Chapter 15 Lipids 15.1 Lipids 15.2 Fatty Acids

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 (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

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

Waxes Waxes are esters of saturated fatty acids and long-chain alcohols. coatings that prevent loss of water by leaves of plants. 14 (pronounced “ho-HO bah” 14

Fats and Oils: Triacylglycerols or Triglycerides 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. 15 15

Triacylglycerols (Triglycerides) In a triacylglycerol, glycerol forms ester bonds with three fatty acids. Ester Bonds 16 16

Formation of a Triacylglycerol Glycerol + three fatty acids triacylglycerol + + 3H2O 17 17

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. 18 18

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. 19 19

Diagram of Triacylglycerol with Unsaturated Fatty Acids Unsaturated fatty acid chains with kinks cannot pack closely. 20 20

Percent Saturated and Unsaturated Fatty Acids In Fats and Oils 21 21

Chemical Properties of Triacylglycerols (Triglycerides) Chapter 15 Lipids 15.4 Chemical Properties of Triacylglycerols (Triglycerides) 22 22

Chemical Properties of Triacylglycerols (Triglycerides) The chemical reactions of triacylglycerols 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. 23 23

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. 24 24

Hydrogenation Ni + 3H2 Glyceryl tripalmitoleate Glyceryl tripalmitate (tripalmitolean) Glyceryl tripalmitate (tripalmitin) 25 25

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. 26 26

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 27 27

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. 28 28

Hydrogenation of Unsaturated Fats 29 29

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. 30 30

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. 31 31

Hydrolysis In hydrolysis, triacylglycerols split into glycerol and three fatty acids. an acid or enzyme catalyst is required. + + 32 32

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. 33 33

Saponification + 3NaOH + 3 “soap” 34 34

Learning Check Write the product of the following reaction: + 3 35 35

Solution C O ( H 2 ) 1 4 3 36

Glycerophospholipids Chapter 15 Lipids 15.5 Glycerophospholipids Fatty acid Glycerol Fatty acid PO4 Amino alcohol 37 37

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 38 38

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 39 39

Structure and Polarity of a Glycerophospholipid 40 40

Lecithin and Cephalin Lecithin and cephalin are glycerophospholipids abundant in brain and nerve tissues. found in egg yolk, wheat germ, and yeast. 41 41

Steroids: Cholesterol and Steroid Hormones Chapter 15 Lipids 15.6 Steroids: Cholesterol and Steroid Hormones 42 42

Steroid Nucleus A steroid nucleus consists of 3 cyclohexane rings. 1 cyclopentane ring. no fatty acids. steroid nucleus 43 43

Cholesterol Cholesterol is the most abundant steroid in the body. has methyl CH3- groups, alkyl chain, and -OH attached to the steroid nucleus. 44 44

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 45 45

Cholesterol in Foods Cholesterol is considered elevated if plasma cholesterol exceeds 200 mg/dL. is synthesized in the liver and obtained from foods. 46 46

Learning Check Match the components of the cholesterol molecule with the following: ___ carbon chain ___hydroxyl group ___ steroid nucleus ___methyl group D B A C 47 47

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 48 48

Lipoproteins Lipoproteins combine lipids with proteins and phospholipids. are soluble in water because the surface consists of polar lipids. 49 49

Types of Lipoproteins Lipoproteins differ in density, composition, and function. include low-density lipoproteins (LDLs) and high-density lipoproteins (HDLs). 50 50

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) 51 51

Steroid Hormones Steroid hormones are produced from cholesterol. include sex hormones such as androgens (testosterone) in males and estrogens (estradiol) in females. 52 52

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. 53 53

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. 54 54

Adrenal Corticosteroids 55 55

Learning Check Identify each lipid as a (1) fatty acid, (2) steroid, or (3) triacylglycerol. A. cholesterol B. stearic acid C. glyceryl tristearate D. contains no fatty acids 56 56

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 contains no fatty acids 57 57

Chapter 15 Lipids 15.7 Cell Membranes 58 58

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. 59 59

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. 60 60

Fluid Mosaic Model of Cell Membranes 61 61

Transport Through Cell Membranes The transport of substances through cell membranes involves simple 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. 62 62

Transport Pathways Through Cell Membranes Copyright © 2009 by Pearson Education, Inc. 63 63

Learning Check The transport of particles across a cell membrane from high concentration to low concentration is called 1. facilitated transport. 2. simple diffusion. 3. active transport. 64 64

Solution The transport of particles across a cell membrane from high concentration to low concentration is called 2. diffusion. 65 65