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Threose Nucleic Acid 2/23/11! Something else…! •" Neither the chicken nor the egg came first! Alternative Ideas! •" Transitional forms that were later discarded! Or was it the “egkin”?! Some experiments with peptide nucleic acid! Threose Nucleic Acid (TNA)! (PNA).! PNA: Peptide backbone with bases! •" Threose is one of two sugars with a four- sided ring! Can act as template for polymerization of RNA! •" Fewer issues with incorrect linkages, From activated nucleotides! selection of correct handedness! (Böhler, et al., Nature, 376, 578! •" Replace ribose sugar in RNA with threose! & comments by Piccirilli, pg. 548 17 Aug. 1995! •" Can base pair with RNA! •" Could have preceded RNA! PNA could be simpler to form under prebiotic conditions! Main point is that a simpler thing (not necessarily PNA) ! could have preceded RNA! 1! 2/23/11! Focus on Energy! Membranes! G. Wächtershäuser! Inorganic - organic connection! •" Membranes provide enclosure! FeS2 ! (Iron pyrite)! –"Also fundamental for metabolism! Attracts negatively charged molecules ! •" Membranes never arise from scratch! Surface catalysis provides energy via formation from! –"Always passed down and added to! FeS + H2S! –"All derived from ancestral cell! •" T. Cavalier-Smith proposes membranes! Scene is hot sulfur vents on sea floor! –"Plus nucleic acid formed “ob-cell”! Some successes in simulations! Amino acids formed peptide bonds! –"Merger of 2 ob-cells formed first cell! Thioester World! H O 1." Need precursor to RNA world! H H S H O Thioester! S C. de Duve! C C O 2. !Need energy conversion! In Vital Dust! O !Protometabolism! Thiol + Carboxyl! Background:! H O H H O H O Ester! O Thiols involved in metabolism, particularly in ancient ! C C pathways! O O Hydroxyl + Carboxyl! Also can catalyze ester formation by group transfer! Reactions! e.g. peptide bonds! 2! 2/23/11! Catalytic Multimers! Energy Sources! Basic need is hydrogen atoms! “Multimer” short peptides and esters! C. de Duve! (or electrons in excited states)! ! ! !!(NH2) (OH)! ! !of amino acids and hydroxy acids! + – ! In pure water ! H !!!+ OH more if acidic! H2O! e– + H+ H* excited H! Will form from thioesters. Assume some catalytic ability, lead to protometabolism! Now chlorophyll + sunlight! Transition to Phosphate! On early Earth? ! !! Remember that energy currency in life now is ATP! 1." UV light + Fe+2 ! !Fe+3 + e–! Adenosine Triphosphate! ! ! !e– + H+ H*! H for reactions! used to make bonds, remove H2O! Earlier, inorganic phosphate! – 2." H2S in H2O SH ! !! p–p !diphosphate or polyphosphate! – –2 still involved in ATP reactions !2SH S2 + H2! ! +2 –2 !Fe + S2 + FeS2 !iron pyrite! Thioester - Phosphate - Iron! Multimers Catalysts FeS2! ATP! RNA World! 3! 2/23/11! Clay Life! Other ideas! A. G. Cairns-Smith! Silicate Life? ! !Early Genetic Material! O = Si = O !but O can make another bond instead! A different initial genetic substance + genetic ! O! takeover! silicatesO! Si! O can! provide a variety of minerals! e.g., clay life! O! Layers - clay! Panspermia! Also occasional impurity (Al, Mg, …)! Various versions! Can grow by adding dissolved material ! Tends to copy pattern of impurities in adjacent layers.! Creationism! Could this be a kind of reproduction?! 4! 2/23/11! Defects - different impurity, … (mutations?)! ?! Clay Life ! !Life! Sheets can separate - move - and then! Clay life begins to synthesize, use “organic”! “reproduce”! [carbon] molecules! Clays do have some catalytic activity! Advantages ! !!! Problem! Clay clearly present ! !! How to get to ! Genetic takeover! Simpler genetic structure ! !life as we know it! organics protein/RNA mechanisms! Crystal growth occurs naturally! Clay discarded! Tests! Panspermia! 1." Surviving clay life - unlikely! •" Life arose elsewhere and was delivered here! –"Original idea was bacterial spores! 3." New clay life - maybe in some places! –"Hoyle and Wickramasinghe! 4." Demonstrate in lab! •" Life originates on dust grains, comets, …! –"Or on another planet (meteorites from Not much further development of this idea.! Mars)! •" Directed panspermia! –"Crick and Orgel (tongue in cheek)! –"Earth seeded by intelligent ET! 5! 2/23/11! From “Scientific Creationism” by Henry Morris! Uniformitarianism! Bible! Matter existed ! Matter created by God! in the beginning! in the beginning! Creationism! Sun and stars! Earth before the sun! before the earth! and stars! Land before the oceans! Oceans before the land! •" Traditional biblical literalism! Sun, earth#s first light! Light before the sun! Contiguous atmosphere! Atmosphere between! •" Intelligent design! and hydrosphere! two hydrospheres! –" Seeks evidence of design in complexity! Marine organisms,! Land plants, first life ! first forms of life! forms created! –" Current version of creationist movement! Fishes before fruit trees! Fruit trees before fishes! –" Hoyle and Wickramasinghe later ideas! Insects before birds! Birds before insects! Sun before land plants! •" Life designed by silicon chip! Land vegetation before the sun! •" Where did the chip come from?! Reptiles before birds! Birds before reptiles! •" None of these are scientific theories! Woman before man! Man before woman! –" The key is whether they can be tested! (by genetics)! (by creation)! Rain before man! Man before rain! “Creative” processes still continuing! Creation completed! Struggle and death necessary! Man, the cause of struggle and death! antecedents of man! Myth (Mythos)! Science (Logos)! Revealed truth unquestioned! Provisional truth! Skepticism essential! Artificial Life?! Two strands in! (falsifiability)! Creation Myths:! Method important! •" Polio virus constructed from “scratch” in 2002! Creator Spirit in! Interplay:! •" Have they created life?! “Western” Matter! •" Viruses are parasites, but “protolife”? ! “Eastern”! Theory Experiment/! •" Entire bacterial genome (not the bacterium) observation ! constructed from scratch in 2008! Creationism spontaneous ! –"582,970 base pairs! generation! Paradigm! •" Could we create a bacterium from scratch? self-organization ! Chemical Evolution! of matter! •" Far too complex for current abilities! related?! 6! 2/23/11! Negatives for replacing carbon with silicon:! Exotic Life Forms?! a." C - C bond ! !2 × stronger than Si - Si! b." Si - O !stronger than Si - Si! Antidote to Earth Chauvinism! ! !forms silicates, not .. Si - Si - Si …! c." C forms multiple bonds !(e.g. ! C ≡ N)! 1." Different organic molecules (e.g., PNA)! !possibility of life based on other polymers! !Si rarely does! d." C + O forms !CO or CO2 ! (gas - further reacts)! 2." Not based on Carbon! !Si + O ! !SiO2 ! !- silicate rocks! !Silicon (Si) instead of Carbon?! !(also 4 bonds)! !& more (135 ×) more abundant on Earth! ⇒ !Si unlikely to replace C in “organic” molecules! !but could forms of SiO2 produce clay life?! ! !! 3. Other Solvents! 4. Non-chemical life? !! Earth: !Liquid water !273-373 K! Disembodied intelligence! Alternatives: ! !!Tfreeze! !Tboil! Black cloud life?! Ammonia ! !NH3 ! !195 ! !240! Methyl Alcohol !CH3OH !179 ! !338! Methane ! !CH4 ! ! 91 ! !109! Other forces! -15 Ethane ! !C2H6 ! ! 90 ! !184! Strong nuclear force? ! !τ ~ 10 s! Water is better solvent! Gravity?! Also better for temperature regulation! But others could play a role in colder zones! extend CHZ? ! 7! 2/23/11! Estimates for fl Estimates for fl •" Possible range is very large! •" Arguments for small value! –"Perhaps 10–6 (one in a million) to 1 (all)! –"May need more than liquid water! •" Arguments for large value! •" Large tides, so large moon! –"Life part of overall evolution in complexity! •" Dry land (for polymerization)! –"Arises naturally from interplay of forces! –"Life may be a fluke! •" A rare statistical event! Can we estimate fl from early origin of life?! What is your choice and why?! Very ancient microfossils !(now disputed)! ⇒ !Life arose as early as 3.8 × 109 yr ago! •" The most uncertain factor so far (fl)! ![soon after end of heavy bombardment]! •" Think about various ideas for origin of life! •" Put together a plausible story for the origin of Lineweaver & Davis argued:! life! –" Can use parts of various ideas, but need to be consistent.! Early origin ⇒ fl > 0.33! For suitable planets older than 1 × 109 yrs.! Statistics from one example!! Others have disputed this conclusion! 8!.
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