Several methods of representing a molecule's structure. In Lewis structures, element symbols elipsis
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The Molecular structure of Nucleic Acids: A Structure for Deoxyribose Nucleic Acid was an article published by James D. Watson and Francis Crick in the scientific journal Nature in its 171st volume on page 737-738 (dated April 25, 1953). It was the first publication which described the discovery of the double helix structure of DNA. This discovery had a major impact on genetics in particular and biology in general.
This article is often termed a "pearl" of science because it is short and contains the answer to a fundamental mystery about living organisms. This mystery was the question of how it was possible that genetic instructions were held inside organisms and how they were passed from generation to generation.
The article had extra impact because it surprised many biologists who did not suspect that this answer would be as easy to obtain as it was. The structure itself explains why the discovery was easy; the structure is simple and consequently, how the structure produces its function is easy to understand. That Watson and Crick were able to solve this mystery as quickly as they did is an example of prepared investigators being in the right place at the right time and working tirelessly to find the answer. The article is also symbolic of a transition between two ages of what might be called the "classical age" of biology and a second "age" of molecular biology.
Some consequences for humanity that arise out of the revolution in biology that can be traced back to Watson and Crick’s 1953 article are: pre-natal screening for disease genes, genetically engineered foods, the rational design of treatments for diseases like AIDS, and the use of information obtained by DNA testing as evidence in criminal court.
Linus Pauling was a chemist who was very influential in developing an understanding of the structure of biological molecules. In 1951, Pauling published the structure of the alpha helix, a fundamentally important structural component of proteins. Early in 1953 Pauling published an incorrect triple helix model of DNA. Both Crick, and particularly Watson, felt that they were racing against Pauling to discover the structure of DNA.
Max Delbrück was a physicist who recognized some of the biological implications of quantum physics. Delbruck's thinking about the physical basis of life stimulated Erwin Schrödinger to write the highly influential book, What Is Life? Schrödinger's book was an important influence on Francis Crick, James D. Watson and Maurice Wilkins who won a Nobel prize in Medicine for the discovery of the DNA double helix. Delbruck's efforts to promote the "Phage Group" (exploring genetics by way of the viruses that infect bacteria) was important in the early development of molecular biology in general and the development of Watson's scientific interests in particular.
The “specific pairing” is a key feature of the Watson and Crick model of DNA, the pairing of nucleotide subunits. In DNA the amount of guanine is equal to cytosine and the amount of adenine is equal to thymine. The A:T and C:G pairs are structurally similar. In particular, the length of each base pair is the same and they fit equally between the two phosphate backbones (Figure 2). The base pairs are held together by hydrogen bonds, a type of chemical attraction that is easy to break and easy to reform. After realizing the structural similarity of the A:T and C:G pairs, Watson and Crick soon produced their double helix model of DNA with the hydrogen bonds at the core of the helix providing a way to unzip the two complementary strands for easy replication: the last key requirement for a likely model of the genetic molecule.
Indeed, the base-pairing did suggest a way to copy a DNA molecule. Just pull apart the two phosphate backbones, each with its hydrogen bonded A, T, G, and C components. Each strand could then be used as a template for assembly of a new base-pair complementary strand.
Much of the data that were used by Crick and Watson came from unpublished work by Maurice Wilkins and Rosalind Franklin at King's College London. Key data from Wilkins and Franklin were published in two additional articles in the same issue with the article by Watson and Crick. The article by Watson and Crick did acknowledge that they had been "stimulated" by experimental results from the King's College researchers.
In 1968, Watson published an autobiographical account of the discovery of the structure of DNA called The Double Helix. In his book, Watson stated that he and Crick had obtained some of Franklin's data from a source that she was not aware of. In particular, in late 1952, Franklin had submitted a progress report to the Medical Research Council. Watson and Crick worked in one MRC laboratory in Cambridge while Wilkins and Franklin were in another MRC laboratory in London. These reports were not widely circulated, but Crick read a copy of Franklin's research summary in early 1953. The report contained information that Watson had previously heard in November 1951 when Franklin had talked about her unpublished results during a meeting at King's College. However, at that time, Watson had no training in X-ray crystallography and did not understand what Franklin was saying about the structural symmetry of the DNA molecule. Crick correctly interpreted one of Franklin's findings as indicating that DNA was most likely a double helix with the two nucleotide chains running in opposite directions. Crick was in a unique position to make this interpretation because he had previously worked on the X-ray diffraction data for another large molecule that had the same structural symmetry as DNA. Franklin herself had failed to take part in molecular model building and so missed the chance to explore the structural implications of her own crystallographic results.
It is questioned whether Crick's boss, Max Perutz, acted unethically by allowing Crick access to the MRC report. Perutz felt he had not because the report was not confidential and had been designed as part of an effort to promote contact between different MRC research groups.
The relative influences of molecular structure on brittle fracture by fatigue and under constant load in polyethylenes.
Aug 01, 1996; INTRODUCTION Time dependent brittle fracture in polyethylenes (PE) can be produced under a constant load (CL) or by an...