chemical evolution and the first cells
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Chemical Evolution and The First Cells. Big Bang?. Earth is approx. 4.6 billion years old Formed as a result of the Big Bang which resulted in formation of universe approx. 15 bya NOTE: Currently the Big Bang theory is being challenged by physicists such as Stephen Hawkings. Early Earth.

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big bang
Big Bang?
  • Earth is approx. 4.6 billion years old
    • Formed as a result of the Big Bang which resulted in formation of universe approx. 15 bya
    • NOTE: Currently the Big Bang theory is being challenged by physicists such as Stephen Hawkings
Early Earth
  • Atmosphere: CO2, H2O, CO, H2, N2
  • UV radiation
  • – broke down NH3, H2S, & CH4 rapidly
  • Little to no free oxygen (O2)
4 requirements for chemical evolution of life
4 Requirements for Chemical Evolution of Life:
  • Little to no free O2
  • Source of energy
  • Presence of chemical building blocks
  • Time
how did life 1 st form

How did life 1st form?

2 theories regarding formation of organic molecules

prebiotic soup hypothesis
Prebiotic Soup Hypothesis
  • Life began at earth’s surface
  • 1st proposed by Oparin and Haldane in 1920s
    • Organic molecules could form spontaneously
    • Oparin hypothesized that these molecules would accumulate in shallow seas
1950s – Miller-Urey experiment
  • Evidence since Oparin’s time indicates organic polymers form on rock or clay surfaces
iron sulfur world hypothesis
Iron-Sulfur World Hypothesis
  • Life began at hydrothermal vents
  • Hot water, CO, minerals
  • Better protected from meteorites at bottom of ocean
  • Testing is difficult
evolution of first cells
Evolution of first cells
  • Could polymers spontaneously organize into more complex structures?
  • Evidence:
    • Protobionts
    • Microspheres
  • How could “pre-cells” make the jump to become living cells?
self replicating molecules
Self-replicating Molecules
  • Currently information flows from

DNA  RNA  protein

  • RNA world model states RNA was 1st info molecules
    • RNA has catalytic properties (ribozymes)
RNA arose 1st, catalyzed own replication
  • RNA also catalyzed protein synthesis
  • Perhaps RNA made double-stranded copies of itself
  • Natural Selection at molecular level:
    • DNA became info storage molecule
    • RNA remains involved in protein synthesis
    • Protein enzymes catalyze most cellular reactions
evidence of biological evolution
Evidence of Biological Evolution
  • Fingerprints of organic C in rock from 3.8 bya
  • Microfossils (?) from 3.5 bya
  • Stromalites
first cells
First Cells
  • Prokaryotes
  • Heterotrophs
  • Anaerobes
    • Ferment organic compounds to yield ATP without oxygen
natural selection in 1 st cells
Natural Selection in 1st cells
  • As organic molecules used up, only certain organisms could survive
  • Early photosynthesis probably split H2S instead of H2O, releasing S instead of O
  • 1st to split H2O in photosynthesis were cyanobacteria
build up of o 2 in atmosphere affected life profoundly
Build up of O2 in atmosphere affected life profoundly
  • 2 bya
  • Many obligate anaerobes perished
    • Some survive in places O2 didn’t reach
    • Some anaerobes neutralize O2
  • Aerobes evolved respiratory pathways to extract more energy from food with O2, selective advantage
Aerobic Respiration stabilized levels of CO2 and O2 in the atmosphere
  • A second consequence of photosynthesis: build up of the ozone layer
  • Once O2 builds up and ozone layer forms, conditions no longer support abiotic synthesis of molecules
endosymbiont theory
Endosymbiont Theory
  • Explains the appearance of eukaryotic organisms 2.2 bya
  • Organelles such as mitochondria and chloroplasts originated from mutualistic relationships:
    • Mitochondria – aerobic bacteria living within anaerobic cells
    • Chloroplasts – photosynthetic bacteria living within heterotrophic bacteria
evidence of endosymbiosis
Evidence of Endosymbiosis
  • Have own circular DNA
  • Can grow and reproduce on their own
  • Size of prokaryotic cells
  • Double membrane
  • Limited protein synthesis
  • Affected by antibiotics that affect pro- but not eukaryotes