Number of structural gene in Lac operon
a) 3
b) 4
c) 5
d) 6
Correct Answer - A
Lactose operone or Lac operon
The lac operon is a region of DNA in the genome of E. coli that
contains following genetic elements ?
i) Three structural genes :- These code for 3 proteins that are
involved in catabolism of lactose. These genes are ‘Z’ gene (codes
for P-galactosidase), ‘Y’ gene (codes for galactoside permease), and
‘A’ gene (codes for thiogalactoside transacetylase).
ii) Regulatory gene (lac i) It produces repressor protein.
iii) A promotor site (P) :- It is the binding site for RNA polymerase. It
contains two specific regions ?
a) CAP site (Catabolite activator protein binding site).
b) RNA polymerase binding site
iv) An operator site (0) :- Repressor binds to this site and blocks
transcription.
3 Structural genes are expressed only when ‘0’ site is empty
(repressor is not bound) and the CAP site is bound by a complex of
cAMP and CAP (catabolite gene activator protein)