Module 6, Lecture 3: G-protein Coupled Receptors
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Questions and Answers

What role does cAMP play in the signaling pathway described?

  • It binds directly to DNA to influence gene expression.
  • It acts as a secondary messenger to regulate enzyme activity. (correct)
  • It inhibits the production of glucose in response to stress.
  • It serves as a primary messenger to initiate the response.

    • Which of the following accurately describes the function of Protein Kinase A (PKA) in the cAMP signaling pathway?

  • PKA phosphorylates target proteins to induce metabolic changes. (correct)
  • PKA directly binds to epinephrine to amplify the signal.
  • PKA functions as a primary receptor for incoming signals.
  • PKA converts ATP into cAMP to propagate the signal.

    • What is a key feature of the signaling pathways involving CREB and CRE?

  • They significantly increase the concentration of epinephrine.
  • They lead to the assembly of transcriptional machinery for long-term responses. (correct)
  • They do not require signal amplification for effectiveness.
  • They initiate a rapid response by changing membrane potentials.

    • In the context of energy metabolism, what is the significance of signal amplification in the cAMP signaling pathway?

    <p>It ensures that even a single epinephrine molecule can cause a massive increase in glucose levels.</p> Signup and view all the answers

    Which aspect of GPCRs is crucial for their functionality in the signaling pathway discussed?

    <p>They span the membrane multiple times and associate with G-proteins.</p> Signup and view all the answers

    What is the primary role of Protein Kinase A (PKA) in glycogen metabolism during a stress response?

    <p>To phosphorylate phosphorylase kinase to activate glycogen phosphorylase</p> Signup and view all the answers

    Which molecule serves as a secondary messenger that activates PKA in the signaling pathway?

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

    What effect does PKA have on glycogen synthase during a stress response?

    <p>It phosphorylates and inactivates glycogen synthase</p> Signup and view all the answers

    During the fight-or-flight response, what is the source of glucose in skeletal muscles?

    <p>Glucose-6-phosphate</p> Signup and view all the answers

    What role does CREB play in the signaling pathway mediated by PKA?

    <p>It phosphorylates specific transcription factors to regulate gene expression</p> Signup and view all the answers

    Which process is primarily regulated by glycogen phosphorylase during a stress response?

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

    How does the body ensure a rapid response to increased epinephrine levels?

    <p>By modifying existing enzymes through phosphorylation</p> Signup and view all the answers

    What is the immediate outcome of activating glycogen phosphorylase in liver cells?

    <p>Release of free glucose into the bloodstream</p> Signup and view all the answers

    Which of the following compounds is NOT a product of glycolysis?

    <p>Glucose-6-phosphate</p> Signup and view all the answers

    What happens to the amount of ATP available to muscles during a stress response?

    <p>It increases due to the breakdown of glycogen</p> Signup and view all the answers

    Study Notes

    Module 6, Lecture 3: G-protein Coupled Receptors (GPCRs)

    • GPCRs are a large family of receptors involved in numerous human physiological processes
    • Many human diseases are linked to GPCR-related disorders
    • GPCRs are targets for most pharmaceuticals
    • GPCRs share a common structure with seven transmembrane alpha helix domains.
    • These domains create four extracellular and four cytoplasmic segments, forming a signal-binding domain and an internal domain interacting with a trimeric G protein.

    Examples of GPCRs

    • Stress response receptors
    • Light-activated rhodopsins in the eye
    • Odorant receptors
    • Hormone and neurotransmitter receptors
    • Plant growth hormone receptors
    • Glucose-sensing GPCR system (yeast)

    GPCR Signal Transduction

    • Involves activation of the receptor-associated trimeric G-protein which activates adenylyl cyclase.
    • Adenylyl cyclase modulates the cytosolic concentration of cyclic AMP (cAMP).
    • cAMP has multiple effects, including impacting energy release for stress responses.

    Adrenergic Receptors

    • Subclasses include alpha-2 and beta-adrenergic receptors.
    • Epinephrine can bind to both, inducing different responses based on receptor type and cell type.
    • Beta adrenergic receptors stimulate glycolysis and lipolysis in the liver and adipose tissues; increase heart muscle contraction; and relax smooth muscle in the intestine.
    • Alpha-2 adrenergic receptors are generally inhibitory, constricting blood vessels to regulate blood flow.

    GPCR Activation

    • Receptor activation leads to a conformational change in the intracellular domain.
    • This change allows high-affinity interaction with the trimeric G protein, causing dissociation of GDP and binding of GTP to the G-protein subunit.
    • The activated G-alpha subunit further activates effector molecules.

    Adenylyl Cyclase and cAMP

    • Adenylyl cyclase catalyzes the conversion of ATP to cAMP.
    • cAMP levels are maintained by the balance between adenylyl cyclase and phosphodiesterase.
    • Phosphodiesterase breaks down cAMP to 5'AMP.
    • cAMP concentration is crucial for signaling pathway activation or inactivation.

    Cyclic AMP (cAMP) as a Secondary Messenger

    • cAMP is a small, soluble molecule acting as a secondary messenger.
    • cAMP concentration determines activation or inactivation of downstream signaling effectors.
    • cAMP affects various target proteins, including enzymes.

    Protein Kinase A (PKA) Activation

    • Inactive PKA is a tetrameric protein with two regulatory and two catalytic subunits.
    • cAMP binding to regulatory subunits causes a conformational change activating catalytic units, releasing them.

    PKA Role in Stress Response

    • PKA enhances the breakdown of glycogen to glucose, making glucose available for energy use during stress responses.
    • PKA regulates glycogen synthase (inhibiting) and glycogen phosphorylase (activating).

    Signal Amplification

    • Signal amplification is a crucial aspect of cellular responses, where a small signal can trigger a large-scale response.
    • This involves activation of enzymes that subsequently activate other molecules leading to a chain reaction.

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    Description

    This quiz covers G-protein coupled receptors (GPCRs), a vital component in human physiology and pharmacology. Explore the structure, function, and significance of GPCRs, along with their role in various diseases and drug targeting. Test your knowledge on signal transduction and specific examples of GPCRs.

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