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The History and Development of DNA.
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The History and Development of DNA Rosalind Franklin: Early Ideas of DNA (1951): Franklin put forward the idea that DNA chains were of a helical structure that were very closely packed and the phosphate groups were near the outside. Crick and Watson: 3-Chain Model (1951/1952): Crick and Watson needed to decide about the number of polynucleotide chains within the DNA molecule. They questioned the angle and radii at which the DNA strands twisted around the central axis. They decided upon models of which a sugar-phosphate backbone revolved around. The forces that held the chains together seemed to be salt bridges in which divalent cations like Mg2+ held together two or more phosphate groups. A shape began to emerge. Three chains twisted about each other in a way that gave rise to crystallographic repeat every 2.8nm along the helical axis. Franklin's Response to the Crick-Watson 3-Chain Model (1952): Franklin objected to the proposed 3-chain model. She stated...
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