BIOC2600 1.3

• Blood glucose level is maintained near 80 - 100 mg/dl even though carbohydrate intake varies in a day.
• Our body digests and absorbs carbohydrates as glucose.
• Glucose-6-phosphate can then enter glycolysis, PPP or replenish blood glucose.
• UDP-glucose is the immediate donor of glucose residues for glycogen synthesis.
• Glycogen chain is elongated by glycogen synthase.
• Glucose-6-phosphate is converted to Glucose-1-phosphate and then to UDP-glucose by glycogen synthase.
• A chain of 6-7 sugars is removed from a branch of at least 11 sugars long and each new branch point must be at least 4 sugars away from the nearest existing branch point.
• Glycogen breakdown begins with the conversion of Glucose-1-phosphate, the end product of glycogen phosphorylase reaction, to Glucose-6-phosphate by phosphoglucomutase.
• To make the (α1 to 6) bonds found at the branch points of glycogen, glycogen-branching enzymes are used.
• The glucose residue of UDP-glucose is transferred to the nonreducing end of a glycogen branch to make a new (α1 to 4) linkage.
• Glycogen synthesis can take place in almost all animal tissues, especially prominent in liver and skeletal muscles.
• The starting point of glycogen synthesis is Glucose-6-phosphate.
• Liver glycogen storage can be depleted in 12 to 24 hours.
• Glycogen may represent up to 10% of the weight of the liver and 1 to 2% of the weight of muscles.
• Glycogen is found primarily in liver and skeletal muscle in large cytosolic granules.
• Muscle glycogen can be depleted in less than 1 hour during vigorous exercise.
• In liver and skeletal muscles, the glucose units of the outer branches of glycogen enter the glycolytic pathway via the action of three enzymes: Glycogen phosphorylase, Glycogen debranching enzyme, and Phosphoglucomutase.
• Our body can make glucose by gluconeogenesis.
• Glycogen phosphorylase removes the terminal glucose residues from the nonreducing end until it reaches a point four glucose residues away from the (α1 to 6) branch point.
• The reaction of glycogen phosphorylase produces glucose - 1 - phosphate (G1P) which CANNOT enter glycolysis.
• Glycogen phosphorylase reaction will resume on the new unbranched polysaccharide chain.
• Liver glycogen is a reservoir of glucose for other tissues when dietary glucose is not available (between meals or during fasting).
• Glycogen in muscles is a quick source for energy for either aerobic or anaerobic metabolism, especially during exercise.
• Excess glucose is converted to glycogen for storage in vertebrates.
• The branches are transferred by glycogen debranching enzyme leaving a single glucose residue at the branch point ( ).
• The single glucose residue is then released and can enter directly into glycolysis.