In the following schematic diagram of a simple signaling pathway, protein Z regulates the activity of protein X, which is an upstream protein kinase, through a negative feedback loop. Which of the following better describes protein Z?
A) It is a protein kinase that is activated by phosphorylation.
B) It is a protein kinase that is inactivated by phosphorylation.
C) It is a protein phosphatase that is activated by phosphorylation.
D) It is a protein phosphatase that is inactivated by phosphorylation.

Question

In the following schematic diagram of a simple signaling pathway, protein Z regulates the activity of protein X, which is an upstream protein kinase, through a negative feedback loop. Which of the following better describes protein Z? 
A) It is a protein kinase that is activated by phosphorylation. 
B) It is a protein kinase that is inactivated by phosphorylation. 
C) It is a protein phosphatase that is activated by phosphorylation. 
D) It is a protein phosphatase that is inactivated by phosphorylation.

Quizplus · Accepted Answer

Protein Z, when phosphorylated by the protein kinase Y, catalyzes the removal of the phosphate from the protein kinase X, rendering it inactive in a feedback inhibition mechanism.

In the Following Schematic Diagram of a Simple Signaling Pathway