Download Chapter 14 Carbohydrates Carbohydrates Carbohydrates Types of

Chapter 14
Carbohydrates
Carbohydrates
Carbohydrates are
• a major source of energy from
our diet.
• composed of the elements C,
H, and O.
• also called saccharides, which
means “sugars.”
14.1
Carbohydrates
1
Carbohydrates
2
Types of Carbohydrates
The types of carbohydrates are
• monosaccharides, the simplest carbohydrates.
• disaccharides, which consist of two monosaccharides.
• polysaccharides, which contain many monosaccharides.
Carbohydrates
• are produced by
photosynthesis in plants.
• such as glucose are
synthesized in plants from
CO2, H2O, and energy from
the sun.
• are oxidized in living cells
to produce CO2, H2O, and
energy.
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Aldoses
Monosaccharides
Monosaccharides consist of
• 3-6 carbon atoms typically.
• a carbonyl group (aldehyde or ketone).
• several hydroxyl groups.
Aldoses are monosaccharides
with
• an aldehyde group.
• many hydroxyl (-OH) groups.
triose
(3 C atoms)
tetrose (4 C atoms)
pentose (5 C atoms)
hexose (6 C atoms)
O
║
C─H aldose
│
H─ C─OH
│
H─ C─OH
│
CH2OH
Erythose, an aldotetrose
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Ketoses
Learning Check
Ketoses are monosaccharides
with
• a ketone group.
• many hydroxyl (-OH) groups.
CH2OH
│
C=O
Identify each as aldo- or keto- and as tetrose, pentose, or hexose.
ketose
│
H─ C─OH
│
H─ C─OH
│
H─C─OH
│
CH2OH
O
CH2OH
C H
H C OH
C O
H C OH
HO C H
H C OH
H C OH
H C OH
CH2OH
CH2OH
A
Fructose, a ketohexose
B
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Chapter 14
Solution
A. aldohexose
Carbohydrates
14.2
Fischer Projections of
Monosaccharides
B. ketopentose
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Fischer Projections
10
D
A Fischer projection
• is used to represent carbohydrates.
• places the most oxidized group at the top.
• shows chiral carbons as the intersection of vertical and
horizontal lines.
and L Notations
In a Fischer projection, the −OH group on the
• chiral carbon farthest from the carbonyl group
determines an L or D isomer.
• left is assigned the letter L for the L-form.
• right is assigned the letter D for the D-form.
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12
Examples of D and L Isomers of
Monosaccharides
H
HO
Identify each as the D or L isomer.
A.
B.
O
O
C
Learning Check
H
O
OH
C
H
H
C
OH
H
OH
H
OH
H
OH
H
OH
CH2OH
D-Glucose
HO
H
H
H
H
OH
H
OH
HO
CH 2OH
CH 2OH
D-Ribose
CH2OH
C H
H
HO
H
H
HO
H
HO
__-Ribose
HO
OH
H
H
H
__- Threose
H
OH
OH
CH2OH
CH2OH
CH2OH
L-Galactose
O
O
C H
H
HO
C.
O
__- Fructose
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Solution
D-Glucose
Identify each as the D or L isomer.
A.
B.
D-glucose is
• found in fruits, corn
syrup, and honey.
O H
• an aldohexose with
C
the formula C6H12O6.
H C OH
• known as blood sugar
HO C H
in the body.
• the monosaccharide in
H C OH
polymers of starch,
H C OH
cellulose, and
CH2OH
glycogen.
C.
CH2OH
O
C H
H
HO
H
H
HO
H
HO
CH2OH
L-Ribose
O
O
C H
HO
14
HO
OH
H
H
H
CH2OH
L-Threose
H
OH
OH
CH2OH
D-Fructose
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Inc.
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Blood Glucose Level
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D-Fructose
In the body,
• glucose has a normal blood level of 70-90 mg/dL.
• a glucose tolerance test measures blood glucose for
several hours after ingesting glucose.
D-Fructose
• is a ketohexose,
C6H12O6.
• is the sweetest
carbohydrate.
• is found in fruit juices
and honey.
• converts to glucose
in the body.
CH2OH
C O
HO
H
H
H
OH
OH
CH2OH
D-Fructose
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Copyright © 2009 by Pearson Education, Inc.
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D-Galactose
Learning Check
D-Galactose
Draw the structure of D-fructose.
O
• is an aldohexose,
C6H12O6.
• is not found free in
nature.
• is obtained from
lactose, a disaccharide.
• has a similar structure
to glucose except for
the –OH on carbon 4.
C H
H
OH
HO
H
HO
H
H
OH
CH2OH
D-Galactose
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Solution
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Chapter 14
14.3
Haworth Structures of
Monosaccharides
CH2OH
C O
HO
H
H
OH
H
OH
Carbohydrates
CH2OH
O
CH2OH
OH
OH
OH
D-Fructose
OH
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Drawing the Cyclic Structure for
Glucose
Cyclic Structures
STEP 1: Number the carbon chain and turn clockwise to
form a linear open chain.
Cyclic structures
• are the prevalent form of monosaccharides with 5 or 6
carbon atoms.
O
22
H O
C
O
1
H C OH
H
2
HO 3C H
• form when the hydroxyl group on carbon 5 reacts with
the aldehyde group or ketone group.
H 4C OH
H 5C OH
H OH H
O
HOCH 2 C C C C C
6
5
4
3
2
1
H
OH OH H OH
6CH2OH
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Cyclic Structure for Glucose
(continued)
Cyclic Structure for Glucose
STEP 2: Fold clockwise to make a
hexagon.
• Bond the carbon 5 –O– to carbon
1.
• Place the carbon 6 group above
the ring.
• Write the –OH groups on carbon 2
and carbon 4 below the ring.
• Write the –OH group on carbon 3
above the ring.
• Write a new –OH on carbon 1.
STEP 3: Write the new –OH on carbon 1
• down for the α form.
• up for the β form.
CH2OH
6
O
CH2OH
5
4
OH
1
OH
3
CH2OH
O
OH
2
OH
OH
OH
O
OH
OH
OH
α
β
OH
OH
OH
α-D-Glucose
β-D-Glucose
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α-D-Glucose and β-D-Glucose in
Summary of the Formation of
Cyclic Glucose
Solution
When placed in solution,
• cyclic structures open and close.
• α-D-glucose converts to β-D-glucose and vice versa.
• at any time, only a small amount of open chain forms.
CH2OH
CH2OH
O
OH
OH
OH
OH
α-D-Glucose
H
OH
OH
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D-Glucose
(36%)
(open)
(trace)
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Cyclic Structure of Fructose
C O
CH2OH
HO C H
CH2OH
D-Fructose
CH2OH
α-D-Fructose
(64%)
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O
O
C H
H
HO
HO
OH
H
CH2OH
OH
OH
OH
β-D-Glucose
Write the cyclic form of α-D-galactose.
OH
OH
H C OH
H C OH
CH2OH
O
OH
OH
OH
Learning Check
Fructose
• is a ketohexose.
• forms a cyclic structure.
• reacts the —OH on carbon 5 with the C=O on
carbon 2.
CH2OH
O
O
C
OH
CH2OH
H
O
OH
OH
H
H
OH
CH2OH
D-Galactose
β-D-Fructose
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Chapter 14
Solution
14.4
Chemical Properties of
Monosaccharides
CH2OH
O
OH
Carbohydrates
OH
OH
OH
α-D-Galactose
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Oxidation of D-Glucose
Reducing Sugars
Reducing sugars
• are monosaccharides that oxidize to give a carboxylic
acid.
• undergo reaction in the Benedict’s test.
• include the monosaccharides glucose, galactose, and
fructose.
O
O
C OH
C H
H C OH
H C OH
HO
H
H
H
OH
OH
+ 2Cu2+
[O]
HO
H
(blue)
H
H
OH
OH
+ 2Cu2O
(red)
CH2OH
CH2OH
D-Gluconic acid
D-Glucose
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Reduction of Monosaccharides
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Learning Check
Write the products of the oxidation and reduction
of D-mannose.
The reduction of
monosaccharides
• involves the carbonyl
group.
• produces sugar
alcohols, or alditols.
• such as D-glucose
gives D-glucitol, also
called sorbitol.
O
C H
HO
H
HO
H
H
H
OH
OH
CH2OH
D-Mannose
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Solution
Chapter 14
Carbohydrates
Write the products of the oxidation and reduction of
D-mannose.
O
O
HO
H
HO
H
H
H
C OH
C H
CH2OH
Reduction
HO
H
HO
H
OH
H
OH
H
Oxidation
HO
D-Mannitol
OH
H
OH
H
D-Mannose
H
HO
H
OH
OH
CH2OH
CH2OH
CH2OH
14.5
Disaccharides
D-Mannonic
acid
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Important Disaccharides
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Maltose
Maltose is
A disaccharide consists of two monosaccharides.
Monosaccharides
Disaccharide
Glucose + glucose
maltose + H2O
Glucose + galactose
lactose + H2O
Glucose + fructose
sucrose + H2O
•
•
•
•
a disaccharide also known as malt sugar.
composed of two D-glucose molecules.
obtained from the hydrolysis of starch.
linked by an α-1,4-glycosidic bond formed from
the α −OH on carbon 1 of the first glucose and
−OH on carbon 4 of the second glucose.
• used in cereals, candies, and brewing.
• found in both the α- and β -forms.
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Formation of Maltose
40
Lactose
Lactose
• is a disaccharide of βD-galactose and α- or
β-D-glucose.
• contains a β -1,4glycosidic bond.
• is found in milk and
milk products.
α-Form
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Sucrose
Learning Check
Sucrose or table sugar
• is obtained from sugar cane and sugar beets.
• consists of α-D-glucose and β-D-fructose.
• has an α,β-1,2-glycosidic bond.
Write the structures of the two monosaccharides that
form when sucrose is hydrolyzed.
α-D-Flucose
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β –D-Fructose
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Solution
44
Sweetness of Sweeteners
Sugars and artificial
sweeteners
Write the structures of the two monosaccharides that
form when sucrose is hydrolyzed.
• differ in
sweetness.
• are compared to
sucrose (table
sugar), which is
assigned a value
of 100.
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Learning Check
Solution
Identify the monosaccharides in each of the following:
A. Lactose
(3) β-D-Galactose
(1) α-D-Glucose (2) β-D-Fructose
Identify the monosaccharides in each of the following:
A. Lactose
(1) α-D-Glucose (3) β-D-Galactose
B. Maltose
(1) α-D-Glucose (2) β-D-Fructose
(3) β-D-Galactose
B. Maltose
(1) α-D-Glucose
C. Sucrose
(1) α-D-Glucose (2) β-D-Fructose
(3) β-D-Galactose
C. Sucrose
(1) α-D-Glucose
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(2) β-D-Fructose
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Chapter 14
Carbohydrates
Polysaccharides
Polysaccharides
• are polymers of D-glucose.
• include amylose and amylopectin,
starches made of α-D-glucose.
• include glycogen (animal starch in
muscle), which is made of α-Dglucose.
• include cellulose (plants and wood),
which is made of β-D-glucose.
14.6
Polysaccharides
CH2OH
O
OH
OH
OH
OH
α-D-Glucose
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Structures of Amylose and
Amylopectin
50
Amylose
Amylose is
• a polymer of α-Dglucose molecules.
• linked by α-1,4
glycosidic bonds.
• a continuous
(unbranched) chain.
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Amylopectin
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Glycogen
Amylopectin
• is a polymer of α-Dglucose molecules.
• is a branched-chain
polysaccharide.
• has α-1,4-glycosidic
bonds between the
glucose units.
• has α-1,6 bonds to
branches.
Glycogen
• is the polysaccharide
that stores α-D-glucose
in muscle.
• is similar to amylopectin,
but is more highly
branched.
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Cellulose
Learning Check
Identify the polysaccharides and types of glycosidic
bonds in each of the following.
Cellulose
• is a polysaccharide
of glucose units in
unbranched chains.
• has β-1,4-glycosidic
bonds.
• cannot be digested
by humans because
humans cannot
break down β-1,4glycosidic bonds.
A.
B.
C.
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Solution
A. Cellulose
β-1,4-glycosidic bonds
B. Amylose
Amylopectin
α-1,4-glycosidic bonds
α-1,4- and α-1,6-glycosidic bonds
C. Glycogen
α-1,4- and α-1,6-glycosidic bonds
(more branched than amylopectin)
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