AP BIOLOGY History of Life on Earth—How Life Probably Emerged.
AP BIOLOGY THE HISTORY of EARTH
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AP BIOLOGY THE HISTORY of EARTH CHAPTER 25 CAMPBELL and REECE
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AP BIOLOGY THE HISTORY of EARTH. CHAPTER 25 CAMPBELL and REECE. Conditions on early Earth made the Origin of Life possible. Macroevolution : evolutionary change above the species level examples: emergence of terrestrial vertebrates mass extinctions impact on diversity of life - PowerPoint PPT Presentation
Transcript of AP BIOLOGY THE HISTORY of EARTH
AP BIOLOGYTHE HISTORY of EARTH
CHAPTER 25CAMPBELL and REECE
Conditions on early Earth made the Origin of Life possibleMacroevolution : evolutionary change
above the species levelexamples:1. emergence of terrestrial vertebrates2. mass extinctions impact on diversity of
life3. origin of key adaptations like flight in
birds
Where did 1st cell come from?4 main stages could have produced very
simple cells:1. The abiotic synthesis of small organic
molecules2. Joining of these small molecules into
macromolecules (proteins, nucleic acids)3. Packaging of these macromolecules into
protocells, droplets with membranes that maintained internal chemistry different from their surroundings
4. Origin of self-replicating molecules that eventually made inheritance possible
Synthesis of Organic Cpds on early EarthPlanets of our
solar system formed ~ 4.6 billion yrs ago
1st few hundred million yrs conditions would not have allowed life on Earth
1st AtmosphereCollisions would
have vaporized any water preventing seas from forming
Atmosphere thick with gases released from volcanic activity
1st Atmosphere1920’s: Oparin
(Russian chemist) and Haldane (British scientist) each came to conclusion early atmosphere was reducing environment (gain e-) in which organic compounds could have formed from simpler molecules
1st Organic CompoundsEnergy sources:
LightningThermal energyIntense UV
radiation
Primordial SoupHaldane had hypothesized the early seas
site of 1st organic compounds 1st cellsMiller & Urey (Univ. of Chicago) in
1950’s Tested Oparin & Haldane ‘s premiseCreated a reducing atmosphereAdded compounds considered to have been
found existing on early earth (hydrogen gas – H2, ammonia – NH3, methane – CH4, and H2O vapor)
Miller & UreyExperiment: In 1953, Stanley Miller set up a closed system to
simulate conditions thought to have existed on early Earth1. Water mixture in “sea” flask was heated; vapor entered atmosphere
flask2. “Atmosphere” flask contained mix of hydrogen gas, methane, ammonia,
and water vapor (believed to mimic early Earth’s atmosphere)3. Sparks were discharged to mimic lightning 4. Condenser cooled the “atmosphere”, “raining” water and any
dissolved molecules down into sea flask5. As material cycled through apparatus, Miller periodically collected
samples for analysisResults: Miller identified variety of organic molecules common
in organisms (including simple molecules like formaldehyde (CH2O) and hydrogen cyanide (HCN) and more complex molecules (like amino acids and hydrocarbons)
Conclusion: Organic molecules (a 1st step in the origin of life) may have been synthesized abiotically on early Earth
Miller & Urey’s Results
Miller-Urey Experiment Clip
Miller & Urey’s ResultsHave been repeated using same or
similar ingredients, different recipes for the atmosphere and they also produced organic compounds
Still ?s about amounts of methane, ammonia (was there really enough to make it a reducing environment?)
Some repeated experiment in non-reducing, non-oxidizing conditions & still produce organic compounds
Miller-Urey Experiment demonstrates:1. Abiotic synthesis of organic molecules
is possible under various assumptions about the composition of Earth’s early atmosphere
2. Meterorites may also have been source of minerals and organic molecules
Contain amino acids, lipids, simple sugars, uracil
Murchison MeteoriteFell to Earth in so named town in
Australia in 1969large (100 kg) and was quickly retrieved2010 article published in Scientific
American: results of mass spectrometry (separating compounds based on charge & size) have revealed at least 14,000 unique molecules
Abiotic Synthesis of Macromolecules
2009 study showed the abiotic synthesis of RNA monomers can occur spontaneously from simpler precursor molecules
Drip solutions with amino acids (aa) or RNA nucleotides onto hot sand, rock, or clay polymers of aa & RNA (w/out using enzymes or ribosomes)
Protocells (Protobionts)
Basic characteristics of life : reproduction & metabolism:So 1st cells would have had to be able to reproduce which would have required them to have a source of nitrogenous bases, sugars, phosphate groups
Now complex enzymes make this all happen
Vesicles as 1st step?When lipids & other organic molecules added
to water vesicles spontaneously formlipid bilayer (separation of hydrophilic & hydrophobic molecules)
These abiotically produced vesicles “reproduce” and grow on their own.
Clay, like from early Earth will be absorbed into the vesicles
some vesicles demonstrate semi-permeability
Self-Replicating RNARNA (when folded)can act
as enzymeRNA catalysts called: ribozymesSome can make complimentary strands of short pieces of RNA mutations more stable &/or successful
RibozymeOnce self-
replicating RNA possible much easier for further changes to happen.
Once double-stranded DNA appeared it would have been more stable so RNA left with role we see today
