Recently, it has been proposed that human DNA and RNA are structurally distinct. As the scientific theory of the origin and evolution of man indicates, the structure, a double helix, of these two salts, i.e., both the RNA and the DNA, has actually been present for billions of years. Numerous human traits and attributes are a result of these complex salts. The DNA double helical structure includes the phosphates, sugar, and nitrogen base found there. From the nitrogen basis, there are four bases: Adenine, Thymine, Guanine, and Cytosine. The DNA's genetic blueprint is determined by the arrangement of these four bases. According to US National Library of Medicine, Human DNA has about 3 billion bases with 99% of the bases being similar in all human beings. Watson and Crick are among the greatest contributors to the understanding of human DNA. Their studies have pioneered knowledge of what most people call DNA with less knowledge about what it is. However, some people do not understand what DNA is, and they find it hard to understand. Crick and Watson try to bring forth a simplistic mechanical approach to the understanding of the chemical composition of DNA as opposed to quantum mechanics explanation that is complex in approach.
Nature of Crick and Watson’s Discovery
Both Crick and Watson, in 1953, suggested a structure for Deoxyribose Nucleic Acid (D.N.A). Their proposition differed from the suggestions made by Corey and Pauling; whose proposed structure consisted of three chains that were intertwined. In Corey’s model of DNA structure, phosphates were placed close to the fiber axis and the nitrogen base placed on the outer side. According to Watson and Crick, that structure put forward by Pauling and Corey was not compelling because hydrogen bond was necessary to hold the structure together. Later on, Watson received a proposition by Fraser that consisted of a three-chain structure. For this new structure, the phosphates had been placed on the outer side while the bases were on the inner side and had been linked together by hydrogen bonds. Both Crick and Watson did not comment on the structure as they termed it as ill-defined.
Watson and Crick performed an X-ray to the structure of DNA and made their suggestion, which holds until today. In their structure, DNA structures have two helical chains that are coiled in such a way that an axis runs through the center of the structure. In their model, Watson and Crick have the chains follow a right-handed helix with the atom sequences running in the opposite direction. The chains, as they describe, appears like those in Furberg’s model in which the sugar part of the DNA is almost perpendicular to the base attached to it. According to this duo, the structure is made of residues which repeat after every 10 residues.
Watson and Crick’s Style of Collaboration and Competition
An examination of Watson and Crick’s suggested model is almost like the Fraser’s. Perhaps, Fraser had gone a mile ahead of both Watson and his counterpart, and thus they feared being overtaken by Fraser. In their model, Watson and Crick termed their structure as radical, and thus they picked Fraser’s approach that phosphates were on the outer side and the four bases on the inner side. Crick and Watson proposed the existence of the two helical chains that were coiling in the z-direction with an approximated 36o angle between two adjacent residues. This was an exact look at Fraser’s model, and they still recognized the presence of Phosphates, sugar and the four nitrogen bases as Pauling and Covey had put it. Watson and Crick again suggested that there was only two possible combination of the bases; that is, adenine combines with thymine and guanine combining with cytosine. According to them, the appearance of these base combinations does not follow any specific order.
The limitation of the assumption of the pairing of the bases was the cases where specific pairs of the bases are formed. In such a case, if the sequence in one chain is given, the sequence in the next chain is automatically formed and can be easily predicted. For DNA, Watson and Crick established that the ratios of guanine to cytosine and adenine to thymine are approximately a unit. The impact of having this combination giving a unit is that it becomes inconceivable to build the DNA structure with ribose sugars as the deoxyribose. If the building happens, an extra oxygen is obtained which forms a weak Van der Waals bond. Basically, we can conclude that Watson and Crick incorporated the knowledge of other scientists in developing their model. They also technically ruled out Fraser’s model since it would compete for their research.
Questions of Scientific Integrity
Watson and Crick’s work did not go unchallenged. One of the major critics of their model was Dr. Donohue Jerry who challenged the two on the interatomic distances of the components of the DNA’s double helix structure. Other questions raised include the reasons for failing to comment on Fraser’s model, which had a significant impact on their new radical structure. They also were to explain the structural difference presented by X-ray diffraction studies of the DNA, obstinate to the biological explanation of DNA. That the DNA has a complex molecular structure. The contrast exhibited by X-ray diagrams show that the DNA structure is extremely simple. The X-ray analyzed structure give a series of evenly spaced points along the helices. They also were challenged on how Bessel functions are applicable in explaining the intensity and helix pitch of the points formed along the helices.
The Role of Franklin and Co-workers in Crick and Watson’s model
The contributions Dr. R. E Franklin were highly invaluable. The Franklin’s group had performed a series of lab experiments that were never published. The experiments were phenomenal in concluding both Watson, and Crick unanimously made. Gosling and Franklin produced a para-crystalline structure of DNA which produced a fiber diagram which aided in arriving at the conclusion that the 3-4-a reflexion was as a result of the repeated inter-nucleotide structure along the axis of the fiber.
Conclusion
There was a collective contribution by a number of scientists towards arriving at the present DNA structure. The proposition of the Double Helix structure by Watson and Crick was the strongest milestone in understanding human DNA structure. The two scientists acknowledge the contributions made by a number of other earlier scientists and all other unpublished documents. The information on DNA and RNA structures has been highly advanced with the development of modern technological devices that can give colored and more detailed structure shapes. As Watson and his partner had suggested, modern day technology upholds their ideas and increases the ease with which DNA structure can be understood.
Bibliography
Francis Crick. 1988. How to Live with a Golden Helix. What Mad Pursuit: A Personal View of Scientific Discovery. New York: Basic Books.
List of human proteins in the Unireport Human reference proteome; accessed January 28, 2015.
Olby, R. C. 1974. The Path to the Double Helix .Macmillan, London.
Romero, I.G, Ruvinsky I. & Gilad, Y. 2012. “Comparative studies of gene expression and the evolution of gene regulation”. Nature Reviews Genetics. 13, no. 7: 505-516.
Watson J. D. & Crick F. H. 1953. Medical Research Council Unit for the Study of the Molecular Structure of Biological Systems. Cavendish Laboratory, Cambridge.
