The History of DNA

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The History of DNA
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Early Work

• Friedrich Miescher, 1869, first isolates a
  substance from the nucleus of cells that he calls
  nuclein. His student, Richard Altmann, calls
  the substance nucleic acid.
• Biochemists identify two types of nucleic acids,
  later called RNA and DNA.
• In 1929, Phoebus Levine at the Rockefeller center
  identifies the four bases of DNA.

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What Does DNA Do?

• Though early researchers knew that DNA was found
  in chromosomes, they doubted that it was the
  hereditary material. There were only four bases.
  How could for bases code for all sorts of
  proteins?
• Some researchers, including Linus Pauling,
  thought that the protein also found in
  chromosomes was probably the hereditary factor.

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Frederick Griffith

• In 1928, Frederick Griffith carried out
  experiments on pneumonia bacteria in mice.
• Discovery something in heat-killed virulent
  bacteria could be transferred to live, harmless
  bacteria and make them virulent.

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Griffiths Experiment
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Oswald Avery

• Avery continued working with Griffiths findings
  in hope of discovering what factor in bacteria
  carried the trait of virulence.
• Isolated proteins, carbohydrates, nucleic acids
  and applied them to non-virulent bacteria. Only
  nucleic acids (DNA) caused a change.

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Averys Work
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Erwin Chargaff

• Chargaff studied DNA itself, in hopes of
  providing some clues about its structure.
• Discovered that there are always equal amounts of
  the bases Adenine and Thymine, and equal amounts
  of Cytosine and Guanine.
• Chargaff proposed that these bases pair with one
  another in some way.

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Hershey and Chase

• Used bacteriophages and discovered that DNA is
  genetic material
• Hershey and Chase Bacteriophage Experiment

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Hershey and Chase
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Linus Pauling

• Hypothesized that DNA was triple stranded
• This was proven wrong but helped Watson and Crick
  discover the actual double helix structure of DNA
• Linus Pauling Structure

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Wilkins and Franklin

• Rosalind Franklin and Maurice Wilkins worked with
  X-ray crystalography to find more clues about the
  structure of DNA.
• Franklins X-ray images suggested a helical
  structure.

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Franklin and Wilkins
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Watson and Crick

• James Watson and Francis Crick were also working
  on discovering the structure of DNA.
• Applied Chargaffs rule, assumed that A always
  pairs with T, C with G.
• Watson was not entirely convinced of the helical
  structure that Franklin had suggested, and his
  critique of her work led her to doubt herself.

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Watson and Crick

• Wilkins consulted with Watson and Crick. Without
  Franklins knowledge, he handed them the data
  that he and Franklin had worked on.
• Watson immediately recognized the significance.
  He and Crick went to work on a model of DNA.

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Alec Jeffreys

• 1984
• Discovered technique
• for genetic fingerprinting
• Can match two sample of DNA together
• Used during crime scene investigation