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In addition, many important genes of prokaryotes are stored in separate circular DNA structures called plasmids. [56] Like eukaryotes, prokaryotes may partially duplicate genetic material, and can have a haploid chromosomal composition that is partially replicated. [57]
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 ...
Eukaryotic chloroplasts, as well as the other plant plastids, also contain extrachromosomal DNA molecules. Most chloroplasts house all of their genetic material in a single ringed chromosome, however in some species there is evidence of multiple smaller ringed plasmids.
This can either involve the replication of DNA in living organisms such as prokaryotes and eukaryotes, or that of DNA or RNA in viruses, such as double-stranded RNA viruses. [3] Synthesis of daughter strands starts at discrete sites, termed replication origins, and proceeds in a bidirectional manner until all genomic DNA is replicated.
Examples of bacterial species that have been found to possess multiple replicons include Rhodobacter sphaeroides (two), Vibrio cholerae, [3] and Burkholderia multivorans (three). These "secondary" (or tertiary) chromosomes are often described as molecules that are intermediate between a true chromosome and a plasmid and are sometimes called ...
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 mobilome is the entire set of mobile genetic elements in a genome. Mobilomes are found in eukaryotes, [1] prokaryotes, [2] and viruses. [3] The compositions of mobilomes differ among lineages of life, with transposable elements being the major mobile elements in eukaryotes, and plasmids and prophages being the major types in prokaryotes. [4]
Evolution in bacteria was previously viewed as a result of mutation or genetic drift. [11] Today, genetic exchange, or gene transfer is viewed as a major driving force in the evolution of prokaryotes. [11] This driving force has been widely studied in organisms like E. coli. [12]