The final transition to living entities that fulfill all the definitions of modern cells depended on the ability to evolve effectively by natural selection.
The phospholipid, the primary material of cell membranes, is an example of a common oily compound prevalent in the prebiotic seas.
[citation needed] Primitive reproduction may have occurred when the bubbles burst, releasing the results of the experiment into the surrounding medium.
Rather it is suggested they were composed of fatty acids, as they can freely exchange ions, allowing geochemically sustained proton gradients at alkaline hydrothermal vents that might lead to prebiotic chemical reactions via CO2 fixation.
[9] The common ancestor of the now existing cellular lineages (eukaryotes, bacteria, and archaea) may have been a community of organisms that readily exchanged components and genes.
Proteins are much more flexible in catalysis than RNA due to the existence of diverse amino acid side chains with distinct chemical characteristics.
For instance, recent studies of transfer RNAs, the enzymes that charge them with amino acids (the first step in protein synthesis) and the way these components recognize and exploit the genetic code, have been used to suggest that the universal genetic code emerged before the evolution of the modern amino acid activation method for protein synthesis.
[11][12][15][16][17] The first RNA polymers probably emerged prior to 4.17 Gya if life originated at freshwater environments similar to Darwin's warm little pond.
Based on a phylogenetic analysis, Dacks and Roger[19] proposed that facultative sex was present in the common ancestor of all eukaryotes.
[23] Evolutionary trees based only on SSU rRNA alone do not capture the events of early eukaryote evolution accurately, and the progenitors of the first nucleated cells are still uncertain.
[24] One hypothesis is that the first nucleated cell arose from two distinctly different ancient prokaryotic (non-nucleated) species that had formed a symbiotic relationship with one another to carry out different aspects of metabolism.
It is postulated that this symbiotic partnership progressed via the cellular fusion of the partners to generate a chimeric or hybrid cell with a membrane bound internal structure that was the forerunner of the nucleus.
[26] "The First Cell arose in the previously prebiotic world with the coming together of several entities that gave a single vesicle the unique chance to carry out three essential and quite different life processes.
These were: (a) to copy informational macromolecules, (b) to carry out specific catalytic functions, and (c) to couple energy from the environment into usable chemical forms.
Each of these three essential processes probably originated and was lost many times prior to The First Cell, but only when these three occurred together was life jump-started and Darwinian evolution of organisms began."
(Koch and Silver, 2005)[27] "The evolution of modern cells is arguably the most challenging and important problem the field of Biology has ever faced.
Scientific interest in cellular evolution started to pick up once the universal phylogenetic tree, the framework within which the problem had to be addressed, was determined.