Glycogen is a huge polymer of glucose residues linked by α1-4 glycosidic bonds with branches every 10 residues or so by α1-6 glycosidic bonds.  Glycogen gives an significant energy reserve for the body.  The two main storage sites are the liver and skeletal muscle where the glycogen is stored as granules in the cytosol.  The granules hold not only glycogen but also the enzymes and regulatory proteins which are requires for synthesis and glycogen degraation.  Glycogen  metabolism  is important  because it enables the blood glucose level to be maintained  by meals (by glycogen stores in the liver)  and  also  provides  an energy  reserve  for muscular  activity.  The  preservation  of  blood  glucose  is  necessary  in  order  to  supply  tissues  with  an  easily metabolizable   energy  source,  particularly  the  brain  that  uses  only  glucose except after a long starvation period.