Question

It looses its ability to hydrolise GTP back to GDP which would have inactivated it, so the cell now thinks that the ligand, a growth factor, is continously activating the receptor-----------

Answer 1

When the G-protein in a cell signaling pathway loses its ability to hydrolyze GTP back to GDP, the receptor remains continuously active as it cannot be inactivated. This can occur when a ligand, such as a growth factor, continuously activates the receptor.

Step-by-step explanation:

Cell signaling using G-protein-linked receptors occurs as a cyclic series of events. Before the ligand binds, the inactive G-protein can bind to a newly revealed site on the receptor specific for its binding. Once the G-protein binds to the receptor, the resulting change in shape activates the G-protein, which releases guanosine diposphate (GDP) and picks up guanosine 3-phosphate (GTP).

The subunits of the G-protein then split into the a subunit and the By subunit. One or both of these G-protein fragments may be able to activate other proteins as a result. After awhile, the GTP on the active a subunit of the G-protein is hydrolyzed to GDP and the By subunit is deactivated. The subunits reassociate to form the inactive G-protein and the cycle begins anew.