Trp operon

Molecular biology

1. U. MONIKA I- M.Sc bio chemistry GENE REGULATION 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.

4. 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.

5. 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.

6. 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.

7. 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.

8. 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.

9. 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.

10. STRUCTURAL AND FUNCTIONAL GENES This operon contains 5 structural genes. ------- Trp E Trp D ENCODES Trp C PROTEIN Trp B Trp A ---------

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

12. 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.

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

14. 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.

15. WHEN TRYPTOPHAN LEVEL IS LOW

16. WHEN TRYPTOPHAN LEVEL IS HIGH

17. ATTENUATION PROCESS

18. OVERALL PROCESS

19. 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.