Gene expression- lac operon

  • Created by: Saf54
  • Created on: 13-02-19 12:18
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  • Gene expression
    • Regulating gene expression
      • Enzymes that catalyse metabolic reactions in basic cellular functions
        • Synthesised at constant rates
      • Enzymes that are only needed under specific conditions
        • Synthesised at varying rates according to the needs of the cell
    • The lac operon
      • E.coli metabolises glucose as respiratory substrate
        • If glucose is absent and lactose is present
          • Lactose induces the production of 2 enzymes
            • Lactose permease- allows lactose to enter bacterial cell
            • B galactosidase-hydrolyses lactose into glucose+galactose
            • It’s the lactose not the absence of glucose that induces enzymes
    • What is the lac operon?
      • Length of DNA , 6000 base pairs long
        • Contains an operator region, lacO,that’s next to the structural genes
      • LacZ codes for enzyme B galactosidase
      • LacY codes for lactose permease
      • Next to operator region (lacO) is the promoter region P
        • The enzyme RNA polymerase binds to begin transcription of lacZ and lacY
    • how the lac operon works
      • Next to operon is repressor gene I that codes for repressor protein lacI
        • When regulatory gene is expressed, repressor protein binds to operator
          • Preventing RNA polymerase from binding to the promoter region
            • Repressor protein prevents genes lacZ&lacY from being expressed
              • Enzymes for lactose metabolism aren’t made
      • Switching genes off
      • Switching genes on
        • Repressor protein binds to operator preventing transcription
          • Stops RNA polymerase from binding to the promoter region
            • Lactose binds to repressor protein
              • Repressor protein leaves the operator
                • RNA polymerase can bind and transcribe the genes
                  • Produces B galactosidase & lactose permease


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