Pharmacology: G Protein-Coupled Receptors
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What is the structure of G protein-coupled receptors?

7 transmembrane domains

Which type of G protein is responsible for activating adenylate cyclase?

  • Gas (correct)
  • G protein kinase
  • Gaq
  • Gai
  • G protein-coupled receptors are the largest single class of targets for therapeutic drugs.

    True

    G proteins link GPCRs to effector proteins that generate intracellular ________ messengers.

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

    Match the G protein with its function: Gas, Gai, Gaq

    <p>Activates adenylate cyclase = Gas Inhibits adenylate cyclase = Gai Activates phospholipase C = Gaq</p> Signup and view all the answers

    What is the main function of adenylate cyclase in the signal transduction pathway?

    <p>Cyclisation of ATP to cAMP</p> Signup and view all the answers

    Which molecule catalyzes the exchange of GDP for GTP in the activation of G protein?

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

    GTP hydrolysis leads to the formation of GDP in the inactivation of G protein.

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

    In the return to the resting state, the _____ dissociates from the G protein.

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

    What is the primary characteristic of G-protein receptors?

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

    Why are G-protein receptors called 'metabotropic' receptors?

    <p>They involve the action of 1 or more metabolic pathways</p> Signup and view all the answers

    G-protein coupled receptors have 7 helical transmembrane domains.

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

    G-protein coupled receptors can be linked to ______ channels, can generate second messengers, and can cause protein phosphorylation.

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

    Match the following neurotransmitters with their respective receptor types:

    <p>Adrenaline and Noradrenaline = Alpha and Beta adrenoceptors Acetylcholine = Muscarinic receptors Salbutamol = Beta-2 adrenoceptor</p> Signup and view all the answers

    What type of receptors do hormones or slow neurotransmitters bind to?

    <p>G protein-coupled receptors</p> Signup and view all the answers

    Salbutamol is an alpha1 adrenoceptor agonist.

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

    What is the effect of activating beta adrenoceptors?

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

    Acetylcholine is a _______________________ agonist.

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

    Match the following G protein-coupled receptors with their respective agonists:

    <p>Adrenoceptors = Noradrenaline and adrenaline Muscarinic receptors = Acetylcholine Beta-2 adrenoceptors = Salbutamol</p> Signup and view all the answers

    What is the effect of alpha2 adrenoceptors?

    <p>Inhibits adenylate cyclase</p> Signup and view all the answers

    G protein-coupled receptors respond to fast acting neurotransmitters.

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

    What is the effect of activating alpha1 adrenoceptors?

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

    The three main classes of Galpha proteins are Gas, Gaq, and _______________________.

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

    What is the effect of activating G protein-coupled receptors?

    <p>Change in cell function via intracellular G protein</p> Signup and view all the answers

    What happens when Gas activates adenylate cyclase?

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

    Protein phosphatases cause protein activation.

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

    What is the role of protein kinases in protein regulation?

    <p>to phosphorylate proteins and cause activation</p> Signup and view all the answers

    G protein receptors are also known as ______________ receptors.

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

    What is the function of the alpha subunit in G protein signaling?

    <p>binds GTP and has GTPase activity</p> Signup and view all the answers

    Gaq activates adenylate cyclase.

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

    What is the role of effector proteins in G protein signaling?

    <p>to generate second messengers</p> Signup and view all the answers

    Binding of a first messenger generates a ______________ messenger.

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

    Match the G protein with its function:

    <p>Gas = activates adenylate cyclase Gai = inhibits adenylate cyclase Gaq = activates phospholipase C</p> Signup and view all the answers

    What is the outcome of the G protein signal transduction pathway?

    <p>all of the above</p> Signup and view all the answers

    What is the characteristic of G-protein receptors that makes them 'metabotropic'?

    <p>They involve the action of one or more metabolic pathways</p> Signup and view all the answers

    G-protein coupled receptors can be linked to ion channels.

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

    What is the largest superfamily of receptors?

    <p>G Protein coupled receptors</p> Signup and view all the answers

    G-protein coupled receptors are characterized by having ______________ transmembrane domains.

    <p>7 helical</p> Signup and view all the answers

    What is a characteristic of receptor superfamilies?

    <p>Similar transduction processes</p> Signup and view all the answers

    Superfamilies are distinguished by what stimulates the receptor.

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

    What type of compounds are endogenous to G protein receptors?

    <p>Neurotransmitters, Hormones, Opioids, Amines, Peptides, Proteins, Light-sensitive compounds, Odours</p> Signup and view all the answers

    G protein receptors interact with ______________ proteins.

    <p>Heterotrimeric G</p> Signup and view all the answers

    How many major types of receptors are there?

    <p>4</p> Signup and view all the answers

    Match the following compounds with their respective receptor types:

    <p>Neurotransmitters = G-protein coupled receptors Hormones = G-protein coupled receptors Opioids = G-protein coupled receptors Light-sensitive compounds = G-protein coupled receptors</p> Signup and view all the answers

    What happens when an agonist binds to a receptor?

    <p>The receptor binds to a G protein</p> Signup and view all the answers

    G protein activation leads to the hydrolysis of GTP to GDP.

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

    What is the result of smooth muscle relaxation?

    <p>Activation of beta2-adrenoreceptors</p> Signup and view all the answers

    Ga protein binds to _______ cyclase.

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

    What is the result of GTP binding to Ga?

    <p>Ga catalyzes the exchange of GDP for GTP</p> Signup and view all the answers

    Smooth muscle contraction is caused by the activation of beta2-adrenoreceptors.

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

    What happens to the receptor after agonist binding?

    <p>It returns to its normal state</p> Signup and view all the answers

    The binding of an agonist to a receptor causes a conformational change, increasing the affinity of the _______ protein.

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

    Match the following receptors with their respective effects on smooth muscle:

    <p>Beta2-adrenoreceptors = relaxation Muscarinic acetylcholine receptors = contraction</p> Signup and view all the answers

    Ga protein dissociates from adenylate cyclase after GTP is hydrolyzed to GDP.

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

    Study Notes

    G Protein-Coupled Receptors

    • Largest superfamily of receptors, with the largest single class of targets for therapeutic drugs
    • These GTP- and GDP-binding proteins, comprising three subunits α, β, and γ, play a crucial role in mediating the signal transduction pathways initiated by G protein-coupled receptors.
    • Activate signal transduction pathways, such as adenylate cyclase, phospholipase C, phosphodiesterase, and ion channels
    • Respond to various ligands, including hormones, neurotransmitters, opioids, amines, peptides, proteins, light-sensitive compounds, and odors

    Structure of GPCR

    • 7 transmembrane domain receptors, also called metabotropic receptors or heptahelical receptors
    • Ligand binding sites are located on the extracellular surface
    • Heterotrimeric G protein binds to the intracellular surface

    Examples of GPCRs

    • Adrenoceptors, muscarinic acetylcholine receptors, serotonin receptors, dopamine receptors, and many others
    • Salbutamol, a β2-adrenoceptor agonist, relieves bronchospasm in asthma

    Physiological Roles of GPCRs

    • Autonomic nervous system: muscarinic acetylcholine receptors activate phospholipase C, while β-adrenoceptors activate adenylate cyclase
    • Vision: light activates rhodopsin, a GPCR
    • Smell: odorant molecules activate GPCRs, which stimulate adenylate cyclase
    • Behaviour and mood: various neurotransmitters and neuropeptides interact with GPCRs to modulate mood and behaviour

    G Protein Signalling

    • Comprise 3 subunits: α, β, and γ
    • α-subunit binds GTP and has GTPase activity
    • 3 main classes of Gα proteins: Gαs, Gαi, and Gαq
    • Gαs activates adenylate cyclase, while Gαi inhibits adenylate cyclase, and Gαq activates phospholipase C

    Adenylate Cyclase Signal Transduction Pathway

    • Ligand binds to receptor, activating G protein
    • G protein activates adenylate cyclase, which converts ATP to cAMP
    • cAMP activates protein kinase A, leading to a response

    Phospholipase C Signal Transduction Pathway

    • Ligand binds to receptor, activating G protein
    • G protein activates phospholipase C, which breaks down phosphatidylinositol 4,5-bisphosphate into inositol 1,4,5-trisphosphate and diacylglycerol
    • Inositol 1,4,5-trisphosphate releases Ca2+, while diacylglycerol activates protein kinase C, leading to a response

    G-Protein Receptors

    • Metabotropic receptors are associated with one or more metabolic steps.
    • G-protein receptors are called metabotropic because they involve the action of 1 or more metabolic pathways.

    Structure of G-Protein Coupled Receptors

    • G-protein coupled receptors have 7 helical transmembrane domains, making them "hepta helical".
    • They can be linked to ion channels, generate second messengers, or cause protein phosphorylation.

    Receptor Superfamily

    • Receptor superfamily consists of 4 major types of receptors with similar transduction processes and general structures.
    • Superfamilies are distinguished by how the signal is transduced, not by what stimulates the receptor or how the stimulation changes cell function.

    G-Protein Coupled Receptors

    • G-protein coupled receptors are the largest superfamily.
    • They can respond to endogenous compounds such as neurotransmitters, hormones, opioids, amines, peptides, proteins, light-sensitive compounds, and odours.

    Signal Transduction Pathways

    • Signal transduction pathways linked to G-protein receptors include adenylate cyclase, phospholipase C, phosphodiesterase, and ion channels.

    How G-Protein Coupled Receptors Work

    • Drug binds to G-protein receptor, leading to a change in cell function via intracellular G-protein.

    Binding Sites of G-Protein Receptors

    • G-protein receptors have two binding sites: in the membrane (N-terminus) or extracellular (C-terminus).

    Enzymes or Channels

    • Enzymes or channels are effectors of G-protein coupled receptors.

    Hormones and Neurotransmitters

    • G-protein coupled receptors respond to slow-acting hormones or neurotransmitters (seconds).

    Examples of G-Protein Coupled Receptors

    • Adrenoceptors, muscarinic aCh receptors, and beta-2 adrenoceptor agonist salbutamol (relieves bronchospasm in asthma) are examples of G-protein coupled receptors.

    G-Protein Proteins

    • Three main classes of G-alpha proteins are Gas, Gaq, and Gai, which activate adenylate cyclase, inhibit adenylate cyclase, and activate phospholipase C, respectively.

    Protein Kinases and Phosphatases

    • Protein kinases and phosphatases are responsible for protein regulation, with kinases phosphorylating proteins (add P group) for activation, and phosphatases dephosphorylating proteins (remove P group) for deactivation.

    G-Protein Signal Transduction Pathway

    • Agonist binds to receptor, activating G-protein, which activates effector, generating a second messenger, activating protein kinase, and causing a response through a cascade response.

    Activation of G-Protein

    • Agonist binds to receptor, causing a conformational change, increasing affinity of G-protein, and activating it.

    Activation of Adenylate Cyclase

    • Ga dissociates from other G-proteins, binds to adenylate cyclase, converts ATP to cAMP, hydrolyses GTP to GDP, dissociates from adenylate cyclase, returns to G-proteins, and receptor dissociates from G-proteins.

    G-Protein Receptors

    • Metabotropic receptors are associated with one or more metabolic steps.
    • G-protein receptors are called metabotropic because they involve the action of 1 or more metabolic pathways.

    Structure of G-Protein Coupled Receptors

    • G-protein coupled receptors have 7 helical transmembrane domains, making them "hepta helical".
    • They can be linked to ion channels, generate second messengers, or cause protein phosphorylation.

    Receptor Superfamily

    • Receptor superfamily consists of 4 major types of receptors with similar transduction processes and general structures.
    • Superfamilies are distinguished by how the signal is transduced, not by what stimulates the receptor or how the stimulation changes cell function.

    G-Protein Coupled Receptors

    • G-protein coupled receptors are the largest superfamily.
    • They can respond to endogenous compounds such as neurotransmitters, hormones, opioids, amines, peptides, proteins, light-sensitive compounds, and odours.

    Signal Transduction Pathways

    • Signal transduction pathways linked to G-protein receptors include adenylate cyclase, phospholipase C, phosphodiesterase, and ion channels.

    How G-Protein Coupled Receptors Work

    • Drug binds to G-protein receptor, leading to a change in cell function via intracellular G-protein.

    Binding Sites of G-Protein Receptors

    • G-protein receptors have two binding sites: in the membrane (N-terminus) or extracellular (C-terminus).

    Enzymes or Channels

    • Enzymes or channels are effectors of G-protein coupled receptors.

    Hormones and Neurotransmitters

    • G-protein coupled receptors respond to slow-acting hormones or neurotransmitters (seconds).

    Examples of G-Protein Coupled Receptors

    • Adrenoceptors, muscarinic aCh receptors, and beta-2 adrenoceptor agonist salbutamol (relieves bronchospasm in asthma) are examples of G-protein coupled receptors.

    G-Protein Proteins

    • Three main classes of G-alpha proteins are Gas, Gaq, and Gai, which activate adenylate cyclase, inhibit adenylate cyclase, and activate phospholipase C, respectively.

    Protein Kinases and Phosphatases

    • Protein kinases and phosphatases are responsible for protein regulation, with kinases phosphorylating proteins (add P group) for activation, and phosphatases dephosphorylating proteins (remove P group) for deactivation.

    G-Protein Signal Transduction Pathway

    • Agonist binds to receptor, activating G-protein, which activates effector, generating a second messenger, activating protein kinase, and causing a response through a cascade response.

    Activation of G-Protein

    • Agonist binds to receptor, causing a conformational change, increasing affinity of G-protein, and activating it.

    Activation of Adenylate Cyclase

    • Ga dissociates from other G-proteins, binds to adenylate cyclase, converts ATP to cAMP, hydrolyses GTP to GDP, dissociates from adenylate cyclase, returns to G-proteins, and receptor dissociates from G-proteins.

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    Description

    This quiz covers the structure and function of G protein-coupled receptors, a key concept in pharmacology. It assesses the understanding of the receptors' role in cell signaling and pharmacological responses.

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