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Lipids Lipids of Physiologic Significance
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BIOMEDICAL IMPORTANCE The lipids The common property – insoluble in water – soluble in nonpolar solvents They are important dietary constituents – high energy value – fat-soluble vitamins – essential fatty acids Fat is stored in adipose tissue
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BIOMEDICAL IMPORTANCE Thermal insulator electrical insulators cellular constituents – Membranes Transport – Lipoproteins Lipid biochemistry is necessary – obesity, diabetes mellitus, atherosclerosis, polyunsaturated fatty acids in nutrition and health
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Classification Simple lipids – Esters of fatty acids with various alcohols Complex lipids – groups in addition to an alcohol and a fatty acid – Phospholipids Glycerophospholipids Sphingophospholipids – Glycolipids – Other complex lipids Sulfolipids and aminolipids Lipoproteins
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Classification Precursor and derived lipids Neutral lipids – acylglycerols (glycerides),cholesterol, and cholesteryl esters
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Free fatty Free fatty acids – Saturated -anoic – Unsaturated -enoic 1,2,3,… α, β, γ,… ω or n carbons Δ
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Saturated fatty acids
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Unsaturated Fatty Acids Monounsaturated Polyunsaturated Eicosanoids – eicosa- (20-carbon) polyenoic fatty acids Prostanoids – Prostaglandins(PGs) – Prostacyclins (PGIs) – Thromboxanes (TXs) Leukotrienes (LTs) Lipoxins (LXs)
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Prostaglandins The number of double bonds – PG1, PG2, PG3 Different substituent groups (on ring) – A, B,C,etc
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The leukotrienes and lipoxins Lipoxygenase pathway three or four conjugated double bonds Leukotrienes cause bronchoconstriction as well as being potent proinflammatory agents and play a part in asthma
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Unsaturated Fatty Acids Geometric isomerism – Cis on the same side – Trans if on opposite sides as a by-product of the saturation of fatty acids ingestion of ruminant fat Significance – Molecular packing in membranes
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Unsaturated fatty acids of physiologic and nutritional significance
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Structure of some unsaturated fatty acids
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Physical and Physiologic Properties of Fatty Acids Chain Length and Degree of Unsaturation – even-numbered-carbon fatty acids – The melting points
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TRIACYLGLYCEROLS (TRIGLYCERIDES) THE MAIN STORAGE FORMS OF FATTY ACIDS Mono- and diacylglycerols
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PHOSPHOLIPIDS MAIN LIPID CONSTITUENTS OF MEMBRANES derivatives of phosphatidic acid Phosphatidylcholines (Lecithins) the most abundant phospholipids of the cell membrane represent a large proportion of the body’s store of choline
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PHOSPHOLIPIDS Surfactant – Dipalmitoyl lecithin respiratory distress syndrome Phosphatidylethanolamine (cephalin) Phosphatidylserine Phosphatidylinositol Cardiolipin
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Lysophospholipids
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Phospholipids Plasmalogens
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Sphingomyelins
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GLYCOLIPIDS GLYCOSPHINGOLIPIDS – NERVE TISSUES – CELL MEMBRANE Galactosylceramide – Sulfatide Sulfogalactosylceramide Glucosylceramide – Glycosphingolipid of extraneural tissues
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Simple glycosphingolipids Complex glycosphingolipids – Gangliosides Sialic acid The simplest ganglioside found in tissues is G M3 Functions – Receptor, …
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STEROIDS Cholesterol – Atherosclerosis – As Precursor Sterol – Has one or more hydroxyl groups and no carbonyl or carboxyl groups
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Stereoisomers – “Chair” or a “boat”form – The rings can be either cis or trans – β bonds above the plane of the rings – α bonds bonds attaching groups below
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an all-trans configuration between adjacent rings
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a cis configuration between rings A and B
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Cholesterol Cholesteryl ester
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Ergosterol Precursor of Vitamin D
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Polyprenoids Synthesized from five-carbon isoprene units Include – Ubiquinone – Dolichol – Vitamins A, D, E, and K, and β-carotene (provitamin A)
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LIPID PEROXIDATION A SOURCE OF FREE RADICALS – Lipids exposed to oxygen – deterioration of foods (rancidity) – damage to tissues Cancer, inflammatory diseases, atherosclerosis, and aging – Peroxide formation from fatty acids containing methylene-interrupted double bonds – Antioxidants Vitamin E, Beta-carotene Urate and vitamin C
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AMPHIPATHIC LIPIDS Form – Membranes, Micelles, Liposomes, & Emulsions Contain polar groups – Fatty acids, phospholipids, sphingolipids, bile salts, and, to a lesser extent, cholesterol Part of the molecule is hydrophobic, and part is hydrophilic
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Micelles – When a critical concentration of these lipids is present in an aqueous medium – Facilitating absorption of lipids Liposomes – Formed by sonicating an amphipathic lipid in an aqueous medium – as carriers of drugs
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Emulsions – Much larger particles
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Waxes Serve as – Energy Stores and Water Repellents Esters of long-chain (C 14 to C 36 ) saturated and unsaturated fatty acids with long-chain (C 16 to C 30 ) alcohols Their melting points (60 to 100 °C) are generally higher than those of triacylglycerols
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Triacontanoylpalmitate, the major component of beeswax
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