All cells need to interpret their environment. Efficient processing of signals from the extracellular milieu is achieved through dynamic signal-transduction systems. The components of this system that come into contact first with external signals are cell-surface receptors. RTKs (Receptor Tyrosine Kinases) comprise one large group of receptors that respond to polypeptide growth factors and have intrinsic tyrosine kinase activity. On ligand binding, receptor signaling is activated. The activation of RTKs initiates signal transduc...