Step 1: Understanding the Concept:
As DNA helicase unwinds the double helix at the replication fork, the DNA ahead of the fork becomes overwound or "supercoiled" due to torsional stress.
Step 2: Detailed Explanation:
Topoisomerases (such as DNA Gyrase in bacteria) are enzymes that cut the DNA backbone, allow the strands to rotate to relieve the stress, and then reseal the backbone.
Without this enzyme, the DNA would become so tangled and tight that replication would stop.
- DNA Ligase seals "nicks" between DNA fragments.
- Helicase breaks hydrogen bonds to unzip the strands.
- Primase places the RNA primer needed for DNA polymerase to start.
Step 3: Final Answer:
The enzyme that relieves torsional strain or supercoiling is Topoisomerase.