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Microbiology: Genetic Material Structure and Gene Regulation in Bacteria

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  • What is the structure of bacterial chromosomes?
    Bacteria have one circular chromosome that is not membrane-bound and is supercoiled and highly organized with histone-like proteins.
  • What role do histone-like proteins play in bacterial DNA?
    They keep DNA supercoiled and organized; without them, DNA loses its supercoiled nature.
  • How is bacterial DNA organized within the cell?
    The chromosome is anchored to the plasma membrane and supercoiled to fit inside the small bacterial cell.
  • What is the central dogma of molecular biology?
    DNA is transcribed into RNA, which is then translated into protein.
  • What is the difference between the sense and antisense DNA strands?
    The sense strand (5’ to 3’) has the same sequence as mRNA, while the antisense strand (3’ to 5’) serves as the template for transcription.
  • What is the function of the promoter in bacterial gene expression?
    It is a specific DNA sequence where RNA polymerase binds to initiate transcription.
  • How does the bacterial operon structure facilitate gene regulation?
    Operons group promoter, operator, activator-binding sites, and functionally related structural genes to allow coordinated regulation and polycistronic mRNA production.
  • What is the role of the operator in an operon?
    It is a DNA sequence where a repressor protein can bind to block RNA polymerase and inhibit transcription.
  • How does repression regulate gene expression in bacteria?
    Repression turns off gene expression when certain substances are present, saving energy by preventing unnecessary protein synthesis.
  • What is induction in bacterial gene regulation?
    Induction activates gene expression in response to the presence of specific substances, such as sugars that need to be metabolized.
  • How does the tryptophan operon regulate amino acid synthesis?
    In absence of tryptophan, the repressor is inactive, allowing transcription of genes for tryptophan synthesis; when tryptophan is present, it acts as a corepressor activating the repressor to block transcription.
  • What is a corepressor in gene regulation?
    A compound that binds to a repressor protein and activates it to inhibit transcription.
  • How does the lactose operon function in E. coli?
    In absence of lactose, the active repressor binds the operator to block transcription; when lactose is present, it is converted to allolactose which inactivates the repressor, allowing gene expression.
  • What proteins are encoded by the lactose operon structural genes?
    lacZ codes for β-galactosidase, lacY for permease (lactose transporter), and lacA for transacetylase.
  • What is catabolite repression in bacteria?
    A global control mechanism where presence of glucose represses the expression of genes for metabolizing other sugars like lactose.
  • How does cAMP and CAP regulate the lac operon?
    When glucose is low, cAMP levels rise and bind inactive CAP, activating it; active CAP binds the CAP site to enhance RNA polymerase binding and transcription.
  • What happens during diauxic growth in bacteria?
    Bacteria consume glucose first, then after a lag phase, switch to metabolizing lactose, showing two exponential growth phases.
  • What is quorum sensing in bacteria?
    A mechanism where bacteria detect population density via autoinducers to coordinate gene expression, such as bioluminescence.
  • How does the Lux operon regulate bioluminescence in Vibrio fischeri?
    At high cell density, autoinducer concentration rises, activating LuxR which binds the activator site to promote transcription of luciferase genes producing light.
  • What is polycistronic mRNA?
    A single mRNA molecule that encodes multiple proteins, typical of bacterial operons.