Leslie E. Orgel

Evolution of the genetic apparatus

Abstract It is argued that the evolution of the genetic apparatus must have required the abiotic formation of macromolecules capable of residue-by-residue replication. This suggests that polynucleotides were present even in the most primitive ancestors of contemporary organisms. Models which explain the evolution of the association between polynucleotide and polypeptide sequences are discussed.

Spectra of Transition‐Metal Complexes

The electronic transitions observed in complexes of the transition‐metal ions are interpreted in terms of a slightly modified crystal‐field theory. Parameters of chemical interest are derived.

Ageing of clones of mammalian cells.

The chief purpose of this article is to review some recent work on the ageing of mammalian cells and to comment on the theoretical interpretation of the experimental findings. No claim will be made that cellular ageing is a primary cause of the ageing changes observed in whole animals; the evidence supporting such a causal connexion is inconclusive.

Electronic properties of transition-metal oxides—I: Distortions from cubic symmetry

Abstract The distortions from cubic symmetry which occur in certain transition-metal oxides, particularly those with the spinel structure, are discussed in terms of crystal (ligand) field theory. It is shown that many such distortions, including all the large ones, are related in a simple fashion to the electronic configuration of the metal ion and may be considered to arise as a consequence of a Jahn-Teller type of distortion.

The origin of life—a review of facts and speculations

Three popular hypotheses attempt to explain the origin of prebiotic molecules: synthesis in a reducing atmosphere, input in meteorites and synthesis on metal sulfides in deep-sea vents. It is not possible to decide which is correct. It is also unclear whether the RNA world was the first biological world or whether some simpler world preceded it.

Studies in Prebiodc Synthesis: II. Synthesis of purine precursors and amino acids from aqueous hydrogen cyanide

There is much evidence suggesting that hydrogen cyanide was important in prebiotic synthesis. Here we discuss the relevant aqueous solution chemistry, since we believe it to be pertinent to prebiotic synthesis. In mildly alkaline solutions (pH 7 to 10) two modes of destruction compete. Hydrolysis to formamide and formic acid is first-order in HCN, while polymerization involving the formation of C C bonds is quadratic in HCN. Within the pH range 8 to 9 and the temperature range 0 to 60°C, the two reactions become equally important for concentrations between 0·01 M and 0·1 M ; hydrolysis dominates in more dilute and polymerization in more concentrated solutions. Concentration of HCN in the liquid phase by freezing out ice permits efficient polymerization from initially very dilute solutions. Intermediates in the polymerization proceBS include a very reactive trimer, aminomalononitrile, and a relatively stable tetramer, diaminomaleonitrile. The latter is converted to 4-aminoimidazole-5-carbonitrile and related compounds either by photochemical rearrangement or by reaction with formamidine. The imidazole derivatives are then readily converted to purines including adenine, guanine and hypoxanthine. We have also made some observations on the formation of ex-amino acids from HCN oligomers and polymers. Various theories of prebiotic purine formation are considered in the light of the quantitative kinetic data. We conclude that the arguments for a photochemical step are persuasive and that polymerization subsequent to concentration in a eutectic phase is an attractive posiibility.

Search for organic and volatile inorganic compounds in two surface samples from the Chryse Planitia region of Mars

Two surface samples collected from the Chryse Planitia region of Mars were heated to temperatures up to 500�C, and the volatiles that they evolved were analyzed with a gas chromatograph-mass spectrometer. Only water and carbon dioxide were detected. This implies that organic compounds have not accumulated to the extent that individual components could be detected at levels of a few parts in 109 by weight in our samples. Proposed mechanisms for the accumulation and destruction of organic compounds are discussed in the light of this limit.

RNA catalysis and the origins of life

The role of RNA catalysis in the origins of life is considered in connection with the discovery of riboszymes, which are RNA molecules that catalyze sequence-specific hydrolysis and transesterification reactions of RNA substrates. Due to this discovery, theories positing protein-free replication as preceding the appearance of the genetic code are more plausible. The scope of RNA catalysis in biology and chemistry is discussed, and it is noted that the development of methods to select (or predict) RNA sequences with preassigned catalytic functions would be a major contribution to the study of lifes origins.

Cyanoacetylene in Prebiotic Synthesis

Cyanoacetylene is a major nitrogen-containing product of the action of an electric discharge on a mixture of methane and nitrogen. It reacts with simple inorganic substances in aqueous solution to give products including asparticacid, asparagine, and cytosine.

Studies in prebiotic synthesis: III. Synthesis of pyrimidines from cyanoacetylene and cyanate☆☆☆

Abstract Cyanoacetylene (I) is one of the major nitrogen-containing products of the action of an electric discharge on a mixture of nitrogen and methane. Hence we believe it may have been important in prebiotic chemistry. Cyanoacetylene undergoes hydrolysis in dilute alkali to give cyanoacetaldehyde which may then form the aldol dimer (IV). In the reaction of cyanoacetylene with cyanate, cytosine is formed mainly in a reaction sequence involving the stable intermediate cyanovinylurea. Cyanogen or cyanoformamide can replace cyanate in this synthesis. Since cytosine hydrolyzes quite readily to uracil, these reactions constitute a prebiotic synthesis of the pyrimidines. The concentrations of reactants required to give reasonable cytosine yields are quite low. However, the instability of cyanate and cyanoacetylene restricts severely the range of prebiotic environments in which such a synthesis could have occurred.