BIOC 2580 Lecture Notes - Lecture 13: Erwin Chargaff, The Double Helix, Cytidine
14 Jun 2016
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Erwin chargaff and his colleagues found that in all cellular dnas the number of adenosine residues were equal to the number of thymidine residues and the number of guanosine were equal to the number of cytidine residues. This is known as the chargaff"s rules : a=t and g=c. However, % of gc and at varied among diff organisms. Used x-ray chromatography to identify the secondary structure of dna. Chromosomes are extremely long dna molecules and they tend to shear and fragment during isolation. Each fragment is similar but not identical and it is difficult to form well-ordered crystals with them. Such crystals don"t produce the spot patterns of a high-resolution x-ray diffraction of pattern. Rosalind franklin obtained the first useful x-ray diffraction images of dna: photo 51 . And that they had two periodicities along the long axis; a primary one of 3. 4 and a secondary one of 34 .
