Nucleic acids helical structure

Finally, the recent discovery of the unusual left-handed polydinucleotide helices for the alternating purine-pyrimidine polymers opens up a whole new field of nucleic acid secondary structures. The relevance and importance of these new structures in the visualization of overwound, as well as underwound, and supercoiled DNA molecules in biological.systems need hardly be emphasized. 

James D. Watson (1928-) and Francis H. C. Crick (1916- ) publish two landmark papers in the journal Nature. The papers are entitled Molecular structure of nucleic acids a structure for deoxyribose nucleic acid and Genetic implications of the structure of deoxyribonucleic acid. Watson and Crick propose a double helical model for DNA and call attention to the genetic implications of their model. Their model is based, in part, on the x-ray crystallographic work of Rosalind Franklin (1920-1958) and the biochemical work of Erwin Chargaff (1905- ). Their model explains how the genetic material is transmitted. 

Lomant AJ, Fresco JR (1975) Structural and energetic consequences of noncomplementary base opposition in nucleic acid helices. Prog Nucl Acid Res Mol Biol 15 185-218... 

The most common element of secondary structure in proteins is the helix. Helices are enriched at protein/protein interfaces, where a helixxleft motif is often employed to recognize hot spot residues at the protein/protein interface. Helices are also enriched in protein/nucleic acid interactions, where the helical motif facilitates molecular recognition by projecting residues into the grooves of nucleic acid helices. 

It fits nicely into the picture of dual structure-phase views of biomesogenic organizations that objects of rod-like appearance , for instance the little world of the tobacco mosaic virus (which - its overall design reduced to a simple rod-like entity - became the starting point of Onsager s theory [37]), as well as much simpler protein and nucleic acid helices are typical mesophase formers in the classical liquid-crystal phase... 

Dolinnaya NG, Fresco JR (1992) Single stranded nucleic acid helical secondary structure stabilized by ionic bonds d(A -G)10. Proc Natl Acad Sci USA 89 9242-9246... 

E. J. Gabbay Topography of nucleic acid helices in solution II. Structure... 

Although helices are uncommon in manmade arehiteeture, they are a common structural theme in biological maeromole-eules—proteins, nucleic acids, and even polysaeeharides. (Loretta Chapet, Santa Fe, NM/ Q Sarbo)... 

These studies showed thaL in the absence of nucleic acid, the backbone 1 aPNA had significant a-hehcal content at pH 7 whereas the backbone 2 aPNA was largely in a random coil conformation at physiological pH. The latter aPNA did become a-helical at higher pHs in a manner reminiscent of the structurally related amphipathic peptides. 

Dey S., Alpha Helical Peptide Nucleic Acids (Alpha PNAs) - Integration of Protein Structure and Nucleic Acid Function. PhD thesis. Case Western Reserve University, Cleveland, OH, January 2001. 

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. 

Acridine and its derivatives are also fused nitrogen heterocycles similar to acridones, which display a high fluorescence quantum yield and possess the ability to intercalate tightly, though reversively, to the DNA helical structure [73], with large binding constants [74]. As a result, acridine dyes are recognized in the field of the development of probes for nucleic acid structure and conformational determination [75-77]. 

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. 

Figure 2.16 Orientations found in DNA helices. (Adapted with permission from Figure 2.11 of Saenger, W. Principles of Nucleic Acid Structure, Springer-Verlag, New York, 1984 copyright 1984, Springer-Verlag, New York and Figure 1.22 A, B, C of Cowan, J. A. Inorganic Biochemistry, An Introduction, 2nd ed., Wiley-VCH, New York, 1997. Copyright 1997, Wiley-VCH.)...

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.

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