Prebiotic Lipidic Amphiphiles and Condensing Agents on the Early Earth

Abstract

It is still uncertain how the first minimal cellular systems evolved to the complexity required for life to begin, but it is obvious that the role of amphiphilic compounds in the origin of life is one of huge relevance. Over the last four decades a number of studies have demonstrated how amphiphilic molecules can be synthesized under plausibly prebiotic conditions. The majority of these experiments also gave evidence for the ability of so formed amphiphiles to assemble in closed membranes of vesicles that, in principle, could have compartmented first biological processes on early Earth, including the emergence of self-replicating systems. For a competitive selection of the best performing molecular replicators to become operative, some kind of bounded units capable of harboring them are indispensable. Without the competition between dynamic populations of different compartments, life itself could not be distinguished from an otherwise disparate array or network of molecular interactions. In this review, we describe experiments that demonstrate how different prebiotically-available building blocks can become precursors of phospholipids that form vesicles. We discuss the experimental conditions that resemble plausibly those of the early Earth (or elsewhere) and consider the analytical methods that were used to characterize synthetic products. Two brief sections focus on phosphorylating agents, catalysts and coupling agents with particular attention given to their geochemical context. In Section 5, we describe how condensing agents such as cyanamide and urea can promote the abiotic synthesis of phospholipids. We conclude the review by reflecting on future studies of phospholipid compartments, particularly, on evolvable chemical systems that include giant vesicles composed of different lipidic amphiphiles.

Darwin's Warm Little Pond: A One‐Pot Reaction for Prebiotic Phosphorylation and the Mobilization of Phosphate from Minerals in a Urea‐Based Solvent

“…Additional peaks are the major side products resulting from carbamylation of glycerol phosphates ( Figure S3). Miller-Urey type reactions, [14,16] with magnesium as the dominant divalent cation due to the higher solubility of its salts and an abundant source from weathering of mafic and ultramafic rocks. [23] Additionally,t he availability of SO 4 2À on ap rebiotic Earth is possible through disproportionation of volcanic SO 2 .…”

“…TheU AFW eutectic is aprebiotically plausible solvent. Urea is produced in Miller-Urey type reactions, [14] when ammonium cyanide is exposed to sunlight, [15] and is ahydrolysis product of cyanamide; [16] ammonium formate is ahydrolysis product of HCN. [17] Upon heating, the UAFW eutectic is partially converted to formamide ( Figure 1, Table S1), creating afour-component solvent, and providing afacile pathway for generating this co-solvent of considerable prebiotic interest [8c, 18] that has also been shown, by itself,t oe nhance phosphorylation from mineral sources.…”

Bringing Prebiotic Nucleosides and Nucleotides Down to Earth

“…Currently, prebiotic syntheses giving reasonable yields of specific a-amino acids [4] and N-heterocycles [5] are mastered best, followed by those of lipids [6] and sugars. Currently, prebiotic syntheses giving reasonable yields of specific a-amino acids [4] and N-heterocycles [5] are mastered best, followed by those of lipids [6] and sugars.…”

“…[3] Theprebiotic bricks of life as we know it are more or less of the composite type and can be roughly divided into four compound classes,1 ) a-amino acids,2 )polyhydroxyaldehydes,k etones,a nd polyols,3 )N-heterocycles,a nd 4) longalk(en)yl-chain fatty acids and alcohols.T hey should all covalently assemble (condense) in water, or without any solvent, under prebiotically and geochemically plausible reaction conditions from repeated units of similar fragments or molecules into macromolecules that bear aresemblance to known biomacromolecules,s uch as proteins (polypeptides), carbohydrates (polysaccharides), nucleic acids (polynucleotides), and lipid amphiphiles (phospholipids). Currently, prebiotic syntheses giving reasonable yields of specific a-amino acids [4] and N-heterocycles [5] are mastered best, followed by those of lipids [6] and sugars. [7] Specific prebiotic syntheses of nucleosides and nucleotides,however, have been unhappily at the bottom of this heap for too long.Nucleosides are composed of two precursor classes,o ne of which is particularly stable and usually readily accessed, namely the N-heterocycles.T he other compound class,p rebiotic carbohydrates,israther problematic from astability point of view.…”

Minimalist Protocell Design: A Molecular System Based Solely on Proteins that Form Dynamic Vesicular Membranes Embedding Enzymatic Functions

“…Even DNA‐based spherical phase‐separated shell systems have been described . Liposomes, based on phospholipids that can accommodate enzymatic reactions, RNA replication and complex cellular protein translation, are protocell models based on complex assemblies of molecules of various classes and require enzymatic catalysis or complex prebiotic reaction sequences in order to be accessible . It is possible to envision the construction of protocell models based on nonlipid building blocks enabling self‐assembly or microphase separation from natural and synthetic building blocks .…”