A certain effector protein can be activated by phosphorylation at a key tyrosine

Question

A certain effector protein can be activated by phosphorylation at a key tyrosine residue. An upstream kinase rapidly phosphorylates this tyrosine in the presence of a signal. However, the kinase also phosphorylates and activates a slow-acting phosphatase that can dephosphorylate the phosphotyrosine. Which curve in the following graph would you expect to represent the activity of the effector molecule over time? The input signal is present during the period indicated in gray. The dashed line represents the response in the absence of the phosphatase.

Explanation / Answer

The answer for this question should be curve 'B'.

First, let us start with what is given -

1. Effector protein gets rapidly activated through a upstream kinase in presence of signal.

2. This kinase also activates a slow-acting phosphatase that dephosphorlyates the effector protein.

3. Curve A representing activation of Effector protein in absence of phosphatase.

Solution:

When we observe the dotted lines, curve A - we see that the effector protein rapidly gets activated and the Relative response (log scale) does not drop due to absence of phosphatase.

So, in presence of phosphatase we should expect a drop in relative response. Among the given curves, curve B seems to be most likely option because - it retains the rapid phosphorylation of effector protein and then with time drop is seen due to activation of slow acting phosphatase.

Hope this helped.

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