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La cosecha del ‘53: cincuenta años del experimento de Miller
Antonio Lazcano AraujoFacultad de Ciencias, UNAME-mail: [email protected]
Rasmussen (2000) Nature 405:677
Walsh & Lowe (1985) Nature 314:530
TRACES OF ARCHEAN LIFE (?)
Schopf (1993) Science 260:530
Westfall et al (2001) Precamb Res 106:93
Closing in on a time frame for the origin of life on the Earth
3.54.04.5 3.0
fossil record cooling of the Earthimpact frustrations
The age of the Earth (billion of years ago)
Understanding the origin of life is hindered by the lack of
1. geological evidence of the prebiotic environment 2. fossil record of prebiological system; and 3. an all-embracing, generally agreed definition of life
The origin of life was
a) autotrophic capable of synthesizing its own components from CO2
b) heterotrophic formed from a primitivesoup
c) extraterrestrial came from outer space(panspermia)
A pyrite-mediated origin of life? CO2
H2S
Organic compounds
Metabolic networks
Autotrophic organism
Wächtershäuser (1988)
pyrite (FeS2)
FeS
A heterotrophic origin of life?
reducing atmosphere
primitive soup
synthesis of organic compounds
primordial heterotrophs
1) Proust 1807 HCN polymer + adenine (?)
2) Wöhler 1828 NH4NCO urea
3) Strecker 1850 HCH3CHO + NH3 + HCN alanine
4) Butlerow 1861 HCHO sugars
OH-
OH-
Early abiotic synthesis of biochemical monomers
Some interstellar molecules
H2, OH, SiS, HCl, NaCl, KCl, CH, CH+, CN, CO, CS, C2
H2O, H2S, N2H+, SO2, HCO+, HCN, C2H, C3, C2O, COS
NH3, H2CO, HNCO, H2CS, C2H2
SiH4, HC3N, H2CN, CH4, C5, H2C=C=O, HCOOH, HNCO
CH3OH, CH3CCN, HCONH2
CH3COH, CH3C2H, CH3NH2, H2CCHCN, HC5N
HCOOCH3, CH3CH2, (CH3) 2O, HCN7N
HC9N, HC11N
aromatic hydrocarbons alcohols (C1-C4)aliphatic hydrocarbons aldehydes (C2-C4)sulfonic acids polyols (C2-C4)phosphonic acids monocarboxylic acids (C1-C8) ketones (C3-C5)dicarboxylic acids (C2-C5) hydroxy acids (C2-C9)amines (C1-C4) amino acids pyridines ureaquinolines purinespolypyrroles pyrimidines
Compounds in the Murchison meteorite
permafrost
pore waterHCN, RCHONH3, CH2=CH-CN
heat source
C + 2H2 -> CH4 N2 + 3H2 -> NH3 O2 + 2H2 -> H2O S + H2 -> H2S CO2 + 6H2 -> CH4 + 2H2O
The Urey atmosphere
1. Amino acids from Strecker synthesis 2. Purines from HCN polymerization 3. Pyrimidines from cyanoacetylene & urea 4. Sugars from HCHO polymerization
Prebiotic syntheses that work
1953: Annus mirabilis
Watson & CrickDouble-helix model of DNA
Sanger & Thompson Complete sequencing of a protein
S.L.Miller Prebiotic synthesis of organic compounds
Types of planetary atmospheres
Reducing: CH4, NH3, N2, H2O, H2
CO2, N2, H2O, H2
CO2, H2, H2O
Neutral: CO2, N2, H2O
Oxidizing: CO2, N2, H2O, O2
Meteor Crater, Arizona
Pyrite-mediated organic synthesis
and several other reactions
1) 2CH3-SH + CO NiS/FeS CH3CO(SCH3) + H2S
2) CH3-SH + CO + H2O NiS/FeS CH3-COOH + H2S
3) amino acids + CO NiS/FeS dipeptides
reducing atmosphere produces the right prebiotic relevance denied
stuff by many --but not all input in meteorites must have occurred survival & availability of
input doubtful high-temperature must have occurred suite of organic productsvent chemistry restricted so far
source advantages disadvantages
Prebiotic Synthesis
Have too many cooks spoiled the soup?
extraterrestrialorganics pyrite
primordial soup
CH4NH3
HCN
extraterrestrialorganics
organics from space
Bada & Lazcano (2002) Science 296: 1982
*A
A
A
*U
*A
*U
*U
*UUU
*A
*A
montmorillonite Ferris 2002
activated derivatives and common minerals may have led to the synthesis of prebiotic genetic polymers
Base pairing is for free
What was the nature of the backbone?
Mendeleyev and the abiotic origin of oil
Fe3C + H2O hydrocarbons
alkenes acid conditions alcohols
Fe3C + H2O alkanes + alkenes1)
2)
From hydrocarbons to amphiphilic compounds
hydrophobic
hydrophilic
many different catalytic agents
polymers with sequences of nucleobases
membrane-forming compounds
The evidence suggests that before the origin of life there were already
DNA
DNA RNA protein
RNA is a nucleic acid with a RIBOSE-PHOSPHATE backbone
WHAT’S IN A NAME?
WHAT’S IN A NAME?
RNA is a nucleic acid with a RIBOSE-PHOSPHATE backbone
-ose is for sugars and
Rockefeller Institute of Biochemistry
Store genetic information (like DNA)
Catalize chemical reactions (like proteins)
RNA molecules:
Butlerov´s formose reaction
H2CO sugarsOH-
Decker et al (1982)
Sugars are unstable organic compounds
sugar half-life (min)
ribose 73
2-deoxyribose 225
ribose-5-phosphate 7
ribose-2,4-biphosphate 31
- store genetic information
- replicate other RNAs
- activate amino acids
- bind themselves to amino acids
- catalyze peptide-bond formation
RNA molecules can
Moore & Steitz (2002)
Cells with DNA, RNA & proteins
RNA & protein biosynthesis
RNA world
?
Archaea
Eucarya
Bacteria
LATIN
Catalonian
Spanish Romanian
FrenchProvençal
Italian
ancient..... butclearly not primitive
Mycoplasma genitalium
TIGR Microbial Database
Figure 1. Prokaryotic genome size distribution (N=641)
Archaea
Eucarya
Bacteria
RNA World
Primitive soup
?
RNA - protein
DNA, RNA, protein
