DNA timeline


Friedrich Miescher


Friederich Miescher was a biologist and physician. He was the first to realize DNA as a distinct molecule. He differentiated proteins and nucleic acids from cell nuclei. He determined that nuclein was was made up of hydrogen, oxygen, nitrogen, and phosphorous.

Frederick Griffith


Frederick Griffith was a bacteriologist who focused on the epidemiology and pathology of bacterial pneumonia. Griffith’s experiment included mice and two strains of Pneumococcus (type III-S and type II-R). III-S was the lethal strand and II-R was fought off by the immune system. Everytime Griffith injected a mouse with living S cells, it died. Even when he combined S cells with R cells, the mice died. When Griffith injected the mice with dead S cells, it did not kill the mouse because the lethal enzymes were denatured through heat. From the experiment, Griffith came up with the transformation phenomenon. This means that a change in genotype and phenotype due to assimilation of foreign DNA.

Avery, McCarty, and MacLeod


Before their experiment, scientists believed that protein was the “transforming principle” that Griffith discovered in his experiment. Avery, McCarty, and MacLeod concluded that DNA is the transforming principle.

Erwin Chargaff


Erwin Chargaff was a biochemist at Columbia University medical school. Chargaff became interested in DNA and nucleic acids after Avery’s discovery. Erwin Chargaff developed two rules about DNA. First rule- the number of guanine equals the number of cytosine and adenine equals the number of thymine in DNA strands. Second rule- DNA composition differs from species to species.

Linus Pauling


Linus Pauling was a chemist and biochemist. Pauling was one of the founders of quantum chemistry and molecular biology. He discovered the structure of protein based off of his background in chemistry.

Hershey and Chase


Hershey and Chase studied bacteriophage (viruses that attack bacteria). They wanted to know if the instructions came from protein or DNA. To figure this out, they performed an experiment with 35S and 32P. They concluded that DNA was injected into the host cells and made the genetic material of phage, not protein.

Watson and Crick


James Watson was a molecular biologist, geneticist, and zoologist. Francis Crick was a molecular biologist, biophysicist, and neuroscientist. Watson and Crick were curious about the structure of DNA. After years of research and incorrect findings from other scientists, Watson and Crick introduced the double helix model of DNA.

Rosalind Franklin


The only scientist with a degree in chemistry that was working on figuring out the structure of DNA. Franklin became well respected in the field of x-ray crystallography and then began her work in DNA. Franklin’s experience in crystallography led Watson and Crick to their conclusion about DNA structure. Based on her research, Franklin concluded that there were two antiparallel sugar-phosphate backbones with nitrogenous bases.

Maurice Wilkins


Maurice Wilkins was a physicist and molecular biologist. His research contributed to the understanding of phosphorescence, isotope separation, optical microscopy, and x-ray diffraction. Wilkins is best known for his work on the structure of DNA using x-ray technology to develop Watson and Crick’s theory.

Meselson and Stahl


Matthew Meselson was a geneticist and molecular biologist. Franklin Stahl was also a geneticist and molecular biologist. Meselson and Stahl were curious about Watson’s hypothesis that DNA structure is semiconservative. Meselson and Stahl are known for the experiments that confirmed that DNA is semiconservative.