Glycogenolysis: Breakdown of Glycogen to Glucose

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Questions and Answers

What type of glycosidic bond is primarily found in glycogen?

α(1→2) linkage

β(1→6) linkage

α(1→4) linkage (correct)

β(1→4) linkage

During which state does the liver increase its glycogen stores?

Starvation

Sleep

Well-fed state (correct)

Short fasting period

What is the molecular mass range of a single glycogen molecule?

10^6 to 10^7 daltons (correct)

10^5 to 10^6 daltons

10^3 to 10^4 daltons

10^4 to 10^5 daltons

Where are glycogen molecules typically found within a cell?

Cytoplasmic granules Signup and view all the answers

How is muscle glycogen affected by short periods of fasting?

Remains unaffected Signup and view all the answers

Which enzyme is responsible for converting glucose 1-phosphate to glucose 6-phosphate?

Phosphoglucomutase Signup and view all the answers

McArdle Syndrome is caused by a deficiency in which enzyme?

Glycogen phosphorylase Signup and view all the answers

Which enzyme cleaves the remaining single glucose residue from the branch point during glycogenolysis?

Debranching enzyme Signup and view all the answers

Which glycogen storage disease is characterized by fasting hypoglycemia and an abnormal glycogen structure?

Cori Disease Signup and view all the answers

Which clinical manifestation is NOT associated with Pompe Disease?

High blood lactate levels during exercise Signup and view all the answers

What is the primary cause of muscle weakness in McArdle Syndrome?

Deficiency in skeletal muscle glycogen phosphorylase Signup and view all the answers

Which glycogen storage disease is associated with myoglobinemia?

McArdle Syndrome Signup and view all the answers

Which of the following steps is regulated by hormonal signals?

Cleavage of alpha 1,4 glycosidic bonds in glycogen Signup and view all the answers

Which of the following is NOT a primary source of blood glucose?

Lipolysis Signup and view all the answers

What is the preferred energy source for the brain?

Glucose Signup and view all the answers

Which type of cells are specifically mentioned as requiring glucose due to having few or no mitochondria?

Erythrocytes Signup and view all the answers

What role does muscle glycogen primarily serve?

Providing energy for muscle contraction Signup and view all the answers

Approximately how much glycogen is stored in a well-fed adult liver?

100g Signup and view all the answers

Which process provides a rapid release of glucose in the absence of dietary sources?

Glycogenolysis Signup and view all the answers

What percentage of fresh weight of resting muscle does glycogen make up?

1-2% Signup and view all the answers

Which metabolic pathway is immediately engaged when glycogen stores are depleted?

Gluconeogenesis Signup and view all the answers

Which type of glycogen storage disease is characterized by Glucose 6-Phosphatase deficiency?

Type Ia: Von Gierke Disease Signup and view all the answers

Which tissues are primarily affected by Glucose 6-Phosphate Translocase deficiency (Type Ib)?

Liver and kidney Signup and view all the answers

What is a symptom of severe prolonged fasting associated with Type Ib disease?

Hypoglycemia Signup and view all the answers

What is a characteristic symptom of Von Gierke Disease not directly related to glucose metabolism?

Hyperlipidemia Signup and view all the answers

What treatment is specifically mentioned for managing symptoms of Type Ib disease?

Nocturnal gastric infusions of glucose or cornstarch Signup and view all the answers

Which molecule serves as the initial acceptor of glucose residues from UDP-glucose during glycogen synthesis?

Glycogenin Signup and view all the answers

What type of bond is primarily formed by glycogen synthase during glycogen elongation?

(1→4) glycosidic bond Signup and view all the answers

Which amino acid's side chain hydroxyl group serves as the site for the initial glucosyl unit attachment on glycogenin?

Tyrosine Signup and view all the answers

What enzyme helps in re-phosphorylating UDP to UTP during glycogen synthesis?

Nucleoside diphosphate kinase Signup and view all the answers

Where does glycogenin remain localized in the glycogen structure?

At the core of the glycogen granule Signup and view all the answers

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

Providing glucose residues for extending chains Signup and view all the answers

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

UDP-glucose pyrophosphorylase Signup and view all the answers

Which specific reaction is catalyzed by glycogenin via autoglucosylation?

Initial attachment of glucose residues to its own tyrosine residue Signup and view all the answers

What primarily characterizes lysosomal storage diseases?

Accumulation of abnormal amounts of carbohydrates or lipids Signup and view all the answers

During what condition does glycogenolysis in the liver accelerate?

Periods of fasting Signup and view all the answers

Which statement accurately describes the hormonal regulation of glycogen synthase and glycogen phosphorylase?

They are hormonally regulated to meet the needs of the body as a whole Signup and view all the answers

How does calcium (Ca^{2+}) activate glycogen phosphorylase during muscle contraction?

By binding to the calmodulin subunit of phosphorylase kinase Signup and view all the answers

What role does AMP play in muscle during extreme conditions of anoxia?

It activates glycogen phosphorylase b without being phosphorylated Signup and view all the answers

Which hormone stimulates glycogen degradation in both muscle and liver?

Epinephrine Signup and view all the answers

Which process is accelerated during the well-fed state in the liver?

Glycogenesis Signup and view all the answers

What is the effect of insulin on glycogen degradation?

Inhibits glycogen degradation Signup and view all the answers

Which enzyme reconverts glycogen synthase b to the active 'a' form?

Protein phosphatase-1 Signup and view all the answers

What molecule allosterically inhibits glycogen phosphorylase a in the liver but not in muscle?

Non-phosphorylated glucose Signup and view all the answers

What is the effect of cAMP on glycogen synthase?

It inactivates glycogen synthase by phosphorylation. Signup and view all the answers

Which state correlates with the increased activation of glycogen synthase b by glucose 6-phosphate?

Well-fed state Signup and view all the answers

What triggers the activation of muscle phosphorylase kinase b during muscle contraction?

Membrane depolarization and calcium release Signup and view all the answers

How does the binding of calcium to calmodulin affect phosphorylase kinase b?

It activates the enzyme without the need for phosphorylation. Signup and view all the answers

What is the role of protein kinases in the regulation of glycogen synthase?

They phosphorylate glycogen synthase to the inactive form. Signup and view all the answers

Which molecule is NOT associated with activating glycogen degradation in muscle?

Protein kinase A Signup and view all the answers

Which enzyme catalyzes the synthesis of cAMP following the binding of glucagon or epinephrine to GPCR?

Adenylyl cyclase Signup and view all the answers

What is the role of protein kinase A (PKA) in glycogen metabolism?

It activates phosphorylase kinase by phosphorylation Signup and view all the answers

How is glycogen phosphorylase regulated in glycogen degradation?

By phosphorylation by active phosphorylase kinase Signup and view all the answers

Which statement best describes the summary of the regulation of glycogen degradation?

It involves a cascade of reactions amplifying the hormonal signal to degrade glycogen. Signup and view all the answers

Which of the following is true for glycogen synthase regulation?

The active form is dephosphorylated Signup and view all the answers

What is the function of inhibitor proteins in the regulation of glycogen metabolism?

They inhibit protein phosphatase 1 Signup and view all the answers

Which hormones are primarily involved in signaling the need for glycogen degradation?

Glucagon and epinephrine Signup and view all the answers

What role does protein phosphatase 1 play in glycogen metabolism?

It removes phosphate from proteins to activate them Signup and view all the answers

Which molecule forms a complex with $Ca^{2+}$ to activate hepatic phosphorylase kinase b during the 'fight or flight' response?

Calmodulin Signup and view all the answers

What triggers the release of $Ca^{2+}$ from the ER into the cytoplasm in hepatocytes?

Binding of epinephrine to a-adrenergic G protein-coupled receptors Signup and view all the answers

How does AMP activate muscle glycogen phosphorylase without phosphorylation?

By binding to glycogen phosphorylase b Signup and view all the answers

Which enzyme's activation is associated with high AMP concentrations under anoxia and ATP depletion in muscles?

Glycogen phosphorylase Signup and view all the answers

A defect in which enzyme type results in glycogen storage diseases (GSDs) leading to abnormal glycogen structure or accumulation?

Enzymes required for glycogen synthesis or degradation Signup and view all the answers

Which linkage type is found at the branch points of glycogen after about eight to ten glucosyl residues?

$\alpha$(1-6) Signup and view all the answers

During the 'fight or flight' response, which secondary messenger is responsible for hepatic glycogenolysis?

$Ca^{2+}$ Signup and view all the answers

Which enzyme forms the primer required for glycogen synthesis?

Glycogenin Signup and view all the answers

What is the immediate product formed when glucose is transferred from UDP-glucose to the nonreducing end of glycogen?

An $\alpha$(1-4) linkage Signup and view all the answers

Which enzyme is responsible for creating branches within the glycogen molecule?

Amylo-$\alpha$(1-4)-(1-6)-transglucosidase Signup and view all the answers

What is the function of the enzyme amylo-α(1→4)→(1→6)-transglucosidase?

To transfer a chain of six to eight glucosyl residues to a non-terminal residue via an α(1→6) linkage Signup and view all the answers

What is the primary product obtained when glycogen is degraded?

Glucose 1-phosphate Signup and view all the answers

How many glucosyl residues apart are branches located on average in glycogen?

Eight glucosyl residues apart Signup and view all the answers

Which enzyme is responsible for sequentially cleaving α(1→4) glycosidic bonds during glycogen degradation?

Glycogen phosphorylase Signup and view all the answers

What distinguishes amylose from glycogen?

Amylose is an unbranched molecule of glucosyl residues, while glycogen is highly branched. Signup and view all the answers

What is a 'limit dextrin' in the context of glycogen metabolism?

A glycogen structure that glycogen phosphorylase cannot degrade further Signup and view all the answers

Which coenzyme is required by glycogen phosphorylase for its activity?

Pyridoxal phosphate (PLP) Signup and view all the answers

What happens to the nonreducing ends of glycogen after the action of amylo-α(1→4)→(1→6)-transglucosidase?

They can be further elongated by glycogen synthase Signup and view all the answers

Study Notes

Here are the study notes for the text:

Degradation of Glycogen - Glycogenolysis

Glycogen degradation involves 3 steps:
- Step 1: Glycogen phosphorylase cleaves alpha 1,4 glycosidic bonds in the glycogen molecule to form glucose 1-phosphate
- Step 2: Debranching enzyme moves a block of 3 glucose residues from a branch point to the end of a glycogen chain and cleaves the remaining single glucose residue from the branch point
- Step 3: Phosphoglucomutase converts glucose 1-phosphate to glucose 6-phosphate

Glycogen Storage Diseases (GSDs)

Caused by defects in enzymes involved in glycogen metabolism
Examples:
- Type V: McArdle Syndrome - deficiency in skeletal muscle glycogen phosphorylase
- Type II: Pompe Disease - deficiency in lysosomal alpha-1,4-glucosidase
- Type III: Cori Disease - deficiency in debranching enzyme and/or phosphoglucomutase

Synthesis of Glycogen (Glycogenesis)

Involves 2 stages:
- Initiation: Glycogenin serves as a primer for glycogen synthesis, and glycogen synthase elongates the glycogen chain
- Elongation: Glycogen synthase catalyzes the transfer of glucose from UDP-glucose to the non-reducing end of the growing chain
Branching: Branching enzyme (amylo-alpha(1→4)→(1→6)-transglucosidase) creates branches in the glycogen molecule

Regulation of Glycogen Synthesis and Degradation

Hormonal regulation:
- Insulin inhibits glycogen degradation and stimulates glycogen synthesis
- Glucagon and epinephrine stimulate glycogen degradation and inhibit glycogen synthesis
Allosteric regulation:
- Glycogen synthase is activated by glucose 6-phosphate and inhibited by ATP and ADP
- Glycogen phosphorylase is activated by Ca²⁺ and inhibited by ATP and glucose 6-phosphate
Calcium activation:
- In muscle, Ca²⁺ binds to calmodulin, which activates phosphorylase kinase b
- In liver, epinephrine binds to α-adrenergic receptors, leading to Ca²⁺ release and activation of phosphorylase kinase b

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This quiz explains the steps involved in the degradation of glycogen into glucose, including the role of glycogen phosphorylase and debranching enzyme.

Glycogenolysis: Breakdown of Glycogen to Glucose

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Questions and Answers

What type of glycosidic bond is primarily found in glycogen?

During which state does the liver increase its glycogen stores?

What is the molecular mass range of a single glycogen molecule?

Where are glycogen molecules typically found within a cell?

How is muscle glycogen affected by short periods of fasting?

Which enzyme is responsible for converting glucose 1-phosphate to glucose 6-phosphate?

McArdle Syndrome is caused by a deficiency in which enzyme?

Which enzyme cleaves the remaining single glucose residue from the branch point during glycogenolysis?

Which glycogen storage disease is characterized by fasting hypoglycemia and an abnormal glycogen structure?

Which clinical manifestation is NOT associated with Pompe Disease?

What is the primary cause of muscle weakness in McArdle Syndrome?

Which glycogen storage disease is associated with myoglobinemia?

Which of the following steps is regulated by hormonal signals?

Which of the following is NOT a primary source of blood glucose?

What is the preferred energy source for the brain?

Which type of cells are specifically mentioned as requiring glucose due to having few or no mitochondria?

What role does muscle glycogen primarily serve?

Approximately how much glycogen is stored in a well-fed adult liver?

Which process provides a rapid release of glucose in the absence of dietary sources?

What percentage of fresh weight of resting muscle does glycogen make up?

Which metabolic pathway is immediately engaged when glycogen stores are depleted?

Which type of glycogen storage disease is characterized by Glucose 6-Phosphatase deficiency?

Which tissues are primarily affected by Glucose 6-Phosphate Translocase deficiency (Type Ib)?

What is a symptom of severe prolonged fasting associated with Type Ib disease?

What is a characteristic symptom of Von Gierke Disease not directly related to glucose metabolism?

What treatment is specifically mentioned for managing symptoms of Type Ib disease?

Which molecule serves as the initial acceptor of glucose residues from UDP-glucose during glycogen synthesis?

What type of bond is primarily formed by glycogen synthase during glycogen elongation?

Which amino acid's side chain hydroxyl group serves as the site for the initial glucosyl unit attachment on glycogenin?

What enzyme helps in re-phosphorylating UDP to UTP during glycogen synthesis?

Where does glycogenin remain localized in the glycogen structure?

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

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

Which specific reaction is catalyzed by glycogenin via autoglucosylation?

What primarily characterizes lysosomal storage diseases?

During what condition does glycogenolysis in the liver accelerate?

Which statement accurately describes the hormonal regulation of glycogen synthase and glycogen phosphorylase?

How does calcium (Ca^{2+}) activate glycogen phosphorylase during muscle contraction?

What role does AMP play in muscle during extreme conditions of anoxia?

Which hormone stimulates glycogen degradation in both muscle and liver?

Which process is accelerated during the well-fed state in the liver?

What is the effect of insulin on glycogen degradation?

Which enzyme reconverts glycogen synthase b to the active 'a' form?

What molecule allosterically inhibits glycogen phosphorylase a in the liver but not in muscle?

What is the effect of cAMP on glycogen synthase?

Which state correlates with the increased activation of glycogen synthase b by glucose 6-phosphate?

What triggers the activation of muscle phosphorylase kinase b during muscle contraction?

How does the binding of calcium to calmodulin affect phosphorylase kinase b?

What is the role of protein kinases in the regulation of glycogen synthase?

Which molecule is NOT associated with activating glycogen degradation in muscle?

Which enzyme catalyzes the synthesis of cAMP following the binding of glucagon or epinephrine to GPCR?

What is the role of protein kinase A (PKA) in glycogen metabolism?

How is glycogen phosphorylase regulated in glycogen degradation?

Which statement best describes the summary of the regulation of glycogen degradation?

Which of the following is true for glycogen synthase regulation?

What is the function of inhibitor proteins in the regulation of glycogen metabolism?

Which hormones are primarily involved in signaling the need for glycogen degradation?

What role does protein phosphatase 1 play in glycogen metabolism?

Which molecule forms a complex with $Ca^{2+}$ to activate hepatic phosphorylase kinase b during the 'fight or flight' response?

What triggers the release of $Ca^{2+}$ from the ER into the cytoplasm in hepatocytes?

How does AMP activate muscle glycogen phosphorylase without phosphorylation?

Which enzyme's activation is associated with high AMP concentrations under anoxia and ATP depletion in muscles?

A defect in which enzyme type results in glycogen storage diseases (GSDs) leading to abnormal glycogen structure or accumulation?

Which linkage type is found at the branch points of glycogen after about eight to ten glucosyl residues?

During the 'fight or flight' response, which secondary messenger is responsible for hepatic glycogenolysis?

Which enzyme forms the primer required for glycogen synthesis?

What is the immediate product formed when glucose is transferred from UDP-glucose to the nonreducing end of glycogen?

Which enzyme is responsible for creating branches within the glycogen molecule?

What is the function of the enzyme amylo-α(1→4)→(1→6)-transglucosidase?

What is the primary product obtained when glycogen is degraded?

How many glucosyl residues apart are branches located on average in glycogen?

Which enzyme is responsible for sequentially cleaving α(1→4) glycosidic bonds during glycogen degradation?

What distinguishes amylose from glycogen?

What is a 'limit dextrin' in the context of glycogen metabolism?

Which coenzyme is required by glycogen phosphorylase for its activity?

What happens to the nonreducing ends of glycogen after the action of amylo-α(1→4)→(1→6)-transglucosidase?