326R RECOMBINATION TRANSFORMATION

326R RECOMBINATION TRANSFORMATION - 1 MICROBIAL GENETICS...

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MICROBIAL GENETICS MICROBIAL GENETICS 1
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MICROBIAL GENETICS RECOMBINATION Homologous, Site-specific, illegitimate Breaking and Re-joining Parental chromosomes, Recombinant chromosomes TRANSFORMATION Streptococcus pneumoniae: Wild-type, smooth colonies, capsule production, pathogenic Rough mutant, no capsule production, non-pathogenic Transformation of auxotrophic mutants Donor cells, donor DNA, recipient cells, recombinants, transformants Phenotypes, Selection Transformation by plasmid DNA Antibiotic resistance plasmids Penicillin-resistance, penicillinase, beta-lactamase 2
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3 Genetic information is very stable (in most organisms) because nature has evolved mechanisms to repair damaged DNA and to ensure great fidelity in DNA replication, As a result, mutations occur very randomly. That is very good for each species because they continue to survive and compete successfully in their environment. On the other hand, new kinds of organisms are clearly needed from time to time, for example to take advantage of changing environments, either good or bad changes in the environment. There are two ways that new organisms can arise. Mutation. Some times, mutants are improved organisms and can grow and survive and compete better than the original organism. An example is ability to grow in the presence of some antibiotic. Other times, mutations will create defects and the mutants which suffer those mutations will not be able to survive. Genetic Exchanges. The second way is by combining genes from different organisms to create new organisms. These exchanges move genes or larger fragments of chromosomes from one organism to another and create recombinant organisms with combinations of properties from the original organisms. A. NATURAL EXCHANGES OF CHROMOSOMES OR CHROMOSOME FRAGMENTS IN MICROBES. Genetic exchanges occur in microbes by three natural mechanisms; Transformation, Transduction, and Conjugation. Transformation involves the breakage of lysis of one cell (the donor) with the resulting breakage of the chromosome and release of chromosomal fragments into the environment, the uptake of those chromosomal fragments another cell (the recipient) and the incorporation of donor DNA fragment into the chromosome of the recipient. Transduction is the movement of chromosomal fragments from one cell (the donor) by growth of some phage on the
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326R RECOMBINATION TRANSFORMATION - 1 MICROBIAL GENETICS...

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