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chapter 9 - Chapter 9 Gene Transfer Mutations and Genome...

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Chapter 9 Gene Transfer, Mutations, and Genome Evolution DNA sequence is not static Horizontal gene transfer – exchanging genes between organisms Transformation Conjugation Transduction Mutation s – occur constantly for different reasons Deletions Insertions Effects of Gene Transfer Spreads useful genes among bacteria Antibiotic-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 a dead cell etc.) from the environment Some cells are naturally competent (Bacillus) Some cells can be made competent in lab: Salt treatments – neutralize charge on cell so DNA is not repelled Electroporation - 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 – bacterial 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
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DNA is transferred to new host Can bring new bacterial genes to host Generalized transduction - During viral infection, random pieces of bacterial DNA are accidentally packaged into viral capsid. Any part of the host chromosome can be transferred to a recipient cell. (usually lytic) - can have bacterial DNA and any DNA Specialized transduction - only very specific small portions of the bacterial chromosome can be transferred to a recipient. (usually lysogenic) - has lambda DNA and bacterial DNA; because of the way it is transferred Donor DNA is either incorporated into recipient chromosome or degraded.
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