Question 3
(Essay)
(a) Describe by labeled diagram the structural components of the lac operon in E. coli.
a() State the function of the lac regulator gene.
b() State the function of fi -galactosidase in the lac system.
c() Show by diagram the manner in which lactose brings about transcription of the three structural genes of the lac operon.
d() Explain why certain mutations in the regulator gene (I -) of the lac system result in maximal synthesis of fi -galactosidase, permease, and transacetylase even in the
absence of the inducer (lactose).
Answer
(a) See appropriate diagrams in the text.
a() The regulator gene produces a repressor protein that interacts with the operator to shut off transcription. In the presence of lactose, the repressor protein does not interact with the operator.
b() fi -galactosidase cleaves the lactose sugar into its components, glucose and galactose.
c() See appropriate diagrams in the text.
d() Such mutations provide modified proteins that are unable to associate with the operator to shut off transcription.
