Last common ancestor

Although, on an evolutionary time scale, this was recent the last common ancestor of vertebrates and arthropods existed some 600 million years ago (Jamroz et al., 1993)... 

The family of eukaryotic Ras-like small GTPases may be divided into subfamilies, namely those of ARF, Rab, Ran, Ras, Rho, and Sar (ARF, RAB, RHO, RAS, RHO, SAR), which all contain representatives from fungi, plants, and metazoa. Consequently, these subfamilies and their cellular functions are likely to have emerged early in eukaryotic history. This implies that the last common ancestor of fungi, plants, and metazoa possessed vesicular transport (ARF and Sar), membrane trafficking (Rab), nuclear transport (Ran), signal transduction (Ras), and regulation of the actin cytoskeleton (Rho) functions. 

Cardol P, Matagne RF, Remade C (2002) Impad of mutations affeding ND mitochondria-encoded subunits on the adivity and assembly of complex I in Chlamydomonas. Implication for the strudural organization of the enzyme. J Mol Biol 319 1211-1221 Castresana J, Moreira D (1999) Respiratory chains in the last common ancestor of living organisms. J Mol Evol 49 453-460... 

Ever since Woese and Fox (1977) suggested that the last common ancestor of all life was a precellular incompetent progenote and Van Valen and Maiorana (1980) suggested that eukaryotes evolved from archaebacteria there has been confusion over this issue. Woese and Fox s never remotely tenable idea of the cenancestor as a simple precellular entity has been adequately... 

A sister relationship of the Rickettsiales group and mitochondria revealed in phylogenetic analysis of resident mitochondrial genes does not necessarily mean that their last common ancestor was an obligate endosymbiont. The order Rickettsiales comprises not only true rickettsiae, currently classified... 

High yield of ATP from aerobic respiration made possible the development of typically eukaryotic features (Vellai et al. 1998). It is suggested that the last common ancestor of all eukaryotes was an aerobically respiring organism capable of complete oxidation of carbohydrates to carbon dioxide and water. Some unicellular eukaryotes have either retained or secondarily acquired the ability for anaerobic respiration and hydrogen-evolving fermentation, which has allowed their adaptation to life under microaerophilic or anaerobic conditions. 

Despite their antiquity (perhaps 2.5 billion years old), the resurrected ancestral elongation factors are inferred for bacteria that lived long after the origin of life. Nevertheless, the notion that early life lived at high temperatures, in water, and at nearly neutral pH is consistent with available data. For example, a recent reconstruction of the phylogenetic tree of life based on 31 common gene families supports the notion that the last common ancestor lived at high temperatures.65... 

The transition from first to last common ancestor. 

The experimental data that prove the existence of the three primary kingdoms do not tell us much about the last common ancestor, but we can still say that such a progenitor must have existed, because all cells of the three kingdoms have the same genetic code, the same metabolic currency based on ATP, and roughly 50% of bacterial genes have homologues in eukaryotes. 

As for the first living cells (the first common ancestor) we know even less, but again we are not completely in the dark. The evidence that we do have tells us that they came from the ribotype world, and therefore their genomes were made almost completely of RNAs. This means that during the transition from first to last common ancestor, the cells substituted RNA with DNA in their genes, probably by using enzymes that were very similar to reverse transcriptases. Traces of this substitution, in fact, seem to have survived, because many modern enzymes that produce DNA (the DNA polymerases) are still capable of functioning as reverse transcriptases (Poole et al., 1998). 

In addition to changing the genome s nucleic acids, it is possible that other modifications took place during the evolution from first to last common ancestor, but for the moment we know virtually nothing about these developments. The characteristics of the last common ancestor are therefore highly hypothetical, and yet many have already decided that they were bacterial features. Such a conclusion has... 

The last common ancestor did not have the impressive structures that we usually associate with eukaryotes - it did not have a nucleus, a cytoskeleton, mitochondria, chloroplasts, mitosis, meiosis or sexuality - and yet it did already have the basic features that deep down characterise the eukaryotic cell. Despite the lack of a nucleus, in short, the last common ancestor was not a bacterium, because it did not have the functional features that are specific of bacteria. 

Delaye L, Becerra A, Lazcano A. The last common ancestor what s in a name Orig. Life Evol. Biosph. 2005 35 537-554. 

The inter-aeon boundary between the Hadean and Archean is presently not defined (Nisbet, 1991). There are various options (i) the date of the first life on Earth (ii) the date of the last common ancestor (iii) a round number, such as exactly 4 Ga—4,000,000,000 years ago (iv) the oldest record of a terrestrial rock ( 4 Ga ago) (v) the oldest record of a terrestrial mineral crystal (—4.3-4.4 Ga ago). 

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