▁in ▁the ▁cell . ▁▁ ▁First , ▁it ▁is ▁responsible ▁for ▁un link ing , ▁or ▁dec aten ating , ▁DNA ▁following ▁DNA ▁rep lication . ▁The ▁double - hel ical ▁nature ▁of ▁DNA ▁and ▁its ▁sem icon serv ative ▁mode ▁of ▁rep lication ▁causes ▁the ▁two ▁newly ▁rep licated ▁DNA ▁str ands ▁to ▁be ▁inter link ed . ▁These ▁links ▁must ▁be ▁removed ▁in ▁order ▁for ▁the ▁chrom os ome ▁( and ▁pl asm ids ) ▁to ▁seg reg ate ▁into ▁daughter ▁cells ▁so ▁that ▁cell ▁division ▁can ▁complete . ▁ ▁Top ois omer ase ▁IV ' s ▁second ▁function ▁in ▁the ▁cell ▁is ▁to ▁relax ▁positive ▁super co ils . ▁It ▁shares ▁this ▁role ▁with ▁DNA ▁g yr ase , ▁which ▁is ▁also ▁able ▁to ▁relax ▁positive ▁super co ils . ▁T ogether , ▁g yr ase ▁and ▁to pois omer ase ▁IV ▁remove ▁the ▁positive ▁super co ils ▁that ▁accum ulate ▁ahead ▁of ▁a ▁trans loc ating ▁DNA ▁polym er ase , ▁allowing ▁DNA ▁rep lication ▁to ▁continue ▁unh inder ed ▁by ▁topological ▁stra in . ▁ ▁DNA ▁g yr ases ▁are ▁analog ous ▁en zym es ▁in ▁other ▁organ isms . ▁ ▁While ▁to pois omer ase ▁IV ▁does ▁relax ▁positive ▁super co ils ▁like ▁DNA ▁g yr ase , ▁it ▁does ▁not ▁introduce ▁further ▁negative ▁super co iling ▁like ▁the ▁latter ▁en zym e . ▁ ▁Top ois omer ase ▁IV ▁can ▁un k not ▁right - hand ed ▁kn ots ▁and ▁dec aten ate ▁right - hand