Two protein kinases, K1 and K2, function sequentially in an intracellular signal

Question

Two protein kinases, K1 and K2, function sequentially in an intracellular signaling cascade. If either kinase contains a mutation that permanently inactivates its function, no response is seen in cells when an extracellular signal is received. A different mutation in K1 makes it permanently active, so that in cells containing that mutation a response is observed even in the absence of an extracellular signal. You characterize a double mutant cell that contains K2 with the inactivating mutation and K1 with the activating mutation. You observe that the response is seen even when no signal is received by these cells. In the normal signaling pathway, does K1 activate K2 or does K2 activate K1? Explain your answer.

Explanation / Answer

from the given information it can be drawn that

1. protein kinases,K1 activates protein kinases K2 In the normal signaling pathway

2.If protein kinases,2 is permanently activated, a response is observed independent of the status of protein kinases,1 signaling pathway.

3.If the order were reversed, protein kinases,2 would need to activate protein kinases,1,

4.as K1 contains an inactivating mutation.

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