Deoxyribonucleic Acid (DNA) is the blueprint upon which all life is based, each organism having its own unique sequence or “code”. Although it is quite common to see images of the DNA double-helix today, the structure of DNA was first discovered by Dr. James Watson and Dr. Francis Crick in 1953, just over 50 years ago. This discovery allowed for an understanding of DNA base pairing and replication, and has been hailed as the foundation for modern biology.

The DNA code consists of just four base pairs - the purines adenine (A) and guanine (G) and the pyrimidines thymine (T) and cytosine (C). Each of these bases includes a phosphate and sugar (deoxyribose) backbone which are linked together to form a continuous strand. This molecular composition of DNA was known before Watson and Crick’s seminal discovery, but the ultimate structure was not understood.

At the same time that Watson and Crick endeavored to understand the structure of DNA, Rosalind Franklin was utilizing X-ray crystallography to give an idea of the overall shape of the molecule. It was her work that first gave the two scientists the idea that DNA had a double-helical structure. They also proposed a base-airing system where G pairs with C and A with T. This was based on previous work showing that the G and C bases always existed in equal numbers in a single strand of DNA; likewise, A and T bases were equivalent. This system is now referred to as Watson-Crick base pairing.

From there, the structure began to come together. By utilizing an ingenious method of model-building to “tinker” with and understand the final form, much as we would use computer modeling to work out details today, they built what is now known as the B form of DNA (B-DNA). It consisted of two strands running anti-parallel to each other in a twisted, helical structure approximately ten base pairs long per full turn. Further, each strand is an exact opposite template to the other. Noting this mirrored structure, the Drs. Watson and Crick correctly predicted that the molecule could self-replicate with a high degree of accuracy by splitting and forming a new full strand from each of the old template molecules.

Watson and Crick published a “Molecular structure of nucleic acids; a structure for deoxyribose nucleic acid” in Nature journal in 1953. Although this was a paper of tremendous importance, it was a scant two pages long. They received the Nobel Prize for their work in 1962.