Practice question

Escherichia coli chromosome replication initiates at single defined origin oriC and proceeds concurrently in both directions around circular map toward terminus region opposite origin. Terminus contains polar Ter sequences bound by Tus protein that arrest helicase, allowing forks to meet. Bidirectional progression doubles replication speed compared to unidirectional mode, ensures complete duplication within 40 minutes at 37°C. Theta intermediates seen by Cairns autoradiography demonstrate bidirectional bubble expansion. Although rolling circle replication occurs in conjugative plasmids, main chromosomal mode is definitively bidirectional, conserved across many bacteria and eukaryotic replicons.