Starch, cellulose and glycogen are all polysaccharides made up of glucose subunits. Starch and glycogen are made up of 𝜶-glucose subunits, whereas cellulose is made up of 𝛃-glucose subunits. Cellulose is unbranched and a straight-chain polymer of glucose, whereas starch and glycogen are branched. Let’s learn more about these polysaccharides and their differences.
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Difference between Starch, Cellulose and Glycogen
The table below shows the main differences between starch, cellulose and glycogen.
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It is a polymer of 𝜶-glucose subunits |
It is made up of 𝛃-glucose subunits |
It is a polymer of 𝜶-glucose subunits |
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It contains two types of polymers, amylose (unbranched and coiled) and amylopectin (branched) |
It is made up of unbranched, straight chains having hydrogen bonding between adjacent chains |
It is highly branched and similar to amylopectin |
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The 𝜶-glucose subunits are joined by 1,4 glycosidic bonds in amylose and 1,4 and 1,6 glycosidic bonds in amylopectin |
𝛃-glucose monomers are linked by 1,4 glycosidic bonds |
The 𝜶-glucose subunits are joined by 1,4 and 1,6 glycosidic bonds |
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Amylose is unbranched and amylopectin is branched |
It is unbranched |
It is highly branched |
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It is the main storage carbohydrate in plants |
It is the main component of the plant cell wall |
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.
Starch is the main dietary energy source for humans. It is present in most cereals, roots, tubers and also in some vegetables.
Structure of Cellulose
Cellulose is the main structural component of the plant cell wall. It is exclusively present in plants. Cellulose is the most abundant organic compound of the plant kingdom. It is made up of 𝛃-glucose subunits that are joined by 1–4 glycosidic bonds. It is a straight and unbranched polymer of glucose. The hydrogen bonding between glucose units of adjacent chains makes strong fibres.
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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