Biochemistry and Bioinformatics

**Chapter 1**

**Abstract**

bioinformatics

**3**

**1. Introduction**

Where Quantum Biochemistry

Excited Conformationally-

AT DNA Base Pair

*and Dmytro M. Hovorun*

of the nucleic acids at the quantum level.

*Ol'ha O. Brovarets', Kostiantyn S. Tsiupa*

Meets Structural Bioinformatics:

Tautomeric States of the Classical

This Chapter summarizes recent quantum-chemical (QM) investigations of the novel conformational and tautomeric states on the potential energy hypersurface of the classical AT/AU nucleobase pairs. For the first time, it was observed 28 local minima for each base pair excluding enantiomers - planar, non-planar base pairs and structures with wobble geometry. Considered excited conformationallytautomeric states of the classical AT DNA base pair have been revealed in the Nucleic Acid Database by structural bioinformatics. These data shed light on the biological significance of the unusual AT/AU nucleobase pairs for the functioning

**Keywords:** quantum biology, AT and AU nucleobase pairs, tautomeric state, conformational state, wobble geometry, quantum-chemical calculation, structural

Since the discovery of the spatial organization of the DNA molecule by James Watson & Francis Crick [1, 2], it is traditionally believed that canonical Watson-Crick AT and GC DNA base pairs are quite conservative structures. These classical DNA base pairs almost do not have tautomeric variability and essential conformational mobility at the dynamical behavior of DNA molecule [2]. Generally, it is suggested that bases in the *anti*-conformation able to form a pair according to the so-called Watson-Crick (WC) scheme joined through the three intermolecular hydrogen (H) bonds [3]. At the same time, many biologists-contemporaries questioned the proposed Watson-Crick conformation, since X-ray resolution does not allow to establish for sure the precise conformation of the base pairs constituting to the DNA double helix. Exactly by this reason Maurice Wilkins – the third author of the discovery of the DNA structure – explained the reason why Rosalind Franklin doubted in modeling the structure of DNA [4]. And even forefathers of the
