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Review of the Lac Operon & Trp Operon exam

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  • Lac Operon
    An inducible operon that is typically off but can be activated by allolactose.
  • Trp Operon
    A repressible operon that is usually on but can be inhibited by tryptophan.
  • What is the function of the genes in the lac operon?
    To metabolize lactose for energy.
  • What is the function of the genes in the trp operon?
    To synthesize the amino acid tryptophan.
  • Lac I
    The repressor gene in the lac operon.
  • Trp R
    The repressor gene in the trp operon.
  • Allolactose
    A lactose derivative that inactivates the lac I repressor.
  • Tryptophan
    The regulatory molecule that activates the trp R repressor.
  • How many genes are in the lac operon?
    Three genes: lacZ, lacY, and lacA.
  • How many genes are in the trp operon?
    Five genes: trpA, trpB, trpC, trpD, and trpE.
  • What happens to the lac operon in the absence of lactose?
    The lac I repressor is active, repressing transcription and turning the operon off.
  • What happens to the trp operon in the absence of tryptophan?
    The trp R repressor remains inactive, allowing transcription and turning the operon on.
  • Inducible Operon
    An operon that is normally off but can be turned on by an inducer.
  • Repressible Operon
    An operon that is normally on but can be turned off by a corepressor.
  • What is the effect of allolactose on the lac operon?
    It inactivates the lac I repressor, allowing transcription to proceed.
  • What is the effect of tryptophan on the trp operon?
    It activates the trp R repressor, repressing transcription.
  • What happens to the lac operon when lactose is present?
    Lactose inactivates the repressor, turning the operon on.
  • What happens to the trp operon when tryptophan is present?
    Tryptophan activates the repressor, turning the operon off.
  • LacZ, LacY, LacA
    The three genes in the lac operon responsible for lactose metabolism.
  • TrpA, TrpB, TrpC, TrpD, TrpE
    The five genes in the trp operon responsible for tryptophan synthesis.
  • What is the role of the lac I repressor in the lac operon?
    To repress transcription in the absence of lactose.
  • What is the role of the trp R repressor in the trp operon?
    To repress transcription in the presence of tryptophan.
  • Corepressor
    A molecule that activates a repressor protein to inhibit transcription.
  • Inducer
    A molecule that inactivates a repressor protein to initiate transcription.
  • What is the state of the lac operon when the repressor is inactive?
    The operon is turned on, allowing transcription.
  • What is the state of the trp operon when the repressor is active?
    The operon is turned off, repressing transcription.
  • Gene Regulation
    The process of turning genes on and off to control gene expression.
  • Metabolic Pathways
    Series of chemical reactions in a cell that build and breakdown molecules for cellular processes.
  • What is the main difference between the lac and trp operons?
    The lac operon is inducible (normally off), while the trp operon is repressible (normally on).