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Mr. Orend Honors Biology
Useful Polysaccharides
Building Blocks Of Life
Four common polysaccharides found in nature are starch, glycogen, chitin, and cellulose. These
macromolecules are used as direct energy sources, energy storage, and cellular structure. As we will
see below, both plants and animals use polysaccharides in abundance, and they are required for life.
Starch

Starch is a polysaccharide used for energy storage in plant roots and other tissues.

It consists entirely of glucose monomers (a common monosaccharide).

Starch molecules coil into a helical shape, and may be branched or unbranched.

Starch is stored in plants as granules, huge masses of sugar molecules, that serve as stockpiles.

Plant cells need sugar for energy and as a raw material for building other molecules.

Starch can be found in large quantities in potatoes and grains, such as wheat, corn, and rice,
staples of the human diet.
Amylose – an unbranched starch
Amylopectin – a branched starch
Glycogen

Animals store excess sugar in the form of a polysaccharide called glycogen.

Glycogen is identical to starch, except that it is more extensively branched.

Most of our glycogen is stored as granules in the liver and muscle cells.

Glucose is released from these granules when needed for energy.
Structure of glycogen – NOTICE THE
EXTENSIVE BRANCHING!
Cellulose

Cellulose is a very important polysaccharide because it is the most abundant organic compound
on earth.

Cellulose is a major component of tough cell walls that surround plant cells, and is what makes
plant stems, leaves, and branches so strong. Next time you eat a salad, think about how much
you have to chew it in order to be able to swallow all that plant material. It certainly takes a lot of
work, and this is due in part to the structure of cellulose.

Imagine a bunch of long, thick ropes stuck together. This is very much what cellulose is like, but
on a microscopic scale. Cellulose molecules are arranged parallel to each other, and are joined
together with hydrogen bonds. This forms long, cable-like structures, which combine with other
cellulose molecules, and is what produces such a strong support structure.
Function
The rigid structure of cellulose is
what allows plants to stand
upright, and without the strength
of cellulose, we wouldn't have
lumber, paper, or cotton fabric.
Because of its strength,
cellulose is also used in a host
of synthetic products such as
carpeting, thickening agents in shampoo and suntan lotion, cosmetics, plastics (like your toothbrush
handle), and other fabrics like rayon.
Chitin

Chitin (C8H13O5N)n is a polymer of a N-acetylglucosamine, a derivative of glucose.

Chitin is found in many places throughout the natural world, and it is the second most abundant
organic compound in nature, after cellulose.

It is the main component of the cell walls of fungi, and the exoskeletons of arthropods such
as crustaceans (e.g., crabs,lobsters and shrimps) and insects.

The structure of chitin is comparable to the polysaccharide cellulose, forming crystalline cablelike fibers.

In terms of function, it may be compared to the protein keratin, found in nails and hair.