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A circular chromosome is a chromosome in bacteria, archaea, mitochondria, and chloroplasts, in the form of a molecule of circular DNA, unlike the linear chromosome of most eukaryotes. Most prokaryote chromosomes contain a circular DNA molecule. This has the major advantage of having no free ends to the DNA.
Most bacterial chromosomes are circular, although some examples of linear chromosomes exist (e.g. Borrelia burgdorferi). Usually, a single bacterial chromosome is present, although some species with multiple chromosomes have been described. [5]
The haploid circular chromosome in E. coli consists of ~ 4.6 x 10 6 bp. If DNA is relaxed in the B form, it would have a circumference of ~1.5 millimeters (0.332 nm x 4.6 x 10 6). However, a large DNA molecule such as the E. coli chromosomal DNA does not remain a straight rigid molecule in a suspension. [5]
Bacteria do not have a membrane-bound nucleus, and their genetic material is typically a single circular bacterial chromosome of DNA located in the cytoplasm in an irregularly shaped body called the nucleoid. [68] The nucleoid contains the chromosome with its associated proteins and RNA.
A) Circular bacterial chromosomes contain a cis-acting element, the replicator, that is located at or near replication origins. i ) The replicator recruits initiator proteins in a DNA sequence-specific manner, which results in melting of the DNA helix and loading of the replicative helicase onto each of the single DNA strands ( ii ).
In bacteria, which have a single origin of replication on their circular chromosome, this process creates a "theta structure" (resembling the Greek letter theta: θ). In contrast, eukaryotes have longer linear chromosomes and initiate replication at multiple origins within these. [39]
The prokaryotes – bacteria and archaea – typically have a single circular chromosome. [20] The chromosomes of most bacteria (also called genophores ), can range in size from only 130,000 base pairs in the endosymbiotic bacteria Candidatus Hodgkinia cicadicola [ 21 ] and Candidatus Tremblaya princeps , [ 22 ] to more than 14,000,000 base ...
Circular DNA is DNA that forms a closed loop and has no ends. Examples include: Plasmids, mobile genetic elements; cccDNA, formed by some viruses inside cell nuclei; Circular bacterial chromosomes; Mitochondrial DNA (mtDNA) Chloroplast DNA (cpDNA), and that of other plastids; Extrachromosomal circular DNA (eccDNA)