Signal transduction
From the Simple English Wikipedia, the free encyclopedia that anyone can change
 |
The English used in this article may not be easy for everybody to understand. You can help Wikipedia by making this page or section simpler. |
.png/300px-G_protein_signal_transduction_(epinephrin_pathway).png)
In biology, signal transduction means any process by which a cell converts one kind of signal or stimulus into another.
Most often ordered sequences of biochemical reactions inside the cell are involved. These are carried out by enzymes and linked through second messengers. So a "second messenger pathway" is produced. Such processes are usually rapid. They last only milliseconds (in the case of ion flux) or minutes (in the activation of protein and lipid mediated kinase cascades).
In many signal transduction processes, the number of proteins and other molecules that take part increases during the process. So a "signal cascade" develops and often a relatively small stimulus causes a large response.
In bacteria and other single-cell organisms, the variety of signal transduction processes of which the cell is capable influences how many ways it can react and respond to its environment. In multicellular organisms, lots of different signal transduction processes are used to coordinate the behavior of individual cells. By this means the function of the organism as a whole is organized. The more complex the organism, the more complex the repertoire of signal transduction processes the organism must possess.
Thus, sensing of both the external and internal environment at the cellular level, relys on signal transduction. Many disease processes such as diabetes, heart disease, autoimmunity and cancer arise from defects in signal transduction pathways, further highlighting the critical importance of signal transduction to biology as well as medicine.
Contents |
[change] Stimulatory Molecules
Signal transduction usually involves the binding of small extracellular signaling molecules to receptors that face outwards from the plasma membrane and trigger events inside the cell.
These molecules have been functionally classified as:
- hormones (e.g. melatonin),[1]
- growth factors (e.g. epidermal growth factor),[2]
- extra-cellular matrix components (e.g. fibronectin),[3]
- cytokines (e.g. interferon-gamma),[4]
- chemokines (e.g. RANTES),[5]
- neurotransmitters (e.g. acetylcholine),[6] and
- neurotrophins (e.g. nerve growth factor).[7]
[change] Environmental stimuli
In addition to many of the regular signal transduction stimuli listed above, in complex organisms, there are also examples of additional environmental stimuli that initiate signal transduction processes. Environmental stimuli may also be molecular in nature (as above) or more physical, such as, light striking cells in the retina of the eye,[8] odorants binding to odorant receptors in the nasal epithelium,[9] and bitter and sweet tastes stimulating taste receptors in the taste buds.[10]
Unicellular organisms may also respond to environmental stimuli via the activation of signal transduction pathways.
[change] Types of receptor
Receptors can be roughly divided into two major classes:
- Intracellular receptors and
- Cell-surface receptors.
Ligand gated ion channel receptors are a class of receptor that may occur both at the cell-surface or intracellularly.
Receptors that are solely intracellular include those for steroid hormones, thyroid hormone, retinoic acid and derivatives of vitamin D3. In contrast to ligands that bind to cell surface receptors, in order to initiate signal transduction these ligands must cross the cell membrane. See the intracellular receptors section below for more details.
[change] Cell-surface receptors
Cell-surface receptors are integral transmembrane proteins and recognise the vast majority of extracellular signaling molecules.
[change] References
- ↑ Sugden D, Davidson K. et al. (2004). "Melatonin, melatonin receptors and melanophores: a moving story". Pigment Cell Res. 17 (5): 454-460. PMID 15357831.
- ↑ Carpenter G, and Cohen S. (1990). "Epidermal growth factor". J. Biol. Chem. 265 (14): 7709-7712. PMID 2186024.
- ↑ Ward M, and Marcey, D. [1] Retrieved on 2007-03-06
- ↑ Schroder et al. (2004). "Interferon-γ an overview of signals, mechanisms and functions". Journal of Leukocyte Biology 75: 163-189.
- ↑ Chung CW, Cooke RM et al. (1995). "The three-dimensional solution structure of RANTES". Biochemistry 34 (29): 9307-9314. PMID 7542919.
- ↑ Kistler J, Stroud RM et al. (1982). "Structure and function of an acetylcholine receptor". Biophys. J. 37 (1): 371-383. PMID 7055628.
- ↑ Wiesmann, C. and de Vos, AM. (2001). "Nerve growth factor: structure and function". Cell Mol Life Sci 58 (5-6): 748-759. PMID 11437236.
- ↑ Burns ME and Arshavsky VY. (2005). "Beyond counting photons: trials and trends in vertebrate visual transduction". Neuron 48 (3): 387-401. PMID 16269358.
- ↑ Ronnett GV and Moon C. (2002). "G proteins and olfactory signal transduction". Annu Rev Physiol 64: 189-222. PMID 11826268.
- ↑ Wong GT, Gannon KS and Margolskee RF. (1996). "Transduction of bitter and sweet taste by gustducin". Nature 381 (6585): 796-800. PMID 8657284.
[change] Further reading
- Cosma Shalizi's "Signal transduction" Notebook from 2003-01-20 used under the GFDL with permission
- Werner R. Loewenstein, The Touchstone of Life: Molecular Information, Cell Communication, and the Foundations of Life, Oxford University Press, 1999, ISBN 0-19-514057-5
[change] Other websites
- Signal Transduction - The Virtual Library of Biochemistry and Cell Biology
- TRANSPATH(R) - A database about signal transduction pathways
- Science's STKE - Signal Transduction Knowledge Environment, from the journal Science, published by AAAS.
