Transposable Elements in Genetics
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Questions and Answers

What is one potential effect of transposable elements on genes?

  • They only act on prokaryotic genes.
  • They can enhance gene expression without mutations.
  • They completely eliminate genetic material without any consequences.
  • They can insert within a gene to cause a mutation. (correct)
  • Which hypothesis suggests that transposable elements provide important functions for the cell?

  • Selfish-DNA hypothesis
  • Cellular-function hypothesis (correct)
  • Genetic-variation hypothesis
  • Mutation-driven hypothesis
  • What role do transposons play in plasmids?

  • They are not found in plasmids.
  • They reduce plasmid efficiency.
  • They inhibit plasmid fusion.
  • They facilitate the insertion of F plasmids into the E. coli chromosome. (correct)
  • Which hypothesis proposes that transposable elements create evolutionary flexibility by inducing mutations?

    <p>Genetic-variation hypothesis</p> Signup and view all the answers

    What does the selfish-DNA hypothesis state about transposable elements?

    <p>They spread and replicate without benefiting the host cell.</p> Signup and view all the answers

    What are transposable elements primarily known for?

    <p>They cause mutations and DNA rearrangements.</p> Signup and view all the answers

    Who discovered transposable elements and in which organism?

    <p>Barbara Mc Clintock in maize.</p> Signup and view all the answers

    What are flanking direct repeats in relation to transposable elements?

    <p>They are generated during the transposition process.</p> Signup and view all the answers

    What is the role of transposase in transposable elements?

    <p>It controls the transposition of the element.</p> Signup and view all the answers

    How do retrotransposons move within the genome?

    <p>They require an RNA intermediate for transposition.</p> Signup and view all the answers

    What are terminal inverted repeats associated with transposable elements?

    <p>They are inverted complements found at the ends of some elements.</p> Signup and view all the answers

    What common feature do all types of transposition share?

    <p>DNA is replicated at the single strand gaps during transposition.</p> Signup and view all the answers

    Which of the following statements about DNA transposons is true?

    <p>They are also known as class I transposable elements.</p> Signup and view all the answers

    What defines a replicative transposition process?

    <p>The transposable element is copied, and both the original and the copy remain.</p> Signup and view all the answers

    Which of the following is a characteristic of Class II transposable elements?

    <p>They contain reverse transcriptase genes.</p> Signup and view all the answers

    What is a primary feature of insertion sequences found in bacterial transposable elements?

    <p>They are typically 800 to 2000 bp in length.</p> Signup and view all the answers

    What distinguishes composite transposons from insertion sequences?

    <p>Composite transposons can contain genes unrelated to transposition.</p> Signup and view all the answers

    Which of the following is not a function of the transposase gene?

    <p>Encoding reverse transcriptase activity.</p> Signup and view all the answers

    Which example is classified as a Class I transposable element?

    <p>Tn3 (E.Coli)</p> Signup and view all the answers

    What is true about transposable elements lacking insertion sequences?

    <p>They are known as non-composite transposons.</p> Signup and view all the answers

    Which of the following correctly describes the structure of Class I transposable elements?

    <p>They contain only terminal inverted repeats.</p> Signup and view all the answers

    Study Notes

    Transposable Elements

    • Mobile DNA sequences found in all organisms
    • Frequently cause mutations and DNA rearrangements
    • Discovered in the 1940s by Barbara McClintock while studying maize genetics

    General Characters

    • Most generate short, flanking direct repeats at the target site when inserted
    • Many possess short terminal inverted repeats
    • Flanking direct repeats are 3 to 12 bp long and present on both sides of most transposable elements
      • Not part of the transposable element, they are generated during insertion
    • Terminal inverted repeats are 9 to 40 bp long and are inverted complements of one another
      • Found at the ends of many, but not all, transposable elements

    Transposition

    • Movement of transposable elements from one location to another
    • Several different mechanisms are used for transposition in prokaryotic and eukaryotic cells
    • All types of transposition have several features in common:
      • Staggered breaks are made in the target DNA
      • The transposable element is joined to single-stranded ends of the target DNA
      • DNA is replicated at the single-strand gaps

    Mechanisms of Transposition

    • Can occur through a DNA molecule or through the production of an RNA molecule that is then reverse transcribed into DNA
    • DNA Transposons (class I transposable elements): transpose as DNA
    • Retrotransposons (class II transposable elements): transpose through an RNA intermediate
      • RNA is transcribed from the transposable element (DNA) and then copied back into DNA using reverse transcriptase
    • Transposition can be replicative (the element is copied and the copy moves) or non-replicative (the element excises and moves)

    Characteristics of Two Major Classes of Transposable Genetic Elements

    Class I

    • Structure: Short, terminal inverted repeats; short flanking direct repeats at the target site
    • Genes encoded: Transposase gene (and sometimes others)
    • Transposition: Through DNA (replicative or non-replicative)
    • Examples: IS1 (E. coli), Tn3 (E. coli), Ac, Ds (Maize), p elements (Drosophila)

    Class II

    • Structure: Long, terminal direct repeats; short flanking direct repeats at the target site
    • Genes encoded: Reverse transcriptase gene (and sometimes others)
    • Transposition: By RNA intermediate
    • Examples: Ty (Yeasts), copia (Drosophila), Alu (Human)

    Structure of Transposable Elements

    Bacteria

    • Two major groups:
      • Simple transposable elements (insertion sequences): Carry only the information required for movement
      • More complex transposable elements (composite transposons): Contain DNA sequences not directly related to transposition
    • Insertion Sequences:
      • Simplest type of transposable element in bacterial chromosomes and plasmids
      • Carry only the genetic information necessary for their movement
      • Typically 800 to 2000 bp in length and possess terminal inverted repeats and flanking direct repeats at the site of insertion
      • Contain one or two genes that code for transposase
    • Composite Transposons
      • Segment of DNA flanked by two copies of an insertion sequence
      • Consists of a central region with extra genes, flanked by identical or very similar IS elements
      • Contain genes other than those required for transposition
      • Lacking insertion sequences are referred to as non-composite transposons
      • Example: Tn3 (5000 bp - Possesses terminal inverted repeats of 38 bp and generates flanking direct repeats that are 5 bp in length)

    Effects of Transposable Elements

    • Can insert within a gene to cause a mutation or stimulate DNA rearrangement leading to deletions of genetic material
    • Used to purify genes and study their function
      • Can fragment the genome and isolate the mutated fragment, purifying the gene
    • Can turn on and off eukaryotic and prokaryotic genes
    • Located within plasmids and participate in processes like plasmid fusion and the insertion of F plasmids into the E. coli chromosome
    • Play an extremely important role in the generation and transfer of new gene combinations

    Evolutionary Significance of Transposable Elements

    • Cellular-function hypothesis: Suggest that transposable elements provide some important function for the cell
    • Genetic-variation hypothesis: Proposes that transposable elements provide evolutionary flexibility by inducing mutations
    • Selfish-DNA hypothesis: Suggests that transposable elements do not benefit the cell but are widespread because they can replicate and spread

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    Related Documents

    Transposable Elements PDF

    Description

    Explore the fascinating world of transposable elements, the mobile DNA sequences that play a crucial role in genetics. This quiz covers their characteristics, mechanisms of transposition, and historical significance, particularly in relation to Barbara McClintock's discoveries. Test your knowledge on how these elements cause mutations and DNA rearrangements.

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