STORAGE POLYSACCHARIDE - STARCH
- Starches are glucose polymers in which glucopyranose units are bonded by alpha-linkages.
- It is made up of a mixture of amylose(15%-20%) and amylopectin (80%- 85%).
- Amylose consists of a linear chain of several hundred glucose molecules and amylopectin is a branched molecule made of several thousand glucose units(every chain of 24-30 glucose units is one unit of amylopectin).Starches are insoluble in water.
- They can be digested by hydrolysis, catalysed by enzymes called amylases, which can break the alpha-linkages(glycosidic bonds).
- Humans and other animals have amylases, so they can digest starches. Potato, Rice, Wheat, and maize are major sources of starch in the human diet.
- It is exclusively formed in plants and not in Animals.
Figure: Amylopectin is a glucose polymer with mainly a(1-->4) linkages, but it also has branches formed by a(1--->6) linkages. The branches are generally longer than shown above. The branches produce a compact structure, and provide multiple chain ends at which enzymatic cleavage of the polymer can occur.
Figure: Amylose is a linear polymers of glucose mainly linked with a(1-->4) bonds. It can be made of several thousands of glucose units. It is one of the two components of starch, the other being amylopectin.
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