User:J.pshine5t/FUCA

The First Universal Common Ancestor (FUCA) is a proposed non-cellular entity that is the earliest ancestor of the Last Universal common ancestor (LUCA) and its descendants. Meaning that FUCA would be the ancestor to every modern cell as well as ancient, now-extinct cellular lineages not descendant of LUCA. Indeed, he first living organism, LUCA, is thought to already have had a complex metabolism and genome with hundreds of genes, including 355 gene families.

FUCA is assumed to have had other descendants than LUCA, none of which have modern descendants. Some genes of these ancient now-extinct cell lineages are thought to have been horizontally transferred into the genome of early descendants of LUCA.

Origin
Long before the appearance of compartmentalized biological entities like FUCA, life had already began to be organized and emerge in an also pre-cellular era known as the RNA world.

Yet, the universal presence of both biological translation mechanism and genetic code in every biological systems indicates monophyly, a unique origin for all biological systems including viruses and cells.

FUCA would therefore have been able the first organism able of biological translation, that is using RNA molecules to convert information into peptides and produce proteins. This first translation system would have been assembled together with primeval, possibly error-prone genetic code. FUCA would also be the first biological system to have genetic code.

The development of FUCA likely took a long time. FUCA was generated without genetic code, from the ribosome, itself a system evolved from the maturation of a ribonucleoprotein machinery. FUCA appeared when a proto-peptidyl transferase center started to first emerge, when RNA world replicators started to be capable to catalyze the bonding of amino acids into oligopeptides.

The first genes of FUCA were most likely encoding ribosomal, primitive tRNA-aminoacyl transferases and other proteins that helped to stabilize and maintain biological translation. These random peptides produced possibly bound back to the single strand nucleic acid polymers and allowed a higher stabilization of the system that got more robust and was further bound to other stabilizing molecules. When FUCA had matured, its genetic code was completely established.

FUCA therefore was composed by a population of open-systems, self-replicating ribonucleoproteins. With the arrival of these systems, began the progenote era. These systems evolved into maturity when self-organization processes resulted in the creation of a genetic code. This genetic code was, for the first time, capable to organize an ordered interaction between nucleic acids and proteins through the formation of a biological language.

This caused pre-cellular open systems to then start to accumulate information and self-organize, producing the first genomes by the assembly of biochemical pathways, which probably appeared in different progenote populations evolving independently.

Progenotes
Progenote is the name given to designate the semi-open or open biological systems capable to perform an intense exchange of genetic information, before the existence of cells and LUCA. Progenotes composed and were the descendants of FUCA. Progenotes were dominants in the Progenote age, which can be defined as the time where biological systems originated and initally assembled.

The Progenote age happened after the pre-biotic age of the RNA-world and Peptide-world but before the age of organisms and mature biological systems like viruses, bacterias and archeas.

The most successful progenotes populations were probably the ones capable to bind and process carbohydrates, amino acids and other intermediated metabolites and co-factors.

FUCA is thought to have organized the process between the initial organization of biological systems and the maturation of progenotes.

Ribosomal RNA is thought to have emerged at the time of progenotes, before cells or viruses. Viruses might have evolved after FUCA and before LUCA according to the reduction hypothesis, where giant viruses evolved from primordial cells that became parasitic.