Lipids 13.1 – 13.3

1. Lipids13.1 – 13.3 By: Andie Carman and Brianna Taylor

2. 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

3. 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

4. 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

5. 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

6. 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

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

8. 13.2 What are the structures of triglycerides? • 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

9. 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

10. 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

11. Coconut oil • 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

12. 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

13. 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