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A-Level Biology OCR A

Camp Lac Binding Transcription Glucose Rate Crp Lactose

cAMP, in the presence of low glucose, binds to CRP, which then binds to the promoter, increasing the rate of lac operon transcription. High glucose levels reduce cAMP, thus decreasing transcription. This ensures lactose metabolism is prioritized when glucose is scarce.

cAMP, in the presence of low glucose, binds to CRP, which then binds to the promoter, increasing the rate of lac operon transcription. High glucose levels reduce cAMP, thus decreasing transcription. This ensures lactose metabolism is prioritized when glucose is scarce.

Front Describe the role of cAMP in the control of the lac operon.
Back Cyclic AMP & lac operon:
  • Binding of RNA polymerase results in slow rate of transcription that needs to be higher to produce enough enzymes to metabolise lactose 
  • Binding of cAMP to CRP allows CRP to bind to binding site on promoter & increase rate of transcription of lac operon proteins
  • Glucose entering E.coli decreases cAMP - transcription of genes for metabolism of lactose reduced
  • If both glucose and lactose present, glucose still preferred

Low glucose:
High glucose:

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