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AdvBio I, Ch 7 SAQ - Short Answer Questions(Chapter 7...

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Unformatted text preview: Short Answer Questions (Chapter 7, Glygobiology) 1. Explain why all mono- and disaccharides are soluble in water. 2. This compound is L-glyceraldehyde. Draw a stereochemieally correct representation of C—1 and C—2 of Dglucose. CHO l HOmC—H l €14ch 3. Define each in 20 words or less: (a) anomeric carbon; (b) enantiomers; (c) furanose and pyranose; (d) glycoside; (e) epimers; (f) aldose and ketose. 4. Draw the structure of any aldohexose in the pyranose ring form. (b) Draw the structure of the anomer of the aldohexose you drew above. (c) How many asymmetric carbons (chiral centers) does each of these structures have? ((1) How many stereoisomers of the aldohexoses you drew are theoretically possible? 5. In the following structure: CHZDH CHZDH /+—._0 J' D\ H0 If” “ff/H \ UH H OH H DH (a) How many of the monosaccharide units are furanoses and how may are pyranoses? (b) What is the linkage between the two monosaccharide units? (c) Is this a reducing sugar? Explain. 6. Define "reducing sugar." (b) Sucrose is a disaccharide composed of glucose and fructose (Glc((xl ——> 2)Fru). Explain Why sucrose is not a reducing sugar, even though both glucose and fructose are. 7. Match these molecules with their biological roles. (a) glycogen W viscosity, lubrication of extracellular secretions (b) starch H carbohydrate storage in plants (0) trehalose ._ transportistorage in insects (d) chitin M exoskeleton of insects (e) cellulose _ structural component of bacterial cell wall (1‘) peptidoglycan M structural component of plant cell walls (g) hyaluronate M extracellular matrix of animal tissues (h) proteoglycan _ carbohydrate storage in animal liver 8. The number of structurally different polysaccharides that can be made with 20 different monosaccharides is far greater than the number of different polypeptides that can be made with 20 different amino acids, if both polymers contain an equal number (say 100) oftotal residues. Explain why. 9. Describe one biological advantage of storing glucose units in branched polymers (glycogen, amylopectin) rather than in linear polymers. lO. Explain how it is possible that a polysaccharide molecule, such as glycogen, may have only one reducing end, and yet have many nonreducing ends. 1 l. What is the biological advantage to an organism that stores its carbohydrate reserves as starch or glycogen rather than as an equivalent amount of free glucose? 12. Draw the structure ofthe repeating basic unit of (a) amylose and (b) cellulose. 13. Explain in molecular terms why humans cannot use cellulose as a nutrient, but goats and cattle can. 14. The glycosaminoglycans are negatively charged at neutral pH. What components of these polymers confer the negative charge? 15. Sketch the principal components ofa typical proteoglycan, showing their relationships and connections to one another. 16. Describe the differences between a proteoglycan and a glycoprotein. 17. Describe the structure of a proteoglycan aggregate such as is found in the extracellular matrix. " 'fishesweenea'mfeizlyeafiianelweglyeoproteinil”, -e£aprowogl- nggregare‘sfié’h‘sm‘ "'“foun’dinwrheeew ’aeellu' " W fix. 18. What are some of the biochemical effects of the oligosaccharide portions of glycoproteins? 19. Describe the process by which "old" serum glycoproteins are removed from the mammalian Circulatory system. 20. What are lectins? What are some biological processes which involve lectins‘? 7. Match these molecules with their biological roles. (a) glycogen H viscosity. lubrication of extracellular secretions (b) starch W carbohydrate storage in plants (c) trehalose __. transport/storage in insects (d) chitin “ exoskeleton of insects (e) cellulose __ structural component of bacterial cell wall (1‘) peptidoglycan __ structural component of plant cell walls (g) hyaluronate W extracellular matrix of animal tissues (h) proteoglycan __ carbohydrate storage in animal liver 8. The number of structurally different polysaccharides that can be made with 20 different monosaccharides is far greater than the number of different polypeptides that can be made with 20 different amino acids, if both polymers contain an equal number (say 100) of total residues. Explain why. 9. Describe one biological advantage of storing glucose units in branched polymers (glycogen, amylopectin) rather than in linear polymers. 10. Explain how it is possible that a polysaccharide molecule, such as glycogen, may have only one reducing end, and yet have many nonreducing ends. 1 1. What is the biological advantage to an organism that stores its carbohydrate reserves as starch or glycogen rather than as an equivalent amount of free glucose? 12. Draw the structure of the repeating basic unit of(a) amylose and (b) cellulose. Ans: (a) For the structure of amylose, see Fig. 9—15a, p. 305. The repeating unit is cr—D- glucose linked to a-D-glucose; the glycosidic bond is therefore (Otl —> 4). (b) Cellulose has the same structure as amylose, except that the repeating units are B—D—glucose and the glycosidic bond is (Bl —> 4). (See Fig. 9-l7a, p. 307.) 13. Explain in molecular terms Why humans cannot use cellulose as a nutrient. but goats and cattle can. l4. The glycosaminoglycans are negatively charged at neutral pH. What components of these polymers confer the negative charge? 15. Sketch the principal components ofa typical proteoglycan, showing their relationships and connections to one another. ———-————————_._________________________________ Chapter 7 Carbohydrates and Glycobiology -—-———-————_______________________________ 1. To possess optical activity, a compound must be: A) a carbohydrate. B) a hexose. C) asymmetric. D) colored. E) D~glucose 2. Which of the following monosaccharides is not an aldose? A) erythrose B) fructose C) glucose D) glyceraldehyde E) ribose 3. The reference compound for naming D and L isomers of sugars is: A) fructose. B) glucose. C) glyceraldehyde. D) ribose. E) sucrose. 4. When two carbohydrates are epimers: A) one is a pyranose, the other a furanose. B) one is an aldose, the other a ketose. C) they differ in length by one carbon. D) they differ only in the configuration around one carbon atom. E) they rotate plane-polarized light in the same direction. 5. Which of the following is an epimeric pair? A) D-glucose and D—glucosamine B) D—glucose and D-mannose C) D—glucose and L-glucose D) D-lactose and D—sucrose E) L—mannose and L—fructose 6. Which of following is an anomeric pair? A) D-glucose and D-fructose B) D~glucose and L-fructose C) D—glucose and L-glucose D) oc—D~glucose and B-D-glucose E.) oc«D-glucose and B~L—glucose Chapter 7 Carbohydrates and Glycobiology 81 7. When the linear form of glucose cyclizes; the product is a(n): A) anhydride. B) glycoside. C) hemiacetal. D) lactone. E) oligosaccharide. 8. Which of the following pairs is interconverted in the process of mutarotation? A) D—glucose and D-fructose B) D-glucose and D~galactose C) D-glucose and D-glucosamine D) D—glucose and L—glucose E) oc-D-glucose and B-D-glucose 9. Which ofthe following is not a reducing sugar? A) Fructose B) Glucose C) Glyceraldehyde D) Ribose E) Sucrose 10. Which of the following monosaccharides is not a carboxylic acid? A) 6—phospho—gluconate B) gluconate C) glucose D) glucuronate E) muramic acid 11. D-Glucose is called a reducing sugar because it undergoes an oxidation—reduction reaction at the anomeric carbon. One of the products of this reaction is: A) Degalactose. B) D—gluconate. C) D—glucuronate. D) D—ribose. E) muramic acid. 12. From the abbreviated name of the compound Gal(Bl —> 4)Glc, we know that: A) (2—4 of glucose is joined to C—1 of galactose by a glycosidic bond. B) the compound is a D—enantiomer. C) the galactose residue is at the reducing end. D) the glucose is in its pyranose form. E) the glucose residue is the B anomer. 82 Chapter 7 Carbohydrates and Glycobiology 13. Starch and glycogen are both polymers of: A) fructose. B) glucose 1 -phosphate. C) sucrose. D) OL-D—glucose. E) fi~D-glucose. 14. Which of the following statements about starch and glycogen is false? A) Amylose is unbranched; amylopectin and glycogen contain many (Otl _.) 6) branches. B) Both are homopolymers of glucose. C) Both serve primarily as structural elements in cell walls. D) Both starch and glycogen are stored intracellularly as insoluble granules. E) Glycogen is more extensively branched than starch. 15. Which of the following is a heteropolysaccharide? A) Cellulose B. Chitin C. Glycogen D. Hyaluronate E. Starch 16. The basic structure of a proteoglycan consists of a core protein and a: A) glycolipid. B) glycosaminoglycan. C) lectin. D) lipopolysaccharide. E) peptidoglycan. 17. In glycoproteins, the carbohydrate moiety is always attached through the amino acid residues: A) asparagine, serine, or threonine. B) aspartate or glutamate. C) glutamine or arginine. D) glycine, alanine, 0r aspartate. E) tryptophan, aspartate, or cysteine. 18. Which of the following is a dominant feature of the outer membrane of the cell wall of gram negative bacteria? A) Amylose B) Cellulose C) Glycoproteins D) Lipopolysaccharides E) Lipoproteins 19. The biochemical property of lectins that is the basis for most of their biological effects is their ability to bind to: A) amphipathic molecules. 8) hydrophobic molecules. C) specific lipids. D) specific oligosaccharides. E) specific peptides. ...
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