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Scientists identify DNA

This Day in World History

April 25, 1953

Scientists identify DNA

DNA replication split. Source: Dept of Energy Human Genome Project.
The April 25, 1953 edition of the journal Nature included a scientific paper that opened new doors in scientific understanding. The paper, written by James Watson and Francis Crick, described the structure of DNA (deoxyribonucleic acid), the substance that determines the hereditary traits of a living organism.

Watson was an American-born biologist who became interested in the effort to crack the secrets of DNA in his early twenties. Crick, a British-born biologist, began working on the structure of large molecules in living organisms in the 1940s. The two ended up collaborating at the same British laboratory.

What later became known as DNA was first discovered by a Swiss chemist in 1869. In 1919, a Lithuanian biochemist published a paper proposing that substances called nucleic acids, or nucleotides, combined to make DNA. In 1944, researchers identified DNA as the determinant of heredity. The next step, by an Austrian biochemist, came in 1950. The combination of nucleotides in different species differs, and the amount of two nucleotides is matched by the amount of two others.

Watson and Crick explained how the nucleotides fit together and what form DNA took. The nucleotides were held in place, they said, by ribbons formed of sugar-phosphate compounds. These ribbons form two strands with the nucleotides that pair together on opposite locations of each strand. The ribbons twist in a spiral structure they called a double helix. They found this structure by using cardboard models of the nucleotides, which they tried assembling in different combinations. They also explained how the DNA could reproduce itself.

Watson and Crick’s work launched a flurry of research to learn more about DNA. While refinements have been made, the basic principles they outlined in 1953 have been proved. The two scientists and a third researcher won the Nobel Prize for Physiology or Medicine in 1962 for this work.

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