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Discovery of Nuclic Acids
A twenty-four years Friedrich Miescher isolated a new compound from de nuclei of white blood cells. This was a novel type of biological molecule. -
Discovery of DNA components
After forty years, Phoebus Levene, a Lithuanian-American Biochemist. He discovered the DNA components, such as: adenine, guanine, thymine, cytosine and deoxyribose phosphate. He also defined the phosphate-sugar-base units called nucleotides -
Levene's Tetranucleotide
He said, 1926, that the molecule had four nucleotides. He also said that DNA could not store genetic code because it was chemically too simple -
Frederic Griffith
Frederic Griffith was the first to reveal the "transforming principle", which led to the discovery of that DNA acts as the carrier of genetic information. He discovered the bacterial transformation. -
Griffith experiment
In one of his experiments, Griffith, was trying to figure out a vaccine for pneumonia. He used mice. Strains R: They were not virulent, which means that the mouse did not cause disease and did not die. Strains S: They were virulent, which means the mouse picked up the disease and died. -
Avery, MacLeod and McCarty Conclusions
They determined the cause of the transformation in Griffith's experiment. They took live R and heat-treated S and mixed with one of two enzymes. One with protease and the other one with DNAse. This proved that the responsible of the transformation was the DNA. The final conclusion of the experiment was that the DNA is the genetic material of the cell. -
Erwin Chargaff
Erwin Chargaff, an austrian biochemist, discovered that in the DNA, the ratios of adenine (A) to thymine (T) and guanine (G) to cytosine (C) are equal. This is the final part of the DNA structure. This was discovered in 1950. He won on 1974 the National Medal of Science. -
The triple helix of Linus Pauling
In 1952, Linus Pauling proposed an idea of three helix DNA. He was unconvinced about his own job. Actually, Robert Corey suggested there was an error, but he continues. When James Watson and Francis Crick read this article, they discovered the error and created the two-helix model. They argued that there was insufficient space to hold all three propellers. -
Hershey-Chase experiments
Alfred Hershey and Martha Chase studied bacteriophages, a virus that attack bacteria. The phages that they used were simple particles formed by protein and DNA.With this and other experiments they conclude that the DNA, and not the protein, was injected to the host cells and constituted the material part of the phages. This awesome work provided clear evidences that the DNA was genetic material. -
Francis Crick and James Watson
In 1953, Francis Crick and James Watson published the famous structure of the two helix of the DNA. They posted in one page in the magazine Nature. Without the work of Rosalind Franklin this result wouldn't be possible. In 1962, they received the medicine Nobel Price. The are known as the "discoverers of the DNA". -
Picture 51
Rosalind Franklin was an a british scientist who, in 1953, took one of the most famous photos of the history. We are talking about the Picture 51. This photo confirms the theory of Watson and Crick, who gave a very little mention to Rosalind. She made a very important part of their progress and was never awarded. She died in 1958 surely due to the high radiation of his work.