Prebiotic chemistry:Prebiotic chemistry:a fuzzy fielda fuzzy field

Jacques ReisseJacques Reisse

Université Libre de BruxellesUniversité Libre de Bruxelles

Académie Royale de BelgiqueAcadémie Royale de Belgique

Prebiotic chemistryPrebiotic chemistry

Ideally : the study of the chemical steps Ideally : the study of the chemical steps leading to the first living systemsleading to the first living systems

ButBut

no fossils, no traces … nothing from these no fossils, no traces … nothing from these first living systems remainsfirst living systems remains

““Results rarely specify their causes Results rarely specify their causes unambiguously. If we have no direct unambiguously. If we have no direct evidences of fossils or human chronicles, evidences of fossils or human chronicles, if we are forced to infer a process only if we are forced to infer a process only from its modern results, then we are from its modern results, then we are usually reduced to speculation about usually reduced to speculation about probabilities.probabilities.” ”

S.J. Gould S.J. Gould

Prebiotic chemistryPrebiotic chemistry

Study of the spontaneous generation of Study of the spontaneous generation of the first living cells.the first living cells.

Study of the progressive transition from Study of the progressive transition from “non living systems” to “living systems”“non living systems” to “living systems”

But But There is no consensus as to what a There is no consensus as to what a

““living system” is .living system” is .

It is not a problem not having aIt is not a problem not having a clear-cut definition of “living systems” clear-cut definition of “living systems”

““In the world of human thought generally, In the world of human thought generally, and in physical science in particular, the and in physical science in particular, the most important and most fruitful concepts most important and most fruitful concepts are those to which it is impossible to are those to which it is impossible to attach a well-defined meaning.attach a well-defined meaning.””

Hendrik A. KramersHendrik A. Kramers

What is certain!What is certain!

Prebiotic chemistry is related to synthetic Prebiotic chemistry is related to synthetic chemistry and to synthetic biology but is chemistry and to synthetic biology but is fundamentally different from these two fields:fundamentally different from these two fields:

there is no chemist at work, “only” the laws there is no chemist at work, “only” the laws of physics and chemistry acting on sub-of physics and chemistry acting on sub-systems (atoms, small molecules) under not systems (atoms, small molecules) under not well known conditions.well known conditions.

The strange status of prebiotic The strange status of prebiotic chemistrychemistry

Prebiotic chemistry is Prebiotic chemistry is notnot the search for the search for the unknown pathways from non living to the unknown pathways from non living to living systems. living systems.

It consists It consists in in inventinginventing possible pathways possible pathways (which will never be fully confirmed). (which will never be fully confirmed).

Prebiotic chemistry requires that Prebiotic chemistry requires that Aristotelian logic be put asideAristotelian logic be put aside

The law of contradictionThe law of contradictionA cannot be both “B” and “non B”A cannot be both “B” and “non B”The law of excluded middleThe law of excluded middleA must be either “B” or “non B”A must be either “B” or “non B”The law of identityThe law of identityA will always be AA will always be A

These axioms are considered as self evidentThese axioms are considered as self evident

Prebiotic chemistry requires the Prebiotic chemistry requires the use of fuzzy or multivalued logicuse of fuzzy or multivalued logic

A is not necessarily B or “not B” but could A is not necessarily B or “not B” but could bebe characterized by a value betweencharacterized by a value between

1 (set “B”) and 0 (set “not B”)1 (set “B”) and 0 (set “not B”)

Zadeh (1965) Zadeh (1965)

A molecular system can be A molecular system can be “partially” living“partially” living

This was necessarily true during the prebiotic This was necessarily true during the prebiotic period (progressive spontaneous generation)period (progressive spontaneous generation)

This is still true today (viruses, spores)This is still true today (viruses, spores)

Analogy between the “non living – living” Analogy between the “non living – living” problem and the species problem, as clearly problem and the species problem, as clearly identified by Lamarck, Darwin… and Aristotleidentified by Lamarck, Darwin… and Aristotle

Lamarck Lamarck and the concept of speciesand the concept of species

““Mais ces classifications, dont plusieurs Mais ces classifications, dont plusieurs ont été si heureusement imaginées par les ont été si heureusement imaginées par les naturalistes, ainsi les divisions et sous-naturalistes, ainsi les divisions et sous-divisions qu’elles présentent, sont des divisions qu’elles présentent, sont des moyens tout à fait artificiels. Rien de tout moyens tout à fait artificiels. Rien de tout cela, je le répète ne se trouve dans la cela, je le répète ne se trouve dans la nature….”nature….”

Darwin Darwin and the concept of speciesand the concept of species

““I look at the term species, as one I look at the term species, as one arbitrarily given for the sake of arbitrarily given for the sake of convenience to a set of individuals closely convenience to a set of individuals closely resembling each other….resembling each other….””

« « Ainsi la nature passe petit à petit des Ainsi la nature passe petit à petit des êtres inanimés aux êtres doués de vie, si êtres inanimés aux êtres doués de vie, si bien que cette continuité empêche bien que cette continuité empêche d’apercevoir la frontière qui les sépare, et d’apercevoir la frontière qui les sépare, et qu’on ne sait auquel des deux groupes qu’on ne sait auquel des deux groupes appartient la forme intermédiaire »appartient la forme intermédiaire »

Aristote Aristote (Histoire des animaux)(Histoire des animaux)

The concept of species is contradictory The concept of species is contradictory with the concept of evolution.with the concept of evolution.

This is true for organisms but also for This is true for organisms but also for molecular or supramolecular systems molecular or supramolecular systems evolving from the “non living” state to the evolving from the “non living” state to the “living” state “living” state

From “non-living” to “living”From “non-living” to “living”a continuous scalea continuous scale

The scale is necessarily arbitraryThe scale is necessarily arbitrary (and dependent on scientific knowledge)(and dependent on scientific knowledge)

““Life index” of H, C, O, N atoms: lLife index” of H, C, O, N atoms: latat = 0 = 0““Life index” of liquid water: lLife index” of liquid water: lwawa = 0 = 0““Life index” of aminoacids:Life index” of aminoacids: llaaaa = 0 ( = 0 (mymy assumption) assumption)““Life index” of mononucleotides: lLife index” of mononucleotides: lmomo > 0 > 0““Life index” of proteins: lLife index” of proteins: lprpr > 0> 0““Life index” of polynucleotides: lLife index” of polynucleotides: lpo po > 0> 0““Life index of viruses: lLife index of viruses: lvivi > 0 > 0““Life index” of bacteria:Life index” of bacteria: llbaba = 1 = 1 ((mymy assumption) assumption)

with lwith lmomo< l< lprpr< l< lpo po <l<lvi vi < l< lbaba

““Life index” of aminoacids versus Life index” of aminoacids versus “Life index” of mononucleotides“Life index” of mononucleotides

Why lWhy laaaa = 0 ? (my assumption) = 0 ? (my assumption)

Because (non racemic) AA are present in Because (non racemic) AA are present in carbonaceous chondrites (Murchison, 1969)carbonaceous chondrites (Murchison, 1969)

Why lWhy lmomo > 0 ?> 0 ? (my assumption)(my assumption)

Because pathways leading to mononucleotide in Because pathways leading to mononucleotide in “prebiotic conditions” are unknown“prebiotic conditions” are unknown

A prebiotic experiment from 1953 A prebiotic experiment from 1953 (before Murchison) (before Murchison)

Why a living index higher for a Why a living index higher for a polymer than for a monomer?polymer than for a monomer?

H-K-OH + H-L-OH + H-M-OH + H-Q-OH H-K-OH + H-L-OH + H-M-OH + H-Q-OH →→

H-K-L-M-Q-OH + 3 HOHH-K-L-M-Q-OH + 3 HOH

Because the condensation of monomers Because the condensation of monomers under “prebiotic conditions” :under “prebiotic conditions” :

- requires activation- requires activation

- requires confinement- requires confinement

Because hydrolysis (Because hydrolysis (←)←) is always a is always a competitive reactioncompetitive reaction

The Pantheon syndromeThe Pantheon syndrome

The « first ancestor » illusionThe « first ancestor » illusion

The Pantheon syndromeThe Pantheon syndrome

The Pantheon syndrome The Pantheon syndrome in prebiotic chemistry in prebiotic chemistry

A dramatic example of the A dramatic example of the Pantheon syndromePantheon syndrome

« Radio-astronomers have discovered a « Radio-astronomers have discovered a vast array of organic molecules in the vast array of organic molecules in the interstellar medium. We are thus led to the interstellar medium. We are thus led to the inescapable conclusion that life must be inescapable conclusion that life must be common place in the cosmos »common place in the cosmos »

C. Ponnamperuma C. Ponnamperuma (1993)(1993)

The “first ancestor” illusionThe “first ancestor” illusion

Less obvious!Less obvious!

The LUCA illusionThe LUCA illusion

LUCA is definitively not the first LUCA is definitively not the first living cellliving cell

It is “simply” the ancestor of present-day It is “simply” the ancestor of present-day living species and (most probably) the living species and (most probably) the ancestor of all the organisms known as ancestor of all the organisms known as fossils or microfossilsfossils or microfossils

LUCA was just the best fit in a large LUCA was just the best fit in a large collection of “pre-LUCA” living systemscollection of “pre-LUCA” living systems

Prebiotic chemistry:Prebiotic chemistry:a fuzzy field under strong constraints a fuzzy field under strong constraints

Epistemological constraintsEpistemological constraints- Not forget what we are searching for- Not forget what we are searching for- Abandon Aristotelian logic- Abandon Aristotelian logicGeochemical constraintsGeochemical constraintsTake into account the conditions prevailing in the young Take into account the conditions prevailing in the young Earth’s hydrosphere (local versus global conditions?) Earth’s hydrosphere (local versus global conditions?) Chemical constraintsChemical constraintsUse efficiently the Van der Waals interactions to imagine Use efficiently the Van der Waals interactions to imagine how very peculiar supramolecular systems appeared how very peculiar supramolecular systems appeared spontaneously spontaneously

The greatest difficulties The greatest difficulties in prebiotic chemistryin prebiotic chemistry

To imagine possible pathways for the To imagine possible pathways for the spontaneousspontaneous formation of a population of formation of a population of far-from equilibrium supramolecular far-from equilibrium supramolecular systems able to evolve by Darwinian systems able to evolve by Darwinian evolutionevolution

To imagine how a language (not only the To imagine how a language (not only the support of) can appear support of) can appear spontaneouslyspontaneously

Merci pour votre attention!Merci pour votre attention!

Comment definir la vie? Comment definir la vie? Editeurs: Hugues Bersini et Jacques Reisse. Editeurs: Hugues Bersini et Jacques Reisse. Vuibert (2007)Vuibert (2007)Jacques Reisse. La longue histoire de la matière PUF (2006)Jacques Reisse. La longue histoire de la matière PUF (2006)From Suns to Life From Suns to Life as co-editor and co-author of two chapters. ( Springer, 2006)as co-editor and co-author of two chapters. ( Springer, 2006)John Cronin and Jacques ReisseJohn Cronin and Jacques ReisseChirality and the Origin of Homochirality Chirality and the Origin of Homochirality “ “Lectures in Astrobiology, vol.1”. Springer (2005)Lectures in Astrobiology, vol.1”. Springer (2005)Jacques ReisseJacques ReisseA propos de l’origine de la matière organique sur la Terre A propos de l’origine de la matière organique sur la Terre primitive et de son évolution durant la période prébiotiqueprimitive et de son évolution durant la période prébiotique « L’environnement de la Terre primitive »« L’environnement de la Terre primitive »Presses Universitaires de Bordeaux (2001)Presses Universitaires de Bordeaux (2001)

Exaptation: an efficient concept in Exaptation: an efficient concept in biological evolutionbiological evolution

« « ExaptationExaptation: features that now enhance : features that now enhance fitness but were not built by natural fitness but were not built by natural selection for their present roleselection for their present role » »

Gould and Urba (1982)Gould and Urba (1982)

Prebiotic chemical evolution requires Prebiotic chemical evolution requires exaptation, at least in its « last stages », exaptation, at least in its « last stages », when natural selection was already an when natural selection was already an efficient processefficient process