discovery of dna structure and function watson and crick pdf

Discovery of dna structure and function watson and crick pdf

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Introduction

DNA structure

Discovery of DNA Structure and Function: Watson and Crick

The discovery of the structure of DNA by James Watson and Francis Crick in is one of the most famous scientific discoveries of all time. It is one of the most famous scientific discoveries of all time. The shadows on the film were then used to work out where the dense molecules lie in the DNA. This technique is called X-ray diffraction.

Citation Information

Watson and F. Crick 1 April 25, 2 , Nature 3 , , We wish to suggest a structure for the salt of deoxyribose nucleic acid D. This structure has novel features which are of considerable biological interest. A structure for nucleic acid has already been proposed by Pauling 4 and Corey 1. They kindly made their manuscript available to us in advance of publication.

Their model consists of three intertwined chains, with the phosphates near the fibre axis, and the bases on the outside. In our opinion, this structure is unsatisfactory for two reasons: 1 We believe that the material which gives the X-ray diagrams is the salt, not the free acid.

Without the acidic hydrogen atoms it is not clear what forces would hold the structure together, especially as the negatively charged phosphates near the axis will repel each other.

Another three-chain structure has also been suggested by Fraser in the press. In his model the phosphates are on the outside and the bases on the inside, linked together by hydrogen bonds.

This structure as described is rather ill-defined, and for this reason we shall not comment on it. We wish to put forward a radically different structure for the salt of deoxyribose nucleic acid 5. This structure has two helical chains each coiled round the same axis see diagram. We have made the usual chemical assumptions, namely, that each chain consists of phosphate diester groups joining beta-D-deoxyribofuranose residues with 3',5' linkages. The two chains but not their bases are related by a dyad perpendicular to the fibre axis.

Both chains follow right-handed helices, but owing to the dyad the sequences of the atoms in the two chains run in opposite directions 6. Each chain loosely resembles Furberg's 2 model No. The configuration of the sugar and the atoms near it is close to Furberg's "standard configuration," the sugar being roughly perpendicular to the attached base. There is a residue on each every 3. The distance of a phosphorus atom from the fibre axis is 10 A. As the phosphates are on the outside, cations have easy access to them.

The structure is an open one, and its water content is rather high. At lower water contents we would expect the bases to tilt so that the structure could become more compact.

The novel feature of the structure is the manner in which the two chains are held together by the purine and pyrimidine bases. The planes of the bases are perpendicular to the fibre axis. They are joined together in pairs, a single base from one chain being hydroden-bonded to a single base from the other chain, so that the two lie side by side with identical z -coordinates. One of the pair must be a purine and the other a pyrimidine for bonding to occur.

The hydrogen bonds are made as follows: purine position 1 to pyrimidine position 1; purine position 6 to pyrimidine position 6. If it is assumed that the bases only occur in the structure in the most plausible tautomeric forms that is, with the keto rather than the enol configurations it is found that only specific pairs of bases can bond together.

These pairs are: adenine purine with thymine pyrimidine , and guanine purine with cytosine pyrimidine 9. In other words, if an adenine forms one member of a pair, on either chain, then on these assumptions the other member must be thymine; similarly for guanine and cytosine. The sequence of bases on a single chain does not appear to be restricted in any way. However, if only specific pairs of bases can be formed, it follows that if the sequence of bases on one chain is given, then the sequence on the other chain is automatically determined.

It has been found experimentally 3,4 that the ratio of the amounts of adenine to thymine, and the ratio of guanine to cytosine, are always very close to unity for deoxyribose nucleic acid. It is probably impossible to build this structure with a ribose sugar in place of the deoxyribose, as the extra oxygen atom would make too close a van der Waals contact. The previously published X-ray data 5,6 on deoxyribose nucleic acid are insufficient for a rigorous test of our structure. So far as we can tell, it is roughly compatible with the experimental data, but it must be regarded as unproved until it has been checked against more exact results.

Some of these are given in the following communications We were not aware of the details of the results presented there when we devised our structure 11 , which rests mainly though not entirely on published experimental data and stereochemical arguments. It has not escaped our notice 12 that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material. Full details of the structure, including the conditions assumed in building it, together with a set of coordinates for the atoms, will be published elsewhere We are much indebted to Dr.

Jerry Donohue for constant advice and criticism, especially on interatomic distances. We have also been stimulated by a knowledge of the general nature of the unpublished experimental results and ideas of Dr.

Wilkins, Dr. One of us J. Acta, 9, Press, Acta, 10, Watson and Francis H. Crick spoke of finding the structure of DNA within minutes of their first meeting at the Cavendish Laboratory in Cambridge, England, in Knowing the structure of this molecule would be the key to understanding how genetic information is copied. In turn, this would lead to finding cures for human diseases.

Aware of these profound implications, Watson and Crick were obsessed with the problem—and, perhaps more than any other scientists, they were determined to find the answer first. Their competitive spirit drove them to work quickly, and it undoubtedly helped them succeed in their quest. They incessantly discussed the problem, bouncing ideas off one another. This was especially helpful because each one was inspired by different evidence. When the visually sensitive Watson, for example, saw a cross-shaped pattern of spots in an X-ray photograph of DNA, he knew DNA had to be a double helix.

Since the groundbreaking double helix discovery in , Watson has used the same fast, competitive approach to propel a revolution in molecular biology. As a professor at Harvard in the s and s, and as past director and current president of Cold Spring Harbor Laboratory, he tirelessly built intellectual arenas—groups of scientists and laboratories—to apply the knowledge gained from the double helix discovery to protein synthesis, the genetic code, and other fields of biological research.

By relentlessly pushing these fields forward, he also advanced the view among biologists that solving major health problems requires research at the most fundamental level of life. According to science historian Victor McElheny of the Massachusetts Institute of Technology, this date was a turning point in a longstanding struggle between two camps of biology, vitalism and reductionism.

While vitalists studied whole organisms and viewed genetics as too complex to understand fully, reductionists saw deciphering fundamental life processes as entirely possible—and critical to curing human diseases.

Historians wonder how the timing of the DNA race affected its outcome. Science, after years of being diverted to the war effort, was able to focus more on problems such as those affecting human health. Yet, in the United States, it was threatened by a curb on the free exchange of ideas. Today, journals also validate the quality of this research through a rigorous evaluation called peer review.

Science publishing was a different game when Watson and Crick submitted this paper to Nature. With no formal review process at most journals, editors usually reached their own decisions on submissions, seeking advice informally only when they were unfamiliar with a subject. The competitive juices were flowing well before the DNA sprint was in full gear. In , Pauling narrowly beat scientists at the Cavendish Lab, a top center for probing protein structure, to the discovery that certain proteins are helical.

The defeat stung. Cavendish was not about to lose twice to Pauling. Pauling's proposed structure of DNA was a three-stranded helix with the bases facing out.

While the model was wrong, Watson and Crick were sure Pauling would soon learn his error, and they estimated that he was six weeks away from the right answer. Pauling was foiled in his attempts to see X-ray photos of DNA from King's College—crucial evidence that inspired Watson's vision of the double helix—and had to settle for inferior older photographs.

In , Wilkins and the head of the King's laboratory had denied Pauling's request to view their photos. It was fitting, then, that Pauling, who won the Nobel Prize in Chemistry in , also won the Nobel Peace Prize in , the same year Watson and Crick won their Nobel Prize for discovering the double helix.

This claim was justified. To some extent, they were synthesizers of these ideas. Doing little laboratory work, they gathered clues and advice from other experts to find the answer. Scientists use many different kinds of visual representations of DNA.

To visualize the answer, Watson built cardboard cutouts of the bases. Early one morning, as Watson moved the cutouts around on a tabletop, he found that only one combination of base molecules made a DNA structure without bulges or strains. The Wilkins and Franklin papers described the X-ray crystallography evidence that helped Watson and Crick devise their structure. The authors of the three papers, their lab chiefs, and the editors of Nature agreed that all three would be published in the same issue.

Watson and Crick knew these data would be published in the same April 25 issue of Nature, but they did not formally acknowledge her in their paper. What exactly were these data, and how did Watson and Crick gain access to them? While they were busy building their models, Franklin was at work on the DNA puzzle using X-ray crystallography, which involved taking X-ray photographs of DNA samples to infer their structure.

By late February , her analysis of these photos brought her close to the correct DNA model. As she was preparing to leave, she turned her X-ray photographs over to her colleague Maurice Wilkins a longtime friend of Crick. Was it unethical for Wilkins to reveal the photographs? Should Watson and Crick have recognized Franklin for her contribution to this paper? For decades, scientists and historians have wrestled over these issues.

Knowledge of this copying mechanism started a scientific revolution that would lead to, among other advances in molecular biology, the ability to manipulate DNA for genetic engineering and medical research, and to decode the human genome, along with those of the mouse, yeast, fruit fly, and other research organisms. In fact, Rosalind Franklin did the same thing, supplementing her short April 25 paper with two longer articles.

Today, scientists publish their results in a variety of formats. They also present their work at conferences. Figure 1 This figure is purely diagrammatic 8.

Introduction

Watson and F. Crick 1 April 25, 2 , Nature 3 , , We wish to suggest a structure for the salt of deoxyribose nucleic acid D. This structure has novel features which are of considerable biological interest. A structure for nucleic acid has already been proposed by Pauling 4 and Corey 1. They kindly made their manuscript available to us in advance of publication. Their model consists of three intertwined chains, with the phosphates near the fibre axis, and the bases on the outside. In our opinion, this structure is unsatisfactory for two reasons: 1 We believe that the material which gives the X-ray diagrams is the salt, not the free acid.

The development of the DNA theory of inheritance culminated in the publication of the molecular structure of DNA 60 years ago. This paper describes this development, beginning with the discovery of DNA as a chemical substance by Friedrich Miescher in , followed by its basic chemical analysis and demonstration of its participation in the structure of chromosomes. Subsequently it was discovered by Oswald Avery in that DNA was the genetic material, and then Erwin Chargaff showed that the proportions of the bases included in the structure of DNA followed a certain law. The paper ends with a short description of the development of the DNA theory of inheritance after the discovery of the double helix. This is a preview of subscription content, access via your institution. Rent this article via DeepDyve. Alloway J.

This speculative Essay explores the consequences of the imagined premature death of Oswald Avery, who in provided evidence that genes are made of DNA. Four imaginary alternate routes to the genetic function of DNA are outlined, each of which highlights different aspects of the actual process of discovery. PLoS Biol 14 12 : e This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Competing interests: The authors have declared that no competing interests exist. In , Oswald Avery — , a Rockefeller Institute microbiologist, underwent surgery for Graves disease.


Many people believe that American biologist James Watson and English physicist Francis Crick discovered DNA in the s. In reality, this is not the case.


DNA structure

Watson and Francis H. Crick announce that they have determined the double-helix structure of DNA, the molecule containing human genes. The molecular biologists were aided significantly by the work of another DNA researcher, Rosalind Franklin, although she is not included in the announcement, nor did she share the subsequent Nobel Prize award for it. In the early s, Watson and Crick were only two of many scientists working on figuring out the structure of DNA.

The human hereditary material known as deoxyribonucleic acid, or DNA, is a long molecule containing the information organisms need to both develop and reproduce. DNA is found in every cell in the body, and is passed down from parent to child. Although the discovery of DNA occurred in by Swiss-born biochemist Fredrich Miescher, it took more than 80 years for its importance to be fully realized. And even today, more than years after it was first discovered, exciting research and technology continue to offer more insight and a better answer to the question: why is DNA important?

Такие серверы весьма популярны среди пользователей Интернета, желающих скрыть свои личные данные. За небольшую плату они обеспечивают анонимность электронной почты, выступая в роли посредников. Это все равно что номерной почтовый ящик: пользователь получает и отправляет почту, не раскрывая ни своего имени, ни адреса. Компания получает электронные сообщения, адресованные на подставное имя, и пересылает их на настоящий адрес клиента. Компания связана обязательством ни при каких условиях не раскрывать подлинное имя или адрес пользователя.

Chemical structure of DNA discovered

Сеньор?.

Discovery of DNA Structure and Function: Watson and Crick

Кровь не. Выпустите меня отсюда. - Ты ранена? - Стратмор положил руку ей на плечо. Она съежилась от этого прикосновения. Он опустил руку и отвернулся, а повернувшись к ней снова, увидел, что она смотрит куда-то поверх его плеча, на стену. Там, в темноте, ярко сияла клавиатура. Стратмор проследил за ее взглядом и нахмурился Он надеялся, что Сьюзан не заметит эту контрольную панель.

Он ни разу не посмотрел по сторонам. - Это так важно? - полувопросительно произнес Джабба. - Очень важно, - сказал Смит.  - Если бы Танкадо подозревал некий подвох, он инстинктивно стал бы искать глазами убийцу. Как вы можете убедиться, этого не произошло. На экране Танкадо рухнул на колени, по-прежнему прижимая руку к груди и так ни разу и не подняв глаз. Он был совсем один и умирал естественной смертью.

2 comments

  • Aleron Q. 16.05.2021 at 00:34

    Many people believe that American biologist James Watson and English physicist Francis Crick discovered DNA in the s. In reality, this is.

    Reply
  • Ingrid B. 19.05.2021 at 18:14

    Deoxyribonucleic acid, or DNA, is a molecule that contains the instructions an organism needs to develop, live and reproduce.

    Reply

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