Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions for the development and functioning of living organisms.
DNA is a long polymer of simple units called nucleotides, which are held together by a backbone made of sugars and phosphate groups.
This backbone carries four types of molecules called bases, and it is the sequence of these four bases that encodes information.
DNA is a normally double stranded macromolecule.
Two polynucleotide chains, held together by weak thermodynamic forces, form a DNA molecule.
Two long strands entwine like vines, in the shape of a double helix.
Double Helix Structure
In 1953, based on X-ray diffraction images taken by Rosalind Franklin and the information that the bases were paired, James D. Watson and Francis Crick suggested what is now accepted as the first accurate model of DNA structure in the journal Nature.
DNA Controversy is a dispute about whether Rosalind Franklin was given proper credit for her contribution to the determination of the structure of DNA.
An enduring controversy has been generated by James D. Watson and Francis Crick`s use of DNA X-ray diffraction data collected by Rosalind Franklin.
Collaboration between Rosalind Franklin and Maurice Wilkins
In January 1951, Franklin started working as a research associate at King`s College London in the Medical Research Council`s Biophysics Unit.
Franklin started to apply her expertise in x-ray diffraction techniques to the structure of DNA.
She discovered that there were two forms of DNA: at high humidity the DNA fiber became long and thin, when it was dried it became short and fat.
These were termed DNA `B` and `A` respectively.
The work on DNA was subsequently divided, Franklin taking the A form to study and Wilkins the `B` form.
Without the knowledge of Rosalind Franklin
The controversy arose from claims that some of the data were shown to Watson and Crick, without her knowledge.
Her experimental results provided estimates of the water content of DNA crystals and these results were consistent with the two sugar-phosphate backbones being on the outside of the molecule.
Interaction between Franklin and Crick/Watson
Franklin personally told Crick and Watson that the backbones had to be on the outside.
Her identification of the space group for DNA crystals revealed to Crick that the two DNA strands were antiparallel.
The X-ray diffraction images collected by Franklin provided the best evidence for the helical nature of DNA.
Interaction between Wilkins and Crick/Watson
In 1951, Franklin had presented some of her experimental findings for DNA at a public seminar to which Watson had been invited by Wilkins.
Crick was given permission by his boss to read an internal report containing those experimental findings.
Crick and Watson felt that they had benefited from collaborating with Wilkins.
They offered him a co-authorship on the article that first described the double helix structure of DNA.
Allegations of intimacyism at King`s College
There have been allegations that Rosalind Franklin was discriminated against because of her gender.
One of the allegations is that King`s, as an institution, was intimacyist.
The allegation held that women were excluded from the staff dining room, and had to eat their meals in the student hall or away from the University.
The other accusation regarding gender is that women were under-represented in Biophysics Unit.
Maurice Wilkins`s stand
On the completion of their model, Francis Crick and James Watson had invited Maurice Wilkins to be a co-author of their paper describing the structure.
Wilkins turned down this offer, as he had taken no part in building the model.
Maurice Wilkins later expressed regret that greater discussion of co-authorship had not taken place as this may have helped to clarify the contribution the work at King`s had made to the discovery.
Watson, Francis Crick, and Maurice Wilkins were awarded the 1962 Nobel Prize for Physiology or Medicine, for their discoveries concerning the molecular structure of nucleic acids and its significance for information transfer in living material, with the help of the research of Rosalind Franklin.
(1) The structure of part of a DNA double helix
(2) Rosalind Franklin
(3) Francis Crick
(4) James Watson
(5) Maurice Wilkins
(6) DNA `B` which was taken by Rosalind Franklin and shown to Crick/Watson