Glycogen phosphorylase reaction

The glycogen phosphorylase reaction.

The branched polysaccharide glycogen represents the main storage form of glucose in the body. Glycogen granules are especially prominent in the cells of muscle and liver tissue. The processes of glycogen synthesis and glycogen degradation are important topics in MCAT preparation for several reasons. Firstly, the enzymatic processes are illustrative of several important general principles in biochemical mechanisms. Additionally, glycogen metabolism is mediated by hormonal control. It plays an important part in blood glucose regulation. This makes glycogen metabolism a favorite topic for the discussion of physiological and metabolic integration as well as signal transduction mechanisms.

WikiPremed Resources

Learning Goals

Proficiency 

Understand which types of glycosidic linkages are present in glycogen and be prepared to describe the structure of glycogen granules.

Be able to describe the mechanism of glycogen phosphorylase.

Comprehend why glycogen debranching enzyme is required for the breakdown of glycogen in addition to glycogen phosphorylase.

Know the steps of the glycogen synthetase mechanism including the role of UDP-glucose pyrophosphorylase in setting the stage.

Understand the intracellular signaling and regulatory mechanisms by which glycogen sythetase is nearly inactive when glycogen phosphorylase is active. Be prepared to relate these mechanisms hormonal control by insulin, glucagon, and epinephrine.

Suggested Assignments

The question server contains a general section covering basic concepts from gluconeogenesis, the pentose phosphate pathway, glyocogen metabolism, fatty acid metabolism, the urea cycle, and metabolic integration. After review complete the crossword puzzle for energy metabolism. Here is the solution to the puzzle.

Review the web resources for glycogen metabolism.

Conceptual Vocabulary for Glycogen Metabolism

Glycogen Metabolism

Each list begins with basic conceptual vocabulary you need to know for MCAT questions and proceeds to advanced terms that might appear in context in MCAT passages. The terms are links to Wikipedia articles.
Glycogen synthase
A key enzyme in glycogenesis, glycogen synthase is a glycosyltransferase that catalyses the reaction of UDP-glucose and (1,4-α-D-glucosyl)n to yield UDP and (1,4-α-D-glucosyl)n+1.
Glycogen phosphorylase
Glycogen phosphorylase catalyzes the rate-limiting step in glycogenolysis in animals by releasing glucose-1-phosphate from the terminal alpha-1,4-glycosidic bond.
Glycogenesis
Glycogenesis is the process of glycogen synthesis, in which glucose molecules are added to chains of glycogen.
Phosphorolysis
Phosphorolysis is the cleavage of a compound in which inorganic phosphate is the attacking group.
Glycogenolysis
Glycogenolysis is the catabolism of glycogen by removal of a glucose monomer and addition of phosphate to produce glucose-1-phosphate.
Glycogenin
Glycogenin is an enzyme involved in converting glucose to glycogen. It acts as a primer, by polymerizing the first few glucose molecules, after which other enzymes take over.
Glycogen debranching enzyme
Glycogen debranching enzyme is a molecule that helps facilitate the breakdown of glycogen, which serves as a store of glucose in the body, through glucosyltransferase and glucosidase activity.
Glycogen branching enzyme
Glycogen branching enzyme is an enzyme that adds branches to the growing glycogen molecule during the synthesis of glycogen.
Glycogen storage disease
A glycogen storage disease is a metabolic disorder caused by enzyme deficiencies affecting either glycogen synthesis, glycogen breakdown or glycolysis (glucose breakdown), typically in muscles and/or liver cells.
Phosphorylase kinase
Phosphorylase kinase (PhK) is a serine/threonine-specific protein kinase which activates glycogen phosphorylase to release glucose-1-phosphate from glycogen.
Protein phosphatase 1
Protein phosphatase 1 plays a crucial role in the regulation of blood-glucose levels in the liver and glycogen metabolism by ensuring the opposite regulation of glycogen breakdown and glycogen synthesis.
Uridine diphosphate glucose
Uridine diphosphate glucose is a nucleotide that is used as an activated form of glucose, a substrate for glycosyltransferases.
Cori ester
Glucose 1-phosphate (also called cori ester) is a glucose molecule with a phosphate group on the 1'-carbon.
Phosphoglucomutase]
Phosphoglucomutase is an enzyme that transfers a phosphate group on an α-D-glucose monomer from the 1 to the 6 position in the forward direction or the 6 to the 1 position in the reverse direction.
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