Biophysics of the DNA molecule

DNA plays a crucial role in all living organisms because it is the key molecule responsible for storage, duplication, and realization of genetic information. DNA is a heteropolymeric molecule consisting of residues (nucleotides) of four types, A, T, C and G. Fig. 1 shows the chemical structure of the DNA single strand and the complementary base pairs. The genetic message is “written down” in the form of continuous text consisting of four letters (DNA nucleotides A, G, T and C). This continuous text, however, is subdivided, in its biological meaning, into sections. The most significant sections are genes, parts of DNA, which carry information about the sequence of amino acids in proteins. The importance of the DNA molecule cannot be overestimated. It is therefore natural that the molecule has been attracting attention not only of biologists and physicians but also of chemists and physicists, even theorists (for a popular introduction into the field of DNA science, see, e.g., Frank-Kamenetskii, 1993; 1997). For more than forty years already, the DNA molecule has been a subject of biophysical studies. Many outstanding physicists, who made their names in various areas of traditional physics, mostly in solid state physics, contributed by studying DNA. I.M. Lifshitz did not publish many papers about DNA. Nevertheless, his role in directing attention of physicists toward DNA biophysics was very significant, especially in the USSR. Although I had been already in the field when Lifshitz stormed it in mid-1960s I also experienced profound influence of his personality and style. Due to his enthusiasm and indisputable reputation among Soviet physicists, DNA and protein biophysics temporarily became a focus of attention of the Soviet physics community. This community was a unique phenomenon in the world of science. Due to I.M. Lifshitz, I had an opportunity to present my work on DNA topology at the famous