Polysaccharides

1
Polysaccharides

• Chapter 17 Section 4
• Pages 485-491

2
Polysaccharides

• Large molecules composed of many monosaccharide
  units joined in one or more chains.
• Most carbohydrates found in nature are large
  polymers of glucose.

3
Starch

• A polysaccharide that is the principal storage
  form of glucose in plants
• Composed of the glucose polymers amylose and
  amylopectin

4
Amylose

• Accounts for 80 of the starch of a plant cell
• Linear polymer of a-D-glucose connected by
  glycosidic bonds between C-1 and C-4
• Due to hydrogen bonding, amylose coils up into a
  helix that repeats every six glucose units
• See Figure 17.10 pg 486 for structure

5
Amylose structures
6
Amylopectin

• Highly branched amylose in which the branches are
  attached to the C-6 hydroxyl groups (see Figure
  17.11 on pg. 487)
• Each branch contains 20-25 glucose units

7
Glycogen

• Major glucose storage molecule in animals
• Structure is similar to that of amylopectin
• Glycogen has more branches and branches are
  shorter

8
Cellulose

• The most abundant organic molecule in the world
• A polymer of ß-D-glucose units linked by ß(1?4)
  glycosidic bonds
• Typically contains about 3000 glucose units
• Structural component of the plant cell wall
• Cannot be digested by humans

9
Cellulose, continued

• Only a few animals such as termites, cows, and
  goats can digest cellulose due to the
  microorganisms that produce the enzyme cellulase.
• In humans, cellulose from fruits and vegetables
  serves as fiber in the diet.