Question

16-22: Two protein kinases, K1 and K2, function sequentially in an intracellular signaling pathway. 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 in the absence of an extracellular signal. In the normal signaling pathway, does K1 activate K2 or does K2 activate K1

Answer 1

K1 is already responsible for intracellular signaling.

Step-by-step explanation:

K1 mutant: no response to extracellular signals.

K2 mutant: no reaction to extracellular signals.

Constitutive active K1 mutant: reaction in the absence or existence of an intracellularly signal.

Double mutant: mutant K2 / constitutive active mutant K1.

In normal cells K2 is activated K1 upstream of K1 or K2.

If K1 activates K2 then there will be no response in a double mutant since K2 is inactive. However, if K2 activates K1, the absence of K2 does not matter because K1 is already responsible for intracellular signaling.