platica toño lazcano
DESCRIPTION
para la clase de Biología CelularTRANSCRIPT
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La cosecha del ‘53: cincuenta años del experimento de Miller
Antonio Lazcano AraujoFacultad de Ciencias, UNAME-mail: [email protected]
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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
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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)
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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
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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)
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A pyrite-mediated origin of life? CO2
H2S
Organic compounds
Metabolic networks
Autotrophic organism
Wächtershäuser (1988)
pyrite (FeS2)
FeS
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A heterotrophic origin of life?
reducing atmosphere
primitive soup
synthesis of organic compounds
primordial heterotrophs
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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
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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
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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
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permafrost
pore waterHCN, RCHONH3, CH2=CH-CN
heat source
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C + 2H2 -> CH4 N2 + 3H2 -> NH3 O2 + 2H2 -> H2O S + H2 -> H2S CO2 + 6H2 -> CH4 + 2H2O
The Urey atmosphere
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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
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1953: Annus mirabilis
Watson & CrickDouble-helix model of DNA
Sanger & Thompson Complete sequencing of a protein
S.L.Miller Prebiotic synthesis of organic compounds
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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
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Meteor Crater, Arizona
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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
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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
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Have too many cooks spoiled the soup?
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extraterrestrialorganics pyrite
primordial soup
CH4NH3
HCN
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extraterrestrialorganics
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organics from space
Bada & Lazcano (2002) Science 296: 1982
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*A
A
A
*U
*A
*U
*U
*UUU
*A
*A
montmorillonite Ferris 2002
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activated derivatives and common minerals may have led to the synthesis of prebiotic genetic polymers
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Base pairing is for free
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What was the nature of the backbone?
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Mendeleyev and the abiotic origin of oil
Fe3C + H2O hydrocarbons
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alkenes acid conditions alcohols
Fe3C + H2O alkanes + alkenes1)
2)
From hydrocarbons to amphiphilic compounds
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hydrophobic
hydrophilic
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many different catalytic agents
polymers with sequences of nucleobases
membrane-forming compounds
The evidence suggests that before the origin of life there were already
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DNA
DNA RNA protein
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RNA is a nucleic acid with a RIBOSE-PHOSPHATE backbone
WHAT’S IN A NAME?
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WHAT’S IN A NAME?
RNA is a nucleic acid with a RIBOSE-PHOSPHATE backbone
-ose is for sugars and
Rockefeller Institute of Biochemistry
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Store genetic information (like DNA)
Catalize chemical reactions (like proteins)
RNA molecules:
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Butlerov´s formose reaction
H2CO sugarsOH-
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Decker et al (1982)
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Sugars are unstable organic compounds
sugar half-life (min)
ribose 73
2-deoxyribose 225
ribose-5-phosphate 7
ribose-2,4-biphosphate 31
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- store genetic information
- replicate other RNAs
- activate amino acids
- bind themselves to amino acids
- catalyze peptide-bond formation
RNA molecules can
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Moore & Steitz (2002)
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Cells with DNA, RNA & proteins
RNA & protein biosynthesis
RNA world
?
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Archaea
Eucarya
Bacteria
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LATIN
Catalonian
Spanish Romanian
FrenchProvençal
Italian
ancient..... butclearly not primitive
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Mycoplasma genitalium
TIGR Microbial Database
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Figure 1. Prokaryotic genome size distribution (N=641)
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Archaea
Eucarya
Bacteria
RNA World
Primitive soup
?
RNA - protein
DNA, RNA, protein