Lecture #20 - BioMI 290 Fall 2007 Lecture 20 Lecture 20...

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BioMI 290, Fall 2007, Lecture 20 1 Lecture 20 Read: BBOM 11e Sec. 7.1-7.2, 10.7 Brief History of The Central Dogma (DNA => RNA=>Protein) (Review: Sec. 2.2, 3.5 - Lecture 6) Discovery of the Genetic Material What is life? A theoretical paper published in 1944 by Erwin Schrodinger Genetic Material must have four properties 1. Storable and Transmittable to Offspring 2. Accessible in a Usable Form 3 St bl 3. Stable 4. Not too Stable (Mutable) “Genetic material must be an “aperiodic solid”
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BioMI 290, Fall 2007, Lecture 20 2 Do Bacteria Have Genes? Popular opinion at that time that bacteria evolved by Lamarkian Evolution: “Inheritance of Acquired Traits” When a large bacterial population is subjected to certain environments that kills most of them, a few may survive and transmit the resistant phenotype. Did the environment select for pre-existing variants that were resistant, or did the environment cause a heritable genetic change? “Fluctuation test” of Luria and Delbruck Max Delbruck (left) and Salvador Luria The first rigorous evidence that mutations in bacteria followed the same Darwinian principles as in eukaryotic cells came from a clever study by Luria and Delbruck [Luria and Delbruck. 1943. Genetics 28: 491-511]. They studied mutations that made E. coli resistant to bacteriophage T1 (a bacterial virus). Phage T1 interacts with specific receptors on the surface of E. coli , enters the cell, and subsequently kills the cell. Thus, when E. coli is spread on a plate with 10 10 phage T1, most of the cells are killed. However, rare T1 resistant (Ton R ) colonies can arise due to mutations in E. coli that alter the T1 receptor in the cell wall. Luria noted that the two theories of mutation made different statistical predictions. If the Ton R mutations were induced by exposure to phage T1, then every population of cells would be expected to have an equal probability of developing resistance and hence a nearly equal number of T1-resistant colonies would be produced from different cultures. For example, if there was a 10 -8 probability that exposure to phage T1
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