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DNA is discovered
DNA was first discovered by a Swiss chemist called Johann Friedrich Miescher, he was the first to define DNA as its own molecule. It happened while he studied the composition of white blood cells and instead isolated a new molecule he called nuclein (DNA with associated proteins) from a cell nucleus. -
DNA is named
German biochemist Albrecht Kossel, responsible for naming DNA (after Friederich Miescher isolated the molecule from a cell nucleus in 1869), identified nuclein as a nucleic acid. He also isolated the five nitrogen bases that are considered the basic building blocks of DNA and RNA. -
Frederick Griffith experiments
Trying to find a cure for pneumonia, he did a series of experiments using two strains of the bacteria that cause the disease. He injected different combinations of those strains in mice to observe the outcome. This was the first experiment to demonstrate that bacteria are capable of transferring genetic information from other bacteria to use DNA as their own through a process known as transformation. -
Avery-MacLeod-McCarty Experiment
Oswald Avery first showed DNA as the transforming principle, which means that he proved it’s DNA, not proteins, that transform cell properties. His experiments had a huge impact on the study of biology since, until then, scientists weren't even sure that bacteria had genes. -
Chargaff’s Rules
Through many experiments, Edward Chargaff came up with two theories: The first one was that nitrogenous bases occur in definite ratios: The amounts of Adenine are equal to the ones of Thymine, and the same goes for Cytosine and Guanine. His second theory was that the relative amounts of these nitrogen species vary from species to species. He also dicovered that DNA is responsible for heredity. His discoverings are refered as Chargaff’s Rules. -
Photo 51
Photo 51 is an X-ray-based image of a paracrystalline gel composed of DNA fiber. It was taken by Raymond Gosling, a graduate student working under the supervision of Rosalind Franklin. The image was tagged "photo 51" because it was the 51st diffraction photograph that Franklin and Gosling had taken. It was critical evidence in identifying the structure of DNA, the double helix. -
The Hershey Chase Experiment
Alfred Hershey and Martha Chase made a series of experiments to confirm whether DNA is the basis of genetic material (and not proteins). Although the existence of DNA had been known to biologists since 1869, at that time it was though that proteins carried the information that determines heredity. But Hershey and Chase demonstrated that DNA was the physical support for the hereditary material. -
The discovery of the double helix
The double helix structure of DNA was discovered by James Watson and Francis Crick, gathering all the findings from previous scientists and biologists. It marked a milestone in the history of science and gave rise to modern molecular biology.