أسئلة الرابعة ميكرو دمياط (قبل التعديل)
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Questions and Answers

What occurs during the lysogenic cycle of a bacteriophage?

  • The phage DNA integrates at a specific site on bacterial DNA. (correct)
  • Only RNA viruses can undergo this cycle.
  • The bacterial cell is completely lysed immediately.
  • The phage DNA is replicated without integration.

Which mechanism describes the transfer of DNA between two bacterial cells through direct contact?

  • Transduction
  • Transformation
  • Conjugation (correct)
  • Binary Fission

What is formed when the donor cell's F plasmid is transferred to the recipient cell during conjugation?

  • An F- cell
  • A transducing phage
  • An Hfr cell
  • An F+ cell (correct)

What is the primary role of the F pili during bacterial conjugation?

<p>To attach the donor to the recipient cell (A)</p> Signup and view all the answers

In specialized transduction, which part of the bacterial chromosome is primarily involved in the genetic transfer?

<p>The piece of chromosome close to the prophage insertion site (A)</p> Signup and view all the answers

What is the primary form of bacterial genetic material?

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

Which type of extra chromosomal DNA can replicate independently within bacteria?

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

Which component of plasmids is responsible for antibiotic resistance?

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

What is transposition in bacterial genetics?

<p>The process of transposons moving within the genome (C)</p> Signup and view all the answers

What is a distinguishing feature of transposons compared to plasmids?

<p>Transposons can only move within the genome (D)</p> Signup and view all the answers

How many copies of an F-plasmid are typically present in a bacterial cell?

<p>10-15 copies (B)</p> Signup and view all the answers

What is the function of tra genes found in plasmids?

<p>To mobilize plasmids via conjugation (B)</p> Signup and view all the answers

What makes IS transposable elements distinctive?

<p>They encode proteins required for their own transposition (B)</p> Signup and view all the answers

What process allows the spread of antibiotic resistance among bacteria?

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

Which organism is known for exhibiting antigenic variation through programmed rearrangements?

<p>N.gonorrhoeae (A)</p> Signup and view all the answers

How can a bacterial cell become competent to uptake naked DNA?

<p>Treatment with calcium chloride and heat-shock (B)</p> Signup and view all the answers

What role do bacteriophages play in DNA transfer between bacteria?

<p>Mediate transduction by encapsulating bacterial DNA (C)</p> Signup and view all the answers

Which method involves direct uptake of naked DNA by a recipient cell?

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

What is the result of a chromosome fragment being encapsulated in a phage coat?

<p>It leads to genetic recombination in the recipient cell (C)</p> Signup and view all the answers

What happens to bacterial cells during the lysogenic phase after bacteriophage integration?

<p>They may remain inactive for generations (A)</p> Signup and view all the answers

What mechanism involves the transfer of DNA between bacteria via a virus?

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

Which statement accurately describes transformation in bacteria?

<p>It involves the uptake of naked DNA from the environment. (C)</p> Signup and view all the answers

What is a significant trait of generalized transduction?

<p>It can transfer any gene from the donor bacterium. (A)</p> Signup and view all the answers

Which of the following is NOT a role of plasmids in bacteria?

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

Which of the following best defines a non-conjugative plasmid?

<p>A plasmid that cannot be transferred to another bacterium. (C)</p> Signup and view all the answers

How do specialized transduction and generalized transduction differ?

<p>Specialized transduction only transfers certain genes; generalized can transfer any gene. (C)</p> Signup and view all the answers

Which term is used to describe the process where bacteria acquire DNA from their environment?

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

What can be inferred about the spread of antibiotic resistance genes in Proteus species?

<p>Resistance can spread via multiple mechanisms, including transduction. (B)</p> Signup and view all the answers

What is the significance of the integrated F factor in bacterial cells?

<p>It creates a high frequency of recombination when excised. (B)</p> Signup and view all the answers

During specialized transduction, what happens to the bacterial chromosome?

<p>A piece of chromosomal DNA is excised along with the phage DNA. (D)</p> Signup and view all the answers

Which of the following best describes the role of F pili in bacterial conjugation?

<p>They enable the connection between donor and recipient cells. (D)</p> Signup and view all the answers

What type of bacterial cells predominantly experience plasmid transfer through conjugation?

<p>More commonly found in Gram-negative bacilli. (C)</p> Signup and view all the answers

In the context of DNA transfer, what occurs when a donor cell with an F plasmid connects to a recipient cell?

<p>One strand of the plasmid is moved and replicates in the recipient. (B)</p> Signup and view all the answers

How does programmed rearrangement contribute to bacterial survival?

<p>By enabling movement of genes to active sites for expression. (A)</p> Signup and view all the answers

What role does calcium chloride play in transforming bacterial cells?

<p>It increases the permeability of the cell membrane to DNA. (D)</p> Signup and view all the answers

What happens during transduction mediated by bacteriophages?

<p>Random bacterial DNA fragments are transferred through viral infection. (B)</p> Signup and view all the answers

What characterizes the lytic cycle of a bacteriophage?

<p>The bacterial DNA can be accidentally packaged and transferred to new cells. (A)</p> Signup and view all the answers

How do competent cells allow for the uptake of naked DNA?

<p>They modify their membrane structure to enhance DNA binding. (D)</p> Signup and view all the answers

What is the role of bacteriophages in horizontal gene transfer?

<p>They facilitate the movement of bacterial DNA without direct contact. (C)</p> Signup and view all the answers

What is the mechanism by which a bacterium can acquire DNA from the environment?

<p>Natural competence for DNA uptake. (A)</p> Signup and view all the answers

What is the significance of antigenic variation in bacteria?

<p>It helps bacteria evade host immune responses. (C)</p> Signup and view all the answers

What mechanism allowed Proteus species to acquire antibiotic resistance genes similar to those in Pseudomonas and Escherichia?

<p>Transduction by bacteriophages (A), Conjugation through pili formation (C), Transformation via environmental DNA (D)</p> Signup and view all the answers

In what way do generalized transduction and specialized transduction differ?

<p>Generalized transduction transfers random DNA; specialized transduction transfers specific DNA. (C)</p> Signup and view all the answers

Which of the following statements accurately describes transformation in bacteria?

<p>It involves uptake of naked DNA from the environment. (A)</p> Signup and view all the answers

Which characteristic differentiates transposons from plasmids in terms of replication?

<p>Transposons lack their own replication genes and rely on the host genome. (A)</p> Signup and view all the answers

Which component plays a critical role in bacterial conjugation?

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

What is a significant function of the tra genes found in certain plasmids?

<p>They code for proteins that facilitate the mobilization of plasmids between bacterial cells. (B)</p> Signup and view all the answers

What is the primary source of genetic material transferred during transduction?

<p>Segment of the host's chromosome (D)</p> Signup and view all the answers

Which statement regarding naked DNA in transformation is true?

<p>It can confer specific traits such as antibiotic resistance. (D)</p> Signup and view all the answers

Which type of plasmid is primarily responsible for carrying genes related to antibiotic resistance?

<p>R plasmids. (D)</p> Signup and view all the answers

What essential property do transposons possess that enables them to integrate into the genome?

<p>They include specialized sequences that facilitate their movement. (A)</p> Signup and view all the answers

Why might a bacterium prefer transformation as a means of genetic exchange?

<p>It circumvents the need for cell-to-cell contact. (D)</p> Signup and view all the answers

What describes the role of bacteriophages in generalized transduction?

<p>They randomly encapsulate host DNA. (D)</p> Signup and view all the answers

What best describes the typical structure of plasmids found in bacteria?

<p>Circular double-stranded DNA capable of independent replication. (C)</p> Signup and view all the answers

Which characteristic of transposons is associated with their classification as 'jumping genes'?

<p>They can move from one location in the genome to another, including plasmids. (A)</p> Signup and view all the answers

Which of the following statements accurately depicts the role of plasmids in bacterial genetics?

<p>Plasmids can carry genes for antibiotic resistance, fertility, and toxins. (B)</p> Signup and view all the answers

What is the primary function of the 'F-plasmid' in bacteria?

<p>To facilitate the formation of sex pili for conjugation. (C)</p> Signup and view all the answers

Flashcards

Bacterial Genome

The complete set of genetic information in a bacterium, typically a single circular DNA molecule.

Nucleoid

The region within a bacterial cell where the circular DNA molecule is located.

Plasmid

Small, circular DNA molecule that exists independently of the bacterial chromosome.

Transposon

A piece of DNA that can move from one location to another within the genome.

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Transposition

The process of a transposon being excised and re-integrated into the DNA molecule.

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IS Element

The simplest type of transposon, encoding only the proteins needed for its own transposition.

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Composite Transposon

A transposon that contains two IS elements flanking a central piece of DNA that might carry genes like antibiotic resistance.

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Tn3 Transposon

A type of transposon that doesn't have IS elements but still encodes proteins for transposition and carries genes for antibiotic resistance or virulence.

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Antibiotic Resistance Spread

Transfer of a plasmid containing antibiotic resistance genes from one bacterium to another via conjugation.

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Antigenic Variation

Changes in surface proteins of a pathogen, like Neisseria gonorrhoeae, through gene movement, allowing it to evade the host's immune system.

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Transformation

The process where a bacterium directly takes up naked DNA from its environment.

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Artificial Transformation

Induced uptake of DNA into a cell in a laboratory setting, often using calcium chloride and heat shock.

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Electroporation

A method to introduce DNA into cells by applying an electric field, creating temporary pores in the membrane.

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Transduction

Transfer of DNA from a donor cell to a recipient cell mediated by a bacteriophage.

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Lytic Cycle

A viral replication cycle where a bacteriophage infects a cell, replicates, and lyses the cell, releasing new phages.

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Generalized Transduction

A type of transduction where any piece of bacterial DNA can be packaged inside a phage and transferred to another bacteria.

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Lysogenic Cycle

A viral replication cycle where the phage DNA integrates into the host bacterial chromosome, becoming a prophage and replicating along with the host DNA. This integration can lead to specialized transduction.

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Specialized Transduction

A type of transduction where only specific bacterial genes near the prophage insertion site are transferred to a recipient cell. This occurs when the phage DNA is excised from the host chromosome, taking a piece of bacterial DNA with it.

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Conjugation

A process of horizontal gene transfer where bacteria exchange genetic material through direct contact. This involves a donor cell with an F plasmid containing the tra gene, which enables the formation of F pili for attachment and DNA transfer.

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F Factor

A plasmid that carries genes for the production of F pili, enabling conjugation. It can integrate into the bacterial chromosome, creating an Hfr cell.

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Hfr Cell

A bacterial cell with the F factor integrated into its chromosome. This integration leads to high recombination rates and allows the transfer of chromosomal genes during conjugation.

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Horizontal Gene Transfer

The transfer of genetic material between organisms that are not related by descent, like bacteria sharing genes through conjugation, transformation, or transduction.

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Non-conjugative Plasmid

A plasmid that cannot initiate conjugation, as it lacks the necessary genes for pilus formation and DNA transfer.

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Functions of a Plasmid

Plasmids can carry genes for antibiotic resistance, toxin production, virulence factors, metabolic pathways, and more, providing bacteria with advantages like survival in harsh environments or even causing disease.

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Laboratory-Induced Competence

Inducing a bacterium to take up foreign DNA. This is done in labs by using methods like adding calcium chloride and heat shock.

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What are plasmids?

Plasmids are small, circular DNA molecules that exist independently of the bacterial chromosome. They replicate independently and can carry genes for various functions, like antibiotic resistance.

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How do plasmids replicate?

Plasmids have their own origin of replication, meaning they can replicate independently from the bacterial chromosome. This allows them to exist and multiply even when the bacterial chromosome is not replicating.

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What is a transposon?

A transposon is a piece of DNA that can move from one location to another within the genome. They are also known as 'jumping genes' and can carry genes like antibiotic resistance.

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What is transposition?

Transposition is the process by which a transposon moves from one location to another within a genome. It involves the transposon being excised and then reintegrated at a new location.

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What is an IS element?

An IS element is the simplest type of transposon. It only encodes the proteins needed for its own transposition, meaning it can only move itself.

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What is a composite transposon?

A composite transposon is a more complex transposon containing two IS elements flanking a central piece of DNA. This central region often carries genes like antibiotic resistance.

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What is a Tn3 transposon?

A Tn3 transposon is a type of transposon that doesn't have IS elements but still encodes proteins for transposition and carries genes like antibiotic resistance or virulence factors.

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How do transposons spread antibiotic resistance?

Transposons can 'jump' from one location to another, potentially landing on a plasmid. If this plasmid is then transferred to another bacterium through conjugation, antibiotic resistance genes carried by the transposon are also transferred, spreading resistance.

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Study Notes

Bacterial Genetics

  • Bacterial genome: single, circular DNA molecule forming the nucleoid
  • Some bacteria have extra-chromosomal DNA: plasmids, transposons
  • Plasmids are pieces of DNA separate from the chromosome, containing an origin of replication and independently replicating
  • Plasmids carry antibiotic resistance (R plasmids), fertility (F plasmids), toxins, enzymes, and bacteriocin
  • Plasmids are used as cloning vectors in molecular biology
  • Plasmids can exist as various sizes and copy numbers (1-2 copies/cell, 10-15 copies/cell, etc.)
  • Plasmids are typically circular and closed-circular (CCC)
  • Some linear plasmids are unstable due to exonuclease attack
  • Conjugative plasmids have tra genes that mobilize plasmid from one cell to another and are transmissible
  • Non-conjugative plasmids can't be mobilized under known conditions
  • Natural plasmids exist naturally in bacteria
  • Artificial plasmids are modified to be used as vectors
  • Transposons: extra chromosomal small pieces of DNA capable of moving themselves from one location to another on the genome
  • They are movable elements (jumping genes)
  • Transposition is the process by which transposons excise and re-integrate into DNA.
  • Transposons often contain an enzyme called transposase
  • Some transposons code for drug resistance
  • Composite transposons contain two insertion sequences (IS elements) flanking a central region of DNA
  • Non-composite transposons do not have IS elements
  • Tn10: encodes for tetracycline resistance
  • Bacteria possess genes on silent storage locations which can be moved to active sites, resulting in antigenic variations and immune evasion
  • Method of Bacterial Gene Transfer, Within the Bacterial Cells, Transposons transfer DNA from one site on bacterial chromosome to another site or to a plasmid, subsequent transfer of the plasmid leads to spread of antibiotic resistance
  • Non-composite transposons: do not have IS but contain genes for transposition, antibiotic resistance or virulence
  • Plasmids can be important for antibiotic resistance, toxins, or enzymes, among other properties
  • Transduction is the transfer of DNA from one bacterium to another by a bacteriophage (virus)
  • Bacteriophages can have lytic or lysogenic cycles:
    • Lytic cycle: bacteriophage destroys host cells
    • Lysogenic cycle: bacteriophage integrates into the host genome
  • Conjugation: gene transfer by direct contact between bacteria cells
  • Conjugation requires a donor (F+ cell with F plasmid containing tra gene) and a recipient (F- cell)
  • F pili form a conjugation bridge enabling plasmid transfer to the recipient (F+ cell)
  • An Hfr (High Frequency Recombination) cell occurs when the F plasmid integrates into the host chromosome. Transfer of chromosomal DNA from the donor to the recipient cell during conjugation
  • Transformation: direct uptake of naked DNA by a recipient cell

Questions

  • Non-conjugative plasmid: a plasmid that cannot trigger the conjugation process
  • Transfer of DNA from donor cells to recipient cells by bacteriophage: transduction

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