Second messengers Original Scenario-Based Practice

Questions

1. 1.

   Deep-sea explorers discover an abyssal organism whose cells flash with bioluminescence whenever an extracellular peptide binds to a surface membrane receptor. Subsequent analysis reveals that receptor activation stimulates an enzyme that cleaves a membrane phospholipid into two distinct fragments: a lipid-soluble component that remains embedded in the plasma membrane, and a small, water-soluble molecule that diffuses through the cytosol to trigger the release of sequestered calcium ions. Which statement correctly identifies this cytosolic molecule and explains its functional role as a second messenger in the signaling pathway?

   • A) Diacylglycerol (DAG), because it dissolves into the cytosol to act as a transcription factor in the nucleus.
   • B) Inositol trisphosphate ($\text{IP}_3$), because it diffuses through the cytoplasm to open ligand-gated calcium channels on the endoplasmic reticulum.
   • C) Adenylyl cyclase, because it functions as an enzymatic second messenger that directly pumps calcium across the plasma membrane.
   • D) Calmodulin, because it is an amphipathic messenger that degrades calcium storage vesicles to trigger bioluminescence.

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