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


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?

Jump to the next Clinical Focus box. Go back to the previous Clinical Focus box.

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

Got questions? Get instant answers now!

________ 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

Got questions? Get instant answers now!


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


Got questions? Get instant answers now!

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.

Got questions? Get instant answers now!

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

Got questions? Get instant answers now!

Questions & Answers

Hi, I'm new here. I'm Bello Abdul Hakeem from Nigeria.
welcome on board
Thanks brother I'm an undergraduate. I hope to study for MBBS.
pls guys help me out
what is limitation of plate
limitation of plate load test . there are some that should be considered while performing load test which are given below, this test is usually performed on relatively similar plate ,usually 1 or 2 square foot area the reason is that the plate of greater are the economically not feasible
Mechanism of bacterial pathogenicity
rashida Reply
write a short note on Algea
najaatu Reply
green minutes plants organisms that are produced in turf.
Algae is a kind of a photosynthetic organism, which is usually grown in the moist areas. These are usually the simple plants that grow near to the water bodies. It contains a kind of chlorophyll pigments that act as a primary coloring agent.
they are eukaryotic and most lived in fresh water. they are photosynthetic that's, they contain chlorophyll and store starch in discrete chloroplast.
are bacteria important to man
just Reply
yes, depending on the type of bacteria .eg the normal florals, the latic acid batteries etc are important to man
I mean latic acid bacterial
I don't understand this topic
Jane Reply
what topic is that
sahi kon hai bhosri ke
saurabh Reply
define metabolism of carbohydrates with example
Thavasi Reply
what is sterilization a
the process of keep equipment free from bacteria
is it only bacteria?
no undesirable fungi and contamination also.
what is streak plate method
what is the biofilm
metabolism is the sum of all the biochemical reaction required for energy generation and use of that energy to synthesize cell materials from small molecules in environment.
what are granulocytes
Shawnitta Reply
granulocytes are type of WBCs which contains granules in the cytoplasm
what is mutation
it is the interchange of genes from their normal sequence
suitable example for prokaryotes
Suvetha Reply
one of the possible early sources of energy was
uv radiation and lighting
e coli is the example of prokaryotes
archaea too
which is the specific virus causing typhoid
Jeremiah Reply
it's caused by a virulent bacteria called Salmonella Typhi
write the life cycle of HIV
Firomsa Reply
describe the internal and external structure of prokaryotic cell in terms of there appearance and functions
Lenia Reply
compare and contrast similar structures found in prokaryotic and eukaryotic cells
control of microorganisms
what is sterilization
how can a doctor treat a person affected by endospore forming bacteria in his/her wound?
Mambo Reply
define disinfectant
the process of killing
the process of killing microorganisms
a 28 years old woman come to your clinic with complain of fever painful genital blisters which express clear fluid when ruptured burning sensation around the bristers what is the diagnosis?
Ramadhani Reply
genital herpes caused by a virus called herpe simplex virus
Practice MCQ 4

Get the best Microbiology course in your pocket!

Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Microbiology' conversation and receive update notifications?