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Gene Regulation in Bacteria - Genetics

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  • What is constitutive transcription?

    Constitutive transcription is continuous transcription of a gene regardless of environmental conditions.

  • What is regulated transcription?

    Regulated transcription is transcription turned on or off in response to changing environmental conditions.

  • Name two levels of gene regulation in bacteria.

    1. Transcriptional regulation (e.g., inducible and repressible transcription)
    2. Posttranscriptional regulation (e.g., mRNA destruction, translation blockage)

  • What is the role of repressor proteins in gene regulation?

    Repressor proteins bind to operator sequences to block RNA polymerase and inhibit transcription (negative regulation).

  • How do activator proteins regulate transcription?

    Activator proteins increase RNA polymerase binding to the promoter, enhancing transcription (positive regulation).

  • What is an operon?

    An operon is a single transcriptional unit containing multiple structural genes controlled by one promoter and operator.

  • What are the three structural genes of the lac operon and their functions?

    lacZ: β-galactosidase; lacY: permease; lacA: transacetylase.

  • What is the function of the lacI gene?

    lacI encodes the lac repressor protein, which binds the operator to inhibit transcription; it is constitutively expressed.

  • How does allolactose regulate the lac operon?

    Allolactose binds the lac repressor, causing it to release from the operator and allowing transcription.

  • What is catabolite repression in the lac operon?

    Catabolite repression is positive regulation where CAP-cAMP complex enhances lac operon transcription when glucose is low.

  • How does glucose availability affect cAMP levels?

    High glucose leads to low cAMP; low glucose leads to high cAMP, which binds CAP to activate transcription.

  • Describe the role of the CAP-cAMP complex in lac operon regulation.

    CAP-cAMP binds near the lac promoter and interacts with RNA polymerase to increase transcription efficiency.

  • What is the difference between inducible and repressible transcription?

    Inducible transcription is turned on by an inducer (e.g., lac operon). Repressible transcription is turned off by a corepressor (e.g., trp operon).

  • How does the trp operon regulate tryptophan biosynthesis?

    When tryptophan is present, it acts as a corepressor activating the repressor to block transcription of the trp operon.

  • What is attenuation in gene regulation?

    Attenuation is a regulatory mechanism that controls transcription termination based on metabolite levels (e.g., trp operon).

  • What is the helix-turn-helix motif?

    A common DNA-binding domain in regulatory proteins that allows specific binding to operator sequences.

  • Why are many DNA binding sites symmetrical?

    Symmetry allows dimeric regulatory proteins to bind DNA more effectively by recognizing inverted repeats.

  • What is the role of alternative sigma factors in bacteria?

    Alternative sigma factors direct RNA polymerase to specific promoters to activate large groups of genes under certain conditions.

  • How is transcription coupled to translation in bacteria?

    In bacteria, translation of mRNA begins while transcription is still in progress, allowing rapid gene expression.

  • What is the function of the operator in an operon?

    The operator is a DNA sequence where repressor proteins bind to regulate transcription.