Explain the basic components of cell signal transduction pathways.

Signal transduction converts extracellular signals into cellular responses through sequential molecular interactions. Key components include: receptors (G protein-coupled receptors, receptor tyrosine kinases, nuclear receptors) that detect signals; second messengers (cAMP, Ca2+, IP3, DAG) that amplify signals intracellularly; protein kinases (PKA, PKC, MAPK) that phosphorylate target proteins; phosphatases that reverse phosphorylation; and transcription factors that alter gene expression. Signal cascades amplify signals, enable integration of multiple inputs, and allow for feedback regulation. Dysregulation of signaling pathways underlies many cancers and metabolic diseases.