2. evolucion unicelular

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Evolución Celular Tuesday, April 17, 12

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Page 1: 2. Evolucion Unicelular

Evolución Celular

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ProtocélulaProtobionte

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3600-3800 m.a.Primera vida en la tierra … 3600 millones de años

de micro-organismos

-Procariontes fueron los únicos organismo presentes por muchos mill de años

- El primer oxígeno atmosférico fuehecho por las cianobacterias

– Plantas no existían aún– Micro-organismos todavía producen la mitad del O2producido globalmente

- Primero eucariotas también fueron células únicas y microscópicas

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Early Earth showing volcanic activity and photosynthetic prokaryotes in dense mats

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Procariontes

Dominan la tierra por muchos años

Bacterias Archeas

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Archea

Crenarchaeota

(110ºC)Euryarchaeotaproducen metano

Halófilosalta concentración de sal

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Cianobacterias

Cianobacteria vivienteTuesday, April 17, 12

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Cianobacterias de Apex Chert(Australia) hace más de 3 mil

millones de años(Brassier et al., 2002, Nature)

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Estromatolitos

Salar de LlamaraTuesday, April 17, 12

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2003

Feb, 2007

Mar, 2007

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El medio ambiente condiciona la vida de los organismos en la naturaleza

Los organismos pueden modificar el medio ambiente en el cual viven

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Acumulación de O22700 m.a.

FotosíntesisOxígeno atmosférico comenzó a acumularsehace 2700 millones de años atrás

• Fotosíntesis se desarrolló probablemente muy temprano en la vida de los procariontes

–Primeras versiones de fotosíntesisno usaron agua ni liberaron O2

• Cianobacteria, organismosfotosintéticos que rompen el agua y liberan O2 son losprimeros responsables del aumento del oxígeno en la atmosfera.

CO2

H2O O2

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Acumulación de O22700 m.a.

Muerte de procariontes anaerobios

Desarrollo de mecanismos de uso de O2 en procesos

celularesTuesday, April 17, 12

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?Tuesday, April 17, 12

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Teoría endosimbiótica seriada

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Evidencias:

Doble membrana (interna parecida a procariotas)

DNA propio

Genoma parecido a bacteria

Síntesis de proteínas (N-formyl-met//met )

Ribosomas

Inhibición de la síntesis proteica

Fisión binaria

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Hatena Nephroselmis(Protista)(Dinoflagelados)

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Hipótesis del fagocito primitivo

C. de Duve

Procarionte

Capacidad fagocítica

Citoesqueleto Ausencia de paredcelular

Formación de vacuolas Endosimbiosis Formación del

núcleo

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Problema:Amplia diversidad de organismos...

como lograr hacer un mapa evolutivo?

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SimilitudesTodos presentan vías metabólicas comunes (glicólisis)

DNA RNA ProteínasCódigo genético común

Todos tienen una membrana

Problema:Amplia diversidad de organismos...

como lograr hacer un mapa evolutivo?

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Carl Woese

Todos los organismos ensamblanproteínas...

rRNA

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Relación cercana entre eucariontes y archeasMenor distancia entre plantas y animales

Consecuencias...

Nuevo arbol de la vida basado en pequeña subunidad rRNA (Woese 1996)

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Nuevo arbol de la vida basado en pequeña subunidad rRNA (Woese 1996)

LUCA(Last Universal Common Ancestor)

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Arbol a partir de genes que sostiene que Archaeay Eucarya son cercanosen relación a Bacteria

Arbol a partir de genes quesostiene que Archaea and Bacteria son cercanos en relacion a Eucarya

Arbol a partir de genes que sostiene que Archaeay Eucarya son cercanosen relación a Bacteria

Arbol a partir de genes quesostiene que Archaea and Bacteria son cercanos en relacion a Eucarya

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Importancia de la transferencia horizontal de genes en la evolución

• Aumento de las evidencia de una transferencia horizontal de genes entre los grupos mayores e.g. genes “bacterianos” específicos en Archaea

Ejemplo: gen de la enzima MGCoA reductasa en grupos de Archaea

Esta Archaea reemplazó su gen por uno de bacteria

Analisis publicado en 1998, 2003

gen de la enzima HMGCoA reductasa en grupos de Archaea

Transferencia horizontal de genes en la evolución

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Ancestro común de toda la vida (“cenancestor”) fue unacomunidad de especies que intercambiaban genes unos con otros

Ramas principales del arbol aparecen claramente pero genes individuales reflejan patrones ancestrales de transferenciade genes

CenancestorComunidad de especies que intercambiaban genes

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EucariotaProtoeucariota

Archea

Bacteria

ReplicaciónTranscripción

Traducción

Metabolismo1.5m.a

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Innovaciones en EUCARIONTES

Núcleo?Filamentos?

Planctomycetes

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Innovaciones en EUCARIONTES

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especially, is often elaborate and includes such structures as sensory bristles,photoreceptors, sinuously beating cilia, leglike appendages, mouth parts, sting-ing darts, and musclelike contractile bundles. Although they are single cells,protozoa can be as intricate, as versatile, and as complex in their behavior asmany multicellular organisms (see Figure 1–32). <ATGG> <TCGC>

In terms of their ancestry and DNA sequences, protists are far more diversethan the multicellular animals, plants, and fungi, which arose as three compara-tively late branches of the eucaryotic pedigree (see Figure 1–21). As with procary-otes, humans have tended to neglect the protists because they are microscopic.Only now, with the help of genome analysis, are we beginning to understandtheir positions in the tree of life, and to put into context the glimpses thesestrange creatures offer us of our distant evolutionary past.

A Yeast Serves as a Minimal Model Eucaryote

The molecular and genetic complexity of eucaryotes is daunting. Even morethan for procaryotes, biologists need to concentrate their limited resources on afew selected model organisms to fathom this complexity.

To analyze the internal workings of the eucaryotic cell, without the addi-tional problems of multicellular development, it makes sense to use a speciesthat is unicellular and as simple as possible. The popular choice for this role ofminimal model eucaryote has been the yeast Saccharomyces cerevisiae (Figure1–42)—the same species that is used by brewers of beer and bakers of bread.

S. cerevisiae is a small, single-celled member of the kingdom of fungi andthus, according to modern views, at least as closely related to animals as it is toplants. It is robust and easy to grow in a simple nutrient medium. Like otherfungi, it has a tough cell wall, is relatively immobile, and possesses mitochondriabut not chloroplasts. When nutrients are plentiful, it grows and divides almost as

GENETIC INFORMATION IN EUCARYOTES 33

Figure 1–41 An assortment of protists: asmall sample of an extremely diverseclass of organisms. The drawings aredone to different scales, but in each casethe scale bar represents 10 mm. Theorganisms in (A), (B), (E), (F), and (I) areciliates; (C) is a euglenoid; (D) is anamoeba; (G) is a dinoflagellate; (H) is aheliozoan. (From M.A. Sleigh, Biology ofProtozoa. Cambridge, UK: CambridgeUniversity Press, 1973.)

I.

Protistas

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especially, is often elaborate and includes such structures as sensory bristles,photoreceptors, sinuously beating cilia, leglike appendages, mouth parts, sting-ing darts, and musclelike contractile bundles. Although they are single cells,protozoa can be as intricate, as versatile, and as complex in their behavior asmany multicellular organisms (see Figure 1–32). <ATGG> <TCGC>

In terms of their ancestry and DNA sequences, protists are far more diversethan the multicellular animals, plants, and fungi, which arose as three compara-tively late branches of the eucaryotic pedigree (see Figure 1–21). As with procary-otes, humans have tended to neglect the protists because they are microscopic.Only now, with the help of genome analysis, are we beginning to understandtheir positions in the tree of life, and to put into context the glimpses thesestrange creatures offer us of our distant evolutionary past.

A Yeast Serves as a Minimal Model Eucaryote

The molecular and genetic complexity of eucaryotes is daunting. Even morethan for procaryotes, biologists need to concentrate their limited resources on afew selected model organisms to fathom this complexity.

To analyze the internal workings of the eucaryotic cell, without the addi-tional problems of multicellular development, it makes sense to use a speciesthat is unicellular and as simple as possible. The popular choice for this role ofminimal model eucaryote has been the yeast Saccharomyces cerevisiae (Figure1–42)—the same species that is used by brewers of beer and bakers of bread.

S. cerevisiae is a small, single-celled member of the kingdom of fungi andthus, according to modern views, at least as closely related to animals as it is toplants. It is robust and easy to grow in a simple nutrient medium. Like otherfungi, it has a tough cell wall, is relatively immobile, and possesses mitochondriabut not chloroplasts. When nutrients are plentiful, it grows and divides almost as

GENETIC INFORMATION IN EUCARYOTES 33

Figure 1–41 An assortment of protists: asmall sample of an extremely diverseclass of organisms. The drawings aredone to different scales, but in each casethe scale bar represents 10 mm. Theorganisms in (A), (B), (E), (F), and (I) areciliates; (C) is a euglenoid; (D) is anamoeba; (G) is a dinoflagellate; (H) is aheliozoan. (From M.A. Sleigh, Biology ofProtozoa. Cambridge, UK: CambridgeUniversity Press, 1973.)

I.

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