Single-strand helical polynucleotides

Structure and Thermodynamic Properties of Single-Strand Helical Polynucleotides... 

Cu2+ ions also disorder single-stranded helical structures by forming crosslinks between and within polynucleotide strands (4). 

Another y9-(1 3)-D-glucan, named schizophyllan as an antitumor polysaccharide, has been obtained from Schizophylium commune [8,9]. Schizophyllan has similar chemical structure and triple-helix as lentinan [17], as shown in Figure 4. Since Sakurai and Shinkai were the first to find that schizophyllan may form a helical complex with single-stranded homo-polynucleotides [18], many works about preparing a complex of schizophyllan and... 

The question of energy transfer is introduced also by the fact that polynucleotides frequently exist not only in single-strand forms but also entirely or partially as double-strand helices in which pyrimidine residues on one chain are hydrogen bonded to purine residues on the other chain. The reactivity of the pyrimidine residue can be strongly affected by the presence of its purine partner. An example of this will be found further on. 

Double helical structures may be constructed from complementary single-stranded polynucleotide chains sharing a common helical axis according to the procedure outlined below. The two strands of the complex are assumed to be regular helices defined by a common set of backbone and glycosyl torsion angles. The data presented here are limited to model poly(dA) poly(dT) double helices stabilized by Watson-Crick base pairs between anti parallel strands. 

One well-established observation is that, under conditions where single-stranded polynucleotides give rise to a d.c. polarographic reduction wave, both native DNA and other double-helical natural and synthetic polynucleotides are inactive 22 23,46-47, 58,59,61) Tjjjs js rea(ji]y interpretable in that, in such helical structures, the adenine and cytosine residues are located in the interior of the helix, and hydrogen bonded in complementary base pairs (see below). Z-DNA, in which cytosine residues are at the surface of the helix, is of obvious interest in this regard, and the B - Z transition in the synthetic poly(dG dC) has been investigated with the aid of differential pulse polarography and UV spectroscopy 60). 

While the importance of IR and Raman spectroscopy for the structural elucidation of purine bases has diminished over the last few decades, its advantages for the study of oligo- and polynucleotides in particular with respect to base pairing is apparent. The IR absorption spectrum of a single-stranded polynucleotide is very similar to that of its component nucleotides, but drastic changes occur on formation of hydrogen-bonded helical structures. 

The analysis obtained with classical polarographic methods corresponds roughly with those reached by the pulse-polarographic technique, but the sensitivity is much lower. The difference between the polarographic behaviour of single-stranded and double-helical form of polynucleotides makes possible the study of the conformation of nucleic acids [81,82,108-113]. Polarography can be utilized also in the study of structural changes of polynucleotides under the influence of the temperature [112,114,115] or irradiation [116]. The photodynamic destabilisation of DNA has been described [117]. 

Ribonucleic Acid. RNA yeast nucleic acid. Polynucleotide directly involved in protein synthesis found in both the nucleus and the cytoplasm oi cells. Description of components of RNA see Nucleic Acids. The Four primary nucleosides are adenosine, guanosine, cytidine and uridine minor nucleosides are also found. The nucleosides are linked by phosphate diester bonds from the 3 -hydroxyl of one D -ribose to the 5 -hydroxyl of the next. The secondary structure of RNA is that of an incompletely Organized single-stranded polynucleotide consisting of some areas with helical structure alternating with non helical lengths. Compere Deoxyribonucleic Acid (DNA). Structure Brown,... 

Many other polynucleotide conformations are possible, including the left-handed helical Z-DNA and more complicated structures thought to be involved in chain replication, together with supercoiling and more globular structures in single-stranded transfer RNA. 

Tensammetry has been widely used for studying the behavior of polynucleotides at the DME [88]. The double-helical DNA (native) is adsorbed at the DME in the region —0.2 and —0.9 V vs. SCE. A pronounced desorption peak appears at —1.1 V (Fig. 38 curve 2). The denatured single-stranded DNA (curve 3) is more strongly adsorbed due to higher adsorbability of DNA bases. Two peaks are observed, the peak at —1.1 V is believed to correspond to an interfacial reorientation of adsorbed DNA segments, whereas the more negative peak (at... 

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