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Polysaccharides
Chapter 17 Section 6
Page 512 - 517
Polysaccharides
• Large molecules composed of many
monosaccharide units joined in one or
more chains.
• Most carbohydrates found in nature are
large polymers of glucose.
Starch
• A polysaccharide that is the principal
storage form of glucose in plants
• Composed of the glucose polymers
amylose and amylopectin
Amylose
• Accounts for 80% of the starch of a plant
cell
• Linear polymer of α-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 17.11 pg 513 for structure
Amylose structures
Amylopectin
• Highly branched amylose in which the
branches are attached to the C-6 hydroxyl
groups (see Figure 17.12 on pg. 513)
• Each branch contains 20-25 glucose units
Glycogen
• Major glucose storage molecule in animals
• Structure is similar to that of amylopectin
• Glycogen has more branches and
branches are shorter
Cellulose
• The most abundant organic molecule in
the world
• A polymer of β-D-glucose units linked by
β(14) glycosidic bonds
• Typically contains about 3000 glucose
units
• Structural component of the plant cell wall
• Cannot be digested by humans
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.