Rather, I want you to understand the molecular meaning of a cascade and gain an understanding of how it can do something. This cascade begins with the dimerization of the receptor which allows cross- phosphorylation and reveals docking sites for adaptor proteins. In this case, it brings Sos close to the membrane, which will in turn activate ras, which is at the membrane. Each enzyme can activate more than one substrate - therefore the cascade can result in amplification. The cascade initiated by receptor tyrosine kinases are two of a handful of well-characterized receptor cascade systems which are used by many cells throughout the animal kingdom and within a multicellular organism.
Nature is both specific and efficient.
It will reuse what it can. It requires sophisticated multiparamenter technologies and understanding that we are only beginning to master. Recall that PDGF will ultimately stimulate division of the fibroblasts. In part, the gene expression induced by this cascade will result in the production of proteins that prepare a cell to divide. The kinases can also activate other enzymes directly relevant to cell division.