Biochemistry: Glycogen Metabolism Flashcards

A set of vocabulary flashcards covering glycogen structure, glycogenesis, glycogenolysis, regulation, and glycogen storage diseases based on the biochemistry lecture.

Glycogen

A storage polysaccharide found in liver and muscle, composed of glucose units linked by $\alpha\text{-1,4}$ glycosidic bonds in linear chains and $\alpha\text{-1,6}$ glycosidic bonds at branching points.

Glycogenin

A polypeptide of $332$ amino acids that serves as a primer and self-glucosylating enzyme for glycogen synthesis.

Glycogenesis

An energy-requiring biosynthetic pathway occurring in the cytoplasm that synthesizes glycogen from excess glucose utilizing high-energy phosphate from UTP.

Glycogenolysis

A phosphorolysis reaction occurring in the cytoplasm that degrades glycogen into glucose-1-phosphate using inorganic phosphate without consuming ATP.

Glycogen Synthase

The key regulated enzyme of glycogenesis that transfers a glucosyl residue from UDP-glucose to the non-reducing end of a glycogen chain, forming an $\alpha\text{-1,4}$ glycosidic bond.

Branching Enzyme

An enzyme, also known as amylo-4,6-transferase, that transfers a chain segment of at least $6$ glucose residues to an adjacent chain to form an $\alpha\text{-1,6}$ linkage.

Glycogen Phosphorylase

The rate-limiting enzyme of glycogenolysis that catalyzes the phosphorolytic cleavage of $\alpha\text{-1,4}$ glycosidic bonds to yield glucose-1-phosphate.

Glucan Transferase

An enzyme in glycogenolysis that transfers a trisaccharide unit of $3$ glucose residues from a branch to an adjacent chain, exposing the $\alpha\text{-1,6}$ branch point.

Debranching Enzyme

An enzyme, also known as amylo-1,6-glucosidase, that hydrolyzes the $\alpha\text{-1,6}$ glycosidic linkage at glycogen branch points, releasing free glucose.

Glucose 6-Phosphatase

An enzyme present in the liver, kidneys, pancreas, and small intestine that converts glucose-6-phosphate to free glucose.

Lafora Disease

An autosomal recessive neurodegenerative disorder caused by a deficiency in laforin, resulting in hyperphosphorylated glycogen and accumulation of insoluble Lafora bodies.

Laforin

A glycogen phosphatase encoded by the EPM2A gene that removes phosphate residues from phosphorylated glycogenin.

Autoglycosylation

The process by which glycogenin glycosylates itself by attaching the glucosyl residue of UDP-glucose to a tyrosine residue on its own polypeptide chain.

Von Gierke Disease

Type I glycogen storage disease caused by a deficiency in liver glucose 6-phosphatase, causing severe fasting hypoglycemia, hepatomegaly, acidosis, and hyperuricemia.

Pompe Disease

Type II glycogen storage disease caused by a deficiency in lysosomal $\alpha\text{-1,4}$ and $\alpha\text{-1,6}$ glucosidase (acid maltase), leading to glycogen accumulation in lysosomes.

Forbes Disease

Type III glycogen storage disease, also known as Cori disease or Limit Dextrinosis, caused by a deficiency in debranching enzyme.

Andersen Disease

Type IV glycogen storage disease, also known as Amylopectinosis, caused by a deficiency in branching enzyme, producing glycogen with abnormally long outer branches.

McArdle Syndrome

Type V glycogen storage disease caused by a deficiency in skeletal muscle glycogen phosphorylase, leading to exercise-induced muscle cramps and fatigue.

Hers Disease

Type VI glycogen storage disease caused by a deficiency in liver glycogen phosphorylase, presenting with hepatomegaly and mild hypoglycemia.

Tarui Disease

Type VII glycogen storage disease caused by a deficiency in phosphofructokinase-1, resulting in exercise-induced muscle fatigue and enzymopathic hemolysis.

Carbo Loading

A dietary procedure involving muscle glycogen depletion via heavy exercise on a low carbohydrate diet, followed by light exercise on a high carbohydrate diet to increase glycogen reserves.