* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Sept24_26_07 - Salamander Genome Project
Gel electrophoresis wikipedia , lookup
Gene regulatory network wikipedia , lookup
Promoter (genetics) wikipedia , lookup
Genetic engineering wikipedia , lookup
Point mutation wikipedia , lookup
Real-time polymerase chain reaction wikipedia , lookup
Messenger RNA wikipedia , lookup
Non-coding DNA wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Amino acid synthesis wikipedia , lookup
Vectors in gene therapy wikipedia , lookup
Transcriptional regulation wikipedia , lookup
RNA interference wikipedia , lookup
RNA polymerase II holoenzyme wikipedia , lookup
Eukaryotic transcription wikipedia , lookup
Silencer (genetics) wikipedia , lookup
Polyadenylation wikipedia , lookup
Genetic code wikipedia , lookup
Gene expression wikipedia , lookup
Biochemistry wikipedia , lookup
Deoxyribozyme wikipedia , lookup
RNA silencing wikipedia , lookup
Epitranscriptome wikipedia , lookup
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? 1. Has a genotype (genetic blueprint that stores and transmits information). 2. Has form and function (i.e. phenotype: expression of genotype). 3. Life evolves. Oparin-Haldane Model for the Origin of Life Simple molecules Complex polymers H20, NH3, CO2 nucleotides, amino acids Nucleic acid RNA, DNA, protein Cellular life RNA: Early Life Forms? Intron in Tetrahymena phenotype genotype “Pick up the tail” Altman and Cech Evidence for RNA as an Early Life Form 1. Stores information and is catalytic 2. Basic component of: a. ribosomes and tRNA b. energy carrier molecules (ATP, GTP) c. electron-transfer cofactors (NAD, SAM) RNA Evolves faster replication time after a few serial transfers Natural Selection favored shorter RNA sequences over time, as a consequence the bacteriophage became less infectious. Mills et al., 1967 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?) 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? Did Earth Have All of the Ingredients? Oparin-Haldane Model Simple molecules H20, NH3, CO2 Complex polymers (1) Was the prebiotic environment permissive? nucleotides, amino acids (2) How is this achieved in H20 given hydrolysis? Nucleic acid RNA, DNA, protein (3) How were membranes assembled? Cellular life (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 (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 Panspermia Hypothesis: Life originated elsewhere and traveled to Earth. Martian bacteria? Murchison Meteorite (contained amino acids) The History of Large Impacts on Earth and It’s Moon Moon (red) Earth (blue) Did meteors bring molecules necessary for life to earth? Yes, but what about friction…… When was earth hospitable enough for life to evolve? Banded iron formation Greenland 3.85 bya magnatite silicate bands Apatite crystals (20 mm) (calcium phosphate minerals carbonaceous material carbonaceous speck with high C12 to C13 ratio What was the oldest common ancestor like? (cenancestor) a. Used DNA and amino acids to make proteins b. Cellular c. Structurally similar to filamentous cyanobacteria. Oldest known fossils of living organisms 3.465 bya Primaevifilum amonenum (Schopf, 1993) Primaevifilum conicoterminatum Phylogeny of all living organisms (small-subunit rRNA) Woese (1996) Aminoacyl tRNA synthase gene families used to root Brown and Doolittle, 1997 • Horizontal Gene Transfer: transfer of genetic information between the genomes of different species. Species Tree Gene Tree Evidence for Horizontal Gene Transfer 18% of the E. coli genome arrived in last 100 my. Lawrence and Ochman, 1998 Strain = MG1655 Will it be possible to reconstruct the branching sequence at the root of the tree of life? 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 2 BY Eukaryotic Algae? Michigan Grypania spiralis Support for the endosymbiont hypothesis Cambrian Explosion Evolutionary Diversification 543-506 mya Cambrian Explosion: All major body plans first made an appearance in the fossil record during a 40 my period Ediacaran Fuanas entirely soft-bodied organisms from 565 mya Brachina delicata Spriggina floundersi (sponges, jellyfish, comb jellies) 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 Burgess Shale Faunas 520 mya (trilobites, segmented worms, molluscs, chordates) New Fossil Finds are Pushing Back Estimates Of Animal Divergence Times (Shu et al. 1999) 530 my Cambrian vertebrate: Haikouichthys eraicunensis Small subunit RNA most basal earliest fossils 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 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! 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 Stasis Is Evolution Too! Darwin’s View Punctuated Equilibrium (Gould and Eldridge, 1972) Jackson and Cheetham, 1994 Why Does Stasis Occur? not for lack of genetic variation dynamic stasis in pliocene bivalves Extinction Mass extinctions account for 4% of all extinctions The big 5 of the phanerozoic. Iridium concentration in clay layer at KT Boundary Other evidence: • Chicxulub crater • Microtektites • Soot deposits • Evidence of tsunami 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