Lecture 11 Origin of Life Chapter 21 pg 446 454 Outline Chemical evolution hypothesis Small organic molecules Prebiotic soup hypothesis Miller and Hurley experiment and Iron sulfur world hypothesis The first cells RNA world Serial endosymbiosis Tree of life domains and kingdom carbon dioxide CO2 water vapor H2O carbon monoxide CO Conditions on early Earth Earth s early atmosphere nitrogen N2 ammonia NH3 hydrogen sulfide H2S methane CH4 Earth was formed 4 6 billion years ago Major Episodes in the History of Life chemical and physical processes on early Earth may have produced very simple cells through a sequence of stages 1 2 3 4 5 abiotic synthesis of small organic molecules chemical evolution hypothesis joining of these small molecules intro macromolecules packing of molecules into protocells origin of self replicating molecules RNA world origin of eukaryotic cells Formation of Organic Molecules Earth s surface cracks in the ocean s floor Two main models explain how the organic precursors of life might have originated The prebiotic soup hypothesis proposes that organic molecules formed near Oparin Haldane hypothesis Miller Urey test The iron sulfur world hypothesis proposes that organic precursors formed at Chemical Evolution hypothesis came from oparin haldane hypothesis test could organic molecules have formed in the conditions of early Earth Miller and Urey s Experiment in chemical evolution formation of amino acids and other organic molecules by exposing a mixture of H2 CH4 H20 NH3 to an electric discharge that stimulated lightning organic molecules would accumulate in the shallow seas to form sea of organic soup organic polymers form spontaneously from monomers on hot rock or clay surfaces Iron Sulfur World Hypothesis fides of iron and nickel hydrothermal vents on the deep ocean floor release hot water carbon monoxide and sul early polymerization may have occurred in hydrothermal vents chemical evolution hypothesis oparin haldane miller just tested the hypothesis Hypothetical ancestor of cells Protobionts scientists have synthesized vesicle like protobionts a protobiont is the hypothetical ancestor of the cell it is an assemblage of organic poly mers they divide in half binary fission they maintain homeostasis some show beginnings of metabolism catalytic ac tivity they are highly organized Central Dogma of Life DNA RNA Proteins proteins are needed to catalyze the regulation of DNA RNA originated before DNA In the hypothetical RNA world RNA molecules both encoded information and carried out catalysis DNA as information storage medium and protein as catalyst emerged later in evolution DNA is replicated and also is transcribed into RNA and the RNA is translated into pro teins The first cells were heterotrophic prokaryotes the first cells were probably heterotrophs anaerobes fermentation shortage of organic compounds first autotrophs green purple sulfur bacteria S Cyanobacteria and Oxygen cyanobacteria first photosynthetic autotrophs 02 blue green pigment phycocyanin and chlorophyll a ozone O3 protected organisms from UV radiation first photosynthetic organisms 3 5 billions of years ago evidence fossils rocks containing chlorophyll stromatolites type of fossil Microfossils fossils too small to be seen without the aid of a microscope Stromatolites are produced by microbes cyanobacteria that form thin microbial films which trap mud over time layers of these mud microbe mats can build up into a layered rock structure Single celled eukaryotic organisms 2 2 billion years ago Oxygen production 2 5 billion years ago Prokaryotes 3 5 billion years ago Earth was formed 4 5 billion years ago Serial Endosymbiosis Serial endosymbiosis suggests that early eukaryotic cells were assemblages of formerly free liv ing prokaryotes chloroplast cyanobacteria mitochondria aerobic bacteria Domain bacteria evolved first then archaea then eukarya domain classification Woese 1970 based on molecular data assign organisms to Do beneficial for both partners mains Bacteria Archaea Eukarya Kingdom classification Whittaker 1969 based on cell structure and mode of nutrition five kingdom classification Archaea Bacteria protists Fungi Plantae and Animalia