DNA Discoveries

Timeline created by Lauren Boyd
  • Griffith

    While studying a possible vaccine for pneumonia in 1928, Griffith used pneumonia bacterium to infect mice and test different effects on the strains and what they did to the mice. Using bacteriophages, he was able to determine which strains of the pneumonia bacterium would kill the mice. Griffith's observations showed that somehow, the cells had to be transformed, but he was unable to conclude what changed the cells.
  • Avery, Macleod, and McCarthy

    Avery, MacLeod, and McCarty isolated DNA and discovered that it was the real transformer of different cells. They found that DNA was what would characterize different cells. Their findings were initially ignored because most people believed that DNA was not complex enough to be the hereditary molecule; popular belief was that proteins were the transformation molecules. However, further scientific observations by other scientists would prove their findings correct.
  • Rosalind Franklin

    The structure of a double helix was discovered in 1953, confirmed by Franklin's famous 'Photo 51.' 'Photo 51' was taken in 1951, further expanding on DNA's structure. Franklin's studies proved that DNA's structure is a double helix.
  • Hershey and Chase

    Hershey and Martha Chase provided further, definitive proof that DNA was the hereditary material of cells at the Carnegie Institution of Washington. They conducted tests using bacteriophages in cells to see if proteins or DNA entered the bacteria cells. In these tests, it was found that DNA did enter the cells while the proteins did not, which made it certain that DNA is the hereditary molecule.
  • Watson and Crick

    James Watson and Francis Crick describe the structure of DNA as a double helix consisting of two strands of DNA that are held together by base pairs.
  • Meselson and Stahl

    Used a nonradioactive isotope solution. When put into a centrifuge the men could see the different isotopes separated. What they noticed was a new medium-heavy weight DNA. They then concluded that DNA splits and then a new strand is formed. This new strand then goes with one of the original strands. Thus that the semi-conservative replication hypothesis was correct.
  • Meselson and Stahl

    Matthew Meselson helped prove that ribosomes were responsible for the creation of proteins. This experiment was also done with E. Coli. and also T4 bacteriophages. Both were then combined and then exposed to a radioactive substance. The researchers then could trace the newly produced viral RNA back to bacterial ribosomes.
  • Meselson and Stahl

    Matthew Meselson and Radding proposed a revised model of genetic recombination.