Who is credited with discovering the structure of dna

Francis Crick and James Watson are most often associated with the famous genetic molecule, but their work in the 1950s came over 80 years after the identification of DNA by a Swiss physician searching for the ‘building blocks’ of life. Friedrich Miescher had focused on proteins in cells, but in 1869 he discovered a strange substance also lurking in the nuclei of the cells. He named it ‘nuclein’, and suspected it would prove at least as vital to cells as proteins.

© Getty Images

Crick and Watson were not the first to show he was right, either. Their celebrated discovery of DNA’s double helix structure was prompted by key experiments by a team led by the American biochemist Oswald Avery. In 1944, working at the Rockefeller University in New York, they published the results of painstaking studies using bacteria that revealed that DNA passed genetic information from one organism to another.

Francis Crick (left) and James Watson © Getty Images

This went against the accepted wisdom that proteins must be the carriers of genetic information, as DNA was ‘obviously’ too simple a molecule to perform so complex a role. Crick and Watson agreed with Avery – but his own claim to a Nobel was blocked by sceptics until the 1960s, by which time he was dead.

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They were hardly modest, these two brash young scientists who in 1953 declared to patrons of the Eagle Pub in Cambridge, England, that they had "found the secret of life." But James Watson and Francis Crick's claim was a valid one, for they had in fact discovered the structure of DNA, the chemical that encodes instructions for building and replicating almost all living things. The stunning find made possible the era of "new biology" that led to the biotechnology industry and, most recently, the deciphering of the human genetic blueprint.

Watson and Crick's discovery didn't come out of the blue. As early as 1943 Oswald Avery proved what had been suspected: that DNA, a nucleic acid, carries genetic information. But no one knew how it worked.

By the early 1950s, at least two groups were hot on the trail. Crick, a British graduate student, and Watson, an American research fellow, were in the hunt at Cambridge University. At King's College in London, Rosalind Franklin and Maurice Wilkins were studying DNA. Wilkins and Franklin used X-ray diffraction as their main tool -- beaming X-rays through the molecule yielded a shadow picture of the molecule's structure, by how the X-rays bounced off its component parts. Franklin, a shy and inward young woman, suffered from patronizing attitudes and sexism that forced her to do much of her work alone. And her senior partner, Wilkins, showed some of Franklin's findings to Watson in January 1953 without her knowledge.

Referring to Franklin's X-ray image known as "Exposure 51," James Watson is reported to have said, "The instant I saw the picture, my mouth fell open and my pulse began to race." Shortly after, Watson and Crick made a crucial advance when they proposed that the DNA molecule was made up of two chains of nucleotides paired in such a way to form a double helix, like a spiral staircase. This structure, announced in their famous paper in the April 1953 issue of Nature, explained how the DNA molecule could replicate itself during cell division, enabling organisms to reproduce themselves with amazing accuracy except for occasional mutations.

For their work, Watson, Crick, and Wilkins received the Nobel Prize in 1962. Despite her contribution to the discovery of DNA's helical structure, Rosalind Franklin was not named a prize winner: She had died of cancer four years earlier, at the age of 37.

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The Discovery of DNA's Structure

Photo of Rosalind Franklin courtesy of Vittorio Luzzati. Photo of x-ray crystallography (Exposure 51) courtesy of King's College Archives. King's College London.

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On February 28, 1953, Cambridge University scientists James D. Watson and Francis H.C. Crick announce that they have determined the double-helix structure of DNA, the molecule containing human genes. The molecular biologists were aided significantly by the work of another DNA researcher, Rosalind Franklin, although she is not included in the announcement, nor did she share the subsequent Nobel Prize award for it.

Though DNA—short for deoxyribonucleic acid—was discovered in 1869, its crucial role in determining genetic inheritance wasn’t demonstrated until 1943. In the early 1950s, Watson and Crick were only two of many scientists working on figuring out the structure of DNA. California chemist Linus Pauling suggested an incorrect model at the beginning of 1953, prompting Watson and Crick to try and beat Pauling at his own game. 

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On the morning of February 28, they determined that the structure of DNA was a double-helix polymer, or a spiral of two DNA strands, each containing a long chain of monomer nucleotides, wound around each other. According to their findings, DNA replicated itself by separating into individual strands, each of which became the template for a new double helix. In his best-selling book, The Double Helix (1968), Watson later claimed that Crick announced the discovery by walking into the nearby Eagle Pub and blurting out that “we had found the secret of life.” The truth wasn’t that far off, as Watson and Crick had solved a fundamental mystery of science–how it was possible for genetic instructions to be held inside organisms and passed from generation to generation.

Watson and Crick’s solution was formally announced on April 25, 1953, following its publication in that month’s issue of Nature magazine. The article revolutionized the study of biology and medicine. Among the developments that followed directly from it were pre-natal screening for disease genes; genetically engineered foods; the ability to identify human remains; the rational design of treatments for diseases such as AIDS; and the accurate testing of physical evidence in order to convict or exonerate criminals.

Crick and Watson later had a falling-out over Watson’s book, which Crick felt misrepresented their collaboration and betrayed their friendship. 

A larger controversy arose over the use Watson and Crick made of work done by another DNA researcher, Rosalind Franklin. Colleague Maurice Wilkins showed Watson and Crick Franklin's X-ray photographic work to Watson just before he and Crick made their famous discovery. The imagery established that the DNA molecule existed in a helical conformation. When Crick and Watson won the Nobel Prize in 1962, they shared it with Wilkins. Franklin, who died in 1958 of ovarian cancer and was thus ineligible for the award, never learned of the role her photos played in the historic scientific breakthrough.

It is a common misconception that James Watson and Francis Crick discovered DNA in the 1950s. In reality, DNA was discovered decades before. It was by following the work of the pioneers before them that James and Francis were able to come to their ground-breaking conclusion about the structure of DNA in 1953.

The story of the discovery of DNA begins in the 1800s…

The molecule of life

The molecule now known as DNA was first identified in the 1860s by a Swiss chemist called Johann Friedrich Miescher. Johann set out to research the key components of white blood cells, part of our body’s immune system. The main source of these cells was pus-coated bandages collected from a nearby medical clinic.

Johann called this mysterious substance ‘nuclein’. Unbeknown to him, Johann had discovered the molecular basis of all life – DNA.

Johann carried out experiments using salt solutions to understand more about what makes up white blood cells. He noticed that, when he added acid to a solution of the cells, a substance separated from the solution. This substance then dissolved again when an alkali was added. When investigating this substance he realised that it had unexpected properties different to those of the other proteins he was familiar with. Johann called this mysterious substance ‘nuclein’, because he believed it had come from the cell nucleus. Unbeknown to him, Johann had discovered the molecular basis of all life – DNA. He then set about finding ways to extract it in its pure form.

Swiss chemist, Friedrich Miescher.
Image credit: Wikimedia Commons

Johann was convinced of the importance of nuclein and came very close to uncovering its elusive role, despite the simple tools and methods available to him. However, he lacked the skills to communicate and promote what he had found to the wider scientific community. Ever the perfectionist, he hesitated for long periods of time between experiments before he published his results in 1874. Before then he primarily discussed his findings in private letters to his friends. As a result, it was many decades before Johann Friedrich Miescher’s discovery was fully appreciated by the scientific community.

For many years, scientists continued to believe that proteins were the molecules that held all of our genetic material. They believed that nuclein simply wasn’t complex enough to contain all of the information needed to make up a genome. Surely, one type of molecule could not account for all the variation seen within species?

The four building blocks of DNA

Albrecht Kossel was a German biochemist who made great progress in understanding the basic building blocks of nuclein.

Albrecht Kossel isolated the five nucleotide bases that are the building blocks of DNA and RNA: adenine, cytosine, guanine, thymine and uracil.

In 1881 Albrecht identified nuclein as a nucleic acid and provided its present chemical name, deoxyribonucleic acid (DNA). He also isolated the five nucleotide bases that are the building blocks of DNA and RNA: adenine (A), cytosine (C), guanine (G), thymine (T) and uracil (U).

This work was rewarded in 1910 when he received the Nobel Prize in Physiology or Medicine.

German biochemist, Albrecht Kossel.
Image credit: Wikimedia Commons.

In the early 1900s, the work of Gregor Mendel was rediscovered and his ideas about inheritance began to be properly appreciated. As a result, a flood of research began to try and prove or disprove his theories of how physical characteristics are inherited from one generation to the next.

In the middle of the nineteenth century, Walther Flemming, an anatomist from Germany, discovered a fibrous structure within the nucleus of cells. He named this structure ‘chromatin’, but what he had actually discovered is what we now know as chromosomes. By observing this chromatin, Walther correctly worked out how chromosomes separate during cell division, also known as mitosis.

Walter Sutton and Theodor Boveri first presented the idea that the genetic material passed down from parent to child is within the chromosomes.

The chromosome theory of inheritance was developed primarily by Walter Sutton and Theodor Boveri. They first presented the idea that the genetic material passed down from parent to child is within the chromosomes. Their work helped explain the inheritance patterns that Gregor Mendel had observed over a century before.

Interestingly, Walter Sutton and Theodor Boveri were actually working independently during the early 1900s. Walter studied grasshopper chromosomes, while Theodor studied roundworm embryos. However, their work came together in a perfect union, along with the findings of a few other scientists, to form the chromosome theory of inheritance.

Walter Sutton (left) and Theodor Boveri (right) worked independently to come up with the chromosome theory of inheritance.
Image credit: Wikimedia Commons.

Building on Walther Flemming’s findings with chromatin, German embryologist Theodor Boveri provided the first evidence that the chromosomes within egg and sperm cells are linked to inherited characteristics. From his studies of the roundworm embryo he also worked out that the number of chromosomes is lower in egg and sperm cells compared to other body cells.

American graduate, Walter Sutton, expanded on Theodor’s observation through his work with the grasshopper. He found it was possible to distinguish individual chromosomes undergoing meiosis in the testes of the grasshopper and, through this, he correctly identified the sex chromosome. In the closing statement of his 1902 paper he summed up the chromosomal theory of inheritance based around these principles:

• Chromosomes contain the genetic material.
• Chromosomes are passed along from parent to offspring.
• Chromosomes are found in pairs in the nucleus of most cells (during meiosis these pairs separate to form daughter cells).
• During the formation of sperm and eggs cells in men and women, respectively, chromosomes separate.
• Each parent contributes one set of chromosomes to its offspring.