Question

14. You are studying a newly discovered growth factor. You find that this growth factor stimulates the proliferation of cells grown in the laboratory. You have also found that the receptor that binds the growth factor is a receptor kinase that activates Ras, which activates the MAP kinase pathway. Which mutations affecting this growth factor pathway would you expect to promote uncontrolled cell proliferation? Select all that apply.

A. a mutation that inactivates the phosphatase that dephosphorylates the activated receptor

B. a mutation that prevents entry into the nucleus of the last kinase in the MAP kinase pathway

C. a mutation that blocks the kinase activity of the receptor

D. a mutation that prevents the GTPase activity of Ras

E. a mutation that prevents dimerization of the receptor

18. What would happen to a signaling pathway if phosphatases had reduced levels of function?

A. The response to the signal would be shorter after activation.

B. The response to the signal would persist longer after activation.

19. A number of mutations have been described in G proteins that have profound effects on their activity. For example, some mutations greatly increase the affinity of the G protein for GDP, making it very difficult for GDP to be exchanged for GTP. Other mutations prevent the hydrolysis of GTP to GDP. For each of the statements that describe a malfunction in cellular response, indicate the type of mutation that is responsible.

A receptor that is continuously activated in the absence of ligand. Which type of mutation is responsible for this malfunction in cellular response?

A. a Ras mutant that cannot hydrolyze GTP to GDP

B. Neither of the other answer options is correct.

Answer 1

14) A and D are the right options as they will promote that the cycle goes on and so will cell proliferation. Phosphorylated activated receptor will keep on activating the other components of the pathway and similarly GTP binded Ras will continue to give signal for cell proliferation.