Abstract
In the “ecosystems-first” approach to the origins of life, networks of non-covalent assemblies of molecules (composomes), rather than individual protocells, evolved under the constraints of molecular complementarity. Composomes evolved into the hyperstructures of modern bacteria. We extend the ecosystems-first approach to explain the origin of eukaryotic cells through the integration of mixed populations of bacteria. We suggest that mutualism and symbiosis resulted in cellular mergers entailing the loss of redundant hyperstructures, the uncoupling of transcription and translation, and the emergence of introns and multiple chromosomes. Molecular complementarity also facilitated integration of bacterial hyperstructures to perform cytoskeletal and movement functions.
Highlights
Several characteristics distinguish unicellular eukaryotes from prokaryotes: 1) eukaryotes tend to be more effectively motile than a comparable mass of prokaryotes; 2) eukaryotes have endomembranes, Int
Integration of partial duplications, would have resulted in incomplete overlapping of some features, resulting in some functions being distributed within eukaryotic cells, including features such as multiple internal membranes; multiple genomes; both nuclear and cytoplasmic DNA; and genes only partially integrated and characterized by having exons punctuated by introns
Integrating multiple species of prokaryotes into a single eukaryotic cell takes care of the diffusion problem, but creates a movement problem of its own – namely how is this cell to move, especially given its increased size and hydrodynamic drag? So larger, integrated cells required the evolution of movement structures, and in particular, the fusion of the bacterial cytoskeletal hyperstructures was needed to form the core of cilia and an actin cytoskeleton and provide motility and coordination of motility
Summary
Several characteristics distinguish unicellular eukaryotes from prokaryotes: 1) eukaryotes tend to be more effectively motile than a comparable mass of prokaryotes; 2) eukaryotes have endomembranes, Int. Composomal catalytic reactions would have resulted in synthetic hypercycles Such distributed hypercyles of composomal reactions would have been more efficient than the random reactions producing the constituents of these composomes from a purely chemical ecology, and inherently inefficient compared with a structurally integrated complex that could itself produce all of the compounds required for its own self-replication. As nature often does in such instances, pruning would have occurred, eliminating as much redundancy as possible, and thereby reducing the size of such meta-cells to produce more efficient, integrated cells Such spatial integration would have required a compatibility between the molecular hyperstructures constituting the cells in each of the mutualistic and symbiotic species of prokaryote that contributed to this new meta-cell; achieving this structural and functional compatibility within a single even larger unit created what we recognize as a eukaryotic cell. We will focus mainly on the integration of structural cellular machinery and the emergence of motile functions, leaving the bulk of discussion of intron-exon, nuclear encapsulation of replication/transcription, and similar issues for other papers
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