Glycogen – History and Property
Glycogen is the only homopolysaccharides of important in human metabolism. Glycogen presence in liver was first detected in 1856 by Claude Bernard, who recognized the relationship between the glycogen of the liver and the sugar present in the blood. Subsequently other researcher proved that the common monosaccharides give rise to liver glycogen. Although the total quantity of glycogen in the human body is low, considerably less than one-tenth percent of the total body weight, its role is primarily that of a storage carbohydrate, similar to the role of starch in plants cells. It occurs predominantly in the liver where it is important in the homeostatic mechanism regulating glucose level of the blood.
Hepatocytes have the highest concentration of glycogen – up to 8% of the fresh weight in well fed state, or 100 – 120 g in an adult. In skeletal muscle, glycogen serves as a source of energy for muscle contraction. In the muscles, glycogen is found in a much lower concentration (1% of the muscle mass), but the total amount exceeds that in liver.
Glycogen is a branched chain polymer of 6,000 to 30,000 glucose units. It is similar to amylopectin in structure but is more highly branched. The average chain length is only 10 to 24 glucose units with 3 to 4 glucose units between branching points. The size of the molecules varies with its source and with the metabolic state of the body. Muscle glycogen is estimated to have a molecular weight of about 1000000 where as the liver of glycogen molecule is much larger, approximately 5 X 1000000. Both molecules, however, constantly change in size as glucose molecules are added or removed.
Glycogen plays an important role in the glucose cycle. The most common disease in which glycogen metabolism becomes abnormal is diabetes, in which, because of abnormal amounts of insulin, liver glycogen can be abnormally accumulated or depleted.
Glycogen – History and Property
