Origin of Life

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Transcript Origin of Life

Origin Of Life
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Francesco Redi’s Experiment
Common thought: Spontaneous
generation of flies from meat
Redi - Italian
physician/scientist in the 1600s
Noticed that maggots turned
into sturdy oval cases, from
which flies eventually emerged
This made him question
spontaneous generation
Performed an experiment
Spallanzani’s Experiment
Around Redi’s time, infection-causing
microorganisms were discovered; they
were thought to have been generated
spontaneously from a “vital force”
found in the air
In 1700s, Italian scientist Lazzaro
Spallanzani designed an experiment to
test the hypothesis of spontaneous
generation Experimental design:
4 flasks of meat broth
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1 open – produced microorganism
1 closed – same
1 boiled and open – same
1 boiled and closed – remained
microorganism free
Objections to Spallanzani’s Work
Opponents to his work claimed that
Spallanzani had heated the experimental
flasks too long, destroying the “vital force”
in the air inside them
Because of this, those that believed in
Spontaneous Generation refused to change
their thoughts
Disproving Spontaneous
Generation once and for all!
By 1800s the debate over spontaneous
generation predominated science
Paris Academy of Science offered a reward
French Scientist Louis Pasteur won by
designing an experiment that answered the
objections to Spallanzani’s experiment
Pasteur’s Experiment
Pasteur made a curve-necked
flask that allowed the air inside
the flask to mix with air outside
the flask
The curve in the neck prevented
solid particles from entering the
body of the flask
Broth boiled inside the
experimental curve-necked
flasks remained clear for up to a
year
But when he broke off the
necks, the broth became cloudy
and contaminated with
microorganisms within a day
Aftermath of Pasteur’s Experiment
Those that defended
spontaneous
generation gave up
their fight
The principle of
biogenesis now
became the
cornerstone of biology
Big Bang
About 17 billion years
ago all the matter and
energy in the universe
was compressed into an
extremely small volume
(a singularity) and then
BOOM!
The big bang sent all
the matter and energy
outward in a giant cloud
Origin of Life -- Breakdown
1. Atmosphere and earth formed- had little or no oxygen
2. The primordial seas formed as the Earth cooled and gases condense
3. The first organic molecules formed
4. Polymers and self replicating molecules were synthesized
5. Organic molecules were organized into protobionts- the precursors
of cells.
6. Primitive heterotrophic prokaryotes formed
7. Primitive autotrophic prokaryotes formed
8. Oxygen and the ozone layer formed
9. Eukaryotic cells formed (endosymbiont theory)- orginated from a
symbiotic relationship between several prokaryotes.
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1 - Earth’s History
Earth is believed to be approximately 4.6 billion years old
Formed from swirling clouds of dust that condensed
Isaac Newton (the light spectrum – roygbv) determined that
planets are moving further and further away from one
another based on the intensity of wavelengths emitted by the
light from those planets (red shift)
1 & 2 - Early Earth
Early Atmosphere
Volcanoes released gases
(carbon dioxide, nitrogen,
hydrogen sulfide, hydrogen,
water vapor, methane, and
ammonia) into the
atmosphere
Creates a reducing (electron
adding) atmosphere
The gases condensed to
form the “soupy seas”.
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3 - The First Organic Compounds
Intense lightning, ultraviolet radiation from
sun, heat, and radioactivity created
enormous amounts of energy in the
environment.
This energy transformed inorganic
molecules into organic molecules including
amino acids, nucleotides and fatty acids.
These first molecules were formed by
chemical evolution
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Who Figured that Out?
Primitive Atmosphere Hypothesis (1923)
Alexander Oparin and J. B. S. Haldane
postulated that the reducing atmosphere and
high UV radiation reaching the surface of
primitive earth enhanced reactions that
joined simple molecules to produce the first
organic molecules.
This would not be possible today, since
oxygen in today's atmosphere attacks
chemical bonds (removing electrons) and the
ozone layer of the earth's atmosphere screens
out most UV radiation
Miller & Urey
Miller and Urey
They tested Oparin’s
hypothesis by recreating the
proposed primitive
atmosphere, simulating
lighting with electric sparks
Over time, amino acids,
sugars, lipids, bases, cAMP,
FAD, NAD, NADP, and
ATP developed within their
experimental chamber
Miller & Urey
Revisions to theory??
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4 - Polymerization
Polymers are formed by dehydration
synthesis (removal of water)
Sidney Fox proved that earth’s clay had the
ability to act as a substrate for dehydration
reactions.
Water containing organic monomers may
have splashed up on warm clay surfaces
and allow for polymerization of monomers
EX: Amino acids would bind together and form
proteinoids (abiotically produced proteins)17
4 - The First Genetic Material
RNA has been theorized as the first genetic
material because self-replicating RNA can
abiotically (w/o enzymes) reproduce in a test tube
Ribozyme- form of RNA that can catalyze
proteins directly
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5 - Protobionts
Protobionts (pre-cursors to cells)
Also called coacervates
Contained permeable membranes and had a
primitive metabolism (carry out chemical rx’s)
Formation
• When lipids are added to water, membrane bound
spheres form (mycells)
 These spheres are capable of growing, dividing, shrinking
and swelling, and have a semi-permeable membrane
• These spheres may contain RNA and/or proteinoids
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Protobionts
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6 - The First Forms of Life
When the first prokaryotic cells arose (between 3.5 and 4.0
billion years ago), there was no usable oxygen gas in existence
Thus, first forms of life must have been anaerobic
Anaerobic prokaryotes appeared and consumed protobionts
and other organic molecules
• this caused a buildup of CO2 from fermentation
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7 - The First Forms of Life
Over 3 billion years ago, autotrophic prokaryotes
appeared when mutant heterotrophs gained the ability to
use sunlight and CO2 for photosynthesis.
This caused the buildup of oxygen in the atmosphere
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First Forms of Life - Fossil
Record
The earliest microfossils (so named because of their
small size) date back to 3.5 billion years ago
Earliest fossils were stromatolites which are the direct
ancestors of cyanobacteria (autotrophic bacteria)
Mats of fossilized stromatolites dating back 2.5 billion
years mark a time when photosynthetic prokaryotes had
produced enough O2 to make an aerobic atmosphere
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Stromatolites
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8 - Oxygen and the Atmopshere
O2 molecules produced by
photosynthetic
prokaryotes eventually
raised to the upper
atmosphere.
Here they were split by
UV light, forming free O
radicals
These combined with O2
molecules which formed
O3 (Ozone)
8 - Oxygen and the Atmopshere
This ozone gas absorbs
intense ultraviolet radiation
from the sun, making it
possible for life to exist on
earth (UV radiation
destroys/damages DNA
molecules)
Abiotic chemical evolution
ended due to less UV light
reaching Earth’s surface
9- The First Eukaryotes
Between 2 and 3 billion years
ago the first eukaryotes
appeared on earth
How they came about
(Endosymbiotic Theory)
Small aerobic prokaryotes
entered and began to live in
larger prokaryotes (acting as
mitochondria…respirators)
A short time later small
photosynthetic prokaryotes
began to enter these larger
cells (acting as chloroplasts
…food producers)
Endosymbiotic Theory
Endosymbiotic theory says that groups of
prokaryotes came together and formed
eukaryotes through symbiotic relationships
Evidence
Mitochondria & chloroplasts have their own DNA
which is circular and “naked”
They have their own ribosomes which resemble those
of bacteria
They are encased by membranes.
They reproduce independently of the host cell by a
process similar to binary fission in bacteria.
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Book Section Correlation
Chapter 16 Bat CAMPBELL textbook
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