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AP Biology Life’s Beginnings on Earth according to science
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FOUR STEPS FOR LIFE TO EMERGE ON EARLY EARTH
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1. ABIOTIC SYNTHESIS OF AMINO ACIDS AND NUCLEIC ACIDS
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Nucleic Acid Formation Nucleic acids- DNA and RNA Stores molecular information Transmits hereditary information. RNA is believed to have evolved first--- not as molecularly stable as DNA
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Amino Acid Formation Monomers of proteins Account for 50% of biomass of cells.
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Protein’s Natural Form Intricate 3D structure Based on amino acid chain Amino acid sequence determines the 3D structure.
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2. MONOMERS MUST JOIN TOGETHER TO FORM MORE COMPLEX POLYMERS USING ENERGY FROM THE ENVIRONMENT
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Monosaccharides Combining Monomer of carbohydrates– sugars. ex: glucose Monosaccharides combine to make polysaccharides– storage for cells and structure for cells. Dehydration reactions synthesize polysaccharides
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Phospholipid Formation Combine to make phospholipid bilayer that forms cell membrane
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Construction of mRNA from DNA DNA RNA Protein DNA in the nucleus programs protein production in the cytoplasm by dictating the synthesis of messenger RNA (mRNA)
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Constructing Chromosomes Chromosomes used for information storage.
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3. DNA/RNA ABLE TO REPRODUCE AND STABILIZE USING CHEMICAL BONDING AND COMPLIMENTARY BONDING
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DNA Replicating Double stranded– sugar- phosphate backbone Nitrogenous bases hold strands together– Adenine with Thymine or Uracil Guanine with Cytosine Single strands held together by covalent bonds Double strands held together by hydrogen bonds
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4. EVOLUTION OF A PROTOBIONT “First life form”
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- Hydrophilic head Hydrophobic tail WATER Membrane Formation
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Representation of a Protobionts Phospholipid membrane and proteins keep the “cell” intact
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SCIENTIFIC SUPPORTING EVIDENCE- -- TESTABLE IN THE LAB
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Stanley Miller 1953, set up a closed system to simulate conditions on early earth.
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LE 26-2 Water vapor CH 4 NH 3 H2H2 Electrode Condenser Cold water Cooled water containing organic molecules Sample for chemical analysis H2OH2O ocean Volcano gases lightning
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Early Earth Hydrogen gas (H2), methane CH4, ammonia (NH3) and water vapor
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Energy Source
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