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Take home message:

The Origin of Life. Take home message:. Science has not provided a step by step recipe for making life. Science has provided data to support some of the possible or necessary steps. What defines life?. Has a genotype (genetic blueprint that stores and transmits information).

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  1. The Origin of Life Take home message: Science has not provided a step by step recipe for making life. Science has provided data to support some of the possible or necessary steps.

  2. What defines life? Has a genotype (genetic blueprint that stores and transmits information). Has form and function (i.e. phenotype: expression of genotype). 3. Life evolves.

  3. Oparin-Haldane Model for the Origin of Life Simple moleculesComplex polymers H20, NH3, CO2nucleotides, amino acids Nucleic acid RNA, DNA, protein Cellular life

  4. RNA: Early Life Forms? Intron in Tetrahymena phenotype genotype Altman and Cech

  5. Evidence for RNA as an Early Life Form Stores information and is catalytic Basic component of: a. ribosomes and tRNA b. energy carrier molecules (ATP, GTP) c. electron-transfer cofactors (NAD, SAM)

  6. RNA Evolves Natural Selection favored shorter RNA sequences over time, as a consequence the bacteriophage became less infectious. faster replication time after a few serial transfers Mills et al., 1967

  7. Test Tube Experiments Show: (1) RNA can evolve (via artificial selection) (2) Ribozymes have been selected to perform a number of protein-like tasks: phosphorylation, aminoacyl transfer, peptide bond formation, carbon-carbon bond formation However, can RNA self-replicate? (i.e. can an RNA dependent replicase be found?)

  8. But Where Did RNA Come From? Seems unlikely that RNA can be made in one step from inorganic molecules. Did a self-replicating system predate RNA? So, before RNA…. Where did simple organic molecules originate?

  9. Did Earth Have All of the Ingredients? Oparin-Haldane Model Simple moleculesComplex polymers H20, NH3, CO2nucleotides, amino acids (1) Was the prebiotic environment permissive? (2) How is this achieved in H20 given hydrolysis? Nucleic acid RNA, DNA, protein (3) How were membranes assembled? Cellular life

  10. (1) Was the pre-biotic environment permissive? Miller (1953): Assuming Atmosphere Reducing H2, CH4, and NH3 amino acids, sugars, nucleotides Mojzsis et al. (1999): Assuming Atmosphere Oxidizing C02, N2: aldehydes (ribose sugar in RNA) Oro’ (1961): Nucleotides from inorganic molecules HCN, NH3 adenine

  11. (2) How is this achieved in H20 given hydrolysis? Polynucleotides 40 nucleotides long have been synthesized using clay as a catalyst. montmorillonite, illite, and hydroxylapatite

  12. Panspermia Hypothesis: Life originated elsewhere and traveled to Earth. Murchison Meteorite (contained amino acids) Martian bacteria?

  13. The History of Large Impacts on Earth and It’s Moon Did meteors bring molecules necessary for life to earth? Moon (red) Earth (blue) Yes, but what about friction……

  14. When was earth hospitable enough for life to evolve? Apatite crystals (20 mm) (calcium phosphate minerals Banded iron formation Greenland 3.85 bya carbonaceous speck with high C12 to C13 ratio magnatite silicate bands carbonaceous material

  15. What was the oldest common ancestor like? (cenancestor) Used DNA and amino acids to make proteins Cellular Structurally similar to filamentous cyanobacteria.

  16. Oldest known fossils of living organisms 3.465 bya Primaevifilum amonenum Primaevifilum conicoterminatum (Schopf, 1993)

  17. Phylogeny of all living organisms (small-subunit rRNA) Woese (1996)

  18. Aminoacyl tRNA synthase gene families used to root

  19. Brown and Doolittle, 1997

  20. Horizontal Gene Transfer: transfer of genetic information between the genomes of different species. Gene Tree Species Tree

  21. Evidence for Horizontal Gene Transfer

  22. 18% of the E. coli genome arrived in last 100 my. Lawrence and Ochman, 1998 Strain = MG1655

  23. Will it be possible to reconstruct the branching sequence at the root of the tree of life?

  24. 0.85-0.9 BY Siberia 0.59 BY China Fossils allow estimation of the divergence time of eukaryotes. 1.4-1.5 BY Australia

  25. 2 BY Eukaryotic Algae? Michigan Grypania spiralis

  26. Support for the endosymbiont hypothesis

  27. Cambrian Explosion Evolutionary Diversification 543-506 mya

  28. Cambrian Explosion: All major body plans first made an appearance in the fossil record during a 40 my period

  29. Ediacaran Fuanas entirely soft-bodied organims from 565 mya Brachina delicata Spriggina floundersi (sponges, jellyfish, comb jellies)

  30. New Fossil Finds are Pushing Back Estimates of Divergence Times Fossil embryos suggest precambrian diversification of bilateralians (Xiao et al. 1998) Possible flatworm or arthropod zygotes and embryos

  31. Burgess Shale Faunas 520 mya (trilobites, segmented worms, molluscs, chordates)

  32. New Fossil Finds are Pushing Back Estimates Of Animal Divergence Times (Shu et al. 1999) 530 my Cambrian vertebrate: Haikouichthys eraicunensis

  33. Small subunit RNA most basal earliest fossils

  34. Cambrian: Diversification of Animal Body Plans Symmetry a. Radial or asymmetrical: Diploblast (endoderm and ectoderm) b. Bilateral: Triploblast (endo, ecto, and mesoderm) Coelomate i. Protostomes ii.Deuterostomes Also: segmented body plans, shells, exoskeletons, appendages, notochords

  35. Was the Cambrian Explosion Explosive? Molecular clock estimates suggest 900-1200 my divergence times for the major animal groups (Wray et al., 1996). i.e. Major animal lineages were established pre - Cambrian. if so There should be fossil evidence!

  36. What Caused the Cambrian Explosion? Environmental change: Higher oxygen may have allowed for larger, energetically costly morphologies. Diversification of phytoplankton may have spurred the evolution of herbivores and predators. Genetic changes? Cloudina

  37. Stasis Is Evolution Too! Darwin’s View Punctuated Equilibrium (Gould and Eldridge, 1972)

  38. Jackson and Cheetham, 1994

  39. Why Does Stasis Occur? not for lack of genetic variation dynamic stasis in pliocene bivalves

  40. Extinction Mass extinctions account for 4% of all extinctions The big 5 of the phanerozoic.

  41. Iridium concentration in clay layer at KT Boundary • Other evidence: • Chicxulub crater • Microtektites • Soot deposits • Evidence of • tsunami

  42. Habitat Destruction Current extinctions are occurring at 100 - 1000 times the normal or background rate. May et al. 1995, Pimm et al., 1995 Human Population by 2050 = 13 billion

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