Question

I would like to know how topoisomerase 1 and 2 works e what is the difference between negative and positive supercoiling.

Answer 1

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 IA topoisomerases change the linking number  of a circular DNA strand by units of strictly 1.
• Type IB topoisomerases change the linking number by multiples of 1 (n).

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.

1. 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.

2. Negative supercoiling is the left-handed, double helical form of DNA. Overwinding.