Handout _19 - 3. Two polynucleotide chains are...

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BIO101 Handout #19 X-Ray Diffraction Data of Rosiland Franklin and Maurice Wilkens 1. DNA is helical. 2. Two regular patterns of 3.4 nm and 0.34 nm. 3. Consistent radius. Erwin Chargaff's Rules 1. [pyrimidines] = [purines]; [T + C] = [A + G] 2. [T] = [A]; [C] = [G] 3. A + T varies among different organisms. G + C Main Features of the Watson and Crick Double Helix Model for DNA 1. Two polynucleotide chains form a right-handed double helix. 2. Helix diameter = 2 nm.
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Unformatted text preview: 3. Two polynucleotide chains are anti-parallel. 4. Sugar phosphate backbone (negative charge) is oriented to the outside; the bases face the interior of the molecule. The bases are planar and "stack" on one another. 5. Opposite strands are bonded by hydrogen bonds. 6. Bases are 0.34 nm apart. One turn of the helix is 3.4 nm. There are 10 bases/turn (1 = 0.1 nm). 7. There is a major and a minor groove between the backbone....
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