The secondary structure of DNA

Watson and Crick solved the secondary structure of DNA by building a model that fitted all the known experimental results. 

The structure consists of two DNA chains arranged together in a double helix of constant diameter (Fig. 6.4). The double helix can be seen to have a major groove and a minor groove which are of some importance to the action of several antibacterial agents (see later). 

The structure relies crucially on the pairing up of nucleic acid bases between the two chains. Adenine pairs only with thymine via two hydrogen bonds, whereas guanine pairs only with cytosine via three hydrogen bonds. Thus, a bicyclic purine base is always linked with a smaller monocyclic pyrimidine base to allow the constant diameter of the double helix. The double helix is further stabilized by the fact that the base pairs are stacked one on top of each other, allowing hydrophobic interactions 

The fact that adenine always binds to thymine, and cytosine always binds to guanine means that the chains are complementary to each other. In other words, one chain can be visualized as a negative image of its partner. It is now possible to see how replication (the copying of the genetic information) is feasible. If the double helix unravels, then a new chain can be constructed on each of the original chains (Fig. 6.5). In other words, each of the original chains can act as a template for the construction of a new and identical double helix. 

It is less obvious how DNA can code for proteins. How can four nucleotides code for over twenty amino acids  

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In 1953, James Watson and Francis Crick made their classic proposal for the secondary structure of DNA. According to the Watson-Crick model, DNA under physiological conditions consists of two polynucleotide strands, running in opposite directions and coiled around each other in a double helix like the handrails on a spiral staircase. The two strands are complementary rather than identical and are held together by hydrogen bonds between specific pairs of... 

The secondary structure of DNA is shown in Figure B. This "double helix" model was first proposed in 1953 by James Watson and Francis Crick, who used the x-ray crystallographic data of Rosalind Franklin and Maurice Wilkins. Beyond that, they were intrigued by the results of analyses that showed that in DNA the ratio of adenine to thymine molecules is almost exactly 1 1, as is the ratio of cytosine to guanine ... 

The torsion angles around the bonds of the sugar-phosphate DNA backbone are of decisive importance for the secondary structure of DNA as well as for base-base recognition. [44] For antisense agents to be effective inhibitors of protein expression in vivo, they have to resist the action of DNA-degrading enzymes and bind to their... 

In 1953, Watson and Crick proposed a three-dimensional structure of DNA which is a cornerstone in the history of biochemistry and molecular biology. The double helix they proposed for the secondary structure of DNA gained immediate acceptance, partly because it explained all known facts about DNA, and partly because it provided a beautiful model for DNA replication. 

Macromolecular Interactions and Their Biological Consequences 9.1. Influence of Tilorone Hydrochloride on the Secondary Structure of DNA... 

DNA The secondary structure of DNA consists of two polynucleotide chains wrapped around one another to form a double helix. The orientation of the helix is usually right handed witii the two chains running antiparallel to one another (Fig. 4.3). 

Similarly to proteins, both DNA and RNA have a secondary and a tertiary structure. The secondary structure of DNA shows two chains running in opposite directions, coiled in a left-handed (double) helix about the same axis. All the bases are inside the helix, and the sugar phosphate backbone is on the outside (see e.g. [1]). The chains are held together by hydrogen bonds between the bases with adenine always paired with thymine and guanine paired with cytosine. The base pairing in DNA is shown below ... 

The solution to this mystery lies in the secondary structure of DNA. 

Thus far, we have been considering the secondary structure of DNA. double helices can fold up on themselves to form tertiary structures created by supercoiling. Supercoiling is most readily understood by considering covalently closed DNA molecules, but it also applies to DNA molecules constrained to be in loops by other means. Most DNA molecules inside cells are subject to supercoiling. 

The previous discussion of the selective oxidation of G in DNA by RNS was based on the significant differences in redox potentials of the canonical nucleobases. However, the secondary structure of DNA can significantly alter the redox potential of G oxidation in at least two ways sequence context effects on the redox potential of G and charge transfer along the helix. The role of charge transfer in... 

To put in perspective the binding of metal ions to ligand-modified nucleic acid duplexes, we summarize the conclusions of these reviews on metal binding to DNA duplexes and emphasize those conclusions that are relevant for the influence of metal coordination on the secondary structure of DNA. These studies have been the prologue of today s efforts to use DNA or its synthetic analogues as scaffold for transition metal ions. 

Critical to Watson and Crick s proposal for the secondary structure of DNA were experiments carried out by Erwin Chargaff. These experiments showed that the number of adenines in DNA equals the number of thymines and the number of guanines equals the number of cytosines. Chargaff also noted that the number of adenines and thymines relative to the number of guanines and cytosines is characteristic of a given species but varies from species to species. In human DNA, for example, 60.4% of the bases are adenines and thymines, whereas 74.2% of them are adenines and thymines in the DNA of the bacterium Sarcina lutea. 

Evidently the conformations of diol epoxide and/or its triol carbocation (TC) and also the secondary structure of DNA are the determinants of the binding process. To elucidate the mechanism of carcinogen-DNA interaction, however, some questions need to be addressed ... 

The secondary structure of DNA was proposed in 1953 by American molecular biologist James D. Watson and English biologist Erancis H. C. Crick (see > Eigure 11.6). This was perhaps the greatest discovery of modem biology, and it earned its discoverers the Nobel Prize in Physiology or Medicine in 1962. 

Describe the secondary structure of DNA as proposed hy Watson and Crick. 

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