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Practice Problems on Carbohydrates

Practice Problems on Carbohydrates

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Practice Problems on Carbohydrates

1. Which one of the following is a heptulose? CH2OH C O H O H HO C H H OH H OH A B H C OH H OCHO H C OH OH H H H CH2OH

OH O H H D H C HO H OH H OH CH2OH O H HO CH2OH H OH H H HO H HO OH OH H H H CH2OH O HO H E H HO CH2OH OH H HO

2. Based on the names, which one of the following does NOT have an aldehyde?

A) B) Tagose C) D) E)

3. Which formula correctly represents a simple ?

A) C5H5O5

B) C5H5O10

C) C4H8O4

D) C6H10O6

E) C4H12O6

Carbohydrates.2

4. Which one of the following structures correctly represents -D-altropyranose?

H HO H CH2OH O CH2OH O CH2OH O HO HO OH H H H H H OH H H OH H HO OH OH OH H HO H HO H H H A B C

H H

CH2OH O CH2OH O HO HO OH H H H OH HO H H H OH H OH HO H D E

5. Which one of the following is not an ?

H CH OH OH OH A 2 B C OH OH HO HO H OH HO O H H H O H CH2 H CH 2 H CH2 HO O

H H D CH2OH E OH H H HO O HO O HO H H OH HO H H H H OH HO H

6. Which one of the following is a ketohexose?

OH OH CH2OH CH2OH OH OH CH2OH A B OH D HO OH C O OH OH OH O O HO O O HOCH2 OH OH CH2OH CH2OH OH E OH HO CH2OH OH O

Carbohydrates.3

7. Which one of the following compounds is a glycoside? O O H C CH H H 3 C CH2O CH OH O CH2OH O 2 O CH3 O HO O H H H C B H H OH H H CH3 O A HO OH O OH C O OH OCH H 3 O H3C C H H H H H O

H CH3 CH2OH O CH2 HO CH3 H H D O O E H HO OCH2 O H OH H OH CH3O H H CH O H 2 H

8. Which one of the following structures correctly represents -L-galactopyranose?

HO OH CH OH CH2OH 2 O O

HO OH OH HO HO A OH B

OH HO OH CH OH O O 2 O HO OH HO OH HO OH OH HO CH2OH CH2OH OH

C D E

9. How many (aldohexoses and 2-ketohexoses) are possible?

A) 8 B) 12 C) 16 D) 24 E) 46

Carbohydrates.4

10. Which one of the following compounds is not a glycoside?

OH HO B CH2OH A O O O OH HO COO HO OCH3 OH NH2

CH3 CH2 D CH OH O HO 2 COOH C CH2 CHO O O O HO COO NH HO CO OH O CH3 OH

E CH2OH O HO + Cl HO O O OH

HO OH

11. Which one of the following molecules is most likely to form a cyclic in neutral solution?

HC O A HC O B C HC O D HC O H C OH H C OH H C OH H C OCH3 H CH H COH H CO H COCH2 CH3 H CH H CO O CH H CH CH2 H2C C H COCH3 H CO H CH H COH CH3 CH OH CH2OH 2 CH2O CH2O CO

E HC O CH3 H C O CH2 H COH

CH3O CH

H COCOCH3

CH2O

Carbohydrates.5

12. Which one of the following is a ?

CH OH 2 H OH CH2OH CH2OH OH H CH2OH CH2OH O H OH OH O O H HO H H H H H H OH H H HO HO O OH H H H H H O H HO OH HO H O H H H H OH CH2OH OH H OH H CH2OH A B C D E

13. Which one of the following compounds is a glycoside? O

HN

O N HO HO O HO O O O HO O OCH3 OH HO H3CO OH OH OCH3 ABC

OH OCH OH 3 O H CO O 3 OCH3 OH H3CO OH OCH3

D E

14. Peonin (shown below) is a red pigment found in the petals of peony flowers. Which monosaccharide(s) would be produced by acid of peonin? OCH3 OH

O H H H OH CH2OH O HO OH HO O H O H H O CH2OH HO II OH H H H H I A) D- and D- B) L-glucose and D-mannose C) D-glucose and D- D) D-glucose only E) L-galactose only Carbohydrates.6

15. Referring to the previous question, what is the stereochemistry of the two glycosidic bonds denoted by I and II?

A) I: and II: B) I: and II: C) I: and II: D) I: and II:

16. Which one of the following statements is NOT correct? A) D-Glucose and D- have the same configuration at the penultimate carbon but different configurations at carbon 4. B) D-Glucose and D-gulose are diastereomers, but D-glucose and L-glucose are enantiomers. C) D-Gulose and D- have the same configuration at the penultimate carbon. D) D-Glucose and D-gulose both must be dextrorotatory because they are both D . E) D-Glyceraldehyde is dextrorotatory, and L-glyceraldehyde is levorotatory.

17. Which of the following statements about D-2- (the monosaccharide in DNA) is/are most likely to be correct?

a. it can exist as two b. it can exist as two anomers c. reaction of it with NaBH4 gives an optically inactive product

A) b only B) c only C) a and b only D) a and c only E) all three statements are correct

Carbohydrates.7

18. Which one of the following would show when dissolved in water?

a)OH b) OH H O H O H H O H OHH OH H HO HO OCH3 H OH H OH

c) OH d) OH e) CHO O H O H H H H H H OH OH OHH OH H OH HO O OH HO O H H OH O H H OH H OH H OH OHH H O H OH H H OH

19. Consider the equilibrium shown below; the optical rotation values are given for each of the cyclic molecules. Which one of the following statements is true?

HO HO HO CH2OH O CH2OH OH CH2OH O

OH HO HO O HO OH OH OH H OH

[ ]D25 = +20 [ ]D25 = +110

A) The and anomers are enantiomers, related by inversion of stereochemistry at C1. B) The process of interconversion is termed racemization C) The acyclic intermediate is achiral D) The and anomers are diastereomers E) Mutarotation occurs for aldose only

Carbohydrates.8

20. A student dissolved -D-galactose in acid, placed the solution in a sealed tube, and then monitored the optical activity of the solution in a polarimeter over time. Which statement best explains the data collected below?

160 140 120 100 80 60 036912 Time (hours)

A) A portion of the -D-galactose was converted to -D- B) A portion of the -D-galactose was hydrolyzed to two smaller sugars C) A portion of the -D-galactose was converted to -D-glucose D) The solution of -D-galactose evaporated over time E) -D-galactose formed an equilibrium mixture with -D-galactose

21. Which one of the following statements is not correct?

A) Individual units of sugars are typically linked by O-glycoside bonds to form oligomers and polymers. B) In the acid-catalyzed formation of a hemiacetal from an aldehyde and an , the carbonyl group is protonated to make it better nucleophile. C) Acetals are resistant to alkaline (basic) conditions. D) readily revert to their aldehyde and alcohol components under neutral, acidic, or basic conditions. E) Bases of nucleic acids are linked to sugars via N-glycoside bonds.

Carbohydrates.9

22. Bromine water can be used to oxidize to aldonic acids. What is the reduction product formed in this reaction?

A) HBrO3 + B) Br3 C) HBr D) HOBr

E) Br2

23. Which one of the following compounds can be readily oxidized by Br2/H2O?

H a) H OH c) H OH e) HO OH OH HO H HO OH H OH H H O O H O OH H O OH

b) OH d) H OH H O OH OH H OHH OH HO OH HO H OH H OH

24. The oxidation of D- by nitric acid gives the same optically active diacid as the oxidation of which other ?

A) L-Talose B) L- C) D-Galactose D) D-Altrose E) L-Gulose

25. D- is converted by nitric acid into the same aldaric acid as that obtained from the reaction of which other sugar with nitric acid?

A) L- B) L- C) D-xylose D) D- E) D-ribose Carbohydrates.10

26. Reduction of D- with NaBH4 forms equal amounts of two products, Y and Z, i.e. 50% yield of each. Product Y does not rotate plane-polarized light. Similar reduction of which one of the following sugars would give product Z in 100% yield?

A) D-xylose B) D-xyulose C) D-glucose D) D-lyxose E) D-ribose

27. An aldohexose was oxidized with nitric acid, and the product was found to be the structure shown below. The original sugar could have been which one of A - E?

COOH H OH H OH HO H H OH COOH

A) D-gulose or L-glucose B) D-glucose or D-talose C) D-altrose or L-talose D) L-idose or D-galactose E) D-idose or L-gulose

Carbohydrates.11

28. Which one of the following molecules gives a positive Tollens’ or Benedict’s test? CH3 O CH3 CH2OH HOCH2 O H H C C HO O 2 O OCH CH OH H O 2 3 HO H OH O O O H HO HO H H H CH OH HO OH 2 CH 3 HOH A B C

CH3 CH2OH O H OH H O O H H H H OH H HO H HO H

CH3O H H OH

D E

29. A positive Benedict’s test is indicated by the precipitation of a brick-red solid from the blue solution. Which one of the following compounds is the brick-red solid?

A) Cu2O

B) CuSO4

C) CuCl2

D) Ag2O E) Ag metal

30. Acid-catalyzed hydrolysis of one mole of gives one mole of glucose and one mole of fructose. Which compound(s) is (are) responsible for the positive Benedict's Test that one obtains after hydrolysis of sucrose?

A) Glucose B) Fructose C) Glucose and fructose D) Sucrose E) Sucrose, glucose, and fructose

Carbohydrates.12

31. A monosaccharide was treated with Benedict’s reagent, which produced a red precipitate. When the resulting solution was acidified, two aldonic acids, D-allonic acid and D-altronic acid, were isolated. Bromine water had no effect on the monosaccharide. What is the most likely identity of the monosaccharide?

A) D- B) D-altrose C) D-idose D) D-tagulose E) D-

32. A reducing monosaccharide is heated in dry with catalytic hydrochloric acid. The product of this reaction is now a nonreducing sugar. What has most likely happened?

A) glycoside formation B) lactone formation C) hydrolysis D) oxidation E) reduction

33. Which one of A – E is least likely to be formed when D-glyceraldehyde is treated with sodium hydroxide?

O H OH CH2OH A) O B) H OH C) OH CH2OH CH2OH CH2OH CH2OH HO CHO H O

D) H OH E) HO H H OH CH2OH CH2OH

Carbohydrates.13

34. The glucose- TPI catalyzes the reversible conversion of glyceraldehyde-3-phosphate and phosphate, as shown below. Which one of A-E is least likely to be an intermediate along the conversion pathway?

CHO CH2OH TPI H OH O 2- 2- CH2OPO3 CH2OPO3

H OH C CHOH CH2OH A) O B) O C) O 2- 2- 2- CHOPO3 CH2OPO3 CH2OPO3

CHO H O C D) OH E) OH 2- CH2OPO3 2- CH2OPO3

The next three questions refer to the following information: Kiliani Fischer extension of D-lyxose gives rise to two aldohexoses, X and Y.

35. What is the stereochemical relationship between the two aldohexoses X and Y?

A) anomers B) enantiomers C) structural isomers D) diastereomers E) identical compounds

Carbohydrates.14

36. When the two aldohexoses X and Y are treated separately with NaBH4, X gives rise to an optically inactive product. Why is the product optically inactive?

A) Treatment with NaBH4 destroys the stereocentres so it is no longer chiral B) The product is a meso compound C) The experimentalist made a mistake – it has to be chiral. D) The starting aldohexose was not chiral, so the product should not be either E) A racemic mixture was formed

37. What is the identity of the optically active product from the reaction of Y with NaBH4?

A) D-talitol B) D-glucitol C) D-mannitol D) D-galactitol E) D-lyxitol

38. A gave an optically inactive product when treated with HNO3. When the same hexose was treated with NaCN/H2O followed by hot aqueous acid, NaOH/H2O, aqueous acid again and finally Na(Hg) at pH 3, two monosaccharides were produced. One of these gave an optically inactive product on treatment with HNO3, while the other gave an optically active product under the same conditions. What is the most likely identity of the original hexose?

A) D-galactose B) D-altrose C) D-mannose D) D-allose E) D-

Carbohydrates.15

NH 39. Which one of A – E is least likely to be involved in the acid- HC catalyzed hydrolysis of the compound on the right? H OH

CH2OH

OH NH2 2 HC HC NH A) B) C) 2 H OH H OH CH2OH 2 CH2OH OH H2C D) E) H OH

CH2OH 2

40. How many of the following compounds can form an acyclic (non-cyclic) structure when treated with a base, such as aqueous NaOH?

Carbohydrates.16

41. Refer to the structure of Splenda in the previous question. What is the sugar corresponding to the furanose ring?

A) 1,6-dideoxy-1,6-dichloro-D-sorbose B) 1,6-dideoxy-1,6-dichloro-L-fructose C) 3-deoxy-3-chloro-D-glucose D) 3-deoxy-3-chloro-L-mannose E) 1,6-dideoxy-1,6-dichloro-D-fructose

42. Which one of the following best explains the origin of the term invert sugar?

A) Sucrose, when dissolves in water, mutarotates to an equilibrium specific rotation of the opposite sign B) The sign of the specific rotation of sucrose is opposite to that of a solution of hydrolyzed sucrose C) Upon dissolution, each stereocentre in sucrose undergoes inversion D) Upon dissolution, the anomeric carbon in the glucose fragment of sucrose undergoes inversion E) Upon treatment with acid, a racemic mixture of sucrose is obtained.

43. When a solution of sucrose is treated with an enzyme from the stomach of the bee, the optical rotation is observed to change from +66 to 40 degrees. This phenomenon is best described as?

A) Racemization B) Oxidation C) Mutarotation D) Hydrolysis E) Isomerization

Carbohydrates.17

44. Which one of the following statements about is true?

A) Cellulose is fermented to by numerous microorganisms B) Ruminants can synthesize a enzyme C) Cellulose and are constitutional isomers D) invariably act outside the cell that synthesized them E) Cellulose represents 10% of the world's total biomass carbon

45. Why must the enzyme cellulase work outside the organism that hosts it?

A) Cellulose is too highly charged to pass through the cell wall B) Cellulose is too insoluble to pass through the cell wall C) Cellulose is too non-polar to pass through the cell wall D) Cellulose is too soluble to pass through the cell wall E) is too soluble to pass through the cell wall

46. Why is a source of glucose for human nutrition, but cellobiose is not? OH OH O OH HO OH O HO HO O OH O HO O O OH HO HO OH OH OH maltose OH cellobiose

A) Human require the - at the reducing end of the sugar. B) Cellobiose is too insoluble to be attacked by human enzymes which only work in solution C) Cleavage of cellobiose gives a monosaccharide which is not glucose D) The cellobiose acetal link is inherently resistant to acid hydrolysis. E) Humans only possess the enzyme to catalyze the hydrolysis the - glycosides, and cellobiose has the -geometry.

Carbohydrates.18

47. Which one of the following statements about is NOT correct?

A) Cellulose and maltose differ in the stereochemistry of the glycosidic bonds B) Amylose and store D-gulose for later use as an energy source C) Cellulose and maltose are both made up of D-glucose units D) Amylopectin contains branched chains of D-glucose units E) Cellulose is a fibrous structural material in plants

48. Which one of the following statements about starch is not correct?

A) Both amylose and amylopectin contain (1 6) glycosidic bonds B) Both amylose and amylopectin are polymers of glucose C) Both amylose and amylopectin yield maltose upon partial hydrolysis D) Both amylose and amylopectin contain (1 4) glycosidic bonds E) Amylose is a linear polysaccharide, while amylopectin is a branched polysaccharide

49. Write out a detailed mechanism for the phosphorylation of glucose by the ATP- dependent enzyme hexokinase. What is the chemical function of Mg2+?

50. Thiamine pyrophosphate, together with lipoic acid, is used for what type of reaction?

A) Phosphorylation B) Reduction C) Oxidative decarboxylation D) Dehydration E) Aldol reaction

Carbohydrates.19

51. Write a mechanism for the conversion of pyruvate to acetyl CoA. Assume all of the required coenzymes are present.

52. The mechanism of transaminase uses which coenzyme as a carrier of an amino group?

A) Alanine B) Coenzyme A C) NAD+

D) Vitamin B6 E)

52. Benedict’s test could be used to differentiate which of the following sugars?

A) Psicose and galactose B) Fructose and tagulose C) Sorbitol and sorbose D) Ribose and glucose E) and glyceraldehyde

Carbohydrates.20

54. Below is a monomeric unit of cellulose. When cellulose is treated with excess in the presence of acid, which oxygen atoms are acetylated?

2 3 1

CH2OH O O O HO OH

4 5

A) 1, 2, 4, and 5 only B) 1 and 3 only C) 2 only D) 2, 4, and 5 only E) All of them

55. In the preparation of the cellulose acetate film, what was the purpose of dibutyl phthalate?

A) It aided in the dissolution of the cellulose (cotton) B) It functioned as a drying agent that removes residual water from the solution C) It makes the cellulose acetate more soluble in water D) If softens the cellulose acetate to prevent from becoming brittle

E) It neutralizes the residual H2SO4

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