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Glucose's Impact on Lac Operon quiz

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  • What is the preferred energy source for most prokaryotes, even in the presence of lactose?
    Glucose is the preferred energy source for most prokaryotes.
  • How does the presence of glucose affect the transcription of the lac operon?
    The presence of glucose inhibits the transcription of the lac operon by keeping cAMP levels low.
  • What happens to cAMP levels when glucose concentrations are low or absent?
    When glucose concentrations are low or absent, cAMP levels increase in the cell.
  • Does cAMP affect the activity of the lac repressor protein?
    No, cAMP does not affect the activity of the lac repressor protein; it influences transcription through other mechanisms.
  • What is the role of CRP (cyclic AMP receptor protein) in lac operon regulation?
    CRP is an activator protein that stimulates lac operon transcription when bound to cAMP.
  • What is the relationship between glucose and cAMP levels in the cell?
    There is an inverse relationship: high glucose means low cAMP, and low glucose means high cAMP.
  • What must happen for CRP to become active and stimulate lac operon transcription?
    CRP must bind to cAMP to become active and stimulate lac operon transcription.
  • Where does active CRP bind in relation to the lac operon?
    Active CRP binds to a specific site upstream of the lac promoter called the CRP binding site.
  • How does active CRP enhance transcription of the lac operon?
    Active CRP helps recruit RNA polymerase to the promoter, increasing transcription of the lac operon.
  • What happens to lac operon transcription when both glucose and lactose are present?
    Lac operon transcription remains low because glucose keeps cAMP levels low, resulting in inactive CRP.
  • Under what conditions is the lac operon fully turned on?
    The lac operon is fully turned on when lactose is present (inactivating the repressor) and glucose is absent (activating CRP via high cAMP).
  • Why does the cell not transcribe the lac operon when glucose is available, even if lactose is also present?
    Because glucose is the preferred energy source, and low cAMP levels prevent CRP activation, so transcription is not stimulated.
  • What is the effect of high cAMP levels on the lac operon?
    High cAMP levels lead to active CRP, which increases the rate of lac operon transcription.
  • What is positive control in the context of the lac operon?
    Positive control refers to the activation of lac operon transcription by active CRP when cAMP levels are high.
  • What two conditions must be met for effective transcription of the lac operon?
    Lactose must be present to inactivate the repressor, and glucose must be low to activate CRP via high cAMP.