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D.1 origin-of-life-on-earth


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D.1 origin-of-life-on-earth

  1. 1. Option D.112 IB Biology 2011 Miss Werba
  2. 2. • The conditions of pre-biotic Earth • Experiments of Miller and Urey • Hypothesis regarding first catalysts • Theory that regarding RNA and replication • Possible origin of membranes and prokaryotic cells • Endosymbiotic theory for the origin of eukaryotesMISS J WERBA – IB BIOLOGY 2
  3. 3. D.1.1 • There are processes that were needed for the spontaneous generation of life on Earth: – Non-living synthesis of simple organic molecules – Assembly of these molecules into polymers – Inheritance possible once self-replicating molecules originated – Packaging of these molecules into membranesMISS J WERBA – IB BIOLOGY 4
  4. 4. D.1.1 6
  5. 5. D.1.1D.1.3D.1.4 • 15 billion years after the “Big Bang”, the planets began to form. • The atmosphere on Earth at this time probably contained a variety of inorganic molecules: – Water vapour – Methane – Ammonia – Hydrogen – Carbon dioxideMISS J WERBA – IB BIOLOGY 7
  6. 6. D.1.1D.1.3D.1.4 • The energy for forming the organic molecules was provided by: – frequent thunder storms and lightning strikes – volcanic activity – meteorite bombardment – high temperatures due to greenhouse gases – UV radiation (no ozone so was extreme)MISS J WERBA – IB BIOLOGY 8
  7. 7. D.1.1D.1.3D.1.4 • These elements and inorganic molecules are presumed to have been sufficient for life to begin. • The organic molecules may have been generated on Earth or introduced from space.MISS J WERBA – IB BIOLOGY 9
  8. 8. D.1.1D.1.3D.1.4 • The hypothesis that life on Earth originated by introduction of complex organic chemicals or even bacteria via comets is called panspermia. • A shower of comets about 4 thousand million years ago could have introduced complex organic molecules and water to the Earth and initiated chemical evolution.MISS J WERBA – IB BIOLOGY 10
  9. 9. D.1.1 • There was little to no oxygen in the atmosphere at the time, as any oxygen was absorbed by rocks. • This meant that there was no oxygen to steal electrons away from other atoms (ie. oxidise them). • This would have resulted in a ‘reducing atmosphere’ which would have made the joining of simple molecules to form more complex ones more likely.MISS J WERBA – IB BIOLOGY 12
  10. 10. D.1.1 • Experiments have shown that it is possible to form organic molecules in a reducing atmosphere • However it is very difficult to do when there is oxygen in the atmosphere • This polymerisation process would allow the larger chemicals needed by cells to form.MISS J WERBA – IB BIOLOGY 13
  11. 11. D.1.1 • How were polymers — the basis of life itself — assembled???? • In solution, hydrolysis of a growing polymer would soon limit the size it could reach. • This has led to a theory that early polymers were assembled on solid, mineral surfaces that protected them from degradation. • In lab experiments they have been synthesized on clay.MISS J WERBA – IB BIOLOGY 14
  12. 12. D.1.1D.1.5 • In current cells, DNA can replicate but it needs the help of enzymes (proteins) to do this. • The proteins are assembled based on information carried on the DNA and transcribed into RNA. • So what came first..... the DNA to make proteins or the proteins to make the DNA?!?!?!?!?MISS J WERBA – IB BIOLOGY 16
  13. 13. D.1.1D.1.5 • The synthesis of DNA and RNA requires proteins. • So: – proteins cannot be made without nucleic acids and – nucleic acids cannot be made without proteins • Wrong!MISS J WERBA – IB BIOLOGY 17
  14. 14. D.1.1D.1.5 • The synthesis of nucleotides and their bases could have happened easily. • Once this had occurred, it is not hard to see how a single strand of RNA could have formed. • Once this had occurred, complementary base pairing could have resulted in the non-enzymatic replication of RNA.MISS J WERBA – IB BIOLOGY 18
  15. 15. D.1.1D.1.5 SOURCE: Purcell, D. (2009)MISS J WERBA – IB BIOLOGY 19
  16. 16. D.1.1D.1.5 • Self-replicating molecules are molecules that are able to undergo replication. • They are able to act as a template for copies of themselves to be made. • The only biological molecules capable of self- replication are DNA & RNA. • Unlike DNA, RNA sequences are capable of self- replication: it can catalyse its formation from nucleotides in the absence of proteins.MISS J WERBA – IB BIOLOGY 20
  17. 17. D.1.1D.1.5 SOURCE: Purcell, D. (2009)MISS J WERBA – IB BIOLOGY 21
  18. 18. D.1.1D.1.5 • The discovery that certain RNA molecules have enzymatic activity provides a possible solution. • These RNA molecules — called ribozymes— incorporate both the features required of life: – storage of information – the ability to act as catalysts • Active ribozymes can be easily assembled from shorter olignonucleotides (strands of nucleotides).MISS J WERBA – IB BIOLOGY 22
  19. 19. D.1.1D.1.5 • Ribozymes have been synthesized in the laboratory and can catalyze exact complements of themselves. • The ribozyme serves as both: – the template on which short lengths of RNA ("oligonucleotides“) are assembled, following the rules of base pairing and – the catalyst for covalently linking these oligonucleotides.MISS J WERBA – IB BIOLOGY 23
  20. 20. D.1.1D.1.5 SOURCE: Purcell, D. (2009)MISS J WERBA – IB BIOLOGY 24
  21. 21. D.1.1D.1.5 • Evidence for this ideas is provided by the fact that many of the cofactors that play so many roles in life are based on ribose: ATP NAD FAD coenzyme A cyclic AMP GTPMISS J WERBA – IB BIOLOGY 25
  22. 22. D.1.1D.1.6 • The development of the lipid bilayer was imitated in the laboratory by Fox and his co-workers • They heated amino acids without water and produced long protein chains • When water was added and the mixture cooled, small stable microspheres or coacervates were formedMISS J WERBA – IB BIOLOGY 27
  23. 23. D.1.1D.1.6 • The coacervates seemed to be able to accumulate certain compounds inside them so that they became more concentrated than outside • They also attracted lipids and formed a lipid-protein layer around themMISS J WERBA – IB BIOLOGY 28
  24. 24. D.1.1D.1.6 • If we assume that the coacervates also combined with self-replicating molecules such as RNA, we are looking at a very primitive organism... • This is thought to have happened about 3.8 billion years agoMISS J WERBA – IB BIOLOGY 29
  25. 25. D.1.1D.1.6 SOURCE: Purcell, D. (2009)MISS J WERBA – IB BIOLOGY 30
  26. 26. D.1.1D.1.6 SOURCE: Purcell, D. (2009)MISS J WERBA – IB BIOLOGY 31
  27. 27. D.1.1D.1.6 • The aggregates or coacervates are also known as protobionts or proto cells. • The most successful liposomes (protobiont in presence of lipids) at surviving would have passed on their characteristics and developed into early prokaryotes!MISS J WERBA – IB BIOLOGY 32
  28. 28. D.1.1D.1.6 SOURCE: McFadden, G. (2009)MISS J WERBA – IB BIOLOGY 33
  29. 29. D.1.1D.1.6 SOURCE: McFadden, G. (2009)MISS J WERBA – IB BIOLOGY 34
  30. 30. D.1.2 • Stanley Miller and Harold Urey worked on trying to confirm some of these ideas regarding pre-biotic Earth. • In 1953, Miller set up an apparatus to simulate conditions on the early Earth. • The apparatus contained a warmed flask of water simulating the primeval sea and an atmosphere of water, hydrogen gas, CH4 (methane), and NH3 (ammonia).MISS J WERBA – IB BIOLOGY 36
  31. 31. D.1.2 37
  32. 32. D.1.2 • Sparks were discharged in the synthetic atmosphere to mimic lightning. • Water was boiled, while a condenser cooled the atmosphere, raining water and any dissolved compounds back to the miniature sea. • The simulated environment produced many types of amino acids and other organic molecules leading them to conclude the pre-biotic synthesis of organic molecules was possible.MISS J WERBA – IB BIOLOGY 38
  33. 33. D.1.2MISS J WERBA – IB BIOLOGY 39
  34. 34. D.1.2 • This spontaneous generation of organic molecules was supported by investigation of meteorites. • In 1970, a meteorite was found to contain 7 different amino acids, 2 of which are not found in living things on Earth.MISS J WERBA – IB BIOLOGY 40
  35. 35. D.1.7MISS J WERBA – IB BIOLOGY SOURCE: McFadden, G. (2009) 42
  36. 36. D.1.7 SOURCE: McFadden, G. (2009)MISS J WERBA – IB BIOLOGY 43
  37. 37. D.1.7 • Prokaryotes had the planet to themselves for about 2 billion years! • Oxygen began to gradually accumulate in the atmosphere on Earth. • Bacteria evolved naturally to contain a form of chlorophyll, which then allowed a simple form of photosynthesis to occur.MISS J WERBA – IB BIOLOGY 44
  38. 38. D.1.7 • This caused an explosive rise in the levels of atmospheric oxygen known as the oxygen catastrophe. • This had an irreversible effect on the subsequent evolution of life. • The remaining chemicals in the “chemical soup” in the oceans were broken down into carbon dioxide and oxidised sediments.MISS J WERBA – IB BIOLOGY 45
  39. 39. D.1.7 • In addition, a layer of ozone (O3) began to form in the upper atmosphere. • This protected the planet from UV radiation from the Sun and blocked the production of new organic chemicals in the “chemical soup”.MISS J WERBA – IB BIOLOGY 46
  40. 40. D.1.8 SOURCE: McFadden, G. (2009)MISS J WERBA – IB BIOLOGY 48
  41. 41. D.1.8 SOURCE: McFadden, G. (2009)MISS J WERBA – IB BIOLOGY 49
  42. 42. D.1.8 SOURCE: McFadden, G. (2009)MISS J WERBA – IB BIOLOGY 50
  43. 43. D.1.8 • Grypania is ~2mm in diameter, so it is too big to be a prokaryotic cell. • Tappania is definitely too big and complicated to be prokaryotic. • Bangiomorpha had 3D structure! Definitely too complicated to be prokaryotic!MISS J WERBA – IB BIOLOGY 51
  44. 44. D.1.8 • The oldest fossils of eukaryotic cells have been found to be approximately 1.5 billion years old. • The endosymbiotic theory from Lyn Margulis (1967) tries to explain how eukaryotic cells may have evolved. • Endosymbiosis: the condition in which one organism lives inside the cell of another organism • Both cells benefit from this - the cells no longer can live separately from each otherMISS J WERBA – IB BIOLOGY 52
  45. 45. D.1.8MISS J WERBA – IB BIOLOGY 53
  46. 46. D.1.8 • Mitochondria and chloroplasts were once free living bacteria cells: – Mitochondria aerobic bacteria – Chloroplasts photosynthetic bacteria • These cells were “swallowed up” by other cells by endocytosis  cells engulfed but not eatenMISS J WERBA – IB BIOLOGY 54
  47. 47. D.1.8MISS J WERBA – IB BIOLOGY 55
  48. 48. D.1.8MISS J WERBA – IB BIOLOGY 56
  49. 49. D.1.8 • Mitochondria: – additional energy (aerobic respiration) and receives protection • Chloroplast: – provide food by photosynthesis and receives protectionMISS J WERBA – IB BIOLOGY 57
  50. 50. D.1.8 • Prokaryotes are similar to mitochondria and chloroplasts: – Similar size – Similar ribosomes (70S) – Contain DNA that is different from the nucleus – Surrounded by double membrane – Formation of new organelles resembles binary fissionMISS J WERBA – IB BIOLOGY 58
  51. 51. D.1.8 • The four eukaryotic kingdoms are: – Protoctista – Fungi – Plantae – Animalia • Eukaryotic cells have some advantages over prokaryotic cells so the early eukaryotes survived and proliferated • Hence the wide diversity of species we know today!MISS J WERBA – IB BIOLOGY 59