origins of life
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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). - PowerPoint PPT PresentationTRANSCRIPT
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Origins of Life
Chapter 12, Section 3
And parts of 12.4
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Early Theories
Spontaneous generation = the idea that living things could come from nonliving things
Three experiments disproved this theory:
1. Francesco Redi (1665)
2. Lazzaro Spallanzani (1767)
3. Louis Pasteur (1862)
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Redi’s Experiment
People thought maggots came from meat Redi showed that maggots came from flies laying
eggs on the meat
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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
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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
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Biogenesis – Life from Life
A possible sequence:
1. Inorganic molecules form and make small organic molecules
2. Small organics join to form macromolecules / polymers
3. Origin of RNA / DNA to make inheritance possible
4. Packaging within membranes
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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?
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Endosymbiosis
Suggested by Lynn Margulis (1970s)
Idea that mitochondria and chloroplasts used to be simple prokaryotic cells that were engulfed by larger prokaryotes
Animation
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Endosymbiosis, cont’d
What evidence supports endosymbiosis? Both mitochondria and chloroplasts:
Have their own DNAHave their own ribosomesCan copy themselvesAre about the same size as prokaryotesHave DNA in the shape of a circle, like
bacterial / prokaryotic DNA