Cell Signalling and Receptor Mechanisms · USMLE Step 1

A water-soluble peptide hormone that acts through a cell-surface receptor most likely uses which signaling mechanism?

  1. Diffusion across the membrane to bind cytoplasmic nuclear receptors
  2. Binding a cell-surface receptor that triggers a second-messenger cascade
  3. Direct entry into the nucleus to modulate gene transcription
  4. Insertion into the membrane to form a ligand-gated ion channel
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Correct answer: Binding a cell-surface receptor that triggers a second-messenger cascade

Hydrophilic peptide hormones cannot cross the lipid bilayer, so they bind to cell-surface receptors (GPCRs or enzyme-linked) and activate intracellular second messenger pathways.

Difficulty: Medium Question 11 of 22

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