The document summarizes the lac operon in E. coli, which regulates the metabolism of lactose. The lac operon consists of structural genes (lacZYA) that encode enzymes for lactose catabolism, and control genes (promoter, operator, and repressor) that regulate expression. In the absence of lactose, the repressor binds the operator/promoter region, blocking transcription. In the presence of lactose or inducer molecules like IPTG, the repressor binds lactose instead, allowing transcription and expression of the structural genes. Glucose inhibits induction by lowering cellular cAMP levels needed for RNA polymerase binding to the promoter. The lac operon demonstrates negative and positive regulation of gene expression.

1. LAC OPERON
BY
A.MANOJ KUMAR M.Sc (BIO-TECH)

2. INTRODUCTION
OPERON:-
An Operon is a group of closely related gene (structural
and control gene)
Which regulate the metabolic pathway in prokaryotes
The Operon hypothesis was first put forward by
francois Jacob and Jacques Monod,while studying the
catabolism of lactose in E.Coli
They were awarded noble prize for this in the year
1965.

3. LAC OPERON
Lactose operon is a set of gene responsible for
the metabolism of lactose in E.Coli.
STRUCTURE OF LAC OPERON
The lac operon consist of
1)Structural Gene(Lac Z,Y,A)
2)Control or Regulatory
Gene(Promoter/Operator/Repressor)

4. GENETIC MAP OF LAC OPERON

5. STRUCTURAL GENES:-
Structural genes are the segment of DNA
responsible for synthesis of enzyme need for the
catabolism of lactose.
Lac-Z codes for the Enzyme β-galactosidase
Lac-Y codes for the Enzyme Galactose Permease
Lac-A codes for the Enzyme Thiogalactoside
Transacetylase
The structural gene produce a single polycistronic
mRNA,from which 3 enzyme are produced.

6. CONTROL OR REGULATORY GENE:-
The structural genes are controlled by
operator,promoter and Repressor.
It is present in upstream to the structural gene.
The control or regulatory gene are control the
activity of structural gene by either induction or
suppression
OPERATOR GENE:-
The operator gene is the segment of DNA
overlap with the promoter region
It controles the transcription of structural mRNA

7. PROMOTER:-
A segment of DNA presence adjacent to the operator
gene
RNA Polymerase bind specifically to the promoter
region and initiates the transcription of structural genes
of lac operon.
REPRESSOR GENE:-
Repressor is a tetrameric regulatory protein produces
repressor molecule.
Repressor molecule binds to the P/O region and blocks
the transcription of structural gene

8. REGULATION OF GENE EXPRESSION IN
LAC OPERON-NEGATIVE REGULATION
When lactose is absent
Repressor is active
Repressor binds the Operator/Promoter region
Operon is repressed
Transcription is blocked
No m-RNA synthesized
This repressor molecule act as a negative of
gene expression

9. NEGATIVE REGULATION

10. REGULATION OF GENE EXPRESSION IN
LAC OPERON-POSITIVE REGULATION
When lactose is present
Repressor binds to the inducer molecule
Repressor will not be able to binds to the
Promoter/Operator segment
Operon became active
Transcription begins
mRNA synthesized occur
Lactose β-galactosidase= Glucose+Galactose

11. POSITIVE REGULATION

12. INDUCER MOLECULES OF LAC OPERON
Lactose isomer (1,6-allow lactose)
IPTG (Isopropyl β-D-1-thiogalactopyranoside)
TMG(Thiomethyl Galactoside)
EFFECT OF GLUCOSE ON THE ACTIVITY OF LAC
OPERON:-
In the presence of glucose,the induction of lac operon is
inhibited
When the cell contain No Lac mRNA
glucose+galactose No Transcription
No β-galactosidase

13. The attachment of RNA polymerase to the
promoter site requires the presence of
Catabolite Activator Protein(CAP) bound to the
cyclic Adenine Monophosphate (cAMP) .
CAP-cAMP Complex function has positive
regulator of lac operon
NO GLUCOSE High cAMP
MORE GLUCOSE Low cAMP

14. CARBON SOURSE
1)GLUCOSE
2)GLYCEROL
3)LACTOSE
4)LACTOSE+GLUCOSE
5)LACTOSE+GLYCEROL
cAMP CONCENTRATION
LOW
HIGH
HIGH
LOW
HIGH

15. THANK YOU...