Intermediary metabolism molecules are orchestrated into logical pathways stemming from history (L-amino acids, D-sugars) and dynamic constraints (hydrolysis of pyrophosphate or amide groups is the driving force of anabolism). Beside essential metabolites, numerous variants derive from programmed or accidental changes. Broken down, variants enter standard pathways, producing further variants. Macromolecule modification alters enzyme reactions specificity. Metabolism conform thermodynamic laws, precluding strict accuracy. Hence, for each regular pathway, a wealth of variants inputs and produces metabolites that are similar to but not (...) the exact replicas of core metabolites. As corollary, a shadow, paralogous metabolism, is associated to standard metabolism. We focus on a logic of paralogous metabolism based on diversion of the core metabolic mimics into pathways where they are modified to minimize their input in the core pathways where they create havoc. We propose that a significant proportion of paralogues of well-characterized enzymes have evolved as the natural way to cope with paralogous metabolites. A second type of denouement uses a process where protecting/deprotecting unwanted metabolites - conceptually similar to the procedure used in the laboratory of an organic chemist - is used to enter a completely new catabolic pathway. (shrink)

Because this lecture was a tribute to the contribution of Monod to science it focused on his views, without discussing the work of others who contributed to his achievements. In particular, because Monod was implicitly a platonician/pythagorean (with his emphasis on the importance of beauty in things), he thought that symmetry had to be introduced in the concept of allostery. In fact this was an extra feature that was absent from the original work of Jean-Pierre Changeux on the enzyme threonine (...) deaminase, where the first hypothesis of the binding of a regulator molecule on the enzyme could be located at a place different from the catalytic substrate binding site was presented (hence the word allostery coined by Monod in the introduction of the conference where the work of Changeux was presented). Symmetry is not a critical component of the concept of allostery. (shrink)

It is perhaps in the functioning of the brain that we can make contextual information most prominent. Indeed, while von Neumann and others invented computers with mimicking the brain in mind, the brain does not appear to behave as a Turing Machine. Neither is it a mechanical automaton. There is no “ghost in the machine.” However, nobody would doubt that the brain manages information, and in a very efficient way. To my view, this is a strong indication that the information (...) we describe when considering messages is a tiny part of what information is. Because we use language, built on the exchange of sequences of symbols, exactly as programs are exchanged in computers, linguists often saw the brain as a Turing Machine. But language is deeply associated to meaning, so that beside grammatical syntactic structures, there may exist a variety of superimposed contexts which transmit information mediated by channels that are not those usually considered. (shrink)

Une approche biologique de la genèse de l'identité individuelle. Pour introduire notre discours biologique au niveau anthropologique, nous ferons le line entre un exposé purement ethnologique et un exposé d'analyse linguistique. Cette insertion est d'autant plus cruciale qu'il s'agit de présenter ici une approche de l'identité perpendiculaire à l'analyse structurale - comme le temps est orthogonal à l'espace. Plutôt donc que d'entrer immédiatement dans le vif du sujet, je vais user d'un langage qui peut paraître quelque peu paradoxal ou inadéquat, (...) en décrivant, parmi la mythologie prégnance, quelque chose qui soit symétrique, et non équivalent, de la mort du père: je vais commencer par évoquer les mythes qui concernent la mort de la progéniture. (shrink)