Origins of Life

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
Redis Experiment

• People thought maggots came from meat
• Redi showed that maggots came from flies laying
  eggs on the meat

4
Spallanzanis 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
Pasteurs 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 doesnt 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 Earths layers (crust, mantle,
  core)
• Gases released from Earths interior formed an
  atmosphere

Early Life on Earth 437
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 dont 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, contd

• 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