Plantlet The Blogging Platform of Department of Botany, University of Dhaka
Polysaccharides are polymeric carbohydrate molecules composed of long chains of monosaccharide unit bound together by glycosidic linkage. Example: starch, glycogen, cellulose, chitin etc.
Characteristics of polysaccharide
- On hydrolysis, they yield monosaccharide units which are usually similar.
- D glucose is the commonest component of polysaccharide.
- They have high molecular weight.
- They are usually amorphous, tasteless, nonsugar, insoluble in water.
- A great majority of carbohydrate of nature occurs in polysaccharide.
- They do not exhibit any properties of aldehyde or ketone.
Starch
Starch is the most abundant polysaccharide after cellulose. It is a storage product and found in tubers, roots, seeds and other storage organs where it functions as a reserve nutrient for the growth and development of the plant.
Starch content of cereal grains range from 10 to 30% and potatoes from 50 to 70% of dry weight.
Components of starch
Amylose (15-20%) and amylopectin (80-85%) are the two component of starch and these two are polysaccharide themselves.
| Amylose | Amylopectin |
| 15-20% of total starch | 80-85% of total starch |
| Amylose has a straight chain | Amylopectin has a branched chain |
| Bond among the glucose is 1, 4 type | Both 1,4 and 1, 6 (to branch out) |
| Less soluble in water | More soluble in water |
| Does not form a gel when hot water is added | Forms a gel when hot water is added |
| Can be hydrolyzed with α amylase and β amylase enzymes completely | Can not be hydrolyzed with α amylase and β amylase enzymes completely |
| Gives a dark blue or black color when iodine solution is added | Gives a reddish brown color when iodine solution is added |
(More will be added later)
