Question

(a) Absence of lactose in the culture medium affects the expression of a lac-operon in E.coli. Why and how? Explain.

(b) Write any two ways in which the gene expression is regulated in eukaryotes. [5]

Answer 1

(a) Lactose acts as an inducer in a Lac-operon. Thus, absence of lactose switches off the operon. The repressor protein produced by the regulatory gene is free in the absence of inducer (lactose). The repressor protein binds with the operator gene preventing RNA polymerase to transcribe the structural gene and hence, the operon is switched off. [3]

(b) In eukaryotes, gene expression is regulated at : [0.5 mark for each point]
(i) Transcriptional level
(ii) Processing level (regulation of splicing)
(iii)Transport of m-RNA from nucleus to the cytoplasm
(iv) Translational level