The Carrier of Genetic Information: DNA Structure

In the late 1940s, the ambition of the young scientist, Francis Crick, in discovering the secret of life started as soon as he began working with X-ray crystallography during the time he was at Cambridge University.¹ In the early 1950s, a young American post-doctoral student with the name of James Watson collaborated with Francis Crick to investigate the DNA molecule. The two scientists badly wanted to find out the structure of the molecule and how it worked, because they thought that if they understood the mysteries of DNA, that could help solve many questions in science, including the one that Watson had: is the DNA molecule the reason for genetic inheritance? Is DNA responsible for passing traits on to an offspring? Therefore, during the 1950s, Watson and Crick began their investigation into this phenomenon of genetic inheritance at Cambridge University.²

Meanwhile, in London at King’s College, Rosalind Franklin and Maurice Wilkins were performing an investigation studying DNA by using the X-ray crystallography technique, which consists of beaming the X-ray through the DNA molecule, creating a crystalline sample. Franklin’s work on DNA clearly was the missing piece to the completion of Watson and Crick´s research into the nucleic acid—the DNA double-helical structure. The first image of DNA was taken in the early 1950s from the work of Rosalind Franklin and was crucial for the discovery of the Watson-Crick structure. The image of the DNA, named “photo 51,” showed the molecule in the form of an “X”, which was a remarkably important clue for Watson and Crick in their discovery of the double-helix structure.³

Watson and Crick were leading the race for the discovery of the DNA molecular structure and composition, among other groups of researchers. Watson and Crick were convinced that if they succeeded in finding the secrets of the DNA molecule (the structure of DNA), then the deoxyribonucleic acid role in heredity would be revealed and other questions in biology and biomedicine would be answered.

In 1886, the Monk Gregor Mendel had discovered the real biological genetic inheritance, which he named Mendelian Inheritance, a process that consists of passing traits from two parents to an offspring.⁴ However, he didn’t know why those traits were passed on from generation to generation, nor did he know what the genes were composed of. After the Mendel Inheritance Model, many scientists, including James Watson, wondered what allowed this phenomenon (passing traits from generation to generation) to happen. It wasn’t until 1943 when researcher Oswald Avery proved that a particular nucleic acid, known as DNA, was the carrier of genetic information, and so the crucial role of DNA in determining genetic inheritance was exposed. Unfortunately, no scientist knew how this process worked until the early 1950s, when Francis Crick and James Watson started looking for answers.

Natural scientists by the 1850s already knew that DNA was composed of chemical components consisting of phosphate, carbon sugar, and a nitrogenous base, including four amino acids (adenine, thymine, cytosine, and guanine).⁵ However, the structure was not yet established, so the information about the chemical components that composed DNA were very efficient for Watson and Crick, since their research consisted more on analyzing and collecting data that already existed rather than experimenting in the lab. Thus, they put all the relevant information together until they finally found the DNA structure.

But it was not until the year 1953 that James Watson and Francis Crick could announce their model of DNA’s double helix while they were in England, hanging out in a famous pub among researchers called The Eagle. Crick told each of the guys in the pub, “We have found the secret of life.”⁶

Indeed! Crick and Watson found the secret of, and they constructed a structure of, the molecular model which represented the now-known chemical and physical properties of the DNA.⁷ In this manner, solving the pulse of the molecular structure of DNA steered Watson and Crick to the right direction for the answer to their biggest question—is the DNA molecule the reason for genetic inheritance?

In fact, Crick and Watson found that DNA is the main reason for genetic inheritance; ultimately, the genetic material that is transmitted from a parent to an offspring is located in the deoxyribonucleic acid (DNA) in the nucleus of the cells.⁸ The discovery of DNA´s double-helical structure has had an enormous impact on the fields of biology and biomedicine research. James Watson, Francis Crick, and Maurice Wilkins were awarded with the Nobel Prize in Medicine in the year 1962. Sadly, the researcher Rosalind Franklin did not receive this prize regardless of her contribution to this discovery.