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Published bySpencer Randall Modified over 9 years ago
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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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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
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Recombination THREE main categories 1. Homologous recombination takes place between similar sequences 2.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”
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1. Homologous Recombination
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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)
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1. Homologous Recombination Recombinase protein
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1. Homologous Recombination
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2. Site-specific Recombination Lambda phage integration and excision
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2. Site-specific Recombination VDJ rearrangement in antibody production
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3. Transposition - Recombination Bacterial antibiotic resistance
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3. Transposition - Recombination Eukaryotic transposable elements Barbara McClintock - Noble prize Normal maize Active C causes synthesis of purple pigment Mutant maize Mutant C Ds insertion inactivates C and prevents pigment synthesis Mutant maize Ac allows Ds to transpose out of C in many cells, results in purple pigmented spots on kernels
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