Download Carbohydrates

Carbohydrates
• Carbohydrates serve as fuel and building
material
• Carbohydrates
– Include both sugars and their polymers
Sugars
• Monosaccharides
•
Are the simplest sugars
•
Can be used for fuel
•
Can be converted into other organic
molecules
•
Can be combined into polymers
Examples of monosaccharides
Triose sugars
(C3H6O3)
H
O
Pentose sugars
(C5H10O5)
H
Aldoses
C
O
H
O
C
C
OH
H
C
OH
H
C
OH
H
C
OH
H
C
OH
HO
C
H
C
OH
H
H
C
OH
H
Ribose
H
H
C
H
C
OH
H
HO
C
H
C
OH
HO
C
H
H
C
OH
H
C
OH
H
C
OH
H
C
OH
H
H
Glucose
Galactose
H
C OH
H
C
O
H
C OH
H
C OH
C
O
O
C OH
H
C OH
HO
H
H
C OH
H
C OH
Dihydroxyacetone
H
C OH
H
C OH
H
H
C OH
H
Ribulose
O
C
H
H
Ketoses
H
C
Glyceraldehyde
Figure 5.3
Hexose sugars
(C6H12O6)
C H
H
Fructose
Monosaccharides
• May be linear
• Can form rings
O
H
1C
6CH OH
2
6CH OH
2
2
H
C
OH
C
OH
OH
5
H
C
OH
6
H
H
OH
4C
C
C
OH
5C
H
H
H
4
H
O
H
3
HO
5C
3
C
H
2C
H
H
4C
1C
CH2OH
O
H
OH
O
OH
6
H
4
H
2C
OH
H
1
OH
3
OH
2
OH
H
H
H
H
1C
HO
3C
O
5
OH
OH
H
Figure 5.4 (a) Linear and ring forms. Chemical equilibrium between the linear and ring
structures greatly favors the formation of rings. To form the glucose ring,
carbon 1 bonds to the oxygen attached to carbon 5.
• Disaccharides
– Consist of two monosaccharides
– Are joined by a glycosidic linkage
(a) Dehydration reaction
in the synthesis of
maltose. The bonding
of two glucose units
forms maltose. The
glycosidic link joins
the number 1 carbon
of one glucose to the
number 4 carbon of
the second glucose.
Joining the glucose
monomers in a
different way would
result in a different
disaccharide.
• Examples of disaccharides
CH2OH
CH2OH
H
O
H
OH H
OH
HO
H
H
H
HO
H
OH
H
OH
H
H
OHOH
H
O
H
OH H
CH2OH
H
1–4
1 glycosidic
linkage
HO
4
O
H
H
OH H
OH
O
H
OH
H
H
OH
OH
H2O
Glucose
Glucose
CH2OH
H
(b) Dehydration reaction
in the synthesis of
HO
sucrose. Sucrose is
a disaccharide formed
from glucose and fructose.
Notice that fructose,
though a hexose like
glucose, forms a
five-sided ring.
Figure 5.5
O
CH2OH
O
H
OH
H
H
CH2OH
H
OH
HO
CH2OH
O
H
H
H
HO
CH2OH
OH
OH
Maltose
H
O
H
OH
H
1–2
glycosidic
1
linkage
H
Fructose
2
H
H
CH2OH
OH H
OH
Sucrose
H
HO
O
HO
H2O
Glucose
CH2OH
O
Polysaccharides
• Polysaccharides
– Are polymers of sugars
– Serve many roles in organisms
Storage Polysaccharides
• Starch
– Is a polymer consisting entirely of glucose
monomers
Chloroplast
Starch
– Is the major storage form of glucose in
plants
1 m
Amylose
Amylopectin
Figure 5.6 (a) Starch: a plant polysaccharide
• Glycogen
– Consists of glucose monomers
Mitochondria Giycogen
– Is the major storage form granules
of glucose in
animals
0.5 m
Glycogen
Figure 5.6 (b) Glycogen: an animal polysaccharide
Structural Polysaccharides
• Cellulose
– Is a polymer of glucose
H
CH2O
H
O
H
OH H
O
CH2O
H
H
O OH
H
4
1
OH H
HO
H
C
– Has different glycosidic linkages than starch
H
4
H
OH
HO
H
OH
 glucose
H
C
OH
HO
C
H
H
C
OH
H
C
OH
H
C
OH
H
OH
 glucose
(a)  and  glucose ring structures
CH2O
H
O
CH2O
H
O
HO
4
1
OH
O
1
OH
4
O
1
OH
OH
OH
CH2O
H
O
CH2O
H
O
O
4
1
OH
O
OH
OH
(b) Starch: 1– 4 linkage of  glucose monomers
CH2O
H
O
HO
Figure 5.7 A–C
OH
CH2O
H
O
OH
O
1
4
OH
O
OH
OH
O
OH
O
O
CH2O
CH2O
OH
OH
H
H
(c) Cellulose: 1– 4 linkage of  glucose monomers
OH
– Is a major component of the tough walls that
enclose plant cells
Cell walls
Cellulose microfibrils
in a plant cell wall
Microfibril
About 80 cellulose
molecules associate
to form a microfibril, the
main architectural unit
of the plant cell wall.
0.5 m
Plant cells
Parallel cellulose molecules are
held together by hydrogen
bonds between hydroxyl
groups attached to carbon
atoms 3 and 6.
Figure 5.8
OH CH2OH
OH
CH2OH
O O
O O
OH
OH
OH
OH
O
O O
O O
O CH OH
OH
CH2OH
2
H
CH2OH
OH CH2OH
OH
O O
O O
OH
OH
OH
OH
O
O O
O O
O CH OH
OH CH2OH
2
H
CH2OH
OH
OH CH2OH
O O
O O
OH
OH
OH O
O OH
O O
O
O CH OH
OH CH2OH
2
H
 Glucose
monomer
Cellulose
molecules
A cellulose molecule
is an unbranched 
glucose polymer.
• Cellulose is difficult to digest
– Cows have microbes in their stomachs to
facilitate this process
Figure 5.9
• Chitin, another important structural
polysaccharide
– Is found in the exoskeleton of arthropods
CH O
– Can
be used as surgical thread
H
2
O OH
H
OH H
OH
H
H
H
NH
C
O
CH3
(a) The structure of the (b) Chitin forms the exoskeleton
of arthropods. This cicada
chitin monomer.
is molting, shedding its old
exoskeleton and emerging
Figure 5.10 A–C
in adult form.
(c) Chitin is used to make a
strong and flexible surgical
thread that decomposes after
the wound or incision heals.