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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.
The term plasmid was coined in 1952 by the American molecular biologist Joshua Lederberg to refer to "any extrachromosomal hereditary determinant." [11] [12] The term's early usage included any bacterial genetic material that exists extrachromosomally for at least part of its replication cycle, but because that description includes bacterial viruses, the notion of plasmid was refined over time ...
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)
More than five decades ago, Jacob, Brenner, and Cuzin proposed the replicon hypothesis to explain the regulation of chromosomal DNA synthesis in E. coli. [18] The model postulates that a diffusible, trans-acting factor, a so-called initiator, interacts with a cis-acting DNA element, the replicator, to promote replication onset at a nearby origin.
They have O-acetyl groups on carbon-6 of some muramic acid residues. The matrix substances in the walls of Gram-positive bacteria may be polysaccharides or teichoic acids. The latter are very widespread, but have been found only in Gram-positive bacteria. There are two main types of teichoic acid: ribitol teichoic acids and glycerol teichoic acids.
As DNA synthesis continues, the original DNA strands continue to unwind on each side of the bubble, forming a replication fork with two prongs. 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 ...
Most circular bacterial chromosomes are replicated bidirectionally, starting at one point of origin and replicating in two directions away from the origin. This results in semiconservative replication, in which each new identical DNA molecule contains one template strand from the original molecule, shown as the solid lines, and one new strand ...
Among the many lines of evidence supporting symbiogenesis are that mitochondria and plastids contain their own chromosomes and reproduce by splitting in two, parallel but separate from the sexual reproduction of the rest of the cell; that the chromosomes of some mitochondria and plastids are single circular DNA molecules similar to the circular ...