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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.
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.
The final genome type found in plants and fungi is a linear genome made up of homogeneous DNA molecules (type 5). [22] [23] [24] Great variation in mtDNA gene content and size exists among fungi and plants, although there appears to be a core subset of genes present in all eukaryotes (except for the few that have no mitochondria at all). [9]
Usually, a single bacterial chromosome is present, although some species with multiple chromosomes have been described. [5] Along with chromosomal DNA, most bacteria also contain small independent pieces of DNA called plasmids that often encode advantageous traits but are not essential to their bacterial host.
The complex contains a single circular chromosome, a cyclic, double-stranded molecule of stable chromosomal DNA, in contrast to the multiple linear, compact, highly organized chromosomes found in eukaryotic cells. [55] In addition, many important genes of prokaryotes are stored in separate circular DNA structures called plasmids. [56]
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)
Archaeal Genetics is the study of genes that consist of single nucleus-free cells. [24] Archaea have a single, circular chromosomes that contain multiple origins of replication for initiation of DNA synthesis. [25] DNA replication of Archaea involves similar processes including initiation, elongation, and termination.
D-loop replication is a proposed process by which circular DNA like chloroplasts and mitochondria replicate their genetic material. An important component of understanding D-loop replication is that many chloroplasts and mitochondria have a single circular chromosome like bacteria instead of the linear chromosomes found in eukaryotes.