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Friedrich Miescher
Miescher first discovered DNA while experimenting on white blood cells by using pus from bandages. He first washed the bandages and poured in a weak alkaline solution. The cells lysed and nuclei precipitated from the solution. From this, he isolated the nuclein (nucleic acid)from the nucleus and had the first purification of DNA. He later concluded that nuclein was made of hydrogen, oxygen, nitrogen, and phosphorus. This first basic understanding that DNA exits led to further extensive research. -
Period: to
DNA Development
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Erwin Chargaff
Chargaff proposed Chargaff's rules which was the ratio of A:T was equal to the ratio of G:C. This was saying that the number of purines was equal to the number of pyrimidines (complementary base pairing). He made this conclusion by extracting DNA from the nuclei and used paper chromatography to separate purines from pyrimidines. From this, he observed that the number of purines was equal to pyrimidines. This added on to the concept, structure, and components of DNA. -
Rosalind Franklin
Franklin made the first x-ray of DNA that showed the helix form of the molecule. She first set up and x-ray crystallography unit at King's College and received 2 sets of photos of crystallized DNA fibers, with one being more hydrated than the other. She concluded that the helix structure was the dimensions of DNA and phosphates were on the outside. This discovery greatly contributed to the findings of DNA structure of Watson and Crick and gave a visual look at the structure of DNA. -
Alfred Hershey and Martha Chase
Hershey and Chase proved DNA was genetic material. This was discovered by an experiment of viruses. First, they labeled the virus's coat with sulfur and the other's DNA with phosphate. Next, the viruses infected the bacteria, injecting the DNA. When the bacteria and viruses were separated, they discovered there was phosphate in the 2nd bacteria but no sulfur in the 1st. They concluded DNA had a correlation with genetic info. This added on to the use of DNA, as it could be related to inheritance. -
James Watson and Francis Crick
Watson and Crick discovered the DNA structure of the double helix. They used research and conclusions from other scientists, such as Chargaff (Chargaff's rule) and Todd (phosphate and sugar backbone). With other research and their own background knowledge, they discovered the double helix model and published it. This was a milestone in molecular biology because led to more insights of the genetic code and protein synthesis. It also help make new methods in genetics like gene sequencing. -
Matthew Meselson and Franklin Stahl
Meselson and Stahl proved DNA replication was semi-conservative. They did an experiment by starting to grow E coli in a heavy nitrogen broth. Later, nitrogen was in E coli's DNA and was moved to a light nitrogen broth and grew. Samples were taken after each generation and had DNA extracted. Generation 1 had half heavy and half light. Generation 2 had half light and half medium. This proved DNA was semi-conservative and inspired what DNA replication, cell division, and inheritance is and its use. -
Bibliography
Miescher:
(No Author Shown) "Concept 15 DNA and proteins are key molecules of the cell nucleus" DNA From The Beginning, Cold Spring Harbor Laboratory, 2002 http://www.dnaftb.org/15/bio.html
Chargaff:
(No Author Shown) "Erwin Chargaff" Famous Scientists, famousscientists.org, August 9th, 2016 https://www.famousscientists.org/erwin-chargaff/ -
Bibliography
Franklin:
(No Author Shown) "Concept 19 The DNA molecule is shaped like a twisted ladder" DNA From The Beginning, Cold Spring Harbor Laboratory, 2002 http://www.dnaftb.org/19/bio-3.html
Hershey and Chase:
Kimball, John "The Hershey and Chase Experiments" The Hershey and Chase Experiments, Creative Commons Attribution, April 19th, 2014 http://www.biology-pages.info/H/Hershey_Chase.html -
Bibliography
Watson and Crick:
(No Author Shown) "The Francis Crick Papers: The Discovery of the Double Helix, 1951-1953" U.S. National Library of Medicine,
National Institutes of Health, January 1st, 1993 https://profiles.nlm.nih.gov/SC/Views/Exhibit/narrative/doublehelix.html -
Bibliography
Meselson and Stahl:
(No Author Shown)"Nucleic Acids and the Genetic Material Problem Set" Nucleic Acids and the Genetic Material Problem Set, University of Arizona, October 3rd, 1996 http://www.biology.arizona.edu/molecular_bio/problem_sets/nucleic_acids/06t.html
