21 BIO 326R Transformation

21 BIO 326R Transformation - BIO 326R Transformation and...

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BIO 326R Transformation and recombination
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History -  Fred Griffith 1928 Injecting mice with Streptococcus pneumoniae Uses a virulent and non-virulent strain of S. pneumoniae Strains are visually distinguishable Virulent strain has capsule and grows as a shiny, smooth colony on plate, while non-virulent strain has no capsule and grows as “rough” colony. Rough, non-virulent strain is a mutant unable to make capsule Injecting a smooth colony into a mouse kills it, a rough colony does not kill Boiling a smooth colony (heat killing) before injection allows the mouse to live Injecting a heat-killed smooth colony and a non-virulent colony simultaneously kills the mouse Isolation of bacteria from mouse shows both smooth and rough bacteria Conclusion: Rough colony was “transformed” into smooth virulent colony
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Bacteria Mouse Recover from mouse Rough (mutant) 0 Smooth (WT) Smooth colonies Heat killed smooth 0 Heat killed smooth + rough Smooth + rough History -  Fred Griffith 1928
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Avery, MacLeod and McCarty Start with Griffith’s transformation experiments Take heat killed smooth bacteria and purify components – test them individually for ability to transform by injecting into mouse with rough bacteria Purified Polysaccharide + rough bacteria: live mouse Purified RNA + rough bacteria: live mouse Purified Protein + rough bacteria: live mouse Purified DNA + rough bacteria: dead mouse Follow-up: treat heat-killed cells with enzymes, inject into mouse with rough bacteria. Results: RNAse (RNA degraded, DNA and protein left intact): dead mouse Protease (Protein degraded, DNA and RNA left intact): dead mouse DNAse (DNA degraded, protein and RNA intact): live mouse Conclusion: DNA is the transforming material This was the first indication that DNA was the stuff that genes are made of.
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21 BIO 326R Transformation - BIO 326R Transformation and...

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