3 (a) The lac operon is a section of DNA present in the genome of the bacterium Escherichia coli. The structural genes of the operon are only fully expressed when E. coli is exposed to high lactose concentrations.

1. (a)(i)Fig. 3.1 is a diagram showing the lac operon and a nearby region of the E. coli genome. [Figure 3.1] Name sections 1, 2, 3 and 4 shown in Fig. 3.1. 1 2 3 4[2]
2. (a)(ii)Certain enzymes need to be present inside E. coli for it to be able to take up and use lactose. When the genes of the lac operon are expressed, the enzymes ẞ-galactosidase and lactose permease are produced in large quantities. Outline the functions of ẞ-galactosidase and lactose permease. ẞ-galactosidase lactose permease[2]
3. (b)(i)Gene I is located a short distance away from the lac operon. The product of gene I, a repressor protein, is a constitutive protein. State what is meant by the term constitutive protein.[1]
4. (b)(ii)Explain why the structural genes of the lac operon are not expressed when lactose is absent.[3]
5. (b)(iii)A strain of E. coli has been produced with a mutation in gene I. Expression of this gene results in a non-functional repressor protein. Suggest a negative effect that this mutation will have on this strain of E. coli.[1]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.