Number two, to know the nucleotide sequence on that gene around the side that is actually to be altered. Now, the important step in this procedure is to basically create a special DNA primer that is complementary to the nucleotide sequence along that gene where we want to make that alteration. And the way that we want to build the DNA primer is we want to change the sequence in that DNA primer so that we change the codon that goes from glutamate to the codon that codes for aspartate. And to see what we mean by that, let's take a look at the following diagram. So, let's suppose that the DNA molecule that contains the gene that encodes for the protein is this DNA molecule here. So we have a circular single strand of DNA that came from some type of plasmid, for example.