Early evolution: prokaryotes, the new kids on the block

Article Abstract:

Author's Abstract: COPYRIGHT 1999, John Wiley & Sons, Inc. Prokaryotes are generally assumed to be the oldest existing form of life on earth. This assumption, however, makes it difficult to understand certain aspects of the transition from earlier stages in the origin of life to more complex ones, and it does not account for many apparently ancient features in the eukaryotes. From a model of the RNA world, based on relic RNA species in modern organisms, one can infer that there was an absolute requirement for a high-accuracy RNA replicase even before proteins evolved. In addition, we argue here that the ribosome (together with RNAs involved in its assembly) is so large that it must have had a prior function before protein synthesis. A model that connects and equates these two requirements (high-accuracy RNA replicase and prior function of the ribosome) can explain many steps in the origin of life while accounting for the observation that eukaryotes have retained more vestiges of the RNA world. The later derivation of prokaryote RNA metabolism and genome structure can be accounted for by the two complementary mechanisms of r-selection and thermoreduction.

RNA

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Where is the root of the universal tree of life?

Article Abstract:

Author's Abstract: COPYRIGHT 1999, John Wiley & Sons, Inc. The currently accepted universal tree of life based on molecular phylogenies is characterised by a prokaryotic root and the sisterhood of archaea and eukoryotes. The recent discovery that each domain (basteria, archaea, and eucarya) represents a mosaic of the two others in terms of its gene content has suggested various alternatives in which eukaryotes were derived from the merging of bacteria and archaea. In all these scenarios, life evolved from simple prokaryotes to complex eukaryotes. We argue here that these models are biased by over confidence inmolecular phylogenies and prejudices regarding the primitive nature of prokaryotes. We propose instead a universal tree of life with the root in the eukoryotic branch and suggest that many prokaryotic features of the information processing mechanism originated by simplification through gene loss and non-orthologous displacement.

Archaeabacteria, Archaea

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Mitochondria and ageing: Winning and losing in the numbers game

Article Abstract:

Study is presented to understand the role of mitochondrial turnover in ageing. Increased density combined with mitochondrial biogenesis might contribute to ageing.

Science & research, Research, Mitochondria

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