Cell Communication 2
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Questions and Answers

What is the common feature shared by all G proteins?

  • They can self-activate
  • They are only found in cardiovascular diseases
  • They serve as enzymes
  • They can self-inactivate (correct)

    • Which type of G protein is involved in the cAMP signal pathway as a stimulatory component?

  • Gi
  • Gq
  • Gs (correct)
  • G12

    • How many types of G protein-coupled receptors (GPCRs) have been identified in humans?

  • 750
  • 500
  • 1000
  • 900 (correct)

    • Which receptor is often used as a model for signal transduction among GPCRs?

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

    What did the scientists receive the Nobel Prize in Physiology and Medicine for in 1994?

    <p>Role of G proteins in cell signaling</p> Signup and view all the answers

    Which type of receptor includes metabotropic receptors that bind to G proteins?

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

    What is the role of cAMP in the signal transduction pathway described?

    <p>Allosterically activates PKA</p> Signup and view all the answers

    Which hormone increases glycogenolysis and suppresses glycogenesis?

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

    What is the primary function of Phosphokinase A (PKA) in the cascade?

    <p>Phosphorylates cellular proteins</p> Signup and view all the answers

    Which process leads to the termination of the GPCR pathway?

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

    What happens when Gs exchanges GDP for GTP?

    <p>Gs is activated</p> Signup and view all the answers

    Which of the following hormones inhibits Adenylyl Cyclase, lowering cAMP levels?

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

    What is the role of a GPCR?

    <p>Generating an intracellular second messenger</p> Signup and view all the answers

    How does the G protein α-subunit become activated?

    <p>Exchanges bound GDP for GTP</p> Signup and view all the answers

    What causes the dissociation of the β/γ complex from the G protein α-subunit?

    <p>Activation by the ligand/GPCR complex</p> Signup and view all the answers

    What increases the intrinsic GTPase activity of G proteins?

    <p>GTPase Activator Proteins (GAPs)</p> Signup and view all the answers

    What enzyme ultimately reduces [cAMP] levels?

    <p>Phosphodiesterase (PDE)</p> Signup and view all the answers

    Which protein hydrolyzes GTP to GDP and becomes inactive after a certain time?

    <p>G protein α-subunit</p> Signup and view all the answers

    What is the role of GAPs in the signal termination pathway?

    <p>Speed up the intrinsic GTPase activity of G protein</p> Signup and view all the answers

    How does β-adrenergic receptor kinase (βARK) contribute to desensitization?

    <p>Draws to the receptor and phosphorylates it</p> Signup and view all the answers

    What happens during receptor sequestration?

    <p>Removal of receptors from the membrane through endocytosis</p> Signup and view all the answers

    How does β-arrestin contribute to resensitization in the signal termination pathway?

    <p>Dissociates from receptors in endocytic vesicles</p> Signup and view all the answers

    What leads to the deactivation of the pathway in response to low concentrations of epinephrine?

    <p>Dissociation of epinephrine from its receptor</p> Signup and view all the answers

    Which protein initiates receptor sequestration and removal from the membrane?

    <p>β-adrenergic receptor kinase (βARK)</p> Signup and view all the answers

    What is the main function of GPCRs in cell signaling?

    <p>Mediate responses to signals from other cells</p> Signup and view all the answers

    Which type of G protein is associated with the cAMP signal pathway as an inhibitory component?

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

    How many types of GPCR have been identified in humans for detecting hormones and endogenous ligands?

    <p>350</p> Signup and view all the answers

    What is the role of G proteins in cellular signaling?

    <p>Act as molecular binary switches with built-in timers</p> Signup and view all the answers

    Which receptor type is a prototype for all GPCRs and is commonly targeted by beta blockers?

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

    What did the scientists receive the Nobel Prize in Physiology and Medicine for in 1994 related to G proteins?

    <p>Role of G proteins in signal transduction in cells</p> Signup and view all the answers

    What is the role of the G protein α subunit (Gα) prior to activation?

    <p>It has GDP bound and is inactive</p> Signup and view all the answers

    Which enzyme is responsible for ultimately reducing the levels of [cAMP]?

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

    What activity determines how long the G protein remains 'on'?

    <p>GTPase Activator Proteins (GAPs)</p> Signup and view all the answers

    Which molecule is exchanged for GTP in the G protein α subunit upon activation?

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

    What is the function of Adenylate Cyclase in the signal transduction pathway?

    <p>Activates Protein Kinase A</p> Signup and view all the answers

    How does the activation of Protein Kinase A (PKA) affect downstream targets?

    <p>Stimulates effector enzymes/enzymes</p> Signup and view all the answers

    Which enzyme catalyzes the formation of cAMP in the signal transduction pathway?

    <p>Adenylyl Cyclase</p> Signup and view all the answers

    What is the primary function of Protein Kinase A (PKA) in the signal cascade?

    <p>Phosphorylates cellular proteins resulting in a cellular response</p> Signup and view all the answers

    Which hormone suppresses glycogenesis and increases glycogenolysis?

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

    What is the net effect of the signal cascade involving GPCR, Gs, cAMP, and PKA?

    <p>Amplification of the hormone signal</p> Signup and view all the answers

    Which mechanism causes the termination of the GPCR pathway after the stimulus has ended?

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

    What effect do hormones like somatostatin, adenosine, and PGE1 have on Adenylyl Cyclase activity?

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

    What is the role of GAPs (GTPase activator proteins) in the signal termination pathway?

    <p>Speed up signal termination by increasing G protein's GTP hydrolysis rate</p> Signup and view all the answers

    Which protein initiates receptor sequestration by phosphorylating the receptor and creating a binding site for β-arrestin?

    <p>β-adrenergic receptor kinase (βARK)</p> Signup and view all the answers

    What is the function of β-arrestin (β-arr) in the desensitization process of the signal termination pathway?

    <p>Promote re-sensitization by stopping the interaction between receptor and G protein</p> Signup and view all the answers

    During continued presence of epinephrine, what happens to receptors sequestered in endocytic vesicles?

    <p>They dephosphorylate, allowing them to return to the membrane</p> Signup and view all the answers

    Which process reduces the cellular response to a signal even when the signal continues?

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

    What is the role of intrinsic GTPase activity of G protein in the signal termination pathway?

    <p>Hydrolyze bound GTP to GDP, leading to pathway inactivation</p> Signup and view all the answers

    What is the main function of GPCRs in cell signaling?

    <p>Mediate most responses to signals from the external world and other cells</p> Signup and view all the answers

    Which hormone suppresses glycogenesis and increases glycogenolysis?

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

    What type of receptors include metabotropic receptors that bind to G proteins?

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

    What did the scientists receive the Nobel Prize in Physiology and Medicine for in 1994 related to G proteins?

    <p>Discovery of G-proteins and their role in signal transduction in cells</p> Signup and view all the answers

    Which enzyme catalyzes the formation of cAMP in the signal transduction pathway?

    <p>Adenylate Cyclase</p> Signup and view all the answers

    What happens when Gs exchanges GDP for GTP?

    <p>It activates adenylyl cyclase</p> Signup and view all the answers

    What is the role of GTPase activator proteins (GAPs) in the signal termination pathway?

    <p>Catalyze the hydrolysis of GTP to GDP</p> Signup and view all the answers

    During continued presence of epinephrine, what initiates receptor sequestration?

    <p>Beta-adrenergic receptor kinase (βARK)</p> Signup and view all the answers

    What is the outcome of desensitization in the signal termination pathway?

    <p>Reduced cellular response</p> Signup and view all the answers

    How does β-arrestin contribute to resensitization in the signal termination pathway?

    <p>Dissociates from receptors in endocytic vesicles</p> Signup and view all the answers

    What enzyme is responsible for speeding up the intrinsic GTPase activity of G protein in the signal termination pathway?

    <p>Beta-adrenergic receptor kinase (βARK)</p> Signup and view all the answers

    What action does low concentrations of epinephrine cause in the signal termination pathway?

    <p>Deactivation of the pathway</p> Signup and view all the answers

    What happens to the G protein alpha subunit once it becomes activated?

    <p>It exchanges GDP for GTP</p> Signup and view all the answers

    Which protein stimulates the rapid inactivation of G proteins by strongly stimulating their GTPase activity?

    <p>GTPase Activator Protein (GAP)</p> Signup and view all the answers

    What is the function of Adenylate Cyclase in the cell signaling pathway?

    <p>Generating cAMP from ATP</p> Signup and view all the answers

    How are GTP-bound G protein alpha subunits and beta/gamma complexes involved in cell signaling?

    <p>They activate effector proteins/enzymes</p> Signup and view all the answers

    Which molecule ultimately reduces the levels of intracellular cAMP?

    <p>[cAMP] phosphodiesterase (PDE)</p> Signup and view all the answers

    What causes the dissociation of the beta/gamma complex from the G protein alpha subunit?

    <p>Activation by ligand/GPCR complex</p> Signup and view all the answers

    What is the main effect of the binding of a ligand to a receptor in the signal transduction pathway?

    <p>Activation of Adenylyl Cyclase (AC)</p> Signup and view all the answers

    What is the role of Gs -subunit in the signal transduction pathway?

    <p>Activating Adenylate Cyclase</p> Signup and view all the answers

    Which hormone suppresses glycogenolysis and stimulates glycogenesis?

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

    What is the mechanism by which hormones like somatostatin suppress protein phosphorylation?

    <p>Inhibition of Adenylyl Cyclase</p> Signup and view all the answers

    What is the net effect of the signal cascade involving GPCR, Gs, cAMP, and PKA?

    <p>Amplification of the hormone signal</p> Signup and view all the answers

    How do signal transducing systems adapt to the continued presence of a signal after termination?

    <p>By becoming less sensitive through desensitization</p> Signup and view all the answers

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