Biological Topology - DNA and Proteins

The discovery that DNA forms catenanes and knots, some of them extremely complex, initiated a new field of research which has been called Biochemical Topology [21]. In 1967, Vinograd and co-workers detected in HeLa cell mitochondria isolable DNA molecules that consist of independent, double-stranded, closed circles that are topologically interlocked or catenated like the links in a chain [22, 23]. A few years later, catenanes had been observed everywhere that circular DNA molecules were known [24] and the first knot was found by Liu and coworkers in single-stranded circular phage fd DNA treated with Escherichia coli co-protein [25]. In 1980, knots could also be generated in double-stranded circular DNA [26]. 

The ever-increasing interest in the catenanes and knots of DNA stems not only from their widespread occurrence or from their topological novelty determination of their structures provides precious information about the biological processes which generate them. A whole class of enzymes - topoisomerases - effects these topological transformations perfectly [30, 31]. Their possible role in a large vari- 

6 Molecular Knots - From Early Attempts to High-Yield Template Syntheses 

Before being put into rigorous theory, chemical topology received much interest from many scientists and several contributions of utmost importance are worth mentioning. 

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