Nucleic acids double helical

Figure 10.8 Stages in the self-assembly of adenine-uracil nucleic acid double helices.

Figure 10.9 Energetics of the self-assembly of nucleic acid double helices as a function of increasing number of base pairs.

The hydrophobic effect stabilizes the three-dimensional structures of macromolecules. In the nucleic acid double helical structures, the hydrophobic bases are stacked along the helix axis and shielded from solvent by the hydrophilic sugar-phosphate backbone, which is heavily hydrated. A comparable scheme is found in many crystal structures of nucleosides and nucleotides, where the bases are stacked... 

Hydrogen bonding is clearly ubiquitous in stabilising protein secondary structures and nucleic acid double helices (by Watson-Crick base pairing between anti-parallel phosphodiester chains), and in the wide range of homoglycan secondary to quaternary structures. 

Fig. 9.3 Three-dimensional structures of nucleic acid double helices, (a) DNA B-form double helix, (b) RNA A-fram double helix (Reproduced with permissitm fiom Saenger W (1984) Principles of nucleic add structure. Springer-Verlag, New York. Figs. 10.1 and 11.3, pp 244,262)...

B. Base Pairing in Nucleic Acids Double Helical Structure of DNA... 

A different solution has been proposed by Joyce, Schwartz, Orgel and Miller (1987) with the idea that the first nucleotides were simpler than modern ones, while Wachtershauser (1992) has suggested that they were tribonucleic acids , double-helical molecules that could have been formed on pyrite surfaces. Today there still is no satisfactory solution for the origin of nucleic acids, and the fact that they are objectively difficult molecules remains a serious obstacle for the replication paradigm, but it may not be impossible to overcome it. 

Seeman, N.C., Rosenberg, J.M., Rich, A. Sequence-specific recognition of double helical nucleic acids by proteins. Proc. Natl. Acad. Sci. USA 73 804-809, 1976. 

Synthesis and application in molecular biology of double-helical nucleic acids with covalent-bonded chains 98UK274. 

Acridine dyes used as antiseptics, i.e. proflavine and acriflavine, will react specifically with nucleic acids, by fitting into the double helical structure of this unique molecule. In so doing they interfere with its function and can thereby cause cell death. 

Sticky-ends Complementary single-stranded tails projecting from otherwise double-helical nucleic acid molecules. 

The discovery of the base-paired, double-helical structure of deoxyribonucleic acid (DNA) provides the theoretic framework for determining how the information coded into DNA sequences is replicated and how these sequences direct the synthesis of ribonucleic acid (RNA) and proteins. Already clinical medicine has taken advantage of many of these discoveries, and the future promises much more. For example, the biochemistry of the nucleic acids is central to an understanding of virus-induced diseases, the immune re-sponse, the mechanism of action of drugs and antibiotics, and the spectrum of inherited diseases. 

Fig. 16. An unusual interrupted helix from subtilisin (residues 62-86), in which the helical hydrogen bonds continue to a final tum that is formed by a separate piece of main chain. Such interrupted helices (broken on one side of the double helix) are apparently a fundamental feature of nucleic acid structure as illustrated by tRNA, but are exceedingly rare in protein structure.

In 1953, James Watson and Francis Crick (Figure 9) suggested a structure for deoxyribose nucleic acid (DNA). The suggestion had important novel features. One was that it had two helical chains, each coiling around the same axis but having opposite direction. The two helices going in opposite direction, and thus complementing each other, is a simple consequence of the twofold symmetry of the whole double... 

The two major types of nucleic acids are DNA and RNA. Nucleic acids are polyphosphate esters containing the phosphate, sugar, and base moieties. Nucleic acids contain one of five purine or pyrimidine bases that are coupled within double-stranded helices. DNA, which is an essential part of the cell s chromosome, contains the information for the synthesis of protein molecules. For double-stranded nucleic acids, as the two strands separate, they act as a template for the construction of a complementary chain. The reproduction or duplication of the DNA chains is called replication. The DNA undergoes semiconservative replication where each of the two new strands contains one of the original strands. 

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