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Biology, Seventh Edition Solomon • Berg • Martin The Origin of the first cells Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh Edition CHAPTER 20 The Origin and Evolutionary History of Life • Conditions on early Earth • Age of Earth is ~4.6 billion years • Atmosphere had little free O2 –Included CO2, H2O, CO, H2, N2 –Maybe also NH3, H2S, CH4 Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh Edition CHAPTER 20 The Origin and Evolutionary History of Life • Requirements for chemical evolution to produce life • Absence of oxygen • Energy • Chemical building blocks • Sufficient time Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh Edition CHAPTER 20 The Origin and Evolutionary History of Life • Prebiotic soup hypothesis • Molecules formed near the Earth’s surface • Sugars, nucleotides, amino acids formed spontaneously Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh Edition CHAPTER 20 The Origin and Evolutionary History of Life Miller-Urey experiment Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh Edition CHAPTER 20 The Origin and Evolutionary History of Life • Origin of cells • Spontaneous assembly of small organic molecules into macromolecules • Deep sea vent w/ iron sulfide for energy Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh Edition CHAPTER 20 The Origin and Evolutionary History of Life • Microspheres • Formed from water and polypeptides • Electric gradient on surface • Selective permeability Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh Edition CHAPTER 20 The Origin and Evolutionary History of Life Microspheres – a type of protobiont (early lipid membrane) Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh Edition CHAPTER 20 The Origin and Evolutionary History of Life • RNA for early genetic inheritance. • Self-replicating RNA molecules • Function as both enzyme and substrate for replication –Ribozyme is enzymatic RNA • First step in evolution of the DNA / RNA / protein system Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh Edition CHAPTER 20 The Origin and Evolutionary History of Life • Directed evolution • Large pool of RNA molecules with different sequences • Selected for ability to catalyze a reaction • Amplify / mutate / repeat Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh Edition CHAPTER 20 The Origin and Evolutionary History of Life Directed evolution Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh Edition CHAPTER 20 The Origin and Evolutionary History of Life • In the RNA world, ribozymes catalyzed protein synthesis • DNA formed from double strands of RNA • DNA more stable than RNA Copyright © 2005 Brooks/Cole — Thomson Learning The prokaryotes The first cells Image Credits Gary Gaugler Bacillus anthracis Image Credits: Thermophilic archaebacteria Biology, Seventh Edition CHAPTER 20 The Origin and Evolutionary History of Life • The first cells • Heterotrophs that feed on organic molecules • Anaerobic fermentation process to obtain energy Copyright © 2005 Brooks/Cole — Thomson Learning Origins Evidence for prokaryotic cells is found as early as 3.9 billion years ago The prokaryotes had the Earth to themselves for another 2.4 billion years Prokaryotes show an extraordinary diversity of biochemistry Structurally prokaryotes are quite small and simple (1-10µm in diameter). © 2010 Paul Billiet ODWS Where? “(a) warm little pond, with all sorts of ammonia and phosphoric salts, lights, heat, electricity, etc. present, so that a protein compound was chemically formed ready to undergo still more complex changes” Charles Darwin (1871) organic compounds would accumulate in the Earth's oceans until they "reached the consistency of hot, dilute soup." JBS Haldane (1929) Deep sea hydrothermal vents Volcanoes Outer space. © 2010 Paul Billiet ODWS Biology, Seventh Edition CHAPTER 20 The Origin and Evolutionary History of Life Endosymbiont theory- evolution of eukaryotes • Eukaryotes arose from prokaryotes: a large anaerobic cell teams up with an aerobic cell –Mitochondria and chloroplasts derived from prokaryotes –Ingested but not digested –Reproduced along with host cell Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh Edition CHAPTER 20 The Origin and Evolutionary History of Life The evidence for endosymbiosis • Certain eukaryotic organelles have their own DNA • Single naked loop of DNA, like the prokaryotes • The amount of hereditary information is a lot less than free-living prokaryotes • These organelles have their own ribosomes • Smaller (70S) than those in the cytoplasm (80S) • The ribosomes of mitochondria and chloroplasts are the same size as those in prokaryotes • The protein synthesis of these organelles is semiindependent of that taking place in the cytoplasm • It is inhibited by the same antibiotic that affects prokaryotes (chloramphenicol). © 2010 Paul Billiet ODWS Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh Edition CHAPTER 20 The Origin and Evolutionary History of Life Endosymbiont theory Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh Edition CHAPTER 20 The Origin and Evolutionary History of Life The structural evidence • These organelles are found in membrane envelopes • As though they were captured in a vacuole or vesicle by a larger cell • These organelles are about the same size as a prokaryotic cell. Image Credit: Mitochondrion © 2010 Paul Billiet ODWS Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh Edition CHAPTER 20 The Origin and Evolutionary History of Life Mitochondria • These represent an aerobic prokaryote that took up residence in a larger cell • These are found in all the eukaryotic kingdoms (plants, animals, fungi and protoctista). Image Credit: Mitochondrion © 2010 Paul Billiet ODWS Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh Edition CHAPTER 20 The Origin and Evolutionary History of Life Chloroplasts These represent a cyanobacterium type of prokaryote that was trapped in ancestral plants and some protoctista Image Credit: Cyanobacterium heterocyst © 2010 Paul Billiet ODWS Copyright © 2005 Brooks/Cole — Thomson Learning