Molecular Biology
Chronology
 1869 Swiss Chemist Johann Friedrich
Miescher first isolated DNA from salmon
egg
 1920’s Robert Feulgen developed a DNA
specific dye showing DNA located in the
nucleus, particularly in chromosomes
Chronology
 1928 Fred Griffith, a British microbiologist
was the first to demonstrate the
transformation of a genetic trait.
 Transformation of non virulent,
unencapsulated diplococcus pneumonia
bacteria to a virulent, encapsulated form
Chronology
 1944 Oswald Avery American
microbiologist was able to
demonstrate that Griffith’s
transformation factor was DNA
and not protein.
Chronology
 1952 - Alfred Hershey and
Martha Chase, American
microbiologists were able to
demonstrate that only DNA was
transferred from bacteriophages
to infected bacterial cells.
Chronology
 1951 Erwin Chargraff
demonstrated that the bases in
DNA were found in strict ratios
 Purine bases = pyrimidine bases
A = T and G = C
Chronology
 1953 James Watson (American) and
Francis Crick (British Physicist)
working at Cambridge University in
England demonstrated that the
structure of DNA was a double helix,
ahead of Rosalind Franklin and
Maurice Wilkins (Oxford) and Linus
Pauling (U of California)
Chronology
 1961 M. Nirenberg and H.
Matthaei identified components
necessary for DNA replication.
 In a control using poly U they
found a polymer of
phenylalanine was produced,
showing the first codon, UUU.