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CATABOLITE REPRESSION,INDUCER EXCLUSION,AND DIAUXIC GROWTH
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?
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
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?
HOW DOES GLUCOSE GET IN THE CELL?
Phosphotransferase system (PTS)Group Translocation
WHAT IS LEFT IF GLUCOSE IS COMING INTO THE CELL?
Glucose 6-phosphate
Enzyme IIA HPr Enzyme I Pyruvate
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
CATBOLITE REPRESSION
Enzyme IIA glc – P not available Adenylate cyclase not activated No cAMP to bind CRP CAP site unbound – no activation of operon
WHAT IS LEFT IF GLUCOSE IS NOT COMING INTO THE CELL?
Enzyme IIA - P HPr - P Enzyme I - P PEP
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
WHAT WOULD THE MUTANTS BE LIKE?
Genotype Phenotype?
Enzyme I -
Enzyme II BC - –
Enzyme II A -
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
DIAUXIC GROWTH RESPONSE
Log OD Log [S]
DIAUXIC GROWTH RESPONSE
Lag Phase Ribosome synthesis
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
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
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
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
WHAT WOULD THE MUTANTS BE LIKE?
Genotype Behavior Relative to Diauxic Growth
lacZ-, lacY-
cya-
crp-
