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  • What type of replication occurs during conjugation?
  • What occurs to produce an Hfr E. coli cell?
  • What types of traits are encoded on plasmids?

Transposition

Genetic elements called transposons (transposable elements), or “ jumping genes ,” are molecules of DNA that include special inverted repeat sequences at their ends and a gene encoding the enzyme transposase ( [link] ). Transposons allow the entire sequence to independently excise from one location in a DNA molecule and integrate into the DNA elsewhere through a process called transposition . Transposons were originally discovered in maize (corn) by American geneticist Barbara McClintock (1902–1992) in the 1940s. Transposons have since been found in all types of organisms, both prokaryotes and eukaryotes. Thus, unlike the three previous mechanisms discussed, transposition is not prokaryote-specific. Most transposons are nonreplicative, meaning they move in a “cut-and-paste” fashion. Some may be replicative, however, retaining their location in the DNA while making a copy to be inserted elsewhere (“copy and paste”). Because transposons can move within a DNA molecule, from one DNA molecule to another, or even from one cell to another, they have the ability to introduce genetic diversity. Movement within the same DNA molecule can alter phenotype by inactivating or activating a gene.

Transposons may carry with them additional genes, moving these genes from one location to another with them. For example, bacterial transposons can relocate antibiotic resistance genes, moving them from chromosomes to plasmids. This mechanism has been shown to be responsible for the colocalization of multiple antibiotic resistance genes on a single R plasmid in Shigella strains causing bacterial dysentery. Such an R plasmid can then be easily transferred among a bacterial population through the process of conjugation.

Diagram of a transposon. 1: A typical transposon encodes the enzyme transposase, surrounded by inverted repeat sequences. A segment of chromosome shows that the transposon is interspersed between genes. The transposon is made of a gene for transposase and small bands labeled inverted repeat sequence on either side of the gene. 2: Transposase facilitates recombination between inverted repeats. Transposon is cut from its original location and inserted into a new location. This is shown by an oval labeled transposase causing the DNA segment for fold upon itself so the inverted repeats are nearly touching. 3: Transposon targets specific sequences in DNA that will be duplicated, forming direct repeats on either side of the inserted transposon sequence. This is shows as the transposon now sitting in the middle of a gene labeled disrupted gene.
Transposons are segments of DNA that have the ability to move from one location to another because they code for the enzyme transposase. In this example, a nonreplicative transposon has disrupted gene B. The consequence of that the transcription of gene B may now have been interrupted.
  • What are two ways a transposon can affect the phenotype of a cell it moves to?

[link] summarizes the processes discussed in this section.

Summary of Mechanisms of Genetic Diversity in Prokaryotes
Term Definition
Conjugation Transfer of DNA through direct contact using a conjugation pilus
Transduction Mechanism of horizontal gene transfer in bacteria in which genes are transferred through viral infection
Transformation Mechanism of horizontal gene transfer in which naked environmental DNA is taken up by a bacterial cell
Transposition Process whereby DNA independently excises from one location in a DNA molecule and integrates elsewhere

Part 3

Despite continued antibiotic treatment, Mark’s infection continued to progress rapidly. The infected region continued to expand, and he had to be put on a ventilator to help him breathe. Mark’s physician ordered surgical removal of the infected tissue. Following an initial surgery, Mark’s wound was monitored daily to ensure that the infection did not return, but it continued to spread.

After two additional rounds of surgery, the infection finally seemed to be contained. A few days later, Mark was removed from the ventilator and was able to breathe on his own. However, he had lost a great deal of skin and soft tissue on his lower leg.

  • Why does the removal of infected tissue stem the infection?
  • What are some likely complications of this method of treatment?

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Key concepts and summary

  • Horizontal gene transfer is an important way for asexually reproducing organisms like prokaryotes to acquire new traits.
  • There are three mechanisms of horizontal gene transfer typically used by bacteria: transformation , transduction , and conjugation .
  • Transformation allows for competent cells to take up naked DNA, released from other cells on their death, into their cytoplasm, where it may recombine with the host genome.
  • In generalized transduction , any piece of chromosomal DNA may be transferred by accidental packaging of the degraded host chromosome into a phage head. In specialized transduction , only chromosomal DNA adjacent to the integration site of a lysogenic phage may be transferred as a result of imprecise excision of the prophage.
  • Conjugation is mediated by the F plasmid, which encodes a conjugation pilus that brings an F plasmid-containing F + cell into contact with an F - cell .
  • The rare integration of the F plasmid into the bacterial chromosome, generating an Hfr cell , allows for transfer of chromosomal DNA from the donor to the recipient. Additionally, imprecise excision of the F plasmid from the chromosome may generate an F’ plasmid that may be transferred to a recipient by conjugation.
  • Conjugation transfer of R plasmids is an important mechanism for the spread of antibiotic resistance in bacterial communities.
  • Transposons are molecules of DNA with inverted repeats at their ends that also encode the enzyme transposase, allowing for their movement from one location in DNA to another. Although found in both prokaryotes and eukaryotes, transposons are clinically relevant in bacterial pathogens for the movement of virulence factors, including antibiotic resistance genes.

Fill in the blank

A small DNA molecule that has the ability to independently excise from one location in a larger DNA molecule and integrate into the DNA elsewhere is called a ________.

transposon or transposable element

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________ is a group of mechanisms that allow for the introduction of genetic material from one organism to another organism within the same generation.

Horizontal gene transfer

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True/false

Asexually reproducing organisms lack mechanisms for generating genetic diversity within a population.

False

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Short answer

Briefly describe two ways in which chromosomal DNA from a donor cell may be transferred to a recipient cell during the process of conjugation.

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Describe what happens when a nonsense mutation is introduced into the gene encoding transposase within a transposon.

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Questions & Answers

how do i report widal slide results
Isaac Reply
how food can be used as a substrate for the growth of microorganisms
Ashi Reply
what is the importance of understanding chemistry in the field of microbiology and food technology?
Charmaine Reply
What is different between eukaryotes and prokcaryotic
Abia Reply
main difference is that eukaryotic cells possess membrane bound organelles
Iqra
prokaryotes are primitive organisms that doesn't contain membrane bound nucleus or any orgenelle while in eukaryotes membrane bound orgenelles and nucleus is present
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jane Reply
its mean body structure, function, and systems
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study of internal structure of living things
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anatomy is the study structure of the made human
isir
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la science anatomie c'est la science qui nous aide à étudier l'homme
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I dont know
Jeewraj
Linnaeus used Aristotle's criteria for dividing living organisms into kingdoms. Plants are immobile and insensitive, while animals are mobile and sensitive. the creatures he saw through the microscope were mobile, so he attributed them to animals.
Lad
name the different types of media use in lab to detect the micro organisms
Shehzadi Reply
The different types of media used in the lab to detect the microorganisms is known as cell culture..
Tean
solid media or broth is used to grow and detect microorganisms
Pohor
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Baraka
the study of large living organisms
Pratibha
the study of organisms which are micro in range
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process for sterilization
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is a machine used on the process of sterilisation
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autoclave basically do moist heat sterilization while hot air oven do sterilization by dry heat.....
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HUSSAIN
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HUSSAIN
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depends on what to sterilize
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microbes
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it enable a nurse to know the weight and height of a patient
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Tean
Types of micro organisms
Jennifer Reply
Who discovered plant and animal cell
Jennifer
Robert Hooke
Martha
Father of microbiology
Jennifer Reply
Antonie van Leeuwenhoek
Satarupa
Why are mitochondria and chloroplasts unable to multiply outside of a host cell?
Iqra Reply
iqra mitochondria arises from the division of existing mitochondria and they are fused together. they move around inside the cell with the interactions of the cytoskeleton that's why mitochondria unable to multiply outside the host cells chloroplasts has its own separate DNA from the plant cell.
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Umer
icrobiology is the scientific study of these microorganisms. Microorganisms are those organisms that are too small to see with the naked eye and include things like bacteria, fungi, and viruses
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Arif
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Arif
to differentiate between gram positive and gram negative bacty
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medical microbiology means study of microorganisms which are beneficial or harmful for the body. mostly which are studied under microscope by structure and shape appearance. e.g bacteria, viruses, bacteriophage, fungus hyphae and some blood and other body fluids parasites e.g plasmodium etc.
Rana
arif bhai gram staining in which we are given different dyes to the bacterial cell wall and cytoplasm and nucleus.e.g giemsa stain
Rana
Gram staining uses crystal violet to stain cell walls iodine as a mordant and a fuchsin or safranin counterstain to mark all bacteria
Umer
Gram staining uses crystal violet to stain cell walls iodine as a mordant and a fuchsin or safranin counterstain to mark all bacteria
Umer
Gram staining uses crystal violet to stain cell walls iodine as a mordant and a fuchsin or safranin counterstain to mark all bacteria
Umer
Omar baba crystal violet iodine 70% alcohol fuchicine or safranine after every step washing must be done
Rana
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Cristy
*Fuchsin stain
Cristy
*Safranin
Cristy
thanks
Ganesh
difference between epidermophyton trichophyton and microsporum
Ankita Reply
plz answer the question
Iqra
epidermophyton type of fungi causes superficial and cutaneous mycoses trichophyton is also fungi type including parasitic varieties causes dermatophytosis microsporum is also type of fungi causes dermatophytosis.
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Practice MCQ 4

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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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