BC Glycogen Synthesis and Breakdown

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Questions and Answers

Which enzyme is responsible for glycogen breakdown in muscle cells?

Glycogen synthase

Protein kinase

Glycogen phosphorylase (correct)

Protein phosphatase 1

How does phosphorylation affect the activity of glycogen synthase?

Phosphorylation has no effect on the enzyme activity

Phosphorylation increases the enzyme activity

Phosphorylation converts the enzyme to its active form

Phosphorylation decreases the enzyme activity (correct)

What effect does cAMP have on glycogenolysis and glycogenesis?

cAMP inhibits glycogenolysis and stimulates glycogenesis

cAMP stimulates both glycogenolysis and glycogenesis

cAMP has no effect on glycogenolysis and glycogenesis

cAMP stimulates glycogenolysis and inhibits glycogenesis (correct)

Which hormone increases the phosphorylation of glycogen phosphorylase and glycogen synthase?

Glucagon Signup and view all the answers

Which enzyme is responsible for the dephosphorylation of phosphorylase enzyme?

Protein phosphatase 1 Signup and view all the answers

Which form of glycogen phosphorylase is active?

Phosphorylase a Signup and view all the answers

Which enzyme is defective in a genetic disorder that results in elevated blood glucose levels after eating and low blood glucose levels during fasting?

Glycogen synthase Signup and view all the answers

Which molecule is primarily responsible for storing glucose in animals?

Glycogen Signup and view all the answers

Where is glycogen predominantly stored in the body?

Cytosol of liver and muscle cells Signup and view all the answers

What type of bonds link glucose residues in glycogen?

α(1→4) glycosidic bonds and α(1→6) glycosidic bonds Signup and view all the answers

What is the function of glycogen in the liver?

To maintain blood glucose levels Signup and view all the answers

Which enzyme converts glucose to glucose-6-P in the first step of glycogen synthesis?

Hexokinase Signup and view all the answers

What is the fate of glucose-6-P in the liver?

Glycolysis, Pentose pathway, or dephosphorylation to release glucose into the blood Signup and view all the answers

What is the primary function of glycogen in muscle cells?

To meet the energy requirements of muscle cells Signup and view all the answers

Which enzyme catalyzes the phosphorolytic cleavage of the α (1→4) linkages of glycogen, releasing glucose-1-phosphate as a reaction product?

Glycogen Phosphorylase Signup and view all the answers

Which enzyme transfers a segment from the glycogen chain to a neighboring chain to form the α (1-6) linkage to yield a branch?

Branching enzyme Signup and view all the answers

Which enzyme catalyzes the elongation of glycogen chains by forming α (1-4) linkages between the C4 of the terminal residue of the glycogen chain and C1 of UDP-glucose?

Glycogen Synthase Signup and view all the answers

Which enzyme is responsible for the hydrolysis of the α (1-6) linkage in glycogen, yielding free glucose?

Debranching enzyme Signup and view all the answers

Which enzyme catalyzes the conversion of glucose-1-phosphate to glucose-6-phosphate?

Phosphoglucomutase Signup and view all the answers

Which enzyme catalyzes the conversion of glucose-6-phosphate to glucose in the liver but not in muscle?

Phosphatase Signup and view all the answers

Which enzyme is responsible for the transfer of three glucose residues from the limit branch to the end of another branch in glycogen?

Transferase part of debranching enzyme Signup and view all the answers

Which enzyme deficiency is associated with severe hypoglycemia, lactic acidosis, ketosis, hyperuricemia, and hyperlipemia?

Von Gierke's Disease Signup and view all the answers

Which enzyme deficiency is associated with cardiac failure in infancy and muscle weakness?

Pompe's Disease Signup and view all the answers

Which enzyme deficiency is similar to Type I Glycogen Storage Disease, but milder?

Cori's Disease Signup and view all the answers

Which enzyme deficiency is associated with liver cirrhosis and usually results in death before 24 months?

McArdle's Disease Signup and view all the answers

Which enzyme deficiency is associated with muscle cramps and easily fatigued muscles?

McArdle's Disease Signup and view all the answers

Which enzyme deficiency is similar to Type I Glycogen Storage Disease, but milder and affects the liver?

Cori's Disease Signup and view all the answers

Which enzyme deficiency is similar to Type V Glycogen Storage Disease and affects the muscle?

Tarui's Disease Signup and view all the answers

Which enzyme deficiency is associated with enlarged liver and hypoglycemia?

Von Gierke's Disease Signup and view all the answers

Which enzyme deficiency is associated with liver damage and elevated blood glucose levels after eating?

Glycogen synthase deficiency Signup and view all the answers

Study Notes

Glycogen Breakdown and Synthesis

Phosphorylase is the enzyme responsible for glycogen breakdown in muscle cells.
Phosphorylation inhibits the activity of glycogen synthase.

Regulation of Glycogen Metabolism

cAMP stimulates glycogenolysis and inhibits glycogenesis.
Glucagon increases the phosphorylation of glycogen phosphorylase and glycogen synthase.

Glycogen Phosphorylase

Protein phosphatase is the enzyme responsible for the dephosphorylation of phosphorylase enzyme.
The phosphorylated form of glycogen phosphorylase is active.

Genetic Disorders

A deficiency in glycogen phosphorylase is associated with McArdle's disease, characterized by muscle cramps and easily fatigued muscles.
A deficiency in glycogen synthase is associated with a genetic disorder that results in elevated blood glucose levels after eating and low blood glucose levels during fasting.
A deficiency in glucose-6-phosphatase is associated with Type I Glycogen Storage Disease, characterized by severe hypoglycemia, lactic acidosis, ketosis, hyperuricemia, and hyperlipemia.
A deficiency in liver phosphorylase is associated with a genetic disorder similar to Type I Glycogen Storage Disease, but milder.
A deficiency in muscle phosphorylase is associated with a genetic disorder similar to Type V Glycogen Storage Disease and affects the muscle.
A deficiency in debranching enzyme is associated with a genetic disorder characterized by liver cirrhosis and usually results in death before 24 months.
A deficiency in branching enzyme is associated with a genetic disorder characterized by enlarged liver and hypoglycemia.

Glycogen Structure and Function

Glycogen is a branched polymer of glucose residues linked by α (1→4) and α (1→6) bonds.
Glycogen is primarily responsible for storing glucose in animals.
Glycogen is predominantly stored in the liver and muscle cells.
The function of glycogen in the liver is to regulate blood glucose levels.

Glycogen Synthesis

Glucokinase is the enzyme that converts glucose to glucose-6-P in the first step of glycogen synthesis.
Glucose-6-phosphate is converted to glucose-1-phosphate, which is then used to synthesize glycogen.
Glycogen synthase catalyzes the elongation of glycogen chains by forming α (1-4) linkages between the C4 of the terminal residue of the glycogen chain and C1 of UDP-glucose.

Glycogen Breakdown

Phosphorylase catalyzes the phosphorolytic cleavage of the α (1→4) linkages of glycogen, releasing glucose-1-phosphate as a reaction product.
Debranching enzyme catalyzes the hydrolysis of the α (1-6) linkage in glycogen, yielding free glucose.
Phosphoglucomutase catalyzes the conversion of glucose-1-phosphate to glucose-6-phosphate.
Glucose-6-phosphatase catalyzes the conversion of glucose-6-phosphate to glucose in the liver but not in muscle.

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Description

Test your knowledge on the regulation of glycogen metabolism! Learn about the key enzymes involved, including glycogen synthase and glycogen phosphorylase, and how their activity is affected by phosphorylation and dephosphorylation. Explore the role of phosphorylated glucose in muscle cells and discover how it impacts glycogenolysis.