Chapter 19-1 ~ Origin and History of Life

1. Chapter 19-1 ~ Origin and History of Life Close your eyes and imagine our planet 4 billion years ago… what do you see? How is it different from today?

2. Early history of life • Solar system~ 12-10 billion years ago (bya) • Earth~ 4.6 bya • Life~ 3.5 to 4.0 bya • Prokaryotes~ 3.5 to 2.0 byastromatolites • Oxygen accumulation~ 2.7 byaphotosynthetic cyanobacteria • Eukaryotic life~ 2.1 bya • Muticelluar eukaryotes~ 1.2 bya • Animal diversity~ 543 mya • Land colonization~ 500 mya

3. Interesting facts about the origins of life • There is more metabolic diversity among the two kingdoms of prokaryotes then all the eukaryotes combined • Bacteria separated from Achaea bacteria early on in the history of life ~2 to 3 B.Y.A. • Fungi are more closely related to animals than they are to plants • Fungi and plants worked together to symbiotically colonize land… which happened fairly recently on the geologic time scale…. 475 million years ago

4. Evidence of early life • Stromatolites are fossilized layers of sediment formed from the migration of bacteria upward

5. Early fossils

6. The Origin of Life • Spontaneous generation vs. biogenesis (Pasteur) • The 4-stage Origin of life Hypothesis: • 1- Abiotic synthesis of organic monomers • 2- Polymer formation • 3- Origin of Self-replicating molecules • 4- Molecule packaging (“protobionts”)

7. Origin of Life

8. Organic monomers/polymer synthesis • Abiotic Synthesis Model Oparin /Haldane (1920) working independently hypothesized that simple monomers (monosaccharides, amino acids, and nucleotides) could be synthesized from inorganic molecules in the early atmosphere in the presence of volcanic vapors (reducing atmosphere) with lightning , UV radiation and no Oxygen. • Early atmosphere probably consisted of Water vapor, N2, and CO2 with small amounts of hydrogen gas (H2), methane (CH4), ammonia (NH3), hydrogen sulfide (H2S) and carbon monoxide (CO).

9. Testing the abiotic synthesis hypothesis • Miller/Urey (1953)experiment: • Placed a mixture resembling a strongly reducing atmosphere of water , hydrogen gas (H2), methane (CH4), and ammonia (NH3)… heated it and circulated it past an electric spark for a week. • Results: A variety of amino acids, nitrogen bases, & ATP formed

10. Criticism of the Miller/Urey experiment • Placed ammonia (NH3) in the mixture… not a major component of the early atmosphere… (N2) was plentiful but inert unlike ammonia • Where was ammonia being synthesized in large amounts on primitive earth? • Oparin /Haldane hypothesis was modified to include iron-nickel sulfides produced in the extreme heat of hydrothermal vents that act as catalysts for froming both ammonia, amino acids, and even peptide chains!

11. Polymers Evolve • Fox amino acids can polymerize forming proteinoids, small polypeptides with some catalytic capabilities, from organic monomers dripped on hot sand, clay or rock. Fox also demonstrated in laboratory the formation of microspheres, small cell like structure consisting only of protein, from the coagulation of proteinoids. • Fox proposed the “Protein First Hypothesis” and stated that protein enzymes came before the genes that code for proteins. • This is supported also by the fact that DNA replication is highly dependent upon many protein enzymes.

12. Polymers Evolve • Cairns-SmithPolypeptides and RNA Nucleotides came to be at the same time on a warm bed of clay that consisted of iron and zinc catalysts. Cairns-Smith envisioned the RNA directing the polypeptides to replicate more RNA which would code for more polypeptides. • Cech/Altman RNA first hypothesis… RNA was both the substrate and the enzyme (acting like a polypeptide/protein) creating a world in which all the genes were RNA and not DNA.

13. Protocells or Protobionts…not quite a cell but it is a start… It has a membrane A simple heterotrophicprotocell could have contained RNA acting as a gene and an enzyme…Some simple form of Glycolysis may have been occurring to produce an ATP like molecule for energy Provides a safe place for chemical reactions to occur!

14. RNA the Origin of Life

15. Evolution of the Cell

16. The origin of heredity information made Darwinian evolution possible • Once a membrane formed around the RNA that was producing protein, now there was a selective advantage and the inheritance was possible • RNA eventually gave way to the more stable DNA… the “RNA World” gave way to the “DNA World”!

17. Panspermia • The idea that Earth was seeded from life from outer space • Amino acids are found in some meteors that strike our planet today • Early Earth was bombarded constantly with meteors

18. Is life restricted to Earth… What is your opinion?