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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 ...
Multiple forms of extrachromosomal DNA exist, and, while some of these serve important biological functions, [1] they can also play a role in diseases such as cancer. [2] [3] [4] In prokaryotes, nonviral extrachromosomal DNA is primarily found in plasmids, whereas, in eukaryotes extrachromosomal DNA is primarily found in organelles. [1]
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]
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]
Although probable prokaryotic cell fossils date to almost 3.5 billion years ago, most prokaryotes do not have distinctive morphologies, and fossil shapes cannot be used to identify them as archaea. [58] Instead, chemical fossils of unique lipids are more informative because such compounds do not occur in other organisms. [59]
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.
Prokaryotes lack membrane-bound organelles, such as mitochondria or a nucleus. [6] Instead, most prokaryotes have an irregular region that contains DNA, known as the nucleoid . [ 7 ] Most prokaryotes have a single, circular chromosome , which is in contrast to eukaryotes, which typically have linear chromosomes. [ 8 ]
This is an accepted version of this page This is the latest accepted revision, reviewed on 23 December 2024. DNA molecule containing genetic material of a cell This article is about the DNA molecule. For the genetic algorithm, see Chromosome (genetic algorithm). Chromosome (10 7 - 10 10 bp) DNA Gene (10 3 - 10 6 bp) Function A chromosome and its packaged long strand of DNA unraveled. The DNA's ...