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Unformatted text preview: September 13, 2010 The Structure of DNA • 1947- William Astbury performed the first X-ray diffraction analysis of DNA fibers and determined the bases were about 0.36nm apart • 1947 – J.M. Gulland determined the bases were involved in H- bonds • 1948- Erwin Chargoff found the ratio of pyrimidines to purines was 1:1 o Mole proportion of G=Mole proportion of C o Mole proportion of A=Mole proportion of T The three-dimensional structure of DNA • Discovered in 1953 by James Watson and Francis Crick based on the analysis of X-ray diffraction and careful model building • The two strands form a double helix • Won Nobel Prize with Maurice Wilkins who collaborated on the diffraction • Rosalind Franklin, who did the diffractions, died of Cancer before she could be awarded the Nobel Prize • Sugar-phosphate backbone on the outside of the double helix o Bases extend towards the inside of the molecule • Bases stack on top of one another forming parallel planes • Orientation of the polynucleotide strands in the double helix is...
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