Amylose vs Cellulose
Starch is a carbohydrate which is categorized as a polysaccharide. When ten or higher number of monosaccharides is joined by glycosidic bonds, they are known as polysaccharides. Polysaccharides are polymers and, therefore, have a larger molecular weight, typically more than 10000. Monosaccharide is the monomer of this polymer. There can be polysaccharides made out of a single monosaccharide and these are known as homopolysaccharides. These can be also classified based on the type of monosaccharide. For example, if the monosaccharide is glucose, then the monomeric unit is called a glucan. Starch and cellulose are glucans like that.
This is a part of starch, and it is a polysaccharide. D-glucose molecules are linked to each other in order to form a linear structure called amylose. Large amounts of glucose molecules can participate in forming an amylose molecule. This number can be ranging from 300 to several thousand. When the D-glucose molecules are in cyclic form, number 1 carbon atom can form a glycosidic bond with the 4th carbon atom of another glucose molecule. This is called a α-1,4-glycosidic bond. Because of this linkage amylose has obtained a linear structure.
There can be three forms of amylose. One is a disordered, amorphous form, and there are two other helical forms. One amylose chain can bind with another amylose chain or with another hydrophobic molecule like amylopectin, fatty acid, aromatic compound etc. When only amylose is in a structure, it is tightly packed because they don’t have branches. So the rigidity of the structure is high. Amylose makes 20-30% of the structure of starch.
Amylose is insoluble in water. Amylose is the reason for the insolubility of starch too. It also reduces the crystallinity of amylopectin. In plants, amylose is functioning as an energy storage. When amylose is degraded into smaller carbohydrate forms as maltose, they can be used as a source of energy. When performing the iodine test for starch, the iodine molecules are fit into the helical structure of amylose, hence give the dark purple/blue color.
Cellulose is a polysaccharide which is made out of glucose. 3000 glucose molecules or more than that can be joined together when forming cellulose. Not like other polysaccharides, in cellulose, glucose units are bonded together by β(1→4) glycosidic bonds. Cellulose doesn’t branch, and it is a straight chain polymer. However, due to the hydrogen bonds between molecules it can form very rigid fibers.
Like many other polysaccharides, cellulose is insoluble in water. Cellulose is abundant in the cell walls of green plants and in algae. It gives strength and rigidity to plant cells. This cell wall is permeable to any substance; therefore, allow passing materials in and out of the cell. This is the most common carbohydrate on earth. Cellulose is used to make paper and other useful derivatives. It is further used to produce biofuels.
What is the difference between Amylose and Cellulose?
• Amylose has α-1,4-glycosidic bonds, whereas cellulose has β(1→4) glycosidic bonds.
• Humans can digest amylose but not cellulose.
• Glucose molecules in cellulose are found in an alternative pattern where one is down and one is up, but in amylose, glucose molecules are in the same orientation.
• Amylose is in starch, and they serve as the energy storage compound in plants. Cellulose is mainly a structural compound, which participates in cell wall formation, in plants.
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