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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.
A plasmid is a small, extrachromosomal DNA molecule within a cell that is physically separated from chromosomal DNA and can replicate independently. They are most commonly found as small circular, double-stranded DNA molecules in bacteria; however, plasmids are sometimes present in archaea and eukaryotic organisms.
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)
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. Plasmids can be easily gained or lost by a bacterium and can be transferred between bacteria as a form of horizontal gene transfer .
It can take a century for a stromatolite to grow 5 cm. [10] Bacteria in a capule. Bacteria are one of the world's oldest forms of life, and are found virtually everywhere in nature. [9] Many common bacteria have plasmids, which are short, circular, self-replicating DNA molecules that are separate from the bacterial chromosome. [11]
In many bacteria, the chromosome is a single covalently closed (circular) double-stranded DNA molecule that encodes the genetic information in a haploid form. The size of the DNA varies from 500,000 to several million base pairs (bp) encoding from 500 to several thousand genes depending on the organism. [2]
[131] [132] Some bacteria contain plasmids, small extra-chromosomal molecules of DNA that may contain genes for various useful functions such as antibiotic resistance, metabolic capabilities, or various virulence factors. [133] Whether they have a single chromosome or more than one, almost all bacteria have a haploid genome. This means that ...
Some mitochondria and some plastids contain single circular DNA molecules that are similar to the DNA of bacteria both in size and structure. [71] Genome comparisons suggest a close relationship between mitochondria and Alphaproteobacteria. [72] Genome comparisons suggest a close relationship between plastids and cyanobacteria. [73]