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chapter+9+and+part+of+10 - Chapter 9 Gene Transfer...

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Chapter 9 Gene Transfer, Mutations, and Genome Evolution DNA sequence is not static Horizontal gene transfer Transformation Conjugation Transduction Mutations Deletions Insertions Effects of Gene Transfer Spreads useful genes among bacteria Anti-biotic-resistance genes Spread wherever antibiotics are overused Hospitals, farms Pathogenicity islands Encode genes for cell to act as pathogen Difference between typical E. coli in gut and pathogenic E. coli O157H7 Genes to degrade special metabolites E.g., oil spills Mechanisms of horizontal gene transfer Transformation Transduction Conjugation Transformation- competent cell picks up free DNA from the environment Some cells are naturally competent ( Bacillus ) Some cells can be made competent: Salt treatments Electroration – electrical shock opens pores in cell membrane, DNA enters through pores. If free DNA isn’t incorporated into chromosome, it will be degraded. Free DNA can’t replicate on its own. Transduction – bacrerial DNA is transferred from one bacterium to another by a virus Bacteriophage injects DNA into host DNA is packaged into viral capsid Normally viral DNA is packaged Rarely, bacterial DNA is packaged by mistake DNA is transferred to new host Can bring new bacterial genes to host
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Generalized transduction - During viral infection, random pieces of bacterial DNA are accidentally packaged into viral capsid. Any part of host chromosome can be transferred to a recipient cell. Specialized transduction - only specific small portions of bacterial chromosome can be transferred to a recipient. Donor DNA is either incorporated into recipient chromosome or degraded.
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