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Science has not provided a step by step recipe for making life.

The Origin of Life. 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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Science has not provided a step by step recipe for making life.

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  1. The Origin of Life 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 “Pick up the tail” 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. Another Experiment Showing Evolution of RNA Beaudry and Joyce (1992) Test-tube selection and reproduction of RNA

  8. Contains promotor region for RNA polymerase

  9. Sprinkle mutations throughout the Tetrahymena ribozyme

  10. Select for RNAs that can cleave a DNA substrate Some mutations increased in frequency Many were selected out

  11. Four mutations increased by > 50%

  12. 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, ribonucleotide synthesis However, can RNA self-replicate? (i.e. can an RNA dependent replicase be found?)

  13. 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?

  14. 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

  15. (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

  16. (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

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

  18. 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……

  19. 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

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

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

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

  23. Evidence for Horizontal Gene Transfer

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

  25. 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

  26. 2 BY Eukaryotic Algae? Michigan Grypania spiralis

  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. Process of Fossilization After remains are buried by sediments: Compression/impression/casts/molds:impressions or casts made before decomposition (like footprints). (2) Permineralized fossils: precipitation of minerals in cells before decomposition. Or Occasionally: (1) Unaltered remains: Frozen , amber embedded, peat bogs.

  30. permineralized fossils amber cast Impression fossil

  31. Fossil Record is Biased Fossilization is higher for organisms that are: Durable and likely to be buried in an anoxic environment (low land or marine habitats) Also, there is temporal and geographic bias: Probability that an organism will be fossilized depends on the geographical area and historical time.

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

  33. 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

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

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

  36. Small subunit RNA most basal earliest fossils

  37. 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

  38. 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!

  39. 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? Mass Extinction of proterozoic fauna? Cloudina

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

  41. Jackson and Cheetham, 1994

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

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