Page 18 - CH6 (1)

● Regulation in prokaryotes
○ Gene expression is regulated by controlling the rate of

transcriptional initiation.
○ The activity of RNA polymerase at a given promoter is regulated

by accessory proteins. The accessory proteins affect the ability of
a promoter to recognise start sites.

○ A regulatory protein could be activator or repressor.
○ Accessibility of promoter is also affected by operators. Operator
is the region located adjacent to promoter.

○ Each operon has a specific operator and a specific repressor.
○ Usually operator binds to a repressor protein.

​egulation of Lac Operon
R

Lac​Operon
● Operon − An arrangement where a polycistronic gene is regulated by a
common promoter and regulatory genes

o

v
o

i
r
t

h
o
● Lac​peron, ​p​peron, ​s​peron, ​al​peron are the examples of

o
such systems.
● The elucidation of ​c​peron as a transcriptionally active system was
l
a

o
first done by geneticist Jacob and biochemist Monod.
o
a
● Genes constituting ​c ​peron:
l
Gene Nature Function
l

i​ene Inhibitor It codes for repressor of ​c ​peron.
o
a
g
z Structural It codes for β­galactosidase.
gene
Lactose Galactose + Glucose
y Structural It codes for permease, which increases the
gene permeability of cell to β­galactosidase.