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Deoxyribonucleic acid
was first isolated in 1869 by the Swiss scientist Friedrich Miescher. He called the white, slightly acidic chemical that he found in cells "nuclein." -
what is the DNA made of?
scientists knew what DNA contained - phosphate, sugar, and four nitrogen-containing chemical "bases": adenine (A), thymine (T), guanine (G), and cytosine (C). But no one had figured out what the DNA molecule looked like. -
Oswald Avery and Frederick Griffith
In 1944, they had reported that DNA, not proteins (which was believed at the time), was the hereditary substance in these extracts. They backed there report up by the results of an experiment in which they added protein-digesting enzymes to some of the extracts, and the cells were still transformed, but when the added an enzyme that broke the DNA but not the protein, the hereditary transformation was blocked. -
Erwin Chargaff
He foun that the amount of adenine in DNA always equals the amount of thymine. And he found that the amount of guanine always equals the amount of cytosine. -
James Watson and Francis Crick
They began to examine the DNA’s structure. Using previous X-ray diffraction photos of DNA fibers taken by Maurice Wilkins and Rosalind Franklin, they discovered that it showed an X shape... which is also the characteristic of a helix. -
Rosalind Franklin
Rosalind Franklin used a process know as X ray diffraction to make images of DNA molecules. When a X ray hits a part of the molecule, the ray bounces off. The pattern made by the boucing rays is captured on film. Franklin's images suggested that DNA has a spiral shape. -
Watson and Crick
In the April 25, 1953, issue of the science journal Nature, Watson and Crick wrote: ""We wish to suggest a structure for the salt of deoxyribose nucleic acid (DNA). This structure has novel features which are of considerable biological interest." In 1953, Linus Pauling, the great American chemist, claimed to have discovered the structure of the DNA molecule, but when Watson saw Pauling's research paper (which had not yet been published) on January 28, 1953, he knew it was wrong. A few days later -
Watson and Crick
In 1962, Watson and Crick received the Nobel Prize for Physiology or Medicine with Maurice Wilkins. He had published important crystallography work relating to DNA at the same time as Watson and Crick. Rosalind Franklin, whose photograph provided "a Eureka moment" for Watson, died in 1958 of cancer. Scientists wonder if she would have been honored with the award as well, had she lived. -
DNA molecules
"The instant I saw the picture, my mouth fell open and my pulse began to race," wrote Watson in his book The Double Helix (1968). The photo convinced him that the DNA molecule must consist of two chains arranged in a paired helix, which resembles a spiral staircase or ladder.
