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10 - Life - III

10 - Life - III. Family Tree of Life on Earth. Prokaryotes - no cell nucleus Bacteria Archaea Eukaryotes - cell nucleus. Some Simple Principles Usually Apply. From Simpler Organisms  More Complex Organisms Simple organisms living off of available nutrients

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10 - Life - III

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  1. 10 - Life - III

  2. Family Tree of Life on Earth • Prokaryotes - no cell nucleus • Bacteria • Archaea • Eukaryotes - cell nucleus

  3. Some Simple Principles Usually Apply • From Simpler Organisms  More Complex Organisms • Simple organisms living off of available nutrients • Use of sunlight - photosynthesis to store energy (possibly using H2S instead of H2O) From O-Poor  O-Rich Environment First O-producers: O is a waste product, possibly poisonous. Certainly true for some prokaryotes today Some prokaryotes “indifferent” to O Some prokaryotes require O Almost all eukaryotes require O

  4. “New” systems do NOT occur fully formed but build upon changes made in existing ones • Similar structures in: • Chlorophyll (cyanobacteria, plants) • Hemoglobin (iron-containig porphyrin) • Hemocyanin (2 types - mollusks, arthropods) porphyrin Hemoglobin uses Fe instead of Mg

  5. note • Many organelles: • Have own DNA & protein-making machinery • Genetically related to bacteria • Began as symbiosis with extant bacteria

  6. 4 by 3 by 2 by 1 by today first prokaryotes? Most biochemical machinery already “invented” Cambrian “explosion” - many hard-body species first eukaryotes? Peptide Nucleic Acid (PNA) Therose Nucleic Acid (TNA) Ribonucleic Acid (RNA) - first as catalyst, then as replicator Deoxyribonucleic Acid (DNA)

  7. Other Basic Observations Species do not “repeat” in time - each comes from a specific ancestor under specific conditions Some species essentially unchanged (stromatolite cyanobacteria, for example) While most evolution is divergent, there are cases of “convergent” evolution developing similar structures independently (eyes, for example) “then” # “now” Complex organisms are still a minority complexity us

  8. "Scientists tend to make sense of the past by telling stories in which everything leads up to or away from humans." - Misia Landau Evolution doesn’t really lead toward anything, but away from the status quo in a many-branching tree (we just happen to be one one of them…) Book illustrations don’t help here - often imply each time stage removes predecessors.. Would the rest of life know if we were gone?

  9. The Basis of All Life on Earth: C and H2O • Why C? • abundant in the universe • can make 4 chemical bonds/atom - information storage Example of information storage - suppose our alphabet had only 2 letters - A and B (say) and we could only make “words” 2 letters at a time: Our “Vocabulary” AA, AB, BA, BB AAA AAB, ABA, BAA ABB, BAB, BBA BBB Now expand to 3 letters per word:

  10. H C N O 4 bonds: If only 1 bond: methane formaldehyde hydrogen cyanide Acetylene ethane benzene DNA (“color scheme may differ”)

  11. Why H2O? Potentially the most abundant solid (as ice) in the solar system - helps for transportation to planets Polar molecule - aids in chemical reactions as a good “solvent” (also exists as ions in solution…) Remains as a liquid (solvent) over a wide range of physical conditions (temperature & pressure) due to high heat capacity & heat of vaporization Ice floats on water… - + - + + + - + +

  12. Why not Si? To make complex Si molecules, need Si-Si chains & rings, but Si binds to O more strongly than to other Si Produces non-reactive materials like silica rock (SiO2) and silicones - hard to dissolve into solution. Clues from nature - many meteorites, see amino acids, etc. but no comparable Si compounds. Silicon-based life very unlikely….

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