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Questions and Answers
Questions and Answers
What effect does an increase in AMP levels have on carbohydrate metabolism during strenuous physical activity?
What effect does an increase in AMP levels have on carbohydrate metabolism during strenuous physical activity?
- Inhibition of glycogen synthesis
- Stimulation of gluconeogenesis
- Reduction in glucose mobilization
- Activation of fatty acid catabolic pathways (correct)
How do hormonal and allosteric mechanisms influence metabolic pathways?
How do hormonal and allosteric mechanisms influence metabolic pathways?
- By regulating metabolite flow without major changes in intermediates (correct)
- By causing large fluctuations in metabolite concentrations
- By exclusively affecting lipid metabolism
- By completely inhibiting carbohydrate metabolism
What metabolic state is indicated by high levels of AMP in vertebrates?
What metabolic state is indicated by high levels of AMP in vertebrates?
- Metabolic stress (correct)
- Sufficient ATP production
- A state of muscle recovery
- Surplus energy availability
Which of the following is a consequence of increased AMP levels related to fatty acid and carbohydrate metabolism?
Which of the following is a consequence of increased AMP levels related to fatty acid and carbohydrate metabolism?
What is the primary role of AMP in metabolic regulation during exercise?
What is the primary role of AMP in metabolic regulation during exercise?
What is the primary reason that sugar nucleotides are suitable for biosynthetic reactions?
What is the primary reason that sugar nucleotides are suitable for biosynthetic reactions?
Which enzyme converts glucose 6-phosphate to glucose 1-phosphate?
Which enzyme converts glucose 6-phosphate to glucose 1-phosphate?
What is released during the reaction catalyzed by UDP-glucose pyrophosphorylase?
What is released during the reaction catalyzed by UDP-glucose pyrophosphorylase?
Which nucleotide is crucial for the conversion of glucose 1-phosphate to UDP-glucose?
Which nucleotide is crucial for the conversion of glucose 1-phosphate to UDP-glucose?
What property of nucleotidyl groups aids in distinguishing hexoses used in metabolic pathways?
What property of nucleotidyl groups aids in distinguishing hexoses used in metabolic pathways?
What assists the rapid removal of the product in the formation of sugar nucleotides?
What assists the rapid removal of the product in the formation of sugar nucleotides?
In glycogen synthesis, what type of molecules are added to grow the linear chains?
In glycogen synthesis, what type of molecules are added to grow the linear chains?
What function do branched enzymes serve during glycogen synthesis?
What function do branched enzymes serve during glycogen synthesis?
What is the role of glycogen synthase in glycogenesis?
What is the role of glycogen synthase in glycogenesis?
Which enzyme is responsible for creating the branches in glycogen structure?
Which enzyme is responsible for creating the branches in glycogen structure?
What initiates the assembly of new glycogen chains?
What initiates the assembly of new glycogen chains?
What is required for glycogen synthesis to take place?
What is required for glycogen synthesis to take place?
Which of the following describes the autocatalytic reaction involving glycogenin?
Which of the following describes the autocatalytic reaction involving glycogenin?
What type of regulation coordinates glycogen synthesis and breakdown?
What type of regulation coordinates glycogen synthesis and breakdown?
Which hormone primarily promotes glycogen synthesis?
Which hormone primarily promotes glycogen synthesis?
What happens to glucose when it is released from glycogen?
What happens to glucose when it is released from glycogen?
What is the catalytically active form of skeletal glycogen phosphorylase?
What is the catalytically active form of skeletal glycogen phosphorylase?
Which hormones are involved in the phosphorylation of glycogen phosphorylase b to convert it to glycogen phosphorylase a?
Which hormones are involved in the phosphorylation of glycogen phosphorylase b to convert it to glycogen phosphorylase a?
Which of the following is NOT an allosteric activator of glycogen phosphorylase in muscle?
Which of the following is NOT an allosteric activator of glycogen phosphorylase in muscle?
What role does Ca2+ play in the regulation of glycogen phosphorylase?
What role does Ca2+ play in the regulation of glycogen phosphorylase?
What is the effect of increased cAMP levels on carbohydrate metabolism?
What is the effect of increased cAMP levels on carbohydrate metabolism?
How does phosphorylase b kinase become active?
How does phosphorylase b kinase become active?
Which statement about the enzymatic cascade involving cAMP is true?
Which statement about the enzymatic cascade involving cAMP is true?
What is the end product of glycogen breakdown catalyzed by glycogen phosphorylase?
What is the end product of glycogen breakdown catalyzed by glycogen phosphorylase?
What enzyme is activated by PKA to stimulate glycogen breakdown?
What enzyme is activated by PKA to stimulate glycogen breakdown?
Which hormone is NOT mentioned as regulating the balance between glycogen formation and glucose release?
Which hormone is NOT mentioned as regulating the balance between glycogen formation and glucose release?
What is the effect of ATP on phosphorylase during glycogen breakdown?
What is the effect of ATP on phosphorylase during glycogen breakdown?
What role does glucose play regarding phosphorylase a?
What role does glucose play regarding phosphorylase a?
What characterizes the kinetic behavior of phosphorylase a based on the information provided?
What characterizes the kinetic behavior of phosphorylase a based on the information provided?
Which enzyme converts phosphorylase a to the less active form phosphorylase b?
Which enzyme converts phosphorylase a to the less active form phosphorylase b?
Which statement best describes the effect of Ca2+ in muscle contraction related to phosphorylase b kinase?
Which statement best describes the effect of Ca2+ in muscle contraction related to phosphorylase b kinase?
How does AMP affect the activity of phosphorylase in muscle tissue?
How does AMP affect the activity of phosphorylase in muscle tissue?
What is the role of glucose 6-phosphatase in the ER of liver cells?
What is the role of glucose 6-phosphatase in the ER of liver cells?
Why is glucose 6-phosphatase located in the ER lumen?
Why is glucose 6-phosphatase located in the ER lumen?
Which enzyme deficiency is associated with Type Ia glycogen storage disease?
Which enzyme deficiency is associated with Type Ia glycogen storage disease?
Which condition is NOT a symptom of Type V glycogen storage disease?
Which condition is NOT a symptom of Type V glycogen storage disease?
What is a common symptom of glycogen storage diseases involving liver dysfunction?
What is a common symptom of glycogen storage diseases involving liver dysfunction?
What distinguishes Type II (Pompe) disease from other glycogen storage diseases?
What distinguishes Type II (Pompe) disease from other glycogen storage diseases?
What is the likely impact of a deficiency in GLUT2, as seen in Type XI disease?
What is the likely impact of a deficiency in GLUT2, as seen in Type XI disease?
In which type of glycogen storage disease would you expect symptoms of kidney failure?
In which type of glycogen storage disease would you expect symptoms of kidney failure?
Which enzyme is affected in Type IV (Andersen) glycogen storage disease?
Which enzyme is affected in Type IV (Andersen) glycogen storage disease?
What is a primary symptom of Type IIIa glycogen storage disease?
What is a primary symptom of Type IIIa glycogen storage disease?
Which of the following conditions is linked to muscle phosphorylase deficiency?
Which of the following conditions is linked to muscle phosphorylase deficiency?
What is the expected outcome for infants diagnosed with Type II glycogen storage disease?
What is the expected outcome for infants diagnosed with Type II glycogen storage disease?
What primary organ is primarily affected in Type Ia glycogen storage disease?
What primary organ is primarily affected in Type Ia glycogen storage disease?
Which of the following enzymes is NOT involved in glycogenolysis?
Which of the following enzymes is NOT involved in glycogenolysis?
Questions and Answers
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Flashcards
Flashcards
Glucose 6-phosphate fate in skeletal muscle
Glucose 6-phosphate fate in skeletal muscle
In skeletal muscle, glucose 6-phosphate is a key substrate for glycolysis, a pathway that generates ATP.
Glucose 6-phosphate fate in liver
Glucose 6-phosphate fate in liver
In the liver, glucose 6-phosphate is converted to glucose by glucose 6-phosphatase, an enzyme located in the ER lumen.
Glucose 6-phosphatase
Glucose 6-phosphatase
Glucose 6-phosphatase is an enzyme responsible for the conversion of glucose 6-phosphate to glucose.
Glycogenolysis
Glycogenolysis
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ER (Endoplasmic Reticulum)
ER (Endoplasmic Reticulum)
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ER Lumen
ER Lumen
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Futile Cycle
Futile Cycle
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Glycolysis
Glycolysis
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Glycogen Storage Disease (GSD)
Glycogen Storage Disease (GSD)
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Type Ia (von Gierke) GSD
Type Ia (von Gierke) GSD
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Type Ib GSD
Type Ib GSD
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Type II (Pompe) GSD
Type II (Pompe) GSD
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Type IIIa (Cori or Forbes) GSD
Type IIIa (Cori or Forbes) GSD
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Type V (McArdle) GSD
Type V (McArdle) GSD
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Type VI (Hers) GSD
Type VI (Hers) GSD
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Properties of Sugar Nucleotides
Properties of Sugar Nucleotides
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Formation of Sugar Nucleotides
Formation of Sugar Nucleotides
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Glycogen Synthesis Begins with Glucose 6-Phosphate
Glycogen Synthesis Begins with Glucose 6-Phosphate
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Phosphoglucomutase
Phosphoglucomutase
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UDP-Glucose Pyrophosphorylase
UDP-Glucose Pyrophosphorylase
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What is the equation for the reaction catalyzed by UDP-glucose pyrophosphorylase?
What is the equation for the reaction catalyzed by UDP-glucose pyrophosphorylase?
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What is the significance of UDP-glucose in glycogen synthesis?
What is the significance of UDP-glucose in glycogen synthesis?
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Which nucleotide is required for glycogen synthesis?
Which nucleotide is required for glycogen synthesis?
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Glycogen Synthase
Glycogen Synthase
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Glycogen-Branching Enzyme
Glycogen-Branching Enzyme
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Glycogen Synthesis Requirements
Glycogen Synthesis Requirements
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Glycogenin
Glycogenin
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Glycogenin Mechanism
Glycogenin Mechanism
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Glycogenesis: The First Step
Glycogenesis: The First Step
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Regulation of Glycogen Metabolism
Regulation of Glycogen Metabolism
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Hormonal Regulation of Glycogen Metabolism
Hormonal Regulation of Glycogen Metabolism
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Enzyme Cascade
Enzyme Cascade
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Glycogen Phosphorylase a
Glycogen Phosphorylase a
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Glycogen Phosphorylase b
Glycogen Phosphorylase b
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Phosphorylation Activation of Glycogen Phosphorylase
Phosphorylation Activation of Glycogen Phosphorylase
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Allosteric Effector
Allosteric Effector
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Allosteric Activator
Allosteric Activator
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Allosteric Activators of Glycogen Phosphorylase in Muscle
Allosteric Activators of Glycogen Phosphorylase in Muscle
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cAMP-dependent Protein Kinase (PKA) Role in Glycogen Breakdown
cAMP-dependent Protein Kinase (PKA) Role in Glycogen Breakdown
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Allosteric Regulation
Allosteric Regulation
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Phosphoprotein Phosphatase 1 (PP1)
Phosphoprotein Phosphatase 1 (PP1)
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Phosphorylase a
Phosphorylase a
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Phosphorylase b
Phosphorylase b
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Phosphorylase b Kinase
Phosphorylase b Kinase
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Homeostasis
Homeostasis
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AMP as a Metabolic Stress Signal
AMP as a Metabolic Stress Signal
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Metabolic Response to High AMP
Metabolic Response to High AMP
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Increased Energy Production during Exercise
Increased Energy Production during Exercise
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Metabolic Integration during Exercise
Metabolic Integration during Exercise
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Metabolic Pathways: Interconnected and Responsive
Metabolic Pathways: Interconnected and Responsive
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Study Notes
Study Notes
Glycogen Metabolism in Animals
- Glycogen serves as a readily available glucose source for vertebrate animals, supplying energy to the brain and skeletal muscles.
- Animals store significantly more energy as fat than glycogen, yet cannot convert fat into glucose.
- Glycogen's highly branched structure allows rapid release of glucose and glucose phosphate monomers without increasing cytosol osmolarity.
- Glycogen breakdown (glycogenolysis) occurs via phosphorolysis, generating phosphorylated glucose molecules suitable for glycolysis.
- Skeletal muscles rely heavily on glycogen stores for bursts of activity.
- Liver glycogen releases free glucose into the bloodstream to maintain blood glucose homeostasis when dietary glucose is insufficient, supplying the brain and other tissues.
Glycogen Structure and Function
- Glycogen is a polymeric storage form of glucose found primarily in muscle and liver.
- Glycogen granules are cytosolic and vary in size, structure, and subcellular location, appearing as electron-dense particles.
- Beta-granules, which consist of 20-40 clustered granules and release glucose slowly, can be seen in well-fed animals but are absent after a 24-hour fast.
- Alpha-granules, protein-rich and composed of clustered beta-granules, are prominent in well-fed animals and are often associated with smooth ER tubules.
- Glycogenin dimer acts as the primer for glycogen synthesis.
- Tiers of glucose residues are linked via (alpha 1→4) linkages, with branches created by (alpha 1→6) linkages.
- The branched structure provides many non-reducing ends, crucial for the rapid access and utilization of glucose.
Glycogen Synthesis and Breakdown
- Glycogen synthesis requires both a protein primer and an activated glucose precursor (individual glucose molecules activated as sugar nucleotides).
- Activated glucose is added onto the nonreducing end of the growing linear chains in the outer tiers of glycogen beta-granules.
- A branching enzyme adds branches periodically.
- Glycogen breakdown (glycogenolysis) is catalyzed by glycogen phosphorylase, which cleaves glucose residues from the nonreducing ends of glycogen chains via phosphorolysis.
- Glycogen phosphorylase requires pyridoxal phosphate.
- The enzyme acts repetitively until it reaches a point four residues away from a (1→6) branch point.
- A debranching enzyme transfers branches onto main chains, freeing the residue at the (1→6) branch as free glucose.
- Glucose 1-phosphate is converted to glucose 6-phosphate by phosphoglucomutase to enter glycolysis or, in liver, be hydrolyzed to glucose for release into the bloodstream.
Regulation of Glycogen Metabolism
- Hormone-controlled balance between glycogen synthesis and breakdown is essential for homeostasis.
- Hormones epinephrine, glucagon, and insulin regulate this balance, primarily through allosteric regulation and phosphorylation of synthetic and degradative enzymes.
- Regulatory enzymes and proteins are integral parts of the glycogen granule.
- Glycogen phosphorylase exists in two forms:
- Phosphorylase a = catalytically active
- Phosphorylase b = much less active
- Muscle glycogen phosphorylase is regulated by:
- Hormone-stimulated phosphorylation
- Allosteric effectors (e.g., Ca2+, AMP)
- Elevation of cAMP activates PKA, leading to phosphorylation of phosphorylase b kinase, ultimately catalyzing the phosphorylation of glycogen phosphorylase b, leading to activation and glycogen breakdown.
- Liver glycogen phosphorylase a is considered a glucose sensor, as glucose binding enhances its susceptibility to dephosphorylation by PP1, promoting glycogen breakdown.
- Glycogen synthase also has two forms (phosphorylated and unphosphorylated).
- Glycogen synthase kinase 3 (GSK3) phosphorylates glycogen synthase a, making it inactive, though glucose-6-phosphate can allosterically activate glycogen synthase, making it a substrate for PP1. The action of GSK3 is hierarchical, requiring a priming event of glycogen synthase phosphorylation by Casein kinase II.
Other Significant Points
- Glycogen storage diseases result from genetic defects in glucose 6-phosphatase or glucose 6-phosphate transporter T1, causing type la glycogen storage disease.
- The intriguing protein glycogenin acts as both a primer and an autocatalytic enzyme for glycogen assembly.
- UDP-glucose donates glucose residues for glycogen synthesis by glycogen synthase.
- Carbohydrate and lipid metabolism are integrated by hormonal and allosteric mechanisms.
- Different regulatory mechanisms are in place for muscle glycogenolysis (metabolism in muscle cells) compared to liver glycogenolysis (metabolism in liver cells) because of a difference in tissue requirements. Specifically, muscle utilizes its stored glycogen for only immediate needs, while the liver functions to maintain blood glucose homeostasis.
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