Question

Two protein kinases, PK1 and PK2, work sequentially in an intracellular signaling pathway.You create cells that contain inactivating mutations in the genes that encode either PK1 or PK2 and find that these cells no longer respond to a particular extracellular signal.You also create cells containing a version of PK1 that is permanently active and find that the cells behave as though they are receiving the signal even when the signal is not present.When you introduce the permanently active version of PK1 into cells that have an inactivating mutation in PK2, you find that these cells also behave as though they are receiving the signal even when no signal is present.

A.From these results, does PK1 activate PK2, or does PK2 activate PK1? Explain your answer.
B.You now create a permanently active version of PK2 and find that cells containing this version behave as though they are receiving the signal even when the signal is not present.What do you predict will happen if you introduce the permanently active version of PK2 into cells that have an inactivating mutation in PK1?

Answer 1

a. PK2 activates PK1

b. no response would be produced

Step-by-step explanation:

Kinases are enzymes known to phosphorylate different substrates, thereby activating/inactivating them. In this case, a mutation that produces a constitutively (permanently) active PK1 kinase is itself able to continue the signaling pathway, independently of whether or not PK2 is present. This constitutive mutation shows that PK1 is recruited to continue signaling events within the cell and, therefore, PK1 activation is downstream in the signaling pathway. Conversely, cells containing active PK2 and inactive PK1 would be unable to continue the signaling pathway since PK2 activation is upstream of the induction of PK1, and thereby these cells cannot respond to the signal (PK2 activation).