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G Protein Coupled Receptors quiz #1

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  • What is the structural characteristic of G Protein Coupled Receptors (GPCRs) that distinguishes them from other cell surface receptors?
    GPCRs are composed of a single polypeptide chain that snakes through the cell membrane seven times, forming three extracellular and three intracellular loops.
  • How do GPCRs activate G proteins, and what is the significance of GTP and GDP in this process?
    Ligand binding to a GPCR causes a conformational change that allows the associated G protein to exchange GDP for GTP, activating the G protein, which can then signal downstream. GTP binding activates the G protein, while GDP binding inactivates it.
  • Describe the process of desensitization in GPCR signaling.
    Desensitization occurs when proteins like G Protein Coupled Receptor Kinase 2 bind to GPCRs, preventing G proteins from binding and being activated, thus inhibiting further signaling even if the ligand is still present.
  • Explain the role of GPCRs in the cyclic AMP (cAMP) signaling pathway.
    GPCRs activate G proteins that can stimulate or inhibit adenyl cyclase, the enzyme that produces cAMP. Changes in cAMP levels regulate various cellular functions.
  • How does GPCR signaling influence intracellular calcium levels, and what are the downstream effects?
    GPCRs can activate G proteins that increase cytosolic calcium levels, which then activate proteins like calmodulin and CaM kinases, affecting gene transcription and other cellular processes.
  • What are the key steps in the inositol phospholipid signaling pathway initiated by GPCRs?
    GPCRs activate the Gq protein, which stimulates phospholipase C to cleave PIP2 into IP3 and DAG. IP3 opens calcium channels in the ER, increasing cytosolic calcium, while DAG activates other signaling pathways.
  • Why are GPCR signaling pathways considered interconnected rather than isolated?
    GPCR signaling pathways, such as those involving cAMP, calcium, and inositol phospholipids, often influence each other and share components, allowing for integrated regulation of cellular functions.
  • What structural feature distinguishes G Protein Coupled Receptors (GPCRs) from other cell surface receptors?
    GPCRs are composed of a single polypeptide chain that snakes through the cell membrane seven times, forming three extracellular and three intracellular loops.
  • How does ligand binding to a GPCR lead to G protein activation, and what roles do GTP and GDP play in this process?
    Ligand binding causes a conformational change in the GPCR, allowing the associated G protein to exchange GDP for GTP, which activates the G protein. GTP binding activates the G protein, while GDP binding inactivates it.
  • What is the process of desensitization in GPCR signaling and how does it affect receptor activity?
    Desensitization occurs when proteins like G Protein Coupled Receptor Kinase 2 bind to GPCRs, preventing G proteins from binding and being activated. This inhibits further signaling even if the ligand is still present.