Site directed mutagenesis allows one to introduce virtually any desired mutation in a specific gene. One very useful application of the technique involves modifying a particular protein and evaluating the effect on biological or chemical activity.

In the past, two methods have been used for producing modified proteins.

One is to use chemical agents or ultraviolet light to induce mutations that result in changes in the amino acid sequence of proteins.

The other is to modify certain residues in an isolated protein by treatment with chemical reagents;

an example is the inactivation of a reactive serine in the active site of proteolytic enzymes like chymotrypsin, using diisopropylflurophosphate.

a) Why is site-specific mutagenesis superior to the two older procedures described above? ?
b) In order to carry out the modification of a protein using site-specific mutagenesis in the most efficient way, what sort of information should you have about the protein you wish to modify?