Page 47 - Biology_F5

Biology for Advanced Level Secondary Schools

Branch
CH OH CH OH
2 2
O O
H H H H H H
O OH H O OH H
H OH H OH
O
-(1,4) Linkages -(1,6) Branch point
H COH H COH H COH CH 2 OH CH OH CH 2 CH 2 OH
2
FOR ONLINE READING ONLY
2 2 2
O H O H O H O
OH OH OH H H H H H H H H H
HO OH O OH H O OH H O OH H O OH H O
OH OH OH H OH H OH H OH
n H OH
α (1-4) glycocidic bond Main chain
α (1-4) glycocidic bond
a (1-4) glycocidic bond
(a) (b)
Figure 1.24: Structures of (a) amylose and (b) amylopectin
Glycogen like branches of a tree. They originate
Glycogen is the form in which from a pair of molecules of glycogen in a
polysaccharide is stored in animals and protein which acts as a primer at the core of
fungi. It is often called an animal starch, the structure. Glycogen can be converted
and it is stored mainly in liver and skeletal back into glucose through the process
muscles. Like starch, it is made up of called glycogenolysis. Glycogen is easily
α-glucose molecules and exists as granules. converted back to glucose in order to
Structurally, it resembles amylopectin, provide energy for body activities. When
except that it is more branched, and its glucose cannot be stored as glycogen or
chains are shorter (Figure 1.25). The used immediately for relese of energy, it

glucose chains are organised globularly is converted into fat.

Figure 1.25: Structure of glycogen molecule
Figure 1.26 Structure of glycogen molecule

Cellulose thousands of b-glucose units, joined
Cellulose is an important structural together by 1, 4-glycosidic bonds to form
polysaccharide of plants, which largely long, unbranched chains. Many chains run
constitutes the chemistry of the cell wall. parallel to each other and have cross linkages
It is chemically composed of several between them (Figure 1.26). These help to

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