By: Andie Carman and Brianna Taylor Lipids 13.1 – 13.3 By: Andie Carman and Brianna Taylor

13.1 What Are Lipids Lipids A family of substances that are insoluble in water but soluble in nonpolar solvents of low polarity Example: Diethyl Ether Defined in terms of a property

Classification by Function Three major roles in human biochemistry: Store energy within fat cells Parts of membranes that separate compartments of aqueous solutions from each other Serve as chemical messengers

Storage Energy storage of lipids most important in animals Animals and humans More “economical” to use fats instead of carbohydrates Carbohydrates = quick energy Lipids = longer lasting energy Produce twice as much energy 9 kcal/g vs. 4 kcal/g

Membrane Components Lack of water solubility is important Body chemistry is so greatly based on water Lipids are needed in compounds so membranes can separate compartments that contain aqueous solutions Why are they insoluble? Polar groups are smaller than alkane-like portions Nonpolar portions provide hydrophobic property

Messengers Serve as chemical messengers Primary messengers Deliver signals from one part of the body to another part Example: hormonal steroids Secondary messengers Mediate the hormonal response Example: Prostaglandins and thromboxanes

Classification by structure Classified into four groups Simple lipids Fats and waxes Complex lipids Steroids Prostaglandins, thromboxanes, leukotrienes

13.2 What are the structures of triglycerides? Triesters of glycerol and long-chain carboxylic acids (fatty acids) Ex: animal fats and plant oils Can have a combination of fatty acids What fatty acids have in common: Practically all unbranched carboxylic acids About 10-20 carbons Contain even number of carbon atoms Besides –COOH group, they have no functional groups Most fatty acids that have double bonds, cis isomers predominate

Triglycerides Even numbers of carbon because body builds them entirely from acetate and carbons are put in two at a time Mono- and diglycerides are not infrequent Complex mixtures Some contain three identical fatty acids Most contain two or three different fatty acids Insoluble in water because ester groups are buried in nonpolar environment

13.3 Properties of Triglycerides Fats – come from animals, solid at room temp. Fish and plants, liquid at room temp. Oils- liquid fats Structural differences Depends on degree of unsaturation Physical properties Same properties as fatty acids Solid animal fats – contain saturated fatty acids Vegetable oils – contain unsaturated fatty acids Except coconut oil Essential fatty acids Body cannot synthesize them Must be obtained through daily diet

Coconut oil Polyunsaturated Pure fats and oils Small amount unsaturated acids Liquid because rich in low-molecular-weight fatty acids Polyunsaturated More than one double bond per fatty acid chain Pure fats and oils Colorless, odorless, tasteless Ex: butter Taster and color come from small amounts of other substances dissolved in the fat or oil

Hydrogenation Can reduce carbon-carbon double bonds to single bonds With hydrogen and a catalyst Used to produce Crisco Partial hydrogenation Used to make margarine Less hydrogen is used More unsaturation Source of trans fatty acids

Saponification Glycerides are esters, therefore are subject to hydrolysis Carried out with acids or bases Saponification Base-promoted hydrolysis of fats and oils Produce glycerol and a mixture of fatty acid salts called soaps