DNA: history and discovery

By mbozzo

  • Discovery of Nucleic Acids

    1869 Friedrich Miescher isolated the genetic material from white blood cell nuclei. He noted it had an acidic nature and called it nuclein.

  • Discovery of DNA Components

    1910 Phoebus Levene determined the components of DNA: adenine, guanine, thymine, cytosine, deoxyribose phosphate. Defined phosphate-sugar-base units called nucleotides. Levene proposed that there were four nucleotides per molecule. Said DNA could not store the genetic code because it was chemically far too simple.

  • Frederick Griffith and his Transformation Experiment

    1928 Frederick Griffith studied the epidemiology and pathology of 2 strains of Streptococcus pneumoniae. In January reported the first widely accepted demonstrations of bacterial transformation. Griffith used two strains of Streptococcus:
    Type S: virulent (deadly)
    Type R: non-virulent (harmless)
    Observed bacterial transformation but did not understand the mechanism.

  • Cause of the transformation in Griffith's Experiment

    1944 Avery, MacLeod and McCarty determined the cause of the transformation in Griffith's Experiment.
    They took live R and heat-treated S and mixed it with one of two enzymes: a protease (destroys protein) and a DNAse (destroys DNA). Published in the Journal of Experimental Medicine: DNA not protein was responsible for the bacterial transformation Griffith observed!

  • Hershey-Chase Experiments

    1952 Hershey and Chase used phages and radiolabeled phosphorus and sulfur. Hershey and Chase concluded that DNA, not protein, was the genetic material. A protective protein coat was formed around the bacteriophage, but the internal DNA is what conferred its ability to produce progeny inside bacteria. Conclusion: It's the DNA!

  • Chargaff's Rules

    1952 Erwin Chargaff was Counting Nucleobases. Used paper chromatography and UV spectroscopy to examine the abundance of the nucleobases and he started to notice something VERY odd...
    Came to be known as "Chargoff's Rules"
    Amounts of Adenine = Amounts of Thymine
    Amounts of Cytosine = Amounts of Guanine
    ALWAYS in EVERY SPECIES!!!

  • The race begins

    The race was on to determine the structure of DNA in cells and to determine how it codes for proteins and how it replicates.
    The problem: DNA exists in two forms
    A form (dry form)
    B form (wet form, as DNA exists in cells)

  • Photo 51

    1952 Photo 51 is an X-ray based fiber diffraction image of a paracrystalline gel composed of DNA fiber taken by Raymond Gosling, a graduate student working under the supervision of Rosalind Franklin in May 1952. It was critical evidence in identifying the structure of DNA.

  • Triple Helix?

    1952 Linus Pauling and Robert Corey proposed a triple helix structure for DNA. This hypothesis was incorrect.

  • DNA is a Double-Stranded Helix

    1953 Three papers were published in the same number of Nature: Watson and Crick, Wilkins and Stockes, Franklin and Gosling. The backbone is made of sugar (deoxyribose) and phosphate groups.
    Hydrogen bonds between the nucleobases: A-T and G-C
    The sequence of nucleobases codifies the amino acid sequence of a protein.
    Strings of base pairs that code for a product are called genes.

  • The race is over

    1962 The Nobel Prize in Physiology or Medicine in 1962 was awarded to James Watson, Francis Crick and Maurice Wilkins for their discovery of the molecular structure of DNA, which helped solve one of the most important of all biological riddles.