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Transcript
Isolating the Hereditary Material Continued Oswald Avery Maclyn McCarty Colin MacLeod 1928 1 continued with Griffiths work, first wanting to replicate it because they didn't believe it. took the pathogenic bacteria and treated it with a protein destroying enzyme and noticed that transformation still took place Took an RNA destoying enzyme and transformation still took place took DNA destroying enzyme and there was NO TRANSFORMATION concluded that DNA determines cell function and is responsible for transformation many didn't believe • just four letters? • this was in prokaryotic cells and can't provide reliable mechanism for complex organisms 2 another key discovery was that somatic cells had twice the DNA as gametes but gametes and somatic cells varied in its amount of protein. Erwin Chargaff Late 1940's 3 nucleotides are not found in equal numbers individual cells from the same species with have the same composition no matter their state or environmental situation the DNA from any cell of all organisms should have an expected ratio %A=%T %G=%C Martha Chase Alfred Hershey 1952 4 DNA is the genetic hereditary material radioactively tagged a virus "bacteriophage" which infects e. coli 5 structure of a virus contains Sulfur contains phosphorous virus is nonliving requires a host to replicate tricks host into copying its DNA and creating more viruses 6 Radioactive Phosphorous in DNA non radioactive protein coat Nonradioactive DNA and radioactive Sulfur in protein coat Now we know that DNA is the hereditary material but we still need to know how it is structured........ Review Questions page 223 # 13, 57 and 9 7 8 Attachments DNAi_chargaff_ratiolg.mov