Polysaccharides
Polysaccharides (the prefix “poly” means many) are formed when many single sugars are joined together chemically. Carbohydrates were one of the original molecules that led to the discovery of what we call polymers. Polysaccharides include starch, glycogen (storage starch in animals), cellulose (found in the cell walls of plants), and DNA.
Starch is the predominant storage molecule in plants and provides the majority of the food calories consumed by people worldwide. Most starch granules are composed of a mixture of two polymers: a linear polysaccharide called amylose and a branched-chain polysaccharide called amylopectin. Amylopectin chains branch approximately every 20- 25 saccharide units. Amylopectin is the more common form of starch found in plants. Animals store energy in the muscles and liver as glycogen. This molecule is more highly branched than amylopectin. For longer-term storage, animals convert the food calories from carbohydrates to fat. In the human and animals, fats are stored in specific parts of the body called adipose tissue.
Cellulose is the main structural component of plant cell walls and is the most abundant carbohydrate on earth. Cellulose serves as a source of dietary fiber since, as
explained below, humans do not have the intestinal enzymes necessary to digest it.
Starch and cellulose are both homopolymers (“homo” means same) of glucose. The glucose molecules in the polymer are linked through glycosidic covalent bonds. There are two different stereochemical configurations of glycosidic bonds—an alpha linkage and a beta linkage. The only difference between the alpha and beta linkages is the orientation of the linked carbon atoms. Therefore, glucose polymers can exist in two different structures, with either alpha or beta linkages between the glucose residues. Starch contains alpha linkages and cellulose contains beta linkages. Because of this difference, cornstarch has very different physical properties compared to those for cotton and wood. Salivary amylase only recognizes and catalyzes the breakdown of alpha glycosidic bonds and not beta bonds. This is why most mammals can digest starch but not cellulose (grasses, plant stems, and leaves).
Polysaccharides (the prefix “poly” means many) are formed when many single sugars are joined together chemically. Carbohydrates were one of the original molecules that led to the discovery of what we call polymers. Polysaccharides include starch, glycogen (storage starch in animals), cellulose (found in the cell walls of plants), and DNA.
Starch is the predominant storage molecule in plants and provides the majority of the food calories consumed by people worldwide. Most starch granules are composed of a mixture of two polymers: a linear polysaccharide called amylose and a branched-chain polysaccharide called amylopectin. Amylopectin chains branch approximately every 20- 25 saccharide units. Amylopectin is the more common form of starch found in plants. Animals store energy in the muscles and liver as glycogen. This molecule is more highly branched than amylopectin. For longer-term storage, animals convert the food calories from carbohydrates to fat. In the human and animals, fats are stored in specific parts of the body called adipose tissue.
Cellulose is the main structural component of plant cell walls and is the most abundant carbohydrate on earth. Cellulose serves as a source of dietary fiber since, as
explained below, humans do not have the intestinal enzymes necessary to digest it.
Starch and cellulose are both homopolymers (“homo” means same) of glucose. The glucose molecules in the polymer are linked through glycosidic covalent bonds. There are two different stereochemical configurations of glycosidic bonds—an alpha linkage and a beta linkage. The only difference between the alpha and beta linkages is the orientation of the linked carbon atoms. Therefore, glucose polymers can exist in two different structures, with either alpha or beta linkages between the glucose residues. Starch contains alpha linkages and cellulose contains beta linkages. Because of this difference, cornstarch has very different physical properties compared to those for cotton and wood. Salivary amylase only recognizes and catalyzes the breakdown of alpha glycosidic bonds and not beta bonds. This is why most mammals can digest starch but not cellulose (grasses, plant stems, and leaves).
now i can see why human beings cant digest cellulose...good work @thesoichem
ReplyDeletei love science in general..really interesting..
ReplyDelete