The discovery of the structure of deoxyribonucleic acid (DNA)

Discovery of the Structure of DNA: A Breakthrough in Biological Knowledge

After assembling numerous lines of prior study from various fields, James Watson and Francis Crick made the discovery of the structure of deoxyribonucleic acid (DNA) in 1953. The DNA’s double helix structure is arguably the most recognizable biological molecule ever found in the modern era. This well-known DNA structure was not always a part of our biological knowledge; in fact, it was a riddle until it was uncovered in the 1950s. In a 1953 article that appeared in Nature, Watson and Crick reported on the discovery of the DNA structure. Their discovery which happened while they were at Cambridge University has played an important role in shaping the life sciences including medicine, biochemistry, agriculture, and genetics. This essay seeks to assess the lineages and ideas from different strands of research which made a crucial contribution to Watson and Crick’s discovery of the molecular nature of the DNA.

Research Clues Leading to the Discovery

In coming up with the structure of the DNA model, Watson and Crick made use of various research studies by different scholars from different fields. Watson and Crick were mainly focused on existing pieces of information which they collected and analysed in new and insightful ways. The most crucial clues of their discovery were from other researchers and scientists’ lab experiments. One important piece of information was drawn from the Austrian biochemist Erwin Chargaff who analysed different species and came up with various compositions of the DNA. Chargaff made various observations regarding four major components of the DNA; A, T, C, and G bases which turned out to be paramount in the formulation of Watson and Crick’s DNA model. The observations were that the four components were not present in equal quantities; there were variations in the number of bases among species though not between individuals from the same species; A had equal amounts as T and consequently, C had equal amounts as G.

Breakthrough in DNA Structure Discovery

The breakthrough in the DNA structure discovery came from the X-ray crystallographic data after several years since the discovery of the DNA body. This was necessitated by the advancement in various techniques in biotechnology, chemical analysis, chemical bonding as well as microscopy which were common during the mid-19th century. The investigation of the DNA can be traced back to 1869 during an isolation of a new substance from the white blood cells’ nuclei by the Swiss biochemist Friedrich Miescher who was mainly interested in the chemical components of cells. The analysis of this new substance by Miescher revealed that it was different from other known groups of biological molecules such as the proteins and carbohydrates since it contained phosphorus. Further analysis of the substance continued to yield other secrets such as the 1879 discovery by Walther Flemming of tiny thread-like structures. These structures which became known as chromosomes were later discovered to have DNA. Later research in 1900 revealed that the basic building blocks of DNA were four heterocyclic bases; Adenine (A), Guanine (G), Cytosine (C) and Thymine (T) as well as phosphate and sugar (deoxyribose).

Important Clues from X-Ray Crystallography

Perhaps, the most significant clues for the discovery of the DNA structure arose in the late 1940s from three separate researchers. One of these researchers was Maurice Wilkins from the King’s College, London who was concerned with the long fibres he observed in the DNA body. Wilkins began x-ray investigations whereby he produced various pictures, and in 1951, he involved a reputable British physical chemist, Rosalind Franklin who was internationally recognized for her perfect X-ray crystallography. Together, they were able to produce the best X-ray images for DNA which gave birth to the idea that perhaps the DNA molecule was helical in shape. These x-ray pictures gave James Watson who was an expert in molecular biology and Francis Crick, an expert in maths and physics an important clue on the DNA shape.

Structure of DNA Revealed

From Franklin’s clear crystallography, Watson and Crick got an important clue on the structure of the DNA. According to Watson, the image illustrated an X-shaped diffraction pattern which suggested that the DNA was a helical, two-stranded structure. As a result of these clear clue, Watson and Crick collected various data from research studies by Franklin, Wilkins, and Chargaff thereby assembling their 3D DNA structure. The DNA model as illustrated by Watson and Crick is a right-handed antiparallel helix with double strands. The external elements of the helix include sugar-phosphate backbones while the internal includes nitrogenous bases which make up hydrogen bonded pairs that are responsible for holding the DNA strands in place. The DNA structure also contains two chains which are coiled around a common fibre axis. Drawing from the density of the X-ray, Watson, and Crick denoted that there are two chains as opposed to the common assumption that there is only one chain since the chemical formula illustrates only one.

Complementary Base Pairing and Function of DNA

The X-ray picture further revealed that the two strands of the DNA double helix have hydrogen bonds holding them together between nitrogen bases that are present in opposite strands. The bases pairs are complimentary in nature whereby the A bases on one strand are complemented by T bases on the other and vice versa. Likewise, the G bases on one strand are complimented by C bases on the opposite strand and vice versa. This explains Chargaff’s rules whereby the composition of A must always equal that of T and consequently that of C must equal that of G. Watson and Crick’s structure unlocked many doors into the understanding of various aspects regarding the function of the DNA. The model welcomed a new era of molecular biology discoveries seen in the contemporary world.

Conclusion

In summary, the discovery of the molecular structure of the DNA by Watson and Crick could not have been possible without the input of multiple strands of previous research from different fields and scholars. The discovery was made in 1953 and spread through an article published by Watson and Crick in Nature. Unlike other contributors to the discovery of the DNA structure, Watson and Crick did not conduct lab experiments but rather relied on existing pieces of information which they collected and analysed in new and insightful ways. One important research study used was from Erwin Chargaff who analysed different species and came up with the four compositions of the DNA; A, T, C and G. The most important clue to their discovery came from the X-ray crystallographic data of Maurice Wilkins and Rosalind Franklin. The crystallographic image revealed the X-shaped molecular pattern which suggested that the DNA was a helical, two-stranded structure. Before that, several investigations had been done by various researchers without success in revealing the actual structure of the DNA cell.

Bibliography

Watson, James D., and Francis HC Crick. “Molecular structure of nucleic acids.” Nature 171, no. 4356 (1953): 737-738.