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GENE CONTROL TRYPTOPHAN REPRESSION/DE-REPRESSION ATTENUATION PowerPoint Presentation
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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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slide1

1

GENE CONTROL

TRYPTOPHAN

REPRESSION/DE-REPRESSION

ATTENUATION

slide2

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)

slide3

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

slide4

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

slide5

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

slide6

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

slide7

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?

slide8

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

slide9

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

slide10

10

  • TRYPTOPHAN OPERON LEADER PEPTIDE AMINO ACID SEQUENCE
  • HISTIDINE OPERON LEADER PEPTIDE
  • TRANSCRIPTION AND TRANSLATION CAN BE COUPLED IN PROKARYOTIC CREATURES
slide11

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?

slide12

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?

slide13

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

slide14

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

slide15

15

MODERATE [ENOUGH] TRP~tRNA INSIDE CELLS

ATTENUATION

5'

mRNA

TRP~tRNA DISAPPEARS

TRANSCRIPTION

CONTINUES

slide16

16

TRYPTOPHAN FREQUENCY

E. COLI CHROMOSOME

TRYPTOPHAN OPERON

LEADER PEPTIDE

slide17

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