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Questions and Answers

What is the main role of enzyme cascades during signal amplification?

  • They slow down the cell's response.
  • They inhibit the binding of hormones.
  • They deactivate G proteins.
  • They amplify the cell's response. (correct)

    • What happens to the number of active G proteins when a single hormone binds to a receptor?

  • It increases dramatically, potentially up to 10 molecules. (correct)
  • It reduces the number of active G proteins.
  • It remains the same as inactive G proteins.
  • It activates only one G protein.

    • How does cyclic AMP (cAMP) contribute to signal transduction?

  • It activates multiple protein kinase A (PKA) molecules. (correct)
  • It directly phosphorylates glycogen phosphorylase.
  • It binds to receptor molecules instead of PKA.
  • It inhibits the activity of adenylyl cyclase.

    • What is the approximate amplification factor that can occur with a single hormone molecule?

    <p>10,000 times</p> Signup and view all the answers

    What is the role of phosphorylase kinase in the amplification process?

    <p>It activates glycogen phosphorylase to produce glucose.</p> Signup and view all the answers

    What activates adenylyl cyclase in the signaling pathway?

    <p>Binding of GTP to Gα</p> Signup and view all the answers

    What is the role of cAMP in cellular signaling?

    <p>It serves as a second messenger</p> Signup and view all the answers

    Which enzyme rapidly converts cAMP to AMP to help eliminate the signal?

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

    What is the primary function of protein kinase A (PKA) in the signaling pathway?

    <p>To transfer phosphate from ATP to target proteins</p> Signup and view all the answers

    What initiates the activation of the G-protein linked receptors?

    <p>Conformational change in Gα subunit</p> Signup and view all the answers

    Which part of the G-protein complex completes the heterotrimer?

    <p>Gβ and Gγ</p> Signup and view all the answers

    What occurs to Gα after it binds to GTP?

    <p>It dissociates from Gβ and Gγ</p> Signup and view all the answers

    Which residues does PKA phosphorylate in target proteins?

    <p>Serine or Threonine</p> Signup and view all the answers

    What is the role of gene regulatory proteins in cellular signaling pathways?

    <p>They facilitate the transcription of multiple genes.</p> Signup and view all the answers

    Which of the following is a signaling pathway that is triggered by adrenaline?

    <p>β-adrenergic pathway</p> Signup and view all the answers

    What does phospholipase C (PLC) cleave to trigger intracellular signaling?

    <p>A membrane phospholipid</p> Signup and view all the answers

    What are the second messengers produced from phospholipase C activity?

    <p>Inositol-1,4,5-Trisphosphate and Diacylglycerol</p> Signup and view all the answers

    Which of the following biological processes can be triggered by Ca2+ as an intracellular messenger?

    <p>Muscle contraction</p> Signup and view all the answers

    How does Protein Kinase C (PKC) primarily respond after activation?

    <p>It phosphorylates target proteins.</p> Signup and view all the answers

    What effect does the release of Ca2+ ions have on cellular functions?

    <p>It regulates ion channels and proteins.</p> Signup and view all the answers

    Which substance is NOT produced as a result of PLC activity?

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

    What role do scaffolding proteins play in signaling efficiency?

    <p>They group together proteins involved in the same pathway.</p> Signup and view all the answers

    Which of the following describes how a G protein shuts off the signal?

    <p>By hydrolyzing GTP to GDP.</p> Signup and view all the answers

    What happens to a receptor when signal molecules leave it?

    <p>It becomes inactive.</p> Signup and view all the answers

    How does pathway branching affect cellular responses?

    <p>It allows different cells to respond uniquely to the same signal.</p> Signup and view all the answers

    What is the function of phosphodiesterases in cell signaling?

    <p>They hydrolyze cAMP to AMP, terminating the signal.</p> Signup and view all the answers

    Which feature defines the specificity of cell signaling?

    <p>Different cells having distinct sets of proteins.</p> Signup and view all the answers

    During self-inactivation in G-protein signaling, what directly leads to the signal being turned off?

    <p>GTP is hydrolyzed to GDP on the Gα subunit.</p> Signup and view all the answers

    What is indicated by the term 'cross-talk' in cell signaling?

    <p>Different signaling pathways can influence one another.</p> Signup and view all the answers

    What effect do caffeine, theophylline, and theobromine have on cAMP levels?

    <p>They inhibit cAMP phosphodiesterase</p> Signup and view all the answers

    How is the signal turned off after receptor activation via a G-protein?

    <p>Through receptor phosphorylation by β-arrestin</p> Signup and view all the answers

    What role does protein phosphatase play in cellular signaling?

    <p>It dephosphorylates target proteins to reverse signals</p> Signup and view all the answers

    What is a consequence of Vibrio cholerae's enterotoxin on the G-protein signaling pathway?

    <p>It maintains the G-protein in an active state</p> Signup and view all the answers

    Which biological process does a rise in intracellular Ca2+ primarily trigger?

    <p>Multiple cellular responses</p> Signup and view all the answers

    What is the function of β-arrestin in the signaling pathway?

    <p>Inhibits receptor-G protein interaction</p> Signup and view all the answers

    What is the role of cAMP in improving memory?

    <p>It activates kinases that phosphorylate target proteins</p> Signup and view all the answers

    What happens when intracellular signaling cascades are not turned off effectively?

    <p>They can result in pathological conditions.</p> Signup and view all the answers

    Study Notes

    G-Protein Coupled Receptors (GPCR)

    • GPCRs are cell surface receptors that bind to extracellular signaling molecules and activate intracellular signaling pathways.
    • GPCRs have seven transmembrane helices and interact with heterotrimeric G-proteins for activation.

    Heterotrimeric G-proteins

    • G-proteins are made of three subunits: α, β, and γ.
    • The α subunit binds to GDP in its inactive state.
    • Upon activation, the α subunit releases GDP and binds to GTP, leading to the dissociation of the β and γ subunits.

    Adenylyl Cyclase Pathway

    • The activated α subunit can activate adenylyl cyclase, which catalyzes the conversion of ATP to cyclic AMP (cAMP).
    • cAMP is a second messenger that activates protein kinase A (PKA).
    • PKA phosphorylates target proteins, altering their activity.

    Inositol Phospholipids Pathway

    • Some G-proteins activate phospholipase C instead of adenylyl cyclase.
    • Phospholipase C cleaves phosphatidylinositol, generating two second messengers: inositol 1,4,5-trisphosphate (InsP3) and diacylglycerol (DAG).
    • InsP3 triggers the release of calcium ions (Ca2+) from intracellular stores.
    • DAG activates protein kinase C (PKC).
    • Increased Ca2+ and PKC activation lead to various cellular responses, including cell growth, cytoskeleton regulation, and protein secretion.

    Signal Amplification

    • Enzyme cascades amplify the cell's response by multiplying the number of activated molecules at each step.

    Signal Specificity

    • Different cells respond differently to the same signal due to variations in their proteins and pathways.
    • Pathway branching and "cross-talk" allow for the coordinated integration of multiple signals.

    Signal Efficiency

    • Scaffolding proteins increase the signal transduction efficiency by bringing together different relay proteins involved in the same pathway.

    Signal Termination

    • Signal termination mechanisms are essential for maintaining homeostasis.
    • The α subunit's GTPase activity hydrolyzes GTP to GDP, inactivating the G-protein.
    • Phosphodiesterase converts cAMP to AMP, reducing the intracellular cAMP concentration.
    • Phosphorylation of the receptor by a G-protein receptor kinase promotes the binding of β-arrestin, preventing further receptor activation.
    • Protein phosphatases dephosphorylate target proteins, reversing their activation.

    Cholera Toxin

    • Vibrio cholerae bacteria secrete an enterotoxin that modifies the α subunit of the stimulatory G-protein, preventing GTP hydrolysis.
    • This results in the permanent activation of the adenylyl cyclase pathway, leading to excessive cAMP production and severe watery diarrhea.

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