Discovery of the Structure of DNA

Discovery of the Structure of DNA - of 2 nm, 0.34 nm, and...

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Discovery of the Structure of DNA Erwin Chargaff, 1940’s and early 50's DNA was thought to contain equal amounts of A, T, T, and C. Chargaff found that the base composition of DNA differs among species. His data showed that in each species, the percent of A equals the percent of T, and the percent of G equals the percent of C. so that 50% of the bases were purines (A + G) and 50% were pyrimidines (T + C) Chargafff’s rule: The amount of A = T and the amount of G = C. M.H.F. Wilkins and Rosalind Franklin, early 50’s Wilkins and Franklin studied the structure of DNA crystals using X-rays. They found that the crystals contain regularly repeating subunits. Structures that are close together cause the x-ray to bend more than structures that are further apart. The X pattern produced by DNA suggested that DNA contains structures with dimensions
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Unformatted text preview: of 2 nm, 0.34 nm, and 3.4 n. The dark structures at the top and bottom of their X-ray photograph of DNA indicate that DNA contains repeating units, suggesting a helix. James Watson and Francis H.C. Crick, 1953 Watson and Crick used Chargaff's base data and Franklin’s X-ray diffraction data to construct a model of DNA. The model showed that DNA is a double helix with sugar-phosphate backbones on the outside and the paired nucleotide bases on the inside, in a structure that fit the spacing estimates from the X-ray diffraction data. Chargaff's rules showed that A = T and G = C, so there was complementary base pairing of a purine with a pyrimidine, giving the correct width for the helix. The paired bases can occur in any order, giving an overwhelming diversity of sequences....
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This note was uploaded on 11/10/2011 for the course BIOLOGY bi 101 taught by Professor - during the Fall '10 term at Montgomery.

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