And so in this process, the EGF signal transduction pathway stimulates cell differentiation, cell growth and cell proliferation of two types of cells, epidermal cells and epithelial cells. Now, once this pathway actually carries out its specific purpose, how exactly does a normal cell terminate this process? Well, there are three major methods. Method number one is the fact that because we have a G protein involved and G proteins have Gtpa's activity, what that means is they have a built in clock that allows it to actually shut itself down following activation. So sometime after this has been activated into the GTP form, this green structure, the G protein, because it has Gtph activity, it is able to actually take a water molecule from the cytoplasm and hydrolyze the GTP back into GDP. And once it inactivates itself, this can no longer stimulate the rest of the process.