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The tryptophan operon

Presented by: Chandana kalita MSc Biotechnology 2 nd sem Roll no. 03 Gauhati University. The tryptophan operon. Operon in gene regulation in prokaryotes. Gene regulation: The synthesis of particular gene product is controlled by mechanisms collectively called gene regulation

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The tryptophan operon

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  1. Presented by: Chandanakalita MScBiotechnology 2ndsem Roll no. 03 GauhatiUniversity The tryptophan operon

  2. Operon in gene regulation in prokaryotes • Gene regulation:The synthesis of particular gene product is controlled by mechanisms collectively called gene regulation • Operon:A few genes that are controlled collectively by one promoter

  3. OPERON CONTD… • Its structure: Each operon consists of few structural genes called cistrons and some cis-acting element such as promoter (P) and operator (O) • Its regulation: There are one or more regulatory gene outside of the operon that produce certain factors –repressors or activators

  4. Types of Control

  5. Types of operons

  6. The trpoperon • Discovered in 1953 by Jacques monodand his colleagues • First repressibleoperon to be discovered • First characterized in E.coli

  7. The trpoperon • Repressible system • 5 polycistronic structural gene plus regulatory genes • Gene products synthesize tryptophan -needed unless tryptophan is available in the medium

  8. Two mechanisms for regulating tryptophan synthesis • REPRESSION • ATTENUATION

  9. 1.Repression:

  10. 2. Attenuation of trpoperon • Special sequences in DNA of leader region • Leader/ attenuator region • Pair of inverted repeats • Alternate binding possibilities

  11. Position of ribosome on leader transcript determines if transcription is terminated or not • If starved for tryptophan = lacktrp-tRNA • If no trp-tRNA, ribosome stalls at trpcodons. With Ribosome on region 1, the 1-2 loop can’t form • So, the 2-3 loop for anti-termination forms. Thus region 3 can’t pair with region 4 and the RNA polymerase can now continue

  12. THANK YOU

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