MadSci Network: Science History

Re: What were the initial theories for the structure of DNA before the double-helix

Date: Thu Jun 8 14:42:23 2000
Posted By: Sarah Tegen, Grad student, Molecular and Cell Biology, UC-Berkeley
Area of science: Science History
ID: 959514272.Sh

There were several theories about the structure of DNA before Watson and Crick figured it out.

Linus Pauling was well known for having discovered the three dimensional structure in proteins called alpha helices. In the early 1950s when it was determined that DNA was genetic material, Pauling decided to study its structure. He proposed that DNA consisted of a triple helix, with the sugar phosphate backbones in the middle, and the bases exposed on the outside of the helix. It turned out that his theory was wrong.

The correct theory of DNA structure was published by Watson and Crick. They proposed that DNA consists of a double helix, with the sugar phosphate backbone on the outside and the bases on the inside, pairing between the chains. This was an elegant solution as it also suggested a way for the DNA to be faithfully replicated. Though Watson and Crick received the Nobel prize for the work, Rosalind Franklin also played a significant role (and also deserved the prize, though she died before it was awarded). Actually it was Franklin, a chemist by training, who realized (using a technique called X- ray diffraction), first that DNA must be a double helix with the suagar- phosphates on the outside. Her X-ray data photos were shared with Watson and Crick (by her colleague John Randall), without her knowledge, and they pieced together the same conclusions. Unfortunately for Franklin, Watson and Crick published first, and got all the credit for the discovery.

The Nobel Prize for Medicine in 1962 was shared by Watson and Crick, and Maurice Wilkins, an Irish biophysicist. He was the first person to extract DNA fibers and subject them to X-ray diffraction. It has been suggested that Franklin should have been awarded the Nobel prize along with Watson and Crick. However, if Franklin were awarded the prize, Wilkins would have to be included too. And the Nobel Prize can only be awarded to three individuals. So the question remained: who to leave out? As it turned out Franklin died from ovarian cancer at the age of 37, before the prize was awarded. Additionally, Nobel prizes are not awarded posthumously, so now there were only three people to award the prize to. I guess we'll never know who the Nobel Prize for the discovery of DNA really should have gone to.

The following points to an interesting article about DNA that appeared in Time Magazine in 1999:,5744,254176,00.html

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