Answer
Protein kinases add phosphate to other proteins, altering the activity of the phosphorylated proteins as part of cell signal transduction. In many pathways there is a phosphorylation cascade in which a series of protein kinases are phosphorylated along a chain.
Work Step by Step
This works since phosphate is a large, strongly charged molecule which can alter protein shape and, thus, function, by its very presence. It is a common and very important part of signal transduction.
