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Questions and Answers
What is the primary action of the activated αs-subunit in Gs-coupled receptors?
What is the primary action of the activated αs-subunit in Gs-coupled receptors?
Which of the following correctly describes the outcome of reduced cAMP in cells with Gi-coupled receptors?
Which of the following correctly describes the outcome of reduced cAMP in cells with Gi-coupled receptors?
What is the role of IP3 in the Gq-coupled receptor mechanism?
What is the role of IP3 in the Gq-coupled receptor mechanism?
Which receptor is associated with the action of adrenaline and noradrenaline through Gs-coupled mechanisms?
Which receptor is associated with the action of adrenaline and noradrenaline through Gs-coupled mechanisms?
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What response is most likely mediated by PKC activation in Gq-coupled receptors?
What response is most likely mediated by PKC activation in Gq-coupled receptors?
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Study Notes
Gs-PCR Mechanism
- Ligand binding (e.g., adrenaline to β-adrenergic receptor) activates the Gs-coupled receptor.
- G protein (αs-subunit) exchanges GDP for GTP, becoming activated.
- Activated αs-subunit stimulates adenylyl cyclase.
- Adenylyl cyclase converts ATP to cAMP.
- cAMP activates protein kinase A (PKA).
- PKA triggers downstream effects (e.g., glycogen breakdown, smooth muscle relaxation).
Gi-PCR Mechanism
- Ligand binding (e.g., acetylcholine to muscarinic M2 receptor) activates the Gi-coupled receptor.
- G protein (αi-subunit) exchanges GDP for GTP, becoming activated.
- Activated αi-subunit inhibits adenylyl cyclase.
- Decreased adenylyl cyclase activity reduces cAMP production.
- Reduced cAMP leads to decreased PKA activity.
- Altered cellular responses result from changes in cAMP and PKA.
Gq-PCR Mechanism (IP₃ and DAG Pathway)
- Ligand binding (e.g., acetylcholine to muscarinic M3 receptor) activates the Gq-coupled receptor.
- G protein (αq-subunit) exchanges GDP for GTP, becoming activated.
- Activated αq-subunit stimulates phospholipase C (PLC).
- PLC cleaves phosphatidylinositol 4,5-bisphosphate (PIP₂) into:
- IP₃: Binds to IP₃ receptors on the endoplasmic reticulum, releasing calcium ions (Ca²⁺).
- DAG: Activates protein kinase C (PKC), which phosphorylates target proteins.
- Increased calcium ions (Ca²⁺) and PKC activity cause various cellular responses (e.g., muscle contraction, secretion).
Gs-Coupled Receptor Examples
- β-adrenergic receptors (β1, β2, β3): Respond to adrenaline and noradrenaline.
- Dopamine D1 receptors.
- Histamine H2 receptors.
Gi-Coupled Receptor Examples
- α2-adrenergic receptors: Inhibit norepinephrine release.
- Dopamine D2 receptors.
- Opioid receptors (μ, κ, δ): Mediate pain relief and other effects.
Gq-Coupled Receptor Examples
- α1-adrenergic receptors: Mediate smooth muscle contraction.
- Muscarinic M1 and M3 receptors.
- Histamine H1 receptors.
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Description
Explore the mechanisms of Gs, Gi, and Gq protein-coupled receptors in this quiz. Learn how ligand binding influences cellular responses through second messengers like cAMP and IP₃/DAG pathways. Test your understanding of these critical signaling pathways in cell biology.
