Glucose and Glycogen Regulation
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Questions and Answers

What role does insulin play in glycogen synthesis in myocytes?

  • It decreases hexokinase activity.
  • It promotes the relocation of GLUT4 to the plasma membrane. (correct)
  • It increases blood glucose levels.
  • It inhibits glycogen synthase.
  • Which of the following statements about carbohydrate regulation in liver cells is true?

  • Insulin and glucagon have the same effects on carbohydrate metabolism.
  • Epinephrine has an antagonistic effect to glucagon in liver carbohydrate metabolism. (correct)
  • Epinephrine only stimulates glycogen synthesis in liver cells.
  • Only insulin stimulates glucose production in liver cells.
  • What is the main difference between carbohydrate metabolism in muscles and liver cells?

  • Insulin does not affect muscle cells in carbohydrate metabolism.
  • Muscles contribute to blood glucose levels like liver cells.
  • Liver cells respond to glucagon while muscles do not. (correct)
  • Muscles lack the ability to synthesize glycogen.
  • What effect does epinephrine have on glycolysis in liver and muscle cells?

    <p>It acts oppositely on glycolysis in liver compared to muscle cells.</p> Signup and view all the answers

    Which of the following best describes the simultaneous action of hormones such as insulin?

    <p>They act on different pathways and enzymes to result in a cohesive metabolic effect.</p> Signup and view all the answers

    What is the most common glycogen storage disease?

    <p>Von Gierke Disease</p> Signup and view all the answers

    What enzyme deficiency leads to Pompe Disease?

    <p>α(14)-glucosidase</p> Signup and view all the answers

    Which process is primarily involved in elongating glycogen chains?

    <p>α(1→4) linkage reaction</p> Signup and view all the answers

    Which condition is a result of deficiency in muscle glycogen phosphorylase?

    <p>McArdle Syndrome</p> Signup and view all the answers

    What is a key characteristic of covalent modifications of enzymes?

    <p>They often involve phosphorylation and dephosphorylation.</p> Signup and view all the answers

    Which component is responsible for priming glycogen synthesis?

    <p>Glycogenin</p> Signup and view all the answers

    What happens when the rate of conversion from substrate to product is equal to the reverse rate?

    <p>A steady state is maintained.</p> Signup and view all the answers

    The FDA approved a recombinant form of which enzyme in 2006 for treating Pompe Disease?

    <p>α(14)-glucosidase</p> Signup and view all the answers

    What is the primary function of glycogen in the body?

    <p>To store excess glucose for later use.</p> Signup and view all the answers

    Which type of bond links the glucose units in glycogen?

    <p>α1→4 and α1→6 Glycosidic bond</p> Signup and view all the answers

    Which of the following correctly describes the process of phosphorolysis in glycogen degradation?

    <p>It removes glucose residues from the non-reducing end.</p> Signup and view all the answers

    Where is glucose-6-phosphatase predominantly found?

    <p>In liver and kidney cells.</p> Signup and view all the answers

    What is the outcome of the debranching process in glycogen degradation?

    <p>Production of glucose.</p> Signup and view all the answers

    Which of the following statements is true regarding muscle and adipose tissue cells?

    <p>They do not have glucose-6-phosphatase.</p> Signup and view all the answers

    Which enzyme is responsible for a continuous, small scale degradation of glycogen?

    <p>Acid maltase (α(14)-glucosidase).</p> Signup and view all the answers

    Which process primarily consumes glucose-6-phosphate in the liver?

    <p>All of the above.</p> Signup and view all the answers

    What is the primary effect of insulin on glycogen synthesis?

    <p>Stimulates glycogen synthesis</p> Signup and view all the answers

    Which hormone is responsible for increasing cyclic-AMP levels in the body?

    <p>Adrenaline</p> Signup and view all the answers

    Which of the following is directly inhibited by insulin during carbohydrate metabolism?

    <p>Phosphorylase kinase</p> Signup and view all the answers

    In which tissue does glucagon primarily exert its effects?

    <p>Liver</p> Signup and view all the answers

    What is the effect of glucagon on gluconeogenesis?

    <p>Stimulates gluconeogenesis</p> Signup and view all the answers

    Which of the following is NOT an effect of insulin?

    <p>Stimulates gluconeogenesis</p> Signup and view all the answers

    What is the general role of phosphoprotein phosphatase related to insulin action?

    <p>It dephosphorylates glucose transporter</p> Signup and view all the answers

    Which pathway is primarily stimulated by epinephrine in muscle tissue?

    <p>Glycogen breakdown</p> Signup and view all the answers

    What is the primary regulatory mechanism of PFK-1 in glycolysis?

    <p>Allosteric regulation by ATP and citrate</p> Signup and view all the answers

    Which hexokinase isozyme is primarily found in the liver?

    <p>Hexokinase IV (glucokinase)</p> Signup and view all the answers

    What effect does fructose-2,6-bisphosphate have on glycolysis and gluconeogenesis?

    <p>Activates glycolysis and inhibits gluconeogenesis</p> Signup and view all the answers

    How does the activity of glucokinase change when blood glucose levels increase?

    <p>Is activated and increases</p> Signup and view all the answers

    What is the effect of ATP on pyruvate kinase activity in glycolysis?

    <p>Inhibition when energy is abundant</p> Signup and view all the answers

    Which enzyme initiates the gluconeogenesis pathway from pyruvate?

    <p>Pyruvate carboxylase</p> Signup and view all the answers

    What role does insulin play in the regulation of glycogen metabolism?

    <p>Promotes glycogen synthesis</p> Signup and view all the answers

    Which of the following is an allosteric inhibitor of PFK-1?

    <p>Citrate</p> Signup and view all the answers

    What is the function of glycogen phosphorylase in the liver?

    <p>Catalyze the breakdown of glycogen</p> Signup and view all the answers

    Which enzyme is responsible for converting fructose-6-phosphate to fructose-1,6-bisphosphate?

    <p>Phosphofructokinase</p> Signup and view all the answers

    What happens to glycogen phosphorylase when high levels of glucose are detected?

    <p>Converts from active form a to inactive form b</p> Signup and view all the answers

    What is the consequence of acetyl-CoA on the regulation of pyruvate?

    <p>Allosterically regulates both glycolysis and gluconeogenesis</p> Signup and view all the answers

    Which molecule serves as a signal of high-energy status to inhibit glycolysis?

    <p>Citrate</p> Signup and view all the answers

    Study Notes

    Glucose and Glycogen Regulation

    • Glucose levels in the blood (glycemia) are tightly controlled through various processes involving glucose production and consumption.
    • Excess glucose is stored as glycogen, which cannot be stored in large quantities due to its osmotic nature.
    • Glycogen is a branched polymer of glucose linked together through α(1→4) and α(1→6) linkages.
    • Glycogen is primarily stored in the liver (up to 10% weight) and skeletal muscles (up to 1-2% weight).

    Glycogen Degradation

    • Glucose residues are removed from the non-reducing ends via phosphorolysis
    • Glycogen phosphorylase catalyzes the removal of glucose-1-phosphate from glycogen.
    • Debranching enzyme is involved in the removal of branches from the glycogen molecule.
    • Glucose-1-phosphate is converted to glucose-6-phosphate.
    • Glucose-6-phosphate can be used in glycolysis, the pentose pathway, or gluconeogenesis to regenerate glucose.
    • Liver cells contain glucose-6-phosphatase, which is absent in muscle cells. This allows for the release of glucose into the bloodstream.

    Glycogen Storage Diseases

    • Glycogen storage diseases result from deficiencies in enzymes involved in glycogen metabolism.
    • Pompe disease is a lysosomal (1→4)-glucosidase deficiency leading to glycogen accumulation in lysosomes.
    • McArdle syndrome is caused by a deficiency in skeletal muscle glycogen phosphorylase.
    • Von Gierke disease is the most common glycogen storage disease, resulting from a glucose-6-phosphatase deficiency.

    Regulation of Glycolysis and Gluconeogenesis

    • Glycolysis and gluconeogenesis are regulated to maintain a dynamic steady state. Regulation happens at the level of the three irreversible steps.
    • Key enzymes in these pathways (e.g., PFK-1, pyruvate kinase, glucose-6-phosphatase) are regulated allosterically and/or via covalent modification.
    • Fructose-2,6-bisphosphate plays a crucial regulatory role, activating glycolysis and inhibiting gluconeogenesis.
    • ATP and citrate inhibit glycolysis.
    • ADP and AMP activate glycolysis and inhibit gluconeogenesis.
    • These pathways are regulated as a coordinated system to prevent futile cycles.

    Regulation of Glycolysis at Hexokinase Level

    • Hexokinase IV (glucokinase) in liver cells has a higher Km for glucose and is not inhibited by glucose 6-phosphate.
    • This allows the liver to uptake and metabolize glucose even at low blood glucose concentrations.

    Regulation of Glycolysis at PFK Level

    • PFK-1 is allosterically regulated by ATP and citrate.
    • Its activity is higher when ATP levels are low and citrate levels are high.

    Regulation of Glycolysis at Pyruvate Kinase Level

    • Pyruvate kinase is allosterically regulated by ATP, acetyl-CoA, fatty acids, and alanine.
    • Insulin promotes the activation of pyruvate kinase in the liver.

    Regulation of Glycogen Synthesis and Breakdown

    • Glycogen synthase is activated by insulin and de-activated by glucagon.
    • Glycogen phosphorylase is activated by glucagon, epinephrine, and AMP and inactivated by insulin and PP1.

    Hormonal Regulation of Carbohydrate Metabolism

    • Insulin stimulates glycogen synthesis and inhibits glycogen breakdown.
    • Glucagon and epinephrine stimulate glycogen breakdown and inhibit glycogen synthesis.
    • They have opposing effects on glycolysis and gluconeogenesis and on the different tissues.

    Summary of Glycogen Regulation

    • Coordinated regulation of glycolysis and gluconeogenesis is achieved to prevent futile cycles and maintain glucose homeostasis.

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    Description

    Test your knowledge on the regulation of glucose and glycogen metabolism, including their storage, degradation, and biochemical pathways. This quiz covers key processes like glycolysis, gluconeogenesis, and the role of enzymes in glucose metabolism.

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