lecture_19__05 - Beadle and Tatum: "one gene one...

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Beadle and Tatum: "one gene one enzyme" experiment, 1941 http://staff.jccc.net/pdecell/transgenetics/beasdtatum.gif creation of mutants using a DNA- damaging agent (X rays) selection of mutants on minimal media (lacking many nutrients present in rich media) categorization into requirements for amino acids, nucleic acids, etc complementation with specific compounds also described in Campbell, pg 304-305 (rich)
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Practical applications from bacterial genetics: Necessary tools: selective media Two types (for the purposes of this course): 1. nutritional selection media for selection among auxotrophic mutants what is an auxotroph? a nutritional mutant that is unable to synthesize one or more essential molecules that are normally synthesized by wild-type strains of the same species therefore an auxotroph cannot grow on media lacking the molecules(s) that it cannot synthesize a prototroph is the opposite of an auxotroph, and can synthesize everything it needs for growth on minimal media what is "media"? the substance that microorganisms grow on example: an arginine, tryptophan auxotroph (arg - trp - ) can grow on rich media, but cannot grow on minimal media lacking either arginine or tryptophan rich media - arginine - tryptophan - tryptophan - arginine bacterial colony
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amino acids components of nucleic acids (i.e. specific bases) molecules necessary to metabolize specific carbon sources glucose media example: the genes encoded by the lac operon are necessary for growth on lactose media lac - mutant on: lactose media ? mutation of which genes in the lac operon would cause the phenotype shown above? The essential molecules can be anything necessary for growth, for instance:
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for instance: ampicillin , kanamycin , tetracyclin, chloramphenicol, streptomycin most bacteria are sensitive to these antibiotics, but they can gain resistance with usually a single gene. 2nd type of selective media: drug selection (antibiotics)
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lecture_19__05 - Beadle and Tatum: "one gene one...

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