76 Questions
What type of glycosidic bond is primarily found in glycogen?
α(1→4) linkage
During which state does the liver increase its glycogen stores?
Well-fed state
What is the molecular mass range of a single glycogen molecule?
10^6 to 10^7 daltons
Where are glycogen molecules typically found within a cell?
Cytoplasmic granules
How is muscle glycogen affected by short periods of fasting?
Remains unaffected
Which enzyme is responsible for converting glucose 1-phosphate to glucose 6-phosphate?
Phosphoglucomutase
McArdle Syndrome is caused by a deficiency in which enzyme?
Glycogen phosphorylase
Which enzyme cleaves the remaining single glucose residue from the branch point during glycogenolysis?
Debranching enzyme
Which glycogen storage disease is characterized by fasting hypoglycemia and an abnormal glycogen structure?
Cori Disease
Which clinical manifestation is NOT associated with Pompe Disease?
High blood lactate levels during exercise
What is the primary cause of muscle weakness in McArdle Syndrome?
Deficiency in skeletal muscle glycogen phosphorylase
Which glycogen storage disease is associated with myoglobinemia?
McArdle Syndrome
Which of the following steps is regulated by hormonal signals?
Cleavage of alpha 1,4 glycosidic bonds in glycogen
Which of the following is NOT a primary source of blood glucose?
Lipolysis
What is the preferred energy source for the brain?
Glucose
Which type of cells are specifically mentioned as requiring glucose due to having few or no mitochondria?
Erythrocytes
What role does muscle glycogen primarily serve?
Providing energy for muscle contraction
Approximately how much glycogen is stored in a well-fed adult liver?
100g
Which process provides a rapid release of glucose in the absence of dietary sources?
Glycogenolysis
What percentage of fresh weight of resting muscle does glycogen make up?
1-2%
Which metabolic pathway is immediately engaged when glycogen stores are depleted?
Gluconeogenesis
Which type of glycogen storage disease is characterized by Glucose 6-Phosphatase deficiency?
Type Ia: Von Gierke Disease
Which tissues are primarily affected by Glucose 6-Phosphate Translocase deficiency (Type Ib)?
Liver and kidney
What is a symptom of severe prolonged fasting associated with Type Ib disease?
Hypoglycemia
What is a characteristic symptom of Von Gierke Disease not directly related to glucose metabolism?
Hyperlipidemia
What treatment is specifically mentioned for managing symptoms of Type Ib disease?
Nocturnal gastric infusions of glucose or cornstarch
Which molecule serves as the initial acceptor of glucose residues from UDP-glucose during glycogen synthesis?
Glycogenin
What type of bond is primarily formed by glycogen synthase during glycogen elongation?
(1→4) glycosidic bond
Which amino acid's side chain hydroxyl group serves as the site for the initial glucosyl unit attachment on glycogenin?
Tyrosine
What enzyme helps in re-phosphorylating UDP to UTP during glycogen synthesis?
Nucleoside diphosphate kinase
Where does glycogenin remain localized in the glycogen structure?
At the core of the glycogen granule
What is the primary function of UDP-glucose in glycogen synthesis?
Providing glucose residues for extending chains
Which enzyme catalyzes the conversion of glucose 6-phosphate to UDP-glucose?
UDP-glucose pyrophosphorylase
Which specific reaction is catalyzed by glycogenin via autoglucosylation?
Initial attachment of glucose residues to its own tyrosine residue
What primarily characterizes lysosomal storage diseases?
Accumulation of abnormal amounts of carbohydrates or lipids
During what condition does glycogenolysis in the liver accelerate?
Periods of fasting
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
How does calcium (Ca^{2+}) activate glycogen phosphorylase during muscle contraction?
By binding to the calmodulin subunit of phosphorylase kinase
What role does AMP play in muscle during extreme conditions of anoxia?
It activates glycogen phosphorylase b without being phosphorylated
Which hormone stimulates glycogen degradation in both muscle and liver?
Epinephrine
Which process is accelerated during the well-fed state in the liver?
Glycogenesis
What is the effect of insulin on glycogen degradation?
Inhibits glycogen degradation
Which enzyme reconverts glycogen synthase b to the active 'a' form?
Protein phosphatase-1
What molecule allosterically inhibits glycogen phosphorylase a in the liver but not in muscle?
Non-phosphorylated glucose
What is the effect of cAMP on glycogen synthase?
It inactivates glycogen synthase by phosphorylation.
Which state correlates with the increased activation of glycogen synthase b by glucose 6-phosphate?
Well-fed state
What triggers the activation of muscle phosphorylase kinase b during muscle contraction?
Membrane depolarization and calcium release
How does the binding of calcium to calmodulin affect phosphorylase kinase b?
It activates the enzyme without the need for phosphorylation.
What is the role of protein kinases in the regulation of glycogen synthase?
They phosphorylate glycogen synthase to the inactive form.
Which molecule is NOT associated with activating glycogen degradation in muscle?
Protein kinase A
Which enzyme catalyzes the synthesis of cAMP following the binding of glucagon or epinephrine to GPCR?
Adenylyl cyclase
What is the role of protein kinase A (PKA) in glycogen metabolism?
It activates phosphorylase kinase by phosphorylation
How is glycogen phosphorylase regulated in glycogen degradation?
By phosphorylation by active phosphorylase kinase
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.
Which of the following is true for glycogen synthase regulation?
The active form is dephosphorylated
What is the function of inhibitor proteins in the regulation of glycogen metabolism?
They inhibit protein phosphatase 1
Which hormones are primarily involved in signaling the need for glycogen degradation?
Glucagon and epinephrine
What role does protein phosphatase 1 play in glycogen metabolism?
It removes phosphate from proteins to activate them
Which molecule forms a complex with $Ca^{2+}$ to activate hepatic phosphorylase kinase b during the 'fight or flight' response?
Calmodulin
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
How does AMP activate muscle glycogen phosphorylase without phosphorylation?
By binding to glycogen phosphorylase b
Which enzyme's activation is associated with high AMP concentrations under anoxia and ATP depletion in muscles?
Glycogen phosphorylase
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
Which linkage type is found at the branch points of glycogen after about eight to ten glucosyl residues?
$\alpha$(1-6)
During the 'fight or flight' response, which secondary messenger is responsible for hepatic glycogenolysis?
$Ca^{2+}$
Which enzyme forms the primer required for glycogen synthesis?
Glycogenin
What is the immediate product formed when glucose is transferred from UDP-glucose to the nonreducing end of glycogen?
An $\alpha$(1-4) linkage
Which enzyme is responsible for creating branches within the glycogen molecule?
Amylo-$\alpha$(1-4)-(1-6)-transglucosidase
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
What is the primary product obtained when glycogen is degraded?
Glucose 1-phosphate
How many glucosyl residues apart are branches located on average in glycogen?
Eight glucosyl residues apart
Which enzyme is responsible for sequentially cleaving α(1→4) glycosidic bonds during glycogen degradation?
Glycogen phosphorylase
What distinguishes amylose from glycogen?
Amylose is an unbranched molecule of glucosyl residues, while glycogen is highly branched.
What is a 'limit dextrin' in the context of glycogen metabolism?
A glycogen structure that glycogen phosphorylase cannot degrade further
Which coenzyme is required by glycogen phosphorylase for its activity?
Pyridoxal phosphate (PLP)
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
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
This quiz explains the steps involved in the degradation of glycogen into glucose, including the role of glycogen phosphorylase and debranching enzyme.
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