General Definition: signal transduction pathway from

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What is a signal transduction pathway?

The steps through which a signal on the cell’s surface is converted to a series of specific cellular responses are called a signal transduction pathway.

The process is described below:
a) Fibroblast growth factors (FGFs) represent one of five classes of peptide growth factors. The binding of FGF-2
to it’s receptor FGFR induces receptor dimerisation and autophosphorylation.
b) These phosphorylated tyrosines act as binding sites for the growth factor receptor bound protein 2 (GRB2).
c) GRB2, with Son of sevenless protein (SOS) bound to it, binds to the RTK, which activates SOS. SOS is a guanine
nucleotide exchange factor (GEF).
d) SOS activates the low-molecular-weight GTPase Ras, by inducing it to release GDP and exchanging it for GTP.
e) GTPase activating proteins (GAPs) accelerate the intrinsic GTP hydrolytic activity of Ras, thereby promoting
the formation of the inactive GDP-bound in the form of Ras.
f) Active Ras triggers a cascade of protein phosphorylation involving mitogen-activated protein kinase kinase
kinase (Raf), mitogen activated ERK activating kinase (MEK) and extracellular signal regulated kinase (ERK).
g) Upon activation, the ERKs phosphorylate cytoplasmic targets translocates to the nucleus, where they stimulate
gene expression through the activation of transcription factors.


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