bio- chap 16

bio- chap 16 - I. DNA as the Genetic Material A. Search for...

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I. DNA as the Genetic Material A. Search for genetic material 1. originally thought it was proteins due to great heterogeneity and specificity of function -> requirements for hereditary material 2. not much known about nucleic acids a. physical an chemical properties too uniform to account for multitude of specific traits inherited by an org. 3. Frederick Griffith’s experiment, 1928 (Evidence that DNA can transform bacteria) a. two strains of stretococcus pneumoniae -> S strain (pathogenic) and R strain (nonpathogenic) b. heat killed S strain was harmless c. when heat killed S strain mixed with R strain, living R strain cells converted to pathogenic form and was inherited by all descendants d. referred to phenomenon as transformation : change in genotype or phenotype due to the assimilation of external DNA by a cell 4. Oswald Avery a. purified various chemicals from heat killed pathogenic bactiera and tried to tansform live nonpathogenic bacteria with each chemical b. only DNA worked c. 1944: Avery, McCarty and MacLeod announce that transforming agent was DNA-> discovery greeted with skepticism, didn’t believe that genetic material of bacteria would = that of more complex orgs. 5. Martha Chase and Alfred Hershey, 1952 (Evidence that Viral DNA Can Program Cells a. virus = simpler than cells, DNA with a protective coat of protein. In order to infect a cell, it must take over all metabolic machinery b. (bacterio)phages- viruses that infect bacteria c. discover DNA is genetic material of T2phage (infects Ecoli) d. use diff radioactive isotopes to tag DNA ( 32 P) and protein ( 35 S) by growing it with that isotope e. viruses allowed to infect Ecoli and whirled in blender to shake loose any parts of phages that remain outside bacteria cells, then spun in centrifuge f. radioactivity of cell pellet of bacteria formed at the bottom, and
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bio- chap 16 - I. DNA as the Genetic Material A. Search for...

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