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At least 307 records · Page 17Linked to original sources
PubMed1999

Origin of life. II. From prebiotic replicators to protocells.

Primitive microvesicles (coacervates, microspheres, marigranules, etc.), free-born in aqueous media, are only protometabolic proteinoids surrounded by an amphiphilic protomembrane. In contrast, surface-born microvesicles could be initiated in the pores of watered rocks providing primary boundaries coated by amphiphilic compounds and acting as sinks for primitive peptides and their coding nucleobases N-P anchored on polyphosphates. Only presumed replication of these prenucleic infopolymers would qualify the basipetally budded microvesicles as protocells.

Cell Membrane↗
PubMed2001

The origin of life. I: When and where did it begin?

For decades most scientists assumed that life emerged billions of years ago in a "primordial soup" somewhere on the Earth's surface. Evidence is mounting, however, that life may have begun deep beneath the surface, perhaps near a volcanic ocean vent or even inside the hot crust itself. Since there are hints that life's history on Earth extends back through the phase of massive cosmic bombardment, it may be that life started on Mars and came here later, perhaps inside rocks ejected from the Red Planet by large impacts. The traffic of intact rocks between Mars and Earth is now an established fact, and experiments confirm that microbes could survive the rigours of the journey through space if cocooned within such material. Unfortunately, this planetary cross-contamination compromises astrobiologists' hope of finding a second genesis in the solar system.

Animals↗
PubMedDate not supplied

Macromolecules and the origin of life.

From our knowledge of present day organisms, it is hard to imagine a living assembly, even at its most primitive stage, without macromolecules. In order to look for the macromolecules which possibly participated in the assembly of the primitive organisms, the reaction and formation of polymers in HCN under irradiation of ultraviolet ray of 184.9 nm. was studied. As an example of a simple way of producing an assembly of macromolecules, the mechanism of coacrevation was studied by using gelatin as the material.

Biopolymers↗
PubMed1977

Chance and the origin of life.

Random chemical reactions in the Earth's primitive hydrosphere could have generated no more than 200 bits of information, whereas the first Darwinian organism must have encoded about a million bits, and therefore could not have arisen by chance. This information gap is bridged by separating reproduction from organism, and postulating a reproductive chemical community that would generate information by proto-Darwinian evolution. The information content of the initial community could have been as low as 160 bits, and its evolution might have led to the first Darwinian cell.

Amino Acids↗
PubMed2000

Origin of life. A simpler nucleic acid.

What was the genetic material of the earliest life forms on Earth if it was not RNA? As Orgel explains in his Perspective, the answer may be simpler nucleic acid polymers perhaps like the RNA analogs called (L)-a-threofuranosyl oligonucleotides or TNAs (Schöning et al.). These molecules have threose rather than ribose in their sugar-phosphate backbones and yet retain many of the properties of RNA including the ability to pair up in double helices.

Base Pairing↗
PubMed2004

Organic aerosols and the origin of life: an hypothesis.

Recent experimental work has verified the prediction that marine aerosols could have an exterior film of amphiphiles; palmitic, stearic and oleic acids were predominant. Thermodynamic analysis has revealed that such aerosols are energetically capable of asymmetric division. In a prebiotic terrestrial environment, one of the products of such aerosol fission would have been bacterially sized (microns), the other would have been virally sized (tens of nanometers). Plausible avenues for chemical differentiation between the two particles are discussed, and the probabilities for the transition from geochemistry to biochemistry updated in light of recent palaeo fossil studies.

Aerosols↗
PubMed2002

The cold origin of life: B. Implications based on pyrimidines and purines produced from frozen ammonium cyanide solutions.

A wide variety of pyrimidines and purines were identified as products of a dilute frozen ammonium cyanide solution that had been held at -78 degrees C for 27 years. This demonstrates that both pyrimidines and purines could have been produced on the primitive earth in a short time by eutectic concentration of HCN, even though the concentration of HCN in the primitive ocean may have been low. We suggest that eutectic freezing is the most plausible demonstrated mechanism by which HCN polymerizations could have produced biologically important prebiotic compounds.

Cold Temperature↗
PubMed1981

A theory of the origin of life.

Life on Earth is essentially nucleic acids (NAs) influencing peptide synthesis such that NA replication is favored. It is proposed that the ability to synthesize polypeptides evolved gradually - one peptide bond at a time. The proposed evolution of the peptide synthesis apparatus begins with a 'transfer NA' (tNA) which catalyzes the transfer of activated amino acids to accessible amino groups in its environment. The resulting 'capped molecules' (with single amino acid 'caps') in turn favor NA replication. The proposed evolution of the peptide synthesis apparatus from the tNA onward is characterized by a progressive increase in the number of amino acids per cap: two tNAs jointly produce a 'dipeptide cap', three tNAs jointly produce a 'tripeptide cap', etc. Messenger NAs evolve because they can specify the composition and sequence order of the peptide caps. Lastly, ribosomal NAs evolve. The origin, expansion, and standardization of the genetic code are discussed. It is proposed that the presence triplet code evolved by a process of codon length refinement, and the originally codons of varying lengths were allowable, as were unassigned bases between codons. An environmental supply of activated compounds for early evolving entities is proposed. An 'environmental retention and redistribution process' is proposed to have acted as a functional substitute for the cell wall and cell division of early evolving entities.

Amino Acids↗
PubMed1993

Liquid water and the origin of life.

Liquid water has many peculiarities which confer special properties. The most important among them probably are the ability to establish hydrogen bonds, a high polarity and a high dielectric constant. In the presence of liquid water, large organic molecules have to manage the conflict between hydrophobic groups and hydrophilic groups. This duality can generate interesting prebiotic situations such as the stereoselective aggregation of short peptide sequences of alternating hydrophobic-hydrophilic residues into thermostable beta-sheets endowed with chemical activity. Liquid water is also a powerful hydrolytic agent. As such, it allows pathways which would have few chances to occur in an organic solvent.

Amino Acids↗
PubMed1995

Electroweak enantioselection and the origin of life.

All biomolecules are of one hand--but what determines which hand? Why is life based on L-amino acids and D-sugars rather than D-amino acids and L-sugars? We believe the symmetry-breaker could be the weak force, which causes enantiomers to differ very slightly in energy. In this paper we present our calculations of this parity-violating energy difference (PVED) for a range of important biomolecules, and in nearly all cases it is indeed the 'natural' enantiomer which is the more stable.

Amino Acids↗
PubMed1978

Bioorganic chemistry and the origin of life.

A challenging theme in bioorganic chemistry is the unification of established theories of biochemistry and organic chemistry to provide new patterns for interpretation and experimentation. Especially relevant examples of such interactions can be drawn from the field of enzyme catalysis and, in particular, the role of cofactors therein. Knowledge of the chemical mechanisms by which some of the cofactors function has progressed rapidly with the aid of studies of the cofactors themselves (or compounds of related structure, "models") stripped of the accompanying apoenzyme. The striking successes in this field likely arise from a fundamental resemblance between bioorganic chemistry (especially coenzyme models) and chemical evolution before the appearance of coded polypeptide enzymes.

Biochemistry↗
PubMed1998

New polyazaporphine chemistry for the origin of life.

Molecular orbital spectral predictions suggest that 2,5,7,10,12,15,17,20-octaaza-21H, 23H-porphine has a visible spectral range closely matching that of chlorophyll-a. Since the octaazaporphine is, in its core, a simple derivative of an (HCN)12 oligomer, this fact, together with its spectral properties, would suggest that it occupies a high rank as a primordial porphinic solar energy transducer for photochemistry essential to life's formation. The demonstration that the mass 324 hexahydrooctaazaporphine is formed in protic media by the cyclotetramerization of imidazol-4-aminohydroxonium ion or the derived nitrenium ion, and that a mass 318 species consonant with that of the Huckel aromatic octaazaporphine is observed in the course of these studies, strongly supports the proposed octaazaporphine synthesis in a prebiotic hydrocyanic acid milieu.

Chlorophyll↗
PubMed2000

Formation of peptide bonds from metastable versus crystalline phase: implications for the origin of life.

Formation of peptide bonds was attempted by thermal activation of dry amino acids from aqueous solution that simulated prebiotic evaporative environments. The evaporation trend of amino acids solutions shows a bifurcation and can lead to either a crystalline phase (near equilibrium) or a metastable non-crystalline phase (far from equilibrium). Only amino acids in this metastable phase are able to form peptide bonds by thermal activation at temperatures that are generated by solar radiation today. We suggest that this metastable phase is the ideal initial material to trigger amino acid assemblage with protein-like structure because provide the driving force (supersaturation) for an intense interaction between monomers of different amino acids and allows activation of these monomers in plausible prebiotic conditions.

Amino Acids↗
PubMed2002

Chirality and the origin of life: in situ enantiomeric separation for future space missions.

Two different methods of derivatization were studied in order to select and optimize one for the in situ enantiomeric separation of amino acids present in Martian samples. The method, using DMF-DMA [N,N-dimethylformamide dimethyl acetal], is simple and easily automated. However, byproducts of the reaction interfere in the gas chromatograms and mass spectrometry detection is needed for in situ analysis. The chloroformate derivatization has several advantages, including the use of achiral robust capillary column, room temperature reaction, and short analysis. The choice of the definitive derivatization method will depend on the energy and time devoted to the analysis of amino acids in the next Mars exploration missions.

Amino Acids↗
PubMed1992

Radionuclide-induced evolution of DNA and the origin of life.

Artesian groundwaters of high radionuclide concentration are ubiquitous and may have provided the large, sustained energy sources that were required to drive the multistage process of DNA and primordial cell evolution. The rapid, early development of the genetic code as well as its degeneracy can be attributed to exceptionally high radiation-induced mutation rates in this unique environment. The ability of double-strand DNA to direct enzymatic repair of radiation damage to single strands contributed importantly to its selective evolution. It is postulated that the polymerization of nucleotides took place at elevated temperatures within alpha-particle tracks of high ion and free-radical density, followed by rapid quenching to ambient conditions. It also is evident that radiation resistance and ploidy were important selection factors in cellular evolution.

Biological Evolution↗
PubMed1985

RNA catalysis and the origin of life.

Until the discovery of catalytic RNAs, first the self-splicing intron in Tetrahymena and then the bacterial RNAse P, cellular enzymes had always seemed to be protein in nature. The recognition that RNA can catalytically make and break phosphodiester bonds simplifies some of the assumptions required of a rudimentary self-replicating entity. Available information on the chemistry of RNA-catalyzed reactions is reviewed, with particular attention to self-splicing introns and tRNA processing by RNase P. An explicit model for a self-replicating RNA is described. The model postulates a nucleotide binding/polymerization site in the RNA, and takes advantage of intrinsic fluidity in RNA higher order structure to dissociate parent and progeny complementary strands.

Animals↗
PubMed2005

Ice and the origin of life.

Sea ice occurs abundantly at the polar caps of the Earth and, probably, of many other planets. Its static and dynamic properties that may be important for prebiotic and early biotic reactions are described. It concentrates substrates and has many features that are important for catalytical actions. We propose that it provided optimal conditions for the early replication of nucleic acids and the RNA world. We repeated a famous prebiotic experiment, the poly-uridylic acid-instructed synthesis of polyadenylic acid from adenylic acid imidazolides in artificial sea ice, simulating the dynamic variability of real sea ice by cyclic temperature variation. Poly(A) was obtained in high yield and reached nucleotide chain lengths up to 400 containing predominantly 3'--> 5' linkages.

Adenosine Monophosphate↗
PubMed1994

Impact melting of frozen oceans on the early Earth: implications for the origin of life.

Without sufficient greenhouse gases in the atmosphere, the early Earth would have become a permanently frozen planet because the young Sun was less luminous than it is today. Several resolutions to this faint young Sun-frozen Earth paradox have been proposed, with an atmosphere rich in CO2 being the one generally favored. However, these models assume that there were no mechanisms for melting a once frozen ocean. Here we show that bolide impacts between about 3.6 and 4.0 billion years ago could have episodically melted an ice-covered early ocean. Thaw-freeze cycles associated with bolide impacts could have been important for the initiation of abiotic reactions that gave rise to the first living organisms.

Amino Acids↗