Changes in signal transduction and disease Original Scenario-Based Practice

Questions

1. 1.

   In an advanced marine biology laboratory, researchers isolate a pathogenic toxin from a deep-sea microbe that selectively disables the intrinsic GTPase activity of the stimulatory $G_{\alpha}$ subunit in epithelial cells. While the G protein can still undergo ligand-triggered exchange of GDP for GTP, it can no longer convert bound GTP back to GDP. Based on the mechanisms governing signal transduction and cellular pathology, which consequence will directly occur within these affected cells?

   • A) The receptor becomes permanently phosphorylated, preventing any future interaction with G proteins and causing immediate pathway desensitization.
   • B) Adenylyl cyclase remains constitutively active, leading to sustained, abnormally high levels of intracellular cyclic AMP and uncontrolled downstream signaling.
   • C) Intracellular protein kinase A (PKA) remains permanently inactivated because cyclic AMP cannot dissociate from its regulatory subunits.
   • D) Cytoplasmic phosphodiesterases are irreversibly stimulated, causing rapid degradation of all intracellular cyclic nucleotides.

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