The DNA double helix

The procedure through which the structure of DNA was found to be a double helix has been well documented elsewhere. It is important to see the structure in the context of the previous chemical and biological evidence – example for the double helix was only regular in the way that X-ray diffraction experiments suggested if G was paired with C and T with A. More remarkably Watson and Crick were able to suggest much more about the biochemistry of DNA than the mere shape of the molecule alone. They proposed that the replication of DNA must be semi-conservative with separation of the strands before synthesis of complementary DNA. Subsequently, the  very  nature of DNA as  an  informational macromolecule led  them to  suppose the  existence of codons and  therefore to  an  adaptor hypothesis. In conjunction with the discovery of mRNA they proposed that in order for amino acids to reflect DNA sequence a molecule must intervene among the two. This led Crick to draw a molecule with many similarities to tRNA. The combination of these hypotheses surrounding DNA structure has led to the elucidation of most of our understanding of molecular biology from gene to mRNA to protein via tRNA.