Topological solitons in an DNA molecule spin chain

Abstract

It is now well known that DNA can be regarded as a physical elastic object in a viscous environment. Two strands of double helix are antiparallel and two polynucleotide chains are coiled about the same axis such that B-DNA (Z-DNA) has right-handed (left -handed) helical sense. The existence of super coiled DNA has been confirmed in experiments long ago and it was found that in vivo chromosomal DNA molecules contain topological domains along which super coiling canoccue.1−3 DNA molecules from prokaryotes (cells without nuclear membranes) oft en adopt the interwound structures which are called plectonemic” super coils. In eukaryotes (cells with nuclei and other organelles with their own internal membranes) chromosomal DNA molecules are also known to be organized into topological independent loops.2−5 Statistical mechanics of super coiled DNA has been studied by several authors.6