Editing Signal transduction (section)

==Cellular responses==
Gene activations<ref name="lalli">{{Cite journal |vauthors=Lalli E, Sassone-Corsi P |date=July 1994 |title=Signal transduction and gene regulation: the nuclear response to cAMP |journal=The Journal of Biological Chemistry |volume=269 |issue=26 |pages=17359–62 |doi=10.1016/S0021-9258(17)32442-0 |pmid=8021233 |doi-access=free}}</ref> and metabolism alterations<ref name="rosen">{{Cite journal |vauthors=Rosen OM |date=September 1987 |title=After insulin binds |journal=Science |volume=237 |issue=4821 |pages=1452–8 |bibcode=1987Sci...237.1452R |doi=10.1126/science.2442814 |pmid=2442814}}</ref> are examples of cellular responses to extracellular stimulation that require signal transduction. Gene activation leads to further cellular effects, since the products of responding genes include instigators of activation; transcription factors produced as a result of a signal transduction cascade can activate even more genes. Hence, an initial stimulus can trigger the expression of a large number of genes, leading to physiological events like the increased uptake of glucose from the blood stream<ref name=rosen/> and the migration of [[neutrophils]] to sites of infection. The set of genes and their activation order to certain stimuli is referred to as a [[genetic program]].<ref name="massaque">{{Cite journal |vauthors=Massagué J, Gomis RR |date=May 2006 |title=The logic of TGFbeta signaling |journal=FEBS Letters |volume=580 |issue=12 |pages=2811–20 |doi=10.1016/j.febslet.2006.04.033 |pmid=16678165 |doi-access=free}}</ref>

Mammalian cells require stimulation for cell division and survival; in the absence of [[growth factor]], [[apoptosis]] ensues. Such requirements for extracellular stimulation are necessary for controlling cell behavior in unicellular and multicellular organisms; signal transduction pathways are perceived to be so central to biological processes that a large number of diseases are attributed to their dysregulation.
Three basic signals determine cellular growth:
* Stimulatory (growth factors)
** Transcription dependent response<br />For example, steroids act directly as transcription factor (gives slow response, as transcription factor must bind DNA, which needs to be transcribed. Produced mRNA needs to be translated, and the produced protein/peptide can undergo [[posttranslational modification]] (PTM))
** Transcription independent response<br />For example, [[epidermal growth factor]] (EGF) binds the [[epidermal growth factor receptor]] (EGFR), which causes dimerization and autophosphorylation of the EGFR, which in turn activates the intracellular signaling pathway .<ref name="sako">{{Cite journal |vauthors=Sako Y, Minoghchi S, Yanagida T |date=March 2000 |title=Single-molecule imaging of EGFR signalling on the surface of living cells |journal=Nature Cell Biology |volume=2 |issue=3 |pages=168–72 |doi=10.1038/35004044 |pmid=10707088 |s2cid=25515586}}</ref>
* Inhibitory (cell-cell contact)
* Permissive (cell-matrix interactions)
The combination of these signals is integrated into altered cytoplasmic machinery which leads to altered cell behaviour.