Chapter 13 Lipids Sections 13.1-13.3

13.1 What are Lipids? Found in living organisms They are insoluble in water but soluble in nonpolar solvents (diethyl ether) Lipids are defined by property and not structure Stores energy in fat cells, part of membranes that separate aqueous solutions, and serve as chemical messengers

Fat energy burn about 9kcal/g and carbohydrates are only 4kcal/g Lipids provide membranes for the body and has hydrophobic properties Steroid hormones deliver signals from one part to another We can classify lipids into four groups Simple lipids, such as fats and waxes Complex lipids Steroids Prostaglandins, thromboxanes, and leukotriens

13.2 What Are the Structures of Triglycerides? Animal fats and plant oils are triglycerides Triglycerides are triesters of glycerol and long-chain carboxylic acids called fatty acids Triglycerides are always glycerol Practically all unbranched carboxylic acids Even number of carbons; 10-20 No other functional group besides –COOH and double bonds

The cis isomers predominate There are mono- and diglycerides but are less common

13.3 What Are Some Properties of Triglycerides? Fats from animals are usually solid but fats from plants or fish are liquid Liquid fats are called oils Solid animal fats contain mostly saturated fatty acids Vegetable oil contains high amounts of unsaturated fatty acids

Most vegetable oil has high amounts of unsaturated fatty acids Linoleic and linolenic acids are called essential fatty acids; the body cant synthesize them so they need to be consumed Most vegetable oil has high amounts of unsaturated fatty acids Exception: coconut oil Oils with more than one double bond per fatty acid chain are called polyunsaturated Pure fats and oils are colorless, odorless and tasteless Tastes, odors and colors are caused by small amounts of other substances dissolved in the fat or oil

Hydrogenation Unsaturated liquid oils are converted to solids Carbon to carbon double bonds are reduced to single bonds by treating them with hydrogen and a catalyst Fats with no double bonds would be too solid

Source of trans fatty acids Partial hydrogenation creates a product with the right consistency for cooking Produces Crisco, Spry and Dexo Margarine is made by partial hydrogenation of vegetable oils

Saponification Oldest known chemical reaction Glycerides are subject to hydrolysis which can be carried out with acids or bases Base promoted hydrolysis of fats and oils producing glycerol and a mixture of fatty acid salts Produces soaps