15.1 Lipids 15.2 Fatty Acids. Copyright 2009 by Pearson Education, Inc.

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1 Chapter 15 Lipids 15.1 Lipids 15.2 Fatty Acids Copyright 2009 by Pearson Education, Inc. 1

2 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. 2

3 Types of Lipids The types of lipids containing fatty acids are waxes fats and oils (triacylglycerols) glycerophospholipids prostaglandins The types of lipids that do not contain fatty acids are steroids 3

4 Classes of Lipids 4

5 Fatty Acids Fatty acids are long-chain carboxylic acids. typically carbon atoms. insoluble in water. saturated or unsaturated. Olive oil contains 84% unsaturated fatty acids and 16% saturated fatty acids. Copyright 2009 by Pearson Education, Inc. 5

6 Saturated and Unsaturated Fatty Acids Fatty acids are saturated with all single C C bonds. unsaturated with one or more double C=C bonds. 6

7 Properties of Saturated Fatty Acids 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. 7

8 Properties of Unsaturated Fatty Acids 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 8

9 Melting Points of Some Saturated Fatty Acids Copyright 2009 by Pearson Education, Inc. 9

10 Melting Points of Some Unsaturated Fatty Acids 10

11 Learning Check 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 11

12 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 oleic acid mp 13 C linoleic acid mp -17 C saturated most unsaturated 12

13 Chapter 15 Lipids 15.3 Waxes, Fats, and Oils 13

14 Waxes Waxes are esters of saturated fatty acids and long-chain alcohols. coatings that prevent loss of water by leaves of plants. 14

15 Fats and Oils: Triacylglycerols Fats and oils are also called triacylglycerols. esters of glycerol. produced by esterification. Formed when the hydroxyl groups of glycerol react with the carboxyl groups of fatty acids. Copyright 2009 by Pearson Education, Inc. 15

16 Triacylglycerols In a triacylglycerol, glycerol forms ester bonds with three fatty acids. Ester Bonds Copyright 2009 by Pearson Education, Inc. 16

17 Formation of a Triacylglycerol Glycerol + three fatty acids triacylglycerol + + 3H 2 O 17

18 Learning Check What are the fatty acids in the following triacylglycerol? 18

19 Solution Stearic acid Oleic acid Myristic acid 19

20 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. 20

21 Oils with Unsaturated Fatty Acids Oils 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. 21

22 Diagram of Triacylglycerol with Unsaturated Fatty Acids Unsaturated fatty acid chains with kinks cannot pack closely. 22

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

24 Chapter 15 Lipids 15.4 Chemical Properties of Triacylglycerols Copyright 2009 by Pearson Education, Inc. 24

25 Chemical Properties of Triacylglycerols The chemical reactions of triacylglycerols are similar to those of alkenes and esters. In hydrogenation, double bonds in unsaturated fatty acids react with H 2 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. 25

26 Hydrogenation of Oils The hydrogenation of oils adds hydrogen (H 2 ) to the carbon atoms of double bonds. converts double bonds to single bonds. increases the melting point. produces solids, such as margarine and shortening. 26

27 Hydrogenation Ni + 3H 2 Glyceryl tripalmitoleate (tripalmitolean) Glyceryl tripalmitate (tripalmitin) 27

28 Learning Check What products are obtained from the complete hydrogenation of glyceryl trioleate? 1. Glycerol and 3 oleic acids 2. Glyceryltristearate 3. Glycerol and 3 stearic acids 28

29 Solution What products are obtained from the complete hydrogenation of glyceryl trioleate? 2. Glyceryltristearate 29

30 Olestra TM, 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. 30

31 Cis and Trans Fatty Acids Unsaturated fatty acids can be cis with bulky groups on same side of C=C. CH 3 (CH 2 ) 5 (CH 2 ) 7 COOH cis H C=C H trans have bulky groups on opposite sides of C=C. CH 3 (CH 2 ) 5 H H C=C (CH 2 ) 7 COOH trans 31

32 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 LDLcholesterol and lower HDL-cholesterol. 32

33 Hydrogenation of Unsaturated Fats 33

34 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. 34

35 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. 35

36 Hydrolysis In hydrolysis, triacylglycerols split into glycerol and three fatty acids. an acid or enzyme catalyst is required

37 Saponification and Soap Saponification 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. 37

38 Saponification + 3NaOH + 3 soap 38

39 Learning Check What products are obtained from the complete hydrolysis of glyceryl trioleate? 1. Glycerol and 3 oleic acids 2. Glyceryl tristearate 3. Glycerol and 3 stearic acids 39

40 Solution What products are obtained from the complete hydrolysis of glyceryl trioleate? 1. Glycerol and 3 oleic acids 40

41 Learning Check Write the product of the following reaction:

42 Solution C H 2 C H C H 2 O O O O C ( C H 2 ) 14 C H 3 O C ( C H 2 ) 14 C H 3 O C ( C H 2 ) 14 C H 3 42

43 Chapter 15 Lipids 15.5 Glycerophospholipids Fatty acid Glycerol Fatty acid PO 4 Amino alcohol 43

44 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 PO 4 Amino alcohol 44

45 Polarity of Glycerophospholipids A glycerophospholipid has two nonpolar fatty acid chains. a phosphate group and a polar amino alcohol. CH HO CH 2 CH 2 N CH 3 HO CH 2 CH 2 NH 3 Choline CH 3 Ethanolamine + NH 3 HO CH 2 CH COO Serine Amino alcohols 45

46 Structure and Polarity of a Glycerophospholipid 46

47 Lecithin and Cephalin Lecithin and cephalin are glycerophospholipids abundant in brain and nerve tissues. found in egg yolk, wheat germ, and yeast. Copyright 2009 by Pearson Education, Inc. 47

48 Learning Check Identify each as A. fatty acid B. triacylglycerol C. amino alcohol D. glycerophospholipid 1. glyceryl trioleate 2. cephalin 3. choline 4. palmitic acid 48

49 Solution Identify each as A. fatty acid B. triacylglycerol C. amino alcohol D. glycerophospholipid 1. glyceryl trioleate B. triacylglycerol 2. cephalin D. Glycerophospholipid 3. choline C. amino alcohol 4. palmitic acid A. fatty acid 49

50 Chapter 15 Lipids 15.6 Steroids: Cholesterol and Steroid Hormones Copyright 2009 by Pearson Education, Inc. 50

51 Steroid Nucleus A steroid nucleus consists of 3 cyclohexane rings. 1 cyclopentane ring. no fatty acids. steroid nucleus 51

52 Cholesterol Cholesterol is the most abundant steroid in the body. has methyl CH 3 - groups, alkyl chain, and -OH attached to the steroid nucleus. 52

53 Cholesterol in the Body 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. A normal, open artery. An artery clogged by cholesterol plaque 53

54 Cholesterol in Foods Cholesterol is considered elevated if plasma cholesterol exceeds 200 mg/ dl. is synthesized in the liver and obtained from foods. 54

55 Learning Check Match the components of the cholesterol molecule with the following: carbon chain hydroxyl group steroid nucleus methyl group D B A C 55

56 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 56

57 Lipoproteins Lipoproteins combine lipids with proteins and phospholipids. are soluble in water because the surface consists of polar lipids. 57

58 Types of Lipoproteins Lipoproteins differ in density, composition, and function. include low-density lipoproteins (LDLs) and highdensity lipoproteins (HDLs). 58

59 Transport of Lipoproteins in the Body 59

60 Steroid Hormones Steroid hormones are chemical messengers in cells. sex hormones. - androgens in males (testosterone) - estrogens in females (estradiol) Adrenocortical hormones from adrenal glands. - mineralocorticoids (electrolyte balance) - glucocorticoids (regulate glucose level) 60

61 Steroid Hormones Steroid hormones are produced from cholesterol. include sex hormones such as androgens (testosterone) in males and estrogens (estradiol) in females. Copyright 2009 by Pearson Education, Inc. 61

62 Adrenal Corticosteroids Steroid hormones called adrenal corticosteroids are produced by the adrenal glands located on the top of each kidney. include aldosterone, which regulates electrolytes and water balance by the kidneys. include cortisone, a glucocorticoid, which increases blood glucose level and stimulates the synthesis of glycogen in the liver. 62

63 Anabolic Steroids Anabolic steroids are derivatives of testosterone. are used illegally to increase muscle mass. have side effects including fluid retention, hair growth, sleep disturbance, and liver damage. Copyright 2009 by Pearson Education, Inc. 63

64 Adrenal Corticosteroids Copyright 2009 by Pearson Education, Inc. 64

65 Learning Check Identify each lipid as a (1) fatty acid, (2) steroid, or (3) triacylglycerol. A. cholesterol B. stearic acid C. glyceryl tristearate D. estradiol E. contains no fatty acids 65

66 Solution Identify each lipid as a (1) fatty acid, (2) steroid, or (3) triacylglycerol. A. 2 cholesterol B. 1 stearic acid C. 3 glyceryl tristearate D. 2 estradiol E. 2 contains no fatty acids 66

67 Chapter 15 Lipids 15.7 Cell Membranes 67

68 Cell Membranes Cell membranes separate cellular contents from the external environment. consist of a lipid bilayer made of two rows of phospholipids. have an inner portion made of the nonpolar tails of phospholipids with the polar heads at the outer and inner surfaces. 68

69 Fluid Mosaic Model of Cell Membranes The lipid bilayer contains proteins, carbohydrates, and cholesterol. has unsaturated fatty acids that make cell membranes fluid-like rather than rigid. has proteins and carbohydrates on the surface that communicate with hormones and neurotransmitters. 69

70 Fluid Mosaic Model of Cell Membranes 70

71 Transport Through Cell Membranes The transport of substances through cell membranes involves diffusion (passive transport), which moves particles from a higher to a lower concentration. facilitated transport, which uses protein channels to increase the rate of diffusion. active transport, which moves ions against a concentration gradient. 71

72 Transport Pathways Through Cell Membranes Copyright 2009 by Pearson Education, Inc. 72

73 Learning Check The transport of particles across a cell membrane from high concentration to low concentration is called 1. facilitated transport. 2. diffusion. 3. active transport. 73

74 Solution The transport of particles across a cell membrane from high concentration to low concentration is called 2. diffusion. 74