The presentation discusses gene regulation in prokaryotes, focusing on the transcriptional level and the lac operon model developed by Jacob and Monod. It explains the components of the lac operon including promoter, regulator gene, operator, structural genes, and inducer, alongside its role in lactose metabolism. Additionally, the document contrasts inducible and repressible operons, highlighting the function of the trp operon in tryptophan biosynthesis regulation.

1. Presentation on
“GENE REGULATION IN PROKARYOTES”
Presented by
Gautam Patidar
M.Sc. (Ag) Student
Department of Genetics and Plant Breeding
JNKVV, Jabalpur

2. 1. Gene
In Molecular genetics, It is a segment of DNA which encodes
of instructions to make protein.
2. What is Gene Regulation?
Gene regulation is the process used to regulate or control the
timing, location and amount in which genes are expressed.
It is complicated process which is carried out by Regulatory
proteins.
Ex:- Insulin synthesis by Pancreatic cells.

3. • Gene Regulation in prokaryotes primarily occur at the
Transcriptional level.
• In Prokaryotes, It is explained by Lac Operon Model.
• Lac Operon Model was developed by scientists Francois
Jacob and Jacques Monod in bacteria E. coli (1961).
• They discovered the activities of genes which controls
lactose metabolism in E. coli through synthesis of an
enzyme, β-galactosidase.

5. What is Lac Operon?
Lac :- Lactose Metabolism.
Operons :- A group or cluster of genes that are transcribed together to
give a single messenger RNA (mRNA) molecule, which therefore
encodes multiple proteins.
Such Polycistronic mRNA is typically found in prokaryotes.
It is also known as Inducible operon.

6. Different Parts of Lac Operon :-
1. Promoter:- Region of DNA where RNA Polymerase enzyme binds.
2. Regulator gene:- It synthesizes repressor proteins.
Also known as LacI or repressor gene.
3. Operator:- Region where repressor proteins binds.
4. Structural genes :- It encodes protein which is required to complete lactose
metabolism. Eg. LacZ, LacY and LacA gene.
5. Inducer:- Lactose molecule that turns ON the transcription of structural gene.

8. Lactose (Inducer) is Absent

10. Lactose (Inducer) is Present

12. Functions of Protein formed in Lactose Metabolism:-
1. LacZ gene :- Synthesize enzymes β-galactosidase.
Helps in breakdown of Lactose molecules into
glucose and galactose which is source of energy for cell.
2. LacY gene :- Synthesize enzyme Permease.
Helps in entry of lactose molecules into cells.
3. LacA gene :- Synthesize enzyme Transacetylase.
. Helps in activation of β-galactoside.

13. Trp operon
The Tryptophan operon, found in E. coli bacteria, is a group of genes that encode
biosynthetic enzymes for the amino acid tryptophan.
The trp operon is expressed (turned “on”) when tryptophan levels are low and
repressed (turned “off”) when they are high.
The trp operon is regulated by the trp repressor. When bound to tryptophan, the trp
repressor blocks expression of the operon.
It is also called Repressible operon.

16. Inducible Operon Repressible Operon
In this operon, Inducer (lactose) binds
with repressor protein to make them
Inactive and transcription process turn
ON.
In this Operon, Co-reprssor (tryptophan)
binds with repressor protein to make
them Active and transcription process
turn OFF.
Repressor is active under normal
conditions.
Repressor is inactive under normal
conditions.
Inducer turn ON the transcription. Inducer turn OFF the transcription.
Often employed in Catabolic pathway. Often employed in Anabolic pathway.
Ex:- Lac Operon Ex:- Trp Operon

17. Some Operons in Bacteria :-