The document discusses the tryptophan (trp) operon in bacteria such as E. coli. The trp operon contains 5 structural genes that code for enzymes involved in the biosynthesis of tryptophan. It is regulated by a repressor protein called trpR that binds to the operator region and prevents transcription when tryptophan is present. When tryptophan levels are low, the repressor cannot bind and transcription of the structural genes occurs. The trp operon was an important early example of gene regulation and negative feedback that is commonly used to demonstrate these concepts.

1. U. MONIKA
I- M.Sc bio chemistry
TRYPTOPHAN OPERON

2. INTRODUCTION
Gene regulation or genetic
regulation is the controlled expression of genes in response to
internal and external signals.
Gene regulation refers to the processes that
cells use to turn the information on genes into gene products.
This functional gene product may be RNA or
protein by TRANSCRIPTION & TRANSLATION.

3. The expression of gene is very precisely
regulated in accordance with their structure and functions.
There are two levels of gene regulation,
 TRANSCRIPTION
mRNA is produced from DNA.
 TRANSLATION
Proteins are made from mRNA.

5. Most gene expressions are regulated through
controlling transcription.
Proteins are used to regulate the rate of
transcription of genes.
Some genes are turned on by proteins whereas
some genes are turned off by the proteins.

6.  REPRESSOR PROTEIN
Stop the gene expression by blocking
transcription.
 ACTIVATOR PROTEIN
Increase the gene expression by
promoting the ability of RNA polymerase to associate with a
gene and begin synthesizing mRNA.
OPERON : Collection of genes that are regulated together.

7. TRP OPERON
A group of genes used together that codes
for the components for production of tryptophan.
Trp operon is present in many bacteria., but
was first characterized in E.COLI.
First repressible operon to be discovered.

9. The operon is regulated so when tryptophan is
present in the environment and when the genes for tryptophan
synthesis are not expressed.
It was an important experimental system for
learning about gene regulation.
Commonly used to teach gene regulation.
Operates by negative repressible feedback
mechanism.

10. MECHANISM
The repressor for the trp operon is produced
upstream by the trpR gene , expressed at low level.
Synthesized trpR monomers associate into
dimers.
When tryptophan is present, these tryptophan
repressor dimers bind to tryptophan , causing a change in the
repressor confirmations, allowing the repressor to bind to the
operator.

11. This prevents RNA polymerase from binding to
and transcribing the operon , so tryptophan is not
produced from its precursor.
When tryptophan is absent , the repressor is
in its inactive confirmation and cannot bind the
operator region , so transcription is not inhibited by the
repressor.

13. STRUCTURAL AND FUNCTIONAL GENES
This operon contains 5 structural genes.
-------
1) Trp E
2) Trp D ENCODES
3) Trp C PROTEIN
4) Trp B
5) Trp A
---------

14. Each genes codes for a specific proteins for
the bio synthesis of tryptophan.
1. trp E ANTHRANILATE
2. trp D SYNTHASE
3. trp C INDOLE GLYCEROL PO4
SYNTHASE
4. trp B TRYPTOPHAN
5. trp A SYNTHASE

15. Also contains one repressive regulator gene
called trp R .
Trp R has a promoter trp P , where RNA
polymerase binds and synthesizes mRNA for regulatory
protein .
The protein that is synthesized by trp R then binds
to the operator trp O which then causes the transcription
to be blocked.

17. The trp operon contains a leader peptide
and an attenuator sequence which allows for graded
regulation.

18. ATTENUATION
Controls the progression of RNA polymerase into
the trp structural genes.
Reducing the expression of trp operon when trp
levels are high.
Instead of blocking the initiation of
transcription., it prevents completion of transcription.

20. WHEN TRYPTOPHAN LEVEL IS LOW

21. WHEN TRYPTOPHAN LEVEL IS HIGH

24. CONCLUSION
Trp operon is an ANABOLIC pathway,
which requires lots of energy. Gene regulation is more
complex in EUKARYOTES than prokaryotes.
Key element in Attenuation process.