Platica ToñO Lazcano

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