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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
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
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
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?
• 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