1. How did life begin?

2. Conditions on early Earth made the origin of life possible
4 main stages could have produced very simple cells:
The abiotic synthesis of small organic molecules
Joining of these small molecules into macromolecules (proteins, nucleic acids)
Packaging of these macromolecules into protocells, droplets with membranes that maintained internal chemistry different from their surroundings
Origin of self-replicating molecules that eventually made inheritance possible 2

3. Synthesis of Organic Cpds on early Earth
Planets of our solar system formed ~ 4.6 billion yrs ago
1st few hundred million yrs conditions would not have allowed life on Earth

4. 1st Atmosphere
Collisions would have vaporized any water preventing seas from forming
Atmosphere thick with gases released from volcanic activity

5. 1st Atmosphere
1920’s: Oparin (Russian chemist) and Haldane (British scientist) each came to conclusion early atmosphere was reducing environment (gain e-) in which organic cpds could have formed from simpler molecules

6. In 1953, Stanley Miller and Harold Urey conducted lab experiments that showed that the abiotic synthesis of organic monomers (amino acids) in a reducing atmosphere is possible. Rain brings to earth and sea
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7. Miller & Urey’s Experiment

8. 1st Organic Compounds Energy sources: Lightening Thermal energy
Intense UV radiation

9. The key building blocks of life are not hard to come by…
Amino acids have also been found in meteorites
RNA monomers have been produced
spontaneously from simple molecules
In water, lipids and other organic molecules can spontaneously form vesicles with a lipid bilayer
Vesicles exhibit simple reproduction
Resultprotocells
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10. Miller & Urey’s Results

11. Miller & Urey’s Results
Have 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 cpds

12. Miller-Urey Experiment demonstrates:
Abiotic synthesis of organic molecules is possible under various assumptions about the composition of Earth’s early atmosphere
Meterorites may also have been source of minerals and organic molecules
Contain amino acids, lipids, simple sugars, uracil

13. Murchison Meteorite
Fell to Earth in so named town in Australia in 1969
large (100 kg) and was quickly retrieved
2010 article published in Scientific American: results of mass spectrometry (separating cpds based on charge & size) have revealed at least 14,000 unique molecules

14. 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)

15. Protocells 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

16. Vesicles as 1st step?
When lipids & other organic molecules added to water  vesicles spontaneously form
lipid bilayer (separation of hydrophiloic & 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

17. Self-Replicating RNA RNA can act as enzyme
RNA catalysts called: ribozymes
Some can make complimentary strands of short pieces of RNA  mutations  more stable &/or successful

18. Ribozyme
Once 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

19. an index of vesicle number
Figure 25.3
0.4
Precursor molecules plus
montmorillonite clay
an index of vesicle number
Relative turbidity,
0.2
Precursor
molecules only 20 40 60
Time (minutes)
(a) Self-assembly
1 m
Vesicle
boundary
Figure 25.3 Features of abiotically produced vesicles.
20 m
(b) Reproduction
(c) Absorption of RNA 19

20. Why the 2 spikes in oxygen?
Most atmospheric oxygen (O2) is of biological origin
1,000
100 10 1
(percent of present-day levels; log scale)
Atmospheric O2
0.1
“Oxygen
revolution”
0.01
Figure 25.8 The rise of atmospheric oxygen.
0.001
0.0001
Time (billions of years ago)
Photosynthesis and the Oxygen Revolution 20

21. First: ancient cyanobacteria
Second: eukaryotic cells containing chloroplasts
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22. How did we get beyond bacteria?
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23. The First Eukaryotes The endosymbiotic theory
An endosymbiont is a cell that lives within a host cell
Lynn Margulis 23

24. Plasma membrane Cytoplasm DNA Ancestral prokaryote Nucleus Endoplasmic
Figure
Plasma membrane
Cytoplasm
DNA
Ancestral
prokaryote
Nucleus
Endoplasmic
reticulum
Nuclear envelope
Figure 25.9 A hypothesis for the origin of eukaryotes through serial endosymbiosis. 24

25. heterotrophic eukaryote
Figure
Plasma membrane
Cytoplasm
DNA
Ancestral
prokaryote
Nucleus
Endoplasmic
reticulum
Nuclear envelope
Aerobic heterotrophic
prokaryote
Figure 25.9 A hypothesis for the origin of eukaryotes through serial endosymbiosis.
Mitochondrion
Ancestral
heterotrophic eukaryote 25

26. heterotrophic eukaryote Ancestral photosynthetic
Figure
Plasma membrane
Cytoplasm
DNA
Ancestral
prokaryote
Nucleus
Endoplasmic
reticulum
Photosynthetic
prokaryote
Mitochondrion
Nuclear envelope
Aerobic heterotrophic
prokaryote
Figure 25.9 A hypothesis for the origin of eukaryotes through serial endosymbiosis.
Mitochondrion
Plastid
Ancestral
heterotrophic eukaryote
Ancestral photosynthetic
eukaryote 26

27. What evidence would support an endosymbiotic origin of mitochondria and plastids?
Inner membranes are similar to plasma membranes of prokaryotes
Division is similar in these organelles and some prokaryotes
These organelles transcribe and translate their own DNA
Their ribosomes are more similar to prokaryotic than eukaryotic ribosomes
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