What Is Starch?

Starch is the most important source of carbohydrates in the human diet and accounts for more than 50% of our carbohydrate intake. It occurs in plants in the form of granules, and these are particularly abundant in seeds (especially the cereal grains) and tubers, where they serve as a storage form of carbohydrates. 

Starch is a mixture of two polymers: amylose and amylopectin. Natural starches consist of about 10%–30% amylose and 70%–90% amylopectin. Amylose is a linear polysaccharide composed entirely of D-glucose units joined by the α-1,4-glycosidic linkages.

Amylopectin is a branched-chain polysaccharide composed of glucose units linked primarily by α-1,4-glycosidic bonds but with occasional α-1,6-glycosidic bonds, which are responsible for the branching. A molecule of amylopectin may contain many thousands of glucose units with branch points occurring about every 25–30 units.

What You Need To Know About Starch

• Starch is the complex sugar of glucose (polysaccharide) that is stored as carbohydrates in plants.
• It consists of two types of molecules, the linear and helical amylose and branched amylopectin.
• The glucose components of starch are produced during photosynthesis where plants use light, water and carbon dioxide. 
• Glycogen is stored in adipose tissues and primarily in the cells of the liver and skeletal muscle.
• Starch occurs in the form of grains.
• The molar mass of starch is variable.
• Starch has coiled and unbranched chains (amylose) or long, branched chains (amylopectin).
• Starch is made up of glycosidic bond, amylose and amylopectin which differ in their properties. Amylose contains unbranched, long chain with α(1-4) glycosidic bonds with varied molecular weight. Amylopectin on the other hand, contains highly branched chains, with the α(1-4) glycosidic bonds and α(1-6) linkages at their branching point (occurring at every 24 to 30 residues).
• Starch is less compact than glycogen, forming grains in cells.
• Starch is mainly found in cereals, vegetables, roots, tubers etc.
• The molecular formula of starch is (C6H10O5)n +H2O.

What Is Glycogen?

Glycogen is the energy reserve carbohydrate of animals. Practically all mammalian cells contain some stored carbohydrates in the form of glycogen, but it is especially abundant in the liver (4%–8% by weight of tissue) and in skeletal muscle cells (0.5%–1.0%). Like starch in plants, glycogen is found as granules in liver and muscle cells. When fasting, animals draw on these glycogen reserves during the first day without food to obtain the glucose needed to maintain metabolic balance.

Glycogen is a branched polymer of glucose. Glucose residues are linked linearly by α-1,4 glycosidic bonds, and approximately every ten residues a chain of glucose residues branches off via α-1,6 glycosidic linkages. The α-glycosidic bonds give rise to a helical polymer structure.

Glycogen is hydrated with three to four parts water and forms granules in the cytoplasm that are 10-40nm in diameter. The protein glycogenin, which is involved in glycogen synthesis, is located at the core of each glycogen granule. Glycogen is an analogue of starch, which is the main form of glucose storage in most plants, but starch has fewer branches and is less compact than glycogen.

What You Need To Know About Glycogen

• Glycogen is the polymeric carbohydrate of glucose that is the major component for animals, bacteria and fungi.
• It is composed of many glucose atoms which are connected by bonds to make up the complete structure of glycogen.
• Glycogen is produced from glucose where excess glucose is converted to glycogen for storage when the insulin levels are high.
• Starch is stored in plant cells referred to as amyloplast found in seeds and fruits.  
• Glycogen occurs in the form of small granules.
• Molar mass of glycogen is 666.577 g/mol.
• Glycogen has short but highly branched chains with high molecular weight.
•  Glycogen has the α(1-4) glycosidic bonds with the α(1-6) glycosidic bonds at the branching points (occurring at every 8 to 12 residues).
• Glycogen is more compact than starch, forming glycogen granules in cells.
• Glycogen is abundantly present in liver and also found in the brain, skeletal muscle etc.
• The molecular formula of glycogen is (C24H42O21).

Also Read: Difference Between Amylose And Amylopectin

Difference Between Starch And Glycogen In Tabular Form

Similarities Between Starch And Glycogen

• Both are made of the monosaccharide alpha glucose.
• Both are used as energy storage.
• Amylopectin in starch and glycogen both have 1,4 and 1,6 glycosidic bonds.
• Both form glycosidic bonds between monosaccharide molecules in condensation reactions.
• Both are compact molecules.
• Both are insoluble.
• Both can be broken down to glucose molecules for energy.

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