Endocrine Regulation of Glycogen Metabolism

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Questions and Answers

What is the first step in the biosynthesis of glycogen?

Activation of glucose-1-phosphate to UDP-glucose

Isomerization of glucose-1-phosphate to glucose-6-phosphate

Transfer of the glucosyl residue to an amylose chain

Isomerization of glucose-6-phosphate to glucose-1-phosphate (correct)

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

Glucose-6-phosphate dehydrogenase

Phosphoglucomutase (correct)

Glycogen synthase

UDP-glucose pyrophosphorylase

What is formed after the activation of glucose-1-phosphate during glycogenesis?

Glycogen

Glucose-6-phosphate

UDP-glucose (correct)

Glucose

In glycogenesis, what happens to UDP-glucose after its formation?

It transfers a glucosyl residue to an amylose chain Signup and view all the answers

Which of the following is NOT part of the three sequential steps in glycogenesis?

Glycolysis of glucose Signup and view all the answers

Which enzyme is primarily responsible for the process of glycogenolysis?

Glycogen phosphorylase Signup and view all the answers

What role does epinephrine play in glycogen metabolism?

Activates glycogen phosphorylase Signup and view all the answers

What is the state of glycogen synthase when phosphorylated?

Inactive Signup and view all the answers

Which molecule is involved in activating glycogen phosphorylase through phosphorylation?

cAMP Signup and view all the answers

What is the effect of Inhibitor 1 on glycogen phosphorylase?

Deactivates phosphorylase-b Signup and view all the answers

What is the role of cAMP in the activation of protein kinase A (PKA)?

It binds to the regulatory subunit to activate PKA. Signup and view all the answers

What does the binding of epinephrine lead to the conversion of?

ATP to cAMP and pyrophosphate (PPi) Signup and view all the answers

How does PKA affect glycogenolysis when activated?

By converting phosphorylase-b to its active form, phosphorylase-a. Signup and view all the answers

What mechanism is shared between the activation of the b-adrenergic receptor and the glucagon receptor?

Activation of adenylate cyclase. Signup and view all the answers

Which enzyme is activated by cAMP to influence glycogen metabolism?

Protein kinase A (PKA) Signup and view all the answers

What is the effect of PKA on glycogenesis?

Inhibits glycogenesis by converting glycogen synthase I to the inactive form. Signup and view all the answers

What are the products formed by the action of adenylate cyclase?

cAMP and pyrophosphate (PPi) Signup and view all the answers

Which of the following describes the effect of epinephrine-secretion in the liver or muscle cells?

Increases cAMP levels to promote glycogenolysis. Signup and view all the answers

What occurs after cAMP binds to the regulatory subunit of PKA?

The regulatory and catalytic subunits dissociate. Signup and view all the answers

Study Notes

Epinephrine and Glycogen Metabolism

Epinephrine binds to β-adrenergic receptors, activating adenylate cyclase.
Activation of adenylate cyclase converts ATP to cyclic AMP (cAMP), a secondary messenger.
cAMP activates protein kinase A (PKA) by binding to its regulatory subunits, releasing the catalytic subunits.

Glycogenolysis and Glycogenesis Regulation

Glycogenolysis is stimulated by the conversion of phosphorylase-b (inactive) to phosphorylase-a (active) via PKA activation.
Glycogenesis is inhibited as PKA facilitates the conversion of glycogen synthase I (active) to glycogen synthase D (inactive).
Phosphatase activity is inhibited, further promoting glycogen breakdown and reducing synthesis.

Glycogen Synthesis Steps

Glycogen biosynthesis involves three steps:
- Conversion of glucose-6-phosphate to glucose-1-phosphate by phosphoglucomutase.
- Activation of glucose-1-phosphate to UDP-glucose.
- Transfer of glucose units from UDP-glucose to growing glycogen chains.

Role of Glucagon

Similar to epinephrine, glucagon binds to its receptor, activating adenylate cyclase and increasing cAMP levels.
The effect of glucagon mirrors that of epinephrine, promoting glycogenolysis while inhibiting glycogenesis.

Tissue-Specific Metabolism

The brain and red blood cells uptake glucose through insulin-independent GLUT receptors (GLUT1), engaging in glycolysis and the pentose phosphate pathway for energy and NADPH production.
Muscle cells utilize glucose via the insulin-sensitive GLUT4 transporter, enabling efficient energy utilization.

Additional Notes

Inhibitor 1 regulates the activity of protein phosphatase, affecting the phosphorylation status of glycogen synthase and phosphorylase.
Overall, epinephrine plays a crucial role in increasing blood glucose availability during stress by promoting glycogenolysis and inhibiting glycogenesis in the liver and muscles.

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Description

This quiz focuses on the role of epinephrine in the endocrine regulation of glycogen metabolism. It covers key concepts including the b-adrenergic receptor, cAMP, and enzyme activities associated with glycogen phosphorylase and synthase. Test your understanding of these biochemical processes and their implications.