2006-2007

Origin of Life(Ch. 26)

“…“…sparked by sparked by just the right just the right combination of combination of physical events physical events & chemical & chemical processes…”processes…”

“…“…sparked by sparked by just the right just the right combination of combination of physical events physical events & chemical & chemical processes…”processes…”

Bacteria Archae-bacteria

AnimaliaFungiProtista Plantae

4500

4000

3500

3000

2500

2000

500

1500

0

1000

Formation of earth

Molten-hot surface ofearth becomes cooler

Oldest definite fossilsof prokaryotes

Appearance of oxygenin atmosphere

Oldest definite fossilsof eukaryotes

First multicellularorganisms

Appearance of animalsand land plants

Colonization of landby animalsPaleozoic

Mesozoic

Cenozoic

Mill

ion

s o

f y

ears

ag

o

AR

CH

EA

N PR

EC

AM

BR

IAN

PR

OT

ER

OZ

OIC

• The evolutionary tree of life can be documented with evidence.

• The Origin of Life on Earth is another story…

• The evolutionary tree of life can be documented with evidence.

• The Origin of Life on Earth is another story…

What is Life?• First we have to define LIFE…

– organized as cells– respond to stimuli– regulate internal processes

• homeostasis– use energy to grow

• metabolism– develop

• change & mature within lifetime

– reproduce• heredity

– DNA / RNA• adaptation & evolution

Life comes from Non-Life• Where is the line between

living and non-living?• “A vehicle (organism) built by

design information (DNA) for the purpose of replicating that information”

• Good– but too inclusive??? (computer viruses, etc.)

• Terrestrial life is cellular (sorry viruses).

No worries—Alive or Not,

I exist!!!

The Origin of Life is Hypothesis

• Special Creation– Life was created by a

supernatural or divine force.– not testable

• Extraterrestrial Origin (Panspermia)– The original source of organic

(carbon) materials was comets & meteorites striking early Earth.

– testable• Spontaneous Abiotic Origin

– Life evolved spontaneously from inorganic molecules.

– testable

Conditions on early Earth

• Reducing atmosphere– water vapor (H2O), CO2, N2, NOx, H2, NH3,

CH4, H2S

– lots of available H & its electron– no free oxygen

• Energy source– lightning, UV radiation,

volcanic

low Olow O22 = =

organic molecules organic molecules do not breakdown do not breakdown as quicklyas quickly

low Olow O22 = =

organic molecules organic molecules do not breakdown do not breakdown as quicklyas quickly

What’s missingfrom that

atmosphere?

5 Steps to go from Non-Life to Life

1. Formation (or presence) of Biological Molecules

2. Isolation of Biological Molecules from Surroundings (aka “Cells”)

3. Development of Metabolism.4. Development of Information

Molecules.5. Reproduction.

Water vapor

Condensed liquid with complex, organicmolecules

CondenserMixture of gases("primitiveatmosphere")

Heated water("ocean")

Electrodes discharge sparks

(lightning simulation)

Water

Origin of Organic Molecules

• Abiotic synthesis– 1920

Oparin & Haldane propose reducing atmosphere hypothesis

– 1953Miller & Urey test hypothesis

• formed organic compounds

–amino acids–adenine

CH4

NH3

H2

Stanley MillerUniversity of Chicago

produced-amino acids

-hydrocarbons-nitrogen bases-other organics

It’s ALIVE!

Origin of Cells (Protobionts)• Bubbles → separate inside from outside• → metabolism & reproduction

20 μm

(a) Simple reproduction. This liposome is “giving birth” to smallerliposomes (LM).

(b) Simple metabolism. If enzymes—in this case, phosphorylase and amylase—are included in the solution from which the droplets self-assemble, some liposomes can carry out simple metabolic reactions and export the products.

Glucose-phosphate

Glucose-phosphate

Phosphorylase

Starch

Amylase

Maltose

Maltose

Phosphate

Bubbles…Tiny bubbles…

Origin of Genetics• RNA is likely first genetic material

– multi-functional– codes information

• self-replicating molecule • makes inheritance possible• natural selection & evolution

– enzyme functions• ribozymes• replication

– regulatory molecule– transport molecule

• tRNA & mRNA

Dawn of Dawn of natural selectionnatural selection

A ribozyme capable of replicating RNA

Ribozyme(RNA

molecule)

Template

Nucleotides

Complementary RNA copy

3′

5′

5′

Key Events in Origin of Life

• Key events in evolutionary history of life on Earth– life originated

3.5–4.0 bya– “Heterotroph

Hypothesis”: cells eating other cells for ~700 million years.

Prokaryotes• Prokaryotes dominated life

on Earth from 3.5–2.0 bya

3.5 billion year old fossil of bacteria

chains of one-celledchains of one-celledcyanobacteriacyanobacteria

modern bacteria

Stromatolites• Fossilized mats of

prokaryotes resemble modern microbial colonies

Lynn Margulis

Oxygen atmosphere• Oxygen begins to accumulate 2.7 bya

– reducing → oxidizing atmosphere• evidence in banded iron in rocks = rusting• makes aerobic respiration possible

– photosynthetic bacteria (blue-green algae)

First Eukaryotes• Development of internal

membranes– create internal micro-environments– advantage: specialization = increase

efficiency• natural selection!

infolding of theplasma membrane

DNAcell wall

plasmamembrane

ProkaryoticProkaryoticcellcell

Prokaryotic Prokaryotic ancestor of ancestor of eukaryotic eukaryotic

cellscells

EukaryoticEukaryoticcellcell

endoplasmicreticulum (ER)

nuclear envelope

nucleus

plasma membrane

~2 bya~2 bya

Endosymbiosis

Ancestral Ancestral eukaryotic celleukaryotic cell

Eukaryotic cellEukaryotic cellwith mitochondrionwith mitochondrion

internal membrane system

aerobic bacterium mitochondrion

Endosymbiosis

• Evolution of eukaryotes– origin of mitochondria– engulfed aerobic bacteria, but

did not digest them– mutually beneficial relationship

• natural selection!

mitochondrion

chloroplast

Eukaryotic cell withEukaryotic cell withchloroplast & mitochondrionchloroplast & mitochondrion

Endosymbiosis

photosyntheticbacterium

Endosymbiosis

• Evolution of eukaryotes– origin of chloroplasts – engulfed photosynthetic bacteria,

but did not digest them– mutually beneficial relationship

• natural selection!

EukaryoticEukaryoticcell with cell with

mitochondrionmitochondrion

• Evidence– structural

• mitochondria & chloroplasts resemble bacterial structure

– genetic• mitochondria & chloroplasts

have their own circular DNA, like bacteria

– functional• mitochondria & chloroplasts

move freely within the cell• mitochondria & chloroplasts

reproduce independently from the cell

Theory of Endosymbiosis

Lynn Margulis

Cambrian explosion• Diversification of Animals

– within 10–20 million years most of the major phyla of animals appear in fossil record

543 mya543 mya

Ca

mb

rian

Pro

tero

zoic

eo

n

Ord

ovi

cia

n

Silu

rian

De

von

ian

Ca

rbo

nife

rou

s

Pe

rmia

n

Tria

ssic

Jura

ssic

Cre

tace

ou

s

Pa

leo

ge

ne

Neo

gene

Num

ber of fam

ilies ( )

Number oftaxonomic

familiesExtinction rate

Cretaceous mass extinction

Permian mass extinction

Millions of years agoE

xtin

ctio

n ra

te (

)

Paleozoic Mesozoic

0

20

60

40

80

100600 500 400 300 200 100 0

2,500

1,500

1,000

500

0

2,000

Ceno-zoic

Diversity of life & periods of mass extinction

Cambrian explosion

• The Chicxulub impact crater in the Caribbean Sea near the Yucatan Peninsula of Mexico indicates an asteroid or comet struck the earth and changed conditions 65 million years ago

• The Chicxulub impact crater in the Caribbean Sea near the Yucatan Peninsula of Mexico indicates an asteroid or comet struck the earth and changed conditions 65 million years ago

Cretaceous extinction

Early mammal evolution

• 125 mya mammals began to radiateout & fill niches

Classifying Life• Molecular data

challenges 5 Kingdoms• Monera was too diverse

– 2 distinct lineages of prokaryotes• Protists are still too diverse

– not yet sorted out

3 Domain system• Domains = “Super” Kingdoms

– Bacteria– Archaea

• extremophiles = live in extreme environments– methanogens– halogens– thermophiles

– Eukarya• eukaryotes

–protists– fungi–plants–animals

Archaebacteria&

Bacteria

Classification• Old 5 Kingdom system• New 3 Domain system

– reflects a greater understanding of evolution & molecular evidence• Bacteria

• Archaebacteria

• Eukaryotes

– Protists

– Plants

– Fungi

– Animals

Prokaryote

Eukaryote

KingdomProtist

KingdomFungi

KingdomPlant

KingdomAnimal

KingdomArchaebacteria

KingdomBacteria

2006-2007

Any Questions??Is there life elsewhere?Is there life elsewhere?

Does it look like life on Earth?Does it look like life on Earth?

Certainly not cellular life.

“Synthia” – Created in 2010 by the Venter InstituteVery simple bacterium with a completely synthesized chromosome

Some computer programs sure behave a lot like life does...

Have Humans Created Life?Have Humans Created Life?

2006-2007

Review Questions

• 1. What is (are) the drawback(s) associated with the hypothesized abiogenetic formation of organic monomers in early Earth's atmosphere? *1)the relatively short time between

intense meteor bombardment and appearance of the first life forms

• the lack of experimental evidence that organic monomers can form abiogenetically

• uncertainty about which gases comprised early Earth's atmosphere

A. 1 onlyB. 2 only • 3 only• 1 and 3• 2 and 3

2. In the Miller- Urey experiment, application of electric sparks to simple gasses resulted in the formation of

• Steroids• Oxygen• Cellulose• Simple amino acids• DNA

The following questions refer to the following choices:

1. aerobic autotrophs2. aerobic heterotrophs3. anaerobic heterotrophs4. anaerobic autotrophs

•What is the most likely order in which the choices above evolved on Earth?•Give two pieces of evidence to support your order for #3.