Race for the Double Helix

James Watson and Francis Crick had an article posted in the popular science magazine, Nature. This particular article led them to become Nobel Prize winners. This article contained the most important discovery of the 20th century. Watson and Crick worked 18 months to make this possible, with much help from other scientists' research. Their discovery: the structure of DNA. At the time no one even knew if DNA or protein was the key to inheritance. The movie, Race for the Double Helix, shows the events that made this Watson's structure possible, leading up to the publication of the Nature article.

Watson and Crick's article came with much skepticism from the scientific community, as was expected with such an outstanding feat. They start by explaining why other scientists models are flawed and therefore cannot be the structure. They cite how Pauling and Corey's nucleic acid model consisted of three chains, with phosphates near the fibre axis, and bases on the outside. Watson and Crick believed that this could not be true since the X-ray diagrams show the salt, not the free acid, and some of their van der Waals distances seem too small. They also comment on Fraser's suggestion of a three-chain structure where phosphates were set on the outside and bases on the inside, linked with hydrogen bonds. Due to the lack of information, however, they do not explain why this model cannot work. After identifying the flaws of these previously suggested structures, they go on to suggest their own.

The major significance of the Watson~Crick model was the double helix: two helical chains coiled around the same central axis. The chains run opposite each other due to the dyad laying perpendicular to the fibre axis. Because they run opposite each other, the sequence of one side determines the sequence of the other. The novel feature of the structure is the manner in which the two chains are held together by the purine and pyrimidine bases. The planes of the bases are perpendicular to the fibre axis. They’re joined together in pairs, a single base from the other chain, so that the two lie side by side with identical z-co-ordinates. One of the pair must be a purine and the other a pyrimidine for bonding to occur. (Watson. Crick., 1953)

Bibliography

Watson, James, and Francis Crick. "A Structure for Deoxyribose Nucleic Acid." LionBook. 25 Aug. 2003. Web. May 2011. <http://faculty.fullerton.edu/kkantardjieff/C340/DH-Paper.pdf>.