2.Compare the functions of starch and glycogen with a note about their different linkages.

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 2.Compare the functions of starch and glycogen with a note about their different linkages.

answers: 

Difference between Starch, and Glycogen

The table below shows the main differences between starch, cellulose and glycogen.

Difference between starch, cellulose and glycogen

Starch


Glycogen

It is a polymer of 𝜶-glucose subunits


It is a polymer of 𝜶-glucose subunits

It contains two types of polymers, amylose (unbranched and coiled) and amylopectin (branched)


It is highly branched and similar to amylopectin

The 𝜶-glucose subunits are joined by 1,4 glycosidic bonds in amylose and 1,4 and 1,6 glycosidic bonds in amylopectin


The 𝜶-glucose subunits are joined by 1,4 and 1,6 glycosidic bonds

Amylose is unbranched and amylopectin is branched


It is highly branched

It is the main storage carbohydrate in plants


It is the main storage carbohydrate in animals and fungi

Structure of Starch

Starch is the main storage carbohydrate of plants. It is made up of 𝜶-glucose subunits. It contains two types of polymers, amylose and amylopectin.

  • Amylose – It is water-soluble and unbranched. Starch contains around 15-20% of amylose. It has coiled, unbranched chains of 𝜶-glucose units joined by 1–4 glycosidic linkage.
  • Amylopectin – It is water-insoluble and branched. Starch contains around 80-85% of amylopectin. It has 𝜶-glucose units joined by 1–4 glycosidic linkage and branching occurs through 1–6 glycosidic linkage. It has branching after around every 20 subunits.

Amylose and amylopectin

Starch is the main dietary energy source for humans. It is present in most cereals, roots, tubers and also in some vegetables.

Structure of Glycogen

It is the main storage carbohydrate in animals and fungi. It is highly branched and the structure is similar to that of amylopectin. It is a polymer of 𝜶-glucose subunits joined together by 1,4 and 1,6 glycosidic bonds. It has branching after around every 10 subunits.

Glycogen is also known as animal starch. It is stored in the liver, muscle and brain. When the body requires energy, glycogen is broken down to glucose by a process called glycogenolysis. The enzyme glycogen phosphorylase catalyses the breakdown of glycogen. Glycogen is converted to glucose-1-phosphate, which is then converted to glucose-6-phosphate by the enzyme phosphoglucomutase.

When the blood glucose level increases, glucose is converted into glycogen. The process of synthesis of glycogen is called glycogenesis. This interconversion of glucose to glycogen is under hormonal control. Glucagon and epinephrine promote glycogenolysis, and insulin stimulates glycogenesis.



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