Lecture 4 Origins Evolution of Life 1 Prebiotic earth 2 Early Life a Chemicals formed in ocean increasing chemical complexity a Microbial organisms 3 5 2 6 BYA b Multicellular organisms by 1 BYA 3 Advanced life a Complex life forms 550 MYA i Aquatic and terrestrial animals and plants 4 What came first Metabolism or information a Metabolism first i Primordial soup put random stuff together and get out organic molecules ii Iron sulfur world hypothesis superheated water in magma chambers dissolves minerals and sulfides expelled acidic water cools and minerals and sulfides precipitate out H2S released from hydrothermal vents created activated trolite which is catalyst for citric acid cycle 1 Superheated water in magma chambers dissolves lots of minerals sulfides and is expelled out highly acidic 2 Water cools and they precipitate out 3 H2S expelled out from hydrothermal vents reduces pyrite near vent 4 This reduced pyrite trolite is a catalyst for chemical rxns with organic molecules in citric acid cycle iii Lab experiments show citric acid cycle can occur with just those ingredients but with CO not CO2 iv Evidence metal atoms form core for key enzymes 1 Hemoglobin Fe Cytochrome C Cu Fe Nitrogenase Fe Mo 2 Thermophilic closer to root of tree of life b Info first i Chemical rxns not reliably reproducible without info system ii Cant evolve without passing on info iii Just because rxns are happening doesn t mean theyre reproducible 1 No info system setting rxns no evolution to increase fit iv Why 1 Store info about how to survive in enviro a Code for set of enzymes 2 Improve survival a DNA RNA 3 Need genetic info to make enzymes v Info flow similar in present day organisms genetic code common to nearly all organisms 1 Implies universal genetic code evolved from LUCA vi Properties of info system 1 Stability constancy of info vs mutations need during cell replication 2 Fidelity accuracy of info readout fidelity vs reading errors need during translation to proteins 3 Redundancy number of info copies vs mutations 4 Entropy degradation of info vii RNA can be more easily degraded 1 Single stranded more error prone 2 No redundancy no double stand 3 Ribose more reactive than deoxyribose 4 Autocatlytic 5 DNA reverse of all of these viii RNA is primitive genetic material RNA world 1 Carries genetic info 2 Can catalyze rxns like proteins not present yet need proteins to make 3 Higher evolvability need to evolve quickly to fast changing proteins RNA fixes this environments 5 Four requirements for life i Abiotic synthesis 1 Make small organic molecules ii Join building blocks into macromolecules 1 Proteins DNA RNA iii Spontaneous organization 1 Form protobionts iv Self replication 1 Make copies for inheritance b Chemical evolution i No O2 in early atmosphere ii Simple molecules reacted to make organic compounds c Cold version Abiotic organic molecules i Arrive on meteors ii Used atmospheric substituents like those near Jupiter in experiments iii Asteroid had 6 amphipathic lipids d Hot version i Organic molecules made near geothermal vents by presence of metal catalysts 6 How did the rxns happen a Inorganic substrate catalyzed by metal atoms 7 Protobionts 8 Spontaneous organization a Hydrophobic interactions of amphipathic lipids a Aggregations of abiotically produced molecules like forerunners of living organisms b Biological order at expense of universal order allows for unique internal chemistry 9 RNA world a RNA was the main type of information system in the early world i Can be an enzyme splices itself experiment where isolated RNA and still spliced experiment on tetrhymena ii Susceptible to mutations which would be beneficial in a rapidly changing world like the early Earth tRNA and ribosomes evidence RNA can be an enzyme iii 10 Proton gradients a At alkaline thermal vents in deep ocean b Alkaline effluent into rock allowed early cells to take advantage of moving protons alkaline hydrothermal vents are around for much longer than black smokers In rockio means evolution of DNA world in these rocks of the alkaline hydrothermals c ATP synthase shared by all life d e Free living cells evolved with lipids and cell walls to leave the rock f Rock cells allowed high concentrations of monomers to build up i Can polymerize to make proteins nucleic acids allowing info storage to develop ii Lipid and cell membranes came later 1 Maybe arose twice once for bacteria another for archaea 11 Summary a LUCA developed before divergence b Bacteria i Universal genetic code ii Ribosome RNA translation iii DNA transcription iv ATP synthase i Peptidoglycan cell wall ii Cell membrane 1 Ester linked 2 Unbranched lipids iii DNA replication vs 1 c Archaea and Eukarya i Cell wall without peptidoglycans ii Cell membrane is 1 Ether linked 2 Branched lipids iii DNA replication vs 2 d Eukarya only i No cell wall ii Cell membrane 1 Ester linked 2 Unbranched lipids iii DNA replication vs 2
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