DNA timeline

By: Mar'Quise Carter

Frederick Griffith

-Frederick Griffith was born in Hale, Cheshire, England in 1877.

-He was one of two children and both were employed by the British government as microbiologists. Griffith attended Liverpool University, graduating in 1901.

-In 1910, he joined the military, accepting the role as medical officer in the pathology laboratory of the Ministry of Health in London. Why Pneumonia? Frederick Griffith was working to discover a vaccine for the prevention of pneumonia because it was the leading cause of death at the time. His work focused on determining the specific strains of the bacteria. He would study these strains from the samples he took from people infected with the bacteria. This is where he hypothesized that one strand could turn into another. This is when he started his experiments that would lead to his discovery of the Transforming Principle.

-In 1928, while working with the British Ministry of health, Griffith was trying to create a vaccine to prevent Streptococcus pneumonia infection. He performed an experiment using pneumonia, bacteria, and mice. His results from these experiments were his claim to fame, the discovery of the Transforming Principle.


Graduated from Liverpool University
His experiment lead him to fame, enabling his discovery of the Transformation Principle.
Published the results from his experiment in the Journal of Hygiene in 1928.


Oswald Avery

-By the 1940, scientists understanding of the principles of inheritance had moved on considerably - genes were known to be the discrete units of heredity, as well as generating the enzymes which controlled metabolic functions. However, it wasn't until 1944 that deoxyribonucleic acid(DNA) was identified as the transforming principle.

-The man who made the breakthrough was Oswald Avery, an immunochemist at the Hospital of the Rockefeller Institute for Medical Research. Avery had worked for many years with the bacterium responsible for pneumonia, pneumococcus, and had discovered that if a live but harmless form of pneumococcus was mixed with an inert but lethal form, the harmless bacteria would soon become deadly.

-In 1944, after much deliberation, Avery and his colleagues published a paper in the Journal of Experimental Medicine, in which they outlined the nature of DNA as the 'transforming principle'. Although the paper was not widely read by geneticists at the time, it did inspire further research, paving the way for one of the biggest discoveries of the 20th century.

Erwin Chargaff

-In 1944, scientist Erwin Chargaff had read Oswald Avery's scientific paper, which identified DNA as the substance responsible for heredity. The paper had a huge impact on Chargaff and changed the future course of his career. He later recollected, “Avery gave us the first text of a new language, or rather he showed us where to look for it.

-Chargaff was determined to begin work on the chemistry of nucleic acids. His first move was to devise a method of analysing the nitrogenous components and sugars of DNA from different species.

-He subsequently submitted two papers to the Journal of Biological Chemistry (JBC) detailing the complete qualitative analysis of a number of DNA preparations. Despite the significance of the paper’s findings, the JBC was initially reluctant to publish it, illustrating the ignorance about nucleic acids amongst elite scientists at the time.

-Chargaff continued to improve his research methods and was eventually able to rapidly analyse DNA from a wide range of species. In 1950, he summarised his two major findings regarding the chemistry of nucleic acids: first, that in any double-stranded DNA, the number of guanine units is equal to the number of cytosine units and the number of adenine units is equal to the number of thymine units, and second that the composition of DNA varies between species. These discoveries are now known as 'Chargaff's Rules'.

Rosalind Franklin

-Rosalind Franklin was born in london in 1920 and conducted a large portion of the research which eventually led to the understanding of the structure of DNA - a major achievement at a time when only men were allowed in some universities' dining rooms.

-After achieving a doctorate in physical chemistry from Cambridge University in 1945, she spent three years at the Laboratoire Central des Services Chimiques de L'Etat in Paris, learning the X-Ray diffraction techniques that would make her name. Then, in 1951, she returned to London to work as a research associate in John Randall's laboratory at King's College.

-Franklin's role was to set up and improve the X-ray crystallography unit at King's College. She worked with the scientist Maurice Wilkins, and a student, Raymond Gosling, and was able to produce two sets of high-resolution photographs of DNA fibres. Using the photographs, she calculated the dimensions of the strands and also deduced that the phosphates were on the outside of what was probably a helical structure.

-Franklin's photographs were described as, "the most beautiful X-ray photographs of any substance ever taken" by J. D. Bernal, and between 1951 and 1953 her research came close to discovering the structure of DNA. Unfortunately, she was ultimately beaten to the post by Thomas Watson and Frances Crick.


Alfred Hershey and Marsha Chase

-Alfred Hershey and Martha Chase did the Hershey-Chase blender experiment that proved phage DNA, and not protein, was the genetic material. Alfred Hershey was born in Owosso, Michigan. He graduated from Michigan State in 1930 with a B.S., and in 1934 with a Ph.D. After his Ph.D., Hershey accepted a position at the Washington University School of Medicine in the Department of Bacteriology, where he started working on bacteriophage.

-At the time, there weren't many people working on bacteriophage. Two other scientists who read Hershey's papers, Max Delbrück and Salvador Luria, were collaborating on experiments using bacteriophage. In 1943, Delbrück invited Hershey to Nashville to visit his lab. In 1946, working with Delbrück, Hershey discovered that phage can recombine when co-infected into a bacteria host. This led to a new area of phage genetics.

-As leading researchers in the field of bacteriophage, Delbrück, Luria, and Hershey established the American Phage Group which had a tremendous influence on bacteriophage research.

Hershey stayed at the Washington University School of Medicine until 1950. He then accepted a position from the Carnegie Institution of Washington's Department of Genetics at Cold Spring Harbor. Here he and Martha Chase did the Hershey-Chase blender experiment. For this, and his body of work on bacteriophage, Hershey shared the 1969 Nobel Prize for Physiology and Medicine with Max Delbrück and Salvador Luria.

-In 1962, Hershey became the Director of the Genetics Research Unit at Cold Spring Harbor Laboratory. His lab continued to work on bacteriophage, focusing on phage recombination and genetics. In 1974, Hershey retired, though he was still a regular visitor to Cold Spring Harbor Laboratory. In 1979, a building on the grounds was dedicated to him.

Hershey was known to be an excellent writer and editor. His papers were clear and concise and he helped other scientists learn the craft of scientific writing. He enjoyed gardening and woodworking, as well as classical music. In the early 80s, he became interested in computers and used them to catalog his classical music collection. He was busy, active, and still learning even in retirement.

James Watson and Francis crick

-In 1951, James Watson visited Cambridge University and happened to meet Francis Crick. Despite an age difference of 12 years, the pair immediately hit it off and Watson remained at the university to study the structure of DNA at Cavendish Laboratory.

-Using available X-ray data and model building, they were able to solve the puzzle that had baffled scientists for decades. They published the now-famous paper in Nature in April, 1953 and in 1962 they were awarded the Nobel Prize for Physiology or Medicine along with Maurice Wilkins.

-Despite the fact that her photographs had been critical to Watson and Crick's solution, Rosalind Franklin was not honoured, as only three scientists could share the prize. She died in 1958, after a short battle with cancer.