14 - Bacterial Chromosomes and Their Replication

Abstract

This chapter focuses on bacterial chromosome and their replication. Most bacteria contain a single circular chromosome, but exceptions to this rule have recently come to light. Since bacterial chromosomes are not paired, bacteria are haploid, and they lack structural proteins. Bacterial chromosomes can be very short and the bacterial genome is frequently augmented by separate DNA structures called plasmids, which vary in length from under 5 kb to more than 100 kb in length. Plasmids control the frequency of their own replication, generally through the action of diffusible substances, proteins or RNA, so that the number of copies per cell of a particular plasmid is maintained. DNA replication can be divided into stages: initiation, elongation and termination, followed by segregation of the replicated DNA, so that one chromosome is inherited by each of the daughter cells at the subsequent division. Replication begins with initiation. During this process a protein complex is formed at a particular DNA sequence (the origin, or oriC), which results in the separation of the strands of the helix to make available single strands that are able to act as templates for daughter DNA synthesis.