Ans.
The phosphatases are enzyme molecules that remove phosphate groups from their substrates. In signal transduction pathways, phosphatases deactivate protein kinases by breakdown of phosphoric acid mono esters into free hydroxyl group and a phosphate ion. It causes termination of signal transduction as protein kinases are no longer active to transmit signals.
Thus, the correct answer is 'they inactivate protein kinases to turn off signal transduction.'
