Carbohydrates.1
Practice Problems on Carbohydrates
1.
Which one of the following is a heptulose?
CH2OH
H
H
O
OH
OH
C
HO
H OH
OH
H
A
C O
H
O
CHO
H
H
H
OH
OH
H
H
D
HO H
CH2OH
H
HO
2.
H
HO
HO
H
HO
CH2OH
O
H
H
H
CH2OH
HO
Based on the names, which one of the following does NOT have an aldehyde?
A) Idose
B) Tagose
C) Fucose
D) Sedoheptulose
E) Cellobiose
3.
OH
OH
H
O
OH
H
H
H OH
H
HO
H C OH
CH2OH
CH2OH
E
H C OH
H
H
O
B
C H
Which formula correctly represents a simple monosaccharide?
A) C5H5O5
B) C5H5O10
C) C4H8O4
D) C6H10O6
E) C4H12O6
Carbohydrates.2
4.
Which one of the following structures correctly represents -D-altropyranose?
H
H
HO
CH2OH O
OH
H
HO
H
H
OH
H
HO
CH2OH
H
H
H
O
OH
OH
HO
H
HO
H
A
OH
H
H
C
H
CH2OH O
OH
H
H
HO
HO
H
CH2OH
H
H
HO
H
H
O
OH
OH
HO
OH
H
D
E
Which one of the following is not an aldose?
H
A
CH2OH
B
HO
OH
OH
H
H O
OH OH
C
HO
OH HO O
H
CH2
H
H
D
H
CH2OH
O
H
H
HO
HO
6.
O
OH
B
H
5.
CH2OH
H
H
HO
HO
H
H
H
CH2
HO
H
E
HO
H
OH
HO
OH
O
HO
OH
H
H
H CH2
H
Which one of the following is a ketohexose?
A
OH
CH2OH
OH
HO
OH O
CH2OH
OH
OH
E
CH2OH
HO
OH O
B
OH
OH
O
OH
CH2OH
OH
CH2OH
OH
C
HO
OH
OH O
D
HOCH2
CH2OH
O
O
OH
Carbohydrates.3
7.
Which one of the following compounds is a glycoside?
O
O
H
H
CH2O H
HO
A
CH2O H
O
B
H
H
HO
H
O
OCH3
H
H
H
H
CH3
O
C
H
H
O
C
OH
O
H
H3C C
O
H
H
CH3
O
E
O
H
H
CH2
OH
O
O
H
H
HO
H
CH3O
CH2O H
HO
H
O
OCH2
OH
H
H
H
Which one of the following structures correctly represents -L-galactopyranose?
OH
HO
CH2OH
O
CH2OH
O
OH
OH
HO
HO
HO
B
OH
A
OH
HO
O
HO
C
OH
CH2OH
O
OH
CH2OH OH
9.
CH2O
O
O
H
CH2
8.
C
CH3
OH
OH
CH3
D
C
H
O
OH
O
CH3
H
OH
HO
HO
CH2OH
D
O
HO
OH
OH
E
How many hexoses (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?
A
O
OH
HO
O
B
OH
COO
CH2OH
HO
HO
CH2
D
O CH2
O
HO
HO
OCH3
OH
NH2
C
O
CH3
CHO
HO
NH
COO
OH
CH2 OH
O
O
COOH
CO
O
CH3
OH
E
CH2OH
O
HO
HO
+ Cl
O
O
OH
HO
11.
OH
Which one of the following molecules is most likely to form a cyclic hemiacetal in
neutral solution?
A
HC O
B
HC O
C
HC O
H C OH
H C OH
H C OH
H C H
H C O
H C H
H C O
O C H
H C OCH3
H C O
CH2OH
CH2
CH2OH
D
H C OH
H2C
H C H
CH2O
HC O
H C OCH3
CH3
C
CH3
H C O CH2
H C H
H C OH
CH2O
C O
E
HC O
H C O CH2
H C OH
CH3O C H
H C OCOCH3
CH2O
CH3
Carbohydrates.5
12.
Which one of the following is a ketose?
CH2OH
H
O
H
H
OH
CH2OH
O
H
HO
OH
H
OH
H
H
B
OH
H
O
OH
H
H
H
H
H
H
CH2OH
OH
OH
H
H
H
CH2OH
A
13.
OH
H
H
H
O
HO
H
O
HO
CH2OH
H
O
H
H
OH
OH
D
C
HO
HO
CH2OH
CH2OH
H
E
Which one of the following compounds is a glycoside?
O
HN
O
HO
O
HO
HO
O
O
H3CO
O
OCH3
HO
N
HO
OH
A
OH
B
OCH3
H3CO
H3CO
O
OH
OCH3
OCH3
OH
E
D
14.
OH
OCH3
C
OH
OH
O
O
Peonin (shown below) is a red pigment found in the petals of peony flowers.
Which monosaccharide(s) would be produced by acid hydrolysis of peonin?
OCH3
OH
O
H
CH2OH
H
H
HO
HO
O
O
O
II
OH
H
H
I
A) D-glucose and D-mannose
B) L-glucose and D-mannose
C) D-glucose and D-galactose
D) D-glucose only
E) L-galactose only
H
H
OH
HO
O
H
H
OH
CH2OH
H
Carbohydrates.6
15.
16.
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:
Which one of the following statements is NOT correct?
A) D-Glucose and D-gulose 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-glyceraldehyde have the same configuration at the
penultimate carbon.
D) D-Glucose and D-gulose both must be dextrorotatory because they are both
D sugars.
E) D-Glyceraldehyde is dextrorotatory, and L-glyceraldehyde is levorotatory.
17.
Which of the following statements about D-2-deoxyribose (the monosaccharide in
DNA) is/are most likely to be correct?
a. it can exist as two furanose anomers
b. it can exist as two pyranose 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 mutarotation when dissolved in water?
OH
O
a)
H
HO
b)
H
OH H
O
H OH
OH
O H
c)
H
HO
H
OH H
H OH
19.
OH
OH
H
H
OH H
OCH3
HO
H OH
d)
H
OH
O H
e)
H
H
OH H
OH
H
HO
O
H OH H
OH
OH
H O
H
OH
OH
H
OH H
OH
H
H OH
O
CHO
OH
OH
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
CH2 OH
HO
O
OH
HO
CH2 OH
OH
HO
CH2OH
OH
O
OH
HO
OH
H
[ ]D25 = +20
OH
[ ]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
O
anomers are diastereomers
E) Mutarotation occurs for aldose monosaccharides 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
0
3
6
Time (hours)
9
12
A) A portion of the -D-galactose was converted to -D-fructose
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)
21.
-D-galactose formed an equilibrium mixture with -D-galactose
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
alcohol, the carbonyl group is protonated to make it better nucleophile.
C) Acetals are resistant to alkaline (basic) conditions.
D) Hemiacetals 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 aldoses 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?
a)
HO
H
b)
OH
H
O OH
OH H
OH
H OH
e)
H OH
HO
OH
O
HO
24.
c)
H OH
H
OH H
OH H
H O
d)
H
HO
O
H
HO
OH
H
OH
O
OH
OH
OH H
OH
H OH
The oxidation of D-talose by nitric acid gives the same optically active diacid as
the oxidation of which other sugar?
A) L-Talose
B) L-Altrose
C) D-Galactose
D) D-Altrose
E) L-Gulose
25.
D-Arabinose 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-ribose
B) L-xylose
C) D-xylose
D) D-lyxose
E) D-ribose
Carbohydrates.10
26.
Reduction of D-ribulose 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?
O
HOCH2
H
O
H
OH
H
H
O
CH3
CH3
HO
C
H2C
O
O
H
H
H
CH3
H
A
HO
H
HO
O OH
H
H
H
CH3O
H
HO
O
OH
CH2OH
C
B
H
O
OH
HO
OH
CH3
H
D
29.
OCH2CH3
O
CH2OH
O
CH2OH
O O
H
H
OH
H
HO
H
H
OH
E
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 sucrose 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-allose
B) D-altrose
C) D-idose
D) D-tagulose
E) D-psicose
32.
A reducing monosaccharide is heated in dry methanol with catalytic hydrochloric
acid. The carbohydrate 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
A)
B)
H
OH
CH2OH
CH2OH
CH2OH
HO
D)
H
O
CH2OH
CHO
H
OH
H
OH
CH2OH
E)
H
O
HO
H
CH2OH
C)
OH
OH
CH2OH
Carbohydrates.13
34.
The glucose-metabolism enzyme TPI catalyzes the reversible conversion of
glyceraldehyde-3-phosphate and dihydroxyacetone phosphate, as shown below.
Which one of A-E is least likely to be an intermediate along the conversion
pathway?
CHO
H
CH2OH
TPI
OH
O
CH2OPO32-
H
C
CH2OPO32-
OH
A)
O
B)
O
CH2OPO32-
CH2OPO32-
H
CHO
D)
OH
CH2OPO32-
CH2OH
CHOH
E)
C
C)
O
CHOPO32-
O
OH
CH2OPO32-
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 hexose 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-sorbose
Carbohydrates.15
39.
NH
Which one of A – E is least likely to be involved in the acidcatalyzed hydrolysis of the compound on the right?
HC
H
OH
CH2OH
2
A)
HC
B)
H
OH
CH2OH
2
OH
NH2
C)
HC NH2
H
OH
CH2OH
OH
D)
H2C
H
OH
CH2OH
40.
E)
2
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 cellulose is true?
A) Cellulose is fermented to ethanol by numerous microorganisms
B) Ruminants can synthesize a cellulase enzyme
C) Cellulose and starch are constitutional isomers
D) Cellulases 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) Amylose is too soluble to pass through the cell wall
46.
Why is maltose a source of glucose for human nutrition, but cellobiose is not?
OH
HO
HO
OH
O
OH
O
maltose
OH
HO
HO
O
OH
HO
OH
OH
O
OH
O
HO
cellobiose
O
OH
OH
A) Human enzymes require the -anomer 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 polysaccharides is NOT correct?
A) Cellulose and maltose differ in the stereochemistry of the glycosidic bonds
B) Amylose and amylopectin 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 polysaccharide 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 ATPdependent 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) Vitamin C
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) Erythrose and glyceraldehyde
Carbohydrates.20
54.
Below is a monomeric unit of cellulose. When cellulose is treated with excess
acetic anhydride in the presence of acid, which oxygen atoms are acetylated?
1
2
CH2OH
O
3
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