Download 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:
1.
2.
3.
Francesco Redi (1665)
Lazzaro Spallanzani (1767)
Louis Pasteur (1862)
Redi’s Experiment
 People thought maggots came from meat
 Redi showed that maggots came from flies laying
eggs on the meat
Spallanzani’s Experiment
 People still thought that
microorganisms could
spontaneously generate
 Spallanzani boiled two
flasks of broth, then left
one open and sealed one

People convinced that spontaneous
generation exists said that boiling the
broth killed a “vital principle” in the air

Bacteria grew in the open
flask
The sealed flask
remained sterile
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
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
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
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
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
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
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
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
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
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
Lipid-membrane Hypothesis
 Lipids spontaneously
form membraneenclosed spheres called
liposomes
 Liposomes could act as
membranes around a
variety of organic
molecules, separating
them from the
environment
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
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?
Endosymbiosis
 Suggested by
Lynn Margulis
(1970s)
 Idea that
mitochondria and
chloroplasts used
to be simple
prokaryotic cells
that were engulfed
by larger
prokaryotes
Animation
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