Cell Signalling and Receptor Mechanisms · USMLE Step 1

Which of the following best distinguishes metabotropic receptors from ionotropic receptors?

  1. Metabotropic receptors open ion channels directly; ionotropic ones do not
  2. Metabotropic receptors act via G proteins; ionotropic directly gate ion flow
  3. Metabotropic receptors are intracellular; ionotropic are on the cell surface
  4. Metabotropic receptors always activate kinases; ionotropic always block ions
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Correct answer: Metabotropic receptors act via G proteins; ionotropic directly gate ion flow

Metabotropic receptors (such as GPCRs) signal via G proteins and second messengers, indirectly affecting cell physiology; ionotropic receptors directly open ion channels on ligand binding to regulate ion flow.

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