In the 1940s a team of scientists led by Oswald Avery showed that DNA is the molecule that carries the genetic code, the information used to build and operate our bodies. In the early 1950s, many people were studying DNA to try and find out how this information is stored and used. The first step towards understanding how DNA stores and uses information was to find the structure of the DNA molecule.

In May 1951 James Watson met Maurice Wilkins, who was working at King's College in London. Maurice Wilkins showed James Watson some early pictures of DNA crystals made using X-rays. These pictures were made by the arrangement of atoms inside the DNA molecule. Many different arrangements of the atoms could make similar pictures, and so the structure of the DNA molecule was still a mystery. James Watson was fascinated by this mystery and decided to try and find the structure of DNA.

James Watson knew very little about the X-ray pictures. He decided to come to work at the Cavendish Laboratory in Cambridge to find out more about them. When he arrived at Cambridge he met Francis Crick, and they began working together to try and find the structure of DNA.

Figure 1: Francis Crick & James Watson having coffee in their office at the Cavendish Laboratory.	Figure 2: X-ray diffraction image of 'B-type' taken by Rosalind Franklin.

James Watson and Francis Crick spent many months building models of molecules, and comparing them to the information they had from the X-ray pictures of DNA, but still they couldn't find the correct structure of DNA. They told Maurice Wilkins about what they were trying to do and he showed them a new and better X-ray picture of DNA, which had been taken by Rosalind Franklin. James Watson and Francis Crick used this new and clearer picture to help them solve the mystery.

In spring 1953, James Watson and Francis Crick discovered the structure of DNA. They showed that the molecule has a double helix structure, similar to a twisted ladder. They suggested that genetic information is stored in the rungs of the ladder, and that one half of the ladder could be used as a template for making the other half. Their suggestions of how information is stored and used by DNA were confirmed by the end of the 1950s.

You can find out about the discovery of the structure of DNA from the DNA section of www.cambridgephysics.com