (18:0), and oleic acid (18:1) – in most unsaturated fatty acids, the cis isomer predominates; the trans isomer is rare – unsaturated fatty acids have lower melting points than their saturated counterparts; the greater the degree of unsaturation, the lower the melting point Difference between Cis & Trans • If the acyl chains are on the same side of the bond, it is cis, example: oleic acid. • if on opposite sides, it is trans-, example: elaidic acid, the trans isomer of oleic acid • Double bonds in naturally occurring unsaturated long-chain fatty acids are nearly all in the cis configuration, the molecules being "bent" 120 degrees at the double bond. Thus, oleic acid has an L shape, whereas elaidic acid remains "straight.“ Clinical Significance • Consumption of trans fatty acids not good for health. • Previously in Margarine Higher number of Trans FA. • Now soft margarine low in trans fatty acids or containing none at all. Hydrogenation Plant • Hydrogenation involves: – Heating oil – Pressurizing oil – hydrogen gas – Using platinum catalyst • Trans fats are a by product of hydrogenation • 0 g trans fats does not mean zero • It means <0.5 g per serving! How Can Fatty Acids Modulate the Immune System? • Why do we need immune modulation in the first place? • Answer: Similar to avoid excessive, chronic inflammation which leads to tissue destruction. • FAs such as DHA and EPA can reduce production of inflammatory cytokines (IL6, IL-12, IL-23) • FAs can increase phagocytic activity • FAs can decrease lymphocytic proliferation • FAs can influence immune cell migration