And just like the g proteins we spoke of in the previous lectures, this small g protein in its inactive state binds GDP. And in its active state it binds GTP. And so what happens is once two the SOS binds onto one, the GRB two that activates this protein called SOS, showed in purple, that allows it to bind this Ras. Now, Ras is a small g protein and once this binding takes place, it essentially constricts this space and allows this molecule to expel the GDP guanosine diphosphate and instead it buys a peak guanosine triphosphate and that activates this Ras protein. So in step three we have the SOS then binds Ras, a small g protein. This activates Ras by expelling a GDP and binding instead a GTP.