Question

Mention the difference between amylose and amylopectin.

Answer 1

Starch is a polysaccharide. It is a polymer of $\text{ }\alpha -\text{ }$ D- glucose and composed of two distinct components which are water-soluble component amylose and water-insoluble amylopectin. Amylopectin and amylose have unique chemical and physical properties. Amylose and amylopectin are found in the plant as a linear and branched structure respectively.

Complete answer:
Polysaccharides are the neutral polymeric compounds in which the hundred or even thousands of monosaccharides units are joined by the glycosidic linkage. One of the main polysaccharides found in plants is starch .starch is a polymer of $\text{ }\alpha -\text{ }$D- glucose, and consists of two components:
- Water-soluble component amylose
-Water-insoluble component amylopectin
These are explained as follows:
Amylose: Amylose is a water-soluble fraction of starch. It is a linear polymer of $\text{ }\alpha -\text{ }$D- glucose it contains about 200-1000 $\text{ }\alpha -\text{ }$D- glucose units which are linked to one other through $\text{ }\alpha -\text{ }$glycosidic linkage involving $\text{ }{{\text{C}}_{\text{1}}}\text{ }$ of one glucose and $\text{ }{{\text{C}}_{4}}\text{ }$of the next.
Amylopectin: It is a water-insoluble fraction of starch. It is a highly branched chain polymer.it consists of a large number of short chains of 25 -30 D-glucose units. In this case, the main chain involves $\text{ }\alpha -\text{ }$the linkage $\text{ }{{\text{C}}_{\text{1}}}\text{ }$ of one $\text{ }\alpha -\text{ }$D- glucose and $\text{ }{{\text{C}}_{4}}\text{ }$of the other. The $\text{ }{{\text{C}}_{\text{1}}}\text{ }$of terminal glucose in each chain is further linked to $\text{ }{{\text{C}}_{6}}\text{ }$of the other glucose units in the next chain through $\text{ }{{\text{C}}_{\text{1}}}-\text{ }{{\text{C}}_{6}}\text{ }$ $\text{ }\alpha -\text{ }$linkage. This gives a highly branched structure.
Some of the important difference between amylose and amylopectin as follows,

| Amylose | Amylopectin
---|---|---
1.| Amylose is a Straight chain polymer of D-glucose. | Amylopectin is a branched-chain polymer of D-glucose.
2.| It Contains$\text{ 20 }{\scriptstyle{}^{0}/{}_{0}}\text{ }$of starch | It Contains$\text{ 80 }{\scriptstyle{}^{0}/{}_{0}}\text{ }$of starch
3.| It is less solubility in water| It is more soluble in water
4.| It is a straight-chain structure | It has a branched structure
5.| Amylose gives blue colour with iodine| Amylose do not give blue colour with iodine
6.| It is soluble in hot water without swelling | It is soluble in hot water
7.| It does not form a gel when added to hot water.| It forms a gel when added to hot water.

Note: In the laboratory, amylose is used as a DNA marker. Iodine molecules fit inside the helical structure of amylose makes the structure easy to absorb certain wavelengths. Hence starch is used for the iodine test. Amylopectin does not give blue colour with iodine.