Search results
Results from the WOW.Com Content Network
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 ...
The second chromosome has also been called a chromid, in that they have similar codon usage to the chromosome, are essential to life like the main chromosome, but has plasmid-type elements such as the origin of replication. Many other sequenced Paracoccus also have chromids. [25] Vibrio have two circular chromosomes.
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]
Extrachromosomal DNA exists in prokaryotes outside the nucleoid region as circular or linear plasmids. Bacterial plasmids are typically short sequences, consisting of 1 to a few hundred kilobase (kb) segments, and contain an origin of replication which allows the plasmid to replicate independently of the bacterial chromosome. [10]
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.
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.
The genomes of most eukaryotic mitochondria and plastids are in a single circular chromosome, in line with their bacterial ancestor. However, a good number of eukaryotic species do harbor linear Mitochondrial DNA (mtDNA), some even broken into multiple molecules, across a wide variety of taxa: animals (mammals, medusozoans, sponges), fungi (especially yeast), plants, and Alveolatas.
Replication occurs much faster in prokaryotic cells than in eukaryotic cells; bacteria sometimes only take 40 minutes, while animal cells can take up to 400 hours. Eukaryotes also have a distinct operation for replicating the telomeres at the end of their last chromosomes. Prokaryotes have circular chromosomes, causing no ends to synthesize.