The Genetic Material Timeline

P.A. Levene

Sep 5, 1920

Levine determined the basic structure of nucleotides that make up DNA. Levine found out that nucleotides are the subunits of nucleic acids and consist of a five-carbon sugar, a phosphate group, and a nitrogenous base.

Fredrick Griffith

Oct 11, 1928

Griffith studied studied different strains of streptococcus pneumoniae. That strain causes pneumonia. The strain that does not cause the illness is the one that is not coated (rough). The strain that does cause the illness is coated with sugar (smooth).

Oswald Avery

Dec 11, 1944

Avery isolated many different macromolecules like lipids and DNA from dead S cells. He concluded that DNA from the dead S cells that had been released changed the R cells. The R cells became S cells from the released DNA.

Erwin Chargaff

Dec 12, 1950

Chargaff analyzed the amounts of substances such as adenine, guanine, thymine, and cytosine in the DNA of many species. He found patterns in the amounts of the substances. His data created a new rule.
Chargaff's Rule: C=G and T=A

Linus Pauling

Dec 12, 1950

Pauling, by the diffraction of X-rays, studied structures of molecules and atoms. (DNA) He also studied the structure of proteins. Pauling contributed to finding structure of small molecules.

Rosalind Franklin

Mar 24, 1951

Rosalind's photo 51 and X-ray data helped later scientists discover that DNA is a double helix. The data helped other figure out the detail and structure to the shape.

Hershey and Chase

Aug 11, 1952

Hershey and Chase injected a virus into bacteria. Virus' cannot replicate themselves, there-fore they have to inject genetic material into other living cells for reproduction. The biologists labeled the protein and DNA that had a potential to be injected from the virus to the cells. The DNA is what was actually injected and what transformed the cells.

James Watson and Francis Crick

Dec 12, 1953

Both biologists used Chargaff's data to measure the width of the helix and the spacing of the bases. Together they built a model that would later help other biologists with research.
Important feature in their model:
-two outside strands consist of alternating deoxyribose and phosphate
-cytosine and guanine bases pair to each other by three hydrogen bonds
-thyamine and adenine bases pair to each other by two hydrogen bonds

Maurice Wilkins

Dec 13, 1960

Wilkins studied nucleic acids in cells as well as genetics and DNA. Wilkins discovered well-defined patterns that helped lead to figuring the structure of DNA. After more research he confirmed the Watson-Crick idea for DNA structure.