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Review of the Lac Operon & Trp Operon quiz

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  • What type of operon is the lac operon and why?
    The lac operon is an inducible operon because it is normally off but can be turned on (induced) in the presence of lactose.
  • What type of operon is the trp operon and why?
    The trp operon is a repressible operon because it is normally on but can be turned off (repressed) when tryptophan is present.
  • How many genes are found in the lac operon and what are their names?
    The lac operon contains three genes: lacZ, lacY, and lacA.
  • How many genes are found in the trp operon and what are their names?
    The trp operon contains five genes: trpA, trpB, trpC, trpD, and trpE.
  • What is the main function of the genes in the lac operon?
    The genes in the lac operon metabolize lactose, breaking it down to extract energy.
  • What is the main function of the genes in the trp operon?
    The genes in the trp operon synthesize the amino acid tryptophan.
  • What is the repressor gene for the lac operon?
    The repressor gene for the lac operon is lacI.
  • What is the repressor gene for the trp operon?
    The repressor gene for the trp operon is trpR.
  • What molecule acts as the regulatory molecule (inducer) for the lac operon?
    Allolactose, a derivative of lactose, acts as the inducer for the lac operon.
  • What molecule acts as the regulatory molecule (corepressor) for the trp operon?
    Tryptophan itself acts as the corepressor for the trp operon.
  • What happens to the lac operon when lactose is absent?
    When lactose is absent, the lacI repressor is active, repressing transcription and keeping the operon off.
  • What happens to the trp operon when tryptophan is absent?
    When tryptophan is absent, the trpR repressor is inactive, so transcription proceeds and the operon is on.
  • How does allolactose affect the lacI repressor protein?
    Allolactose binds to and inactivates the lacI repressor, allowing transcription of the lac operon.
  • How does tryptophan affect the trpR repressor protein?
    Tryptophan binds to and activates the trpR repressor, which then represses transcription of the trp operon.
  • How do the regulatory mechanisms of the lac and trp operons compare?
    The lac operon is inducible (normally off, turned on by inducer), while the trp operon is repressible (normally on, turned off by corepressor); their regulatory mechanisms are essentially opposites.