Difference Between Amylose and Amylopectin

Main Difference – Amylose vs Amylopectin

Starch is a colorless and odorless solid substance that can be found in plants as their storage carbohydrate. Starch is a polysaccharide. It is composed of a number of glucose monomers. These glucose molecules are bound to each other through glycosidic bonds in order to form polysaccharide. Starch is composed of two types of molecules known as amylose and amylopectin. Amylose molecules are formed from several glucose units arranged in a linear manner. Amylopectin is formed from several glucose units arranged in a branched manner. This is the key difference between amylose and amylopectin molecules present in starch.

Key Areas Covered

1. What is Amylose
      – Definition, Occurrence, and Reactions
2. What is Amylopectin
      – Definition, Occurrence, and Reactions
3. What are the Similarities Between Amylose and Amylopectin
      – Outline of Common Features
4. What is the Difference Between Amylose and Amylopectin
      – Comparison of Key Differences

Key Terms: Amylopectin, Amylose, Glycosidic Bonds, Glucose, Monosaccharide, Polysaccharide, Starch

What is Amylose

Amylose is a straight chain polymer of D-glucose units. It is a polysaccharide made out of several monosaccharide units. The monosaccharide involved in the formation of amylose is D-glucose. Therefore, amylose is considered as a polymer.

20-25% of starch content is amylose. The type of chemical bond present between glucose monomers is called α 1-4 glycosidic linkage. This is because the OH group attached to the first carbon of a glucose molecule is removed along with an H atom attached to the fourth carbon of another glucose molecule in the formation of amylose. This is known as a condensation reaction since the removed OH group, and H atom together forms a water molecule.

Main Difference - Amylose vs Amylopectin

Figure 1: Amylose 3D Projection

When iodine solution is added to starch, it turns to a dark blue/ black color. This color change is given by amylose present in starch along with amylopectin. Amylose is more soluble in water than amylopectin. Amylose can be hydrolyzed into glucose units by enzymes such as α amylase and β amylase.

What is Amylopectin

Amylopectin is a branched chain polymer of D-glucose units. It is a polysaccharide that is composed of monosaccharides. Monosaccharides are D-glucose molecules. Starch contains about 80% of amylopectin.

Amylopectin molecules are composed of glucose units bonded to each other via α 1-4 glycosidic linkages and α 1-6 glycosidic linkages. These α 1-6 glycosidic linkages cause the branched structure of amylopectin. Here, the glucose molecules are bonded to each other through the fourth carbon atom as well as the sixth carbon atom.

Difference Between Amylose and Amylopectin

Figure 2: Branching in Amylopectin

The color change given by amylopectin when iodine solution is added is reddish brown color. In the presence of α amylase and β amylase enzymes, α 1-4 glycosidic linkages can be hydrolyzed but α 1-6 glycosidic linkages cannot be hydrolyzed.

Amylopectin is less soluble in water. But amylopectin is soluble in hot water with swelling. It can from starch gel or paste when it cools down.

Similarities Between Amylose and Amylopectin

Both are polysaccharide molecules.
Both are composed of D-glucose units.
Both molecules have α 1-4 glycosidic linkages.
Both types are found in starch granules.

Definition

Amylose: Amylose is a straight chain polymer of D-glucose units.

Amylopectin: Amylopectin is a branched chain polymer of D-glucose units.

Percentage in Starch

Amylose: Amylose content in starch is about 20%.

Amylopectin: Amylopectin content in starch is about 80%.

Structure

Amylose: Amylose is a straight chain structure.

Amylopectin: Amylopectin is a branched structure.

Glycosidic Bonds

Amylose: Amylose has α 1-4 glycosidic linkages.

Amylopectin: Amylopectin has α 1-4 glycosidic linkages and α 1-6 glycosidic linkages.

Solubility in Water

Amylose: Amylose is less soluble in water.

Amylopectin: Amylopectin is more soluble in water.

Color Change with Iodine

Amylose: Amylose gives a dark blue/black color when iodine solution is added.

Amylopectin: Amylopectin gives a reddish brown color when iodine solution is added.

Hydrolysis with Enzymes

Amylose: Amylose can be hydrolyzed with α amylase and β amylase enzymes completely.

Amylopectin: Amylopectin cannot be hydrolyzed with α amylase and β amylase enzymes completely.

Formation of Gel

Amylose: Amylose does not form a gel when hot water is added.

Amylopectin: Amylopectin forms a gel when hot water is added.

Conclusion

Amylose and amylopectin are two types of polysaccharides that can be found in starch granules. They have both structural and chemical differences as well as similarities. The main difference between amylose and amylopectin is that amylose is a straight chain polymer whereas amylopectin is a branched chain polymer.

References:

1. “Amylose: Structure, Formula & Function.” Study.com, Available here. Accessed 27 Sept. 2017.
2. “14.7: Polysaccharides.” Chemistry LibreTexts, Libretexts, 14 Oct. 2016, Available here. Accessed 27 Sept. 2017.

Image Courtesy:

1. “Amylose 3Dprojection.corrected” By glycoform – Own work (Public Domain) via Commons Wikimedia
2. “Amylopektin Sessel” By NEUROtiker – Own work (Public Domain) via Commons Wikimedia