DNA topology is the study of those DNA forms that remain fixed for any deformation that does not involve breakage. DNA molecules that are chemically identical (same nucleotide length and sequence) but differ in their topology are called topoisomers. There are three topological DNA forms that are the natural consequence of the structure and metabolism of the double helix: knotted, catenated, and supercoiled DNA. Cellular DNA is either circular or constrained by being tethered at intervals to organizing structures. Thus, DNA knot and catenane resolution and supercoiling maintenance must occur locally. Controlling the topology of its DNA is critical to the cell. If unresolved, DNA knots could potentially have devastating effects on cells; DNA catenanes prevent genetic and cellular segregation. DNA negative supercoiling is essential for cell viability. Topoisomerases are enzymes within cells whose function is to control DNA topology.
In this session, we will appreciate the packaging challenges within cells, explore the topology of DNA, and learn how cells deal with DNA entanglements.