The Beginning of Life




 I. Conditions necessary to allow life
 to begin




Earth was a very hostile environment 4 bill...
First Atmosphere

      • Hydrogen gas
      • Nitrogen
      • Carbon monoxide
      • Carbon dioxide
      • No gaseous ...
I. Conditions necessary to allow
     life to begin




four formaldehyde
molecules with
four pyrrole rings




          ...
Origin of Organic Compounds

• Amino acids, other organic compounds
  can form spontaneously under conditions
  like those...
II. Origin of cells – precursor to
          living cells




                          Proto-Cells
 • Microscopic spheres...
II. Origin of cells – precursor to
               living cells




Membrane of fatty acids and alcohol surrounding
RNA-coa...
Could precursors and /or proto-cells have arrived from outer space?



                                              BBC N...
III. The first true cells




                                     3.5 billion y –old
                                    ...
Stromatolites – fossils of cyanobacteria; 3by-old




                     Proterozoic Eon

      • Origin of photosynthet...
IV. Where did eukaryotic organelles come from?
The evolution of the eukaryotic cell




     Where did all these organelle...
DNA




  ER ?

                       infolding of plasma membrane
                                                      ...
Evidence


  Endosymbiosis example in modern time

    Amoeboid organism with green alga within




                  Occu...
V. The timeline of development




       hydrogen-rich anaerobic atmosphere                                 atmospheric o...
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The+Beginnings+Of+Life

  1. 1. The Beginning of Life I. Conditions necessary to allow life to begin Earth was a very hostile environment 4 billion years ago Fig. 20-4b, p.321 1
  2. 2. First Atmosphere • Hydrogen gas • Nitrogen • Carbon monoxide • Carbon dioxide • No gaseous oxygen I. Conditions necessary to allow life to begin electrodes to spark vacuum CH4 discharge pump NH3 gases H2O H2 water out condenser water in water droplets water containing organic compounds boiling water liquid water in trap Fig. 20-4c, p.321 2
  3. 3. I. Conditions necessary to allow life to begin four formaldehyde molecules with four pyrrole rings chlorophyll a 6H porphyrin ring system Stepped Art Fig. 20-5, p.322 3
  4. 4. Origin of Organic Compounds • Amino acids, other organic compounds can form spontaneously under conditions like those on early Earth • Clay may have served as template for complex compounds • Compounds may have formed near hydrothermal vents RNA ‘Ribozyme’ produced in the laboratory Store biological information and also act as catalyst (enzyme) Could something like this have been the first source of genetic material? RNA World • DNA is genetic material now • DNA-to-RNA-to-protein system is complicated • RNA may have been first genetic material • RNA can assemble spontaneously • How switch from RNA to DNA might have occurred is not known 4
  5. 5. II. Origin of cells – precursor to living cells 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 • Nanobes may resemble proto-cells Amino acids heated, then moistened. Formed protein membranes. 5
  6. 6. II. Origin of cells – precursor to living cells Membrane of fatty acids and alcohol surrounding RNA-coated clay . Fig. 20-7b, p.323 II. Origin of cells – precursor to living cells 6
  7. 7. Could precursors and /or proto-cells have arrived from outer space? BBC News Monday, 29 January, 2001 Scientists have managed to create quot;primitive cellsquot; in an experiment which may indicate that life began in space and was delivered to Earth. Researchers working with the American space agency NASA say their quot;proto-cellsquot; mimic the membranous structures found in all living things. They were produced in a laboratory experiment that duplicated the harsh conditions of cold interstellar space. This new work suggests that the early chemical steps believed to be important for the origin of life do not require an already-formed planet. Instead, they seem to take place in deep space long before planet formation occurs. This implies that the vastness of space is filled with chemical compounds which, if they land in a hospitable environment like our Earth, can readily jump-start life. living membrane-bound proto-cells cells self-replicating system enclosed in a selectively permeable, protective lipid sphere enzymes and DNA RNA other proteins formation of formation of protein-RNA systems, lipid spheres evolution of DNA spontaneous formation of lipids, carbohydrates, amino acids, proteins, nucleotides under abiotic conditions 7
  8. 8. III. The first true cells 3.5 billion y –old prokaryote Anaerobic or aerobic? Fig. 20-8a, p.324 The First Cells • Originated in Archeon Eon • Were prokaryotic heterotrophs • Secured energy through anaerobic pathways – No oxygen present – Relied on glycolysis and fermentation 8
  9. 9. Stromatolites – fossils of cyanobacteria; 3by-old Proterozoic Eon • Origin of photosynthetic Eubacteria – Cyclic pathway first – Noncyclic pathway next (cyanobacteria) • Oxygen accumulates in atmosphere • Origin of aerobic respiration Eukaryotes 2.1 bya Fig. 20-8b, p.324 9
  10. 10. IV. Where did eukaryotic organelles come from? The evolution of the eukaryotic cell Where did all these organelles come from? IV. Where did eukaryotic organelles come from? The evolution of the eukaryotic cell 10
  11. 11. DNA ER ? infolding of plasma membrane Fig. 20-10a, p.326 Possible origin of nucleus IV. Where did eukaryotic organelles come from? The evolution of the eukaryotic cell Origin of mitochondria and chloroplasts 11
  12. 12. Evidence Endosymbiosis example in modern time Amoeboid organism with green alga within Occurred by phagocytosis Evidence photosynthetic organelle that resembles a cyanobacterium mitochondrion nucleus 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 12
  13. 13. V. The timeline of development hydrogen-rich anaerobic atmosphere atmospheric oxygen, 10% archaean lineage d ancestors of h eukaryotes endomembrane system and nucleus noncyclic pathway of photosynthesis cyclic pathway f of photosynthesis e b a origin of g aerobic respiration prokaryotes 3.8 billion 3.2 billion 2.5 billion years ago years ago years ago atmospheric oxygen, 20%; the ozone layer slowly develops k origin of animals j k origin of fungi origin of eukaryotes, the first protists i endosymbiotic origin k origin of lineage of mitochondira j leading to plants endosymbiotic origin of chloroplasts Aerobic species becomes endosymbiot of anaerobic forerunner of eukaryotes. 1.2 billion 900 million 435 million years ago years ago years ago Fig. 20-12b, p.328 13

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