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LECTURE1Adunn - Lecture 1A Bacterial genetics Readings Ch 5...

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Lecture 1A: Bacterial genetics Readings Ch 5, pages 181-207; 209-213
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Typical Prokaryotic cell - Prokaryotes include bacteria and blue-green algae -defining feature is DNA not located in membrane-bounded nucleus - genomic DNA is circular - often contains extra small DNAs called plasmids - viruses that grow in bacteria are called bacterophages, or phages
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Bacterial colonies, each derived from a single cell Figure 5-3 Distinguishing lac + and lac - by using a red dye
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Table 5-1
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Bacterial genetics: - markers are drug sensitivities and metabolic requirements - E. coli can grow on minimal plates with only carbon and nitrogen sources, salts and minerals, and energy source. - Mutations produced by treating cells with chemical mutagens - wild type cells called prototrophic , meaning they can synthesize all required factors for growth on minimal media - mutant type cells called auxotrophic , meaning they cannot synthesize one or more of the required factors.
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Model Organism Escherichia coli Model Organism E. Coli In the 1940s, Josh Lederberg and Ed Tatum began studying the sex-like heredity of E. coli cells, called bacterial conjugation. E. Coli has a single chromosme of 4.6 million base pairs with about 4000 genes. Grows rapidly in laboratory at 37 o C in liquid media or on agar plates. Can store bacterial strains for years in cryopreservative solutions at -80 0 C.
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Lederberg and Tatum experiment: first demonstration of bacterial conjugation Figure 5-5b Occurs at frequency of 1/10 7
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No recombinants are produced without cell contact Figure 5-6 Neither strain yields prototrophic colonies. Proves that auxotrophs produced by mixing cells no due to diffusion of a small molecule from one strain to the other. Cells must come into physical contact to produce prototrophs.
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Bacterial conjugation involves the fertility factor F -1953, William Hayes discovered that some cells could not transfer markers to recipient cells. However, these cells could gain the ability to transfer markers after conjugation with a second strain that was competent to transfer markers.
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