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Reviewer for Carbohydrates
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1Carbohydrates Chapter 1
Carbohydrates Chapter 1
DR. LEONARDO C. MEDINA, JR.
2Chapter Outline1. Carbohydrates: A First Class of Biochemicals2. Classification of
Carbohydrates3. Importance of
Carbohydrates
4. Monosaccharides
5. Structure of Glucose and Other Aldoses
3Chapter Outline (continued)
6. Cyclic Structure of Glucose; Mutarotation
7. Hemiacetals and Acetals8. Structures of Galactose
and Fructose9. Pentoses10. Disaccharides
11. Structures and Properties of Disaccharides
12. Sweeteners and Diet13. Redox Reactions of
Monosaccharides14. Polysaccharides Derived
from Glucose
4Carbohydrates: Carbohydrates: A First Class of A First Class of BiochemicalsBiochemicals
5 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
6Classification Classification of of
CarbohydratesCarbohydrates
7A carbohydrate can be classified as:
1.monosaccharide
2.disaccharide
3.oligosaccharide
4.polysaccharide
8Monosaccharides A monosaccharide is a carbohydrate that
cannot be hydrolyzed to simpler carbohydrate units.
The monosaccharide is the basic carbohydrate unit of cellular metabolism.
9Disaccharides A disaccharide yields two
monosaccharides either alike or different when hydrolyzed:
disaccharide + water
2 monosaccharidesH+ or
enzymes
10
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.
11
Oligosaccharides
An oligosaccharide has two to six monosaccharide units linked together.
12
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.
13
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
14
Importance of Importance of CarbohydratesCarbohydrates
15
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.
16
MonosaccharidesMonosaccharidesMonosaccharides
17
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, C6 H12 O6 , and
thus deliver the same amount of cellular energy. They differ in structure, but are biologically
interconvertible.
18
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
19
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
20
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
21
Structures of Glucose Structures of Glucose and Other and Other AldosesAldoses
22
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
23
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.
24
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.
25
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.
26
An example of the Kilani-Fischer synthesis in which two aldotetrose molecules are formed from an aldotriose molecule.
27
Cyclic Structure of Cyclic Structure of Glucose; Glucose; MutarotationMutarotation
28
Mutarotation of D-glucose
29
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.
30
Three-dimensional representations of the chair form of -D-glucopyranose
31
Hemiacetals and Acetals
HemiacetalsHemiacetals and and AcetalsAcetals
32
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
33
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
34
Structures of Structures of GalactoseGalactose and Fructoseand Fructose
35
Galactose
O
CH2OH
HO
OH
OH
OH O
CH2OH
HO
OH
OHOHH
CHO
OH
HHO
HHO
OHH
CH2OH
D-galactose -D-galactopyranose -D-galactopyranose
36
FructoseCH2OH
O
HHO
OHH
OHH
CH2OH
O
OH
CH2OH
OH
OH
CH2OH
37
DisaccharidesDisaccharidesDisaccharides
38
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
39
Structures and Properties of Disaccharides
Structures and Structures and Properties of Properties of DisaccharidesDisaccharides
40
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
41
Sweeteners and Diet Sweeteners Sweeteners and Dietand Diet
42
43
Redox Reactions of Monosaccharides
RedoxRedox Reactions of Reactions of MonosaccharidesMonosaccharides
44
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
45
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
46
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.
47
Polysaccharides Derived from
Glucose
Polysaccharides Polysaccharides Derived from Derived from
GlucoseGlucose
48
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.
49
Representation of amylose.
50
51
52
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.
53
Cellulose
Cellulose is the most abundant organic substance found in nature.
It is the chief structural component of plants and wood.
54
Two representations of cellulose. In the three- dimensional drawing, note the hydrogen bonding that links the extended cellulose polymers to form cellulose fibers.
55
Carbohydrates Chapter 1Chapter OutlineChapter Outline (continued)Carbohydrates: A First Class of BiochemicalsSlide Number 5Slide Number 6Slide Number 7MonosaccharidesDisaccharidesMonosaccharides & DisaccharidesOligosaccharidesPolysaccharidesOther Ways to Classify CarbohydratesImportance of CarbohydratesImportance of CarbohydratesMonosaccharidesMonosaccharidesSlide Number 18Slide Number 19Slide Number 20Structures of Glucose and Other AldosesEpimersSlide Number 23Slide Number 24Slide Number 25Slide Number 26Cyclic Structure of Glucose; MutarotationSlide Number 28AnomersSlide Number 30Hemiacetals and AcetalsSlide Number 32GlycosideStructures of Galactose and FructoseGalactoseSlide Number 36DisaccharidesDisaccharidesStructures and Properties of DisaccharidesSlide Number 40Slide Number 41Slide Number 42Redox Reactions of MonosaccharidesOxidationSlide Number 45Redox Test for CarbohydratesPolysaccharides Derived from GlucoseStarchSlide Number 49Slide Number 50Slide Number 51Slide Number 52Slide Number 53Slide Number 54Slide Number 55