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At least 163 records · Page 9Linked to original sources
PubMed1976

Multi-hit theory of the origin of life: problems of growth rate of protobionts and of speed of earliest evolution. I.

The previously proposed theory of biogenesis being a multi-hit process (due to random assemblage, within an aggregate of abiogenic nucleic acids (NAs) and proteins, of a set of functional molecules necessary for primitive life) is developed further taking into account speed of reactions and reproduction of protobionts, random distribution of functional molecules in protocell fission, and speed of earliest evolution. A hypothetical model of a protobiont being possibly ancestral to "our" life is designed. Probabilities of a multi-hit origin of such protobionts are estimated accounting not only for inclusion by chance of functional protein and NA molecules but also for exclusion of deleterious enzymes, and respecting the number of possible primitive codes. It is shown that "fluid organisms" are impossible and that individuation is a key structure of life. Life based on only NA (genobiosis) in contrast to life with genotype (NA) plus phenotype (protein) being infinitely evolvable (holobiosis), and life based on proteins alone are discussed. It is shown that protein + NA-life is in favour to those other life forms, and that the probability of origin of at least simple types of of holobiotic protobionts might be high enough for repeated biogeneses under early earth conditions. Though protobionts may have had generation times of 10(3) years speed of early evolution as well as stability of functional molecules could have been sufficient for allowing of evolution to reach the level of procaryots within the 10(8) to 10(9) years available.

Biological Evolution↗
PubMed2001

Enantiomeric crystallization from DL-aspartic and DL-glutamic acids: implications for biomolecular chirality in the origin of life.

Amino acids in living systems consist almost exclusively of the L-enantiomer. How and when this homochiral characteristic of life came to be has been a matter of intense investigation for many years. Among the hypotheses proposed to explain the appearance of chiral homogeneity, the spontaneous resolution of conglomerates seems one of the most plausible. Racemic solids may crystallize from solution either as racemic compounds (both enantiomeric molecules in the same crystal), or less commonly as conglomerates (each enantiomer molecule separate in different enantiomeric crystals). Only conglomerates can develop a spontaneous resolution (one of the enantiomeric molecule crystallizes preferentially, the other one remains in solution). Most of natural amino acids are racemic compounds at moderate temperatures. How can we expect a hypothetical spontaneous resolution of these amino acids if they are not conglomerates? In this paper we show how DL-aspartic and DL-glutamic amino acids (racemic compounds), crystallize at ambient conditions as true conglomerates. The experimental conditions here described, that allows this 'anomalous' behaviour, could be also found in natural sedimentary environments. We suggest that these experimental procedures and its natural equivalents, have a potential interest for the investigation of the spontaneous resolution of racemic compounds comprising molecules associated with the origin of life.

Aspartic Acid↗
PubMed1998

Peptides by activation of amino acids with CO on (Ni,Fe)S surfaces: implications for the origin of life.

In experiments modeling volcanic or hydrothermal settings amino acids were converted into their peptides by use of coprecipitated (Ni,Fe)S and CO in conjunction with H2S (or CH3SH) as a catalyst and condensation agent at 100 degreesC and pH 7 to 10 under anaerobic, aqueous conditions. These results demonstrate that amino acids can be activated under geochemically relevant conditions. They support a thermophilic origin of life and an early appearance of peptides in the evolution of a primordial metabolism.

Acetic Acid↗
PubMed2006

Thermal energy and the origin of life.

Life has evolved on Earth with electromagnetic radiation (light), fermentable organic molecules, and oxidizable chemicals as sources of energy. Biological use of thermal energy has not been observed although heat, and the thermal gradients required to convert it into free energy, are ubiquitous and were even more abundant at the time of the origin of life on Earth. Nevertheless, Earth-organisms sense thermal energy, and in suitable environments may have gained the capability to use it as energy source. It has been proposed that the first organisms obtained their energy by a first protein named pF(1) that worked on a thermal variation of the binding change mechanism of today's ATP sythase enzyme. Organisms using thermosynthesis may still live where light or chemical energy sources are not available. Possible suitable examples are subsurface environments on Earth and in the outer Solar System, in particular the subsurface oceans of the icy satellites of Jupiter and Saturn.

ATP Synthetase Complexes↗
PubMed2006

Small molecule interactions were central to the origin of life.

Many scientists believe life began with the spontaneous formation of a replicator. This idea has been supported by "prebiotic" syntheses carried out by chemists using modern apparatus and purified reagents. The probability that such reactions would take place spontaneously on the early Earth is minute. These points are illustrated here by considering the often cited oligomerization of activated RNA components by clay minerals. A more likely alternative for the origin of life is one in which a collection of small organic molecules multiply their numbers through catalyzed reaction cycles, driven by a flow of available free energy. Although a number of possible systems of this type have been discussed, no experimental demonstration has been made. The inclusion of a "driver" reaction, directly coupled to the energy source, may lead to a solution.

Adenine↗
PubMed2002

The cold origin of life: A. Implications based on the hydrolytic stabilities of hydrogen cyanide and formamide.

It has been suggested that hydrogen cyanide (HCN) would not have been present in sufficient concentration to polymerize in the primitive ocean to produce nucleic acid bases and amino acids. We have measured the hydrolysis rates of HCN and formamide over the range of 30-150 degrees C and pH 0-14, and estimated the steady state concentrations in the primitive ocean. At 100 degrees C and pH 8, the steady state concentration of HCN and formamide were calculated to be 7 x 10(-13) M and 1 x 10(-15) M, respectively. Thus, it seems unlikely that HCN could have polymerized in a warm primitive ocean. It is suggested that eutectic freezing might have been required to have concentrated HCN sufficiantly for it to polymerize. If the HCN polymerization was important for the origin of life, some regions of the primitive earth might have been frozen.

Cold Temperature↗
PubMed1992

Endogenous production, exogenous delivery and impact-shock synthesis of organic molecules: an inventory for the origins of life.

Sources of organic molecules on the early Earth divide into three categories: delivery by extraterrestrial objects; organic synthesis driven by impact shocks; and organic synthesis by other energy sources (such as ultraviolet light or electrical discharges). Estimates of these sources for plausible end-member oxidation states of the early terrestrial atmosphere suggest that the heavy bombardment before 3.5 Gyr ago either produced or delivered quantities of organics comparable to those produced by other energy sources. Which sources of prebiotic organics were quantitatively dominant depends strongly on the composition of the early terrestrial atmosphere. In the event of an early strongly reducing atmosphere, production by atmospheric shocks seems to have dominated that due to electrical discharges. Organic synthesis by ultraviolet light may, in turn, have dominated shock production, but only if a long-wavelength absorber such as H2S were supplied to the atmosphere at a rate sufficient for synthesis to have been limited by ultraviolet flux, rather than by reactant abundance. In the apparently more likely case of an early terrestrial atmosphere of intermediate oxidation state, atmospheric shocks were probably of little importance for direct organic production. For [H2]/[CO2] ratios of approximately 0.1, net organic production was some three orders of magnitude lower than for reducing atmospheres, with delivery of intact exogenous organics in interplanetary dust particles (IDPs) and ultraviolet production being the most important sources. At still lower [H2]/[CO2] ratios, IDPs may have been the dominant source of prebiotic organics on the early Earth. Endogenous, exogenous and impact-shock sources of organics could each have made a significant contribution to the origins of life.

Atmosphere↗
PubMed2006

Self-organizing proto-replicators and the origin of life.

Standard theories suggest that the first informational replicator involved RNA molecules (or a more primitive analogue) and that a preliminary step for the development of such replicating systems may have been the emergence of subunits capable of forming chains and interchain pairings. Following these hypotheses, this discussion describes various abstract simulations designed to investigate the structures resulting from such interactions for generalised subunits. Three classes of pairing strategy were considered for a range of subunit concentrations. The resulting dynamic self-organization of the systems produced high levels of structural complexity (some at low subunit concentrations and in the presence of disruptive subunits) and a significantly increased percentage of complementary base pairing (particularly in the more substantial structures). These properties of the systems, which did not require pre-existing replicators, templates or functional catalysts, were shown to be sensitive to the form of pairing strategy, subunit concentrations and various conditions that could theoretically be altered by products of the systems. Though no systems behaved as a replicator, some possessed collections of properties from which a replicating system might theoretically be constructed without requiring the introduction of additional classes of properties. The implications of such systems were considered with respect to the origin of life.

Catalysis↗