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Lac Operon quiz #1

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  • What is the function of the lacI gene in the regulation of the lac operon?
    The lacI gene encodes the repressor protein that binds to the operator region of the lac operon, preventing transcription when lactose is absent. When lactose is present, it binds to the repressor, causing it to release from the operator and allowing transcription.
  • Which is an arrangement of genes consisting of an operator, promoter, and structural genes that are transcribed together in prokaryotes?
    An operon is an arrangement of genes consisting of an operator, promoter, and structural genes that are transcribed together in prokaryotes.
  • Which diagram shows a system in which the lac operon genes are about to be transcribed?
    A diagram showing the lac operon with the repressor protein removed from the operator (due to high lactose) and, optionally, the CAP-cAMP complex bound upstream of the promoter (if glucose is low) indicates that the lac operon genes are about to be transcribed.
  • Which statement best describes the lac operon in E. coli?
    The lac operon in E. coli is a group of genes that are transcribed together and encode proteins needed to break down lactose; its expression is regulated by both lactose and glucose concentrations.
  • In the lac operon, the product of the structural gene lacZ is capable of ________.
    In the lac operon, the product of the structural gene lacZ is capable of breaking down lactose into glucose and galactose by encoding the enzyme beta-galactosidase.
  • What is the role of the lacY gene in the lac operon?
    The lacY gene encodes permease, a protein that facilitates the entry of lactose into the cell for metabolism.
  • How does the presence of high glucose affect cAMP levels in the cell?
    High glucose inhibits adenylyl cyclase, resulting in low cAMP levels, which prevents activation of the lac operon by the CAP-cAMP complex.
  • What is the function of the CAP binding site in the lac operon?
    The CAP binding site is located upstream of the promoter and allows the CAP-cAMP complex to bind and enhance transcription of the lac operon when glucose is low.
  • Why is the lac operon only weakly expressed when both lactose and glucose are present in high concentrations?
    When both are high, lactose removes the repressor, allowing transcription, but high glucose prevents CAP-cAMP activation, resulting in only weak expression.
  • What happens to lac operon expression if lactose is low, regardless of glucose concentration?
    If lactose is low, the repressor remains bound to the operator, blocking transcription of the lac operon no matter the glucose level.
  • What is the relationship between a gene and an operon in prokaryotic gene regulation?
    An operon is a group of genes with related functions that are transcribed together under the control of a single promoter and operator. In prokaryotes, genes within an operon are co-regulated and expressed as a single mRNA, allowing coordinated regulation of their functions. Each gene within the operon encodes a specific protein, and the operon structure enables efficient control of gene expression in response to environmental signals.