During this essay I will look look at the biological importance of polysaccharides and what makes them so important for us, by looking into the structure the bonding types and chemical properties of polysaccharides.
Polysaccharides are repeating units of carbohydrates or chains of monosaccharides joint together by various glycosidic bonds . These covalent bonds form after condensation reaction takes place as the monosccharides bond. These chains can be branched or unbranched.
These long chains are insoluble, and have the general formula of Cn(H2O)n-1 .
We divide polysaccharides into two group : Storage polysaccharides and Structural polysaccharides.
Starch is an storage polysaccharides made up of alpha glucose molecules. These alpha glucose molecules are made up of two components : Amylose and Amylopectin. Amylose is about 300 glucose molecules joint together by an alpha 1-4 glycosidic bond, but the CH2OH would not fit if the chain would be in a straight line , they are too bulky. Therefore the molecule curves bending it into a very compact helical shape. And when the molecule takes it’s shape , hydrogen bonds keeps the molecule stable. Amylose makes up around 15-20% of starch , the other 85-80% are amylopectin.
Amylopectin is a branched chain of alpha glucoses joint with the 1-6 glycosidic bond.
This branching bond occurs every 25-30 glucose units.
These branches give a lot of end points making it easy for enzymes to attach on and quickly degenerate the molecule. In contrast amylose contains very few alpha 1-6 bonds, which means that hydrolysation is slower, but the molecule has higher density and be insoluble. Starch is the main carbohydrate food store in plants. And the plant stores excess glucose as starch because it is compact so one molecule of starch is equal to many molecules of glucose, this also lowers the osmotic gradient in the cell. As glucose it could leave the cell and starch is not very reactive however it can easily be.