Receptor Types and Signaling Mechanisms
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Questions and Answers

What is the main function of guanylyl cyclase in its receptor form?

  • Dimerize with other receptors
  • Convert ATP to cAMP
  • Convert GTP to cGMP (correct)
  • Phosphorylate serine and threonine residues

    • What causes the activation of receptor guanylyl cyclase?

  • Binding of TGFß
  • Binding of ANP (correct)
  • Binding of growth factors
  • Binding of insulin

    • What do receptor serine/threonine kinases primarily phosphorylate?

  • GTP to cGMP
  • Serine and threonine residues on target proteins (correct)
  • cAMP to AMP
  • Tyrosine residues on receptor proteins

    • What initiates the MAP kinase signalling pathway?

    <p>RAS activation</p> Signup and view all the answers

    Which receptors are involved in insulin-mediated glucose uptake?

    <p>Receptor tyrosine kinases</p> Signup and view all the answers

    What is the role of phosphotyrosine motifs created by receptor tyrosine kinases?

    <p>They recruit intracellular signalling proteins</p> Signup and view all the answers

    What is the effect of atrial natriuretic peptide (ANP) when signaling through guanylyl cyclase?

    <p>Vasodilation of blood vessels</p> Signup and view all the answers

    Which type of receptor is formed by the dimerization of two molecules of insulin?

    <p>Receptor tyrosine kinase</p> Signup and view all the answers

    What initiates the mechanism of signalling for receptor tyrosine phosphatase?

    <p>Ligand binding to the receptor</p> Signup and view all the answers

    Which of the following best describes the role of tyrosine phosphatase activity in receptor signalling?

    <p>Dephosphorylates target proteins to modulate their activity</p> Signup and view all the answers

    What is a distinctive feature of receptor tyrosine kinases compared to G protein-coupled receptors?

    <p>Catalytic activity that triggers phosphorylation</p> Signup and view all the answers

    In the context of signalling pathways, what is a primary function of CD45?

    <p>Induces the maturation of lymphocytes</p> Signup and view all the answers

    How do GPCRs primarily relay their signals?

    <p>Via secondary messengers like cAMP</p> Signup and view all the answers

    What is the main difference in signal duration between GPCRs and RTKs?

    <p>RTKs activate for hours while GPCRs for seconds</p> Signup and view all the answers

    What common outcome do both GPCRs and RTKs achieve in their signalling pathways?

    <p>Phosphorylation of target proteins</p> Signup and view all the answers

    What type of receptors do not require dimerization for their activation?

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

    What is the main effect of cholera toxin on the Ga subunit?

    <p>It causes ADP-ribosylation, preventing GTP hydrolysis.</p> Signup and view all the answers

    Which of the following statements about the action of G proteins is incorrect?

    <p>Gi subunits stimulate adenylyl cyclase.</p> Signup and view all the answers

    What is the main physiological effect of increased levels of cAMP and PKA due to pertussis toxin acting on G proteins?

    <p>Induction of whooping cough</p> Signup and view all the answers

    What is the function of adenylyl cyclase in the G protein signaling pathway?

    <p>Convert ATP into cAMP.</p> Signup and view all the answers

    Which subtypes of muscarinic receptors are classified as Gq-coupled stimulatory receptors?

    <p>M1, M3, and M5</p> Signup and view all the answers

    What is the consequence of activating protein kinase A (PKA) after cAMP binding?

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

    Which receptors are known to couple with Gs subunits?

    <p>Beta-adrenergic receptors.</p> Signup and view all the answers

    What is the primary role of phospholipase C (PLC) in signal transduction?

    <p>Cleavage of PIP2 into IP3 and DAG</p> Signup and view all the answers

    How does pertussis toxin affect the Gi subunit?

    <p>It locks the subunit into an inactive configuration.</p> Signup and view all the answers

    Which response is mediated by G proteins containing the alphaq11 subunit in acetylcholine signaling?

    <p>Mediated salivary secretion</p> Signup and view all the answers

    What happens to IP3 after it functions in signaling within the cytosol?

    <p>It is converted into IP2, halting the signal</p> Signup and view all the answers

    Which of the following describes the role of G proteins in cellular signaling?

    <p>They mediate the exchange of GDP for GTP.</p> Signup and view all the answers

    What is the role of cAMP in the signaling pathway activated by GPCR?

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

    What autonomic effects are primarily associated with muscarinic receptors?

    <p>Salivary secretion and bronchial smooth muscle contraction</p> Signup and view all the answers

    What is the role of DAG in the signaling process following the action of phospholipase C?

    <p>It recruits protein kinase C (PKC) in the membrane</p> Signup and view all the answers

    How does activation of M3 receptors by alphaq11-containing G proteins affect respiratory function?

    <p>It causes bronchospasm</p> Signup and view all the answers

    What initiates the activation of phospholipase Cß?

    <p>Binding of a hormone to a G protein-coupled receptor</p> Signup and view all the answers

    What is the primary function of calmodulin in cellular signaling?

    <p>Binding calcium ions to stimulate other proteins</p> Signup and view all the answers

    Why does diacylglycerol (DAG) remain in the plasma membrane?

    <p>It is hydrophobic and interacts with the lipid bilayer</p> Signup and view all the answers

    What intracellular responses do calmodulin kinases (CaMKs) mediate?

    <p>Phosphorylation of serine and threonine residues</p> Signup and view all the answers

    What effect does activated protein kinase C (PKC) have on cells?

    <p>Regulation of cellular transcription factors</p> Signup and view all the answers

    How does IP3 facilitate the release of calcium ions into the cytosol?

    <p>By interacting with receptors on the endoplasmic reticulum</p> Signup and view all the answers

    What is the mechanism through which alpha1 adrenergic receptors induce vasoconstriction?

    <p>Increased intracellular calcium levels</p> Signup and view all the answers

    Which component serves as the most critical calcium-binding protein mediating intracellular responses?

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

    What is the primary function of Ras-GEF in the activation of Ras?

    <p>It exchanges the GDP bound to Ras for GTP.</p> Signup and view all the answers

    Which statement correctly describes the role of adaptor proteins in RAS activation?

    <p>They dock on phosphotyrosine residues and recruit RAS-GEF.</p> Signup and view all the answers

    In the MAPK signaling cascade, what is the primary role of MAPKKK?

    <p>It acts as the first kinase and phosphorylates MAPKK.</p> Signup and view all the answers

    What occurs once the Ras protein is activated?

    <p>It becomes covalently attached to a lipid and anchors to the plasma membrane.</p> Signup and view all the answers

    How are tyrosine kinases activated in tyrosine kinase-associated receptors?

    <p>Via dimerization of the receptor which activates associated kinases.</p> Signup and view all the answers

    What do activated tyrosine kinases do in this signaling mechanism?

    <p>They phosphorylate themselves and the receptor to form phosphotyrosine motifs.</p> Signup and view all the answers

    Which function explains the role of phosphotyrosine motifs in signaling by tyrosine kinase-associated receptors?

    <p>They provide a docking site for intracellular signaling molecules.</p> Signup and view all the answers

    Which kinase is typically referred to as the third kinase in the MAPK signaling cascade?

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

    Study Notes

    Receptor Types and Signaling Mechanisms

    • Four main receptor classes: ligand-gated ion channels, G-protein coupled receptors (GPCRs), enzyme-linked receptors, and nuclear receptors.
    • G-protein activation: GPCR activation triggers GDP-GTP exchange on the G protein alpha subunit. The alpha-GTP subunit dissociates from the beta-gamma complex, activating downstream effectors.
    • Adenylyl cyclase (AC) activation: Activated G protein (Gas) stimulates AC, converting ATP to cAMP (a second messenger).
    • Protein Kinase A (PKA) activation: cAMP binds to PKA's regulatory subunits, releasing the catalytic subunits, which become active.
    • Cholera toxin (CTx) effect: CTx ADP-ribosylates the Gas subunit, preventing GTP hydrolysis; leading to sustained cAMP production and diarrhea.
    • Pertussis toxin (PTx) effect: PTx ADP-ribosylates Gai, preventing its inhibitory action on AC, leading to increased cAMP and whooping cough symptoms.
    • Gq/11 protein activation: Gq/11 activates phospholipase C (PLC), cleaving PIP2 into IP3 and DAG.
    • IP3 function: IP3 releases calcium from the endoplasmic reticulum (ER) into the cytoplasm.
    • DAG function: DAG activates protein kinase C (PKC) in the membrane.
    • Calcium signaling: Calcium acts as a second messenger; CaM (calmodulin) binds to calcium, activating CaMKs (calmodulin kinases).
    • Calmodulin kinases (CaMKs): CaMKs phosphorylate target proteins, influencing various cellular responses, including smooth muscle contraction.
    • Alpha1-adrenergic receptor function: Gq-coupled, increasing intracellular calcium leading to vasoconstriction.
    • Beta2-adrenergic receptor function: Gs-coupled, increasing cAMP, leading to vasodilation.

    Enzyme-Linked Receptors

    • Receptor guanylyl cyclases: Convert GTP to cGMP, activating downstream kinases. ANP (atrial natriuretic peptide) is an example.
    • Receptor serine/threonine kinases: Phosphorylate target proteins (e.g., SMAD proteins), mediating responses like cell proliferation.
    • Receptor tyrosine kinases (RTKs): Phosphorylate themselves and other proteins, initiating phosphorylation cascades. Examples include insulin signaling.
    • Tyrosine kinase-associated receptors: Lack intrinsic kinase activity but associate with cytoplasmic kinases (e.g., JAK2), triggering similar phosphorylation cascades. Examples include signaling by cytokines.
    • Receptor tyrosine phosphatases: Dephosphorylate target proteins, modulating cellular activity by reversing phosphorylation events initiated by other receptors. Examples include lymphocytes maturation (activation of CD45)

    GPCRs vs. RTKs

    • GPCRs: 7 transmembrane helices; no intrinsic enzymatic activity; signal relayed via secondary messengers (e.g., cAMP, IP3/DAG); shorter duration of signaling.
    • RTKs: Single transmembrane helix; intrinsic enzymatic activity; signal relayed via phosphorylation cascades; longer signaling duration.

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    Description

    This quiz explores the four main classes of receptors and their signaling mechanisms, focusing on G-protein coupled receptors (GPCRs), adenylyl cyclase activation, and the effects of cholera and pertussis toxins. Test your knowledge on how these receptors function and their implications in physiological responses.

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