09062011FNTR342-LipidDigest

09062011FNTR342-LipidDigest - Digestion Absorption and...

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Digestion, Absorption, and Properties of Lipids Reading: Gropper, 4 th ed, Ch 6, pp. 128–139; Ch 2, pp. 40–45 Gropper, 5 th ed, Ch 5, pp. 131–144; Ch 2, pp. 48–51
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2 Objectives for today: Review chemical structures of lipids Review sites of digestion and mechanisms of absorption
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3 Lipids: a broad and diverse range of structures Soluble in organic solvents (hydrophobic) Most also have hydrophilic groups Few lipids are utilized as energy source
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4 Role of Dietary Lipids Provide a dense energy supply (9 kcal/g) Increase satiety by slowing intestinal transit time Supply essential fatty acids Facilitate absorption of fat-soluble vitamins (A, D, E, K)
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5 Classes Simple Fatty acids: saturated and unsaturated Acylglycerols (glycerides) Mono-, di-, triacylglycerols ~95% of dietary lipid intake Waxes (fatty acid esters with alcohol groups) Compound Lipids Phospholipids: lecithin and sphingomyelin Glycolipids Lipoproteins
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6 Classes (cont.) Derived Lipids Sterols and steroids Cholesterol, steroid hormones, vitamin D
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7 Fatty acid structure Hydrocarbon chain (4 to 28 carbons long) Usually even carbon numbers (some fish FA may have odd carbon numbers) Carboxyl acid end (hydrophilic) Methyl end (hydrophobic) Fig. 6-1a, p. 130
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8 Saturation: level of carbon double bonding Saturated = no double bond Monounsaturated (MUFA) = 1 double bond Polyunsaturated (PUFA) = ≥ 2 double bond Cis and Trans orientation of double bond Cis configuration (same side) kinks the hydrocarbon chain Trans configuration (opposite) does not kink the chain Fatty acid structure… C = C H R R H C = C H R R H cis = “on this side” trans = across
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9 Fig. 6-1c, p. 130
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10 Fatty acid nomenclature Common name: palmitic acid, palmitoleic, arachidonic 2200 system counts from the carboxyl end: 16:0, 16:1 9 , 20:4 5,8,11,14 n (or ϖ ) system counts from the methyl end: 16:0, 16:1 (n-7), 20:4 (n-6)
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11 Fig. 6-2, p. 130
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12 Table 6-1, p. 131
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13 Essential Fatty Acids Not synthesized in animal cells: Linoleic acid (18:2 n-6) α -linolenic acid (18:3 n-3) Lack 12 and 15 desaturases These two fatty acids must be obtained from plants These two fatty acids generate two families of eicosanoids (20-carbon fatty acids with potent activities)
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14 Two Essential Fatty Acids 12 15 12
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15 Omega-6 versus Omega-3 Fatty Acids Omega-3 fatty acids α -linolenic acid Eicosapentaenoic acid (20:5 n-3)(EPA) Docosahexaenoic acid (22:6 n-3)(DHA)
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09062011FNTR342-LipidDigest - Digestion Absorption and...

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