This content covers DNA topology — specifically supercoiling and its enzymatic regulation by topoisomerases — within the domain of molecular biology. The core principle is that double-stranded DNA conformation is described by linking number (the sum of twist, the helical winding of one strand about the other, and writhe, the crossing of the double helix over itself), that topologically constrained (covalently closed circular) DNA cannot change its linking number without strand breakage, and that deviation from the relaxed linking number (10.4 base pairs per turn) produces positive supercoiling (overwound, more stable, strands harder to separate) or negative supercoiling (underwound, strands easier to separate); topoisomerases (Type I, single-strand break, ±1 linking number change, no energy required; Type II, double-strand break, ±2 linking number change, energy-dependent) modify this linking number. This connects DNA structural topology to essential molecular biology processes such as replication and transcription, which require strand separation.
This content covers DNA topology — specifically supercoiling and its enzymatic regulation by topoisomerases — within the domain of molecular biology. The core principle is that double-stranded DNA co…