Polysaccharides Chapter 17 Section 6 Page

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 pg 513 for structure

Amylose structures

Amylopectin Highly branched amylose in which the branches are attached to the C-6 hydroxyl groups (see Figure on pg. 513) Each branch contains 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.