It is well-known that in water phosphate readily reacts with calcium, precipitating as insoluble apatite. How phosphorus could have been available for prebiotic reactions is still an open problem. We suggest that phosphorus-containing compounds might have accumulated in a hydrophobic medium, since the absence of calcium ions would have prevented them from precipitating as apatite. Hydrophobic compounds may have been synthesized on the early Earth through the polymerization of methane or through Fischer-Tropsch-type reactions. Moreover, hydrophobic compounds would have been delivered to the early Earth by extraterrestrial infall. In previous articles (Morchio and Traverso [1999], Morchio et al. [2001]) we suggested that such hydrophobic material would have formed a hydrophobic layer on the surface of the sea, which would have provided an environment thermodynamically more suitable than water for the concentration and polymerization of organic molecules fundamental to life, particularly amino acids and (pyrimidine) bases. It may be hypothesized that elemental phosphorus or phosphorus-containing compounds (such as phosphite) deriving from volcanic eruptions would have ended up raining down into the hydrophobic layer, accumulating due to the absence of calcium ions, in an environment protected against hydrolysis. Phosphorus-containing compounds might have interacted with hydrophobic molecules in the layer giving rise to polymers. In particular, phosphite might have reacted with the hydrophobic amino acids, giving rise to phosphoamino acids, which, in turn, might have interacted with pyrimidine bases (relatively abundant in the layer) giving rise to peptides and oligonucleotide-like polymers. Indeed, it has been experimentally shown (Zhou et al. [1996]) that, in an anhydrous organic medium (pyridine), dialkilphosphite reacts with amino acids to form phosphoamino acids, which interact with pyrimidine nucleosides to give nucleotides, short oligonucleotides and phosphoryl peptides.

On the basis of the previous article (Morchio and Traverso [1999]), we discuss the possible interactions between the first proteic fragments developed in the hydrophobic layer made of hydrocarbons, which would have covered the surface of the primitive seas, and the nitrogenous bases, particularly the pyrimidinic ones, which would have found in such hydrophobic layer favourable conditions to their prebiotic synthesis. These interactions would have presumably brought, on the basis of the physicochemical laws, at the moment the only ones at work, to the linkage of various bases and so to the construction of the first nucleic acid chains (most likely RNA). Interestingly enough this result would have been obtained by inserting two more bases between those hydrogen bound to the amino acids and this might have been the ground for the future "triplets". These interactions might have been particularly significant because of two important consequences: the birth of a rough genetic code and the starting of interactions of the co-operative type between bases and amino acids that would have made the growth of both proteic and nucleic acid fragments easier and faster. We conclude that the development of the genetic code was neither a "frozen accident" nor an occurrence directed by any information flow.

Although the origin of life has been traditionally placed in water, this gives rise to a number of thermodynamical problems. The hypothesis advanced in this work is that the first steps towards life took place in the hydrocarbon layer that presumably covered the surface of the primordial ocean. Here hydrophobic amino acids might have found a thermodynamically suitable ambient where to concentrate and polymerize. Moreover, the low dielectric constant of such a hydrophobic superficial layer might have favoured possible electrostatic interactions among peptidic chains. We suggest that this might have constituted a thermodynamically favourable basis for the development of organized molecular systems.

Ten years after the establishment of the "Osaka Group for the Study of Dynamic Structures" (1987-1997) some of its founders and adherents "confess" what they think about the achievements of structuralism in the decade and the perspectives of the Group. Away from the geno-centric view of neo-Darwinism, the organism is reaffirmed as central entity in biology, either as expression of a morphogenetic field (with genotype as selector) or as a set of conventional rules governing the genotype. Structuralism also opposer to the imperialism and arrogance implicit in the orthodox theory of evolution. (A second group of five contributions, perhaps the last, is presented in this issue. A first group of nine papers appeared in issue 91-1, 1998).

Protein evolution is characterized by several processes. In the theory of neutral evolution the rate of mutation is considered a linear process in which the amount of aminoacidic substitutions in proteins is constant in time. A simulation approach has been developed by using a model of amino-acidic substitution. The frequency of spontaneous mutations has been assumed to be equal to about 10(-9)/base/year. The aim of the present work is to show that starting from a constant mutation rate (nucleotide substitutions) the corresponding process of aminoacidic substitutions becomes non-linear if some criteria of mutation selection are introduced. The basic criteria used are the physical-chemical characteristics of aminoacids, the same criteria that have made it possible to classify aminoacids. Different classifications based on differences in such criteria give different results, indicating that the degenerate nature of the genetic code determines a non-linear behaviour of protein evolution. Simulations have been performed on short protein subsequences of five aminoacids. A further analysis has been made to verify, on the basis of the code structure and of accepted selection criteria, the mechanisms of aminoacidic substitutions and the existence of preferential paths. We have concluded that aminoacidic substitution is not a simple stochastic process, but that complex Markov's chains are involved. The consequences are important, although generally ignored.

Known data on the conjugation of Paramecia primaurelia cells of different mating types are examined critically and, when possible, quantitatively. The collision probability is discussed in terms of a ''random walk'' and the binding energy is evaluated. It is concluded that only ionic bonds are consistent with the data. A tentative molecular model to unify data within a logical framework is proposed. The model seems to confirm the importance of a systemic control of the life of paramecium, as previously pointed out by Sonneborn.

In this paper we conjecture that neuronal networks develop following an optimality principle. We point out that a neuronal outgrowth in culture may be seen as the solution of a classical optimization problem: the "Steiner Problem". A neuron might grow minimizing a "cost", which may be determined by the viscoelastic properties of the neuron cytoplasm. We then discuss the role of chemiotactic factors such as the Nerve Growth Factor (NGF) in an optimized neuronal development in vivo. Finally we suggest, with some mathematical arguments, that the optimization of the elastic forces in the growing neuron may give rise to a "fractal" structure.

Tendon fibres of different-aged rats were submitted to denaturation and their isometric and isotonic behaviour was recorded. The fit of the curves led to analytical expressions depending on the parameters which characterize the age of the subject. A rheological model is given which satisfies the experimental data and which is interpretable in a molecular way.

The creep behavior of collagen tendons chemically contracted in KSCN solutions was investigated. Particularly, emphasis was given to the role of calcium and other polyvalent metals and to the role of storage time on the creep behavior of tendons removed from rats of different age. The results rule out the possibility that calcium and polyvalent metals are connected with the aging of tendons. The effect of storagein vitro produces effects qualitatively similar to those observed during agingin vivo. It is suggested that an oxidative crosslinking process occurringin vitro is responsible for the effects observed.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTTransport properties of collagen membranesA. Gliozzi, R. Morchio, and A. CiferriCite this: J. Phys. Chem. 1969, 73, 9, 3063–3070Publication Date (Print):September 1, 1969Publication History Published online1 May 2002Published inissue 1 September 1969https://pubs.acs.org/doi/10.1021/j100843a047https://doi.org/10.1021/j100843a047research-articleACS PublicationsRequest reuse permissionsArticle Views119Altmetric-Citations15LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access options Get e-Alerts