1. Define the following terms
(1) Polysaccharide (2) Furanose (3) Pyranose (4) Chiral carbon (5) Conformation (6) Configuration (7) Epimer (8) Enantiomer (9) Diastereomer
(10) Stereoisomer (11) Lectin (12) Anomeric carbon atom (13) Glycosidic bond (14) Glycoform (15) Molecular recognition (16) O-Glycosidic linkage (17) N-glycosidic linkage
Carbohydrate and Glycobiology
2. Mono-Choice Questions
(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 following is an anomeric pair? A. D-glucose and D-fructose B. D-glucose and L-fructose C. D-glucose and L-glucose D. α-D-glucose and β-D-glucose Ε. α-D-glucose and β-L-glucose (6) When the linear form of glucose cyclizes, the product is a(n): A. anhydride. B. glycoside. C. hemiacetal. D. lactone. E. oligosaccharide. (7) 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 Ε. α-D-glucose and β-D-glucose (8) Which of the following is not a reducing sugar? A. fructose B. glucose C. glyceraldehyde D. ribose E. sucrose (9) From the abbreviated name of the compound Gal(β1 → 4)Glc, we know that: A. C-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 β anomer. (10) Starch and glycogen are both polymers of: A. fructose. B. glucose1-phosphate.
C. sucrose. D. α-D-glucose. Ε. β-D-glucose. (11) Which of the following statements about starch and glycogen is false? A. amylose is unbranched; amylopectin and glycogen contain many (α1 → 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. (12) Which of the following is a heteropolysaccharide? A. cellulose B. chitin C. glycogen D. hyaluronate E. starch (13) 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, or aspartate. E. tryptophan, aspartate, or cysteine. (14) The biochemical property of lectins that is the basis for most of their biological effects is their ability to bind to: A. amphipathic molecules. B. hydrophobic molecules. C. specific lipids. D. specific oligosaccharides. E. specific peptides. (15) Carbohydrates are A. polyhydroxy aldehydes. B. polyhydroxy ketones. C. polyhydroxy acids. D. polyhydroxy alcohols. E. A and B. (16) The simplest carbohydrates are A. D- and L-glyceraldehyde. B. dihydroxyacetone and D- and L-glyceraldehyde. C. dihydroxyacetone and glycerate.
D. all of the above. E. none of the above. (17) The nutritional storage form(s) of glucose in plants. A. glycogen B. amylose C. amylopectin D. B and C E. all of the above (18) How do some viruses gain entry into specific cells? A. by attaching to ion channels B. by cleaving the glycosidic bonds and altering protein shapes C. by binding to glycoproteins on the cell surface that are unique to specific cells D. all of the above. E. none of the above. (19) Which of the following statements is true about the cyclic (ring) form of D–glucose? A. the cyclic form of D–glucose is a furanose. B. the cyclic form of D–glucose involves the formation of a covalent bond between the carbonyl group and the oxygen of a hydroxyl group along the chain. C. the cyclic form of D–glucose is the result of a bond forming between the C–1 and C–6 carbon atoms. D. in aqueous solution, the cyclic form of D–glucose is rare. (20) Which of the following is true about how a disaccharide is formed from two monosaccharides? A. monosaccharides are linked in a reaction that eliminates water. B. disaccharides form when a hydoxyl group of one monosaccharide reacts with the hydroxyl group of another monosaccharide. C. a disaccharide consists of two monosaccharides linked to each other by an N-glycosidic bond. D. disaccharides are formed by a hydrolysis reaction. (21) The reducing end of a disaccharide or a polysaccharide is A. the end with an anomeric carbon that cannot be oxidized. B. the end that does not have an anomeric carbon. C. the end of a chain with a free anomeric carbon (i. e., not involved in a glycosidic bond). D. the end whose sugar cannot take the linear form. (22) What is the C-4 epimer of glucose? A. allose B. mannose C. gulose D. galactose
E. fructose (23) An N-linked glycan would be attached to ______ while an O-linked glycan would be attached to ________. A. Asn; Ser B. Lys; Tyr C. Gln; Thr D. Arg; Ser E. Lys; Ser (24) Which are possible conformations of a furanose molecule? A. envelope and twist. B. chair and boat. C. cis and trans. D. A and B. (25) What type of bond links the monomers of a polysaccharide? A. glucotide bond. B. phosphate ester bond. C. peptide bond. D. glycosidic bond. (26) Who received a Nobel Prize in 1937 for his work on the structures of carbohydrates and the synthesis of Vitamin C? A. Linus Pauling. B. Walter Haworth. C. Max Perutz. D. Emil Fisher. (27) Which statement is false about the sugar units in DNA? A. they are cyclic in DNA. B. it is a deoxy form of ribose. C. it is an epimer of glucose. D. it has a D-configuration. (28) Chitin is A. found in insect and crustacean shells. B. found in fungi cell walls. C. composed of N-acetylglucosamine subunits. D. composed of linear fibrils like cellulose. E. all of the above. (29) A carbohydrate that gives two molecules when it is completely hydrolyzed is known as a
A. monosaccharide. B. disaccharide. C. polysaccharide. D. starch. E. trisaccharide. (30) Which group of carbohydrates cannot be hydrolyzed to give smaller molecules? A. monosaccharides B. disaccharides C. trisaccharides D. oligosaccharides E. polysaccharides (31) In the L- isomer of a Fischer projection of a monosaccharide, the -OH group furthest from the carbonyl is written A. on the left of the top chiral carbon. B. on the right of the top chiral carbon. C. on the left of the middle chiral carbon. D. on the left of the bottom chiral carbon. E. on the right of the bottom chiral carbon. (32) One difference between D-glucose and L-glucose is A. the open-chain form of L-glucose does not exist. B. it is not possible to make L-glucose. C. L-glucose has a 5-membered ring , and D-glucose has a 6-membered ring. D. only D-glucose can act as a substrate in metabolic reactions. E. L-glucose cannot form a closed structure. (33) In a disaccharide, two monosaccharides are joined by what kind of bond? A. double B. anomeric C. alcohol D. glycosidic E. rotational (34) Which of the following contains a β-1,4-glycosidic bond? A. galactose B. lactose C. maltose D. sucrose E. amylose (35) Maltose is a A. monosaccharide.
B. disaccharide. C. trisaccharide. D. polysaccharide. E. phosphosaccharide. (36) Amylose is a A. monosaccharide. B. disaccharide. C. trisaccharide. D. polysaccharide. E. phosphosaccharide. (37) Galactose is a A. monosaccharide. B. disaccharide. C. trisaccharide. D. polysaccharide. E. phosphosaccharide. (38) Which of the following contains α-1,6-branches? A. amylose B. glycogen C. cellulose D. sucrose E. maltose (39) Cellulose is not digestible by humans because it contains glucose units linked by ________-glycosidic bonds. A. α-1,2 B. α-1,4 C. α-1,6 D. β-1,2 E. β-1,4 (40) Amylose is a form of starch which has A. only β-1,4-bonds between glucose units. B. only α-1,4-links bonds glucose units. C. both α-1,4-and β-1,4-bonds between glucose units. D. hemiacetal links joining glucose units. E. carbon-carbon bonds joining glucose units. (41) Amylopectin is a form of starch which has A. only β-1,4-bonds between glucose units. B. only α-1,4-links bonds glucose units.
C. both α-1,4-and α-1,6-bonds between glucose units. D. hemiacetal links joining glucose units. E. carbon-carbon bonds joining glucose units. (42) Cellulose is a polysaccharide which has A. only β-1,4-bonds between glucose units. B. only α-1,4-links bonds glucose units. C. both α-1,4-and α-1,6-bonds between glucose units. D. hemiacetal links joining glucose units. E. carbon-carbon bonds joining glucose units. (43) Humans cannot digest cellulose because they A. lack the necessary enzymes to digest β-glycosides. B. are allergic to β-glycosides. C. are poisoned by β-glycosides. D. have intestinal flora which use up β-glycosides. E. cannot digest chlorophyll. (44) Aspartame? and Saccharin? are two examples of A. disaccharides. B. polysaccharides. C. chlorosaccharides. D. alcohol sweeteners. E. noncarbohydrate sweeteners. (45) Under acid hydrolysis conditions, starch is converted to A. glucose. B. xylose. C. maltose. D. galactose. E. fructose. (46) Fructose does not undergo hydrolysis because it is a A. aldose. B. hexose. C. reducing sugar. D. monosaccharide. E. disaccharide. (47) Galactose is a product of enzymatic hydrolysis of A. lactose. B. glucose. C. maltose. D. erythrose.
E. sucrose. (48) Which is not a glycoconjugate? A. Proteoglycan. B. Glycolipid. C. Glycoprotein. D. Homoglycan. (49) A saccharide is a ________. A. lipid B. carbohydrate C. nucleic acid D. protein (50) Which is a general term indicating a carbohydrate polymer? A. Glycan. B. Polycarb. C. Multimer. D. Oligosaccharide. (51) Which does not apply to dihydroxyacetone? A. Ketose. B. Triose. C. Chiral. D. Water-soluble. (52) Which structure is NOT a carbohydrate? A.
(53) Which is true about naturally occurring monosaccharides? A. The L-isomers predominate. B. The D-isomers predominate. C. The L and D-isomers occur in equal ratios. D. The ratio of L and D-isomers varies widely depending on the source. (54) Examine the Fischer projection below. How is this carbohydrate classified?
A. L enantiomer; aldopentose. B. L enantiomer; ketopentose. C. D enantiomer; aldohexose. D. D enantiomer; ketopentose. (55) The Fischer projections of linear D-glucose and D-galactose are shown below. These two molecules are ________.
A. epimers B. enantiomers
C. anomers D. structural (constitutional) isomers (56) The structures of D-ribose and D-arabinose are shown below. These two molecules are ________.
A. epimers B. enantiomers C. tautomers D. anomers (57) The intramolecular cyclization reaction of glucose in solution ________. A. generates a chiral center B. yields a hemiacetal C. usually forms a pyranose D. All of the above (58) Below is the Fischer projection of D-galactose. Which is the proper Haworth projection of β-D-galactopyranose?
A. I B. II C. III D. IV (59) Below is the structure for a cyclic D-monosaccharide. Which is the anomeric carbon atom?
A. 1 B. 2 C. 3 D. 4 E. 5 (60) The compounds α-D-fructofuranose and β-D-fructofuranose are ________. A. enantiomers B. mutamers C. anomers D. conformational isomers (61) Anomers can be interconverted ________.
A. by rotation about carbon-carbon bonds B. via a linear intermediate C. by an isotopic exchange reaction D. None of the above. Anomers cannot be interconverted. Ans: B (62) The abbreviation for glucose is ________. A. Glu B. Gcs C. Glc D. Gluc (63) The major proteoglycan in cartilage is ________. A. hyaluronic acid B. cellobiose C. link protein D. aggrecan (64) Which of the following polysaccharides contains exclusively glucose in (1 4) glycosidic bonds? A. amylose B. amylopectin C. glycogen D. cellulose E. chitin (65) A. B. C. D. E. (66) A. B. C. D. E. (67) A. B. C. Which of the following explains the importance of sucrose as a disaccharide? the glycosidic bond is much more stable than a typical glycosidic bond the presence of two glucose residues provides a readily available glucose source β-glycosidic bonds are much more stable than -glycosidic bonds since both anomeric carbons are involved in the glycosidic bond, oxidation is limited none of the above How many stereoisomers would be expected from a ketohexose? 4 8 16 32 64 Which of the following formulas would be a carbohydrate C5H12O5 C4H8O6 C6H10O6
3. True/False Questions
(1) Most of the carbohydrates on earth are produced by photosynthesis in plants. (2) All carbohydrates have the empirical formula (CH2O)n. (3) The simplest aldose is the chiral molecule glyceraldehyde. (4) All D-enantiomers of carbohydrates are dextrorotatory. (5) The ketohexoses have fewer chiral carbon atoms than the aldohexoses. (6) The reaction between one molecule of alcohol and one molecule of aldehyde yields an acetal. (7) In solution only one anomeric form of a monosaccharide will be present. (8) Furanoses have more three-dimensional conformations than pyranoses. (9) Steric strain is a major factor in determining the conformations of a monosaccharide that predominate in solution. (10) The chair conformation of furanoses is generally preferred to minimize steric repulsion. (11) Vitamin C is an enediol of a lactone and is vital in the synthesis of collagen. (12) The sugar derivative found in DNA is an oxidized form of ribose. (13) Sugar alcohols do not have a carbonyl group. (14) DNA could be referred to as a glycoside. (15) Both nucleotides and nucleosides are glycosides. (16) For cattle, cellulose is a storage homoglycan. (17) The main difference between structures of amylopectin and glycogen is the specific sugar subunit. (18) Homoglycans are used for storage, while heteroglycans are used for cell structure. (19) α-amylases hydrolyze α(1→4) linkages and β-amylases hydrolyze β(1→4) linkages, but neither attack α1→6) linkages.
(20) Enzymes that hydrolyze cellulose cannot hydrolyze amylopectin. (21) Cellulose cannot be degraded in cattle. (22) Enzymatic lengthening and degradation of glycogen occurs only at the non-reducing ends. (23) An oligosaccharide nodulation factor from one species can stimulate symbiosis in another species. (24) Unlike proteins, whose primary structures are encoded in DNA, polysaccharides have very little structural variations. (25) Heteroglycan chains may or may not be covalently bound to proteins in proteoglycans. (26) The heteroglycan component of the cell wall is the same in all bacteria, but the cross-linking polypeptide is not. (27) Some glycoproteins may have identical protein components and variable polysaccharide components. (28) The large number of possible oligosaccharide structures in glycoproteins is limited in cells by the kinds of enzymes available for their synthesis. (29) Sucrose is a disaccharide. (30) A reducing sugar gives a precipitate of silver metal with Benedict's reagent. (31) Sucrose is made up of glucose units only. (32) Amylopectin is a straight-chain polysaccharide. (33) Sucrose is a reducing sugar.
4. Matching Questions
(1) Select the correct carbohydrate for each description. A. sucrose B. glycogen C. galactose D. maltose E. glucose F. cellulose G. fructose H. lactose I. amylase
1) a carbohydrate that cannot be digested by humans 2) a disaccharide that occurs as a breakdown product of starch 3) a carbohydrate that stores energy in the human body 4) a carbohydrate that is used to build cell walls in plants 5) a monosaccharide that combines with glucose to form lactose 6) a disaccharide found in milk and milk products 7) a disaccharide consisting of glucose and fructose 8) a monosaccharide found in fruit juices and honey, the sweetest carbohydrate 9) an unbranched carbohydrate that stores glucose in plants 10) the product when maltose is hydrolyzed (2) Indicate the monosaccharide(s) produced upon hydrolysis of each carbohydrate. A. glucose + galactose B. glucose + fructose C. glucose 1) amylopectin 2) lactose 3) glycogen 4) maltose 5) sucrose
5. Short Answer Questions
(1) Draw the Fischer projection structures of all of the trioses and name them. (2) How is the D or L configuration determined? (3) Compare the structures of amylopectin and amylose. (4) How does glycogen differ from starch in structure and function? (5) Draw Howorth projection formulas for dimmers of glucose with the following types of glycosidic linkages: 1). A β(1→4) linkage (both molecules of glucose in the β form) 2). An α, α(1→1) linkage 3). A (1→6) linkage (both molecules of glucose in the β form) (6) Glycogen is highly branched. What advantage, if any, does this provide an animal? (7) No animal is able to digest cellulose. Try to explain this statement with the fact that many animals are herbivores that depend heavily on cellulose as a food source. (8) What are the chemical and structural differences between cellulose and glycogen?
(9) List some of the reasons carbohydrates are considered important molecules. (10) Using the structure of D-altrose, shown below, show a Haworth projection for the β anomer.
(11) Starch, cellulose, and glycogen are all polysaccharides composed of glucose. What makes each of these polysaccharides unique in spite of the fact that all are composed solely of glucose? (12) List some of the reasons carbohydrates are considered important molecules.
6. Fill in The Blanks
(1) ________ is the major storage polysaccharide for animals, while ________ is the major storage polysaccharide for plants. (2) Cellulose is a polymer of ________, a common monosaccharide. (3) ________ and ________ are the two kinds of sugars found in bacterial cell walls. (4) The ________ projection illustrates saccharides as linear, whereas the ________ projection suggests the spatial relationships of saccharides. (5) Structurally, starch exists as both unbranched polysaccharide chains called ________ and branched polysaccharide chains called ________. (6) A _______________ is a stereoisomer that is not a mirror image.
(7) A _______________ is a five-membered ring formed from a monosaccharide. (8) When an open-chain monosaccharide cyclizes into a ring, it forms a _______________. (9) Plant starch is composed of amylose, a linear polymer of glucose, and a branched polymer of glucose referred to as _______________. (10) Maltose is composed of two molecules of glucose linked together by a(n) ____________ glycosidic bond.
(11) _______________ is a galactose joined to a glucose by a β-1,4 glycosidic bond. (12) In N-linked glycoproteins, the carbohydrate portion is attached to a(n)_____________ residue in the protein. (13) A given protein with several potential glycosylation sites can cave many different glycosylated structures called ________________. (14) The influenza virus recognizes _______________ residues of glycoproteins present on cell surface.
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