1. The Lac Operon An operon is a length of DNA, made up of structural genes and control sites. The structural genes code for proteins, such as enzymes.

2. I P O Z Y • I – The Regulatory gene; not actually part of the operon, but its product, the repressor protein, plays an important part in the functioning of the operon. • P – The Promoter region; a length of DNA to which the enzyme RNA polymerase binds to begin the transcription of the structural genes, Z and Y. • O – The Operator region; a length of DNA next to the structural genes. It can switch them on and off. • Z –Structural gene; codes for the enzyme beta-galactosidase, consists of a sequence of base pairs that can be transcribed into a length of mRNA. • Y – Structural gene, codes for the enzyme lactose permease. Consists of a sequence of base pairs that can be transcribed into a length of mRNA.

3. When lactose is absent from the growth medium.

4. When Lactose is added to the growth medium.

5. Why is the Lac operon so important? • The lac gene and its derivatives are amenable to use as a reporter gene in a number of bacterial-based selection techniques such as two hybrid analysis, in which the successful binding of a transcriptional activator to a specific promoter sequence must be determined. [1] • The Lac operon also controls transcription as if an RNA polymerase is released the repressor protein cannot bind to the operator and so genes can be transcribed from the structural genes and then leave the cell nucleus to be translated. However in contrast to this if an RNA polymerase is not released the repressor protein will bind to the operator preventing genes from being transcribed and therefore not translated.