The DNA Molecule
In the autumn of 1951, James Watson (left) and Francis Crick (right) started work on unravelling the structure of DNA. It was known at the time that DNA was present in the nucleus of every living cell, and that it had something to do with heridity, but without a knowledge of its structure little more could be understood about how it actually worked. They approached the problem with the same methodology that had been pioneered by Linus Pauling, who after years of exhaustive study had earlier discovered that many proteins exhibited a helical structure. Their task was to devise a structure which would account for all the chemical and X-ray evidence, and at the same time be consistent with all the structural features of the units involved - such as the size and shape, bond angles and lengths, configurations and conformations. X-ray diffraction photographs of DNA fibres taken by Rosalind Franklin and Maurice Wilkins showed a distinctive X-shape, which was characteristic of a helix structure, but strong arcs on the meridian indicated a repeating structure 3.4 Å apart. And from the chemical evidence, it was known that part of the structure was comprised of 4 heterocyclic bases, adenine (A), guanine (G), cytosine (C) and thymine (T), somehow linked together with sugar units and phosphates. One of the biggest puzzles was that although the proportion of these bases varied from one DNA to another, it was always found that the number of A = T, and G = C.
Adenine
Guanine
Cytosine
Thymine
The 4 bases which make up DNA
(Click on each image to get its 3D molfile).
Using molecular models, Watson and Crick devised a structure in which all of the building blocks fitted together without crowding ...
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...tracted from organic remains (blood, saliva, etc) left at crime scenes to identify the criminal. It can also be used to determine parentage, the gender of animals and birds (where it is difficult to do so by just looking at them!), and to prove whether traditional medicines contain extracts from endangered species. This process is called DNA fingerprinting.
Bibliography:
The Path to the Double Helix: The Discovery of DNA, Robert C. Olby (Dover Pubns; ISBN: 0486681173, 1994)
Organic Chemistry, Morrison and Boyd (Allyn and Bacon, Boston, 1983).
Biochemistry, L. Stryer (Freeman, San Francisco, 1975).
Interactive DNA structure (Imperial College, requires Chime)
Interactive DNA Structure from the University of Massachusetts (requires Chime).
The Curtis model of H-bonding in the T-A and C-G base pairs (Imperial College London, requires Chime).
Watson met the King’s College team head named Maurice Wilkins, who worked closely with Rosalind Franklin. Rosalind Franklin, a British biophysicist, was the person who discovered the DNA structure using x-ray crystallogr...
In 1953, after carefully studying this molecule and scientific reports generated from several predecessors, scientists Jason Watson and Frances Crick divulged their determination that the structure
The following is a review of the book, The Double Helix, by James D. Watson that was published in 1968. Here the Norton Critical Edition will be used for page numbering and insights for this review, which was edited by Gunter S. Stent and published in 1980. The Double Helix is a personal recollection of the period of time when the structure of DNA was discovered. James D. Watson (Watson) along with Francis Crick (Crick) were the two scientists who published a paper in 1953 which purposed a structure for DNA. For the most part their structure has stood the test of time, and since that time period many people have wanted to know details of how they discovered DNA’s structure (pp. 3). Therefore Watson’s purpose in writing the book was to describe his personal view of the events that lead to discovery of DNA’s three-dimensional structure, when they happened in 1952-53. He is well qualified to give an account of these things, for he was there in the middle of everything; he was one of the main players. In order to describe the events, apart from his sharp memory, Watson used letters he wrote to his family to help him remember dates and details, as well as suggestions from his associates who reviewed his manuscript. In the following paragraphs I will summarize the text, and follow that with my own review of
The molecule consisted of a double helix with phosphates, deoxyribose sugar molecules, and nitrogenous bases. If the spirals were split, the DNA could replicate, which explained why genes were transferred from parents to their children. Additionally, the order of compounds on the DNA indicated that there was a unique ‘code’ on each strand. Watson and Crick believed that this ‘code’ was translated into specific proteins. , ,
The study of nucleic acids has now become a fruitful and dynamic scientific enterprise. Nucleic acids are of unique importance in biological systems. Genes are made up of deoxyribonucleic acid or DNA, and each gene is a linear segment, or polymer, of a long DNA molecule. A DNA polymer, or DNA oligonucleotide, contains a linear arrangement of subunits called nucleotides. There are four types of nucleotides. Each nucleotide has three components; a phosphate group, a sugar and a base that contains nitrogen within its structure. The sugar moiety in DNA oligonucleotides is always dexoyribose, and there are four alternative bases: adenine (A), thymine (T), guanine (G), and cytosine (C). The phosphate groups and the deoxyribose sugars form the backbone of each DNA stand. The bases are joined to the deoxyribose sugar and stick out to the side. Both oligomers, DNA and RNA, consist of 5’->3’ phosphodiester-linked nucleotide units that are composed of a 2’-deoxy-D-ribose (DNA) or D-ribose (RNA) in their furanose forms and a heteroaromatic nucleobase (A, T, G, and C; A, U, G, C), and the resulting oligonucleotide chain is composed of a polar, negatively charged sugar-phosphate backbone and an array of hydrophobic nucleobases. The amphiphilic nature of these polymers dictates the assembly and maintenance of secondary and tertiary structures the oligonucleotides can form. In the DNA duplex structure, genetic information is stored as a linear nucleotide code. This code can be accessed and replicated. RNA, or ribonucleic acid, is another structurally related essential biopolymer. RNA differs from DNA in having the sugar ribose in place of the deoxyribos...
The discovery of DNA is quite mind-blowing. Rumor has it that James Watson and Francis Crick discovered DNA, but they actually did not. It all started in 1869, with a well-known German biochemist named Friedrich Miescher who isolated, analyzed, and recognized a distinctive macromolecule known as DNA. Years later, on the morning of February 28, 1953, Watson and Crick came into the picture, as they announced that they “had discovered the secret of life” (Markel 2013). Their discovery of the double helix made them publish a paper in the 1953 issue of Nature, describing the structure of DNA, which resulted them to receive the Nobel Prize in 1962.
Chemistry dictates the structure of DNA. DNA is a polymer of monomers called nucleic acids. These are made of a nitrogenous base, a phosphate group and a sugar. It is the negative charge on the phosphate group that makes DNA an acid. There are 4 different bases: adenine, thymine, guanine and cytosine. In groups of three, these four bases can code for any protein coded for in an organism’s genome. Two strands of nucleic acids stack on top of each other in a double helix. The backbone of the nucleic acids consists of the interaction between phosphate groups and the hydroxide groups of nucleic acids. These are held together by covalent bonds called phosphodiester bonds. The helix itself is held together by hydrogen bonds. Although h...
"The discovery of the structure by Crick and Watson, with all its biological implications, has been one of the major scientific events of this century." (Bragg, The Double Helix, p1) In the story of The Double Helix, James Watson tells of the road that led to the discovery of life's basic building block-DNA. This autobiography gives insight into science and the workings within a professional research laboratory that few members of society will ever be able to experience. It also gives the reader an idea of the reality of life for one scientist and how he struggled with the problem of DNA. However, the author's style is marked by his lack of objectivity and inclusion of many biased opinions and personal prejudices.
In the last 30 years, data obtained from spectrometric measurements, Xray and electron diffraction studies, and other experiments have yielded precise information about bond distances, angles, and energies. In many cases, the data confirmed conclusions reached earlier. In other cases, valuable new insights were acquired. Structure theory has advanced far beyond the simple electron dot representations and now rests securely on the foundations of quantum and wave mechanics. Although problems involving only simple molecules can now be solved with mathematical rigor, approximations such as the valence bond theory and the molecular orbital theory are very successful in giving results that agree with experimental measurements.
DNA testing has been the center of attention in many criminal justice cases. The United States corrections centers have utilized the DNA testing process. Seventeen death row inmates have been exonerated by the use of these tests. Earl Washington was convicted of rape and murder in 1984. Although he confessed to the rape, he was also diagnosed as being mentally retarded. In October of 2000 Mr., Washington was given a DNA test and was excluded as the rapist and murderer. The Virginia Governor pardoned Mr. Washington after he had served 16 years in prison with 14 of them being on death row (ACLU, 2011). DNA testing has become the rule rather than the exception; but what happens with the DNA after a person has been acquitted, dismissed, or exonerated. Where does DNA go to die or does it? Is the DNA destroyed, or is it retained in miscellaneous databanks for further retrieval and use? In 2010, the United States Congress began a campaign designed to encourage the states to require DNA to be taken from suspects whether they had been charged with a crime or not. In the case of S. and Marper v the United Kingdom found that the retention of the applicants' fingerprints, cellular samples and DNA profiles was in violation of Article 8 of the European Convention on Human Rights. Is creating a policy in the United States that demand DNA from suspects helps in finding subsequent criminals or is it just leading to a track and trace policy?
Tsou, J. A., Hagen, J. A., Carpenter, C. L., & Laird-Offringa, I. A. (2002, August 05). DNA
DNA (deoxyribonucleic acid) is a self-replicating molecule or material present in nearly all living organisms as the main constituent in chromosomes. It encodes the genetic instructions used in the development and functioning of all known living organisms and many viruses. Simply put, DNA contains the instructions needed for an organism to develop, survive and reproduce. The discovery and use of DNA has seen many changes and made great progress over many years. James Watson was a pioneer molecular biologist who is credited, along with Francis Crick and Maurice Wilkins, with discovering the double helix structure of the DNA molecule. The three won the Nobel Prize in Medicine in 1962 for their work (Bagley, 2013). Scientist use the term “double helix” to describe DNA’s winding, two-stranded chemical structure. This shape looks much like a twisted ladder and gives the DNA the power to pass along biological instructions with great precision.
...e also realized that an adenine-thymine pair with two hydrogen bonds was identical in shape to a guanine-cytosine pair with two hydrogen bonds. This opened up the possibility of A-T and G-C pairs, rather than pairs of identical bases. Using Pauling’s ignorance of his mistake to their advantage, Watson and Crick rushed to put the metal model together and write a paper to be published in Nature so they could beat Pauling to the answer. Although they had been exceedingly cautious not to get ahead of themselves and publish a premature manuscript that would later turn out to have a major fault, they now felt they had enough evidence to confidently publish their findings. Indeed, a few days later, they sent the manuscript to the scientific journal with a strong cover letter from Bragg and their research was soon thereafter published, changing the scientific world forever.
What is DNA? DNA is deoxriybonucleic acid which is a molecule that is in a double-helix structure described by James Watson and Francis Crick in 1953. DNA contains our genetic code which is composed of triphosphate molecules, which are also known as the ‘building blocks’ of DNA. There are four bases included in the DNA molecule they are called the four nitrogenous bases. The bases are Thymine, adenine, guanine (purines), thymine and cytosine (pyrimidines) (http://forensicsciencecentral.co.uk/dna.shtml). This shows that DNA isn’t so easy to understand, there is certain bases to make up the DNA molecule. This is important because it helps compose the pieces to DNA and helps find traces to the victim. “The more useful sources include blood, semen, vaginal fluid, nasal secretions and hair with roots” (http://forensicsciencecentral.co.uk/dna.shtml). This quote is important because it singles out the most occurrence of DNA. In order for DNA testing to take place scientists will have t...
...f the structure of DNA by James Watson and Francis Crick in 1953 that was extremely influential for future researchers. They determined that DNA was a double helix structure composed of base pairings, with a sugar phosphate backbone. This model explained how “genes can duplicate themselves [and] would eventually lead to our current understanding of many things, from genetic disease to genetic engineering” (Salem).