Lecture 2 spring 2011

Lecture 2 spring 2011 - Early Life and Microbial...

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Early Life and Microbial Classification Microbes were the earliest life forms, evidence for existence 3.8 billion years ago Fossils and geochemistry indicate that as soon as the surface of earth cooled, multiple metabolisms were present Original thoughts were of anaerobic metabolism Panspernia- earth was seeded?
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Early Earth Earth is ~4.5-5 billion years old Chemistry Early Earth was Anoxic (no Oxygen gas) CH 4 , CO 2 , N 2 , NH 4 + , H 2 S, FeS, CO and H 2 Temperature initially >100°C, then cooled With radiation (energy), biomolecules formed and polymerized Volcanic activity
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Prebiotic soup model Organic building blocks of life arose abiotically Simple amino acids extracted from meteorites Life Complex macromolecules formed Apparatus for self replication Membrane compartmentalization Energy
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Surface vs ocean-based evolution The deep marine hydrothermal setting provides a suitable site for the origin of life. Atmospheric composition less relevant; UV photolysis absent, reduced conditions, more stable temperature. Experiments show cold conditions are necessary for purine formation. Other experiments showed the formation of seven different amino acids and 11 types of nucleobases in ice when ammonia and cyanide were left in a freezer for 25 years. The formation of RNA molecules 400 bases long under freezing conditions using an RNA template has been demonstrated. Perhaps fluctuating environments necessary; cold/hot, concentration by evaporation from impacts
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Metabolist model Central components of metabolism (i.e., TCA cycle) arose from self- sustaining chemical reactions Abiotic reactions by compounds with catalytic transition metal centers, i.e. iron sulfide Self-replication of macromolecules and membrane compartmentalization follows
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Life Complex macromolecules formed Structure and form
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Lecture 2 spring 2011 - Early Life and Microbial...

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