In: Biology
22. You are studying a toxin that prevents RAS, a GTPase from hydrolyzing GTP. You find that this toxin increase the amount of cell growth. Please explain this finding.
23. You find that some cells have mutations that permanently deactivate Raf in this pathway. Please state whether you agree or the Ras-affecting drug from the previous question will increase the amount of cell growth in the inactive Raf mutants.
Agree or Disagree?
1)Ras protein has a GTPase binding domain and when it is bound to GTP, it is in active form. Ras then binds to protein kinases activating them to phosphorylate downstream signalling molecules to continue the growth signalling pathways which encourages the cell to grow and divide.
GTP when hydrolyses to GDP, inactivates Ras, thus terminating the signalling pathway. There fore this toxin increases the amount of cell growth because Ras is active all the time.
2)Raf is a kinase which activates mitogen activated protein kinases in mapk pathway. This kinase is activated by Ras protein in the signal transduction. If Ras is always bound to GTP, it is constitutively active which means Raf is active, further activating downstream protein kinases. In inactive Raf mutants it will decrease signal transduction due to inactive /mutant Raf which no longer can carry on the protein cascade for activating gene expression for increased cell growth.