“Linear chromosome”的意思、由来-开放百科全书

A linear chromosome is a type of chromosome, found in most eukaryotic cells, in which the DNA is arranged in multiple linear molecules of DNA. In contrast, most prokaryotic cells contain circular chromosomes, where the DNA is arranged in one large circular molecule. However, linear chromosomes are not limited to eukaryotic organisms; some prokaryotic organisms do have linear chromosomes as well, such as Borrelia burgdorferi.^[1] It is possible to take a prokaryotic cell with a circular chromosome, linearize the chromosome, and still have a viable organism.^[2]

Linear chromosomes have a few advantages and disadvantages to circular chromosomes. One reason that many organisms have evolved to having linear chromosomes is the size of their genome. Linear chromosomes make it easier for transcription and replication of large genomes. If an organism had a very large genome arranged in a circular chromosome, it would have the potential problems when unwinding due to torsional strain. As mentioned before, linear chromosomes are not perfect and have their disadvantages; the biggest being the terminal ends of the chromosomes, or telomeres. Generally, telomeres tend to be unstable and lead to mutations or tumors.^[3] Additionally, due to the methods of DNA replication the ends of the telomeres will not completely be replicated and will be lost, which is known as the "end replication problem". Most eukaryotic cells are able to prevent crucial DNA from being lost by the use of telomerase, an enzyme that synthesizes telomeric DNA, which allows the telomeric DNA to be cut short instead of cutting crucial DNA.^[4] Lastly, even though an organism may have evolved to having linear chromosomes, it is still possible for said organism to revert to having a circular chromosome. When this happens, the organism will essentially delete part of or all of its telomere ends of their linear chromosomes and recombine the strands into the circular shape. ^[1]

References

1. ^¹{{Cite journal|last=Volff|first=J. N.|last2=Altenbuchner|first2=J.|date=2000-05-15|title=A new beginning with new ends: linearisation of circular chromosomes during bacterial evolution|journal=FEMS Microbiology Letters|volume=186|issue=2|pages=143–150|issn=0378-1097|pmid=10802162}}
2. ^{{Cite journal|last=Cui|first=Tailin|last2=Moro-oka|first2=Naoki|last3=Ohsumi|first3=Katsufumi|last4=Kodama|first4=Kenichi|last5=Ohshima|first5=Taku|last6=Ogasawara|first6=Naotake|last7=Mori|first7=Hirotada|last8=Wanner|first8=Barry|last9=Niki|first9=Hironori|date=February 2007|title=Escherichia coli with a linear genome|journal=EMBO Reports|volume=8|issue=2|pages=181–187|doi=10.1038/sj.embor.7400880|issn=1469-221X|pmc=1796773|pmid=17218953}}
3. ^{{Cite journal|last=Ishikawa|first=F.|last2=Naito|first2=T.|date=1999-06-23|title=Why do we have linear chromosomes? A matter of Adam and Eve|journal=Mutation Research|volume=434|issue=2|pages=99–107|issn=0027-5107|pmid=10422538}}
4. ^{{Cite journal|last=Heumann|first=John M.|date=November 1976|title=A model for replication of the ends of linear chromosomes|journal=Nucleic Acids Research|volume=3|issue=11|pages=3167–3171|issn=0305-1048|pmid=188017|pmc=343160}}