1 carbohydrates chapter 27 hein * best * pattison * arena colleen kelley chemistry department pima...
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Carbohydrates Chapter 27
Carbohydrates Chapter 27
Hein * Best * Pattison * Arena
Colleen KelleyChemistry DepartmentPima Community College
© John Wiley and Sons, Inc.
Version 1.0
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Chapter Outline27.1 Carbohydrates: A First Class of Biochemicals
27.2 Classification of Carbohydrates
27.3 Importance of Carbohydrates
27.4 Monosaccharides
27.5 Structure of Glucose and Other Aldoses
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Chapter Outline (continued)
27.6 Cyclic Structure of Glucose; Mutarotation
27.7 Hemiacetals and Acetals
27.8 Structures of Galactose and Fructose
27. 9 Pentoses
27.10 Disaccharides
27.11 Structures and Properties of Disaccharides
27.12 Sweeteners and Diet
27.13 Redox Reactions of Monosaccharides
27.14 Polysaccharides Derived from Glucose
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Carbohydrates: Carbohydrates: A First Class of A First Class of BiochemicalsBiochemicals
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• Carbohydrates are generally defined as polyhydroxy aldehydes or ketones or substances that yield these compounds when hydrolyzed.
H
CHO
C OH
C OHH
H
glyceraldehyde
C
C O
C OHH
H
dihydroxyacetone
H OH
H
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Classification Classification of of
CarbohydratesCarbohydrates
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A carbohydrate can be classified as:
1.monosaccharide
2.disaccharide
3.oligosaccharide
4.polysaccharide
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Monosaccharides
• A monosaccharide is a carbohydrate that cannot be hydrolyzed to simpler carbohydrate units.
• The monosaccharide is the basic carbohydrate unit of cellular metabolism.
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Disaccharides• A disaccharide yields two
monosaccharides – either alike or different – when hydrolyzed:
disaccharide + water 2 monosaccharidesH+ or
enzymes
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Monosaccharides & Disaccharides
• Disaccharides are often used by plants or animals to transport monosaccharides from one cell to another.
• The monosaccharides and disaccharides generally have the ending –ose – for example, glucose, sucrose, and lactose.
• These are water-soluble carbohydrates, which have a characteristically sweet taste and are called sugars.
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Oligosaccharides
• An oligosaccharide has two to six monosaccharide units linked together.
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Polysaccharides• A polysaccharide is a macromolecular
substance that can be hydrolyzed to yield many monosaccharide units:
polysaccharide + water monosaccharidesH+ or
enzymes
• Polysaccharides are important structural supports, particularly in plants, and also serve as a storage depot for monosaccharides, which cells use for energy.
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Other Ways to Classify Carbohydrates• As a triose, tetrose, pentose, hexose, or
heptose• As an aldose or ketose• As a D or L isomer• As a (+) or (-) isomer• As a furanose or a pyranose• As having an alpha () or beta ()
configuration
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Importance of Importance of CarbohydratesCarbohydrates
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Importance of Carbohydrates
1. Carbohydrates are very effective energy-yielding nutrients.
2. Carbohydrates can serve as very effective building materials.
3. Carbohydrates are important water-soluble molecules.
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MonosaccharidesMonosaccharidesMonosaccharidesMonosaccharides
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Monosaccharides
• The hexose monosaccharides are the most important carbohydrate sources of cellular energy.
• Three hexoses – glucose, galactose, and fructose – are of major significance in nutrition.– All three have the same formula, C6H12O6, and thus
deliver the same amount of cellular energy.– They differ in structure, but are biologically
interconvertible.
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• Glucose (dextrose) is the most important of the monosaccharides.
• It is an aldohexose and is found in the free state in plant and animal tissue.
H
CHO
OH
HHO
OHH
OHH
CH2OH
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• Galactose is also an aldohexose and occurs, along with glucose, in lactose and in many oligo- and polysaccharides such as pectin and gums.
H
CHO
OH
HHO
HHO
OHH
CH2OH
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• Fructose, also know as levulose, is a ketohexose that occurs in fruit juices, honey, and along with glucose, as a constituent of sucrose.
CH2OH
O
HHO
OHH
OHH
CH2OH
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Structures of Glucose Structures of Glucose and Other Aldosesand Other Aldoses
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Epimers• Any two monosaccharides that differ
only in the configuration around a single carbon atom are called epimers.
• D- and L-glyceraldehyde are epimers.
H
CHO
C OH
CH2OH
D-glyceraldehyde
HO
CHO
C H
CH2OH
L-glyceraldehyde
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Figure 27. 1 Configurations of the D-family of aldoses. The hydroxyl group on the new chiral carbon atom, added in going from triose to tetrose to pentose to hexose, is shown in red.
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Figure 27. 1 Configurations of the D-family of aldoses. The hydroxyl group on the new chiral carbon atom, added in going from triose to tetrose to pentose to hexose, is shown in red.
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Figure 27. 1 Configurations of the D-family of aldoses. The hydroxyl group on the new chiral carbon atom, added in going from triose to tetrose to pentose to hexose, is shown in red.
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Figure 27.2 An example of the Kilani-Fischer synthesis in which two aldotetrose molecules are formed from an aldotriose molecule.
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Cyclic Structure of Cyclic Structure of Glucose; MutarotationGlucose; Mutarotation
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Figure 27.3 Mutarotation of D-glucose
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Anomers
• When two cyclic isomers differ only in their stereo arrangement about the carbon involved in mutarotation, they are called anomers.
• Mutarotation is the process by which anomers are interconverted.
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Figure 27. 4 Three-dimensional representations of the chair form of -D-glucopyranose
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Hemiacetals Hemiacetals and Acetalsand AcetalsHemiacetals Hemiacetals and Acetalsand Acetals
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• Cyclic structures of monosaccharides are intramolecular hemiacetals.
• Five- or six-membered rings are especially stable.
O
CH2OH
HO
HO
OH
HO
hemiacetal structure in -D-glucopyranose
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Glycoside• When a monosaccharide hemiacetal reacts with
an alcohol, the product is an acetal.
• In carbohydrate terminology, this acetal structure is called a glycoside.
O
CH2OH
RO
HO
OH
HO
acetal structure
glycosidic linkage
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Structures of Structures of Galactose and Galactose and
FructoseFructose
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Galactose
O
CH2OH
HO
OH
OH
OH O
CH2OH
HO
OH
OHOHH
CHO
OH
HHO
HHO
OHH
CH2OH
D-galactose -D-galactopyranose -D-galactopyranose
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FructoseCH2OH
O
HHO
OHH
OHH
CH2OH
O
OH
CH2OH
OH
OH
CH2OH
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DisaccharidesDisaccharidesDisaccharidesDisaccharides
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Disaccharides• Disaccharides are carbohydrates composed
of two monosaccharide residues united by a glycosidic linkage.
• sucrose + water glucose + fructose
• lactose + water galactose + glucose
• maltose + water glucose + glucose
H+ or sucrase
H+ or
lactase
H+ or
maltase
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Structures and Structures and Properties of Properties of DisaccharidesDisaccharides
Structures and Structures and Properties of Properties of DisaccharidesDisaccharides
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• Disaccharides contain an acetal structure (glycosidic linkage), and some also contain a hemiacetal structure.
• Maltose: O
CH2OH
O
OH
HO
OH
O
CH2OH
HO
HO
OH
-1,4-glycosidic linkage
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Sweeteners Sweeteners and Dietand Diet
Sweeteners Sweeteners and Dietand Diet
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Redox Reactions of Redox Reactions of MonosaccharidesMonosaccharides
Redox Reactions of Redox Reactions of MonosaccharidesMonosaccharides
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Oxidation• The aldehyde groups in monosaccharides can
be oxidized to monocarboxylic acids by mild oxidizing agents such as bromine water.
H
CHO
OH
HHO
OHH
OHH
CH2OH
+ Br2 + H2O
H
COOH
OH
HHO
OHH
OHH
CH2OH
+ 2HBr
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Reduction• Monosaccharides can be reduced to their
corresponding polyhydroxy alcohols by reducing agents such as H2/Pt or sodium amalgam, Na(Hg).
H
CHO
OH
HHO
OHH
OHH
CH2OH
+ H2 / Pt
H
CH2OH
OH
HHO
OHH
OHH
CH2OH
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Redox Test for Carbohydrates
• Under prescribed conditions, some sugars reduce silver ions to free silver, and copper (II) ions to copper (I) ions.
• Such sugars are called reducing sugars.
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Polysaccharides Polysaccharides Derived from Derived from
GlucoseGlucose
Polysaccharides Polysaccharides Derived from Derived from
GlucoseGlucose
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Starch• Starch is found in plants, mainly in the seeds,
roots, or tubers.
• Corn, wheat potatoes, rice and cassava are the chief sources of dietary starch.
• The two main components of starch are amylose and amylopectin. – Amylose molecules are unbranched chains
composed of about 25-1300 -D-glucose units joined by -1,4-glycosidic linkages.
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Figure 27.7 Representation of amylose.
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Glycogen• Glycogen is the energy-storage carbohydrate of
the animal kingdom.
• It is formed by the polymerization of glucose and is stored in the liver and in muscle tissues.
• Structurally, it is very similar to the amylopectin fraction of starch, except that it is more highly branched.
• The -1,6-glycosidic linkages occur on one of every 12-18 glucose units.
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Cellulose
• Cellulose is the most abundant organic substance found in nature.
• It is the chief structural component of plants and wood.
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Figure 27.9 Two representations of cellulose. In the three-dimensional drawing, note the hydrogen bonding that links the extended cellulose polymers to form cellulose fibers.
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