Working out the order in which the individual components in a signaling pathway act is an essential step in defining the pathway. Imagine that two protein kinases, PK-B and PK-X, act sequentially in an intracellular signaling pathway: - When either kinase is completely inactivated, cells do not respond to the normal extracellular signal. - Cells containing a mutant form of PK-B that is permanently active respond even in the absence of an extracellular signal. - Doubly mutant cells that contain inactivated PK-X and permanently active PK-B respond in the absence of a signal. A. In the normal signaling pathway, does PK-B activate PK-X or does PK-X activate PK-B? Explain your reasoning.

In the usual signalling pathway, PK2 triggers and initiates PK1. We can deduce this from the fact that if PKI is fully initiated, a response is seen and the response is seen as not dependent on the status of PK2, which pinpoints to the fact that PK2 is promoted ensuing of PK1. Let's infer that if the experimental setup happened to be altered in such a way as it causes PKI to be mutationally non-functional and PK2 possessed a stimulating mutation, no response can be said to be seen due to the fact that PK2 won't initiate PK1.