Cell signaling Original Scenario-Based Practice

Questions

1. 1.

   In the deep-sea organism Luminaria abyssus, specialized cells known as lanternocytes emit flashes of light in response to an extracellular peptide called luminin. Luminin binds to a cell-surface G-protein coupled receptor that stimulates adenylyl cyclase to synthesize cyclic AMP (cAMP), which subsequently activates protein kinase A to initiate the luminescent cascade. Marine biologists identify a bioactive compound that diffuses into lanternocytes and irreversibly inhibits the intracellular enzyme phosphodiesterase. If lanternocytes are exposed to luminin in the presence of this inhibitor, which molecular consequence will most likely occur?

   • A) Protein kinase A remains completely inactive because the generation of AMP is required to release its catalytic subunits.
   • B) The G-protein coupled receptor remains irreversibly bound to GTP, preventing any termination of reception at the cell surface.
   • C) Cyclic AMP levels remain persistently elevated, causing prolonged activation of protein kinase A and sustained downstream signaling.
   • D) Adenylyl cyclase is immediately inactivated by accumulating cyclic AMP via direct substrate-level inhibition, shutting down the pathway.

Answers and step-by-step solutions appear after you finish the test.