Functions of glycogen

 Glycogen is a multi-branched polysaccharide of glucose that serves as a form of energy storage in animals and fungi. The polysaccharide structure represents the main storage form of glucose in the body. In animals it functions in the following manner: In liver – The synthesis and breakdown of glycogen is regulated to maintain blood glucose levels while in the muscle - The synthesis and breakdown of glycogen is regulated to meet the energy requirements of the muscle cell. 
Glycogen is synthesized from glucose as follows:  in the first step glucose is converted to glucose-6-phosphate, using one ATP, this reaction is catalyzed by hexokinase. Glucose-6-phosphate is then converted to glucose-1-phosphate, (this reaction is catalyzed by phosphoglucomutase), glucose-1-phosphate is then activated by UTP, forming UDP-glucose which is acted upon by UDP glucose pyrophosporylase. As UDP-glucose attaches to the end of the glycogen chain (catalyzed by glycogen synthase), UDP is released (and converted to UTP by ATP). Glycogen-branching enzyme is involved in formation of branches.

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