Origen de la vida en la Tierra: principales teorías y evidencias

Teorías sobre el origen de la vida

Tema 2: Origen de la vida en la TierraX

• 1 .- Creacionismo
• 2 .- Generación espontanea
• 3 .- Panspermia
• 4 .- Origen químico

Ciencias para el Mundo Contemporáneo. Agencia Canaria de Investigación, Innovación y Sociedad de la Información 2010X

La teoría creacionista

Durante muchos siglos, la Creación por parte de un Dios fue la única explicación del misterio del origen del hombre, y de todos y cada uno de los seres.

Ciencias para el Mundo Contemporáneo. Agencia Canaria de Investigación, Innovación y Sociedad de la Información 2010X

La teoría de la generación espontanea

La vida puede surgir de forma espontánea, a partir de la materia inerte (barro, estiércol, cadáveres, ropa sucia, etc.) por la acción de una 'vis vitalis' (poder vital) existente en el mundo. La idea se basaba, está claro, en observaciones de aquello que sucedía en la realidad.Experimento de Redi (s. XVII) Refuta la generación espontánea de insectos

• Open jars
• Tightly sealed jars
• Jars covered with cloth netting

Experimento de Pasteur (s. XIX)

Refuta la generación espontánea de microorganismos

Cuello del frasco curvado con calor

Polvo y microbios retenidos

Caldo vertido en frasco

Hervido del caldo

Frasco vertical. El caldo permanece sin microbios

Frasco inclinado

Caldo contaminado con microbiosX

Teoría de la panspermia (s. XIX-XX)

La vida se ha generado en el espacio exterior, y viaja por éste de un sistema a otro. La vida en la Tierra habría llegado por medio de microrganismos o de sus esporas que viajaban en meteoritos.

Ciencias para el Mundo Contemporáneo. ACIISI 2010; BiologyNow-@ 2015 W. W. Norton & Company, Inc. El análisis del meteorito Murchison (caído en Australia en 1969) muestra numerosos compuestos orgánicos, incluyendo aminoácidos y bases puricas y pirimidínicas. Se le estima una edad aproximada de 4.650 millones de años.

Evolution -@ 2016 W. W. Norton & Company, Inc .; http://www.astrofisicayfisica.com/2010/02/el-meteorito- murchison-revela.html

El asteroide 2008 TC3

Impactó en desierto de Núbia, en Sudan, y lleva aminoácidos que se cree que se han producido en el espacio.

27 280 EGYPT 290 Wadi Halfa SUDAN 300 Station 6 railroad NUBIAN DESERT Abu Hamed MELA A NASA satellite photographed the impact of the asteroid on October 7, 2008. The yellow arrow traces the path the asteroid followed, and the reddish-orange blob shows the point at which it exploded after entering Earth's atmosphere.

The asteroid broke into fist-sized pieces that fell into the Nubian Desert in Sudan. The dark color of the fragments made them conspicuous on the desert sand, and many of the fragments were recovered by NASA scientists in February 2009.

nº 1 11 10

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La teoría del origen químico (años veinte. XX)

Las condiciones de la Tierra primitiva condujeron a la formación espontánea de Biomoléculas simples, a través de procesos químicos y físicoquimicos, lo que dio lugar a las primeras formas de vida.

Aleksandr Oparin (1894-1980)

John B.S. Haldane (1892-1964)

Biology Now - C 2015 W. W. Norton & Company, Inc.X

La Tierra en sus orígenes según Oparin

Según Oparin, la atmósfera primitiva estaba formada por metano (CH4), amoniaco (NH3), vapor de agua (H2O) y sulfuro de hidrógeno (H2S). Era una atmósfera que no tenía oxígeno, reductora ..

Procesos prebióticos y evolución química

Segons Oparin

Energía :: la radiación solar, Atmósfera primitiva (carácter reductor) ¿O2?, CH4, NH3 y H2 la actividad eléctrica de la atmósfera fuentes de calor como los volcanes

Moléculas orgánicas simples

Moléculas orgánicas complejas

Formaldehid (H2CO), cianur d'hidrogen (HCN), etc

Aminoacids, proteines, bases nitrogenades, etc

Almidón 0 Glucosa 1-fosfato Fosforilasa

Esquema de un coacervado. Santillana S.A., 2010

"Coacervados" crecen y se dividen (medio océanos)

"Probionte" Procarionte anaeróbico heterótrofo

Origen de las moléculas orgánicas: Experimentos de S. Miller y H. C. Urey (1952)

¿Se puede producir la evolución química con moléculas simples y energía?

Stanley L. Miller (acababa de graduarse)

Harold C. Urey (Premio Nobel por otras historias)

Experimentos de Miller (y Urey)

Electrodo Tubo de cristal (contiene vapor de agua)

Descarga eléctrica

Matraz grande contiene gases ( CH4, NH3, H2)

Llave de paso para tomar muestras

H H H H-C-H N H H H-H

Condensador

Gotas de agua

Matraz pequeño de cristal (contiene agua hirviendo)

Sifón

Calor

Biology Now - C 2015 W. W. Norton & Company, Inc.X

Experimentos de Miller (y Urey) - Resultados

do Tubo de cristal (contiene vapor de agua)

Descarga eléctrica

grande cases 1

Llave de paso para tomar muestras

+ Stark P102 THIS BBA 1

+5 pares RUN #10 CH4, N2, H2, H2O

Run # 6 Sa BeA

Calor

CH4, NH3, H2, H20 +Should + Fe (H) 2 3 See BOA

Biology Now - @ 2015 W. W. Norton & Company, Inc.

Artículo original de Miller (Science, 1953)

ties of the compounds manometrienlly (5). In the other, the material is applied to the paper along 8 cm of the base line rather than as a spot and, after resolu- tion, arens 8 x 5 em containing the various compounds are eut from the paper and rolled in shell vials. Ten anesthetized houseflies are then introduced into each vial, and the toxicity of the compounds is character- ized by rate of knockdown and 24-hr mortality. The paper chromatographie method is useful in studying the metabolism of phosphorus insecticides in plants, mammals, and insects. With it, for example, we have been able to demonstrate the conversion of parathion and its methyl analog to the corresponding phosphates by an enzyme system found in Periplaneta americana (L.) (2). Further studies are in progress. The method has also been of value in studying the action of heat on purified parathion and methyl para- thion and in isolating the compounds formed and in studying their biological properties (1).

References . METCALF, R. L., and MAaca, R. B. To be published. Aun. Estomoi. Soc. Amer. (In press). KRITCHEVSKY, T. IL., and Tisztses, A. Selener, 214, 209 (1951), 4. HANES, C. S., and Isumawoon, F. A. Nature, 184, 1107 (1949). 5. MERTCALF, R. JA, and MARCH, B. B. 2. Koon. Entomst., 43, 721 (1949). Manuscript received September 15, 1959.

A Production of Amino Acids Under Possible Primitive Earth Conditions

Stanley L. Miller1, 2 G. H. Jones Chemical Laboratory, University of Chicago, Chicago, Illinois

The idea that the organic compounds that serve as the basis of life were formed when the earth had an atmosphere of methane, ammonia, water, and hydro- gen instead of carbon dioxide, nitrogen, oxygen, and water was suggested by Oparin (1) and has been given emphasis recently by Urey (2) and Bernal (3). In order to test this hypothesis, an apparatus was built to circulate CH., NH., H2O, and H, past an electric discharge, The resulting mixture has been tested for amino acids by paper chromatography. Electrical discharge was used to form free radicals instead of ultraviolet light, because quartz absorbs wavelengths short enough to cause photo dissociation of the gases. Electrical discharge may have played a significant role in the formation of compounds in the primitive atmosphere, The apparatus used is shown in Fig. 1. Water is boiled in the flask, mixes with the gases in the 5-1 flask, circulates past the electrodes, condenses and empties back into the boiling flask. The U-tube pre- vents circulation in the opposite direction. The acids " National Science Foundation Fellow, 1902-08. " Thanks are dee Harold C. Urry for many helpful sugges tions and guidance in the course of this Investigation. 598

and amino acids formed in the discharge, not being volatile, accumulate in the water phase, The eirenia- tion of the gases is quite slow, but this seems to be an asset, because production was less in a different apparatus with an aspirator arrangement to promote circulation. The discharge, a small corona, was pro- vided by an induction coil designed for detection of lenks in vacuum apparatus. The experimental procedure was to seal off the open- ing in the boiling flask after adding 200 ml of water, evacuate the air, add 10 em pressure of H2, 20 cm of CH4, and 20 em of NH .- The water in the flask was boiled, and the discharge was run continuously for a week. During the run the water in the flask became notice. ably pink after the first day, and by the end of the week the solution was deep red and turbid. Most of the turbidity was due to colloidal silica from the glass. The red color is due to organic compounds adsorbed on the allies. Also present are yellow orgnnie com- pounds, of which only a small fraction can be ex- tracted with ether, and which form a continuous streak tapering off at the bottom on a one-dimensional chro- matogram run in butanol-acetic acid. These substances are being investigated further. At the end of the run the solution in the boiling flask was removed and 1 ml of saturated HgCl_ was added to prevent the growth of living organisms. The ampholytes were separated from the rest of the con- stituents by adding Ba(OH), and evaporating in teuo to remove amines, adding H,SO, and evaporat- Stixsek, Vol. 117

AUMATIC ->PHENOL 10.3% NHẤT BUTANOL-ACETIC ACID ·SALAME P-ALANINE M.BUTYRIC ACID

ing to remove the acids, neutralizing with Ba(OH)„, filtering and concentrating in vacno. The amino acids are not due to living organisms because their growth would be prevented by the boil- ing water during the run, and by the HgCI2, Ba (OH)2. H2SO, during the analysis. In Fig. 2 is shown a paper chromatogram run in »-butanol-acetic acid-water mixture followed by water- saturated phenol, and spraying with ninhydrin. Iden- tification of an amino neid was made when the R, value (the ratio of the distance traveled by the amino acid to the distance traveled by the solvent front), the shape, and the color of the spot were the same on a known, unknown, and mixture of the known and un- known; and when consistent results were obtained with chromatograms using phenol and 77% ethanol. On this basis glycine, a-alanine and B-alanine are identified. The identification of the aspartie neid and a-amino-n-butyric acid is less certain because the spots are quite weak. The spots marked A and B are uniden- tiffed as yet, but may be beta and gamma amino acids. These are the main amino acids present, and others are undoubtedly present but in smaller amounts. It is estimated that the total yield of amino acids was in the milligram range. In this apparatus an attempt was made to dupli- cate a primitive atmosphere of the earth, and not to obtain the optimum conditions for the formation of amino acids. Although in this case the total yield was small for the energy expended, it is possible that, with more efficient apparatus (such as mixing of the free radicals in a flow system, use of higher hydrocarbons from natural gas or petroleum, carbon dioxide, ete., and optimum ratios of gases), this type of process would be a way to commercially producing amino neids. A more complete analysis of the amino neids and other products of the discharge is now being per- formed and will be reported in detail shortly. May 15, 1958

References 1. Oranix, A. 1. The Origin of Life, New York : Msemillas (1938). 2. UREY, IL. C. Proc. Moll. Acud. Bei. U. 8., 38, 351 (1002) ; THE Planeta. New Haven : Yale Univ. Press Chap. 4 (1952). 3. BERNAL, J. D. Proc. Phys. 800. (London), 62A, 537 (1949) ; 62B, 597 (1949) : Phyeles! Basis of Life. London : Rout- ledge and Kegan Paul (1951). Manuscript received February 18, 1903.

A Vacuum Microsublimation Apparatus John R. Maher1 Chemistry Branch, Sixth Arwy Area Medical Laboratory, Fort Baker, California

The analytical biochemist is frequently confronted with the task of isolating microquantities of sub- stances in a chemically pure state from small quan- tities of tissues or biologieal fluids. Koffer (2) edited a book covering the use of microsublimation, melting point, eutectics, etc., in identifying mieroquantities of organic material. The advantages of sublimation over other methods of purification have been discussed by Hubacher (2). Mamy types of vacuum sublimation apparatus have been described (1-3). The equipment described here is imexpensive and can be assembled readily by any laboratory worker with a modicum of glassblowing skill. To a thick-walled, round-bottom, Pyrex test tube, 30 x 200 mm, is attached a glass side arm about one in. from the bottom. Using a suspension of very fine- emery in glycerin or fine valve grinding compound, the open end of the test tube is ground against the aluminum block of a Fisher Johns melting point ap- paratus (Fisher Scientific Co., St. Louis, Mo.) until it makes a vacuum-tight seal when dry. This is the vacuum hood. Microbeakers are prepared from flat- + The author is Indebted to Robert Puckett, of this Inbora- tory, for technical assistance in preparing this apparetus. 599

Tenéis que saber qué es este experimento, que descubrió y el porqué de su importancia

RUN #4 CH4, NHa, Ha, H2O

Matraz pequeño de cristal (contiene agua hirviendo)

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