DNA160-page3 - mutations in R-strain bacteria. Evidence # 3...

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DNA: Structure and Replication - 3 Evidence #2 Starting in the 1930's, a group of microbiologists, headed by Oswald Avery, suspected Griffith's research transformation substance must be the genetic molecule. Avery repeated Griffith's experiments, adding a series of enzymes (from the pancreas) that selectively destroyed DNA, RNA or protein. (Recall Levene's discovery of the two different nucleic acids.) They performed the following experiments. 1. Mice + DNA-digesting enzyme + heat-killed S + R ----> Live Mice 2. Mice + RNA-digesting enzyme + heat-killed S + R ----> Dead Mice 3. Mice + Protein-digesting enzyme + heat-killed S + R --> Dead Mice In 1944, Avery concluded that DNA was the genetic molecule. Transformation was prevented only when DNA was destroyed. Many scientists still disputed this conclusion, since the structure of DNA was not known, and Avery could not say how DNA might work. Some thought the experiments simply caused
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Unformatted text preview: mutations in R-strain bacteria. Evidence # 3 Bacteriophages (viruses that invade bacteria and convert the bacteria into virus making machines) proved to be the means by which the question was finally answered. In 1952, Hershey and Chase (and others) confirmed that DNA was the genetic molecule. Viruses have just DNA (or sometimes just RNA) and a protein coat. Proteins contain sulfur, but not phosphorus and DNA contains phosphorus, but not sulfur. Hershey and Chase used radioactive sulfur and radioactive phosphorus to "label" T 2 bacteriophages (viruses that infect bacteria). They then tracked the invasion of phages into host bacteria (a strain of E coli) to determine what part of the new generation phages became radioactive. Since only the DNA of the new generation of phages was radioactive, Hershey and Chase were able to confirm that DNA was the genetic molecule....
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This note was uploaded on 12/29/2011 for the course BIO 151 taught by Professor Edwards during the Spring '10 term at SUNY Stony Brook.

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