And if there's nothing bound to the operator, that RNA polymerase can move along the structural genes and synthesize the mRNA molecule that is needed to create the enzymes that are involved in synthesizing the tryptophan amino acid. So for the case of the tryptophan opera, there are five structural genes that code four different enzymes needed to synthesize the tryptophan amino acid. Now let's take a look at the operator. So what is the purpose of the operator? So the operator is a segment of this Operon to which a repressive protein in its active form binds to. Now what exactly is a repressive protein?