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CHAPTER 27
CARBOHYDRATES
SOLUTIONS TO REVIEW QUESTIONS
1.
In general, the carbohydrate carbon oxidation state determines the carbon’s metabolic
energy content. The more oxidized a carbon is, the less energy it can provide in biological
systems.
2.
The notations D and L in the name of a carbohydrate specify the configuration on the last
chiral carbon atom (from C-1) in the Fischer projection formula. If the ¬ OH is written
to the right of that carbon the compound is a D-carbohydrate. If the ¬ OH is written to
the left it is an L-carbohydrate. for example, D-glyceraldehyde and L-glyceraldehyde
differ only at the chiral C ¬ OH; D-glyceraldehyde has the ¬ OH on the right while
L-glyceraldehyde has the ¬ OH on the left.
3.
The notations (+) and (-) in the name of a carbohydrate specify whether the compound
rotates the plane of polarized light to the right (+) or to the left (-).
4.
Galactosemia is the inability of infants to metabolize galactose. The galactose
concentration increases markedly in the blood and also appears in the urine.
Galactosemia causes vomiting, diarrhea, enlargement of the liver, and often mental
retardation. If not recognized a few days after birth it can lead to death.
5.
There are four pairs of epimers among the D-aldohexoxes in Figure 27.1. They are: allose
and altrose; glucose and mannose; gulose and idose; and galactose and talose.
6.
A carbohydrate forms a five member or six member heterocyclic ring (one oxygen atom,
the rest carbon atoms). If it forms a five-member ring, it is termed a furanose, after the
compound furan. If it forms a six-membered ring it is termed a pyranose, after the
compound pyran.
Pyran
Furan
O
7.
C4H4O
C5H6O
O
a-D-glucopyranose and b -D-glucopyranose differ in the configuration at the number 1
carbon in the cyclic structure. In the open-chain structure, carbon 1 is the aldehyde group,
and is not chiral. In the cyclic structure that carbon contains a hemiacetal structure, which
is chiral. When the ring forms, carbon 1 can have two configurations leading to the two
structures called a and b.
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CH2OH
O
CH2OH
O
OH
OH
OH
OH
HO
HO
OH
OH
In the Haworth structure for glucose the ¬ OH on carbon 1 is written down for the a
structure and up for the b structure.
8.
The cyclic forms of monosaccharides are hemiacetals, because the number one carbon
has an ether and an alcohol group; whereas a glycoside is an acetal which contains two
ether linkages.
9.
Mutarotation is the phenomenon by which the a or b form of a sugar, when in solution,
will undergo change to reach an equilibrium mixture, not necessarily 50%-50%, of the
two forms. To achieve this equilibrium, the chain must open up and then reclose. On
closing, it has the possibility of closing in either the a or b form as the equilibrium
mixture is achieved.
10.
Major sources:
(a) sucrose: sugar beets and sugar cane
(b) lactose: milk
(c) maltose: sprouting grain and partially hydrolyzed starch
11.
The following parts are related to the eight D-aldohexoses shown in the text (Figure 27.1):
(a) If each of the aldohexoses is oxidized by nitric acid to dicarboxylic acids, allose
and galactose would become meso forms.
CHO
COOH
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
HNO
3
99:
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
CH 2OH
allose
COOH
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CHO
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
COOH
HNO
3
99:
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
CH 2OH
galactose
(b)
COOH
Names and structures of enantiomers of D-altrose and D-idose:
CHO
CHO
CHO
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
CH 2OH
D-altrose
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
CH 2OH
L-altrose
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
CH 2OH
D-idose
CHO
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
CH 2OH
L-idose
12.
Invert sugar is sweeter than sucrose because it is a 50-50 mixture of fructose and glucose.
Glucose is somewhat less sweet than sucrose, but fructose is much sweeter, so the
mixture is sweeter.
13.
Amylose is a linear polymer of D-glucopyranose units linked by a-1,4-glycosidic bonds
while cellulose is a linear polymer of D-glucopyranose units linked by b -1,4-glycosidic
bonds. Amylose molecules take the shape of a “coil” while cellulose molecules form fibers.
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14.
In the Benedict test, both concentrated and dilute glucose solutions will give a red
precipitate of Cu 2O. However, during the reaction the dilute solution will appear
more greenish-yellow while the concentrated solution will appear more reddish.
15.
The two main components of starch are amylose and amylopectin. They are both
composed of glucose units joined by a-1,4-glycosidic linkages. The difference is that
amylopectin also has branching which occurs through a-1,6-glycosidic linkages about
every 25 glucose units.
16.
Some people, as they grow older, stop producing the enzyme lactase and thus lose the
ability to digest lactose. This leads to lactose intolerance, a condition that produces gas
and intestinal discomfort.
17.
Glycosaminoglycans are sugar polymers that contain derivitives of glucose, e.g.,
glucosamine. These polysaccharides act as shock absorbers between bones.
18.
Blood types A and B differ in one place. In the fourth pyran ring at C-2, blood type B has
an OH group, while blood type A has an amide group.
19.
The main purpose of complex carbohydrates on the cell surface is so that an organism can
distinguish their own cells from invading or foreign bacteria.
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CHAPTER 27
SOLUTIONS TO EXERCISES
1.
2.
(b)
CH 2OH
ƒ
C“O
ƒ
CH 2OH
There are no chiral carbon atoms in dihydroxyacetone.
If dihydroxyacetone is reacted with hydrogen in the presence of a platinum catalyst,
the product will be glycerol.
CH 2OH
ƒ
H ¬ C ¬ OH
ƒ
CH 2OH
(a)
D-glyceraldehyde
L-glyceraldehyde
H¬C“O
ƒ
H ¬ C ¬ OH
ƒ
CH 2OH
H¬C“O
ƒ
HO ¬ C ¬ H
ƒ
CH 2OH
(a)
(b)
If D-glyceraldehyde is reacted with hydrogen in the presence of a platinum catalyst,
the product will be glycerol.
CH 2OH
ƒ
H ¬ C ¬ OH
ƒ
CH 2OH
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3.
The structure of an epimer of D-mannose will differ from D-mannose at one chiral carbon
atom. The epimer could differ at carbon 2 or carbon 3 or carbon 4 or carbon 5. One
possible epimer is
CHO
CHO
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
CH 2OH
D-mannose
4.
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
CH 2OH
an epimer of D-mannose at carbon 4
The structure of an epimer of D-galactose will differ from D-galactose at one chiral carbon
atom. The epimer could differ at carbon 2 or carbon 3 or carbon 4 or carbon 5. One
possible epimer is
CHO
CHO
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
CH 2OH
D-galactose
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
CH 2OH
an epimer of D-galactose at carbon 2
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5.
The enantiomers are L-galactose, L-mannose and L-ribose which are mirror images of
D-galactose, D-mannose and D-ribose.
CHO
CHO
CHO
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
CH 2OH
L-galactose
6.
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
CH 2OH
L-mannose
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
CH 2OH
L-ribose
The enantiomers are L-glucose, L-fructose and L-2-deoxyribose which are mirror images
of D-glucose, D-fructose and D-2-deoxyribose.
CHO
CH 2OH
CHO
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
CH 2OH
L-glucose
ƒƒ
C ““ O
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
ƒ
ƒ
H ¬¬¬¬¬ H
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
CH 2OH
CH 2OH
L-fructose
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L-2-deoxyribose
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7.
Either the Fischer projection formula or Haworth formulas are satisfactory.
H
OH
≈ ≈
C
ƒ
H ¬ C ¬ OH
ƒ
HO ¬ C ¬ H O
ƒ
H ¬ C ¬ OH
ƒ
H¬C
ƒ
CH2OH
CH2OH
O
H
HO
≈ ≈
C
ƒ
H ¬ C ¬ OH
ƒ
HO ¬ C ¬ H O
ƒ
HO ¬ C ¬ H
ƒ
H¬C
ƒ
CH2OH
HO
CH2OH
O
OH
OH
OH
≈ ≈
C
ƒ
HO ¬ C ¬ H
ƒ
HO ¬ C ¬ H O
ƒ
H ¬ C ¬ OH
ƒ
H¬C
ƒ
CH2OH
CH2OH
O
OH
H
OH
HO
OH HO
HO
OH
OH
a-D-glucopyranose
8.
H
b -D-galactopyranose
OH
a-D-mannopyranose
Either the Fischer projection formulas or Haworth formulas are satisfactory.
H
HO
≈ ≈
C
ƒ
H ¬ C ¬ OH
ƒ
HO ¬ C ¬ H O
ƒ
H ¬ C ¬ OH
ƒ
H¬C
ƒ
CH2OH
CH2OH
O
OH
OH
H
OH
≈ ≈
C
ƒ
H ¬ C ¬ OH
ƒ
HO ¬ C ¬ H O
ƒ
HO ¬ C ¬ H
ƒ
H¬C
ƒ
CH2OH
HO
H
≈ ≈
C
ƒ
HO ¬ C ¬ H
ƒ
HO ¬ C ¬ H O
ƒ
H ¬ C ¬ OH
ƒ
H¬C
ƒ
CH2OH
HO
CH2OH
O
CH2OH
O
OH
OH
HO
OH
b -D-glucopyranose
OH
a-D-galactopyranose
- 425 -
OH
OH HO
HO
b -D-mannopyranose
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9.
The glucose units in starch are connected by a-1-4-glycosidic linkages. The human
digestive system has the enzymes that catalyze the hydrolysis of starch to maltose or
isomaltose and then to glucose.
10.
The glucose units in cellulose are connected by b -1-4-glycosidic linkages. The human
digestive system does not have the enzymes to catalyze the hydrolysis of cellulose.
11.
Kiliani-Fischer synthesis of D-glucose from the proper D-tetrose (D-erythrose)
HC“O
H
OH
H
OH
CH2OH
HCN
D-erythrose
CN
H
OH
H
OH
H
OH
CH2OH
HO
H
H
H
HO
H
H
CN
H
OH
OH
CH2OH
CN
OH
H
OH
OH
CH2OH
H2O
H+
H2O
H
HO
H
H
COOH
H
OH
OH
CH2OH
H
HO
H
H
COOH
OH
H
OH
OH
CH2OH
Na(Hg)
HC“O
HO
H
H
OH
H
OH
CH2OH
Na(Hg)
HCN
HO
HO
H
H
CN
H
H
OH
OH
CH2OH
H
HO
H
H
CN
OH
H
OH
OH
CH2OH
HC“O
H
OH
HO
H
H
OH
H
OH
CH2OH
D-glucose
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12.
Kiliani-Fischer synthesis of D-ribose starts with the proper D-triose, D-glyceraldehyde.
HC“O
H
OH
CH2OH
HCN
HO
H
CN
H
OH
CH2OH
H
H
CN
OH
OH
CH2OH
D-glyceraldehyde
CN
H
OH
H
OH
H
OH
CH2OH
H2O
H+
H2O
H+
H
H
COOH
OH
OH
CH2OH
COOH
H
OH
H
OH
H
OH
CH2OH
Na(Hg)
Na(Hg)
HC“O
H
OH
H
OH
CH2OH
HO
H
H
CN
H
OH
OH
CH2OH
H
H
H
CN
OH
OH
OH
CH2OH
HCN
HC“O
H
OH
H
OH
H
OH
CH2OH
D-ribose
13.
Yes, D-2-deoxymannose is the same as D-2-deoxyglucose. The structures of D-mannose
and D-glucose differ at carbon 2, so if the carbon 2 OH group on both molecules is
changed to H, there is no difference between the two molecules.
14.
No, D-2-deoxygalactose is not the same as D-2-deoxyglucose. D-galactose differs from
D-glucose at carbon 4, so replacement of the carbon 2 OH with an H does not makes
these two sugars identical.
15.
The monosaccharide composition of:
(a) sucrose: one glucose and one fructose unit
(b) glycogen: many glucose units
(c) amylose: many glucose units
(d) maltose: two glucose units
16.
The monosaccharide composition of:
(a) lactose: one glucose and one galactose unit
(b) amylopectin: many glucose units
(c) cellulose: many glucose units
(d) sucrose: one glucose and one fructose unit
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17.
Both cellobiose and isomaltose are disaccharides composed of two glucose units.
However, in cellobiose monosaccharides are linked by a b -1,4-acetal bond while for
isomaltose the linkage is a-1,6.
CH2OH
O
CH2OH
O
CH2OH
O
OH
OH
OH
HO
O
OH
OH
OH
O
HO
OH
CH2
O
cellobiose
OH
OH
HO
OH
isomaltose
18.
Both maltose and isomaltose are disaccharides composed of two glucose units. The
glucose units in maltose are linked by an a-1,4-glycosidic bond while the glucose units in
isomaltose are linked by an a-1,6-glycosidic bond.
CH2OH
O
OH
CH2OH
O
OH
CH2OH
O
OH
O
HO
OH
OH
OH
HO
OH
maltose
O
CH2
O
OH
HO
OH
OH
isomaltose
19.
Lactose will show mutarotation; sucrose will not. The hemiacetal structure in lactose will
open allowing mutarotation. Since sucrose has an acetal structure and no hemiacetal, it
will not undergo mutarotation.
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20.
Both maltose and isomaltose will show mutarotation. Both disaccharides contain a
hemiacetal structure which will open allowing mutarotation.
21.
CH2OH
O
CH2OH
O
OH
CH2OH
O
HO
OH
OH
OH
O
OH
OH
O
HO
OH
CH2
O
cellobiose
OH
OH
HO
OH
isomaltose
The shaded hemiacetal structures allow these two disaccharides to be reducing sugars.
22.
CH2OH
O
OH
CH2OH
O
OH
CH2OH
O
O
HO
OH
OH
OH
HO
CH2OH
O
OH
O
OH
OH
OH
maltose
OH
lactose
The shaded hemiacetal structures allow these two disaccharides to be reducing sugars.
23.
The systematic name for isomaltose is a-D-glucopyranosyl-(1,6)-a-D-glucopyranose. The
systematic name for cellobiose is b -D-glucopyranosyl-(1,4)- b -D-glucopyranose.
24.
The systematic name for maltose is a-D-glucopyranosyl-(1,4)-a-D-glucopyranose. The
systematic name for lactose is b -D-galactopyranosyl-(1,4)-a-D-glucopyranose.
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25.
The principal differences and similarities between the members of the following pairs:
(a) D-glucose and D-fructose. Glucose is an aldose; fructose is a ketose. Glucose often
forms a pyranose ring structure; fructose commonly is found in a furanose
structure. Both are hexoses and both are reducing sugars.
(b) Maltose and sucrose. Maltose is composed of two glucose units; sucrose is
composed of one glucose and one fructose unit. Maltose is a reducing sugar;
sucrose is not. Both are common disaccharides, with formulas C12H 22O11 .
(c) Cellulose and glycogen. Cellulose is composed of glucose units linked by
b -1, 4-glycosidic linkages; glycogen is composed of glucose units linked by
a-1, 4-glycosidic linkages and a-1, 6-glycosidic linkages. Glycogen is much more
readily hydrolyzed or digested than cellulose. Both are large polymers of glucose.
Glycogen is of animal origin; cellulose is from plants.
26.
The principal differences and similarities between members of the following pairs:
(a) D-ribose and D-2-deoxyribose. The D-2-deoxyribose has no OH group on the
number 2 carbon, only 2 hydrogen atoms. Both are five carbon sugars.
(b) Amylose and amylopectin. Amylose is a straight chain polysaccharide; amylopectin
has branched chains, and more monomer units per molecule. Both are large
polysaccharides composed of a-D-glucose units.
(c) Lactose and isomaltose. These sugars are disaccharides. Lactose is composed of
one galactose unit and one glucose unit while isomaltose is composed of two
glucose units. The monosaccharide units in lactose are linked by a b -1,4-glycosidic
bond while the units in isomaltose are linked by an a-1,6-glycosidic bond. Both
disaccharides also contain hemiacetal structures.
H ¬¬ C ““ O
27.
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
COOH
+
HNO3 ¡
CH 2OH
D-galactose
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
COOH
mucic acid (galactaric acid)
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- Chapter 27 -
HC ““ O
28.
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
COOH
+
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
HNO3 ¡
CH 2OH
D-mannose
29.
COOH
mannaric acid
The formulas for the four L-ketohexoses are
CH 2OH
CH 2OH
ƒƒ
C ““ O
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
CH 2OH
A
ƒƒ
CH 2OH
ƒƒ
C ““ O
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
C ““ O
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
CH 2OH
B
Epimers are: A and B, B and C, B and D, C and D
- 431 -
CH 2OH
C
CH 2OH
ƒƒ
C ““ O
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
CH 2OH
D
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30.
The formulas for the four L-aldopentoses are
HC ““ O
HC ““ O
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
CH 2OH
A
HC ““ O
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
CH 2OH
B
CH 2OH
C
Epimers are: A and B, A and C, B and D, C and D
31.
(a)
b -D-glucopyranosyl-(1,4)- b -D-galactopyranose
CH2OH
O
CH2OH
O OH
OH
O
OH
HO
OH
OH
(b)
b -D-galactopyranosyl-(1,6)-a-D-mannopyranose
HO
CH2OH
O
OH
O¬CH2
O OH
HO
OH
OH
32.
(a)
HO
b -D-mannopyranosyl-(1,4)- b -D-galactopyranose
H
CH 2OH
O
H
OH HO
HO
H
H
CH 2OH
O
H
OH
H
O
H
H
H
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OH
OH
H
HC ““ O
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
CH 2OH
D
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(b)
b -D-galactopyranosyl-(1,6)-a-D-glucopyranose
HO
CH 2OH
O
H
H
OH
CH 2
O
H
H
H
33.
OH
CH 2OH
O
H
OH
H
H
OH
HO
OH
maltose
OH
OH
HO
OH
OH
34.
H
CH 2OH
O
O
OH
O
H
CH 2OH
O
CH 2OH
O
O
OH
OH
cellobiose
OH
HO
OH
OH
35.
CH 2OH
O
OH
CH 2OH
O
O
CH2OH
O
OH
OH
OH
HO
OH
OH
HO
O
OH
CH2
O
OH
HO
OH
OH
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36.
CH 2OH
O
CH 2OH
O
OH
CH 2OH
O
OH
O
OH
OH
HO
HO
OH
OH
O
OH
CH2
O
OH
HO
OH
OH
37.
38.
(a)
(b)
(c)
D-galactose
(a)
(b)
(c)
D-ribose
a-D-glucopyranose
b -D-ribofuranose
b -D-glucopyranose
a-D-fructofuranose
39.
lactose, b -D-galactopyranosyl-(1,4)-a-D-glucopyranose
40.
maltose, a-D-glucopyranosyl-(1,4)-a-D-glucopyranose
41.
Glucose is called blood sugar because it is the most abundant carbohydrate in the
blood and is carried by the bloodstream to all parts of the body.
42.
Aspartame supplies many fewer calories than sucrose. In addition, oral bacteria cannot use
aspartame as efficiently as sucrose and will form fewer dental carries.
43.
High-fructose corn syrup is produced by breaking down some corn starch polymers to
D-glucose monomers which are then converted to D-fructose, a very sweet monosaccharide.
44.
(a)
(b)
The sugar acid could be most easily derived from b -D-mannopyranose.
COOH
COOH
COOH
O
OH HO
O
O
O
OH HO
O
OH HO
O
n
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45.
Compound A must be a reducing disaccharide because it produces a reddish color in the
Benedict test. Sucrose is nonreducing so compound A must be maltose.
46.
(a)
All starred carbons (4) in the following compound are chiral:
HC “ O
H * OH
H * OH
H * OH
H * OH
CH2OH
(b)
CH2OH
*
O
*
OH
(c)
47.
*
*
*
OH
OH
OH
All starred carbons (5) in the structure drawn in part (b) are chiral carbons.
If the compound (I) shown below rotates light 25° to the right, its enantiomer will rotate
light 25° to the left.
HC ““ O
HC ““ O
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
CH 2OH
I
ƒ
ƒ
H ¬¬¬¬¬ OH
ƒ
ƒ
HO ¬¬¬¬¬ H
ƒ
ƒ
CH 2OH
enantiomer of I
These compounds are not epimers because they differ at more than one chiral carbon.
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48.
A nonreducing disaccharide composed of two molecules of a-D-galactopyranose can
have no hemiacetal structures. Thus, the hemiacetal structure of one a-D-galactopyranose
must be used to form the glycosidic link to the hemiacetal structure of the other
a-D-galactopyranose unit.
CH2OH
CH2OH
O
HO
O
HO
OH
OH
OH
OH
O
49.
Cellulose, amylose, and amylopectin are polymers of glucose. Cellulose exists in the
form of fibers, is not digestible by humans, and therefore remains in the digestive tract as
fibers. amylose and amylopectin are digested to glucose which is dissolved into the
bloodstream.
50.
(a)
(b)
D-galactose
and D-glucose differ only at carbon 4. Thus, D-galactose must be
changed at carbon 4 to be converted to D-glucose.
D-galactose is an epimer of D-glucose.
51.
No, the classmate should not be believed. Although D-glucose and D-mannose are related
as epimers, it is pairs of enantiomers which have equal and opposite optical rotation.
52.
(a)
CH2OH
O
OH
HO
OH
O
HO CH2
O
HO
CH2OH
HO
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(b)
CH2OH
CH2OH
O
O
OH
OH
HO
OH
HO
OH
OH
O
HO CH2
O
HO CH2
HO
(c)
acid
H2O
O
OH
HO
CH2OH
CH2OH
HO
HO
Fructose is sweeter than sucrose. When sucrose is broken down to its two
component monosaccharides, glucose and fructose, the candy becomes sweeter.
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