Triple-helix DNA molecule picture

DNA molecule has a double-stranded structure. This structure is formed with anti-parralel polynucleotide chains of purine and pirimidine base, randomly variated. DNA duplexes could be found in several spacial shapes, or conformations. The most common are so called B, A and Z forms. These are distinguished basing on chain turn length, number of nucleotide bases per turn, angle of slope of the nucleodide plane to the helix axis, and could be as left-, as righthanded [1].

The essential role of chains relative orientaition belongs to the hydrogen bonds formed between Watson-Crick complimentary nucleotide bases (A-T, G-C) [2]. However, double-stranded structyre is not only possible DNA structure. It was shown, that some DNA molecules with wide oligopurine or oligopyrimidine could form three-stranded structure in some conditions [3]. These structures are stabilized by internal Hoogsteen bases pairing. Thus the final helx complex is non-symmetric, as one of chains interacts with big groove bases of the same duplex [4].

During studies of the phenomenon, there were multiple attempts to find any application for these structures. Thus, the possibility of usage of synthetic triplex-forming oligonucleotides was evaluated for usage as sequence-specific agents, affecting expression of dedicated gene [5]. The potential of such peptide-nucleotide constructs was demonstrated [6]. Artifitial triplex and even pentaplex structures exist, created with isoguanine-isocytosine sequences [7].

Triplex DNA from methanotrophic archea Triplobacter sp.is shown on this model basing on X-ray data. This structure is non-standard, as stabilized by internal symmetric hydrogen bonds pairs and is stable in extremely acid media only. This DNA triplex type is underdescribed, the data on its physiological role and possible practical usage is still not studied enough. It is believed, such DNA conformations provides the possibility to Triplobacter to perform fission in three cells from one at once, which is unique for living beasts [8].

Plastic B-form DNA molecule model could be purchased. A- and Z-forms could be fabricated upon request in any color combination, also as in any scale.

More:
DNA damage with UV: DNA — photolyase.
Molecular visualisation of DNA-polimerase IV.