Glycogen Metabolism and Regulation
85 Questions
0 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the role of glucagon and epinephrine in glycogen metabolism?

  • They promote glycogen synthesis exclusively.
  • They only function in muscle glucose uptake.
  • They are irrelevant in glycogen metabolism.
  • They initiate glycogen breakdown while inhibiting synthesis. (correct)

    • How does protein kinase A affect glycogen synthase activity?

  • It enhances the activity of glycogen synthase.
  • It completely deactivates all forms of glycogen synthase.
  • It phosphorylates glycogen synthase leading to decreased activity. (correct)
  • It does not influence glycogen synthase.

    • What is the main action of protein phosphatase 1 (PP1) in glycogen metabolism?

  • It enhances glycogen breakdown.
  • It phosphorylates glycogen synthase to activate it.
  • It stimulates muscle contraction.
  • It dephosphorylates phosphorylase a and phosphorylase kinase. (correct)

    • What molecular action marks the transition from glycogen degradation to glycogen synthesis after exercise?

    <p>Dephosphorylation of key enzymes by protein phosphatases.</p> Signup and view all the answers

    What happens to glycogen synthase when phosphoryl groups are removed by PP1?

    <p>It is converted to a more active form.</p> Signup and view all the answers

    Which of the following best describes the relationship between glycogen breakdown and synthesis?

    <p>They are reciprocally regulated.</p> Signup and view all the answers

    What is the function of regulatory subunits associated with PP1?

    <p>They serve as scaffolds to organize enzymes.</p> Signup and view all the answers

    What triggers the cAMP cascade that initiates glycogen breakdown?

    <p>Glucagon and epinephrine signaling.</p> Signup and view all the answers

    What initiates the cAMP cascade that activates protein kinase A to initiate glycogen degradation?

    <p>Epinephrine or glucagon</p> Signup and view all the answers

    Which mechanism does protein kinase A utilize to reduce the activity of PP1 in muscle cells?

    <p>Phosphorylating an inhibitor that affects PP1</p> Signup and view all the answers

    What role does insulin play in glycogen synthesis?

    <p>Stimulates the conversion of glucose into glucose 6-phosphate</p> Signup and view all the answers

    How does the inactivation of glycogen synthase kinase affect glycogen synthesis?

    <p>It converts glycogen synthase b into its active form.</p> Signup and view all the answers

    What is the primary mechanism by which glucose influences the function of liver phosphorylase a?

    <p>It promotes the conversion of phosphorylase a into phosphorylase b.</p> Signup and view all the answers

    What ensures that glycogen degradation and synthesis do not occur simultaneously?

    <p>The lag between inactivation of phosphorylase and activation of synthase</p> Signup and view all the answers

    How does the binding of insulin to its receptor initiate its effects?

    <p>By triggering the phosphorylation of insulin receptor substrates</p> Signup and view all the answers

    What happens to the amount of liver phosphorylase a when glucose is infused into the blood?

    <p>It decreases rapidly.</p> Signup and view all the answers

    What converts phosphorylase b into its active form?

    <p>Dephosphorylation by PP1</p> Signup and view all the answers

    How does PP1 become active with respect to phosphorylase?

    <p>By dissociating from phosphorylase a when it shifts to the T form</p> Signup and view all the answers

    What effect does glucose have on glycogen synthase when phosphorylase a is inactivated?

    <p>It causes an increase in glycogen synthase a activity.</p> Signup and view all the answers

    What are the three key elements of the glucose-sensing system in the liver?

    <p>Communication between allosteric sites, PP1, and binding to phosphorylase</p> Signup and view all the answers

    What is the effect of phosphorylase b having a low affinity for phosphatase?

    <p>Allows for the quick activation of glycogen synthase</p> Signup and view all the answers

    What is the main product formed when glycogen is cleaved by glycogen phosphorylase?

    <p>Glucose 1-phosphate</p> Signup and view all the answers

    What type of reaction occurs during the action of glycogen phosphorylase?

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

    What enzyme is responsible for converting glucose 1-phosphate into glucose 6-phosphate?

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

    Which bond does glycogen phosphorylase cleave during glycogen breakdown?

    <p>Alpha-1,4 bonds</p> Signup and view all the answers

    Why is phosphorolysis considered energetically advantageous compared to hydrolysis?

    <p>It does not require ATP for phosphorylation.</p> Signup and view all the answers

    What limits the action of glycogen phosphorylase during glycogen degradation?

    <p>It stops cleaving when close to branch points.</p> Signup and view all the answers

    What happens to glucose 1-phosphate in physiological conditions?

    <p>It remains trapped within the cell.</p> Signup and view all the answers

    What must occur to glycogen for it to remain a suitable substrate for further degradation after initial cleavage?

    <p>Remodeling by additional enzymes.</p> Signup and view all the answers

    What factor differentiates liver phosphorylase from muscle phosphorylase?

    <p>Liver phosphorylase is insensitive to regulation by AMP.</p> Signup and view all the answers

    Which type of muscle fiber predominantly uses glycogen as its main fuel source?

    <p>Type IIb fibers</p> Signup and view all the answers

    What is the primary biochemical pathway utilized by type I muscle fibers for energy?

    <p>Fatty acid degradation</p> Signup and view all the answers

    What initiates the phosphorylation of phosphorylase b in both liver and muscle?

    <p>Secretion of hormones like glucagon and epinephrine</p> Signup and view all the answers

    Which component is crucial for the activation of phosphorylase kinase in skeletal muscle?

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

    Which state of phosphorylase b is primarily associated with reduced activity?

    <p>T state</p> Signup and view all the answers

    What structural change occurs during the transition from T state to R state in phosphorylase?

    <p>Movement of a loop out of the active site</p> Signup and view all the answers

    How does the phosphorylation of phosphorylase kinase occur?

    <p>Via the action of protein kinase A</p> Signup and view all the answers

    Why are type IIb muscle fibers rich in glycolytic enzymes?

    <p>They need to process glucose quickly in low oxygen conditions.</p> Signup and view all the answers

    What is a notable feature of type IIa muscle fibers?

    <p>They show trainable characteristics in oxidative and glycolytic capacities.</p> Signup and view all the answers

    What is the role of the transferase enzyme in glycogen degradation?

    <p>It shifts a block of glucosyl residues between outer branches.</p> Signup and view all the answers

    Which enzyme converts glucose 1-phosphate into glucose 6-phosphate?

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

    How does glucose 6-phosphatase facilitate the export of glucose from the liver?

    <p>By cleaving the phosphoryl group from glucose 6-phosphate.</p> Signup and view all the answers

    What is the default state of liver phosphorylase?

    <p>Active and in the R state</p> Signup and view all the answers

    What activates muscle phosphorylase b during muscle contraction?

    <p>High concentrations of AMP</p> Signup and view all the answers

    What happens to liver phosphorylase a when blood glucose levels are sufficient?

    <p>It transitions to the less active T state.</p> Signup and view all the answers

    Which compound acts as a negative allosteric effector for muscle phosphorylase b?

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

    What type of enzyme is glucose 6-phosphatase classified as?

    <p>A hydrolase</p> Signup and view all the answers

    Which of the following statements about muscle phosphorylase b is incorrect?

    <p>It is more active in the presence of glucose.</p> Signup and view all the answers

    Which of the following roles does the liver play regarding glucose?

    <p>It releases glucose into the blood as needed.</p> Signup and view all the answers

    What dual function does the enzyme that includes transferase and alpha-1,6 glucosidase serve?

    <p>It remodels glycogen for further degradation.</p> Signup and view all the answers

    Which residue is crucial for the action of phosphoglucomutase?

    <p>A phosphorylated serine residue</p> Signup and view all the answers

    In what way does glucose 6-phosphate influence muscle phosphorylase b?

    <p>It inhibits it by stabilizing its T state.</p> Signup and view all the answers

    What is the significance of the bifunctional nature of the enzyme containing transferase and alpha-1,6 glucosidase activities?

    <p>It simplifies glycogen remodeling for degradation.</p> Signup and view all the answers

    Which feature distinguishes liver glycogen phosphorylase from muscle glycogen phosphorylase?

    <p>Sensitivity to glucose levels</p> Signup and view all the answers

    What is the primary product released during the breakdown of glycogen by glycogen phosphorylase?

    <p>Glucose 1-phosphate</p> Signup and view all the answers

    Which type of reaction does glycogen phosphorylase utilize to cleave glycogen?

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

    What advantage does phosphorolytic cleavage of glycogen provide muscle cells?

    <p>It prevents the expenditure of ATP in phosphorylation.</p> Signup and view all the answers

    What prevents glycogen phosphorylase from completely degrading glycogen at branch points?

    <p>Alpha-1,6 bonds</p> Signup and view all the answers

    Which statement accurately describes phosphorylase's action on glycogen?

    <p>It stops cleaving when it reaches six glucose residues from a branch point.</p> Signup and view all the answers

    What is the consequence of glycogen phosphorylase stopping at branch points?

    <p>Only a limited number of glucose units can be released.</p> Signup and view all the answers

    What is formed by the phosphorolysis of glycogen?

    <p>Glucose 1-phosphate</p> Signup and view all the answers

    What is the primary difference between liver and muscle phosphorylase regarding AMP regulation?

    <p>Muscle phosphorylase is insensitive to AMP regulation.</p> Signup and view all the answers

    Which type of muscle fiber predominantly relies on cellular respiration for energy?

    <p>Type I fibers</p> Signup and view all the answers

    What is the characteristic of type IIb muscle fibers that distinguishes them from type I fibers?

    <p>They primarily utilize glycogen for energy.</p> Signup and view all the answers

    How does the transition from the T state to the R state affect phosphorylase activity?

    <p>The catalytic site becomes more active.</p> Signup and view all the answers

    What role does phosphorylase kinase play in the activation of phosphorylase b?

    <p>It phosphorylates phosphorylase b to form phosphorylase a.</p> Signup and view all the answers

    Which statement about type IIa muscle fibers is incorrect?

    <p>They are primarily glycolytic.</p> Signup and view all the answers

    What initiates the phosphorylation of phosphorylase b in muscle cells during contraction?

    <p>Release of calcium from the sarcoplasmic reticulum</p> Signup and view all the answers

    Which subunit of phosphorylase kinase serves as the calcium-binding protein?

    <p>The calmodulin subunit</p> Signup and view all the answers

    What factor is crucial for the activity of phosphorylase kinase in skeletal muscle?

    <p>Calcium availability</p> Signup and view all the answers

    What distinguishes the structure of phosphorylase a from phosphorylase b?

    <p>The R state of phosphorylase a is more stable than the T state of phosphorylase b.</p> Signup and view all the answers

    What is the primary role of alpha-1,6 glucosidase in glycogen degradation?

    <p>It hydrolyzes alpha-1,6 linkages, releasing glucose.</p> Signup and view all the answers

    How does the presence of glucose influence the activity of liver phosphorylase a?

    <p>It shifts it to a less active state.</p> Signup and view all the answers

    What is the main function of glucose 6-phosphatase in the liver?

    <p>To facilitate the release of free glucose into the blood.</p> Signup and view all the answers

    What is the result of the action of the transferase enzyme during glycogen degradation?

    <p>It exposes a single glucose residue for hydrolysis.</p> Signup and view all the answers

    What catalyst facilitates the conversion of glucose 1-phosphate to glucose 6-phosphate?

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

    What type of enzyme is classified as a bifunctional enzyme involved in glycogen degradation?

    <p>Transferase and alpha-1,6 glucosidase</p> Signup and view all the answers

    Which molecule acts as a positive effector for muscle phosphorylase b?

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

    The default state of liver phosphorylase is primarily in which form?

    <p>Active phosphorylase a</p> Signup and view all the answers

    What role does glucose 6-phosphate primarily play in muscle cells?

    <p>It is utilized for ATP generation.</p> Signup and view all the answers

    What is a significant allosteric effector for phosphorylase b in muscle cells?

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

    In what state is phosphorylase b primarily found in resting muscle cells?

    <p>Inactive b form</p> Signup and view all the answers

    During the action of glycogen phosphorylase, which linkage does it primarily cleave?

    <p>Alpha-1,4 linkage</p> Signup and view all the answers

    Which enzyme is responsible for hydrolyzing the alpha-1,6 linkage during glycogen degradation?

    <p>Alpha-1,6 glucosidase</p> Signup and view all the answers

    How does ATP affect the activity of muscle phosphorylase b?

    <p>It inhibits it by stabilizing the T state.</p> Signup and view all the answers

    Study Notes

    Glycogen Metabolism Regulation

    • Glycogen synthesis and breakdown are reciprocally regulated to prevent simultaneous activity.
    • Glucagon and epinephrine initiate cAMP cascades that trigger glycogen breakdown and simultaneously inhibit glycogen synthesis via protein kinase A.
    • Protein kinase A phosphorylates glycogen synthase, decreasing its activity.
    • Protein phosphatase 1 (PP1) dephosphorylates phosphorylase a and phosphorylase kinase, inhibiting glycogen breakdown.
    • PP1 dephosphorylates glycogen synthase b, converting it to the active glycogen synthase a, stimulating synthesis.

    Muscle Glycogen Replenishment

    • After exercise, protein phosphatases like PP1 dephosphorylate proteins stimulating glycogen breakdown.
    • PP1 dephosphorylates phosphorylase a and phosphorylase kinase, decreasing glycogen breakdown.
    • PP1 also dephosphorylates and activates glycogen synthase.
    • PP1 activity is reduced by phosphorylation of regulatory subunits or release of the catalytic subunit when activated by protein kinase A.

    Insulin and Glycogen Synthesis

    • High blood glucose concentration triggers insulin release, stimulating glycogen synthesis.
    • Insulin increases glucose uptake by increasing GLUT4 transporters.
    • Insulin inactivates glycogen synthase kinase (GSK) which normally keeps glycogen synthase phosphorylated and inactive.
    • Protein phosphatases (PP1) remove phosphate groups from glycogen synthase, further activating it.

    Liver Glycogen Metabolism

    • Liver phosphorylase a acts as a glucose sensor.
    • High blood glucose causes glucose to bind to phosphorylase a, altering its conformation from active R form to inactive T form.
    • This conformational change allows for PP1 binding, which dephosphorylates phosphorylase a, converting it into phosphorylase b. PP1 is released, stimulating glycogen synthase.
    • Glucose binding to phosphorylase causes PP1 release and the activation of glycogen synthase.

    Preventing Simultaneous Pathways

    • The timing of activation and inactivation of the pathways ensure they do not occur at the same time.
    • A lag exists between glycogen degradation and synthesis.

    Key Features of Glucose Sensing

    • Communication between glucose binding site and the serine phosphate.
    • PP1 inactivating phosphorylase and activating glycogen synthase.
    • PP1 binding to phosphorylase a prevents premature glycogen synthase activation.

    Studying That Suits You

    Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

    Quiz Team

    Description

    This quiz covers the critical regulation of glycogen synthesis and breakdown, focusing on the roles of glucagon, epinephrine, and protein phosphatases. Understand the mechanisms of regulation to grasp how glycogen metabolism is controlled in response to physiological signals. Test your knowledge of key enzymes and processes involved in muscle glycogen replenishment.

    More Like This

    Glycogen Metabolism Quiz
    10 questions

    Glycogen Metabolism Quiz: Test Your Knowledge

    RapturousComprehension avatar
    RapturousComprehension
    Glycogen Metabolism Quiz
    15 questions

    Glycogen Metabolism Quiz

    DelightedHope avatar
    DelightedHope
    Glycogen Metabolism Review Quiz
    10 questions

    Glycogen Metabolism Review Quiz

    PoshLucchesiite4011 avatar
    PoshLucchesiite4011
    Biology Chapter on Glycogen and Protein Synthesis
    75 questions

    Biology Chapter on Glycogen and Protein Synthesis

    SufficientBohrium avatar
    SufficientBohrium
    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser