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DNA Timeline
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Frederick Griffith
In the 1920's, Griffith was studying two types of bacterium called R-strain and S-strain. He injected the the two strains into mice. He noticed that the S-strain killed the mouse while the R-strain did not. He also injected the mice with heat killed S-strained bacteria. This did not kill the mice like it did before.But when the dead S-strain bacteria was mixed with live R-strain bacteria and injected, the mouse died. Griffith then discovered that something in the killed S-strain was transferred -
Oswald Avery
He tried to answer the question that was raised by Griifith with a group of scientists. His team inactiviated substances in S-strain bacteria. They then killed S-strain bacteria and mixed it with live R-strain. The R-strain was deadly to injected mice when they inactivated protiens. This showed that the protiens were not the genetic material because the R-strain was deadly without the S-strain. -
Erwin Chargaff
He was interested in the four nitrogen bases of DNA. He found that they differed from species to species. He found that the adenine always has the same concentration as thymine. Also, guanine always always has the same concentration as cytosine. -
Rosalind Franklin
Franklin contributed to the findings of the structure of DNA. Franklin completed by looking at two high resolution photos of DNA fibers. From this Franklin came up the basic dimensions of DNA strands and that phosphates were on the outside of the strands. -
Alfred Hershey and Martha Chase
Hershey and Chase did experiments with viruses and bacteria. One thing they found was that viruses are not cells but simply DNA inside a protien coat. To make a virus it has to enter its own genetic materisl. The researchers used radioactive elements to label DNA and viruses. They then identified that viruses enter through the DNA molecule, therefore DNA is genetic material. -
Watson and Crick
In 1953, Watson and Crick were given credit for finding out DNA was a double helix shape based off of Rosalind Franklin's experiments and others. They found that DNA was a nucleotide and multiple DNA is a polynucleotide.
