Glycogen metabolism

I. Glycogen

• Long chain of glucose units hooked together 1,4 linkage
• branched 1,6
• lowers osmotic potential of cell
• storage form of energy in liver and muscle

II. Glycogen breakdown

• glycogen phosphorylase
• inorganic phosphate, not ATP
• glucose 1-P produced
  • less ATP used in glycolysis if glycogen used for energy
• phosphoglucomutase (PGM)----> glucose 6-P
• glucosidase --debranching enzyme
  • 3 glucose residues moved
  • cleaves remaining glucose for free glucose
• In liver
  • glucose 6 phosphotase
  • produce free glucose
  • blood glucose

II. Glycogen synthesis

• glycogen core started
• glycogen synthase
  • UDP-glucose used
• transglycoslyase
  • branching enzyme
  • transfers 8-10 glucose residues

III. Regulation

• Epinephrine and glucagon
  • stimulate cAMP
  • protein kinase
  • phosphorylase kinase
  • phosphorylates glycogen phosphorylase
  • glycogen breakdown
• phosphorylates glycogen synthase, deactivated
• insulin
  • stimulates glycogen synthase
  • dephosphorylation
  • deactivates glycogen phosphorylase