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. And this GTP bound protein is attached onto the adenolate cyclist. Now, the A chain catalyzes the addition of an ADP ribosemoidi onto the arginine residue found on this g protein in the GTP phase. And so this covalent modification of that g protein in the GTP phase stabilizes the structure of the GTP phase.