On February 28, 1953, American molecular biologist James D. Watson and English biophysicist Francis Crick announced to friends that they succeeded to determine the chemical structure of DNA.
Already in the 19th century biochemists were able to isolate DNA and RNA from the cell nuclei mixed together. They later found out that DNA and RNA had to be distinct from each other. The nuclein was identified by Friedrich Miescher in 1869 and he later on isolated the pure DNA from a salmon’s sperm. The term ‘nucleic acid’ was then coined by Richard Altmann and it was only found in the chromosomes. The Lithuanian-American biochemist Phoebus Levene at Rockefeller Institute made further achievements concerning the DNA’s structure, showing that its components, the sugar and phosphate chain were linked in the order phosphate-sugar-base. Each of these was named nucleotide and the scientist assumed that the DNA molecule consisted of a string of nucleotide units, which were linked together through phosphate groups. In his understanding however, the chain was short and its bases repeated in a fixed order, the theory that the DNA was a polymer was later suggested by Torbjorn Caspersson and Einar Hammersten.
Further efforts on the DNA’s structure were made in the 1950’s, and three known groups worked on the topic. Rosalind Franklin and Maurice Wilkins  of King’s College London belonged to the first group, Francis Crick and James Watson from Cambridge formed the second group and Linus Pauling and his team at Caltech depicted the third. Crick and Watson were able to build physical models of metal rods and balls, incorporating the chemical structured of the nucleotides. In the late 1940’s, Pauling and his team discovered many proteins included helical shapes and also Wilkins found out that in the DNA’s structure, helix’ were somehow involved. Watson and Crick then began answering questions like whether the bases pointed toward the helical axis or away or what the angles and coordinated of all atoms and bonds were.
Due to an inspiration by Erwin Chargaff, Watson and Crick used X-ray diffraction and added several data by Rosalind Franklin, which resulted in the accurate model of the DNA’s molecular structure. The extraordinary discovery was announced on February 28, 1953 and the news spread quickly. A new milestone was set in molecular biology.
References and Further Reading:
-  Molecular structure of nucleic acids [PDF]
-  The DNA at the Nobelprize Website
-  Clue to chemistry of heredity found [PDF]
-  James D. Watson: DNA – The Secret of Life, Arrow Books, 2004.
-  Rosalind Franklin and the Beauty of the DNA Structure, SciHi Blog, July 24, 2014
-  Maurice Wilkins and the DNA, SciHi Blog, December 15, 2016
-  Severo Ochoa and the Biological Systhesis of RNA and DNA, SciHi Blog, September 24, 2017
-  James Watson at Wikidata
-  Francis Crick at Wikidata