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Bacterial Genetics - Lecture 5
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Bacterial Genetics - Lecture 5

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Questions and Answers

What feature distinguishes bacterial chromosomes from eukaryotic chromosomes?

  • Bacterial chromosomes are circular and exist free in the cytoplasm. (correct)
  • Bacterial chromosomes are diploid and contain two copies of each gene.
  • Bacterial chromosomes contain multiple linear DNA strands.
  • Bacterial chromosomes are surrounded by a nuclear membrane.

    • How does the length of the DNA molecule in E. coli compare to that in yeast cells?

  • E. coli's DNA is about 1mm long, significantly shorter than that in yeast. (correct)
  • E. coli's DNA is shorter but has a more complex folding structure than yeast.
  • E. coli has a longer DNA molecule due to more genes than yeast.
  • E. coli's DNA is about three times longer than that of yeast.

    • What is the primary role of RNA polymerase during transcription?

  • To degrade mRNA after protein synthesis.
  • To form a single polyribonucleotide strand from DNA. (correct)
  • To replicate the circular DNA molecule.
  • To translate mRNA into proteins.

    • What does the term 'coupled' signify in the context of bacterial transcription and translation?

    <p>They occur simultaneously at the same ribosome.</p> Signup and view all the answers

    Which characteristic is true about the genomes of bacteria?

    <p>Most bacteria are haploid with a single circular chromosome.</p> Signup and view all the answers

    What is the approximate number of genes present in E. coli?

    <p>Approximately 4000 genes.</p> Signup and view all the answers

    Which process follows transcription in the central dogma of molecular biology?

    <p>Translation</p> Signup and view all the answers

    What key function do topoisomerase enzymes serve in bacterial DNA?

    <p>They aid in supercoiling the DNA structure.</p> Signup and view all the answers

    What is the process called when bacterial DNA replication begins at one point and moves in both directions?

    <p>Bidirectional replication</p> Signup and view all the answers

    Which enzymes assist in the supercoiling and resolution of daughter chromosomes during bacterial DNA replication?

    <p>Topoisomerases</p> Signup and view all the answers

    What type of antibiotics bind to RNA polymerase to inhibit the initiation of transcription?

    <p>Rifamycins</p> Signup and view all the answers

    Which of the following antibiotics prevents translation by interfering with the attachment of mRNA to ribosomes?

    <p>Spectinomycin</p> Signup and view all the answers

    What is the typical number of chromosomes present in a growing bacterial cell?

    <p>1 to 4</p> Signup and view all the answers

    Which group of antibiotics is known to block the elongation phase of polypeptide synthesis?

    <p>Tetracyclines</p> Signup and view all the answers

    Antibiotics like aminoglycosides are known for inhibiting which specific phase of protein synthesis?

    <p>Initiation</p> Signup and view all the answers

    Which process is characterized by the random uptake of disintegrating host DNA by a phage during assembly?

    <p>Generalized transduction</p> Signup and view all the answers

    What are pathogenicity islands responsible for in certain bacteria?

    <p>Enabling the bacterium to become pathogenic</p> Signup and view all the answers

    Which of the following statements is true regarding specialized transduction?

    <p>It incorporates highly specific parts of the host genome</p> Signup and view all the answers

    Which bacterium is mentioned as capable of causing disease through a mechanism involving exotoxins?

    <p>Corynebacterium diphtheriae</p> Signup and view all the answers

    Which bacterial capability is commonly associated with the pathogenicity island of Yersinia pestis?

    <p>Iron scavenging</p> Signup and view all the answers

    What is the primary function of plasmids in bacteria?

    <p>Confer drug resistance and toxigenicity</p> Signup and view all the answers

    How do transposons contribute to drug resistance in bacteria?

    <p>They jump between plasmids, creating diverse genetic material</p> Signup and view all the answers

    What is an episome?

    <p>Circular DNA that can integrate into bacterial chromosomes</p> Signup and view all the answers

    Which of the following best describes horizontal gene transfer?

    <p>Any DNA transfer resulting in new gene acquisition</p> Signup and view all the answers

    What is the key characteristic differentiating plasmids from transposons?

    <p>Plasmids can replicate independently; transposons cannot</p> Signup and view all the answers

    What role do R plasmids play in bacterial cells?

    <p>Conferring resistance to antibiotics</p> Signup and view all the answers

    Which type of genetic material is essential for the survival of a bacterium?

    <p>Chromosomal DNA</p> Signup and view all the answers

    What distinguishes plasmids from chromosomal fragments in terms of replication?

    <p>Plasmids have origins of replication, while fragments must integrate into the chromosome.</p> Signup and view all the answers

    What effect do transposons have when they create insertion mutations?

    <p>They disrupt a gene's normal sequence and function</p> Signup and view all the answers

    Which method of gene transfer specifically uses a bacteriophage?

    <p>Transduction</p> Signup and view all the answers

    In the conjugation process, what happens to the F− cell after it receives the F factor from the F+ cell?

    <p>The F− cell becomes an F+ cell capable of conjugation.</p> Signup and view all the answers

    What is a characteristic of high-frequency recombination (Hfr) during conjugation?

    <p>The plasmid integrates into the donor chromosome before transfer.</p> Signup and view all the answers

    Resistance plasmids (R factors) are significant for which aspect of bacterial genetics?

    <p>They confer resistance to a wide range of antibiotics and heavy metals.</p> Signup and view all the answers

    What is the main purpose of transformation in bacteria?

    <p>To absorb naked DNA from the environment into a recipient cell.</p> Signup and view all the answers

    In terms of genetic exchange, what advantage does a bacterium gain by using transduction?

    <p>It uses viral vectors to transfer large DNA segments efficiently.</p> Signup and view all the answers

    What defines the difference between R factors related to antibiotic resistance and those related to virulence?

    <p>Virulence-related R factors can synthesize toxins and adhesion molecules.</p> Signup and view all the answers

    Study Notes

    Bacterial Genetics Overview

    • Bacterial genetics serves as a model system for understanding DNA replication, genetic variation, and gene transfer.
    • Bacteria have a single circular chromosome that is about 1000 times longer than the cell itself, existing in a supercoiled form.
    • The bacterial chromosome is not contained within a nuclear membrane, but rather is found free in the cytoplasm, organized into chromatin bodies.
    • During exponential growth, bacterial chromosomes can replicate approximately every 20 minutes.

    Prokaryotic Genome Characteristics

    • Prokaryotic genomes, such as that of E. coli, are compact with minimal intergenic space, containing around 4000 genes in a DNA molecule approximately 1 mm in length.
    • Yeast cells have around 6000 genes in a genome three times larger than that of E. coli.
    • Bacteria are haploid, possessing a single chromosome with one copy of each gene.

    Central Dogma of Molecular Biology

    • The central dogma is depicted as DNA → RNA → Polypeptide.
    • Transcription involves RNA polymerase synthesizing mRNA from a DNA template.
    • Ribosomes facilitate the translation of mRNA into proteins, utilizing transfer RNA (tRNA).

    Coupled Transcription and Translation

    • In bacteria, transcription and translation occur simultaneously due to the lack of a nuclear membrane.
    • This coupling allows bacteria to respond rapidly to environmental changes.

    DNA Replication in Bacteria

    • Replication initiates at a single point on the circular DNA, proceeding bidirectionally.
    • The number of chromosomes per bacterial cell can range from one to four during growth.
    • Topoisomerases assist in managing supercoiling and separating daughter chromosomes prior to cell division.

    Enzymes in DNA Replication

    • Specific enzymes are involved in proofreading and preventing supercoiling.
    • Enzymes help in connecting gaps formed during replication.

    Antibiotics Affecting Transcription and Translation

    • Rifamycins inhibit transcription by blocking RNA polymerase initiation, targeting bacterial rather than eukaryotic enzymes.
    • Erythromycin and spectinomycin impede translation by disrupting mRNA-ribosome attachment.
    • Chloramphenicol, lincomycin, and tetracycline obstruct the elongation of polypeptides by binding to the ribosome.
    • Aminoglycosides, including streptomycin, inhibit both initiation and elongation of peptide synthesis.

    Extrachromosomal Genetic Material

    • Plasmids are circular DNA molecules that replicate independently and can integrate into bacterial chromosomes.
    • They carry genes relevant to drug resistance and virulence factors, such as R plasmids and F plasmids.
    • Transposons (jumping genes) can move between plasmids and chromosomes, facilitating genetic diversity and antibiotic resistance.

    Horizontal Gene Transfer

    • Horizontal gene transfer allows bacteria to acquire new genes from non-parental sources.
    • Mechanisms include transformation (direct DNA uptake), transduction (gene transfer via bacteriophages), and conjugation (DNA transfer through sex pili).
    • Plasmids can carry and propagate resistance traits during this transfer.

    Conjugation Process

    • DNA is exchanged between donor (F+) and recipient (F−) cells through a conjugation tube.
    • In high-frequency recombination (Hfr), plasmids integrate into the donor chromosome, allowing for additional gene transfer.

    Genetic Information Transfer

    • Transformation involves the uptake of genetic material directly from the environment.
    • Transduction allows viral mechanisms to facilitate the transfer of bacterial genes.

    Pathogenicity Islands

    • Horizontally transferred genes can endow bacteria with pathogenic traits, called pathogenicity islands.
    • These islands coordinate multiple genes enhancing virulence, such as the ability to produce toxins.

    Mutations and Genetic Changes

    • Mutations can result from errors in DNA replication or exposure to mutagens, leading to alterations in nucleotide sequences.
    • Bacteria possess DNA repair mechanisms, but excessive damage may result in permanent mutations.

    Summary of Gene Transfer Mechanisms

    • Major mechanisms include transformation, transduction, and conjugation, each contributing to genetic diversity and adaptability in bacterial populations.

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    Description

    Explore the fascinating world of bacterial genetics in this quiz from Dr. Janita Pinto's lecture. Discover how bacterial DNA replication, genetic characteristics, and their transfer to future generations are studied. This quiz will challenge your understanding of the bacterial chromosome and its structure.

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