Bio 102 - Exam 3

Bio 102 - Exam 3 - Bio 102 Exam 3 Chapter 20 Earth is...

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Bio 102 Exam 3 Chapter 20 Earth is 4.6bil year old 3.8bya organic molecules 3.5bya first cell 2bya first definite cells first prokaryote later eukaryote Four requirements for chemical evolution Little/no free oxygen oxygen very reactive would have oxidized organic Source of energy needed to build biological molecules from inorganic chemicals Earth had lots of energy from thunderstorm, volcanoes, etc. Availability of building blocks water dissolve inorganic mineral gases present in atmosphere Time for molecules to accumulate, react with each other several hundred million years Formation of organic molecules: raw materials that were probably needed for organic synthesis were water (H 2 O), methane (CH 4 ), hydrogen (H 2 ) ammonia (NH 3 ) During chemical evolution, small organic molecules formed spontaneously and accumulated Two Theories Prebiotic soup hypothesis molecules formed near earth's surface tested in 1950s by Miller and Urey stimulated early earth's atom electrical spark as lightning found organic molecules including amino acids Repeatable! Iron sulfur world hypothesis (most recent) Organic molecules formed at Hydrothermal vent, cracks in ocean's floor where: hot water CO minerals better protected than surface of early earth produce precursor molecules today! Organic molecules to cells Mechanisms to concentrate organic chemicals Evaporation
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Concentration by water freezing Lipid droplets Mineral grains eg. Clay Protobionts Abiotically produced organic polymers, macromolecular assemblages Behave somewhat like living cells grow by absorbing substances from water divide in half when large Homeostasis Microsphere – type of Protobiont formed by adding water with layer of molecule like cell membrane: Selective permeability Molecular reproduction RNA world model chemistry of early earth yielded self replicating RNA molecules Enzymes Substrates for own replication first informational molecule to evolve in the progression toward a self- sustaining, self-reproducing cell. Catalytic properties – bring to two things: Ribozymes – together, catalysis enzymatic RNA thus may catalyze their own reproduction Directed evolution tests large pool of RNA molecules with different sequences selected for ability to catalyze a reaction amplify/mutate/repeat Final RNA, very efficient as catalysts In RNA world, ribozymes catalyzed protein synthesis DNA formed from double strands of RNA DNA more stable than RNA Biological evolution began with the first cells Life existed as early as 3.8 bya Microfossils – ancient remains of microscopic life, suggest that cells may have been thriving as long 3.5bya Oldest fossil cells are 2 billion years old. Earliest cells were prokaryotic
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Bio 102 - Exam 3 - Bio 102 Exam 3 Chapter 20 Earth is...

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