This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
RAS gene is inhibited by: 
Select and explain. 
A. Cyclic GMP, B. Adenosine triphosphate, C. CD-kinase, D. GTPase activating protein
D: GTPase activating protein
Answer: D: GTPase activating protein 
Explanation: Ras is a protein which acts a like a switch to regulate cell division. It is activated when bound to GTP while it is inactivated when bound to GDP. GAP (GTPase Activating protein) regulates the Ras protein by causing hydrolysis of GTP bound to Ras. This leads to inactivation of the Ras thus inhibiting the cell cycle.