Chemeketa Community College Chapter 15: Lipids Larry Emme Chemeketa Community College

Chapter Outline Lipids Fatty Acids Waxes, Fats, & Oils Chemical Properties

Lipids Lipids are biomolecules that contain fatty acids or a steroid nucleus. soluble in organic solvents, but not in water. named for the Greek word lipos, which means “fat.” extracted from cells using organic solvents.

Types of Lipids The types of lipids containing fatty acids are waxes fats and oils called triglycerides (triacylglycerols) glycerophospholipids prostaglandins The types of lipids that do not contain fatty acids are steroids

Classes of Lipids Triglycerides

Fatty Acids Fatty acids are long-chain carboxylic acids. typically 12-18 carbon atoms. insoluble in water. saturated or unsaturated. Olive oil contains 84% unsaturated fatty acids and 16% saturated fatty acids.

Saturated and Unsaturated Fatty Acids Fatty acids are saturated with all single C–C bonds. unsaturated with one or more double C=C bonds.

Properties of Saturated Fatty Acids contain only single C–C bonds. are closely packed. have strong attractions between chains. have high melting points. are solids at room temperature.

Properties of Unsaturated Fatty Acids contain one or more cis double C=C bonds. have “kinks” in the fatty acid chains. do not pack closely. have few attractions between chains. have low melting points. are liquids at room temperature. “kinks” in chain

Melting Points of Some Saturated Fatty Acids

Melting Points of Some Unsaturated Fatty Acids

Learning Check stearic acid (18 C) saturated Assign the melting points of –17 °C, 13 °C, and 69 °C to the correct fatty acid. Explain. stearic acid (18 C) saturated oleic acid (18 C) one double bond linoleic acid (18 C) two double bonds

Solution Stearic acid is saturated and would have a higher melting point than the unsaturated fatty acids. Because linoleic has two double bonds, it would have a lower mp than oleic acid, which has one double bond. stearic acid mp 69 °C saturated oleic acid mp 13 °C linoleic acid mp -17 °C most unsaturated

Waxes, Fats, and Oils 14 14

Waxes Waxes are esters of saturated fatty acids and long-chain alcohols. coatings that prevent loss of water by leaves of plants. 15 (pronounced “ho-HO bah” 15

Fats and Oils: Triglycerides or Triacylglycerols Fats and oils are also called triglycerides. esters of glycerol. produced by esterification. Formed when the hydroxyl groups of glycerol react with the carboxyl groups of fatty acids. 16 16

Triglycerides (Triacylglycerols) In a triglyceride, glycerol forms ester bonds with three fatty acids. Ester Bonds 17 17

Formation of a Triglyceride Glycerol + three fatty acids triglyceride + + 3H2O 18 18

Melting Points of Fats and Oils A fat is usually solid at room temperature. is prevalent in meats, whole milk, butter, and cheese. An oil is usually liquid at room temperature. is prevalent in plants such as olive and safflower. 19 19

Oils with Unsaturated Fatty Acids have more unsaturated fats. have cis double bonds that cause “kinks” in the fatty acid chains. with “kinks” in the chains do not allow the triacylglycerol molecules to pack closely. have lower melting points than saturated fatty acids. are liquids at room temperature. 20 20

Diagram of Triglyceride with Unsaturated Fatty Acids Unsaturated fatty acid chains with kinks cannot pack closely. 21 21

Percent Saturated and Unsaturated Fatty Acids In Fats and Oils 23 23

7 61 32 8 77 15 9 16 75 12 16 72 13 29 58 15 75 10 15 23 62 19 48 33 27 19 54 43 47 10 51 38 11 68 28 4 91 7 2

Chemical Properties of Triglycerides 25 25

Chemical Properties of Triglycerides The chemical reactions of triglycerides are similar to those of alkenes and esters. In hydrogenation, double bonds in unsaturated fatty acids react with H2 in the presence of a Ni or Pt catalyst. In hydrolysis, ester bonds are split by water in the presence of an acid, a base, or an enzyme. 26 26

Hydrogenation of Oils The hydrogenation of oils adds hydrogen (H2) to the carbon atoms of double bonds. converts double bonds to single bonds. increases the melting point. produces solids, such as margarine and shortening. 27 27

Hydrogenation Ni + 3H2 Glyceryl tripalmitoleate Glyceryl tripalmitate (tripalmitolean) Glyceryl tripalmitate (tripalmitin) 28 28

OlestraTM, a Fat Substitute Olestra is used in foods as an artificial fat. sucrose linked by ester bonds to several long-chain fatty chains. not broken down in the intestinal tract. 29 29

Cis and Trans Fatty Acids Unsaturated fatty acids can be cis with bulky groups on same side of C=C. CH3─ (CH2)5 (CH2)7─ COOH cis C=C H H trans have bulky groups on opposite sides of C=C. CH3─ (CH2)5 H C=C trans H (CH2)7─ COOH 30 30

Hydrogenation and Trans Fatty Acids Most naturally occurring fatty acids have cis double bonds. During hydrogenation, some cis double bonds are converted to trans double bonds. In the body, trans fatty acids behave like saturated fatty acids. It is estimated that 2-4% of our total Calories is in the form of trans fatty acid. Several studies reported that trans fatty acids raise LDL-cholesterol and lower HDL-cholesterol. 31 31

Hydrogenation of Unsaturated Fats 32 32

Learning Check (1) True or (2) false: A. There are more unsaturated fats in vegetable oils. B. Vegetable oils have higher melting points than fats. C. Hydrogenation of oils converts some cis-double bonds to trans-double bonds. D. Animal fats have more saturated fats. 33 33

Solution (1) True or (2) false: A. T There are more unsaturated fats in vegetable oils. B. F Vegetable oils have higher melting points than fats. C. T Hydrogenation of oils converts some cis-double bonds to trans- double bonds. D. T Animal fats have more saturated fats. 34 34

Hydrolysis In hydrolysis, triglycerides split into glycerol and three fatty acids. an acid or enzyme catalyst is required. + + 35 35

Saponification and Soap is the reaction of a fat with a strong base. splits triacylglycerols into glycerol and the salts of fatty acids. is the process of forming “soaps” (salts of fatty acids). with KOH gives softer soaps. 36 36

Saponification + 3NaOH + 3 “soap” 37 37

Learning Check Write the product of the following reaction: + 3 38 38

Solution C O ( H 2 ) 1 4 3 39

Glycerophospholipids Fatty acid Glycerol Fatty acid PO4 Amino alcohol 40 40

Glycerophospholipids Glycerophospholipids are the most abundant lipids in cell membranes. composed of glycerol, two fatty acids, phosphate, and an amino alcohol. Fatty acid Glycerol Fatty acid PO4 Amino alcohol 41 41

Polarity of Glycerophospholipids A glycerophospholipid has two nonpolar fatty acid chains. a phosphate group and a polar amino alcohol. CH3 │+ + HO−CH2−CH2−N−CH3 HO−CH2−CH2−NH3 │ Choline CH3 Ethanolamine + NH3 │ Amino alcohols HO−CH2−CH−COO− Serine 42 42

Structure and Polarity of a Glycerophospholipid 43 43

Lecithin and Cephalin Lecithin and cephalin are glycerophospholipids abundant in brain and nerve tissues. found in egg yolk, wheat germ, and yeast. 44 44

Steroids: Cholesterol and Steroid Hormones 45 45

Steroid Nucleus A steroid nucleus consists of 3 cyclohexane rings. 1 cyclopentane ring. no fatty acids. steroid nucleus 46 46

Cholesterol Cholesterol is the most abundant steroid in the body. has methyl CH3- groups, alkyl chain, and -OH attached to the steroid nucleus. 47 47

Cholesterol in the Body A normal, open artery. Cholesterol is obtained from meats, milk, and eggs. is synthesized in the liver. is needed for cell membranes, brain and nerve tissue, steroid hormones, and vitamin D. clogs arteries when high levels form plaque. An artery clogged by cholesterol plaque 48 48

Cholesterol in Foods Cholesterol is considered elevated if plasma cholesterol exceeds 200 mg/dL. is synthesized in the liver and obtained from foods. 49 49

Learning Check Match the components of the cholesterol molecule with the following: ___ carbon chain ___hydroxyl group ___ steroid nucleus ___methyl group D B A C 50 50

Solution Match the components of the cholesterol molecule with the following: _D carbon chain _A_hydroxyl group _C steroid nucleus _B_methyl group D B A C 51 51

Solution Identify each lipid as a (1) fatty acid, (2) steroid, or (3) triglyceride. A. 2 cholesterol B. 1 stearic acid C. 3 glyceryl tristearate D. 2 contains no fatty acids 52 52

The End

End of Chapter Learning Checks Try these after you have reviewed the chapter

Learning Check What characteristic do all lipids have in common? 55 55

Learning Check Answers What characteristic do all lipids have in common? All lipids are insoluble in water. 56

Learning Check Which fatty acid would you predict to have the lowest melting point? 57

Learning Check Answers Which fatty acid would you predict to have the lowest melting point? Both fatty acids are saturated. The fatty acid with the fewest number of carbon atoms should have the lowest melting point. 58

Learning Check The trans isomers of palmitoleic acid CH3(CH2)5CH=CH(CH2)7COOH is shown below. Draw the cis isomer. trans-isomer 59

Learning Check Answers The trans isomers of palmitoleic acid CH3(CH2)5CH=CH(CH2)7COOH is shown below. Draw the cis isomer. trans-isomer cis-isomer 60

CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH Learning Check What is the correct classification of the fatty acid shown below? CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH ω-3 ω-6 61

CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH Learning Check Answers What is the correct classification of the fatty acid shown below? CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH ω-3 ω-6 The double bond is attached to the sixth carbon from the end of the molecule furthest from the carboxyl group. This is an ω-6 fatty acid. 62

Learning Check What is the classification of the following lipid? 63

Learning Check Answers What is the classification of the following lipid? This lipid is an example of a phospholipid. 64

Learning Check What is the classification of the following lipid? 65

Learning Check Answers What is the classification of the following lipid? This molecule is a glycolipid. 66

Learning Check Identify the functional groups in cortisone. 67

Learning Check Answers Identify the functional groups in cortisone. 68