b112_Lecture_26

b112_Lecture_26 - 2/1/2008 BIOL112 Chapter26 TheOriginofLife

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2/1/2008 1 BIOL 112–Chapter 26 The Origin of Life How the First Cell Arose–An Immodest Proposal First complex organic monomers develop in the prebiotic “soup” The monomers joined together to form polymers Protobionts form and maintain an environment different from their surroundings. Genetic material evolves. How to Get Those First Molecules Oparin & Haldane (1920s) – Conditions must have been different in the early earth, a reducing instead of an oxidizing atmosphere. Miller & Urey (1953)–Amino acids from water, hydrogen gas, methane and ammonia. Problems With Miller Urey Experiments (& Others) Roughly equal quantities of D and L amino acids formed. Molecules must be removed from system or they degrade. Accepted geological evidence suggests oxygen was present long before first cells. Geochemists are in agreement that ammonia & methane were not part of early atmosphere. Experiment fails entirely without ammonia & methane. Strongest evidence put forward by evolutionists is that complex molecules must form, because life is here.
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2/1/2008 2 How Polymers Could Form A reducing atmosphere required Clay surfaces can act as catalytic sites Iron pyrite may also act as a catalyst Problems With Polymer Formation Oxygen in atmosphere prevents polymer formation Even without oxygen polymers form very inefficiently and spontaneously degrade Polymer formation is random, undirected How can you get polymers if you can’t get monomers? How Protobionts Could Form A high concentration of mostly nonpolar polypeptides, nucleic acids and polysaccharides can self assemble when shaken.
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b112_Lecture_26 - 2/1/2008 BIOL112 Chapter26 TheOriginofLife

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