Transcript origin of life

The Origin of Life
Oparin’s Heterotroph Hypothesis
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MORE!!!!!
• It is widely held that the sun and planets in
our solar system were formed ~4 ½ to 5 B
years ago from a cloud of cosmic dust &
gas
• The Earth was originally a “hellish” place
• So where did the building blocks of life
come from? A meteor? What?
• The present atmosphere = oxidizing;
Primitive atmosphere = reducing
• Oxidizing: chemical reactions due to oxygen;
21% oxygen and 78% nitrogen
• Objectives:
• Discuss various hypotheses on the Origin
of Life on Earth
• Explain Oparin’s Heterotroph Hypothesis
and how Miller and Urey’s experiments
supported this hypothesis
• Sequence the events that might have led
to the evolution of complex molecules and
the first organisms.
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Bubble Theories
• Compare Prokaryotic Cells (archaebacteria
and eubacteria) to Eukaryotic Cells (plant
and animal cells among others)
Origin of Life Hypotheses
• Special creation
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supernatural or divine
origin
• Extraterrestrial origin
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panspermia
• Spontaneous origin
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life originated from
inanimate materials
Reducing Atmosphere
• The primitive atmosphere was not conducive to life
• Energy sources such as UV rays, gamma rays, lightening,
radiation from the earth were much greater than today
• Early atmosphere is often referred to as a reducing
atmosphere.
 exact conditions unknown
 Oparin thought that there was methane (CH4), water vapor (H2O),
Hydrogen gas (H2), and ammonia (NH4)
 ample availability of hydrogen, carbon, oxygen and nitrogen atoms
 very little free oxygen (O2)
 If free oxygen had been there- life would not have evolved
 As energy hit the molecules in the early atmosphere bonds broke
and new ones were made.
 The ocean became a “hot thin soup” filled with organic molecules.
Schema of the Bubble Hypothesis
Miller-Urey Experiment
Miller-Urey Experiment
• Attempted to reproduce early reducing atmosphere
and produce organic compounds from inorganic
materials
• Tested Oparin’s hypothesis (chemical evolution)
• Materials
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hydrogen-rich atmosphere
electrical discharge
• Succeeded in producing amino acids, urea, lactic acid,
(and nucleotides if phosphorous was added)
• Sidney Fox heated amino acids at high
temperatures in salt water and found aggregates of
large protein growing and budding off to make
more.
• Oparin called these Coacervates.
– The protein complexes surrounded themselves with a
watery shell which allowed the inside to differ from
the outside environment
– As coacervates became more complex they may have
developed biochemical systems with the capacity to
release energy from organic nutrients in the “Hot Thin
Soup”. (the early ocean with all those organic
molecules)
– The first cells were heterotrophs according to Oparin.
Current Theories on the
Origin of Life - Location• Ocean’s edge- with volcanoes
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Oparin’s bubble hypothesis/ coacervate theory
/primordial soup/ chemical evolution
• Under frozen seas
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problematic due to necessary conditions
• Deep in Earth’s crust
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byproduct of volcanic activity
• Within clay
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positively-charged clay
• Deep-sea vents
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conditions suitable for Archaea
Earliest Cells
• Ongoing debate concerning actual path/ start-off point for cell
evolution
• Microfossils have been found in rocks as old as 3.5 billion years
old.
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resemble prokaryotes
 lack nucleus of more complex eukaryotes
• PROKARYOTE
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Pro: before; Karyon: nucleus
Genetic material not bounded by a nuclear membrane; no membranebound organelles
The earliest heterotrophic prokaryotes gave off CO2 as they
ANAEROBICLY RESPIRED!!! A new Gas!!!
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As the number of heterotrophs grew, they ate up the “soup”!
As the CO2 amount grew in the atmosphere, eventually organism may have
evolved that could use CO2 and H2O to make sugars
These organisms were anaerobic autotrophs and they gave off OXYGEN to
the atmosphere!!!! A new Gas!!!!
With O2 in the environment, aerobes could evolve!!!!
Prokaryotes: Archaebacteria
• extreme-condition prokaryotes
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lack peptidoglycan in cell walls
 Methanogens (produce methane CH3)
 extreme halophiles (salt-loving)
 extreme thermophiles (heat-loving)
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thought to have split from Bacteria 2 bya.
Prokaryotes: Eubacteria- true
bacteria
• second major group of prokaryotes
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strong cell walls
simpler gene structure
contains most modern prokaryotes
 includes photosynthetic bacteria (cyanobacteria)
 Pathogenic & non-pathogenic
First Eukaryotic Cells
• EUKARYOTE
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Eu: true; Karyon: nucleus
Genetic material within nuclear membrane; w/
membrane-bound organelles
• Eukaryotes probably arose about 1.5 bya.
Internal membrane-bound structures such as
mitochondria and chloroplasts are thought to have
evolved via endosymbiosis.
o Energy-producing bacteria were engulfed by larger
bacteria.
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 beneficial symbiotic relationship
Endosymbiosis
First Eukaryotic Cells
• Sexual reproduction
Eukaryotic cells can reproduce sexually, thus allowing
for genetic recombination.
o Genetic variation is the raw material necessary for
evolution.
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• Multicellularity
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arisen many times among eukaryotes
fosters specialization (ex. Tissues)
After a buildup of oxygen, ozone formed which blocked the
harmful rays of the sun so life could come onto land.
Extraterrestrial Life
• Universe has 1020 stars similar to our sun.
Conditions may be such that life has evolved on other
worlds in addition to our own.
o Ancient bacteria on Mars.
o Largest moon of Jupiter, Europa, covered with ice.
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 liquid water may be underneath
• What do you think? Hmmm…
Image Credit Comet
Hale-Bopp 1997