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Microbiology: Genetic Variation and Gene Transfer in Bacteria

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  • What are mutations and recombination in bacterial populations?
    Mutations are random changes in nucleotide sequences causing protein changes; recombination is the exchange of DNA strands creating new sequences, both providing genetic diversity.
  • Define vertical gene transfer.
    Vertical gene transfer is the transfer of genetic material from parent to offspring during reproduction, producing genetically identical daughter cells.
  • What is horizontal gene transfer?
    Horizontal gene transfer is the transfer of genes between cells of the same generation, often leading to recombinant cells with new genetic traits.
  • Describe homologous recombination in bacteria.
    It is the exchange of DNA between two similar or nearly identical DNA sequences, facilitated by enzymes like RecA, resulting in new genetic combinations.
  • What role do nucleases play in recombination?
    Nucleases degrade donor DNA if they act before strand exchange, preventing recombination; if strand exchange occurs first, recombination proceeds.
  • Explain the process of bacterial transformation.
    Transformation is the uptake of naked DNA by a competent recipient cell, which incorporates it into its genome, potentially gaining new traits.
  • What is bacterial competence?
    Competence is a physiological state where bacteria produce proteins to uptake DNA from the environment, either naturally or induced artificially.
  • How does conjugation differ from transformation?
    Conjugation requires direct cell-to-cell contact and a conjugative plasmid, transferring DNA between cells of the same type, unlike transformation which involves free DNA uptake.
  • What is the function of sex pili in conjugation?
    Sex pili are plasmid-encoded structures produced by donor cells to attach to recipient cells and establish a cytoplasmic bridge for DNA transfer.
  • Describe the F plasmid and its role in E. coli conjugation.
    The F plasmid carries genes for sex pili and DNA transfer; F+ cells have it and act as donors, while F- cells lack it and act as recipients.
  • What is rolling circle replication during conjugation?
    It is the process where one strand of the F plasmid is nicked and transferred to the recipient while the complementary strand is synthesized, producing two double-stranded plasmids.
  • Define Hfr cells and their significance.
    Hfr cells have the F plasmid integrated into their chromosome, enabling high-frequency transfer of chromosomal genes during conjugation.
  • What happens during specialized transduction?
    A temperate phage excises incorrectly, carrying specific adjacent bacterial genes which are transferred to a new host, altering its genotype.
  • Explain generalized transduction.
    A bacteriophage mistakenly packages random bacterial DNA fragments during lytic cycle and transfers them to another bacterium, enabling gene transfer.
  • Outline the lytic cycle of a T-even bacteriophage.
    Phage attaches, injects DNA, replicates viral components, assembles new virions, and lyses the host cell to release progeny viruses.
  • What is the lysogenic cycle in bacteriophages?
    Phage DNA integrates into host chromosome as a prophage, replicates with host, and can later excise to enter the lytic cycle under stress.
  • How did Griffith's experiment demonstrate transformation?
    Heat-killed encapsulated bacteria transferred DNA to live non-encapsulated bacteria, transforming them to produce capsules and cause disease.
  • What is the role of DNase in Griffith's experiment?
    DNase destroyed DNA from heat-killed bacteria, preventing transformation and showing DNA is the genetic material.
  • How is transformation monitored experimentally?
    By observing phenotypic changes such as capsule formation or marker gene exchange after DNA uptake and recombination.
  • What is electroporation in bacterial genetics?
    A lab technique using high voltage to temporarily increase membrane permeability, allowing DNA to enter bacterial cells.