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Discovery of Nucleic Acids
Friedrich Miescher isolated the genetic material from white blood cell nuclei. He saw it had an acidic nature and caled it nuclein. -
Discovery of DNA components
Phoebus Levene discovered all the components of the DNA and defined phosphate-sugar-base units called nucleotides. (1900-1910) -
Levene's tetranucleotide
Levene thought it was organized in tetrades, he thought there were four nucleotides per molecule. This was such a simple structure that it was impossible for it to contain the genetics. -
Griffith's transformation experiment
Griffith used two types of Streptococcus: type S (smooth), a deadly kind, and type R (rough), a non-virulent kind. He saw that when you heat-killed the smooth strain and mixed it with the rough strain the mice died, while the rough strain by itself and the heat-killed smooth one by itself didn't kill the mice. -
Avery, MacLeod and McCarty
They did the same experiment as Griffith but they created two different mixes: one contained protease, that killed the proteins, and another contained DNAse, that killed the DNA. They injected it into mice and the one with protease died while the one with DNAse lived, that meant that the transformation happened in the DNA. This discovery was published in the February, 1944 Journal of Experimental Magazine. They proposed that DNA was the hereditary material in the bacteria and not proteins. -
Double Hellix?
Watson and Crick wrote a paper where they described DNA as a double helix with sugars and phospates at the center and the nucleobases facing the outside. It was proven incorrect because all the negative charges would make it explode. -
Hershey and Chase
They made an experiment where they used bacteriophages with either radioactive protein capsules or radioactive DNA. They made the phage infect the bacteria and then they used centrifugation to separate the bacterial cells from the supernatant. Doing that, they discovered that when the DNA was radioactive in the phages, the bacterial cells where radioactive, but when the proteins where radioactive the radioactivity stayed in the supernatant. They concluded that DNA was the genetic material. -
Counting nucleobases and Chargaff's rules
Erwin Chargaff started counting nucleobases because he was interested in the percentages of the different ones. He discovered that in every organism that he looked at, the percentage of Adenine and Thymine were really similar while the Cytosine and Guanine percentage were really similar as well. He did not realise the importance of those findings but he shared those discoveries with Watson and Crick and he was then left out of all the recognition of the discovery of DNA. -
Triple Helix?
Linus Pauling and Robert Corey proposed a triple helix structure for DNA. But it was proven wrong, what they probably saw were the two helix but not clearly so they thought there was a third one. -
Actual structure, Noble Prize and Rosalind Franklin
Rosalind took photo 51 of the actual structure of DNA that proved that there were just two helix but placed in the oposite way that Watson and Crick thought. Wilkins took the picture from Rosalind and gave it to them so they could publish it and get the credit as well as finish their papers. The three of them; Watson, Crick and Wilkins, got the Noble prize. Rosalind didn't get it because she was already dead but none of them gave her any credit for all the research she did.