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Pivotal Experiments Frederick Griffith 1927 Worked with non-virulent bacteria Identified two types of colonies that grew after streaking of agar plate. The most prevalent colony type had a rough cell appearance When this was delivered to rats via aerosol, that rats survived The second type of colony that was observed had a smooth appearance. When the rats were treated with this colony type they died. Next: Took rough colonies and added heat attenuated smooth strain (non-virulent), the rats then died after treatment. This suggested that there was a conversion of the strain taking place This turned out to be Transformation. Avery 1946 Repeated Griffith expts Again showed that smooth could covert rough to a virulent strain. Isolated out the DNA and was able to prove that DNA was the material that was being passed on. Saw that the converted rough strain had DNA from the original rough strain as well as the non-virulent smooth strain The Experiment First they treated the bacteria with centafugation, which eliminates large cellular pieces. The result: bacteria still transformed Added protease, which removes all proteins The result: bacteria still transformed Treated the bacteria with deoxyribonuclease, which eliminates all DNA The result: no transformation in the bacteria The trio concluded that DNA is the cause of transformation, where in this experiment virulence is inherited. Chargaff 1950 Isolated out DNA Showed that A paired with T and that C paired with G Therefore this allowed the idea of complimentary strands to be explored Hershey/Chase 1952 Further confirmed that DNA was the genetic material Radiolabeled DNA with an isotope Used bacteriophage to infect target cell. Observed that DNA from bacteria was transferred to the target cell Ex HIV virus targeting of the CD4 T helper cells Control labeling of the bacterial protein showed that it remained in the bacteriophage. Watson/Crick 1953 . Came up with double helix structure for DNA after looking at X ray analysis conducted by Rosalind Franklin CODON: a sequence of 3 nucleotides in mRNA that selects for an Amino Acid. " A genetic 'code word' containing three 'letters.' " " More than one 'word' for each amino acid. " RNA Codon Amino Acid