Origin Of Life

1. Origin Of Life

2. Francesco Redi’s Experiment • Common thought: Spontaneous generation of flies from meat • Redi - Italian physician/scientist in the 1600s • Noticed that maggots turned into sturdy oval cases, from which flies eventually emerged • This made him question spontaneous generation • Performed an experiment

3. Spallanzani’s Experiment • Around Redi’s time, infection-causing microorganisms were discovered; they were thought to have been generated spontaneously from a “vital force” found in the air • In 1700s, Italian scientist Lazzaro Spallanzani designed an experiment to test the hypothesis of spontaneous generation Experimental design: • 4 flasks of meat broth • 1 open – produced microorganism • 1 closed – same • 1 boiled and open – same • 1 boiled and closed – remained microorganism free

4. Objections to Spallanzani’s Work • Opponents to his work claimed that Spallanzani had heated the experimental flasks too long, destroying the “vital force” in the air inside them • Because of this, those that believed in Spontaneous Generation refused to change their thoughts

5. Disproving Spontaneous Generation once and for all! • By 1800s the debate over spontaneous generation predominated science • Paris Academy of Science offered a reward • French Scientist Louis Pasteur won by designing an experiment that answered the objections to Spallanzani’s experiment

6. Pasteur’s Experiment • Pasteur made a curve-necked flask that allowed the air inside the flask to mix with air outside the flask • The curve in the neck prevented solid particles from entering the body of the flask • Broth boiled inside the experimental curve-necked flasks remained clear for up to a year • But when he broke off the necks, the broth became cloudy and contaminated with microorganisms within a day

7. Aftermath of Pasteur’s Experiment • Those that defended spontaneous generation gave up their fight • The principle of biogenesis now became the cornerstone of biology

8. Big Bang • About 17 billion years ago all the matter and energy in the universe was compressed into an extremely small volume (a singularity) and then • BOOM! • The big bang sent all the matter and energy outward in a giant cloud

9. Origin of Life -- Breakdown • 1. Atmosphere and earth formed- had little or no oxygen • 2. The primordial seas formed as the Earth cooled and gases condense • 3. The first organic molecules formed • 4. Polymers and self replicating molecules were synthesized • 5. Organic molecules were organized into protobionts- the precursors of cells. • 6. Primitive heterotrophic prokaryotes formed • 7. Primitive autotrophic prokaryotes formed • 8. Oxygen and the ozone layer formed • 9. Eukaryotic cells formed (endosymbiont theory)- orginated from a symbiotic relationship between several prokaryotes. 9

10. 1 - Earth’s History • Earth is believed to be approximately 4.6 billion years old • Formed from swirling clouds of dust that condensed • Isaac Newton (the light spectrum – roygbv) determined that planets are moving further and further away from one another based on the intensity of wavelengths emitted by the light from those planets (red shift)

11. 1 & 2 - Early Earth • Early Atmosphere • Volcanoes released gases (carbon dioxide, nitrogen, hydrogen sulfide, hydrogen, water vapor, methane, and ammonia) into the atmosphere • Creates a reducing (electron adding) atmosphere • The gases condensed to form the “soupy seas”.

12. 3 - The First Organic Compounds • Intense lightning, ultraviolet radiation from sun, heat, and radioactivity created enormous amounts of energy in the environment. • This energy transformed inorganic molecules into organic molecules including amino acids, nucleotides and fatty acids. • These first molecules were formed by chemical evolution

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14. Who Figured that Out? • Primitive Atmosphere Hypothesis (1923) • Alexander Oparin and J. B. S. Haldane postulated that the reducing atmosphere and high UV radiation reaching the surface of primitive earth enhanced reactions that joined simple molecules to produce the first organic molecules. • This would not be possible today, since oxygen in today's atmosphere attacks chemical bonds (removingelectrons) and the ozone layer of the earth's atmosphere screens out most UV radiation

15. Miller & Urey • Miller and Urey • They tested Oparin’s hypothesis by recreating the proposed primitive atmosphere, simulating lighting with electric sparks • Over time, amino acids, sugars, lipids, bases, cAMP, FAD, NAD, NADP, and ATP developed within their experimental chamber

16. Miller & Urey • Revisions to theory?? 16

17. 4 - Polymerization • Polymers are formed by dehydration synthesis (removal of water) • Sidney Fox proved that earth’s clay had the ability to act as a substrate for dehydration reactions. • Water containing organic monomers may have splashed up on warm clay surfaces and allow for polymerization of monomers • EX: Amino acids would bind together and form proteinoids (abiotically produced proteins)

18. 4 - The First Genetic Material • RNA has been theorized as the first genetic material because self-replicating RNA can abiotically (w/o enzymes) reproduce in a test tube • Ribozyme- form of RNA that can catalyze proteins directly

19. 5 - Protobionts • Protobionts (pre-cursors to cells) • Also called coacervates • Contained permeable membranes and had a primitive metabolism (carry out chemical rx’s) • Formation • When lipids are added to water, membrane bound spheres form (mycells) • These spheres are capable of growing, dividing, shrinking and swelling, and have a semi-permeable membrane • These spheres may contain RNA and/or proteinoids 19

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21. 6 - The First Forms of Life • When the first prokaryotic cells arose (between 3.5 and 4.0 billion years ago), there was no usable oxygen gas in existence • Thus, first forms of life must have been anaerobic • Anaerobic prokaryotes appeared and consumed protobionts and other organic molecules • this caused a buildup of CO2 from fermentation

22. 7 - The First Forms of Life • Over 3 billion years ago, autotrophic prokaryotes appeared when mutant heterotrophs gained the ability to use sunlight and CO2 for photosynthesis. • This caused the buildup of oxygen in the atmosphere

23. First Forms of Life - Fossil Record • The earliest microfossils (so named because of their small size) date back to 3.5 billion years ago • Earliest fossils were stromatolites which are the direct ancestors of cyanobacteria (autotrophic bacteria) • Mats of fossilized stromatolites dating back 2.5 billion years mark a time when photosynthetic prokaryotes had produced enough O2 to make an aerobic atmosphere

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25. 8 - Oxygen and the Atmopshere • O2 molecules produced by photosynthetic prokaryotes eventually raised to the upper atmosphere. • Here they were split by UV light, forming free O radicals • These combined with O2 molecules which formed O3 (Ozone)

26. 8 - Oxygen and the Atmopshere • This ozone gas absorbs intense ultraviolet radiation from the sun, making it possible for life to exist on earth (UV radiation destroys/damages DNA molecules) • Abiotic chemical evolution ended due to less UV light reaching Earth’s surface

27. 9- The First Eukaryotes • Between 2 and 3 billion years ago the first eukaryotes appeared on earth • How they came about (Endosymbiotic Theory) • Small aerobic prokaryotes entered and began to live in larger prokaryotes (acting as mitochondria…respirators) • A short time later small photosynthetic prokaryotes began to enter these larger cells (acting as chloroplasts …food producers)

28. Endosymbiotic Theory • Endosymbiotic theory says that groups of prokaryotes came together and formed eukaryotes through symbiotic relationships • Evidence • Mitochondria & chloroplasts have their own DNA which is circular and “naked” • They have their own ribosomes which resemble those of bacteria • They are encased by membranes. • They reproduce independently of the host cell by a process similar to binary fission in bacteria.

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32. Book Section Correlation • Chapter 16 Bat CAMPBELL textbook 32