Who said dna was a double helix

Taken in , this image is the first X-ray picture of DNA , which led to the discovery of its molecular structure by Watson and Crick. Created by Rosalind Franklin using a technique called X-ray crystallography, it revealed the helical shape of the DNA molecule.

Watson and Crick realized that DNA was made up of two chains of nucleotide pairs that encode the genetic information for all living things. Photo of x-ray crystallography Exposure 51 courtesy of King's College Archives. King's College London. Click for larger image. The progress she made on her own, increasingly isolated and without the benefit of anyone to exchange ideas with, was simply remarkable.

To prove her point, she would have to convert this insight into a precise, mathematically and chemically rigorous model.

She did not get the chance to do this, because Watson and Crick had already crossed the finishing line — the Cambridge duo had rapidly interpreted the double helix structure in terms of precise spatial relationships and chemical bonds, through the construction of a physical model. In the middle of March , Wilkins and Franklin were invited to Cambridge to see the model, and they immediately agreed it must be right.

It was agreed that the model would be published solely as the work of Watson and Crick, while the supporting data would be published by Wilkins and Franklin — separately, of course. Franklin did not attend.

She was now at Birkbeck and had stopped working on DNA. Franklin died of ovarian cancer in , four years before the Nobel prize was awarded to Watson, Crick and Wilkins for their work on DNA structure.

She never learned the full extent to which Watson and Crick had relied on her data to make their model; if she suspected, she did not express any bitterness or frustration, and in subsequent years she became very friendly with Crick and his wife, Odile. Maurice Wilkins and Rosalind Franklin had obtained high-resolution X-ray images of DNA fibers that suggested a helical, corkscrew-like shape.

Linus Pauling, then the world's leading physical chemist, had recently discovered the single-stranded alpha helix, the structure found in many proteins, prompting biologists to think of helical forms. Moreover, he had pioneered the method of model building in chemistry by which Watson and Crick were to uncover the structure of DNA. Indeed, Crick and Watson feared that they would be upstaged by Pauling, who proposed his own model of DNA in February , although his three-stranded helical structure quickly proved erroneous.

The time, then, was ripe for their discovery. After several failed attempts at model building, including their own ill-fated three-stranded version and one in which the bases were paired like with like adenine with adenine, etc. Jerry Donohue, a visiting physical chemist from the United States who shared Watson and Crick's office for the year, pointed out that the configuration for the rings of carbon, nitrogen, hydrogen, and oxygen the elements of all four bases in thymine and guanine given in most textbooks of chemistry was incorrect.

On February 28, , Watson, acting on Donohue's advice, put the two bases into their correct form in cardboard models by moving a hydrogen atom from a position where it bonded with oxygen to a neighboring position where it bonded with nitrogen. While shifting around the cardboard cut-outs of the accurate molecules on his office table, Watson realized in a stroke of inspiration that A, when joined with T, very nearly resembled a combination of C and G, and that each pair could hold together by forming hydrogen bonds.

If A always paired with T, and likewise C with G, then not only were Chargaff's rules that in DNA, the amount of A equals that of T, and C that of G accounted for, but the pairs could be neatly fitted between the two helical sugar-phosphate backbones of DNA, the outside rails of the ladder. The bases connected to the two backbones at right angles while the backbones retained their regular shape as they wound around a common axis, all of which were structural features demanded by the X-ray evidence.

Similarly, the complementary pairing of the bases was compatible with the fact, also established by the X-ray diffraction pattern, that the backbones ran in opposite direction to each other, one up, the other down. Watson and Crick published their findings in a one-page paper, with the understated title "A Structure for Deoxyribose Nucleic Acid," in the British scientific weekly Nature on April 25, , illustrated with a schematic drawing of the double helix by Crick's wife, Odile.

A coin toss decided the order in which they were named as authors. On the morning of February 28, they determined that the structure of DNA was a double-helix polymer, or a spiral of two DNA strands, each containing a long chain of monomer nucleotides, wound around each other.

According to their findings, DNA replicated itself by separating into individual strands, each of which became the template for a new double helix. The article revolutionized the study of biology and medicine. Among the developments that followed directly from it were pre-natal screening for disease genes; genetically engineered foods; the ability to identify human remains; the rational design of treatments for diseases such as AIDS; and the accurate testing of physical evidence in order to convict or exonerate criminals.

The imagery established that the DNA molecule existed in a helical conformation. Franklin, who died in of ovarian cancer and was thus ineligible for the award, never learned of the role her photos played in the historic scientific breakthrough.

But if you see something that doesn't look right, click here to contact us! On February 28, , less than three weeks after making the unexpected announcement that he would step down, year-old Pope Benedict XVI officially resigns. Citing advanced age as the reason for giving up his post as the leader of the 1.