Receptors and ligands Transitional Reasoning Practice

Questions

1. 1.

   A laboratory investigates two distinct signaling molecules, Ligand 1 and Ligand 2, to determine their cellular reception mechanisms. When Ligand 1 is added to the extracellular fluid, it triggers an intracellular signaling cascade, but microinjecting Ligand 1 directly into the cytoplasm produces no response. In contrast, Ligand 2 successfully activates its target pathway whether applied extracellularly or microinjected directly into the cytoplasm. Based on these observations, which conclusion best explains the nature of these ligands and their respective receptors?

   • A) Ligand 1 is a nonpolar steroid hormone that binds to an intracellular receptor, whereas Ligand 2 is a large hydrophilic protein that requires a transmembrane channel.
   • B) Both ligands bind to the same plasma membrane G protein-coupled receptor, but Ligand 1 requires active transport across the membrane to be recycled.
   • C) Ligand 2 is a hydrophilic peptide unable to cross the membrane without endocytosis, whereas Ligand 1 diffuses directly into the nucleus.
   • D) Ligand 1 is a polar molecule whose receptor is embedded in the plasma membrane, whereas Ligand 2 is a lipid-soluble molecule whose receptor resides inside the target cell.

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