Practice question

Unwinding helicase generates positive supercoils ahead of fork increasing helical twist and resisting further strand separation requiring topoisomerase relief. DNA gyrase, type II topoisomerase composed of GyrA and GyrB subunits as A2B2 tetramer, introduces negative supercoils using ATP hydrolysis to counterbalance positive supercoiling essentially removing overwinding stress. It makes transient double-strand cuts, passes another segment through break, and religates. SSB binds single strands but does not resolve topology, ligase seals nicks only. Gyrase thus prevents fork stall and facilitates rapid fork progression.