Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh Edition Solomon Berg Martin The Origin of the first cells

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 20 The Origin and Evolutionary History of Life Conditions on early Earth Age of Earth is ~4.6 billion years Atmosphere had little free O 2 –Included CO 2, H 2 O, CO, H 2, N 2 –Maybe also NH 3, H 2 S, CH 4

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 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 EditionCHAPTER 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 EditionCHAPTER 20 The Origin and Evolutionary History of Life Miller-Urey experiment

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 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 EditionCHAPTER 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 EditionCHAPTER 20 The Origin and Evolutionary History of Life Microspheres – a type of protobiont (early lipid membrane)

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 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 EditionCHAPTER 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 EditionCHAPTER 20 The Origin and Evolutionary History of Life Directed evolution

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 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

The prokaryotes The first cells Image Credits Gary Gaugler Bacillus anthracisBacillus anthracis Image Credits: Thermophilic archaebacteriaThermophilic archaebacteria

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 20 The Origin and Evolutionary History of Life The first cells Heterotrophs that feed on organic molecules Anaerobic fermentation process to obtain energy

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 ODWSODWS

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 ODWSODWS

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 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 EditionCHAPTER 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 semi- independent of that taking place in the cytoplasm It is inhibited by the same antibiotic that affects prokaryotes (chloramphenicol). © 2010 Paul Billiet ODWSODWS

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 20 The Origin and Evolutionary History of Life Endosymbiont theory

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 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: MitochondrionMitochondrion © 2010 Paul Billiet ODWSODWS

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 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 Mitochondrion © 2010 Paul Billiet ODWSODWS

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 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 heterocystCyanobacterium heterocyst © 2010 Paul Billiet ODWSODWS