In 1953, James Watson and Francis Crick published details about the structure of DNA. They used experimental results from other scientists to help them work out the structure and then built a model of a section of a DNA molecule, using pieces of wire and metal, with clamp stands to hold the model in place. This is shown in Fig. 2.1. [Figure 2.1]

1. (a)(i)Watson and Crick used results from work carried out by Erwin Chargaff. He found that the proportions of the bases A, T, C and G were different in different species, but within each species: • the proportion of A was equal to the proportion of T • the proportion of G was equal to the proportion of C. Name the bases A, T, G and C. A T G C[2]
2. (a)(ii)Suggest and explain how Chargaff's findings helped Watson and Crick work out the structure of DNA.[3]
3. (b)Phoebus Levene isolated the nucleotides of DNA and identified the carbohydrate component of each nucleotide. State the name of this carbohydrate component.[1]
4. (c)Before the discovery of the structure of DNA as the molecule of inheritance, scientists thought that proteins were most likely to be the molecules that carried information. Suggest how the structure of proteins made scientists think that these were the molecules that carried information.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.