which of the following prevents supercoiling of the dna strands ahead of the replication bubble?

Topoisomerase (specifically DNA gyrase in prokaryotes and topoisomerase I/II in eukaryotes) prevents supercoiling of the DNA strands ahead of the replication bubble.

Quick Scoop: Core Idea

As the replication fork moves, helicase unwinds the double helix, which tends to create positive supercoils in front of the fork.

Topoisomerases solve this by:

• Introducing transient breaks in one (type I) or both (type II) DNA strands.

• Allowing the DNA to rotate/swivel so torsional stress is released, then resealing the break.

In bacteria, DNA gyrase (a type II topoisomerase) is the classic enzyme that relaxes the positive supercoils ahead of the replication fork.

In eukaryotes, mainly topoisomerase I and II carry out similar relaxation to keep the fork moving smoothly.

So, for a typical multiple‑choice question, the correct option is: Topoisomerase (DNA gyrase / topoisomerase I/II) prevents supercoiling of DNA strands ahead of the replication bubble.

TL;DR: The enzyme that prevents supercoiling ahead of the replication bubble is topoisomerase (DNA gyrase in prokaryotes).

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