FULL REVIEW Exam 2 notes

FULL REVIEW Exam 2 notes - Chapter 20 The Origin and...

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Chapter 20 – The Origin and Evolutionary History of Life I. Chemical Evolution on Early Earth (Oparin and Haldone) a. Four requirements for chemical evolution i. Little or no oxygen – oxygen would oxidize organic molecules; quite reactive ii. A source of energy – violent thunderstorms (lightning), volcanic activity, bombardment from meteorites, and intense radiation from sun iii. Availability of chemical building blocks – water, dissolved inorganic minerals, and gaseous environment of CO 2 , H 2 O, CO, H 2 , N 2 , NH 3 , H 2 S, CH 4 iv. Time – life had several million of years to get started b. Organic Molecules formed on Primitive Earth i. Prebiotic soup hypothesis – organic molecules formed near Earth’s surface 1. Tested by Miller and Urey – they created an atmosphere similar to early Earth and exposed it to electrical discharge; organic molecules and amino acids formed week later ii. Iron-sulfur world hypothesis – organic precursors formed at cracks in the ocean’s floor 1. Iron and nickel sulfides catalyze reactions between CO and H 2 S, producing acetic acid and other simple organic molecules 2. Ammonia is produced, suggesting vents where rich with ammonia in prebiotic world iii. Clay is a possible site for early polymerization because it binds organic molecules and contains zinc and iron ions that serve as catalysts (Tested by Fox) II. First Cells a. Protobionts are assemblages of abiotically produced organic polymers i. Exhibit many functional and structural attributes of living cells ii. Divide in half (binary fission); maintain homeostasis; show beginnings of metabolism (catalytic activity) b. Microspheres are type of protobiont formed by adding water to abiotically formed polypetides i. Produce an electrical potential across their surface (similar to electrochemical gradients of cells) ii. Absorb material from surroundings and respond to change in osmotic pressure c. Molecular Reproduction was a crucial step in the origin of cells i. RNA world model – chemistry of prebiotic Earth gave rise to self-replicating RNA molecules that functioned as both enzymes and substrates for own replication ii. Enzymatic RNAs are called ribozymes – ribozymes initial catalyzed protein synthesis and other important biological reactions; only later did protein enzymes catalyzes these reactions iii. DNA became storage for information because it was more stable – double helix provides increased stability, which is advantageous in prebiotic world iv. DNA became information storage, RNA became involved in protein synthesis, and proteins catalyzed most cell reactions d. Biological Evolution began with the first cells i. First cells were prokaryotic; obtained organic molecules from environment (hetertrophs); anaerobes (obtained energy from fermentation, anaerobic process) ii. First autotrophs used energy of sun to hydrolyze H 2 S, releasing elemental sulfur into atmosphere; cyanobacteria first organism to hydrolyze H 2 O, releasing oxygen into the atmosphere. Initially oxygen
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This note was uploaded on 04/04/2008 for the course BIO 101 taught by Professor Martin during the Fall '08 term at Rutgers.

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FULL REVIEW Exam 2 notes - Chapter 20 The Origin and...

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