Key difference - starch vs. cellulose vs. glycogen
Starch, cellulose, and glycogen are three types of polymeric carbohydrates found in living cells. During photosynthesis, autotrophs produce glucose as a simple sugar. All of these carbohydrate polymers, starch, cellulose and glycogen, consist of the connection of glucose monomer units through various types of glycosidic bonds. They serve as chemical energy sources and as a structural part of the cell. The main difference between starch, cellulose and glycogen is that starch is the main storage carbohydrate source in plants, while cellulose is the main structural component of the cell wall of plants and glycogen is the main storage carbohydrate source in fungi and animals.
This article examines
1. What is starch - structure, properties, source, function 2. What is cellulose - structure, properties, source, function 3. What is glycogen - structure, properties, source, function 4. What is the difference between starch cellulose and glycogen
What is strength
Starch is the polysaccharide that is synthesized by green plants as the main energy store. Glucose is made as a simple organic compound by photosynthetic organisms. It is converted into insoluble substances such as oils, fats and starches for storage. Insoluble storage substances such as starch do not influence the water potential in the cell. You are not allowed to move away from the storage areas. In plants, glucose and starch are converted into building blocks such as cellulose. They are also converted into proteins that are needed for the growth and repair of cell structures.
Plants store glucose in staple foods like fruits, tubers like potatoes, seeds like rice, wheat , corn and cassava. Starch occurs in granules called amyloplasts, which are arranged in semi-crystalline structures. Starch is made up of two types of polymers: amylose and amylopectin. Amylose is a linear and helical chain, but amylopectin is a branched chain. About 25% of the starch in plants is amylose while the rest is amylopectin. Glucose-1-phosphate is first converted into ADP-glucose. ADP-glucose is then polymerized by the enzyme starch synthase via a 1,4-alpha-glycosidic bond. This polymerization forms the linear polymer amylose. The 1,6-alpha-glycosidic bonds are introduced into the chain by the starch branching enzyme that amylopectin produces. Starch grains from rice are shown in Figure 1 .
What is cellulose?
Cellulose is the polysaccharide that consists of hundreds to many thousands of glucose units. It is the main component of the cell wall of plants. Many algae and oomycetes also use cellulose to make their cell walls. Cellulose is a straight-chain polymer in which 1,4-beta-glycosidic bonds are formed between glucose molecules. Hydrogen bonds are formed between several hydroxyl groups on a chain with adjacent chains. This allows the two chains to be held tightly together. Several cellulose chains are also involved in the formation of cellulose fibers. A cellulose fiber, which consists of three cellulose chains, is shown in Figure 2 . Hydrogen bonds between cellulose chains are shown in cyan lines.
What is glycogen
Glycogen is the storage polysaccharide of animals and fungi. It is the analogue of starch in animals. Glycogen is structurally similar to amylopectin, but more branched than the latter. Linear chains are formed via 1,4-alpha-glycosidic bonds and branching occurs via 1,6-alpha-glycosidic bonds. Branching occurs in all 8 to 12 glucose molecules in the chain. Its granules occur in the cytosol of cells. Liver cells and muscle cells store glycogen in humans. As soon as it is needed, glycogen is broken down into glucose by glycogen phosphorylase. The process is known as glycogenolysis. Glucogon is the hormone that stimulates glycogenolysis. 1,4-alpha-glycosidic and 1,6-alpha-glycosidic linkages of glycogen are shown in Figure 3 .
Difference between starch cellulose and glycogen
Starch: Starch is the main source of carbohydrate storage in plants.
Cellulose: Cellulose is the main structural component of the cell wall of plants.
Glycogen: Glycogen is the main source of carbohydrate storage for fungi and animals.
Starch: The monomer of starch is alpha-glucose.
Cellulose: The monomer of cellulose is beta-glucose.
Glycogen: The monomer of glycogen is alpha-glucose.
Bond between monomers
Starch: The 1,4-glycosidic bonds in amylose and 1,4- and 1,6-glycosidic bonds in amylopectin occur between starch monomers.
Cellulose: 1,4-glycosidic bonds occur between the monomers of cellulose.
Glycogen: 1,4- and 1,6-glycosidic bonds occur between the monomers of glycogen.
Nature of the chain
Starch: Amylose is a straight, coiled chain and amylopectin is a long branched chain, some of which are coiled.
Cellulose: Cellulose is a straight, long, unbranched chain that forms hydrogen bonds with neighboring chains.
Glycogen: Glycogen is a short, many branched chain, some of which chains are twisted.
Starch: The molecular formula of starch is (C 6 H 10 O 5 ) n
Cellulose: The molecular formula of cellulose is (C 6 H 10 O 5 ) n.
Glycogen: The molecular formula of glycogen is C 24 H 42 O 21 .
Starch: The molar mass of starch is variable.
Cellulose: The molecular weight of cellulose is 162.1406 g / mol.
Glycogen: The molar mass of glycogen is 666.5777 g / mol.
Starch: Starch is found in plants.
Cellulose: Cellulose is found in plants.
Glycogen: Glycogen is found in animals and fungi.
Starch: Starch serves as a carbohydrate energy store.
Cellulose: Cellulose is involved in building cell structures such as cell walls.
Glycogen: Glycogen serves as a carbohydrate energy store.
Starch: Starch is found in grain.
Cellulose: Cellulose is found in fibers.
Glycogen: Glycogen occurs in small granules.
Starch, cellulose and glycogen are polysaccharides found in organisms. Starch is the most important storage form of carbohydrates in plants. Linear starch chains are called amylose and when they are branched they are called amylopectin. Glycogen is similar to amylopectin, but is highly branched. It is the main form of carbohydrate storage in animals and fungi. Cellulose is a linear polysaccharide that hydrogen bonds between multiple cellulose chains to form a fibrous structure. It is the main component of the cell wall of plants, some algae and fungi. Thus, the main difference between starch cellulose and glycogen is their role in each organism.
Reference: 1. Berg, Jeremy M. “Complex carbohydrates are formed by linking monosaccharides.” Biochemistry. 5th edition. US National Library of Medicine, January 1, 1970. Web. May 17, 2017. <https://www.ncbi.nlm.nih.gov/books/NBK22396/>.
Image courtesy: 1. “Rice starch - microscopy” By MKD - Own work (CC BY-SA 3.0) via Commons Wikimedia 2. “Cellulose spacefilling model” By CeresVesta (talk) (uploads) - Own work (public domain) via Commons Wikimedia 3 . "Glycogen" (Public Domain) via Commons Wikimedia