Practice question

Prokaryotic chromosomes typically consist of single large DNA molecule occupying nucleoid region without nuclear envelope. Most bacteria including Escherichia coli carry circular, supercoiled chromosome of several megabases organized in loop domains constrained by HU, FIS and H-NS proteins. Circular topology confers replicative advantage with single origin oriC and bidirectional replication terminating at dif site. Exceptions exist such as linear chromosomes in Borrelia, Streptomyces and Agrobacterium, but archetypal pattern remains circular double-stranded DNA often associated with plasmids providing accessory functions under selection pressures.