And remember, when the G protein is in its GDP phase, it is in fact turned off. But what happens here is this catalytic A chain moves on and binds onto this g protein in the GTP phase and it catalyzes a covalent modification process. It basically covalently attaches an ADP ribose component onto this G protein in the GTP phase. And this covalent modification stabilizes the structure of this g protein in the GTP phase and that ultimately traps this g protein in its active phase. So once this binding takes place, this g protein continually stimulates the adenolid cyclist to produce the cyclic adenosine monophosphates, which in turn produce more active PKA molecules which in turn carry out their function, as we'll discuss in just a moment. So the catalytic A unit, once it makes its way into the cell, it binds onto the alpha protein in the GTP phase where GTP stands for Guanosine triphosphate.