A second messenger is a molecule that facilitates the intracellular transmission of information from receptor-ligand complexes. Second messengers are responsive to environmental signals, and change in concentration proportionally.
Second messengers can amplify a signal; this is particularly useful if only a relatively small number of transmembrane receptors are activated, allowing for a large response even in low concentrations of signal molecules. Diffusion across organelle membranes, wherein other cellular processes may be influenced, is also possible with second messengers. Multiple simultaneous signalling pathways affect concentrations of second messengers and can fine-tune cellular activity. Problems of cross-talk do occur however because of misinterpretation.
Common second messengers include:
- Cyclic adenosine monophosphate (cAMP)
- Cyclic guanosine monophosphate (cGMP)
- Diacylglycerol (DAG)
- Inositol 1,4,5-trisphosphate (IP3)
- Calcium cation (Ca2+)
- ↑ Berg JM, Tymoczko JL, Gatto GJ, Stryer L. (2015): Biochemistry. 8th ed. New York: W. H. Freeman and Company. pp.397-399