| Single chain amphiphile membranes have long been proposed as precursors to modern cell membranes on the early Earth. Their availability from interstellar sources and syntheses mimicking prebiotic conditions support this claim. Previous research has shown their versatility as container molecules as they can self-assemble, encapsulate solutes, protect internal contents, harbor enzymatic reactions, grow, and divide. However, their structures can be less stable than modern ones as they are more sensitive to ions, pH, temperature, and dilution effects. Furthermore, the properties of single chain amphiphile vesicles are highly dependent on the exact identity of the amphiphiles, considering differing hydrocarbon chains and types of amphiphilic headgroups.;Historically, decanoic acid, along with other fatty acids, was considered an ideal candidate for modeling prebiotic membranes. Its simple chemical structure and behavior (rapid and spontaneous formation of membranes under appropriate conditions) support this hypothesis. These conditions however are limited by pH range and salt tolerance, as well as concentration of the amphiphile. To overcome these limitations the addition of a second amphiphile, glycerol monoacyl amphiphile was added to the fatty acids to determine the stability induced by mixed membranes. All measures of stability were improved upon the addition of this amphiphile, including temperature related stability, demonstrating the advantages of mixed amphiphile bilayers over pure systems.;Stable membranous structures do not, by themselves, present a strong case for the origin of life from a complex chemical matrix, however their interaction with metabolic (metal-ligand complex) and informational (nucleobase) complexes provides backing for such claims. Using a precursor that can be converted into decanoic acid, and therefore vesicular structures, it was demonstrated that the interaction of the metal-ligand/nucleobase components with both themselves and the protocell structures was tremendously important for the conversion of precursor into decanoic acid.;This conversion was hypothesized to lead to a growth of the structures and possibly division. Growth involved the uptake of nutrients (precursor) by the system and their conversion into more membrane forming material, which was proven qualitatively to function in this protocellular model. Division was then performed by extrusion, which led to the reduction and homogenization of the total population size, thereby completing the "life-cycle". This process is yet incomplete until the replication of the "information" becomes a reality.;For information replication to be realized, it will be necessary to incorporate a polymer of nucleic acid into the system. One of the major questions in the origin of life is the ability to form polymers by self-condensation (non template-directed) of available chemical monomers. Interestingly, it was shown that single chain amphiphile vesicles are capable of assisting this process when non-activated ribonucleotides (specifically adenosine), are exposed to cycles of dehydration rehydration at high temperatures. This process may be one of the first steps to creating information polymers from a pool of chemicals non-enzymatically.;This thesis combines fragments of what is currently believed to be key steps in the origin of life to piece together a complete view of the transition from chemical to biological systems, with emphasis on the membrane structures that are assumed to have been critical to the development of a complex biological network. |
