Download 2- origin of the life

The Origin and Early History of Life
Chapter 4
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Where the first cell came from?
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Or….Can life arise from non-life?
Can we test this scientifically?
– Conditions on early earth
– Formation of organic molecules
warm little pond
– Chemical evolution
– Primitive cell
– Prokaryotes
– Eukaryotes
– Multicellular organisms
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What do we know?
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~ 1.5 Million species identified so far
Many more remain unidentified
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Are we alone?
A. Yes
B. No
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Which one represents possible origin of
life on earth?
A.
B.
C.
D.
E.
Extraterrestrial aliens brought it
Came with meteors from other planets
Some superhuman powers created it
Chemicals from primordial soup combined
to make life
None of the above
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We don’t know how life originated.
Probably arose on Earth, but an
alternate theory suggests it arose
elsewhere and drifted through
space to seed the Earth
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What does
life need?
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What does life need?
A way of harnessing energy to do useful work,
• a way of storing and reproducing genetic
information,
• a way to keep the inside separated from the
outside.
Which of these arose first is a matter of
debate.
• Inheritance first or metabolism first? Or both
simultaneously?
• However, once a genetic system is in place,
natural selection will quickly improve the new
life form.
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Some Theories
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Darwin thought life originated in a “warm little
pond”.
However, since his time we know that life can
exist in a much larger range of environments,
and many theories now focus on high
temperature and pressure environments
such as a the bottom of the ocean or deep
underground.
The “RNA World”: a theory that puts
genetics at the center.
Iron-sulfur world: puts metabolism first
Clay minerals: life started as selfreproducing clay crystals
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Origins of Life
“The Scientific Story”
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Prebiotic Earth
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Conditions on the primitive Earth
were not the same as those
present today
Image Credit A.I. Oparin
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No spontaneous generation of life
today (Pasteur)…
because the necessary conditions
no longer exist.
© 2010 Paul Billiet ODWS
J.B.S. Haldane
(credit: Bassano and
Vandyk Studios)
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Origin of the Universe
and the Earth
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Life most likely emerged under high-temperature
conditions.
15 billion years ago
The “Big Bang” led to the formation of the
stars of the “universe”
The sun is the closest star to us
4.6 billion years ago
Planets of our solar system were formed
including our earth
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Conditions on Early EarthReducing Atmosphere
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Early atmosphere is often referred to as a
reducing atmosphere on the primitive
Earth. No free oxygen (O2)
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exact conditions unknown
 ample availability of hydrogen atoms
 very little oxygen
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Conditions of the early earth:
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The Earth’s surface temperature probably hotter than today
very hot, barren rock, volcanoes
Lightning , ultraviolet radiation
gases:
Free hydrogen : hydrogen (H2)
(Hydrogen sulfide/Hydrogen cyanide
saturated hydrides
 methane (CH4)
 ammonia (NH3)
 water vapor (H2O)
Energy for chemical reactions between these gases could
come from electric discharge in storms or solar energy
(no ozone layer)
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Then what?
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The earth’s temperature cooled over many
years resulting in condensation and huge
rains.
Oceans formed and covered the earth.
These oceans were thought to be near
boiling point.
Chemical
Evolution
took
place,
rearranging the atoms of the gases of the
atmosphere in to the building blocks of
organic compounds.
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Organic Compound
Building Block
Protein
Amino Acids
Nucleic Acids
Nucleotides
Carbohydrates
Simple Sugars
Lipids
Glycerol and Fatty Acids
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1950’s Miller-Urey Experiment
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Attempted to reproduce early
reducing
atmosphere
and
produce organic compounds
from inorganic materials
–
hydrogen-rich
–
electrical discharges
After a week 15 amino acids in
the mixture
Other biologically important
molecules had been formed
including ethanoic acid, lactic
acid and urea
Later similar experiments were
done using CO2 that produced
nucleotides.
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Urey and Miller
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Produced
– amino acids
– carbohydrates
– lipids
– Nucleotides
Conclusion?
Perhaps the building blocks
of organic compounds could
have formed on primitive
earth (Chemical Evolution)
Image Credit Stanley Miller
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Conclusion
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These experiments cannot reproduce the
exact conditions on the primitive Earth
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We shall never know exactly what happened
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BUT it can be shown that the basic
building blocks for the large macromolecules
can be synthesised in vitro from inorganic
compounds.
© 2010 Paul Billiet ODWS
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Chemical Evolution
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If life originally arose from non-life, how might
this have happened?
Consider the following scenario
– Synthesis and accumulation of small organic
molecules
– Joining of these monomers into polymers
– Aggregation of these molecules into droplets to
form localized microenvironments
– Origin of heredity
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The Jump…
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It is thought that these compounds began to cluster
together held by lipid molecules accumulating..
These clusters were called coacervates, or
“proteinoid microspheres”
Scientists believe that these “abiotic” proteinoid
microspheres made the jump to become the
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first living cell approximately 3.5 billion years ago.
Spontaneous Generation??
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Polymer Formation
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Sidney Fox (University of Miami) demonstrated the abiotic
polymerization of organic monomers
Polymers were formed when dilute solutions of organic
molecules were dripped onto hot sand, clay, or rock
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“Proteinoids”
- Clay can serve to concentrate these molecules
– Monomers bind to charged sites on clay particles
- Metal ions in clay have catalytic function
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From monomers to polymers
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Amino acids into polypeptides, could
have occurred when dry or highly
concentrated monomers are heated
Condensation reactions take place
forming peptide bonds between amino
acids or phosphodiester bonds form
between nucleotides.
© 2010 Paul Billiet ODWS
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Early catalysts
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As molecules adsorb to the clay
mineral
particles
they
become
concentrated (stick to the surface
particles)
These clay particles (coacervates) may
have been essential catalysts in the
formation of polymers.
© 2010 Paul Billiet ODWS
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The first polynucleotides
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Once formed polynucleotides show a
tendency to copy themselves using
complementary base pairing
This was probably catalysed by the
presence of clay particles and metal ions
These single stranded polynucleotides would
have been the equivalent of RNA.
© 2010 Paul Billiet ODWS
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?
Which came first
A.DNA
Most Likely
B.RNA
C.Protein
DNA
(Genetic information)

RNA
(Information and catalytic)

PROTEIN
(Catalytic and structural)
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RNA World
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One possible solution to needing both DNA
to store genetic information and proteins to
carry out activities
is to use RNA for both.
RNA can store information,
and it can act as an enzyme.
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Perhaps there was a stage in the
development of life with nothing but selfreplicating RNA molecules.
Proteins, DNA, and cell membranes added
later in this scenario.
No real evidence for it, but RNA works as
an enzyme in some of the most basic life
processes, such as making proteins.
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Abiotic RNA Replication
Remember
RNA
enzymes?
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The first hereditary information
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RNA was probably the first hereditary
molecule having the ability to copy itself
RNA shows enzymic (catalytic) properties
called ribozymes
Polynucleotides are very good molecules
at storing and transmitting information
but they lack the versatility for all the
chemical functions of a cell.
© 2010 Paul Billiet ODWS
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A great partnership
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Polypeptides, which can form complex 3-dimensional
structures (proteins), are much better at complex cell
functions
A partnership must have formed
polynucleotides and the polypeptides
between
the
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The polynucleotides directed the synthesis of the
polypeptides
Today it is clear that information only flows from
polynucleotides to polypeptides. Translation had
started.
© 2010 Paul Billiet ODWS
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The origin of DNA
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Later
the
hereditary
information was probably
stored in the form of DNA
which is more stable than
RNA
The passage of information
from RNA to DNA is possible
in nature
The reverse transcriptase
enzyme of the retro viruses
shows this.
© 2010 Paul Billiet ODWS
Image Credit: DNA
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The first membranes, the first cells
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If a piece of RNA codes for a particularly good
protein then there is nothing to stop that protein
being used by other RNA molecules
If however the RNA is enclosed in a membrane
then it can keep it’s protein to itself and gains a
selective advantage
So membranes probably pushed evolution by
natural selection forwards.
© 2010 Paul Billiet ODWS
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Membranes defined the first cell
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The phospholipids form lipid bilayers
when they are surrounded by water
All the components of a simple
prokaryotic cell were now assembled
They diversified in their metabolism
By 2 billion years ago free oxygen was
appearing in the atmosphere due to the
activity of photosynthetic bacteria.
© 2010 Paul Billiet ODWS
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What did this first cell look like?
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The first cell was likely:
• Aquatic
• Prokaryotic
• Anaerobic
• Heterotrophic (Oparin and Haldane’s
Heterotroph Hypothesis)
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Biological Evolution now begins
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The following time line describes some of the big
events:
2 billion years ago
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photosynthetic prokaryotes evolve
releasing O2 into the atmosphere. This brought about two
major changes
– Aerobic environment
– Formation of ozone (O3)
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UV-rays  2O2  O + O + O + O  O3 + O
Aerobic environment led to aerobic organisms evolving
With 18X more energy they could grow faster, reproduce
faster and evolve faster.
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What Happened Next?
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1.5 billions years ago
eukaryotes evolved
Large prokaryotic cell engulfs a
smaller prokaryotic cell. Resulted in
the first eukaryotic cell (mitochondria
and chloroplasts have their own
DNA!!)
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ENDOSYMBIOSIS
BEGINNING OF THE EUKARYOTIC CELLS
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EVIDENCE FOR ENDOSYMBIOSIS
DNA
Life Sciences-HHMI
Outreach. Copyright
2006 President and
Fellows of Harvard
College.
evolution.berkeley.edu/evolibrary/article/0_0_0/endosymbiosis_03
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What likely followed?
- Aquatic multicellularity NFB Evolution
- Terrestrial Autotrophs
- Terrestrial Heterotrophs
How Did Life Begin?
How Did Life
Begin 2
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Iron-Sulfur World
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A “metabolism first” scenario involves
naturally occurring iron sulfide (also called
pyrite) crystals.
These crystals can catalyze both oxidationreduction reactions (producing energy) and
polymerizations of amino acids.
Works especially well at high temperatures
and pressures, such as are found in deep
ocean vents called “black smokers”. Very
small pores in the rocks make good
chambers that take the place of membranes.
An active self-sustaining metabolic system in
the absence of inheritance.
Some nucleic acids randomly polymerized by
the Fe-S crystals eventually colonized the
pores and had the property of self-replication.
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Origin of protobiots
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Bubble theories (Oparin)
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PROTO-CELLS
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Chemical evolution ultimately led to the
formation of proto-cells
– Membrane-surrounded
sacs containing
genetic material and metabolically-active
molecules
Such structures have been experimentally
produced
From these proto-cells, cells ultimately
arose
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Earliest Cells
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Microfossils have been found in rocks as old
as 3.5 billion years old.
– resemble prokaryotes
Stromatolites
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EARLIEST LIFE
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The earliest cells were prokaryotic
– Lack a membrane-bound nucleus
Early in the history of life, populations diverged
into two major lineages
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 bacteria
 archaea & eukaryotes
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Archaebacteria
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Extreme-condition prokaryotes
– lack peptidoglycan in cell walls
 methanogens
 extreme halophiles
 extreme thermophiles
– thought to have split from Bacteria 2 bya.
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Bacteria
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Second major group of prokaryotes
– strong cell walls
– simpler gene structure
– contains most modern prokaryotes
 includes photosynthetic bacteria
 cyanobacteria
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EARLIEST LIFE
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How do we know that domain Eukarya is more
closely related to domain Archaea than to domain
Bacteria?
– Analysis of rRNAs
and other highly
conserved genes and
proteins provide the
strongest evidence
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First Eukaryotic Cells
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Eukaryotes probably arose about 1.5 bya.
– Internal membrane-bound structures such as
mitochondria and chloroplasts are thought to
have evolved via endosymbiosis.
 Energy-producing bacteria were engulfed by
larger bacteria.
 beneficial symbiotic relationship
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First Eukaryotic Cells
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Sexual reproduction
– Eukaryotic cells can reproduce sexually, thus
allowing for genetic recombination.
 Genetic variation is the raw material
necessary for evolution.
Multicellularity
– arisen many times among eukaryotes
 fosters specialization
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What they have and what they don’t
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What about this group?
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That is the end
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Summary
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Fundamental Properties of Life
Origin of Life Hypotheses
Chemical Evolution
Cell Origin Theories
– Bubble Theories
Prokaryotic Cells
– Archaebacteria
– Bacteria
Eukaryotic Cells
Extraterrestrial Life
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Development of new branches on the TREE
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TAXONOMY
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Extraterrestrial Life
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Universe has 1020 stars similar to our sun.
– Conditions may be such that life has evolved on
other worlds in addition to our own.
 ancient bacteria on Mars.
 largest moon of Jupiter, Europa, covered
with ice.
 liquid water may be underneath
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The Domains and Kingdoms
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What have we learned so far?
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Cell theory
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Molecular basis of inheritance
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DNA encodes genes which make-up and control living
organisms.
Evolutionary change
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All living organisms are made of cells, and all living cells
come from other living cells.
Life-forms have evolved varying characteristics to adapt
to varied environments.
Evolutionary conservation
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Some characteristics of earlier organisms are preserved
and passed on to future generations.
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Lets make something with those molecules
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Aggregations of abiotically produced molecules
Preceded living cells
Laboratory experiments have demonstrated their
formation from organic compounds
Protobionts and liposomes
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