In: Biology
Type I topoisomerases are enzymes that cut one of the two strands of double-stranded DNA, relax the strand, and reanneal the strand. They are further subdivided into two structurally and mechanistically distinct topoisomerases: type IA and type IB.
Type II topoisomerases cut both strands of the DNA helix simultaneously in order to manage DNA tangles and supercoils. They use the hydrolysis of ATP, unlike Type I topoisomerase. In this process, these enzymes change the linking number of circular DNA by ±2.
Part 2.
Positive supercoiling is the right-handed, double helical form of DNA. It is twisted tightly in a right handed direction until the helix creates knot. Underwinding.
Negative supercoiling is the left-handed, double helical form of DNA. Overwinding.