So notice that the tryptophan Operon contains the blue section and that is the promoted section. Now the promoted section is important because this is where the RNA polymerase binds to. So when the RNA polymerase approaches the promoter, it binds onto the promoter. 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.