Page 19 - CH6 (1)

a Structural It codes for transacetylase.
gene

a
l
o
● All genes involved in ​c​peron are required for metabolism of lactose.

o
l

● Inducer​− Lactose acts as an inducer for​ac​peron since it regulates
the switching on and off of the operon.
● If lactose is provided to the growth media of bacteria in absence of any
other carbon source, then it is transported inside the cells by
permease.
● For permease to be present and lactose to enter inside the cells, low
a
l
o
level of expression of ​c​peron must be present all the time.

Regulation in Absence of Inducer
● In absence of inducer, ​​ene transcribes to synthesise repressor
g

i
mRNA, which translates to form repressor.
● This repressor binds with the operator region of operon and prevents

(
RNA polymerase to transcribe genes − ​​​​and​​negative

,

y
z
,

a
regulation).
● Therefore, in absence of the products of these genes, metabolism of
lactose ceases.

Regulation in Presence of Inducer

i

(
● Inducer binds with the protein product of gene ​​repressor) and
inactivates it.
● This inactivated repressor is unable to inactivate RNA polymerase

y
,
enzyme and ​​​​and ​​enes synthesise their respective mRNA, which
z

g
a
,

in turn gets translated to form β­galactosidase, permease, and
transacetylase.