History and discovery timeline.

  • P.A. Levene

    P.A. Levene
    P.A. Levene discovered the basic shape of nucleotides that make up DNA
  • Frederick Griffith

    Frederick Griffith
    Griffith expriimented with the bacteria that causes pneumonia. He studied two strains of bacteria, one smooth and one rough. When injected into mice, the mouse with the smooth strain died while the other survived.
  • Oswald Avery

    Oswald Avery
    Oswald and his colleagues identified the molecules that transformed a rough strain bacteria into a smooth strain by isolating the macromolecules, such as DNA, lipids, and proteins from killed "S" cells. When the "R" cells were exposed to the "S" strain DNA, they transformed into "S" cells. He concluded from Griffith's experiment that the DNA released from dead "S" cells were incorporated into the DNA of "R" cells and transformed them into "S" cells.
  • Maurice Wilkins

    Maurice Wilkins
    Wilkins worked at King's College on a technique called X-ray diffusion that involved aiming X rays at the DNA molecule. He found evidence that DNA had a helical structure.
  • Erwin Chargaff

    Erwin Chargaff
    Chargaff analyzed the amount of adenine, guanine, thymine, and cytose in the DNA of various species. A portion of Chargaff's data, known as the Chargaff's rule, was published in 1950. He found that the amount of guanine is equal to the amounnt of cytose, while the amount of thymine is equal to the ammount of adenine within a specie.
  • Rosiland Franklin

    Rosiland Franklin
    Rosalind joined the staff at King's College. She took the famous Photo 51. Photo 51 indicated that the structure of DNA was double helix, or a twisted ladder shape, formed by two strands of nucleotides twisted around each other.
  • Hershey & Chase

    Hershey & Chase
    Their experiment provided strong evidence that DNA, not protein, was the genetic material that could be passed down from generations to generations in viruses.
  • Linus Pauling

    Linus Pauling
    Pauling proposed a triple-stranded helix structure for DNA. He had the phosphate groups of each DNA strand facing into the helical core, with the nitrogenous bases facing out. Three strands would intertwined to make one helical DNA model. However, he forgot about the negative charges of oxygen in each phosphate group. These charges repel one another, making it impossible to hold together.
  • Watson and Crick

    Watson and Crick
    Using Chargaff's data and Franklin's data, Watson and Crick measured the width of the helix and the spacing between the bases. They found out that the DNA structure is two alternating rails of ladders of deoxyribose and phosphate that form th double helix. In 1953, Watson and Crick surprised the scientific community with their published work that suggested a structure for DNA and hypothesized of replication for the molecule deduced from the structure.