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Chapter 18: Lipids CHEM 1152 Dr. Sheppard Spring 2015 Lipids • One of 4 major classes of compounds found in living tissue – Nucleic acids, proteins, carbohydrates, lipids • • • • • • • • • Specific types differ in structure Includes fats, oils, cholesterol Insoluble in water (large nonpolar section) Soluble in organic solvents Energy storage Cell membranes Insulation Hormones/messengers Some vitamins 2 18.1 Classification of lipids Saponifiable = esters Simple = two components (fatty acid and alcohol) Complex = more than two components 3 Some example lipid structures 4 18.2 Fatty acids (FAs) • Simplest type of lipid • Component of other more complex lipids • Carboxylic acid with long (10-20) carbon chain – Even number of carbons – Typically unbranched H H H H H H H H H H H H H H H H C C C C C C C C C C C C C C C H H H H H H H H H H H H H H H O C OH O OH 5 Fatty acids and micelle formation 6 Saturated vs. unsaturated fatty acids • Saturated (“bad” fat) – Only C─C – Highly flexible – Pack together • Unsaturated (“good” fat) – Contains C═C – Cis double bonds – “Kink” in chain reduces possibility of heart disease • Don’t stick to walls of blood vessels • Promote blood flow – Monounsaturated – Polyunsaturated 7 Essential fatty acids • • • • • • Not synthesized by the body Needed as precursors for essential molecules Must be obtained from the diet Plant and fish oils Linoleic acid (18 carbons, 2 double bonds) Linolenic acid (18 carbons, 3 double bonds) 8 Some important unsaturated fatty acids • Oleic acid (18:1) – Olives – 18 carbons, C=C at C9 • Linoleic (18:2) – Corn, soybean oil – Essential FA – Omega-6 FA • Linolenic acid (18:3) – Corn, fish oil – Essential FA – Omega-3 FA 9 Physical properties of fatty acids • Solubility – Insoluble in water – Soluble in organic solvents (ether, chloroform) • Melting point – Saturated = solid at room temperature – MP increases with longer chains – MP decreases with number of unsaturations 10 11 18.3 Structure of Fats and oils • Triglycerides/triacylglycerols (TAGs) – Most abundant class of lipids in animals – Fatty acid triesters of glycerol – Formed from esterification 12 Triglycerides • Function – Energy reserves – Insulation • Stored in adipocytes throughout the body – Hydrolyzed as needed by enzymes called lipases 13 Triglycerides • Mixed vs. simple • mp determined by degree of unsaturation – More unsaturation in plants than in animals – “Fat” = mostly saturated • Solid at room temperature • Meat, butter (animal sources other than fish) – “Oil” = mostly unsaturated • Liquid at room temperature • Olive oil, peanut oil (fish and plants) 14 Triglycerides 15 Mixed or simple? Fat or oil? 16