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Microbiology: Microbial Genetics Flashcards

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  1. Which of the following correctly describes the process of specialized transduction?

    Answer: Only genes adjacent to the prophage integration site are transferred

    In specialized transduction, imprecise excision of the prophage causes nearby host genes to be packaged with phage DNA, so only specific chromosomal regions are transferable.

  2. A bacterium that has gained antibiotic resistance through transformation has most likely:

    Answer: Taken up naked DNA from the environment

    Transformation involves uptake of free exogenous DNA from the environment, and resistance genes on this DNA can integrate into the bacterial chromosome or be maintained as a plasmid.

  3. The Ames test uses bacteria to assess mutagenicity by measuring which of the following?

    Answer: Reversion of histidine-requiring mutants to prototrophy

    The Ames test uses his− Salmonella strains; a mutagen increases the rate of reversion to his+, which is detected as colonies growing on histidine-free medium.

  4. In attenuator-regulated operons such as the trp operon, transcription is terminated prematurely when:

    Answer: Tryptophan is abundant and ribosomes translate the leader peptide rapidly

    When tryptophan is plentiful, charged Trp-tRNA allows rapid translation of the leader peptide, favoring formation of a terminator hairpin that arrests transcription.

  5. Which of the following horizontal gene transfer mechanisms requires direct cell-to-cell contact?

    Answer: Conjugation

    Conjugation requires physical contact between donor and recipient cells through a pilus and mating bridge to transfer DNA.

  6. A point mutation that converts a sense codon to UAA, UAG, or UGA results in which type of mutation?

    Answer: Nonsense mutation

    Nonsense mutations change an amino acid–coding codon into a stop codon (UAA, UAG, or UGA), causing premature termination of translation.

  7. In DNA mismatch repair (MMR), how does the repair system distinguish the template strand from the newly synthesized (potentially mismatched) strand in bacteria?

    Answer: By the methylation status of GATC sequences (Dam methylation)

    The newly synthesized strand is transiently undermethylated at GATC sequences, allowing MMR enzymes to identify and excise errors from the new strand rather than the parental template.