Second Messenger Systems (cAMP, IP3, DAG)
Start with the big picture
In the cAMP pathway, a ligand activates a GPCR coupled to Gs or Gi. Gs stimulates adenylate cyclase to produce cAMP, which activates PKA and leads to target-protein phosphorylation; Gi inhibits adenylate cyclase. Phosphodiesterase breaks down cAMP, while methylxanthines inhibit that enzyme and can sustain the signal. In the IP₃-DAG pathway, Gq activates phospholipase C, which cleaves PIP₂ into IP₃ and DAG. IP₃ promotes calcium release from the endoplasmic reticulum, enabling calcium-calmodulin signaling, while membrane-bound DAG activates PKC. The lesson also compares hormone examples for each pathway and explains signal termination, including receptor desensitization and calcium re-sequestration.
What you'll learn
- Trace GPCR signaling through Gs or Gi to cAMP and PKA.
- Explain how phosphodiesterase affects cAMP signaling.
- Describe Gq signaling through phospholipase C, IP₃, DAG, calcium, and PKC.
- Distinguish representative hormones associated with cAMP and IP₃-DAG pathways.
- Identify mechanisms that terminate or desensitize these signals.
Continue your study
Work through the complete notes and reinforce the topic with the study tools available in the full lesson.
