This post marks the beginning of an extensive series of posts on DNA. The first four posts in the series will cover structures of DNA proposed by various individuals, including one by Linus Pauling, as well as the correct structure discovered by James Watson and Francis Crick. Today, an early structure proposed by Edward Ronwin will be discussed.
Until the 1950s, DNA was not considered to be an important molecule. At that time, it was known that genes were located in chromosomes, structures made up of nucleic acids and proteins that can be found in the nucleus of cells. The nucleic acids, one of which is DNA, were not thought to be the carrier of genetic information, and therefore didn’t garner much interest from scientists. Even Linus Pauling favored the more complicated and abundant proteins as the site of the gene. However, there was still some research being done on DNA.
In November of 1951, the Journal of the American Chemical Society published a paper entitled “A Phospho-tri-anhydride Formula for Nucleic Acids.” This article was written by Edward Ronwin and outlined a possible structure of DNA.
At this time, it was known that DNA was made up of four nucleotides. These nucleotides were understood to each consist of a sugar attached to a phosphate group and to a large flat ring structure called a base. However, it wasn’t known how these nucleotides bonded together to form large molecules. In his structure, Ronwin proposed that the phosphate groups were placed down the middle of the molecule with the large bases sticking out to the sides. According to x-ray data gathered by William Astbury, this was a definite possibility. It also made the molecule much easier to manipulate.
Unfortunately, not everything about Ronwin’s structure made sense. Linus Pauling was quick to point out, through a letter to the Journal of the American Chemical Society, that the Ronwin molecule contained a structure for which no theoretical precedent existed. He added that in normal phosphorous compounds, the phosphorous atom is bonded to four oxygen atoms. However, in Ronwin’s molecule, the phosphorous atom is bonded to five oxygen atoms. Therefore, Pauling concluded, there was no significant evidence for such an extraordinary structure and that Ronwin’s idea deserved no serious consideration.
Not long after his letter appeared, Ronwin responded to Pauling and pointed out the existence of four synthesized phosphorous compounds with five oxygen atoms bonded to the phosphorous atom. This information forced Pauling to retract his earlier statement about precedence, but did not otherwise change his opinion of Ronwin’s work. He quickly drew attention to the fact that these compounds decompose rapidly in the presence of water, a prevalent substance in DNA.
All in all, Pauling was rather offended by Ronwin’s proposition. He noted in a May 1952 letter to John F. Tinker the extreme ease with which a scientist in the field of molecular biology could hypothesize structures, and that no reputable worker in the field would do so without significant supporting evidence.
Although Ronwin’s structure had a variety of faults, it appeared to spark some interest in DNA, at least for Pauling. Before long, other structures would begin to appear, and the race for DNA would be well on its way.
Check back on Thursday for the next post in the DNA series. For more information about DNA, please visit the website Linus Pauling and the Race for DNA: A Documentary History, available at the Linus Pauling Online Portal.