1. Chapter 12, Section 3 And parts of 12.4
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