
When the growth factors fit into the receptors the receptors connect together.  This then causes P chemicals to connect to the receptors surface within the cell.  A chemical reaction occurs in which SH2 connects to P, SH3 connects to SH2, SOS connects to SH3 causing GDP to be released from RAS and GTP to replace it.  This is when the growth signal is sent to the neucleus.  The GTP is then lost and replaced with GDP and the whole thing goes back to normal.

