Sidste fælles forfader
For alternative betydninger, se Lua.
Den sidste fælles forfader, LUA (last universal ancestor), også kaldet LUCA (last universal common ancestor) eller cenancestor, er den seneste organisme som alle nulevende organismer på jorden nedstammer fra.[1] Hermed er den sidste fælles forfader den mest sene fælles forfader (MRCA, Most Recent Common Ancestor) af alt nulevende liv på jorden. LUA estimeres at have levet omkring 3,5 til 3,8 milliarder år siden (engang i æraen Arkæikum i æonen Prækambrium).[2][3]
 | A universal common ancestor is at least 102860 times more probable than having multiple ancestors…[4] A model with a single common ancestor but allowing for some gene swapping among species was... 103489 times more probable than the best multi-ancestor model...[4] |  |
Charles Darwin forslog teorien med en universal fælles nedarvning gennem en evolutionær proces i sin bog On the Origin of Species, og sagde, "Therefore I should infer from analogy that probably all the organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed."[5]
Egenskaber
Baseret på egenskaber i øjeblikket delt af alle uafhængige levende organismer på jorden,[6][7][8][9] er det muligt at udlede de definerende egenskaber af LUCA.
- Den genetiske kode var baseret på DNA.
- DNAet var sammensat af fire nukleotider (deoxyadenosine, deoxycytidine, deoxythymidine og deoxyguanosine), for at udelukke andre mulige deoxynukleotider.
- Den genetiske kode var sammensat af tre-nukleotid codoner, netop producerende 64 forskellige codoner. Siden kun 20 aminosyrer bliver brugt, koder flere codon koder for den samme aminosyre.
- DNAet blev holdt dobbelttrådet af en skabelon-afhængig DNA polymerase.
- DNAets integritet blev vedligeholdt af en gruppe af vedligeholdende enzymer, inklusiv DNA topoisomerase, DNA ligase og andre DNA-reparations enzymer. DNAet blev også beskyttet af DNA-bindende proteiner såsom histoner.
- Den genetiske kode blev udtrykt via RNA intermediater, som var enkelt-trådede.
- ...mere på den engelske Wikipedia.
Kilder/referencer
- ^ Theobald, D. L. (2010), "A formal test of the theory of universal common ancestry", Nature, 465 (7295): 219-22, doi:10.1038/nature09014, PMID 20463738
- ^ Doolittle, W. F. (2000), "Uprooting the tree of life" (PDF), Scientific American, 282 (6): 90-95, doi:10.1038/scientificamerican0200-90, PMID 10710791, arkiveret fra originalen (PDF) 15. juli 2011, hentet 26. december 2011.
- ^ Glansdorff, N.; Xu, Y; Labedan, B. (2008), "The Last Universal Common Ancestor: Emergence, constitution and genetic legacy of an elusive forerunner", Biology Direct, 3: 29, doi:10.1186/1745-6150-3-29, PMC 2478661, PMID 18613974.
- ^ a b Hesman Saey, T. (14. maj 2010). "All Modern Life on Earth Derived from Common Ancestor". Discovery News. Arkiveret fra originalen 25. august 2012. Hentet 26. december 2011.
- ^ Darwin, C. (1859), The Origin of Species by Means of Natural Selection, John Murray, s. 490
- ^ Wächtershäuser, G. (1998), "Towards a reconstruction of ancestral genomes by gene cluster alignment", System. Appl. Microbiol., 21 (4): 473-477.
- ^ Gregory, Michael, What is Life?, Clinton College, arkiveret fra originalen 13. december 2007, hentet 26. december 2011.
- ^ Pace, Norman R. (2001), "The universal nature of biochemistry", PNAS, 98 (3): 805-808, Bibcode:2001PNAS...98..805P, doi:10.1073/pnas.98.3.805, PMC 33372, PMID 11158550, arkiveret fra originalen 17. september 2011, hentet 26. december 2011.
- ^ Wächtershäuser, G. (2003), "From pre-cells to Eukarya — a tale of two lipids", Mol. Microbiol., 47 (1): 13-22, doi:10.1046/j.1365-2958.2003.03267.x, PMID 12492850.
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Tree of life SVG.svg
A phylogenetic tree of life, showing the relationship between species whose genomes had been sequenced as of 2006. The very center represents the last universal ancestor of all life on earth. The different colors represent the three domains of life: pink represents eukaryota (animals, plants and fungi); blue represents bacteria; and green represents archaea. Note the presence of Homo sapiens (humans) second from the rightmost edge of the pink segment. The light and dark bands along the edge correspond to clades: the rightmost light red band is Metazoa, with dark red Ascomycota to its left, and light blue Firmicutes to its right.[1]
A phylogenetic tree of life, showing the relationship between species whose genomes had been sequenced as of 2006. The very center represents the last universal ancestor of all life on earth. The different colors represent the three domains of life: pink represents eukaryota (animals, plants and fungi); blue represents bacteria; and green represents archaea. Note the presence of Homo sapiens (humans) second from the rightmost edge of the pink segment. The light and dark bands along the edge correspond to clades: the rightmost light red band is Metazoa, with dark red Ascomycota to its left, and light blue Firmicutes to its right.[1]
Phylogenetic tree.svg
A phylogenetic tree of living things, based on RNA data and proposed by Carl Woese, showing the separation of bacteria, archaea, and eukaryotes. Trees constructed with other genes are generally similar, although they may place some early-branching groups very differently, thanks to long branch attraction. The exact relationships of the three domains are still being debated, as is the position of the root of the tree. It has also been suggested that due to lateral gene transfer, a tree may not be the best representation of the genetic relationships of all organisms. For instance some genetic evidence suggests that eukaryotes evolved from the union of some bacteria and archaea (one becoming an organelle and the other the main cell).
A phylogenetic tree of living things, based on RNA data and proposed by Carl Woese, showing the separation of bacteria, archaea, and eukaryotes. Trees constructed with other genes are generally similar, although they may place some early-branching groups very differently, thanks to long branch attraction. The exact relationships of the three domains are still being debated, as is the position of the root of the tree. It has also been suggested that due to lateral gene transfer, a tree may not be the best representation of the genetic relationships of all organisms. For instance some genetic evidence suggests that eukaryotes evolved from the union of some bacteria and archaea (one becoming an organelle and the other the main cell).