Who Discovered DNA

P.A. Levene- Nucleotides

Dec 13, 1920

CitationIn the 1920's. the biochemist P.A. Levene determined the basic structure of nucleotides that make up DNA. Nucleotides are the subunits of nucelic acids and consist of a five-carbon sugar, a phosphate group, and a nitrogenous base. The two nucleic acids found in living cells are DNA and RNA.
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Fredrick Griffith

Aug 12, 1928

The first major experiment that led to the discovery of DNA as the first genetic material was performed by Fredrick Griffith in 1928. He studied two strains of the bacteria Streptococcus pneumoniae, which causes pneumonia. He found that one strand could be transformed into the other. Of the two he studied, one had a sugar coat and one did not. The coated strain causes pneumonia and is called the smooth strain.
noncoated strain does not cause pneumonia and is called the rough strain.
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Oswald Avery (link in next avery slide)

Aug 14, 1944

In 1944, Avery and his colleagues identified the molecule that transformed the R strain of bacteria into the S strain. Avery isolatedd different macromolecules, such as DNA, protein and lipids from killed S strains. THen he exposed live R cells the the macromolecules seperately. When the live R cells were exposed to the the S strain DNA , they were transformed into S cells. He concluded that when the S strains in Griffith's experiment were killed, DNA was released.

Avery continued

Aug 14, 1944

Avery's ideas werent't widely accepted by the scientific community, and biologists continued to question and experiment to determine whether proteins or DNA were responsible for the transfer of genetic material.
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Erwin Chargaff

Sep 28, 1950

Erwin analyzed the amount of adenine, guanine, thymine, and cytosine in the DNA of various species. He found that the amount of guanine nearly equals the amount of cytosine and the amount of adenine nearly equals the amount of thymine within a species. This finding is known as Chargaff's rule: C=G and T=A
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Rosalind Franklin – X-ray diffraction

Dec 13, 1951

One of the four scientists that joined the search for the DNA structure. Franklin was a bristish chemist. She indicated that DNA looks like a double helix, or twisted ladder shape, formed by two strands of molecules twisted around each other. x-ray diffraction is a technique that involved aiming x rays at the DNA molecule
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Linus Pauling

Mar 9, 1952

In 1952. Pauling proposed a triple stranded helix structure for DNA. Pauling had the phosphate groups of each DNA strand facing into the helical core, with the nitrogeneous bases facing out. Three such strands then intertwined to make one helical DNA molecule. He had forgotten the negative charges of the oxygen atom in each phosphate group. The changes would repel, making the molecule impossible to hold together.
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Hershey and Chase

Jun 2, 1952

In 1952, Hershey and Chase published results of experiments that provided definitive evidence that DNA is the transforming factor. They used a technique called radioactive labeling to trace the fate of the DNA and protein as the bacteriophages infected bacteria and reproduced. They concluded that the viral DNA was injected into the cell and provided the genetic
information needed to produce new viruses.
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continued

Jun 2, 1952

This experiment provided powerful evdience that DNA, not protein, was the genetic material that could be passed from generation to generation in viruses.

James Watson-DNA structure

Jan 31, 1953

He shared an office with Francis Crick, a Ph.D. student who was also interested in the structure of DNA. Although both were supposed to be working on other projects, in 1953, they built the first accurate model of DNA – one of the great scientific advances of all time. THe DNA structure is compared to a twisted ladder, with the rails of the ladder represented by
the alternating deoxyribose and phosphate.
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Francis Crick-DNA structure

Jan 31, 1953

Besides coming up with the double helix structure for DNA with James Watson, Crick also proposed the Central Dogma and Adaptor Hypothesis. DNA structure is also called the double helix, or a twisted ladder. Crick created the first accuarate model with JAmes WAtson.

Maurice Wilkins

Dec 13, 1953

Wilkins was a british physicist. who helped create the DNA structure along with other scientists. Wilkins and Franklin preseneted the same evidnecethat supported the struce Watson and Crick's theroy.
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