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Catabolite Repression, Inducer Exclusion, and Diauxic Growth

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.

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Catabolite Repression, Inducer Exclusion, and Diauxic Growth

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  1. Catabolite Repression,Inducer Exclusion,and Diauxic Growth

  2. 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?

  3. Wild Type E. coli on minimal medium with Glycerol / IPTG

  4. What is glucose doing? • Inhibiting β-galactosidase? • Glucose, or it’s intermediates, repress lac expression? • Why does cAMP help? • Is CRP affected? • Is AdenylateCyclase affected?

  5. How does glucose get in the cell? Phosphotransferase system (PTS) Group Translocation

  6. What is left if glucose is coming into the cell? • Glucose 6-phosphate • Enzyme IIA • HPr • Enzyme I • Pyruvate

  7. Inducer Exclusion • Enzyme IIA glc (without P) acts as inhibitor of lacpermease • Lactose not taken into cell • Lactose not converted to allolactose by β-galactosidase • Repressor Protein stays on operator

  8. Catbolite Repression • Enzyme IIA glc – P not available • Adenylatecyclase not activated • No cAMP to bind CRP • CAP site unbound – no activation of operon

  9. What is left if glucose is not coming into the cell? • Enzyme IIA - P • HPr - P • Enzyme I - P • PEP

  10. Absence of glucose • Enzyme IIA glc - P does not act as inhibitor of lacpermease • Lactose taken into cell • Lactose converted to allolactose by β-galactosidase • Repressor Protein comes off operator - induction • Enzyme IIA glc – P available • Adenylatecyclase activated • cAMP available to bind CRP • CAP site bound – activation of operon

  11. What would the mutants be like?

  12. Effect of mutations on AdenylateCyclase (Absence of glucose)

  13. Diauxic growth Response Log [S] Log OD

  14. Diauxic growth Response • Lag Phase • Ribosome synthesis

  15. 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 • Adenylatecyclase inactive • cAMP absent • Lac operon not activated

  16. Diauxic growth Response • Entering Stationary Phase (aka secondary lag phase) • Primary metabolism ebbs • Enz IIA – P accumulates • Lac permeaseinhibition relieved • Lactose enters • Induction by allolactose • Adenylatecyclaseincreasingly activated • cAMP begins to form • Lac operonbegins to be activated

  17. Diauxic growth Response • Leaving Stationary Phase (aka secondary lag phase) • Primary metabolism resumes with lactose fermented to mixed acids • Enz IIA – P predominates • Lac permeaseinhibition relieved • Lactose enters rapidly • Induction by allolactose • Adenylatecyclasefully actived • cAMPforms rapidly • Lac operonis activated

  18. Diauxic growth Response • Second exponential phase • Primary metabolism continues with lactose fermented to mixed acids • Enz IIA – P predominates • Lac permeaseinhibition relieved • Lactose enters rapidly • Induction by allolactose • Adenylatecyclasefully activated • cAMPforms rapidly • Lac operonis activated

  19. What would the mutants be like?

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