Glycogen Synthase Mechanism Quiz

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Questions and Answers

What effect does epinephrine have on glycogen metabolism?

It inactivates glycogen synthetase.

It promotes glycogenesis.

It inhibits glycogenolysis.

It activates glycogen phosphorylase. (correct)

Which enzyme is primarily responsible for glycogen synthesis?

Glycogen synthase D

Glycogen phosphorylase

Phosphorylase kinase

Glycogen synthase I (correct)

What activates phosphorylase kinase in glycogen metabolism?

Increased levels of cAMP (correct)

Excess ATP

High levels of glucose

Decreased calcium ions

Which of the following is true about glycogen phosphorylase?

It is active in its phosphorylated form. Signup and view all the answers

What molecular signal is primarily involved in the regulation of glycogen phosphorylase?

cAMP Signup and view all the answers

In the context of the inhibitory mechanism, what is the role of inhibitor 1?

It inhibits glycogen phosphorylase. Signup and view all the answers

What is the primary function of glycogen synthase?

To convert glucose into glycogen Signup and view all the answers

How does phosphorylation affect glycogen metabolism?

It can both activate and deactivate enzymes depending on the context. Signup and view all the answers

What is the role of protein phosphatase 1 in the regulation of glycogen synthase?

It converts glycogen synthase D to glycogen synthase I. Signup and view all the answers

Which form of glycogen synthase is active and does not require glucose-6P?

Glycogen synthase I Signup and view all the answers

What activates protein kinase A (PKA) in the glycogen metabolism pathway?

Cyclic AMP (cAMP) Signup and view all the answers

How is glycogen synthase D inactivated?

By protein kinase A. Signup and view all the answers

What is the effect of cAMP on glycogen synthase?

It negatively regulates glycogen synthase D. Signup and view all the answers

Which substrate is converted into UDP-Glucose in glycogen synthesis?

Glucose-1P Signup and view all the answers

What is the primary function of UDP-Glucose in glycogen synthesis?

To serve as a substrate for glycogen synthase. Signup and view all the answers

Which of the following statements is true regarding glycogen synthase regulation?

The form of glycogen synthase determines the enzyme's activity. Signup and view all the answers

What is the effect of insulin on glycogen metabolism?

Increases glycogenesis Signup and view all the answers

What role does protein phosphatase 1 play in insulin signaling?

Activates glycogen synthase Signup and view all the answers

What happens to phosphorylase activity when insulin is present?

Decreases phosphorylase a activity Signup and view all the answers

Which component is directly increased by insulin activation through the signaling pathway?

Autophosphorylation of the insulin receptor Signup and view all the answers

What is the ultimate result of insulin-mediated activation of protein phosphatase 1?

Increased rates of glycogenesis Signup and view all the answers

Which of the following processes does insulin NOT promote?

Glycogenolysis Signup and view all the answers

How does insulin affect the balance between glycogenesis and glycogenolysis?

Decreases glycogenolysis and increases glycogenesis Signup and view all the answers

Which phosphorylated form of glycogen phosphorylase is active in glycogenolysis?

Glycogen phosphorylase a Signup and view all the answers

What is the first step in the biosynthesis of glycogen?

Isomerization of glucose-6-phosphate to glucose-1-phosphate Signup and view all the answers

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

Phosphoglucomutase Signup and view all the answers

What is the end product of the activation of glucose-1-phosphate during glycogenesis?

UDP-glucose Signup and view all the answers

During glycogenesis, what process follows the activation of glucose-1-phosphate?

Transfer of the glucosyl residue to an amylose chain Signup and view all the answers

What is the significance of the reversible reaction catalyzed by phosphoglucomutase?

It allows the conversion between glucose-6-phosphate and glucose-1-phosphate. Signup and view all the answers

Which process is categorized under catabolism as mentioned in glycogenesis?

Glycogenolysis Signup and view all the answers

Which pathway is NOT directly involved in glycogenesis?

Pentose Phosphate Pathway Signup and view all the answers

What is a key feature of UDP-glucose in the context of glycogenesis?

It acts as an energy donor for glucosyl transfer. Signup and view all the answers

What is the primary function of NADPH produced in the pentose phosphate pathway in the brain?

To maintain glutathione levels Signup and view all the answers

Which glucose transport mechanism is present in red blood cells and the brain?

GLUT1, which is insulin-independent Signup and view all the answers

What product is generated from pyruvate in the brain following glycolysis?

Carbon dioxide and water Signup and view all the answers

Which type of glucose transporter is present in neurons?

GLUT4, which is insulin-sensitive Signup and view all the answers

In muscle and heart cells, how does glucose transport occur?

Using GLUT4, which is insulin-dependent Signup and view all the answers

Which metabolic pathway is noted as quite active in the brain?

Pentose phosphate pathway Signup and view all the answers

What is the role of GLUT2?

It is primarily found in the liver for glucose uptake. Signup and view all the answers

What happens to pyruvate in muscle cells under anaerobic conditions?

It predominantly becomes lactate. Signup and view all the answers

Study Notes

Glycogen Metabolism Overview

Glycogen synthase exists in two forms: active (glycogen synthase I) and inactive (glycogen synthase D).
Glycogen synthase I is activated by protein phosphatase 1 and does not require glucose-6P as an allosteric regulator.
Activation of glycogen synthase D to glycogen synthase I involves UDP-glucose conversion.
Protein kinase A (PKA) inactivates glycogen synthase I, requiring cyclic AMP (cAMP) for allosteric activation.

Endocrine Regulation of Glycogen Metabolism

Epinephrine binds to β-adrenergic receptors, activating adenylyl cyclase (AC) and increasing cAMP production.
cAMP activates PKA, leading to the phosphorylation of glycogen phosphorylase kinase, converting it to an active form which impacts glycogen metabolism.
Insulin signaling initiates autophosphorylation of the insulin receptor, enhancing its ability to phosphorylate target proteins, including glycogen synthase phosphatase 1.
The activation of protein phosphatase 1 promotes glycogenesis and suppresses glycogenolysis.

Glycogenesis Process

Glycogenesis involves three sequential steps:
- Isomerization of glucose-6-phosphate to glucose-1-phosphate through the enzyme phosphoglucomutase.
- Conversion of glucose-1-phosphate to UDP-glucose for activation.
- Addition of glucosyl units from UDP-glucose to a growing glycogen chain.

Tissue-Specific Carbohydrate Metabolism

Brain cells utilize GLUT1 for glucose uptake, operating in an insulin-independent manner.
Glycolysis in the brain produces pyruvate, which is further oxidized in the tricarboxylic acid cycle (TCA).
The pentose phosphate pathway provides NADPH for maintaining glutathione levels, important for antioxidant defense in the brain.
Muscle and heart cells uptake glucose via the insulin-sensitive transporter GLUT4, enhancing glucose availability for cellular metabolism.

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Description

Test your understanding of glycogen synthase conversions, particularly focusing on glycogen synthase D and its active form glycogen synthase I. Explore the enzymatic roles of protein phosphatase 1 and the requirements for activation without glucose-6P. This quiz addresses key concepts in biochemistry.