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



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


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