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Summary 547

Aspirin blocks the qmthesis of prostaglandins that induce pain and fever. It also has been reported that low doses of aspirin reduce the danger of heart attack and stroke by blocking the synthesis of prostaglandins that promote blood clotting. Aspirin's inhibition of the formation of these prostaglandins accounts for its effectivenessas an analgesic (pain killer), antipyretic (fever killer), and anticlotting agent. Leukotrienes are another classof hormone-like substancessynthesized from arachidonic acid. Lettkotriene Bn and leukotriene En are examples of leukotrienes. Unlike the prostaglandins, the leukotrienes contain three car- bon-carbon double bonds in a row in their molecular structures.

I NHz Leukotriene Ea Certain leukotrienes constitute what is referred to as the slow-acting sub- stances of anaphylactic shock. Anaphylactic shock is a drastic allergic responseof the body that can be fatal. Severeallergies to foods such as shellfish or peanuts can trigger anaphylactic shock in susceptible people. The symptoms of anaphylactic shock include closing of the throat, blocking the airways. Heart stoppage also can occur, leading to death. Leukotrienes are also implicated in less severeallergic reactions, asthma, inflammations, and heart attacks. Recent studies suggestthat dietary fish oils can reduce levels of leukotrienes and reduce the risk of heart attack. sflifttrru$&FV are a broad class of naturally occurring, rela- mon glycolipids. and glycolipid mole- tively water-insoluble molecules. Triglycerides-tri- cules have polar heads and hydrophobic tails. The esters of glycerol and fatty acids-are the most bilayer is the fundamental structure of lipo- abundant lipids in tissue. somes and the membranes of cells and organelles. The membranes of all cells are composed of Its behavior is best described by a fluid mosaic lipids. The major lipids of cell membranes are the model. Proteins,which may be peripheral or inte- , the glycolipids, and in animal cells, gral, are associatedwith cell and organelle mem- .Phospholipids have a backboneof glyc- branes. Membrane proteins are often glycoproteins. erol (phosphoglycerides)or of sphingosine (sphin- molecules have no structural features in gomyelins). Cerebrosides,containing glucose or common with other lipids. They are often classified galactose,with a backboneof sphingosineare com- as lipids, however, because,like fatty acid esters, 548 CHAPTER17 Lioids

they are extractable from and animal tissues also affect the body's salt and water balance; aldos- with organic solvents.Aldehyde and ketone func- terone is the most important mineralocorticoid. tions as well as hydroxyl groups appear frequently in Secondary sex hormones produce secondary sex steroid molecules,which sometimescontain a dou- characteristics of the male and female. They are ble bond. the androgens in the male and the estrogens in Cholesterolis the most abundant steroid in ani- the female.Primary sexhormones produced by the mals.Many steroidspresent in lesseramounts in the gonads are responsible for the maturation of the animal body act as hormones. The adrenal cortex, reproductive system. the outer layer ofthe adrenal gland, producesthree Prostaglandins and leukotrienes, two groups of groupsof steroidhormones: the glucocorticoids,the fatty acid-related molecules, exert many hormone- mineralocorticoids, and the secondary sex hor- like effectson the body. Prostaglandinsire used for mones. Glucocorticoids (cortisone, , corti- inducing labor and terminating pregnancy and also costerone) regulate the body's use of glucose and have been used for controlling blood pressureand affect salt and water balance. Mineralocorticoids reducing inflammation.

KgY ?T*ffi5 (17.3) Integralprotein (17.4) Peripheralprotein (17.4) Sphingomyelin(17.3) Complexlipid (17.3) (17.3) Phosphoglyceride(17.3) Steroid(17.5) Corticoid (17.6) Leukotriene(17.11) Phospholipid(17.3) Steroidhormone (17.6) Estrogen(17.8) Lipid (17.1) Progesterone(17.8) (17.5) (17.2) (r7.4) Prostaglandin(17.11) (17.7) Fluid mosaicmodel (17.4) Liposome(17.4) Rancid (17.2) Triglyceride(17.2) Glucocorticoid(17.6) Mineralocorticoid (f 7.6) Saponification(I7.2) (17.1) Glycolipid (17.3) Mixed triglyceride (17.2) Sexhormone(17.5) Hormone (17.6) oil (17.2) Simple triglyceride (17.2)

FXEg€ISTS Waxesand Simple Lipids (sections t7.l,t7.Zl

17.9 Write the general formula for an ester. 17.f 5 (a) lVhat happens, chemically when an oil is hy- 17.10 Name the two classesof organiccompounds that drogenated? (b) \A/tryis this processof great commer- are produced when are hydrolyzed. cial importance? f 7.f l (a) Name the following fatty acids, and state f 7.f 6 \iVhydo animal and vegetableoils become whether they are saturated or unsaturated. rancid when exposedto moist warm air? (b) \tVhichof them are solids and which are liquids at 17.17 Palmolive soap is mostly sodium palmitate. Write room temperature? the structure of this compound. (a) CH.(CHr)roCOOH 17.18 The following compound is hydrolyzed byboiling with sodium hydroxide. What (b) cHr(cHr)4cH:cHCH2cH: (cH2hcooH are the saponification products? (c) CH3(CHr)I4COOH (d) CH3(CH'hCH:CH(CH2)7COOH o 17.12 Decide whether the following fatty acids are most cH2-o-c-(cH2)r4cH3 abundant in animal fat or vegetable oil: (a) stearic acid, o (b) oleic acid, and (c) linoleic acid. 17.13 \.A/hatis a triglyceride? -o-c-(cHz)locHs 17.14 Write the structure for glyceryl trioleate, a simple o triglyceride. Would you expect this compound to be an oil or a fat?\iVhy? CH, -O-'- ('H2)7CH:CH(CH'7CH3 Exercises t49

ComplexLipids and CellMembranes 17.41 How does the structure of digitoxin (the major (Sections17.t,17.41 component of the drug digitalis) differ from that of all the other discussed? 17.19 Name the two categoriesof complexlipids. 17.42 Y{hatis the medicinal use of digitalis? 17.20 Write a general structure for the following complex lipids: (a) a phosphoglyceride and (b) a sphingomyelin. 17.21 What is the difference, structurally, between sphin- Prostaglandinsand leukotrienes gomyelins and phosphoglycerides? (Sections17.10, l7.l l) 17.22 Draw structural formulas for the products of com- plete hydrolysis of phosphatidyl choline. 17.43 Draw the basic structure for a prostaglandin mole- 17.23 Use diagrams to show the difference between a cule. liposome and a micelle. 17.44 How areprostaglandins synthesizedin the body? 17.24 \Nhat is the role of phospholipids in cell structure? 17.45 Prostaglandinsare among the most potent biologi- f 7.25 Explain how the degreeof unsaturation in mem- cal compounds knornm.\fhat are some of their physio- brane lipids affects the flexibility of cell membranes. logic effects? 17.26 Describe the-major features of the of membrane structure. L7.27 \,|{haIare the functions of membrane proteins? AdditionalExercises 17.28 Describe the two types of membrane proteins. 17.46 Match the following. (a) phosphoglyceride (1) long-chain esters Steroids(Sections | 7.5-l 7.t 0) (b) lipid bilayer (2) absent in (c) testosterone (3) fluid mosaic model 17.29 Draw the fundamental chemical structure that (d) lecithin (a) body'ssalt balance applies to all steroid molecules. (e) saponification (5) congestiveheart failure 17.30 \iVhatsteroid forms a large part of animal cell (f) fats (6) phosphateester membranes but is not found in plants? (g) wax (7) fat hydrolysis 17.31 \Mhat is a hormone. and where are steroid hor- (h) digitalis (8) highlysaturated mones produced? (i) cholesterol (9) male sexhormone (j) aldosterone (10) phosphatidyl choline 17.32 Cortisoneis a hormone.Whereis it producedin tffhich the body, and what is its biological function? 17.47 type of lipids are found in cell membranes? 17.33 Explain why a physician might prescribe cortisone 17.48 Explain the relationship between the nature of the shots before a patient has a kidney transplant operation. fatty acids of complex lipids (that is, whether they are saturated or unsaturated) and the fluidity of cell mem- 17.34 What is (a) an androgen and (b) an estrogen? branes. 17.35 Name (a)the primarymale sexhormone and (b) 17.49 Name all the functional groups in the following the three primary female sexhormones. ' compounds: !, i'5ut 17.36 Compare the structural formulas of testosterone (a) cortisone x and progesterone. How are these two molecules differ- (b) phosphatidyl choline ent? (c) testosterone x 17.37 Comment on the use and action of anabolic (d) diethylstilbestrol steroids. (e) prostaglandin E, z 17.38 \rVhatare the functions of the estrogensand prog- (f) sphingosine > esteronein the female ovarian cycle? (g) digitoxin 17.39 'vVhyis progesteroneineffective as an oral contra- (h) choline ; ceptive? (i) triolein. Y 17.40 \A7hatis the action of each of the following as an 17.50 Distinguish between a fat and an oil. oral contraceptive? f 7.5f Explain why saturated fatty acids have higher (a) the pill (b) the minipill (c) DES melting points than unsaturated fatty acids. 550 CHAPTER17 Lipids sHLS"3€SF{RHHE€eV} True/False 15. Prostaglandinsare involved in all the following regu- Iatory functions except l. A triglyceride contains three ester bonds. (a) timing of menstrual cycle. 2. Integral proteins of membranes help move small (b) body temperature regulation. moleculesthrough membranes. (c) musclecontraction. 3. The major component of most membranesis carbohy- (d) stomachacid secretion. drate. 16. \lVhich of the following statements is nottrue about a 4. Cholesterol is a sterol found in virtually all plants and sphingomyelin? . (a) It has an amide bond. 5. Increasing the percentageof unsaturated fatty acids (b) It has a phosphateester bond. in a membrane increasesits flexibility. (c) It has a glycerol backbone. (d) 6. Becausethe lipid moleculesin one layer of amembrane Choline is found at the polar head of the molecule. can move about freely, membranes are very permeable. 17. Sourcesof hormones in the body include (a) 7. The sexhormonetestosterone is producedonlybymales. the adrenal glands. (b) the ovaries. (c) thetestes. (d) alloftheabove. B. Triglyceridescontaining only saturated fatty acids are often spoiled by oxidative rancidity. 1B. The adrenal corticoids called glucocorticoids (a) produce the body'ssexcharacteristics. 9. In a liposome, the hydrophobic hydrocarbon tails (b) are used to reduce the risks of organ transplant form the juncture of the lipid bilayer. operations. 10. Aldosteroneis a mineralocorticoidhormone that (c) include the primary sexhormones. helps maintain the body's salt and water balance. (d) all contain at least one carbohydrate molecule. f9. Liquid oils are changed into solid fats by MultipleChoice (a)hydrogenation. (b)solidification. 11. The polar end of a lipid molecule (c) hydration. (d) rancidization. (a) is characterizedby long hydrocarbon chains. 20. Waxesare formed from long-chain (b) is hydrophobic. (a) acids and amines. (b) amines and . (c) interacts favorably with water. (c) alcohols and aldehydes. (d) acids and alcohols. (d) Both (a) and (b) are correct. 21. \tVhichof the following is norprimarily a female sex 12. The chemical structure common to all steroid mole- hormone? culesis (a) progesterone (b) estradiol (c) mestranol (d) estrone 22. In hydrolytic rancidity of triglycerides, which part of the molecule is attacked? (a) double bond (b) group (c) acid group (d) ester group 23. \iVhich of the following drugs is an important steroid producedby a plant? (a) androgen (b) digitalis (c) progestin (d) estrogen 24. Alkaline hydrolysis of a fat to make soap is called (a) glycolysis. (b) saponification. (c) hydration. (d) anabolication. 25. The "power stations" of a eukaryotic cell are the 13.Hydrolysis of a mixed triglyceride may (a) nucleolus. (b) Golgibodies. (a) give three different alcohols. (c)mitochondria. (d)peroxisomes. (b) give ethyleneglycol. 26. Lysosomesfunction in (c) give three different fatty acids. (a) breaking dor,tmcomplex molecules. (d) givephosphoric acid. (b) cellular reproduction. 14.A lipid moleculecomposed of glycerol,phosphoric (c) transportingproteins acrosscell membranes. acid, and two fatty acids is called a (d) protein synthesis. (a) glycolipid. (b)phosphoglyceride. (c) cholesterol. (d) sphingomyelin.