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Figure 10 Overview of the types of polysaccharides.
2.3.1 Storage Polysaccharides - Starch
Starch is a polymer of glucose molecules. ie. Glucose is the basic unit of starch.
Stored as starch granules in plants.
Starch is NOT found in animals.
Starch exists in 2 forms: (i) long chain of glucose molecules or (ii) branched chains of glucose molecules.
Figure 12 Branched chain starch molecule known as amylopectin.
Good store of energy because
- A large number of glucose units can be stored within a small volume of starch.
- Starch molecule is insoluble in water and thus it does not affect water potential of plant cells.
2.3.2 Storage Polysaccharides - Glycogen
Branched chain of polymer.
Consists of glucose as basic units.
Stored in the liver and skeletal muscles of vertebrate animals.
Liver can store about 100 g of glycogen.
Figure 11 Straight chain starch molecule known as amylose.
Fig 13 Structure of glycogen which is highly branched.
2.3.4 Structural Polysaccharides - Cellulose
Glucose molecules joined to form a long linear chains known as cellulose fibrils.
In the cellulose cell wall, long cellulose fibrils interlock in a criss-cross mesh.
Provides strength for the cell wall.
Figure 14 Structure of cellulose.
Man lack the enzyme (cellulase) to digest cellulose. Thus, cellulose aids in peristalsis – ie a series of rhythmic contractions and relaxations that move food substances down the digestive tract.
Herbivores contain cellulase which breaks down cellulose into glucose.
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