On Tue, 22 Sep 2009 06:29:33 -0700, Stephen Black was heard to say: >On 22 Sep 2009 at 9:13, Mike Palij wrote: >>They were in competition with other teams for >>determing what the actual structure was but the other teams focused on the >>wrong structures -- does anyone remember who those researchers were? > >Linus Pauling.
*BZZZZZT* I'm so sorry but the correct answer is given in the quote below. Pauling was only one of several researchers who guessed wrong (note the wording above "THOSE RESEARCHERS", emphasis added. Departing guests receive a home edition of "Science Jeopardy" as a consolation prize. >Gone but not forgotten. Two Nobels have that effect on people. And here I thought it was all that Vitamin C he gobbled. According to Wikipedia (standard disclaimers apply): |Pauling then proposed that deoxyribonucleic acid (DNA) was a triple |helix;[49] however, his model contained several basic mistakes, including |a proposal of neutral phosphate groups, an idea that conflicted with the |acidity of DNA. http://en.wikipedia.org/wiki/Linus_Pauling Pauling wasn't a helix short but apparently had one too many. Now, from the profile pages of the National Library of Medicine of the National Institute of Health: |Other researchers had made important but seemingly unconnected |findings about the composition of DNA; it fell to Watson and Crick |to unify these disparate findings into a coherent theory of genetic transfer. | |The organic chemist Alexander Todd had determined that the backbone |of the DNA molecule contained repeating phosphate and deoxyribose |sugar groups. The biochemist Erwin Chargaff had found that while the |amount of DNA and of its four types of bases--the purine bases |adenine (A) and guanine (G), and the pyrimidine bases cytosine (C) and |thymine(T)--varied widely from species to species, A and T always appeared |in ratios of one-to-one, as did G and C. 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 1953, 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.), |they achieved their break-through. 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, 1953, 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, 1953, 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. Foremost among the "novel |features" of "considerable biological interest" they described was the pairing |of the bases on the inside of the two DNA backbones: A=T and C=G. The |pairing rule immediately suggested a copying mechanism for DNA: given the |sequence of the bases in one strand, that of the other was automatically |determined, which meant that when the two chains separated, each served |as a template for a complementary new chain. Watson and Crick developed |their ideas about genetic replication in a second article in Nature, published |on May 30, 1953. http://profiles.nlm.nih.gov/SC/Views/Exhibit/narrative/doublehelix.html So, who remebers Jerry Donohue? -Mike Palij New York University m...@nyu.edu --- To make changes to your subscription contact: Bill Southerly (bsouthe...@frostburg.edu)
