Final answer:
Protein kinases can phosphorylate serine, threonine, and tyrosine residues present in the side chains of amino acids. This phosphorylation can lead to changes in the shape and function of the proteins.
Step-by-step explanation:
Protein kinases phosphorylate amino acids in proteins, and this includes phosphorylation of serine, threonine, and tyrosine residues present in the side chains of these amino acids. When a kinase adds a phosphate group to a serine, threonine, or tyrosine residue, it can lead to a change in the shape and function of the protein. This phosphorylation can activate or deactivate the protein's function. Therefore, the statement 'Kinases phosphorylate protein on side chains of amino acids' is true.