Glycogen

• Glycogen is the glucose stores in cells.
• Glycogen is a highly branched β-glucose polymer.
• In muscle, AMP activates phosphorylase directly.
• AMP activates phosphorylase with 2 ADP.
• In muscle, AMP activates phosphorylase with 2 ADP.
• Glycogenesis is when Glc is incorporated into glycogen in the liver and muscle.
• Glycogenolysis is when glucose is mobilized from glycogen in the liver and muscle.
• Hormonal regulation of hepatic glycogenesis and glycogenolysis is done by insulin and glucagon.
• Insulin signals phosphorylations and pathways flip.
• Glycogenolysis in the liver is involved in plasma glycemia maintenance, specifically in the acute and postabsorptive states.
• Glycogenolysis in the muscle is involved in mobilizing glucose for ATP and contraction activity.
• Glycogenesis is the process of replenishing glycogen stores versus immediate needs.
• Inborn errors of metabolism include glycogen storage diseases.
• High blood glucose levels indicate a fed state, where insulin stimulates glycogen synthesis and inhibits glycogen breakdown.
• Glucagon equals a starved state, where it stimulates glycogen breakdown and inhibits glycogen synthesis.
• Blood glucose can be obtained from three primary sources: diet, gluconeogenesis, and degradation of glycogen.
• Blood glucose levels must be constant at all times due to the requirements of red blood cells and the brain.
• Glycogen is the rapid energy store of cells and is used during the first ~10-12 hours of fasting states and exercise.
• Glycogen is a homopolysaccaride composed of only glucose residues designed as a branched chain.
• Glycogen contains two types of glycosidic linkages: α-1,4-linkage predominates whole molecule, branches take place in every 6-10 residues with α-1,6-linkage.
• Glycogen is principally stored in the cytosolic granules of the liver (3-5% of tissue mass) and muscle (0.5-1% of tissue mass).
• Elevated blood glucagon levels are observed between meals and chronically elevated during fasting or low-carbohydrate diet.
• Glucagon, a 3.5 kd peptide from a-cells of endocrine pancreas, is the main hormone that activates hepatic glycogenolysis to maintain normoglycemia.
• Glucagon’s enzyme cascade amplification turns on liver glycogenolysis, balanced inhibition of glycogenesis.
• Cortisol, an adrenocortical steroid that varies diurnally in plasma, may be chronically elevated under continuously stressful conditions.
• Glycogenolysis is the response to low blood glucose from post absorptive utilization and stress.
• Glucagon, a 3500 MW protein (29-aa), is secreted by β-cells of endocrine pancreas, activates glycogenolysis to maintain normal glycemia, and has a t/2 of about 5 minutes.
• Insulin elicits uptake and intracellular use or storage of glucose, an anabolic hormone.
• Inhibition of glycogenolysis is balanced by the action of glucagon.
• Prandial glucose is used up, glycemia falls into hypoglycemia.
• Insulin, secreted by pancreas β-cells when blood glucose is high, is synthesized as a single peptide chain zymogen, proinsulin, and in secretory granules, selective proteolysis releases an internal peptide and a 2-chained insulin hormone.
• Hyperinsulinism associated with “insulin resistance” and if chronic can lead to diabetes type-2 and related pathologies.
• Glycogenolysis is activated in response to stress.
• Glucagon, epinephrine (adrenalin), cortisol, and insulin are the hormones involved in the control of glycogenolysis.
• Decreased blood glucagon levels are observed during and soon after a meal when blood glucose is very high.
• Epinephrine, a tyrosine derivative from adrenal medulla, activates glycogenolysis in response to acute stress.
• Hyperglycemia results in elevated blood insulin associated with fed state.
• Enzymes of glycogen metabolism are bound to the surface of the glycogen particle (molecule) all in the same granule.
• In the liver, the synthesis and breakdown of glycogen is regulated to maintain blood glucose levels.
• Phosphoprotein phosphotase 1 (PPP1) removes the phosphoryl groups from phosphorylase a, converting it to the less active form, phosphorylase b.