MMG 408 1 - EXPERIMENT 1 BACTERIAL MULTIPLICATION AND...

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EXPERIMENT 1: BACTERIAL MULTIPLICATION AND GENETICS Mark Gaynor MMG 408 Fall 2007
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Introduction Bacteria serve as model organism for genomic studies. Specifically, the E.Coli bacterium is most useful in laboratory studies because much of the genome, or genetic sequence, is known. Genetic mapping and comparison using this microbe is very efficient. Bacteriophages are also very useful in genetic studies. Studies with phages have led to discoveries about recombination between mutations, as well as discoveries of the sequence of genomes themselves. By using phages the mutations of different genes can be observed, including recombination, complementation and reversion gene products. Bacteriophages infect bacteria, solely relying on the host bacterium for all means of making more phage. A phage injects its own DNA into the host cell, directing the host to create more phage. This lytic cycle continues until the host cell lyses, releasing many phage into the surrounding environment. The number of phage infected in each cell can be estimated using a one-step growth curve. In this part of the experiment, bacterial cells and phage are mixed, and then aliquots are taken and plated at specific times. The one step growth curve not only expresses the number of phage per bacterial cell at one time, but also pictorially represents the different phases of phage infection in the cells. Bacteriophage experimentation also helps demonstrate many different types of gene mutations. Benzer [(1955) Proc. Natl. Acad. Sci. USA] was the first to correctly show that a gene is not the smallest unit of recombination. He revealed mutations that occurred within the rIIA gene of the T4 bacteriophage. A total of 160 thousand base pairs encode for about 200 genes in this phage. Two of the in particular, rIIA and rIIB, are required for growth on E. coli lysogenic for another phage, lambda. If either gene is mutated in a lambda lysogen no plaques will form on the plate. The progeny of these
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phage will still be mutants unable to multiply in subsequent lambda infections.
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MMG 408 1 - EXPERIMENT 1 BACTERIAL MULTIPLICATION AND...

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