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05.Bacterial Genetics

Artificial transformation what ʼ s done in cell and

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Artificial Transformation (what ʼ s done in Cell and Molecular Labs) • Some Bacteria can be induced to become Artificially Competent and undergo Transformation after some specific Treatment E. coli can be made Artificially Competent by Pretreatment Overnight at 5°C in high Concentrations of Calcium. • Usually involves Circular DNA (Plasmid DNA) - The Bacterium takes-up an Extrachromosomal Genetic Element The Bacterium can be “tricked” into taking-up a Plasmid containing just about any Gene that ʼ s been engineered into a Plasmid. Natural Transformation (what ʼ s done in Nature) • Many (possibly most) Bacteria become Naturally Competent and undergo Transformation at some Point in their Cell Cycle Pseudomonas becomes Naturally Competent early in its Stationary Phase. • Can involve Linear DNA (Chromosomal Segments) or Circular DNA (Plasmids) - The Bacterium takes-up Chromosomal Segments or Plasmids The Bacterium can “sample” alternative Versions of Genes released into the Environment by other Bacteria as they die and/or the Bacterium can “sample” naturally occurring Plasmids encoding for Antibiotic Resistance or Virulence Factors. Why do Bacteria bother with Transformation? • It may be a Large Scale DNA Repair Mechanism This is kind of like how you ʼ d borrow a Friend ʼ s Notes if you missed a Lecture in Organic Chemistry. • It may be a Mechanism for exploring the “Fitness Landscape” This is kind of like you ʼ d compare your Organic Chemistry Notes with your Friends ʼ Organic Chemistry Notes before an Exam.
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Page 7 (B) Conjugation • Conjugation is Gene transfer and Recombination that requires direct Cell-to-Cell Contact • Conjugation is a primitive but effective Sexual Process Since Conjugation starts with two Bacteria and ends with two Bacteria it isn ʼ t really Sexual Reproduction. Conjugation Nomenclature F - (“F Minus”) Bacterium without an F Factor F + (“F Plus”) Bacterium with an Extrachromosomal F Factor Hfr (“H-F-R”) High frequency recombinant Bacterium with an integrated F Factor F´ (“F Prime”) Bacterium with a formerly integrated F Factor that has excised somewhat sloppily and contains some Bacterial Genes Conjugation Outcomes: F + x F - = F + and F + • The F Factor has been transferred Hfr x F - = Hfr and F - • The F Factor (which is Integrated into the Chromosome) is rarely transferred • Large Numbers of Donor Bacterial Genes are transferred (hence the Term “High Frequency Recombinant” (Hfr) - The Transfer of Bacterial Genes is sequential - The Transfer of the entire Genome would take about 100 Minutes • But Bacteria usually can ʼ t stay in direct contact for 100 Minutes - Hfr Genes (the Integrated F Factor) are the last Genes to be transferred • So the F - is rarely converted into an Hfr F´ x F - = F´ and F´ • The F Factor (F´) has been transferred and some Donor Bacterial Genes are transferred, too (it ʼ s an F´)
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Artificial Transformation what ʼ s done in Cell and...

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