Practice question

Chromosome replication in E. coli visualized historically by autoradiography resembles Greek letter theta, where central replication bubble expands between two diverging forks within circular duplex. As synthesis proceeds, unreplicated parental segment plus two replicated arms resemble theta shape. This contrasting model contrasts with sigma rolling circle mode used by many plasmids and phage lambda late replication where one end spills out as concatamer, and linear mode of eukaryotes with multiple origins. Theta mode preserves circular integrity and permits efficient bidirectional progression around circle.