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Meischer
The DNA saga began in 1869, when Swiss biochemist Friedrich Miescher isolated a new substance from the nuclei of white blood cells. Researchers were recently aware that cells were the basic unit of life and Miescher was interested in their chemical components. Each morning, he called at the local clinic to pick up dirty bandages, for in the days before antiseptics these were soaked in pus - a good source of white blood cells with their large nuclei. Adding alkali made the cell nuclei burst open, -
Walther Flemming
http://www.dnalc.org/view/16235-Biography-7-Walther-Flemming-1843-1905-.htmln 1879 the German biologist Walther Flemming discovered tiny thread-like structures called chromatin (later known as chromosomes) within the nucleus - so-called because they readily absorbed colour from the new stains used to reveal cellular components. Studies on cell division were to reveal the key role played by chromosomes in inheritance - how they double up before the cell splits, and then divide into two sets, taking a fresh copy into each 'daughter' cell. -
Hertwig
Further analysis suggested that chromosomes contained DNA, which led another German researcher, Oskar Hertwig, to declare that 'nuclein is the substance which is responsible ... for the transmission of hereditary characteristics'. Not everyone agreed - Miescher for one. Chromosomes also contained protein, and biochemists were just beginning to appreciate what large, complex molecules proteins were. The fragility of DNA was to conceal its underlying complexity for many more years. -
Levene
By 1900, it was Phoebus Levene who showed that the components of DNA were linked in the order phosphate- sugar-base. He called each of these units a nucleotide, arguing that the DNA molecule consisted of a string of nucleotide units linked together through the phosphate groups, which are the 'backbone' of the molecule. -
Chargaff
Click here to learn more:In 1912, Chargaff pioneered the paper chromatography of nucleic acids, using this to determine how much of each of the component nucleotides was contained in a DNA sample. He rapidly demolished Levene's tetranucleotide hypothesis. Each species differed in the amount of A, C, G and T - but within the species, the proportions of each are identical, no matter which tissue the DNA is extracted from. It was just what might be expected for a molecule that is the biological signature for the species. -
Avery
Oswald Avery and a team of medical microbiologists at the Rockefeller Institute in New York in 1928 discovered that DNA could be transferred between living organisms when experimenting with two species of pneumococcus, the bacteria that cause pneumonia (much-feared in the days before antibiotics). -
Hodgkins
The final phase of solving the puzzle of the DNA structure relied on X-ray crystallography. The use of X-rays to solve the structures of large biological molecules began with Dorothy Hodgkin's work on penicillin, lysosyme, and vitamin B12, and Max Perutz's work on haemoglobin from the 1930s. By 1938, William Astbury, a student of William Bragg (who, with son Lawrence, had invented the technique in 1913) had X-ray pictures of DNA, but they were hard to interpret. -
Wilkins and Franklin
In 1951, Wilkins was joined by Rosalind Franklin, a British physical chemist who already had an international reputation for her work on the X-ray crystallography of coals. She set about building a dedicated X-ray lab at King's and was soon producing the best images ever of DNA. These led her to the idea that maybe the DNA molecule was coiled into a helical shape. -
Watson and Crick
Click here to learn more:Crick and Watson did not know whether to build their helix with the phosphates inside or outside, and they were unsure how to incorporate Chargaff's ideas on base pairing in 1953. The final clue came from Jerry Donohue, who pointed out how hydrogen bonding allows A to bond to T and C to G. This allows a double helical structure for DNA, where the two strands have the bases on the inside.
