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1. Assignment topic: Transposons Subject : Molecular biology LCWU Lahore 2. Transposable Elements DEFINITION ã DNA elements capable of moving ( transposing )…
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  • 1. Assignment topic: Transposons Subject : Molecular biology LCWU Lahore
  • 2. Transposable Elements DEFINITION • DNA elements capable of moving ("transposing") about the genome. The movement of genetic information from one chromosomal location, the donor site, to another, the target site.
  • 3. Discovery • Discovered by Barbara McClintock. • Largely from cytogenetic studies in maize, but since found in most organisms. • She liked to call them "controlling elements“ because they affected gene expression. • She got Nobel Prize in 1983 in Physiology and Medicine
  • 4. Genetic Transposition • The ability of genes to change position on chromosomes, a process in which a transposable element is removed from one site and inserted into a second site in the DNA.
  • 5. Mechanism of transposons • Excises the IS element in the donor DNA • Makes staggered cuts in a short sequence in the target DNA • Ligates the three prime termini of the IS element to the five prime ends of the cut donor DNA • Host cell DNA polymerase fills in the single stranded gaps, generating the short direct repeats that flank IS elements and DNA ligase joins the free ends
  • 6. Characteristics • Comprise 45% of human chromosomal DNA “middle repetitive DNA” contribute to spontaneous mutation, • genetic rearrangements, • and horizontal transfer of genetic material. • Aid speciation and genomic change. • In bacteria transposons are often associated with antibiotic resistance genes. • Cells must depress transposition to insure genetic stability.
  • 7. Classification of transposition • Conservative transposition: • The transposable element will only be found at the target site, with no change in copy number. • Also known as “cut-and-paste” transposition.
  • 8. Duplicative transposition: • Will result in two copies of the element, one at the donor site and one at the target site. • copy-and-paste” transposition
  • 9. Types of transposable elements: Class I transposable elements (retro transposons). Class II transposable elements (DNA transposons).
  • 10. Retro transposons: • Retro transposons also called transposons via RNA intermediates are genetic elements that can amplify themselves in a genome and are ubiquitous components of the DNA of many eukaryotic organisms.
  • 11. DNA transposons: • DNA fragments transpose directly from DNA segment to DNA segment, Producing a DNA copy that transposes, cut or paste into a new locus. • Insertion sequences: • Also known as an IS, an insertion sequence element, or an IS element is a short DNA sequence that acts as a simple transposable element. • Size: • 700 to 2,500 bp. • Content: • Contain information that required for transposition.
  • 12. Example: Some maize phenotypes caused by transposable elements excising in somatic tissues.
  • 13. BACTERIAL TRANSPOSONS: • In bacteria, transposons can jump from chromosomal DNA to plasmid DNA and back. • Transposons in bacteria usually carry an additional gene for function other than transposition often for antibiotic resistance.
  • 14. Example
  • 15. Control of Transposons: • Auto regulation: • Transcriptional silencing:
  • 16. Transposons causing diseases: • Hemophilia A and B • Severe combined immunodeficiency • Porphyria • Cancer • Duchenne muscular dystrophy.
  • 17. Biological Significance of Transposons: • To identifying the mutant allele. • To study the chemical mutagenesis methods. • To study gene expression • They provide a means for genomic change and variation, particularly in response to stress.
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