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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]
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.
Recently, similar folds in the membrane have been observed in bacteria that have been exposed to some classes of antibiotics, [14] and antibacterial peptides . [15] The appearance of these mesosome-like structures may be the result of these chemicals damaging the plasma membrane and/or cell wall.
The nucleoid (meaning nucleus-like) is an irregularly shaped region within the prokaryotic cell that contains all or most of the genetic material. [1] [2] [3] The chromosome of a typical prokaryote is circular, and its length is very large compared to the cell dimensions, so it needs to be compacted in order to fit.
The genetic material is freely found in the cytoplasm. Prokaryotes can carry extrachromosomal DNA elements called plasmids, which are usually circular. Linear bacterial plasmids have been identified in several species of spirochete bacteria, including members of the genus Borrelia notably Borrelia burgdorferi, which causes Lyme disease. [3]
Their genome is usually a circular bacterial chromosome – a single loop of DNA, although they can also harbor small pieces of DNA called plasmids. These plasmids can be transferred between cells through bacterial conjugation. Bacteria have an enclosing cell wall, which provides strength and rigidity
V. cholerae has two circular chromosomes. One chromosomes produces the cholera toxin (CT), a protein that causes profuse, watery diarrhea (known as "rice-water stool"). [5] But the DNA does not directly code for the toxin as the genes for cholera toxin are carried by CTXphi (CTXφ), a temperate bacteriophage (virus). The virus only produces the ...