BIOL 2030 Lecture Notes - Lecture 12: Frederick Griffith, Martha Chase, Reverse Transcriptase
Molecular Basis of Heredity
February 1st, 2016
DNA as a source of Genetic Material
• Replicates accurately
• Stores large amounts of information
• Allows for phenotypic variation (traits)
Historical Background:
• Jogann Meischer – isolated a weakly acidic substance…
• Frederick Griffith – demonstrated that cells could be transformed
o Virulent – kills mouse
o Nonvirulent – does not kill mouse
o Heat killed virulent type – does not kill mouse
o Mixture of nonvirulent and heat-killed virulent – kills mouse virulent bacteria
recovered **transformation demonstrated
o The nonvirulent R cells had somehow acquired the ability to cause disease
o Nonvirulent R cells had been transformed
o A transforming factor is present in the heat-killed virulent S cells
o Substance responsible..
▪ Is take up by the R strain
• Avery MacLeod and McCarthy – first demonstration that DNA was the genetic material
o Heat killed virulent S strain and extracted cell content
o Treat cell extract with virulent S strain with enzymes
o Result: transformation of R to S strain
o Conclusion: only DNase destroyed the transforming substance, th e activity is not
destroyed by RNase or protease
• Alfred Hersey and Martha Chase: DNA not protein is transmitted…..
o Life cycle of a phage: virus that infects bacteria
▪ Injects DNA within bacterial chromosome
▪ Phage = 50% protein; 50% DNA
o Experiment:
▪ Bacteria infected with phage that has 35S labeled coat protein
▪ Bacteria infected with phage that has 32P labeled DNA
▪ Separate empty phage protein coat from bacterial cells
▪ Results after phage reproduction:
• 35S – labeled protein not detected in progeny
• 32P – labeled DNA detected in progeny
▪ Therefore, DNA not protein has been transmitted to the progeny
• Heinz Frakenl-Conrat and Bea Singer – demonstrated that RNA can serve as a genetic
material
o Separated proteins from RNA (type A and type B)
o Type A RNA + types B protein (& via versa)
o This creates hybrid TMV = fully active
o Virus particles produced then match the type of RNA
o Retrovirus – RNA DNA via reverse transcriptase
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