Final answer:
Topoisomerase enzymes help in relieving supercoiling during E. coli replication by breaking and reforming DNA's nucleotide base pairs.
Step-by-step explanation:
The number of untwistings, or changes in DNA topology, per E. coli replication depends on the role of topoisomerase enzymes. These enzymes help in relieving supercoiling during replication. When the DNA strands unwind during replication, they can become overwound, resulting in tension and supercoiling. Topoisomerases, specifically topoisomerase II in E. coli, act at the origin of replication to relax the supercoiled chromosome by breaking and reforming DNA's nucleotide base pairs, thus helping to relieve the pressure that results from supercoiling.