Transposons

Transposons

Transposons

  • Transposons are a kind of mobile DNA  (deoxyribonucleic acid) of 2000–20,000 bp.
  • They can transfer DNA (deoxyribonucleic acid) from one site of the bacterial chromosome to another site or to a plasmid.
  • The theroy of transposons or jumping genes was first given by Barbara McClintock, a geneticist working in the field of maize genetics. 
  • The mode of genetic transfer through transposon is called transposition.
  • The transposition differs from recombination in that a segment of DNA (deoxyribonucleic acid)can be transferred from one to another molecule that has no genetic similarity with either the transposable element or the donor DNA (deoxyribonucleic acid).
  • Transposons don’t occur independently but have the characteristic of jumping from one part of a chromosome to another or to a plasmid.
  • They can also jump from one plasmid to another or back to the chromosome, hence, are known as jumping genes.
  •  Transposition in prokaryotes mainly involves 2 steps self-replication and recombination.
  • They jump from one part to another by synthesizing a duplicate of their DNA (deoxyribonucleic acid) and inserting the copy at another site in the bacterial chromosome or the plasmid. 
  • Transposons, unlike plasmids, don’t seem to self-replicating and rely on chromosomal or plasmid DNA for replication
  • Transposons don’t require homology with the recipient site for its transfer.

 

Transposons typically consist of four domains:

  1. The 1st domain may be a short DNA sequence of inserted repeats that are present at the end. This domain mediates the integration of the transposons into the recipient DNA.
  2. The 2nd domain is the gene for the enzyme transposases. These enzymes mediate the excision and integration method.
  3. The 3rd domain is the gene for the repressor, which regulates the synthesis of both transposase and therefore the gene products of the fourth domain. 
  4. The 4th domain is the gene for the expression of enzymes. 
  • Plasmid can contain many transposons carrying drug resistance genes.
  • The transposons code for drug-resistance enzymes, toxins, or a range of metabolic enzymes.
  • These transposons can either cause mutations in the gene into which they insert or alter the expression of nearly genes. 
  • Insertion sequences: The simplest form of transposons is the insertion sequences. These are a type of transposons that have a some bases varying from 800 to 1500 bp.
  • They are found as many copies at the end of larger transposon units. These cause mutation by moving from one side to another side in DNA (deoxyribonucleic acid) sequence and are believed to manage various cellular responses.

Transposons

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