Metabolism glycogen

• What type of carbohydrate is glycogen?

  Glycogen is a homopolysaccharide.
• What are the main glycosidic bonds in glycogen?

  The main glycosidic bond in glycogen is the α 1,4 linkage, with branching points connected by α 1,6 linkages.
• Where is glycogen primarily located in the body?

  Glycogen is mainly present in the cytosol of the liver and muscle.
• What is the function of liver glycogen?

  Liver glycogen maintains normal blood glucose concentration, especially during the early stages of fasting.
• What role does muscle glycogen play?

  Muscle glycogen acts as a source of energy within the muscle itself, especially during muscle contraction.
• What is glycogenesis?

  Glycogenesis is the formation of glycogen in the liver and muscle.
• What substrates are used for glycogenesis in the liver?

  Substrates for glycogenesis in the liver include blood glucose, fructose, galactose, glycerol, and lactate.
• What substrates are used for glycogenesis in muscles?

  In muscles, the substrate for glycogenesis is blood glucose only.
• What percentage of glycogen is stored in the liver and muscle?

  Glycogen is stored mostly in the liver (6-8%) and muscle (1-2%).
• Why is the quantity of glycogen in muscle higher than in the liver?

  The quantity of glycogen in muscle is about three times higher than that in the liver due to more muscle mass.
• How is glycogen stored in the cells?

  Glycogen is stored as granules in the cytosol, where most enzymes for glycogen synthesis and breakdown are present.
• What is the prime function of liver glycogen?

  The prime function of liver glycogen is to maintain blood glucose levels, particularly between meals.
• What happens to liver glycogen stores during fasting?

  Liver glycogen stores increase in a well-fed state and are depleted during fasting.
• What is the role of muscle glycogen during muscle contraction?

  Muscle glycogen serves as a fuel reserve for the supply of ATP during muscle contraction.
• How does glycogen generate energy in the absence of oxygen?

  Glycogen can generate energy through anaerobic pathways, allowing for ATP production without oxygen.
• What is the structure of a glycogen molecule?

  A glycogen molecule consists entirely of glucose units linked in long chains by α1–4 bonds, with branches formed by α1–6 bonds.
• What terminates each chain of glycogen?

  Each chain of glycogen terminates in a non-reducing end, which has a free 4′ OH group.
• What is UDP-glucose and how is it formed?

  UDP-glucose is formed from glucose 1-phosphate and UTP by the enzyme UDP-glucose pyrophosphorylase.
• What is the role of UDP-glucose in glycogen synthesis?

  UDP-glucose reacts with a glycogen primer to initiate glycogen synthesis.
• What is the key enzyme of glycogenesis?

  The key enzyme of glycogenesis is glycogen synthase.
• How does glycogen synthase contribute to glycogenesis?

  Glycogen synthase adds UDP-glucose molecules to the glycogen primer, elongating the α 1-4 branches.
• What is the function of the branching enzyme in glycogenesis?

  The branching enzyme transfers parts of the elongated chains to form new α 1-6 glycosidic bonds, creating branches in glycogen.
• What is glycogenolysis?

  Glycogenolysis is the breakdown of glycogen to glucose in the liver and lactic acid in the muscle.
• What initiates glycogenolysis?

  Glycogenolysis is initiated by the action of phosphorylase, which cleaves α1–4 linkages to yield glucose-1-phosphate.
• What is the role of glycogen phosphorylase in glycogenolysis?

  Glycogen phosphorylase acts on α1–4-glycosidic bonds, breaking them down by phosphorolysis to remove glucose units as glucose-1-phosphate.
• What does the debranching enzyme do during glycogenolysis?

  The debranching enzyme acts on branches containing more than 4 glucose units, transferring 3 units to the next branch and breaking the α1–6 bond to release free glucose.
• What are the products of glycogenolysis?

  The products of glycogenolysis are glucose-1-phosphate and free glucose.
• What happens to glucose-6-phosphate in the liver?

  In the liver, glucose-6-phosphate is converted to glucose by glucose-6-phosphatase.
• What happens to glucose-6-phosphate in muscle?

  In muscle, glucose-6-phosphate enters glycolysis to produce lactate, as there is no glucose-6-phosphatase.
• Why is regulation of glycogenesis and glycogenolysis important?

  Regulation is essential to maintain blood glucose levels.
• Which enzymes control glycogenesis and glycogenolysis?

  Glycogenesis is controlled by glycogen synthase, while glycogenolysis is controlled by glycogen phosphorylase.
• How does hormonal regulation affect glycogen metabolism?

  Hormonal regulation influences the activity of glycogen synthase and glycogen phosphorylase, coordinating glycogenolysis and glycogenesis.
• What happens to glycogen metabolism during fasting?

  During fasting, glycogenolysis is stimulated while glycogenesis is inhibited to provide blood glucose from liver glycogen.
• What happens to glycogen metabolism after a meal?

  After a meal, part of absorbed glucose (40%) goes to circulation, while the remaining (60%) is converted into glycogen in the liver, stimulating glycogenesis and inhibiting glycogenolysis.
• What are glycogen storage diseases?

  Glycogen storage diseases are metabolic defects related to glycogen synthesis and degradation due to enzyme deficiencies.
• How are glycogen storage diseases characterized?

  They are characterized by the deposition of normal or abnormal glycogen in one or more tissues.
• What is Type 1 glycogen storage disease?

  Type 1 glycogen storage disease is Von Gierke’s Disease, caused by a deficiency of glucose-6-phosphatase.
• What are the clinical features of Type 1 glycogen storage disease?

  Clinical features include fasting hypoglycemia, lactic acidemia, and hyperuricemia.
• What is the enzyme deficiency in Type 2 glycogen storage disease?

  Type 2 glycogen storage disease, or Pompe’s Disease, is caused by a deficiency of acid maltase (lysosomal α-glycosidase).
• What are the clinical features of Type 2 glycogen storage disease?

  Clinical features include cardiomegaly and muscle hypotonia, leading to muscle weakness.