Signal Transduction

The cascade of molecular events by which an extracellular signal (drug or endogenous ligand binding to a receptor) is converted into an intracellular response. Signal transduction pathways involve receptor activation, coupling to transducer proteins (G-proteins, kinases), generation of second messengers, and activation of effector molecules. Understanding these pathways is essential for drug target identification and predicting downstream pharmacological effects.

Examples

• Beta-2 adrenergic receptor: Gs-protein → adenylyl cyclase → cAMP → PKA → bronchodilation
• Insulin receptor: tyrosine kinase → IRS-1 → PI3K → Akt → GLUT4 translocation
• TNF receptor: TRADD → NF-kB pathway → inflammatory gene transcription