(a) A cell where PKB is always active has a mutation that results in the permanent activation of GSK3. Based on the information in Figure 2, predict the effect of this mutation on the activity of glycogen synthase. Justify your prediction.

a. Normally, PK2 activates PK1. We are told that PK1 and PK2 normally work sequentially in an intracellular signaling pathway. If PK1 is permanently activated, a response is seen independently of whether or not PK2 is present. If PK1 activated PK2, no response should be seen if PK1 were activated in the absence of PK2.

GSK-3 is an unusual protein kinase in that it displays high, “constitutive” activity in unstimulated cells and is rapidly inactivated upon a variety of cellular stimulations. The most thoroughly documented pathway for the inactivation of GSK-3 is in response to insulin and is mediated by protein kinase B (PKB, also termed Akt), which lies upstream of GSK-3 [8].

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