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Unformatted text preview: 1 Necessary tools: selective media 1. nutritional selection media: selection for speciFc biosynthetic pathways 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 Bacterial genetics: the origin of modern molecular biology • amino acids • components of nucleic acids (i.e. speciFc bases) The essential molecules can be anything necessary for growth, for instance: glucose media example: the genes encoded by the lac operon are necessary for growth on lactose media but not necessary for growth on glucose lac- mutant strain on: lactose media glucose media lac + strain on: lactose media 2. nutritional selection media: genes that are necessary to metabolize speciFc carbon sources 2 for instance: ampicillin , kanamycin , tetracyclin, , streptomycin most bacteria are sensitive to these antibiotics, but they can gain resistance with usually a single gene. example: Ampicillin binds to and inhibits a number of enzymes in the bacterial membrane that contribute to cell wall formation, thus preventing cell reproduction. The ampicillin resistance gene ( amp r ) codes for an enzyme ( β-lactamase ) that is secreted into the periplasmic space of the bacterium where it catalyzes hydrolysis of the β-lactam ring of the ampicillin.Thus, the gene product of the amp r gene destroys the antibiotic....
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