Question

Write the different components of a lac-operon in E. coli. Explain its expression while in an 'open' state. [5]

Answer 1

The lac-operon in E.coli consists of one regulatory gene, promotor gene, operator gene and three structural genes (z, y, and a) [1]. The repressor of the operon is synthesised (all-the-time-constitutively) from the i gene. The repressor protein binds to the operator region of the operon and prevents RNA polymerase from transcribing the operon [1]. In the presence of an inducer, (such as lactose or allolactose), lactose or the inducer binds to the repressor protein, it is made inactive so it cannot bind with operator and hence allows RNA polymerase to access the promotor [1]. As transcription proceeds, $\beta$- galactosidase, permease and transacetylase are formed by translation process for lactose metabolism. [1]

Diagramatic representation is shown below: [1 mark for representation]