However, I wasn't able to make sense of these striking, but perhaps meaningless, regularities.Īs you'll see, Chargaff's base ratios were an important clue in our work on the DNA structure.Īt about the same time, Linus Pauling at Cal Tech used his knowledge of chemistry and a powerful new technique called X-ray crystallography to discover a corkscrew-shaped structure found in many proteins ââ¬â the alpha-helix.įrancis and I followed Pauling's approach of using chemistry and X-ray diffraction patterns to solve the structure of DNA. Instead, the nucleotides must be arranged so that there are about equal amounts of A and T, and about equal amounts of G and C. If Levene's tetranucleotide theory was correct, then the amounts of A, T, G and C would be the same in the DNA of all organisms. Here are my results.Īs you can see, the amount of adenine is very close to the amount of thymine.Īnd there is just as much guanine as there is cytosine. I isolated DNA from different organisms and measured the levels of each of the four nitrogenous bases. I also thought there had to be more to DNA than just simple repetitive tetranucleotide blocks. DNA, not protein, was the Rosetta Stone for unraveling the true secret of life. Information can then be coded into the DNA sequence. In fact, it made more sense if the order of the nucleotides changed. And after Oswald Avery's landmark paper, we knew that DNA had to be intelligent. If DNA had a fixed, repetitive sequence, it wouldn't be intelligent enough to carry any information.
#Online dna model builder series
Nucleotides are linked in a series ââ¬â from one phosphate, to the next sugar, to the next phosphate, and so on.Īlthough Levene had proposed the correct chemical linkages, his tetranucleotide theory was wrong. We wanted to build on what was chemically known about DNA, and determine its actual structure.įor example, Phoebus Levene had shown that each nucleotide building block of DNA is made up of a phosphate group linked to a deoxyribose sugar ââ¬â which, in turn, is linked to one of four nitrogenous bases ââ¬â adenine (A), guanine (G), cytosine (C), and thymine (T). We were interested in DNA ââ¬â the hereditary molecule of life.
In 1953, Francis and I published the first accurate model of the DNA molecule.
Watson and Crick ended their 1953 paper by saying that the base pairing in their DNA helix model "suggests a possible copying mechanism for genetic material." What would this mechanism be? I'm James Watson. Chargaff was not impressed with the duo, especially after Crick admitted to not knowing the chemical structures of the nitrogen bases. While visiting Cambridge in 1952, Erwin Chargaff met Watson and Crick.
0 kommentar(er)
