Signal transduction pathways relay receptor binding into intracellular responses through second messengers, cascades and regulatory proteins, linking signal detection to a specific target-cell response.
Coverage 2016–2016 · Updated 15 Jul 2026
Signal transduction is the chain of molecular events linking receptor activation to a change in cell behaviour.
The chain may include conformational changes, G proteins, kinases, second messengers, transcription factors and feedback. Amplification allows a few signal molecules to influence many targets.
Map a pathway:
One activated receptor can stimulate many downstream enzymes, amplifying a small external signal into a measurable metabolic response.
A pathway is not complete until the signal is switched off or degraded; otherwise the cell cannot respond accurately.
This objective is assessed through structured response, commonly using Explain / Label.
Explain / Label
Build the answer around this relationship: Second messengers relay information from activated receptors inside the cell.
Representative question
Heart rate is affected by the hormone epinephrine. The action of epinephrine is mediated by a chemical called a second messenger. Explain the mechanism of action of a second messenger.
A ligand only affects target cells with the matching receptor. Quorum sensing uses autoinducers and thresholds for group behaviour. Animal signals differ by source, distance, speed, target-cell response, and chemical class. Hydrophilic ligands use transmembrane receptors and relays; steroid and thyroid hormones use intracellular receptors that affect transcription. Named pathways then show the logic: acetylcholine opens sodium channels, GPCRs switch G proteins through GDP-GTP exchange, epinephrine uses cAMP and kinase cascades, insulin RTKs use dimerisation/autophosphorylation to move GLUT4 and promote glycogenesis, steroid hormones change gene expression, and feedback either amplifies or restores stability.
