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GENE CONTROL TRYPTOPHAN REPRESSION/DE-REPRESSION ATTENUATION

1. GENE CONTROL TRYPTOPHAN REPRESSION/DE-REPRESSION ATTENUATION. 2. CELLS GROWING IN ABSENCE OF ADDED TRYPTOPHAN . GLUCOSE. O 2. SOME PROTEINS REQUIRED: GLUCOSE TRANSPORT GLYCOLYSIS ENZYMES ELECTRON TRANSPORT ENZYMES TO SYNTHESIZE ALL 20 AMINO ACIDS INCLUDING-

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GENE CONTROL TRYPTOPHAN REPRESSION/DE-REPRESSION ATTENUATION

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  1. 1 GENE CONTROL TRYPTOPHAN REPRESSION/DE-REPRESSION ATTENUATION

  2. 2 CELLS GROWING IN ABSENCE OF ADDED TRYPTOPHAN GLUCOSE O2 SOME PROTEINS REQUIRED: GLUCOSE TRANSPORT GLYCOLYSIS ENZYMES ELECTRON TRANSPORT ENZYMES TO SYNTHESIZE ALL 20 AMINO ACIDS INCLUDING- 5 REQUIRED TO SYNTHESIZE TRYPTOPHAN FROM CHORISMATE PLUS RIBOSOMES, DNA POLYMERASE ETC, ETC CHORISMATE TRYPTOPHAN REQUIRED FOR (ALL) PROTEIN SYNTHESIS TRYPTOPHAN GENES (OPERON) ON (DE-REPRESSION)

  3. 3 TRYPTOPHAN GENES OFF (REPRESSION) CELLS GROWING IN THE PRESENCE OF TRYPTOPHAN GLUCOSE O2 SOME PROTEINS REQUIRED: GLUCOSE TRANSPORT GLYCOLYSIS ENZYMES ELECTRON TRANSPORT ENZYMES TO SYNTHESIZE 19 AMINO ACIDS TRYPTOPHAN SYNTHESIS ENZYMES ARE NOT NEEDED RIBOSOMES, DNA POLYMERASE ETC, ETC TRYPTOPHAN

  4. 4 TRYPTOPHAN OPERON REPRESSOR [INACTIVE] CO-REPRESSOR - TRYPTOPHAN - BINDS AND ACTIVATES REPRESSOR GLUCOSE MEDIUM - TRYPTOPHAN SYNTHESIS INSIDE CELLS; USED IMMEDIATELY FOR PROTEIN; LOW CONCENTRATION REPRESSOR IS INACTIVE TRYPTOPHAN OPERON IS ON

  5. 5 GLUCOSE AND TRYPTOPHAN MEDIUM - TRYPTOPHAN TRANSPORTED IN ACTS AS CO-REPRESSOR REPRESSOR BECOMES ACTIVE TRYPTOPHAN OPERON IS OFF REPRESSOR AND OPERATOR ARE ON-OFF SWITCH

  6. 6 CELLS GROWING IN ABSENCE OF ADDED TRYPTOPHAN GLUCOSE O2 SOME PROTEINS REQUIRED: GLUCOSE TRANSPORT GLYCOLYSIS ENZYMES ELECTRON TRANSPORT ENZYMES TO SYNTHESIZE ALL 20 AMINO ACIDS INCLUDING- 5 REQUIRED TO SYNTHESIZE TRYPTOPHAN FROM CHORISMATE PLUS RIBOSOMES, DNA POLYMERASE ETC, ETC CHORISMATE TRYPTOPHAN REQUIRED FOR (ALL) PROTEIN SYNTHESIS TRYPTOPHAN GENES (OPERON) ON (DE-REPRESSION) NOT ONLY PRODUCTION OF TRYPTOPHAN, BUT ALSO PRODUCTION IN THE RIGHT AMOUNT - JUST THAT AMOUNT NEEDED FOR PROTEIN SYNTHESIS. ADJUSTING LEVEL OF ON IS DONE BY ATTENUATION

  7. 7 ATTENUATION – ADJUSTING THE “ON” LEVEL REPRESSION ON OFF TWO GENERATIONS BUT- CELLS CAN RESPOND INSTANTLY TO CONTROL THE AMOUNT OF TRYPTOPHAN mRNA AND THE INTRACELLULAR LEVEL OF TRYPTOPHAN WHEN TRANSCRIPTION IS ON THE LEVEL CAN BE ADJUSTED HOW? mRNA TRANSCRIPTION MUST BE LINKED TO? THE AMOUNT OF TRYPTOPHAN IN THE CELLS ATTENUATION - STOPPING TRP mRNA SYNTHESIS (PREMATURELY) AFTER IT HAS BEGUN, IF THERE IS ADEQUATE CONCENTRATION IN THE CELLS. HOW?

  8. 8 ATTENUATION • MODERATE TRP LEVEL INSIDE CELLS • AS TRP LEVEL DROPS TRANSCRIPTION STOPS AT a SITE TRYPTOPHAN ENZYME PRODUCTION STOPS TRYPTOPHAN LEVEL WILL DECREASE TERMINATOR CANNOT FORM ATTENUATION DOES NOT OCCUR ENTIRE OPERON TRANSCRIBED ENZYME PRODUCTION RESUMES TRP LEVEL WILL INCREASE

  9. 9 ATTENUATION • MODERATE TRP LEVEL INSIDE CELLS • AS TRP LEVEL DROPS TRANSCRIPTION STOPS AT a SITE TRYPTOPHAN ENZYME PRODUCTION STOPS TRYPTOPHAN LEVEL WILL DECREASE SD LEADER PEPTIDE CODING REGION TERMINATOR CANNOT FORM ATTENUATION DOES NOT OCCUR ENTIRE OPERON TRANSCRIBED ENZYME PRODUCTION RESUMES TRP LEVEL WILL INCREASE

  10. 10 • TRYPTOPHAN OPERON LEADER PEPTIDE AMINO ACID SEQUENCE • HISTIDINE OPERON LEADER PEPTIDE • TRANSCRIPTION AND TRANSLATION CAN BE COUPLED IN PROKARYOTIC CREATURES

  11. 11 1:2 STOP 3:4 TRP TRP MET TRP TRP 2 3 MET STOP TRP mRNA LEADER REGIONS ALTERNATIVE STRUCTURES (IN VITRO) STEMS AND LOOPS G-C RICH 5' LEADER PEPTIDE CODING REGION TERMINATOR 5' TERMINATOR CANNOT FORM WHAT DETERMINES WHICH OF THESE STRUCTURES FORMS?

  12. 12 IF TERMINATOR FORMS, TRANSCRIPTION WILL BE TERMINATED EARLY IF STEM:LOOP 2:3 FORMS, TERMINATOR CANNOT FORM TRANSCRIPTION WILL PROCEED THOUGH ENTIRE OPERON INTRACELLULAR CONCENTRATION OF TRP [ACTUALLY TRP~tRNA] DETERMINES IF 2:3 OR 3:4 WILL FORM. HOW?

  13. 13 MODERATE TRP LEVEL - INTRACELLULAR ENOUGH TRP~tRNA TO INSERT TRP AT ALL TRP CODONS RNA POLYMERASE 5' LEADER PEPTIDE CODING REGION mRNA • RIBOSOME TRANSLATES LEADER PEPTIDE AS mRNA IS BEING SYNTHESIZED • MODERATE TRP [TRP~tRNA] ALLOWS COMPLETE LEADER PEPTIDE SYNTHESIS • RIBOSOME TRANSLOCATION DOWN mRNA PREVENTS 2:3; ALLOWS 3:4 • STEM:LOOP 3:4 IS TERMINATOR TRANSCRIPTION STOPS PREMATURELY- BEFORE REACHING STRUCTURAL GENES AND TRP CONCENTRATION WILL DROP

  14. 14 AS INTRACELLULAR TRP CONCENTRATION DROPS [USED UP FOR PROTEIN SYNTHESIS]THERE WILL NOT BE ENOUGH TO SUPPORT COMPLETE TRP LEADER PEPTIDE SYNTHESIS RNA POLYMERASE • RIBOSOME STALLS AT TRP CODON • CANNOT TRANSLOCATE; CANNOT COVER REGION 2 • STEM:LOOP 2:3 FORMS • STEM:LOOP 3:4 CANNOT FORM; CANNOT TERMINATE EARLY TRANSCRIPTION PROCEEDS THROUGH ENTIRE OPERON

  15. 15 MODERATE [ENOUGH] TRP~tRNA INSIDE CELLS ATTENUATION 5' mRNA TRP~tRNA DISAPPEARS TRANSCRIPTION CONTINUES

  16. 16 TRYPTOPHAN FREQUENCY E. COLI CHROMOSOME TRYPTOPHAN OPERON LEADER PEPTIDE

  17. 17 SO, LET'S COMPARE REPRESSORS OF CATABOLIC AND ANABOLIC OPERONS, JUST FROM THE COMMON SENSE STANDPOINT EXAMPLE: LACTOSE OPERON, LACTOSE IS THE INDUCER TO TO TURN ON THE LACTOSE OPERON BY INACTIVATING THE LACTOSE REPRESSOR EXAMPLE: TRYPTOPHAN OPERON; TRYPTOPHAN IN THE MEDIUM TURNS OFF THE OPERON BY BINDING AND ACTIVATING THE REPRESSOR

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