Chapter_28_lecture_RAVEN_NG2009 (1)

549 18 single recombination event in each

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Unformatted text preview: single recombination event in each Transduction Generalized transduction -Virtually any gene can be transferred -Occurs via accidents in the lytic cycle where host DNA is degraded into fragments -Viruses package bacterial DNA and transfer it in a subsequent infection to another host bacterium -This bacterial DNA is then integrated into the new host bacterium's genome instead of the viral DNA through homologous recombination eg. lambda phage (limited to phages that exhibit a lysogenic life cycle) Specialized transduction Only a few genes can be transferred (those near site of integration of phage genome) -Occurs via accidents in the lysogenic cycle -Imprecise excision of prophage DNA following induction where bacterial DNA near the site of integration of phage genome is cut along with the prophage while some phage genes remain attached to host genome 19 -The resulting phages may be defective due to loss of part of the phage genome which may have carried genes for viral growth . - Make the host cell diploid for the transduced genes Generalized Transduction 20 Transformation Natural transformation -Occurs in many bacterial species, including Streptococcus which was studied by F. Griffith -DNA that is released from a dead cell is picked up by another live cell (since dead cell reptures and releases DNA fragments) - Proteins involved in the process of natural transformation are encoded by bacterial genome Artificial transformation -Accomplished in the lab -Used to transform E. coli for molecular cloning Bacterial DNA is taken up by homologous recombination => different alleles may lead to a change in phonotype 21 Transformation 22 Prokaryotic Metabolism Acquisition of Carbon -Autotrophs = From inorganic CO2 (OR inorganic molecules) -Heterotrophs = From organic molecules Acquisition of Energy -Chemolithotrophs = From inorganic chemicals -Phototrophs = From sunlight Depending on how they acquire energy, autotrophs and heterotrophs can be classified as: Photoautotrophs carry out photosynthesis / use energy from sunlight to build organic purple and green sulfur bacteria molecules from inorganic molecules -Cyanobacteria Photoheterotrophs use light as a main source of energy but obtain carbon from organic molecules -Purple and green nonsulfur bacteria Chemolithoautotrophs obtain energy by oxidizing inorganic molecules -Nitrifiers (oxidize ammonia or nitrate) Chemoheterotrophs obtain carbon atoms and energy from organic molecules -Majority of prokaryotes -Use organic molecules for C and energy 23 Human Bacterial Disease In the early 20th century, infectious diseases killed 20% of children before the age of five -Sanitation and antibiotics considerably improved the situation In recent years, however, many bacterial diseases have appeared and reappeared 24...
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