C ATABOLITE R EPRESSION, I NDUCER E XCLUSION, AND D IAUXIC G ROWTH.
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Transcript of C ATABOLITE R EPRESSION, I NDUCER E XCLUSION, AND D IAUXIC G ROWTH.
![Page 1: C ATABOLITE R EPRESSION, I NDUCER E XCLUSION, AND D IAUXIC G ROWTH.](https://reader035.fdocuments.in/reader035/viewer/2022062713/56649cd75503460f9499f8c2/html5/thumbnails/1.jpg)
CATABOLITE REPRESSION,INDUCER EXCLUSION,AND DIAUXIC GROWTH
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HOW DOES A TRIPLE SUGAR IRON AGAR WORK?
What are the 3 sugars in TSI?
Which is least abundant?
What happens after 6-10 hours?
What happens next?
Why? How?
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WILD TYPE E. COLI ON MINIMAL MEDIUM WITH GLYCEROL / IPTG
Addition β-galactosidase
activity
lac mRNA levels
none <1 <1
IPTG 100 100
IPTG + Glc 10 10
IPTG + Glc + cAMP
80 80
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WHAT IS GLUCOSE DOING?
Inhibiting β-galactosidase?
Glucose, or it’s intermediates, repress lac expression?
Why does cAMP help? Is CRP affected?
Is Adenylate Cyclase affected?
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HOW DOES GLUCOSE GET IN THE CELL?
Phosphotransferase system (PTS)Group Translocation
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WHAT IS LEFT IF GLUCOSE IS COMING INTO THE CELL?
Glucose 6-phosphate
Enzyme IIA HPr Enzyme I Pyruvate
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INDUCER EXCLUSION
Enzyme IIA glc (without P) acts as inhibitor of lac permease Lactose not taken into cell Lactose not converted to allolactose by β-
galactosidase Repressor Protein stays on operator
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CATBOLITE REPRESSION
Enzyme IIA glc – P not available Adenylate cyclase not activated No cAMP to bind CRP CAP site unbound – no activation of operon
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WHAT IS LEFT IF GLUCOSE IS NOT COMING INTO THE CELL?
Enzyme IIA - P HPr - P Enzyme I - P PEP
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ABSENCE OF GLUCOSE
Enzyme IIA glc - P does not act as inhibitor of lac permease Lactose taken into cell Lactose converted to allolactose by β-
galactosidase Repressor Protein comes off operator -
INDUCTION Enzyme IIA glc – P available
Adenylate cyclase activated cAMP available to bind CRP CAP site bound – ACTIVATION of operon
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WHAT WOULD THE MUTANTS BE LIKE?
Genotype Phenotype?
Enzyme I -
Enzyme II BC - –
Enzyme II A -
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EFFECT OF MUTATIONS ON ADENYLATE CYCLASE (ABSENCE OF GLUCOSE)
Strain Adenylate Cyclase
Wild Type 100
Enzyme I minus
(HPr, E II A never phosphorylated)<5
Enzyme II BC minus
(Glucose doesn’t come in, E II A always phosphorylated
100 ± glucose
Enzyme II A minus
(Cannot activate Adenylate Cyclase)<5
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DIAUXIC GROWTH RESPONSE
Log OD Log [S]
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DIAUXIC GROWTH RESPONSE
Lag Phase Ribosome synthesis
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DIAUXIC GROWTH RESPONSE
Exponential Phase Primary metabolism –
glucose fermented to mixed acid products
Enz IIA not phosphorylated Lac permease inhibited Lactose excluded No induction by
allolactose Adenylate cyclase inactive cAMP absent Lac operon not activated
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DIAUXIC GROWTH RESPONSE
Entering Stationary Phase (aka secondary lag phase) Primary metabolism ebbs Enz IIA – P accumulates Lac permease inhibition
relieved Lactose enters Induction by allolactose Adenylate cyclase increasingly
activated cAMP begins to form Lac operon begins to be activated
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DIAUXIC GROWTH RESPONSE
Leaving Stationary Phase (aka secondary lag phase) Primary metabolism resumes
with lactose fermented to mixed acids
Enz IIA – P predominates Lac permease inhibition
relieved Lactose enters rapidly Induction by allolactose Adenylate cyclase fully actived cAMP forms rapidly Lac operon is activated
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DIAUXIC GROWTH RESPONSE
Second exponential phase Primary metabolism
continues with lactose fermented to mixed acids
Enz IIA – P predominates Lac permease inhibition
relieved Lactose enters rapidly Induction by allolactose Adenylate cyclase fully
activated cAMP forms rapidly Lac operon is activated
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WHAT WOULD THE MUTANTS BE LIKE?
Genotype Behavior Relative to Diauxic Growth
lacZ-, lacY-
cya-
crp-