Dna unwinding, such as that occurring in replication, affects the superhelical density of dna. in the absence of topoisomerases, the dna would become over wound ahead of a replication fork as the dna is unwound behind it. a bacterial replication fork will stall when the superhelical density (sigma) of the dna ahead of the fork reaches sigma = 0.14. bidirectional replication is initiated at the origin of a 6,000 bp plasmid in vitro, in the absence of topoisomerases. the plasmid initially has a sigma of 0.06. how many base pairs will be unwound and replicated by each replication fork before the forks stall? assume that each fork travels at the same rate and that each includes all components necessary for elongation except topoisomerase.