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PubMed1984

The organic aerosols of Titan.

A dark reddish organic solid, called tholin, is synthesized from simulated Titanian atmospheres by irradiation with high energy electrons in a plasma discharge. The visible reflection spectrum of this tholin is found to be similar to that of high altitude aerosols responsible for the albedo and reddish color of Titan. The real (n) and imaginary (k) parts of the complex refractive index of thin films of Titan tholin prepared by continuous D.C. discharge through a 0.9 N2/0.1 CH4 gas mixture at 0.2 mb is determined from x-ray to microwave frequencies. Values of n (approximately equal to 1.65) and k (approximately equal to 0.004 to 0.08) in the visible are consistent with deductions made by ground-based and spaceborne observations of Titan. Many infrared absorption features are present in k (lambda), including the 4.6 micrometers nitrile band. Molecular analysis of the volatile component of this tholin was performed by sequential and non-sequential pyrolytic gas chromatography/mass spectrometry. More than one hundred organic compounds are released; tentative identifications include saturated and unsaturated aliphatic hydrocarbons, substituted polycyclic aromatics, nitriles, amines, pyrroles, pyrazines, pyridines, pyrimidines, and the purine, adenine. In addition, acid hydrolysis produces a racemic mixture of biological and non-biological amino acids. Many of these molecules are implicated in the origin of life on Earth, suggesting Titan as a contemporary laboratory environment for prebiological organic chemistry on a planetary scale.

Aerosols↗
PubMed1990

Cometary delivery of organic molecules to the early Earth.

It has long been speculated that Earth accreted prebiotic organic molecules important for the origins of life from impacts of carbonaceous asteroids and comets during the period of heavy bombardment 4.5 x 10(9) to 3.8 x 10(9) years ago. A comprehensive treatment of comet-asteroid interaction with the atmosphere, surface impact, and resulting organic pyrolysis demonstrates that organics will not survive impacts at velocities greater than about 10 kilometers per second and that even comets and asteroids as small as 100 meters in radius cannot be aerobraked to below this velocity in 1-bar atmospheres. However, for plausible dense (10-bar carbon dioxide) early atmospheres, we find that 4.5 x 10(9) years ago Earth was accreting intact cometary organics at a rate of at least approximately 10(6) to 10(7) kilograms per year, a flux that thereafter declined with a half-life of approximately 10(8) years. These results may be put in context by comparison with terrestrial oceanic and total biomasses, approximately 3 x 10(12) kilograms and approximately 6 x 10(14) kilograms, respectively.

Amino Acids↗
PubMed1995

No soup for starters? Autotrophy and the origins of metabolism.

In recent years, several alternatives to the classical prebiotic-soup model for the origin of life have been proposed. Among these, the theory of Wächtershäuser proposes that an archaic version of the autotrophic reductive citric acid cycle, driven by pyrite formation and contained on the resulting pyrite surface, was the earliest metabolic cycle, from which the central biosynthetic pathways arose, initially without enzymes or nucleic acids.

Amino Acids↗
PubMed1992

Molecular replication.

Simple replicating molecules are likely to have played a critical role in the origin of life. Recent experiments show that non-enzymatic replication is conceivable in a wide range of synthetic chemical systems. The challenge now facing these studies is how to develop information-coding systems from simple prebiotic precursors.

Base Sequence↗
PubMed2001

Some observations on amino acid racemization under pyrolytic temperatures and inorganic oxide-catalyzed intermolecular condensation.

The problem of homochirality is of crucial importance for the origins of Life. While most laboratory studies are focused on the search of physical and chemical sources of handedness in the Universe, they reflect only one aspect of the problem: the origin of homochiral biomolecules. At the same time, any space environments where biomolecules are expected to form and where they have to pass through before the first primitive forms of Life emerge, include strong irradiation or/and high temperatures. This automatically implies the possibility of losing the optical activity, i.e. racemization. The simulation experiments performed by our group deal with the following two aspects of amino acid abiotic chemistry: (1) amino acid pyrolysis associated with their extraterrestrial delivery; and (2) peptide formation from amino acids catalyzed by inorganic oxides. According to our observations, the racemization phenomena are very common in the systems considered, not only under pyrolytic temperatures, but in some cases also under rather mild conditions (<100 degrees C). Our results put additional constraints on the environments where the chirality of biomolecules can be efficiently preserved.

Aluminum Oxide↗
PubMedDate not supplied

Looking for the most "primitive" organism(s) on Earth today: the state of the art.

Molecular phylogenetic studies have revealed a tripartite division of the living world into two procaryotic groups, Bacteria and Archaea, and one eucaryotic group, Eucarya. Which group is the most "primitive"? Which groups are sister? The answer to these questions would help to delineate the characters of the last common ancestor to all living beings, as a first step to reconstruct the earliest periods of biological evolution on Earth. The current "Procaryotic dogma" claims that procaryotes are primitive. Since the ancestor of Archaea was most probably a hyperthermophile, and since bacteria too might have originated from hyperthermophiles, the procaryotic dogma has been recently connected to the hot origin of life hypothesis. However, the notion that present-day hyperthermophiles are primitive has been challenged by recent findings, in these unique microorganisms, of very elaborate adaptative devices for life at high temperature. Accordingly, I discuss here alternative hypotheses that challenge the procaryotic dogma, such as the idea of a universal ancestor with molecular features in between those of eucaryotes and procaryotes, or the origin of procaryotes via thermophilic adaptation. Clearly, major evolutionary questions about early cellular evolution on Earth remain to be settled before we can speculate with confidence about which kinds of life might have appeared on other planets.

Archaea↗
PubMed2005

Polymorphisms in a disintegrin and metalloprotease 33 (ADAM33) predict impaired early-life lung function.

RATIONALE: Asthma commonly originates in early life in association with impaired lung function, which tracks to adulthood. OBJECTIVES: Within the context of a prospective birth cohort study, we investigated the association between single nucleotide polymorphisms (SNPs) in a disintegrin and metalloprotease 33 (ADAM33) gene and early-life lung function. METHODS: Children were genotyped for 17 SNPs in ADAM33. Lung function at age 3 (n = 285) and 5 years (n = 470) was assessed using plethysmographic measurement of specific airway resistance (sRaw). At age 5, we also measured FEV(1). SNPs were analyzed individually using logistic regression, followed by linkage disequilibrium mapping to identify the causal locus. MAIN RESULTS: Carriers of the rare allele of F+1 SNP had reduced lung function at age 3 years (p = 0.003). When the recessive model was considered, four SNPs (F+1, S1, ST+5, V4) showed association with sRaw at age 5 years (p < 0.04). Using linkage disequilibrium mapping, we found evidence of a significant causal location between BC+1 and F1 SNPs, at the 5' end of the gene. Four SNPs were associated with lower FEV(1) (F+1, M+1, T1, and T2; p < or = 0.04). The risk of transient early wheezing more than doubled among children homozygous for the A allele of F+1 (odds ratio, 2.39; 95% confidence intervals, 1.18-4.86; p = 0.02), but there was no association between any SNP and allergic sensitization or physician-diagnosed asthma. CONCLUSIONS: Polymorphisms in ADAM33 predict impaired early-life lung function. The functionally relevant polymorphism is likely to be at the 5' end of the gene.

ADAM Proteins↗
PubMed1998

The organic codes. The basic mechanism of macroevolution.

The origin of the genetic code coincided with the origin of life, while the human codes of cultural evolution emerged almost four billion years later. Modern biology does not recognize any other organic code in nature, and is bound therefore to conclude that the whole of cellular evolution consisted of informational changes. Semantic transformations, natural conventions and biological meaning are things that officially do not exist in the organic world, and play no part in our reconstruction of development and evolution. And yet the properties of organic codes are beginning to emerge in various biological processes. Here it is shown that splicing, signal transduction and pattern formation can be accounted for precisely by the existence of organic codes. It is also shown that those processes were instrumental in bringing about major changes in the history of life, and it is concluded that every main step of macroevolution corresponded to the origin of a new organic code.

Animals↗
PubMed1985

On the role of complementarity in biogenesis: a critical phenomenon approach.

One of the important steps of the prebiotic stage of the origin of life is the increase in information content resulting from the transition of a random assembly of oligomers into a self-replicating polymer. We describe that crucial step as a critical phenomenon, treated within the renormalization group framework. We show that the diversity-selection duality of Darwinian evolution is achieved at this state if we start from four different monomers capable of forming two complementary pairs.

Base Sequence↗
PubMedDate not supplied

Synthesis of lipids on the micelle/water interface using inorganic phosphate and an alkene oxide.

Liposomes can be considered as a model for a protocell in the context of the origin of life. These self-organising systems can self-reproduce under certain experimental conditions. Herein we demonstrate the ability of another lipid aggregate, micelles, to catalyse a reaction leading finally to the formation of new lipids. In contrast to other published work, where the lipids are products of a hydrolysis reaction, here the lipids are built up from simple precursors. In addition, we observe a transformation of micelles into liposomes.

Alkenes↗
PubMed2000

Inhibition of rare earth catalytic activity by proteins.

Catalytic action of rare earth element, Ce(IV) to hydrolyze phosphomonoester bonds was confirmed. This effect was considered to suppress abiotic synthesis of nucleotides and nucleic acids in the primitive sea, and hence the origin of life. However, we found that the presence of proteins, especially albumin, strongly inhibited the catalytic action of Ce(IV). This finding was supported by preferential binding of rare earth elements (REEs) to proteins which was revealed using the radioisotopes of these REEs. Consequently, if a large amount of proteins was synthesized in the primitive sea, abiotic synthesis of phosphomonoester compounds, and hence nucleic acids, might have been possible.

Catalysis↗
PubMed2004

The TNA-family of nucleic acid systems: properties and prospects.

This report summarizes the content of the author's lecture given at the 9th ISSOL Conference on the 'Origin of Life' in Oaxaca on 2 July 2002*. The report consists of introductory remarks followed by a reproduction of the authentic sequence of slides shown during the lecture. Each slide figure is accompanied with a short commentary on the figure's content. The lecture dealt with the structure and the properties of TNA (alpha-threofuranosyl nucleic acid) and included results of some more recent chemical investigations that had been inspired by the simplicity of TNA's molecular architecture.

Base Pairing↗
PubMed2000

[Superbugs viewed from cosmobiology].

Superbugs (microorganisms living in unfamiliar and very harsh environments) are located in the center of scientific interests in the sense that 1) most of their habitats belong to marginal regions of the biosphere, 2) clues for the elucidation of the origin of life can be deduced from them, and 3) they are deeply correlated to the extraterrestrial life. Not only for the basic scientific interests, but also for the applied fields, the spot light is shed to them. We, human beings, have been deeply dependent on other organisms through the global material flow they make. Microorganisms together with plants are the leading characters in this process. Also implicit, our future is surely correlated to microorganisms including superbugs. In this special issue, superbugs; thermophilic, psychrophilic barophilic etc. are summarized, and future development on the study on the superbugs are introduced.

Biological Science Disciplines↗
PubMed2006

About a formamide-based origin of informational polymers: syntheses of nucleobases and favourable thermodynamic niches for early polymers.

Formamide NH(2)CHO chemistry provides a unitary frame into which several pieces of the origin-of-life puzzle may be adjusted. Synthetic processes were uncovered which, starting from formamide and prebiotically easily available common catalysts, yield all the necessary nucleic bases precursors, including acyclonucleosides. Formamide allows phosphorylations and trans-phosphorylations, favours the micellar aggregation of surfactants and, most importantly, determines conditions in which the formation of nucleic polymers is thermodynamically favoured. In the detected conditions, the phosphoester bonds are more stable in the polymeric than in the monomeric form, thus allowing formation and survival of informational nucleic polymers.

Evolution, Chemical↗
PubMed2000

Peptide bond formation in gas-phase ion/molecule reactions of amino acids: a novel proposal for the synthesis of prebiotic oligopeptides.

There is a general fascination with regard to the origin of life on Earth. There is an intriguing possibility that prebiotic precursors of life occurred in the interstellar space and were then transported to the early Earth by comets, asteroids and meteorites. It is probable that some part of the prebiotic molecules may have been generated by gas-phase ion/molecule reactions. Here we show experimentally that gaseous ion/molecule reactions of the amino acids, Glu and Met, may promote the synthesis of protonated dipeptides such as (Glu-Glu)H(+) and (Glu-Met)H(+) and their chemical growth to larger protonated peptides.

Amino Acids↗
PubMed1999

Chemical reduction of phosphate on the primitive earth.

If phosphorus played a role in the origin of life, some means of concentrating micromolar levels of phosphate (derived from the calcium phosphate mineral apatite), must first have been available. Here we show that simulated (mini)lightning discharges in model prebiotic atmospheres, including only minimally reducing ones, reduce orthophosphates, including apatite, to produce substantial yields of phosphite. Electrical discharges associated with volcanic eruptions could have provided a particularly suitable environment for this process. Production of relatively soluble and reactive phosphite salts could have supplied a pathway by which the first phosphorus atoms were incorporated into (pre)biological systems.

Apatites↗
PubMed1996

Elements of a unifying theory of biology.

To discover a unifying theory of biology, it is necessary first to believe in its existence and second to seek its elements. Such a theory would explain the regulation of the cell cycle, differentiation and the origin of life. Some elements of the theory may be obtained by considering both eukaryotic and prokaryotic cell cycles. These elements include cytoskeletal proteins, calcium, cyclins, protein kinase C, phosphorylation, transcriptional sensing, autocatalytic gene expression and the physical properties of lipids. Other more exotic candidate elements include the dynamic enzoskeleton, ATP generation, mechanotransduction, the piezoelectric effect and resonance. Bringing these disparate elements together--and discovering others--will require extensive collaborations between specialists from different sciences. This can only be achieved within the context of an integrated approach to biology.

Animals↗
PubMed1992

Titan: a laboratory for prebiological organic chemistry.

When we examine the atmospheres of the Jovian planets (Jupiter, Saturn, Uranus, and Neptune), the satellites in the outer solar system, comets, and even--through microwave and infrared spectroscopy--the cold dilute gas and grains between the stars, we find a rich organic chemistry, presumably abiological, not only in most of the solar system but throughout the Milky Way galaxy. In part because the composition and surface pressure of the Earth's atmosphere 4 x 10(9) years ago are unknown, laboratory experiments on prebiological organic chemistry are at best suggestive; but we can test our understanding by looking more closely at the observed extraterrestrial organic chemistry. The present Account is restricted to atmospheric organic chemistry, primarily on the large moon of Saturn. Titan is a test of our understanding of the organic chemistry of planetary atmospheres. Its atmospheric bulk composition (N2/CH4) is intermediate between the highly reducing (H2/He/CH4/NH3/H2O) atmospheres of the Jovian planets and the more oxidized (N2/CO2/H2O) atmospheres of the terrestrial planets Mars and Venus. It has long been recognized that Titan's organic chemistry may have some relevance to the events that led to the origin of life on Earth. But with Titan surface temperatures approximately equal to 94 K and pressures approximately equal to 1.6 bar, the oceans of the early Earth have no ready analogue on Titan. Nevertheless, tectonic events in the water ice-rich interior or impact melting and slow re-freezing may lead to an episodic availability of liquid water. Indeed, the latter process is the equivalent of a approximately 10(3)-year-duration shallow aqueous sea over the entire surface of Titan.

Amino Acids↗