In this video Paul Andersen describes the elements of an operon. The promoter allows the RNA polymerase to transcribe the required genes. The operator and repressor regulate the expression of the genes by blocking the RNA polymerase. The genes for a specific task are all located in sequence so that they can all be transcribed at once. He starts be describing how the lac operon can be initiated to break down lactose. He then explains how the trp operon can be activated to create tryptophan. He ends with a simulation of the lac operon.