1. Carbohydrates Carbohydrates serve as fuel and building material
Include both sugars and their polymers

2. Sugars Monosaccharides Are the simplest sugars Can be used for fuel
Can be converted into other organic
molecules
Can be combined into polymers

3. Examples of monosaccharides
Triose sugars (C3H6O3)
Pentose sugars (C5H10O5)
Hexose sugars (C6H12O6)
H C OH
H C OH
HO C H
H C OH
C O
HO C H H C O
Aldoses
Glyceraldehyde
Ribose
Glucose
Galactose
Dihydroxyacetone
Ribulose
Ketoses
Fructose
Figure 5.3

4. Monosaccharides May be linear Can form rings 4C 3 2 OH Figure 5.4
H C OH
HO C H
H C O C 1 2 3 4 5 6 OH 4C
6CH2OH 5C
H OH
2 C 1C
3 C 2C
1 C
CH2OH HO
(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.
Figure 5.4

5. Disaccharides Consist of two monosaccharides
Are joined by a glycosidic linkage

6. Examples of disaccharides
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.
Dehydration reaction in the synthesis of sucrose. Sucrose is a disaccharide formed from glucose and fructose. Notice that fructose, though a hexose like glucose, forms a five-sided ring.
(a)
(b) H HO
H OH OH O
CH2OH
H2O 1 2 4
1– 4 glycosidic linkage
1–2 glycosidic linkage
Glucose
Fructose
Maltose
Sucrose
Figure 5.5
Examples of disaccharides

7. Polysaccharides Polysaccharides Are polymers of sugars
Serve many roles in organisms

8. Storage Polysaccharides
Starch
Is a polymer consisting entirely of glucose monomers

9. (a) Starch: a plant polysaccharide
Chloroplast
Starch
Amylose
Amylopectin
1 m
(a) Starch: a plant polysaccharide
Figure 5.6
Is the major storage form of glucose in plants

10. (b) Glycogen: an animal polysaccharide
Consists of glucose monomers
Is the major storage form of glucose in animals
Mitochondria
Giycogen granules
0.5 m
(b) Glycogen: an animal polysaccharide
Glycogen
Figure 5.6

11. Structural Polysaccharides
Cellulose
Is a polymer of glucose

12. Has different glycosidic linkages than starch
(c) Cellulose: 1– 4 linkage of  glucose monomers H O
CH2OH OH HO 4 C 1
(a)  and  glucose ring structures
(b) Starch: 1– 4 linkage of  glucose monomers
 glucose
 glucose
Figure 5.7 A–C
Has different glycosidic linkages than starch

13. Is a major component of the tough walls that enclose plant cells
Cell walls
Cellulose microfibrils
in a plant cell wall 
Microfibril
CH2OH OH O
Glucose monomer
Parallel cellulose molecules are
held together by hydrogen
bonds between hydroxyl
groups attached to carbon
atoms 3 and 6.
About 80 cellulose
molecules associate
to form a microfibril, the
main architectural unit
of the plant cell wall.
A cellulose molecule
is an unbranched 
glucose polymer.
Cellulose
molecules
Figure 5.8
Is a major component of the tough walls that enclose plant cells

14. Cellulose is difficult to digest
Cows have microbes in their stomachs to facilitate this process
Figure 5.9

15. Chitin, another important structural polysaccharide
Is found in the exoskeleton of arthropods
Can be used as surgical thread
(a) The structure of the
chitin monomer. O
CH2OH OH H NH C
CH3
(b) Chitin forms the exoskeleton
of arthropods. This cicada
is molting, shedding its old
exoskeleton and emerging
in adult form.
(c) Chitin is used to make a
strong and flexible surgical
thread that decomposes after
the wound or incision heals.
Figure 5.10 A–C