Control of Transcription IV: Glucose

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  1. a.      When glucose and lactose both present, E. coli uses __
    i.      Enzymes for glucose breakdown in glycolysis are __present
    1.      Only if __is lactose used as energy
    • glucose                                                             
    • continually
    • lactose is present and glucose is short
  2. a.      Sensing the glucose concentration                                                    
              i.      Depends on interaction of an Allosteric regulatory protein, called __, which accumulates when glucose is __
    ii.      Regulatory protein, __is activator
    • cyclic AMP
    • scarce                                                           
    • catabolite activator protein (CAP),
  3. 1.      When cAMP binds to CAP, it becomes __and does what?
    a.      This attachment increases the affinity of__, which is low even without repressor2.      By facilitating binding of RNA pol to the promoter and thereby increasing the rate of transcription, the attachment of CAP to the promoter directly stimulates gene expression= __
    • active
    • attach to specific site at upstream end of lac promoter
    •  RNA pol for the promoter
    • positive regulation
  4. what happens if glucose increases?
    a.      cAMP fallsà CAP detaches                                                              i.      Due to CAP being inactive, RNA polymerase binds less efficiently to promoter, and transcription of lac operon proceeds at only a low level, even in the presence of lactose
  5. Lac operon under dual control
                                                                  i.      Negative control by lac repressor                                                            ii.      Positive control by CAP
  6. a.      State of lac repressor determines what?; the state of CAP controls the rate of transcription is the operon is repressor-free
    • whether or not transcription of the lac operon’s genes occurs at all
    • rate of transcription is the operon is repressor-free
  7. a.      __also helps regulate other operons that encode enzymes used in catabolic pathways                                                              i.      May affect expression of more than 100 E. coli genes
    1.      When glucose is abundant and CAP inactive, the __
    • CAP
    • synthesis of enzymes that catabolize compoundsother than glucose slows
  8. a.      The ability to catabolize other compounds= survival                                                                                                                                      i.      Compounds present in cell at moment determine which operons are switched on—the result of simple interactions of __and __proteins with promoters of gene in question
    • activator
    • repressor
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Control of Transcription IV: Glucose

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