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Origins of Life

Origins of Life. Chapter 12, Section 3 And parts of 12.4. Early Theories. Spontaneous generation = the idea that living things could come from nonliving things Three experiments disproved this theory: Francesco Redi (1665) Lazzaro Spallanzani (1767) Louis Pasteur (1862).

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Origins of Life

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  1. Origins of Life Chapter 12, Section 3 And parts of 12.4

  2. Early Theories • Spontaneous generation = the idea that living things could come from nonliving things • Three experiments disproved this theory: • Francesco Redi (1665) • Lazzaro Spallanzani (1767) • Louis Pasteur (1862)

  3. Redi’s Experiment • People thought maggots came from meat • Redi showed that maggots came from flies laying eggs on the meat

  4. Spallanzani’s Experiment • People still thought that microorganisms could spontaneously generate • Spallanzani boiled two flasks of broth, then left one open and sealed one • Bacteria grew in the open flask • The sealed flask remained sterile People convinced that spontaneous generation exists said that boiling the broth killed a “vital principle” in the air

  5. Pasteur’s Experiment • Disproved spontaneous generation once and for all • Microorganisms only grew in the flask when the swan neck was broken • The swan neck prevented particles in the air from entering the broth Animation

  6. Biogenesis – Life from Life • A possible sequence: • Inorganic molecules form and make small organic molecules • Small organics join to form macromolecules / polymers • Origin of RNA / DNA to make inheritance possible • Packaging within membranes

  7. Related Vocabulary • Inorganic – any substance that doesn’t contain both carbon (C) and hydrogen (H) • Organic – any substance that contains both C and H; usually comes from something that is, or once was, living • Polymer – substance made up of many repeating subunits (monomers) • Macromolecule – large molecules; biological examples include carbohydrates, lipids, proteins, and nucleic acids

  8. Early Earth • For the first 700 million years, Earth was most likely very hot and in a molten state • Over time, the materials making up Earth separated into Earth’s layers (crust, mantle, core) • Gases released from Earth’s interior formed an atmosphere Early Life on Earth – 4:37

  9. Oparin and Haldane – 1920s • Theory for how life may have developed on early Earth; based on assumptions that: • There was little or no oxygen present • The atmosphere was mainly formed from volcanic vapors – methane, ammonia, hydrogen, water vapor • Felt it would be possible for inorganic molecules to be converted to organic forms using energy from the sun and lightning • At the time, no effective way to test this

  10. Miller and Urey – 1950s • Tested Oparin-Haldane hypothesis • Simulated atmosphere containing gases Oparin & Haldane thought were present • Exposed gases to electric shocks to simulate lightning • Produced small organic compounds – mainly amino acids Animation

  11. Follow-up to Miller/Urey • Based on the gases emitted from volcanoes today, scientists think the atmosphere would have been different from what Oparin & Haldane proposed • More carbon monoxide (CO), carbon dioxide (CO2), nitrogen gas (N2) and water vapor • Similar experiments using this “updated” representation of the atmosphere produced smaller amounts of amino acids

  12. Meteorite Hypothesis • Analysis of meteorites indicate that organic molecules can be found in space • This suggests the following possibilities: • Amino acids may have been present when Earth formed • Organic molecules may have arrived on Earth through meteorite / asteroid impact

  13. Formation of the First Cells • Once organic molecules / compounds are formed, how did they get packaged into cells? • Iron-sulfide bubbles hypothesis • Lipid membrane hypothesis

  14. Iron-Sulfide Bubbles • Iron sulfide rising from deep sea vents combines with cool ocean water to form chimney-like structures with many compartments • Biological molecules may have combined inside these compartments, which acted as membranes • With the right combination of ingredients, the first organic cell membranes may have formed

  15. Lipid-membrane Hypothesis • Lipids spontaneously form membrane-enclosed spheres called liposomes • Liposomes could act as membranes around a variety of organic molecules, separating them from the environment

  16. The First Genetic Material • It has been hypothesized that RNA was the genetic material for the earliest life forms • Cech & Altman (1980s) discovered that RNA can: • Catalyze reactions • Copy itself

  17. The First Eukaryotes • Fossil evidence indicates that the first living things were prokaryotes (bacteria) • First appeared ~3.5 BYA • Eukaryotes – cells with a nucleus and other organelles – don’t appear in the fossil record until approx. 1.5 BYA • How did the first eukaryotic cells develop?

  18. Endosymbiosis • Suggested by Lynn Margulis (1970s) • Idea that mitochondria and chloroplasts used to be simple prokaryotic cells that were engulfed by larger prokaryotes Animation

  19. Endosymbiosis, cont’d • What evidence supports endosymbiosis? • Both mitochondria and chloroplasts: • Have their own DNA • Have their own ribosomes • Can copy themselves • Are about the same size as prokaryotes • Have DNA in the shape of a circle, like bacterial / prokaryotic DNA

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