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Polysaccharides

Satisfactory Essays
Polysaccharides

Polysaccharides are polymers composed of multiple subunits of

monosaccharides (simple sugars). They are formed by condensation

reaction, in the same way as disaccharides are formed, the difference

stands in the larger number of monomer units which they are composed

from . The number of monosacchardies composing the chain is variable,

and there are two types of chains that can be formed: branched or

unbranched. The chains may be folded, thus making them compact and

therefore ideal for storage. The size of the molecule makes them

hydrophopic ( insoluble), which is another feature that makes them

ideal for storage, as they exert no osmotic influence and do not

easily diffuse out of the cell. If undergone to the process of

hydrolysis, polysaccharides can be converted to their constituent

monosaccharides ready for use as respiratory substrates. Examples of

storage polysaccharides are starch and glycogen.

Starch:

Starch is a mixture of two kinds of polymers of - glucose, amylose and

amylopectin. In amylose, the glucose units are joined by a linear

succession of (1 => 4) glycosidic links. The lengths of the amylose

chains vary within the same sample, but over 1000 glucose units occur

per amylose molecule. The formula masses range from 150 000 to 600

000. These molecules are found under the form of large grains,

ubicated in the inside of chloroplasts and in storage organs. They are

visible under a light microscope.

The long amylose molecules coil into spiral-like helices , which tuck

a significant fraction of the OH groups inside and away from the

contact with water. Thus amylose is only slightly soluble in water.

Amylopectin molecules have both (1 => 4) and (1=>6) glycosidic links.

The (1=>6) bridges link the C-1 ends of linear amylose-type to to C-6

positions of glycose units in other long amylose chains. There are

hundreds of such links per molecule, so amylopectin is heavily

branched, and the branches prevent any coiling of the polymer. This

leaves many more OH groups exposed to water than in amylose, so