Question

Explain how does lac operon in E.coli operates:
(a) in the absence of an inducer.
(b) in the presence of an inducer.

Answer 1

in the absence of an indurcer

Answer 2

Lac operan in E.coli

Explanation:

• Lac operon consists of regulator gene, promoter gene, operatoral gene and structural gene. The E. coli bacterium carries numerous genes and these genes turn on and off as per requirement. When these genes are turned on, they undergo enzymes which metabolise the new substrate. This phenomenon is known as induction and small molecules elicting this induction is referred to as inducers.
• In this lac operon, the presence of lactose acts as an inducer. The lac operon contains a promotor, an operator and three closely related structural genes, z, y, a coding for enzymes β-galactosidase, β-galactoside permease and β- galactoside transacetylase respectively.
• β-galactoside permease pumps lactose into the cells whereas β-galactosidase catalyses the conversion of lactose into glucose and galactose. These genes are not expressed in the absence of lactose