Summary:This article by Pray (2008), published in Nature, highlights and explains the history of the discovery of DNA. It points out that, whilst we generally ascribe the discovery of DNA to James Watson and Francis Crick, the work they did was based on ideas going back to the 1860s.
The article follows the chronology of DNA discovery, from Friedrich Miescher discovering nuclein in human white blood cells in 1869 and Pheobus Levene working on the chemistry of biological molecules in the early 20th century through to Chargaff understanding the rules of nucleic acids and Watson and Crick discovering the famous double helix structure.
The overall thesis of the article is that, whilst Watson and Crick are known for discovering the structure of DNA, none of this would have been possible without Chargaff’s finding that A = T and C = G within the structure. It also highlights that x-ray crystallography by Rosalind Franklin and Maurice Wilkins allowed them to build the three-dimensional structure.
What was studied:
This article is essentially a historical study of DNA and the discoveries that led to the knowledge that we now have. It starts by focusing on the work of Miescher, who discovered nucleins (or nucleic acids), although his work was ignored by science at the time. His experiments on white blood cells helped him notice that these substances had a high phosphorous content and were resistant to proteolysis, unlike normal proteins.
It was from this point that Pheobus Levene found that each of these nucleotides was composed of three main components – phosphates, sugars, and bases. He was also the first one to discover that ribose was a carbohydrate that formed part of RNA and that its counterpart in DNA was deoxyribose. He was a prolific scientist and was also the first to connect the way in which RNA and DNA are formed.
It was from this foundation that Chargaff created the rules of DNA that led to the discovery of the double-helix structure. He carried out a number of experiments that aimed to discover whether DNA was a universal molecule – he found that DNA molecules, whilst similar in nature, differ from species to species. All DNA is formed of equal amounts of adenine and thymine, and equal amounts of guanine and cytosine. It is the amount of each of these pairs that differs in each organism. This was the first work that noted that DNA sequences are essentially what differentiates species.
The article also summarizes how Watson and Crick took all this information and put it together to come to their famous discovery. It suggests that their work took into account all of this information, but also involved X-ray crystallography work by other scientists. Watson and Crick also used the work of Linus Pauling to allow them to create a scale-size model of their double helix. In fact, the pair were worried that Pauling would beat them to the discovery of the actual model, but his suggestion three months earlier was incorrect. This is how we come to associate Watson and Crick with DNA.
Glossary:
Nucleic Acid – a type of molecule that is formed of long chains of monomers, or nucleotides
Nucleotides – the building blocks of life which are joined together to create nucleic acids like DNA and RNA
Deoxyribonucleic acid – a molecule formed of nucleotides that contains all of the information an organism needs to exist and reproduce
Crystallography – a way of determining how atoms are put together in a crystal, which can then be x-rayed to determine the atomic and molecular structure of that crystal (Roberts, 1989)
- Pray, Leslie. “Discovery of DNA Structure and Function: Watson and Crick.” Nature Education 1.1 (2008): 100. Print.
- Roberts, Royston M. “Serendipity: Accidental Discoveries in Science.” Serendipity: Accidental Discoveries in Science, by Royston M. Roberts, pp. 288. ISBN 0-471-60203-5. Wiley-VCH, June 1989. (1989): 288. Print.
