Explain how the discoveries by Rosalind Franklin helped Watson and Crick build an accurate model of DNA.
Answers
Rosalind Franklin was a British biophysicist and X-ray crystallographer who made essential contributions to the comprehension of the fine molecular compositions of DNA, viruses, RNA, and various other components.
Franklin is well familiar for her work on the X-ray diffraction images of DNA, while at King's College in London that resulted in the discovery of the DNA double helix for which Watson, Crick, and Wilkins shared the Nobel Prize in the field of medicine in 1962.
Watson and Crick studied in advance the manuscript of Pauling and Corey in 1953.
They concluded that:
(i) Polynucleotide chain of DNA has singular regular helix,
(ii) The helix has a diameter of about 20 Å, and
(iii) The helix makes a full turn at every 34 Å along its length and contains a stack of ten nucleotides per turn because the inter-nucleotide distance is 3.4 Å.
They considered the density of DNA molecule and concluded that the density of a cylinder having 20 Å diameter and 34 Å length is too low if it contained a single stack of ten nucleotides and the density will be too high if it contains three or more stacks often nucleotides. Therefore, the helix must contain two polynucleotide chains or two stacks of ten nucleotides per turn.