Sunday, October 29, 2017

Properties of glycogen

In mammals after feeding, ingested glucose is converted into glycogen in liver and muscle, quantitatively the two major glycogen deposits in the body. Besides maintaining stores of the polysaccharides this conversion also serves to reduce blood glucose levels after a meal, part of the mechanism of blood glucose homeostasis.

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.

For the process of transformation of glycogen into sugar and its secretion into the bloodstream, he coined the term ‘internal secretion’. Subsequently other researcher proved that the common monosaccharides give rise to liver glycogen.

Glycogen is branched polysaccharide storage for glucose of 6,000 to 30,000 glucose units. Each molecule is unique in structure. It is similar to amylopectin in structure but is more highly branched.

It contains two types of glycosidic linkages, extended chains of alpha 1- 4 linked glucose residues with alpha 1-6 branches spaced every four to six residues along the alpha 1 – 4 chain.

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.

From unicellular to plants and mammals the primary role of glycogen and starch is the storage of glucose during times of nutritional or energetic plenty for retrieval during times of deprivation.

This carbohydrate is a glucose storage molecule that when necessary can be quickly broken apart to release glucose.

Liver and skeletal muscles are the major organs of glycogen storage. 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 storage disease are categorized either chronologically by discovery or by type of tissue involved: primarily liver, muscle and/or cardiac.
Properties of glycogen
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