Origin of Eukaryotes Bio 108

Origin of Eukaryotes * The origin of eukaryotes is important to understand the origin of modern complex cells. There are three main separate theories that hypothesize the origins: the three-domain system, eocyte theory, and endosymbiosis. Each one have there own merits and evidence supporting. These theories suggest the evolution of cells from the most primitive prokaryotes, unicellular organism having cells lacking membrane-bound nuclei, to the most complex eukaryotes, single or multicellular organisms with a membrane enclosed nucleolus and organelles. * The Three Domain Hypothesis refers to the proposal by Carl Woese in 1990 that; archaebacteria form a monophyletic group, this clade is sufficiently different from all other prokaryotes to deserve elevation to a separate Domain called Archaea (the other two Domains are Bacteria and Eukarya each arising from a progenote), eukaryotes are more closely related to archaebacteria than to other prokaryotes, and the root of the universal tree of life lies in the branch leading to Bacteria. The three-domain system met with some opposition on the differences between archaea and bacteria. Research of large subunits of RNA polymerase, some aminoacyl-tRNA synthetases (aspartyl, leucyl, tryptophanyl, and tyrosyl), and outer membrane molecules distinctions indicated that Woese was right in the classification and that these organisms were so genetically distinct (in the 165rRNA genes and differences in cell structures) that they needed their own domains. * In the 1984 James Lake theorized eukaryotes evolved from a specific group of ancestrial archea, the eocyte. The idea that eukaryotes could have arisen from a lineage of prokaryotes, using expanded molecular sequence datasets and phylogenetic approaches. Using a matrix of amino acid sites, traditional methods such as maximum parsimony resulted in the 3-domains topology, but an eocyte tree was obtained when maximum-likelihood and Bayesian analyses were