Final answer:
Small GTPases such as the RAS protein toggle between an active state when bound to GTP and an inactive state when bound to GDP. The hydrolysis of GTP to GDP deactivates the protein, which then reassociates with its subunits, and a failure in this process can lead to cancer due to constant activation.
Step-by-step explanation:
Small GTPases, such as the RAS protein, exist in an active or inactive state depending on whether they are bound to guanosine triphosphate (GTP) or guanosine diphosphate (GDP). In their active state, GTPases are bound to GTP and can trigger a variety of downstream cellular responses.
The cycle begins when an external signal molecule binds to a G-protein-coupled receptor. This activates the associated G-protein by causing GDP to be replaced by GTP. The alpha subunit, along with GTP, disassociates from the beta and gamma subunits, and this activated form can then initiate further signaling events within the cell.