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DNA/RNA Metabolism

DNA/RNA Metabolism. Blackburn & Gait, Ch. 5 Neidle, Ch. 4 Recombination • understand basics of the reaction • know advantages/disadvantages of recombination • understand how recombinase protein works • know structure of Holliday junction (X-shaped) • know different types of recombination.

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DNA/RNA Metabolism

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  1. DNA/RNA Metabolism Blackburn & Gait, Ch. 5 Neidle, Ch. 4 Recombination • understand basics of the reaction • know advantages/disadvantages of recombination • understand how recombinase protein works • know structure of Holliday junction (X-shaped) • know different types of recombination

  2. Recombination • Enables the limited exchange of genetic material between paired chromosomes • Occurs between intact double helices • Damage to DNA can stimulate recombination • Enables the immune system to generate a diversity of protein antibodies from a limited set of genes • Enables viruses to integrate their genetic material into a host’s genome • Enables host organism to assort alleles (differing copies of same gene) into novel groups - favorable & unfavorable alleles can be shuffled randomly • Enables repair of a damaged gene in an otherwise favorable chromosome • Enables regulation of gene expression • Enables rearrangement of antibody genes • Can lead to cancers - example: Burkitt’s lymphoma caused by translocation between ch. 8 and 14

  3. Recombination • • THREE main categories • 1. Homologous recombination • takes place between similar sequences • Site-specific recombination Limited sequence similarity between recombining DNAs • 3. Transposition • movement of a DNA element from one position to another, little sequence similarity needed • called “illegitimate recombination”

  4. 1. Homologous Recombination

  5. 1. Homologous Recombination Recombinase protein • One example is that of Cre recombinase from a bacteriophage (virus that infects bacteria) • The enzyme mediates strand cleavage and exchange between two pieces of DNA • An intermediate (half reacted) configuration of the DNA is called a Holliday junction (X-shaped)

  6. 1. Homologous Recombination Recombinase protein

  7. 1. Homologous Recombination

  8. 2. Site-specific Recombination Lambda phage integration and excision

  9. 2. Site-specific Recombination VDJ rearrangement in antibody production

  10. 3. Transposition - Recombination Bacterial antibiotic resistance

  11. 3. Transposition - Recombination Eukaryotic transposable elements Barbara McClintock - Noble prize Normal maize Active C causes synthesis of purple pigment Mutant maize Ac allows Ds to transpose out of C in many cells, results in purple pigmented spots on kernels Mutant maize Mutant C Ds insertion inactivates C and prevents pigment synthesis

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