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P.A. Levene
During the 1920s, biochemist P.A. Levene analyzed the components of the DNA molecule. He found it contained four nitrogenous bases: cytosine, thymine, adenine, and guanine; deoxyribose sugar; and a phosphate group. He concluded that the basic unit (nucleotide) was composed of a base attached to a sugar and that the phosphate also attached to the sugar. He (unfortunately) also erroneously concluded that the proportions of bases were equal. -
Linus Pauling
In 1921 he suggested, and attempted to carry out, an experiment on the orientation of iron atoms by a magnetic field, through the electrolytic deposition of a layer of iron in a strong magnetic field and the determination of the orientation of the iron crystallises by polishing and etching the deposit, and microscopic examination of the etch figures. -
Fredrick Griffith
Experimented on mice. Noticed that there are two strands of pnemonia. One infected the mice with the disease and killed them and the second prevented it. -
Oswald Avery
Indentified the moleculethat changes one strand of pnemonia to the other. -
Maurice Wilkins
Studied the orientation of purines and pyrimidines in tobacco mosaic virus and in nucleic acids, by measuring the ultraviolet dichroism of oriented specimens, and he studied, with the visible-light polarizing microscope, the arrangement of virus particles in crystals of TMV and measured dry mass in cells with interference microscopes. -
James Watson
From September 1950 to September 1951 he spent his first postdoctoral year in Copenhagen as a Merck Fellow of the National Research Council. Part of the year was spent with the biochemist Herman Kalckar, the remainder with the microbiologist Ole Maaløe. Again he worked with bacterial viruses, attempting to study the fate of DNA of infecting virus particles. -
Erwin Chargaff
By 1950 he had experimentally determined certain crucial facts that led directly to the correct elucidation of its molecular structure. In particular, he demonstrated three rules, now known as Chargaff's Rules, which state that in DNA: 1. the number of adenine (A) residues always equals the number of thymine (T) residues; 2. the number of guanine (G) residues always equals the number of cytosine (C) residues; 3. the number of purines (A+G) always equals the number of (T+C) -
Rosalind Franklin
After discovering the existence of the A and B forms of DNA, Rosalind Franklin also succeeded in developing an ingenious and laborious method to separate the two forms, providing the first DNA crystals pure enough to yield interpretable diffraction patterns. She then went on to obtain excellent X-ray diffraction patterns of crystalline B-form DNA and, using a combination of crystallographic theory and chemical reasoning, discovered important basic facts about its structure. -
Francis Crick
A critical influence in Crick's career was his friendship, beginning in 1951, with J. D. Watson, then a young man of 23, leading in 1953 to the proposal of the double-helical structure for DNA and the replication scheme. Crick and Watson subsequently suggested a general theory for the structure of small viruses. -
Hershey and Chase
Published results of experiments that provided evidence that DNA is the transforming factor.
