It took an ex-physicist, F.H.C. Crick and a former ornithologist, J.D. Watson, to crack the secret of life and decode the genetic basis of the gene in the year 1953. The trajectory began, with the suggestion of a “possible copying mechanism of the genetic material” at Cold Spring Harbor Laboratory and the display of a complete table showing the genetic code. The true weight was rested upon the functional implications rather than the structural importance of Deoxyribonucleic acid (DNA), the genetic material that has been regarded to be the essential constituent of chromosomes. It is the carrier of a part, if not most of the specificity of chromosomes and therefore the gene itself. However, it was not until this report was published, that it was shown as to how DNA could operate and how it gets self-duplicated exactly before being transmitted to subsequent generations.
Initially, a proposed structure of salt of DNA was basically suggested that gave some clues to this phenomenon, which were also found to be consistent with the X-Ray data generated for its structural confirmation (Wilkins and co-workers). The chemical formula of DNA was predicted to be a long chain; the backbone consisting of a regular alternation of sugar and phosphate groups and each sugar attached to a nitrogenous base (for illustrations; see the report). Two of the speculated bases were adenine [A] and guanine [G] (i.e., purines) and the other two were thymine [T] and cytosine [C] (i.e., pyrimidines). A unit consisting of phosphate, sugar and base is called a nucleotide.
With this report, certain features of this structure surfaced which were found to be of immense biological and functional interest. DNA consists of no single chain, but a pair of chains coiled around a common fibre axis as also suggested by the density and X-ray evidence. The two chains are in turn held together by hydrogen bonds between bases. A pyrimidine always pairs with a purine e.g., (AT) and (CG), and any other kind of pairing is not somehow accepted in this structure. Also the amounts of adenine and thymine are approximately close, whereas, amounts of adenine to guanine (i.e., cross-ratios) may vary from source to source. Although various permutations and combinations of bases are possible in a long chained molecule like that of DNA, a precise sequence of bases defines the so-called “genetic code” carrying valid genetic information.
The phosphate-sugar (nucleoside) backbone remains constant and regular. Also one chain is complementary to another. This fact then served as an important clue towards the derivation of the fact that DNA can duplicate itself and the authors put forth the idea that, the DNA structure, in reality, is a pair of templates complementary to each other. The model also explained further the process by which this duplication took place through the unwinding of chains leading to breakage of hydrogen bonds and generation of the partner strand after separation the of two coiled or intertwined chains.
Microscopic data on studies on DNA duplication mechanism finally confirmed that, the coiling and uncoiling occurs during the process of cell division (i.e. mitosis). Also, it was predicted that a polypeptide (protein) pair of chains also winds around the same helical axis and that this conformation might be implicated in the control of coiling/uncoiling of DNA, to hold them in position, or some unknown function. The model also speculated that the pairing mechanism in DNA is comparative to the pairing of homologous chromosomes during reduction division (i.e., meiosis).
Although, the structure for DNA solved some of the long standing problems in biology, this modest effort by Watson and Crick also posed some major questions for future research, pertaining to the actual mechanism of winding/unwinding of DNA and the role of protein with biological relevance to this genetic material. As the double helical structure of DNA unfolded and was understood better, it pointed too the “simple secret of life” which is “complementarity”.