Questions and Answers
What is the structure of G protein-coupled receptors?
7 transmembrane domains
Which type of G protein is responsible for activating adenylate cyclase?
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.
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Match the G protein with its function: Gas, Gai, Gaq
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What is the main function of adenylate cyclase in the signal transduction pathway?
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Which molecule catalyzes the exchange of GDP for GTP in the activation of G protein?
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GTP hydrolysis leads to the formation of GDP in the inactivation of G protein.
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In the return to the resting state, the _____ dissociates from the G protein.
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What is the primary characteristic of G-protein receptors?
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Why are G-protein receptors called 'metabotropic' receptors?
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G-protein coupled receptors have 7 helical transmembrane domains.
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G-protein coupled receptors can be linked to ______ channels, can generate second messengers, and can cause protein phosphorylation.
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Match the following neurotransmitters with their respective receptor types:
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What type of receptors do hormones or slow neurotransmitters bind to?
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Salbutamol is an alpha1 adrenoceptor agonist.
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What is the effect of activating beta adrenoceptors?
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Acetylcholine is a _______________________ agonist.
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Match the following G protein-coupled receptors with their respective agonists:
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What is the effect of alpha2 adrenoceptors?
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G protein-coupled receptors respond to fast acting neurotransmitters.
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What is the effect of activating alpha1 adrenoceptors?
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The three main classes of Galpha proteins are Gas, Gaq, and _______________________.
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What is the effect of activating G protein-coupled receptors?
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What happens when Gas activates adenylate cyclase?
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Protein phosphatases cause protein activation.
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What is the role of protein kinases in protein regulation?
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G protein receptors are also known as ______________ receptors.
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What is the function of the alpha subunit in G protein signaling?
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Gaq activates adenylate cyclase.
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What is the role of effector proteins in G protein signaling?
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Binding of a first messenger generates a ______________ messenger.
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Match the G protein with its function:
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What is the outcome of the G protein signal transduction pathway?
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What is the characteristic of G-protein receptors that makes them 'metabotropic'?
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G-protein coupled receptors can be linked to ion channels.
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What is the largest superfamily of receptors?
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G-protein coupled receptors are characterized by having ______________ transmembrane domains.
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What is a characteristic of receptor superfamilies?
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Superfamilies are distinguished by what stimulates the receptor.
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What type of compounds are endogenous to G protein receptors?
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G protein receptors interact with ______________ proteins.
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How many major types of receptors are there?
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Match the following compounds with their respective receptor types:
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What happens when an agonist binds to a receptor?
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G protein activation leads to the hydrolysis of GTP to GDP.
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What is the result of smooth muscle relaxation?
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Ga protein binds to _______ cyclase.
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What is the result of GTP binding to Ga?
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Smooth muscle contraction is caused by the activation of beta2-adrenoreceptors.
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What happens to the receptor after agonist binding?
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The binding of an agonist to a receptor causes a conformational change, increasing the affinity of the _______ protein.
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Match the following receptors with their respective effects on smooth muscle:
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Ga protein dissociates from adenylate cyclase after GTP is hydrolyzed to GDP.
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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.
