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First Atmosphere • Hydrogen gas • Nitrogen • Carbon monoxide • Carbon dioxide • No gaseous oxygen Origin of Organic Compounds • Stanley Miller Experiment – next slide • Amino acids, other organic compounds can form spontaneously under conditions like those on early Earth electrodes to vacuum pump CH4 NH3 H2O H2 spark discharge gases water out condenser water in water droplets water containing organic compounds boiling water liquid water in trap Metabolism • The organic molecules interacted causing chemical reactions, leading to metabolism RNA World • RNA may have been first genetic material • RNA can assemble spontaneously – Self replicating – can copy itself • How switch from RNA to DNA might have occurred is not known Proto-Cells • Microscopic spheres of proteins or lipids can self assemble • Tiny sacs like cell membranes can form under laboratory conditions that simulate conditions in evaporating tidepools • Sidney Fox – proteins chains, protenoids (spheres that were selectively permeable ) • David Deamer – lipids, self-assembled into small, water-filled sacs resembling cell membranes. The First Cells • Originated in Archeon Eon • Were prokaryotic heterotrophs • Secured energy through anaerobic pathways – No oxygen present – Relied on glycolysis and fermentation Order of Origination • Anaerobic heterotrophic prokaryotes • Origin of photosynthetic Eubacteria – cyclic pathway first – noncyclic pathway next – Oxygen accumulates in atmosphere • Origin of aerobic respiration Advantages of Organelles • Infolding of membrane led to some organelles • Nuclear envelope may have helped to protect genes from competition with foreign DNA • ER channels may have protected vital proteins DNA Figure 20.10 Page 335 infolding of plasma membrane Theory of Endosymbiosis • Lynn Margulis • Mitochondria and chloroplasts are the descendents of free-living prokaryotic organisms • Prokaryotes were engulfed by early eukaryotes and became permanent internal symbionts
