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Download Where did life come from? First, where did the earth come from?
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Where did life come from? First, where did the earth come from? • Everything appears to have started with the Big Bang – about 14 billion years ago. • The solar system formed about 5 bya. • Earth formed from an accumulation of materials orbiting the sun – about 4.5 bya. And life??? • Conditions were not suitable for life – – Hot – Much radiation – No organic molecules • Conditions had to change • Organic molecules had to be synthesized • How??? Evolution of Life Early Earth was hot; atmosphere contained poisonous gases. Earth cooled and oceans condensed. Simple organic molecules may have formed in the oceans.. Small sequences of RNA may have formed and replicated. First prokaryotes may have formed when RNA or DNA was enclosed in microspheres. Later prokaryotes were photosynthetic and produced oxygen. An oxygenated atmosphere capped by the ozone layer protected Earth. First eukaryotes may have been communities of prokaryotes. Multicellular eukaryotes evolved. Sexual reproduction increased genetic variability, hastening evolution. Building Life • The early earth had no organic compounds: Where did these come from? • 1953 – Miller and Urey hypothesized that conditions could produce chemical reactions to synthesize organic compounds from inorganic. – The did the experiment and it worked. Miller and Urey Experiment: • Simulated early earth conditions to model formation of organic molecules. Mixture of gases simulating atmospheres of early Earth Spark simulating lightning storms Condensation chamber Cold water cools chamber, causing droplets to form Water vapor Liquid containing amino acids and other organic compounds Now that we have the building materials, what makes a cell? • A membrane - can build this in a dish! • Nucleic acids: DNA (originally RNA?) – can assemble these in a dish. • Protein synthesis machinery – A little more complicated. • Enzymes for energy transfer – can make these work in a dish - sort of - and definitely work in a proteinoid microsphere. Nutrition? • Simplest organisms just absorb organic compounds – Heterotroph hypothesis – Oparin • Photosynthesis – big advance! – Byproduct (oxygen) changed everything. • Availability of free oxygen permitted more efficient release of energy from food. – Aerobic respiration Endosymbiotic Theory- making a eukaryote from prokaryotes Chloroplast Aerobic bacteria Ancient Prokaryotes Nuclear envelope evolving Plants and plantlike protists Photosynthetic bacteria Mitochondrion Primitive Photosynthetic Eukaryote Ancient Anaerobic Prokaryote Primitive Aerobic Eukaryote Animals, fungi, and non-plantlike protists Classification of Living Things DOMAIN Bacteria Archaea KINGDOM Eubacteria Archaebacteria CELL TYPE Eukarya Protista Fungi Plantae Animalia Prokaryote Prokaryote Eukaryote Eukaryote Eukaryote Eukaryote Cell walls with peptidoglycan Cell walls without peptidoglycan Cell walls of cellulose in some; some have chloroplasts Cell walls of chitin Cell walls of cellulose; chloroplasts No cell walls or chloroplasts Unicellular Unicellular Most unicellular; some colonial; some multicellular Most multicellular; some unicellular Multicellular Multicellular MODE OF NUTRITION Autotroph or heterotroph Autotroph or heterotroph Autotroph or heterotroph Heterotroph Autotroph Heterotroph EXAMPLES Streptococcus, Escherichia coli Methanogens, halophiles Amoeba, Paramecium, slime molds, giant kelp Mushrooms, yeasts Mosses, ferns, flowering plants Sponges, worms, insects, fishes, mammals CELL STRUCTURES NUMBER OF CELLS DOMAIN ARCHAEA DOMAIN EUKARYA Kingdoms DOMAIN BACTERIA Eubacteria Archaebacteria Protista Plantae Fungi Animalia
