The discovery of the structure of DNA
In 1943 american scientist Oswald Avery proved that DNA, and not proteins, as had been previously thought, carried the genetic information of a cell, resulting in several attempts to discover the structure of DNA. By the 1950s, a number of dicoveries about DNA had been made, but the full structure was yet to be found. Two main teams were working on it in England: Maurice Wilkins, and Rosalind Franklin were attempting to deduce the structure through X-ray spectroscopy at King's college London, while James Watson and Francis Crick were working on a more theoretical basis, by trying to work out what structures could have the necessary properties for DNA at Cambridge. While Watson and Crick took the credit for the structure of DNA, it is known that much of their work was based on X-ray data shown to them by Maurice Wilkins, and taken by Rosalind Franklin. The data showed the helical structure that is distinctive of DNA. Franklin's role in the discovery of DNA was crucial, and she never received much of the credit for it as she died shortly afterwards of cancer.
Structure of DNA
DNA is a polynucleotide ie. it is composed of many base units called nucleotides. Each DNA nucleotide is composed of a phosphate group, a deoxyribose sugar, and a nitrogenous base (one of thymine, guanine, adenine, and cytosine). The phosphate group and the deoxyribose sugar form an alternating chain, often called the sugar-phosphate backbone, of the DNA molecule, while the nitrogenous bases "stick out" to one side. In the double helix structure, hydrogen bonds form between thymine and adenine and cytosine and guanine, bonding the two chains together.