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Questions and Answers

What is an example of a base-pair mutagen?

  • 5-bromouracil
  • Aflatoxin
  • Photolyase
  • Nitrous acid (correct)
  • Which type of mutation involves the insertion or deletion of a base that alters the downstream reading frame?

  • Frameshift mutation (correct)
  • Silent mutation
  • Point mutation
  • Substitution mutation
  • Which method of horizontal genetic recombination involves the uptake of naked DNA from the environment?

  • Conjugation
  • Replication
  • Transformation (correct)
  • Transduction
  • Which of the following is a mechanism specifically used for repairing thymine dimers caused by UV radiation?

    <p>Excision repair</p> Signup and view all the answers

    Which type of gene is characterized by being always required and hence transcription is always 'on'?

    <p>Constitutive genes</p> Signup and view all the answers

    What type of mutation is caused by ionizing radiation, such as X-rays and gamma rays?

    <p>DNA damage mutation</p> Signup and view all the answers

    What is a common result of a missense mutation?

    <p>A single amino acid change in the protein</p> Signup and view all the answers

    What primarily causes spontaneous mutations in DNA?

    <p>Errors during DNA replication</p> Signup and view all the answers

    Which of the following mutations introduces a stop codon prematurely?

    <p>Nonsense mutation</p> Signup and view all the answers

    In the lac operon, what triggers the transcription of lactose-metabolizing enzymes?

    <p>The presence of lactose</p> Signup and view all the answers

    Study Notes

    Untitled Presentation

    • The presentation has 27 slides.
    • There is content on every slide of the presentation.
    • The presentation has no title given.

    Gene Regulation in Prokaryotes

    • Prokaryotes control gene expression primarily by regulating transcription.
    • Many genes are co-regulated through operon systems.
    • There are three types of genes:
      • Constitutive: Always transcribed, with gene products always needed.
      • Repressible: Usually on but can be turned off, often by the end product of the metabolic pathway.
      • Inducible: Usually off but can be turned on, typically by the presence of a specific substrate.

    Lac Operon

    • Composed of genes responsible for lactose metabolism.
    • Functions as an inducible system.
    • Normally "off" because lactose is not commonly present.
    • Induced when lactose is present.

    Mutation

    • A change in DNA sequence.
    • Can be spontaneous or induced.
    • May or may not alter the amino acid sequence of a protein.
    • Types of mutations:
      • Point Mutations: Single base change.
        • Silent: No change in amino acid sequence.
        • Missense: Single amino acid change.
        • Nonsense: Introduction of a premature stop codon.
      • Frameshift: Insertion or deletion of a base, changing the reading frame downstream.

    Causes of Mutations

    • Chemical mutagens:
      • Base-pair mutagens: Alter base-pairing rules.
      • Base analogs: Incorporated as nucleotides but have altered base-pairing rules.
      • Frameshift mutagens: Intercalate into DNA and cause DNA polymerase to make insertions or deletions.
    • Radiation:
      • Ionizing: Damages DNA, creates free radicals.
      • Nonionizing: Creates thymine dimers.

    Detecting Mutagens: Ames Test

    • Utilizes an auxotrophic strain of Salmonella typhimurium.
    • Requires histidine (his-) for growth.
    • Measures the frequency of revertants to his+ phenotype, which is increased in the presence of mutagens.

    Horizontal Genetic Exchange

    • Transfer of genetic information between members of the same generation.
    • Occurs exclusively in prokaryotes.

    Three Methods of Horizontal Recombination

    • Transformation: Uptake of "naked" DNA by competent cells.
    • Transduction: Transfer of DNA by bacteriophages.
      • Generalized Transduction: Bacteriophage packages host DNA into new phage particles.
    • Conjugation: Transfer of genetic material via a sex pilus.
      • F+ Conjugation: F plasmid containing the genes for sex pilus is transferred from F+ cell to F- cell.

    Transformation

    • Competent cells are able to take up "naked" DNA.
    • Recombination can occur when DNA sequences are homologous, replacing the old DNA sequence with the new one
    • Results in the recipient cell acquiring a new trait.

    Transduction

    • Bacteriophage packages host DNA into new phage particles.
    • Recipient cell acquires new traits.

    Conjugation

    • Requires a sex pilus encoded by the F plasmid.
    • In standard F+ conjugation, a copy of the F plasmid is transferred from the donor (F+) cell to the recipient (F-) cell, making the recipient cell F+.

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    This quiz assesses your understanding of the content covered in a 27-slide presentation. Each slide contains essential information, and this quiz will help you review and retain the key concepts presented. Test your knowledge and ensure you grasp the material thoroughly.

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