Bacteriophage and Its Replication Cycles

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Questions and Answers

What are the main components of a bacterial genome?

  • R factors, F factors, and bacterial chromosome
  • Only plasmids and prophage
  • Bacterial chromosome, plasmids, and prophage (correct)
  • Plasmids and DNA fragments only

Which statement accurately describes plasmids?

  • Plasmids are usually larger and contain more genes than the bacterial chromosome.
  • Plasmids can be lost spontaneously during bacterial replication. (correct)
  • Plasmids can be either circular or linear DNA segments.
  • Plasmids are essential for bacterial growth and replication.

What function do R factors serve in bacteria?

  • They store energy for bacterial metabolism.
  • They promote the formation of sex pili for reproduction.
  • They provide structural integrity to the bacterial cell.
  • They confer resistance to antibiotics and toxins. (correct)

The F factor in plasmids is primarily associated with which function?

<p>Coding for sex pilus formation for bacterial conjugation (A)</p> Signup and view all the answers

Which of the following statements about plasmids is true?

<p>Plasmids may contain genes related to adhesion and invasion. (A)</p> Signup and view all the answers

What shape is the head of a bacteriophage?

<p>Hexagonal (A)</p> Signup and view all the answers

What occurs during the penetration stage of the lytic cycle?

<p>The bacteriophage injects its DNA into the bacterium (C)</p> Signup and view all the answers

Which process describes the detachment of prophage from the bacterial chromosome?

<p>Prophage induction (A)</p> Signup and view all the answers

What is the key distinction of the lysogenic cycle compared to the lytic cycle?

<p>It incorporates phage DNA into the bacterial genome (C)</p> Signup and view all the answers

What is a potential outcome for a bacterium that incorporates prophage DNA?

<p>It may acquire new properties from the phage (B)</p> Signup and view all the answers

Which step occurs last in the lytic cycle?

<p>Release of mature bacteriophages (D)</p> Signup and view all the answers

During specialized transduction, what happens to the bacterial DNA?

<p>It is incorporated into a different bacterium (B)</p> Signup and view all the answers

What is the role of the tail fibers in bacteriophages?

<p>To bind to the bacterial cell wall receptors (C)</p> Signup and view all the answers

Which of the following is NOT a component of the bacteriophage structure?

<p>Ribosomes (C)</p> Signup and view all the answers

What is a mutation?

<p>A permanent change in the DNA base sequence. (B)</p> Signup and view all the answers

Which of the following best describes a single-base mutation?

<p>Replacement of one base in the DNA sequence with another base. (D)</p> Signup and view all the answers

What is a frame-shift mutation?

<p>The addition or removal of one or more nucleotide pairs, changing the reading frame. (A)</p> Signup and view all the answers

What causes spontaneous mutations?

<p>Mistakes during DNA replication. (A)</p> Signup and view all the answers

What is an induced mutation?

<p>A mutation caused by exposure to mutagens such as chemicals or radiation. (C)</p> Signup and view all the answers

Which mechanism of gene transfer involves direct contact between two bacterial cells?

<p>Conjugation (A)</p> Signup and view all the answers

Which statement is true about conjugation?

<p>It requires the presence of a sex pilus and an F plasmid. (C)</p> Signup and view all the answers

What role does the F plasmid play in conjugation?

<p>It carries the genes necessary for the formation of the sex pilus. (D)</p> Signup and view all the answers

Which of the following is NOT a method of gene transfer between bacterial cells?

<p>Transcription (D)</p> Signup and view all the answers

What is the primary consequence of a mutation altering the DNA sequence?

<p>It can potentially change the protein that is encoded. (C)</p> Signup and view all the answers

Which mechanism involves the transfer of DNA through a bacterial virus?

<p>Transduction (C)</p> Signup and view all the answers

What is the primary method by which transformation occurs?

<p>Uptake of DNA from the environment (A)</p> Signup and view all the answers

Which of the following is true about the competence of bacteria in transformation?

<p>Only a few bacterial species can transform naturally. (D)</p> Signup and view all the answers

What occurs during the natural process of transformation?

<p>Dying bacteria release their DNA for absorption. (D)</p> Signup and view all the answers

Which mechanism is characterized by its ability to be artificially induced?

<p>Transformation (C)</p> Signup and view all the answers

Which of the following statements is false regarding transduction?

<p>It can occur between any bacterial strains. (D)</p> Signup and view all the answers

What distinguishes transformation from transduction?

<p>Transformation involves only DNA uptake, not a virus. (B)</p> Signup and view all the answers

Which of the following processes does not utilize a bacterial virus for DNA transfer?

<p>Transformation (B)</p> Signup and view all the answers

What potential limitation does transformation have compared to transduction?

<p>Transformation can only happen in dense bacterial populations. (D)</p> Signup and view all the answers

How is competence primarily defined in the context of bacterial transformation?

<p>The innate capacity of bacteria to take up foreign DNA. (D)</p> Signup and view all the answers

Flashcards

Bacteriophage

A virus that infects bacteria

Lytic Cycle

Bacteriophage replication cycle ending with cell lysis

Attachment/Adsorption

Bacteriophage binding to the host bacterial cell

Penetration

Bacteriophage injecting its DNA into the host cell

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Biosynthesis

Viral nucleic acid and protein synthesis

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Assembly

Joining viral parts to create new bacteriophages

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Release

New phages released, often causing cell lysis

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Lysogenic Cycle

Bacteriophage replication cycle without immediate cell lysis

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Prophage

Integrated phage DNA inside host cell's genome

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Immunity

Resistant to further infection by the same phage type

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Specialized Transduction

Transfer of bacterial DNA along with phage DNA

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New Properties

Bacterial cell gains new traits from prophage

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Transduction

Transfer of bacterial DNA using a virus (bacteriophage).

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Transformation

Direct uptake of donor DNA by a recipient bacterial cell.

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Natural Transformation

Recipient cell takes up DNA released by dying bacteria.

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Bacterial Competence

Ability of a bacterium to take up DNA from the environment.

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Bacterial Variation

A change in bacterial characteristics.

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Mutation

A permanent change in a bacterial DNA base sequence that can alter protein products.

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Single-base mutation

A point mutation; a single base is substituted with a different base in the DNA sequence.

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Frame-shift mutation

One or more nucleotides are added or deleted, changing the reading frame during translation.

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Spontaneous mutation

A mutation that occurs without outside influences, often due to mistakes during DNA replication.

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Induced mutation

A mutation caused by mutagens (e.g., chemicals, radiation).

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Conjugation

Genetic transfer between bacteria where one cell passes DNA to another through a connecting tube.

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F plasmid

Plasmid carrying genes for the sex pilus (conjugation tube) and controlling conjugation.

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Gene transfer

Transfer of genetic material between bacterial cells through conjugation, transduction, or transformation.

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Plasmid Definition

Circular, extra-chromosomal DNA, smaller than bacterial chromosome, often carrying non-essential genes.

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Plasmid Function (F factor)

Codes for sex pilus formation, enabling plasmid transfer between bacteria via conjugation.

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Plasmid Function (R factor)

Codes for antibiotic resistance, heavy metal resistance or toxin resistance. Genes spread through bacteria.

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Plasmid Function (Virulence)

Codes for bacterial properties like adhesion, invasion etc., which make bacteria pathogenic.

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Plasmid Characteristics

Plasmids are small, non-essential, extra-chromosomal DNA, capable of independent replication, and easily transferred.

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Study Notes

Bacteriophage

  • Definition: Virus that infects bacteria.
  • Morphology of Bacteriophage
    • Head: Hexagonal, contains nucleic acid core, with a protein coat (capsid).
    • Tail: Hollow core surrounded by contractile sheath, ends by a plate with fibers.

Replication cycle

  • Bacteriophages can multiply by two alternative mechanisms: the lytic cycle or the lysogenic cycle.
  • The lytic cycle ends with the lysis and death of the host cell, whereas the host cell remains alive in the lysogenic cycle.

Lytic cycle

  • Attachment or adsorption: Bacteriophages use fibers at the end of the tail as attachment sites. The complementary receptor sites are on the bacterial cell wall.
  • Penetration: Bacteriophage injects its DNA (nucleic acid) into the bacterium.
  • Biosynthesis: Once the bacteriophage DNA has reached the cytoplasm of the host cell, the biosynthesis of viral nucleic acid and protein occurs.
  • Assembly: In this process, bacteriophage DNA and capsids are assembled into complete virion.
  • Release: The final stage of viral multiplication is the release of virions from the host cell after lysis.

Lysogenic cycle (Temperate cycle)

  • Some phages do not cause lysis and death of the host cell when they multiply. These lysogenic phages (also called temperate phages) capable of incorporating their DNA into the host cell's DNA to begin a lysogenic cycle.
  • The inserted phage DNA is now called a prophage.

Effect of prophage on the infected bacteria

  • Immunity to infection by another phage of the same type.
  • Acquire new properties

Outcome of the temperate cycle

  • Pass to daughter cells
  • Detach from the bacterial chromosome and start lytic cycle
  • Detach with a part of the bacterial chromosome and when infect another bacteria carries new properties of both the phage and the 1st bacterium (donor bacterium) and this called specialized transduction.

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