Chapter 19: The Origin of Life
and the Evolution of Cells
Lecture Outline
Enger, E. D., Ross, F. C., & Bailey, D. B. (2012). Concepts in biology (14th ed.). New York: McGrawHill. 1
19-1
Early Thoughts About the Origin
of Life

Spontaneous generation
–
–
–
–
–

The idea that living things arise from nonliving things
Proposed by Aristotle
Maggots from rotting meat
Mice from wheat stored in dark, damp places
Frogs from damp mud
Biogenesis
–
–
Life originates from pre-existing life
Supported by experiments by Redi that challenged
spontaneous generation

19-2
Demonstrated that maggots did not come from decaying meat,
but from eggs of flies
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Redi’s Experiment
19-3
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Needham vs. Spallazani

Needham
–
–
–

Spallazani
–
–
–
–
19-4
Boiled mutton broth in containers sealed with cork
The broth became cloudy with microorganisms.
Argued that this supported spontaneous generation
because the broth had been boiled and was sealed from
contamination
Challenged Needham’s data
Did a similar experiment, but sterilized the glass and closed
the containers by melting the glass
Used a control that was not sealed
Showed that the sterile environment sustained no bacterial
growth
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Spallazani’s Experiment
19-5
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Pasteur Settled the Debate
19-6
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Current Thinking About the
Origin of Life

If biogenesis is true, and living things come
from living things, then how did the first living
things arise?
–
–
19-7
There are several hypotheses.
We will never know with certainty because events
in the past are not empirical.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Extraterrestrial Origin for Life
on Earth

Panspermia is the hypothesis that life arose
outside the earth.
–

Evidence from meteorites
–

Meteorites from Mars were found to contain
complex organic molecules.
Evidence from Mars exploration
–
–
19-8
Living things were transported to earth.
Evidence was found that bodies of water
previously existed.
These bodies of water may have supported life.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Earth: Origin for Life on Earth

Focuses on chemical evolution
–

Evidence supporting this hypothesis
–
–
19-9
Proposes that inorganic matter changed into organic
matter
Earth has an appropriate temperature range to allow water
to exist as liquid on its surface.
The atmosphere contains oxygen.
 Most other planets’ atmospheres lack oxygen.
 The earth’s atmosphere may have lacked oxygen before
life.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Earth: Origin for Life on Earth

Evidence supporting this hypothesis
–
–
–
Organic molecules can be generated in the
laboratory in the absence of oxygen.
The earth was likely hotter in the past.
The discovery of extremophiles suggests that
early life may have been very different than life as
we know it.

19-10
Extremophiles are bacteria and archaea that can live in
extreme environments.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The “Big Bang” and the Origin
of the Earth

Evidence indicates that our universe began as a
dense mass of matter containing a lot of energy.
–
–

The protoplanet nebular model proposes that the
solar system was formed from a cloud of gases and
elements formed from previously existing stars.
–
19-11
This mass exploded, forming huge amounts of hydrogen
and helium.
The light from stars is a result of the nuclear fusion of these
atoms.
Gravitational pull was created by collections of particles that
formed the sun and the planets.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Formation of our Solar System
19-12
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Earth’s Early Environment

As the particles that formed Earth
concentrated, thermonuclear reactions
occurred.
–
–
19-13
This made the earth a very hot place.
This formed a molten core encased by a thin
outer crust as it cooled.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Earth’s Early Environment

Over time, the earth cooled, changing it
dramatically.
–
An atmosphere had formed.

Water vapor, carbon dioxide, carbon monoxide,
methane, nitrogen, and ammonia
These would have made the atmosphere a reducing
atmosphere.
– Likely didn’t contain oxygen
–
–
19-14
Cooling would have caused rain that formed
oceans, lakes, etc.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Chemical Evolution of Life
on Earth

All living things contain:
–
–
–

Therefore, it is logical that the evolution of cells
involved the formation of:
–
–
–
–
–
–
19-15
An outer membrane that separates the cell from its
environment
Nucleic acids as genetic material
Enzymes that regulate metabolism
Organic molecules from inorganic molecules
Complex organic molecules from simple ones
Genetic material that is self-replicating
Enzymes
Membranes
A method to obtain energy
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Formation of the First Organic
Molecules

19-16
Oparin and Haldane proposed that organic
molecules could have formed spontaneously in a
reducing environment.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Importance of a Reducing
Atmosphere

A reducing atmosphere would lack oxygen.
–


Today organic molecules are oxidized to simpler
molecules because of the presence of oxygen.
After forming in the atmosphere, the organic
molecules may have been washed from the air
by rain into the oceans.
–
19-17
This would allow organic molecules to join with
one another instead of joining with oxygen.
In the ocean, they could have reacted with one
another to form more complex molecules.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Experimental Evidence
for Chemical Evolution

Stanley Miller
–
–
–
–
–
Tested the hypothesis that organic molecules could
form in a reducing atmosphere
Constructed an apparatus that would simulate the
earth’s early atmosphere
Electrical sparks provided the energy.
The apparatus was heated and cooled several times.
The water was analyzed.

19-18
Found to contain many organic molecules such as
amino acids and sugars
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Miller’s Apparatus
19-19
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Formation of Macromolecules

How did simple organic molecules combine to form
macromolecules?
–
One hypothesis suggests that geologic changes caused the
first ocean to separate.


–
–
19-20
Evaporation of the smaller ocean caused the molecules to
become concentrated.
May have led to dehydration synthesis and the formation of
macromolecules
Another hypothesis suggests that freezing caused the
concentration of molecules that led to dehydration.
A third hypothesis proposes that clay particles caused the
aggregation and concentration of organic molecules.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
RNA May Have Been the First
Genetic Material


Cells that use DNA as genetic material use
complex enzymatic pathways to get the DNA
replicated and transcribed into RNA.
A simpler genetic system must have arisen
as cells evolved.
–
–
19-21
Some viruses use RNA as their genetic material.
These mutate very rapidly, can replicate
themselves and even serve as catalysts
(ribozymes) for specific reactions.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Development of Membranes

Oparin suggested that membranes were a
collection of organic molecules surrounded
by a film of water.
–
–
–
19-22
Called these structures coacervates
They can be generated in a laboratory.
Some contain enzymes.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Development of Membranes

Another hypothesis suggests that cells
began as collections of organic molecules
with a double-layered boundary.
–
–
–
–
19-23
Called microspheres
Can be generated in the laboratory
Contain enzymes and use ATP as an energy
source
Can make polypeptides and nucleic acids
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Development of Membranes

A third hypothesis proposes that membranes
formed from lipids interacting with water.
–
19-24
When lipids and water are mixed, spherical lipid
structures form.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Developing a Genetic System


How did primitive cells become the complex,
self-replicating cells that exist today?
Several steps must have been involved.
–
–
–
–
–
19-25
Proteins must become enzymes.
RNA must control protein synthesis.
DNA must replace RNA as the genetic material.
The first cells must be able to reproduce.
The first cells must be able to obtain energy from
their environment.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Development of Metabolic
Pathways

The first cells would have to have had a way
to add new organic molecules.
–

Two ways to obtain energy
–
–
19-26
This requires energy.
Heterotrophs capture organic molecules from
their environment.
Autotrophs use an external energy source to
make organic molecules.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Heterotroph Hypothesis



Proposed that the first cells lived off organic
molecules present in the ocean
These organisms would have been anaerobic since
the atmosphere was reducing.
As the organisms reproduced and organic molecules
became depleted, mutation could have produced an
organism that could metabolize other material into
organic material.
–
19-27
This would be adaptive and would promote survival.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Autotroph Hypothesis


Proposes that the first organisms were autotrophs
Many Archaea (primitive organisms) that live in
extremely hostile environments are autotrophs.
–

19-28
Use the energy released from inorganic chemical reactions
to make organic molecules.
Early competition between autotrophs would have
led to the evolution of heterotrophic organisms and
autrotrophic organisms that could use other types of
molecules and energy sources.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Summary of Chemical Evolution
19-29
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Development of an
Oxidizing Atmosphere

How would the hypothesized reducing
atmosphere have turned into the oxidizing
atmosphere that exists today?
–
–
19-30
Photosynthesis
Aerobic respiration
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Origin of Photosynthesis

The evolution of photosynthetic autotrophs
(such as cyanobacteria)
–
–
Would result in the release and accumulation of
oxygen in the atmosphere
The presence of oxygen generates an oxidizing
atmosphere.


19-31
An oxidizing atmosphere would not support the
spontaneous generation of organic molecules.
But would support life once the organisms had evolved
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Origin of Aerobic Respiration


19-32
The appearance of oxygen in the
atmosphere allowed for the evolution of
aerobic respiration.
This would have been adaptive because
more ATP can be produced when oxygen is
the final electron acceptor.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Establishment of Three
Major Domains of Life

Recent genetic technologies have allowed for
detailed analysis of organisms’ genetic
natures.
–

This data is used to infer evolutionary relationships.
Woese studied the sequence of rRNA in a
number of prokaryotic cells.
–
Discovered that prokaryotes could be subdivided
into two different types of organisms

19-33
Bacteria and Archaea
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Establishment of Three
Major Domains of Life


Archaea share some characteristics with
eukaryotes.
Woese’s data led to the identification of three
domains.
–
Eubacteria, Archaea and Eucarya


19-34
Eubacteria and Archaea are prokaryotes.
Eucarya is subdivided into several kingdoms.
– Animalia, Plantae, Fungi, Protista
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Major Domains of Life
19-35
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Origin of Eukaryotic Cells


The leading hypothesis proposes that eukaryotic
cells evolved from prokaryotic cells.
The mechanism of this evolution is thought to be the
endosymbiotic theory.
–
–
–
19-36
Eukaryotes arose from the union of several types of
prokaryotic cells.
The organelles of eukaryotic cells (mitochondrion,
chloroplast) originated as free-living prokaryotes.
The combination of two prokaryotic cells resulted in a
symbiotic relationship that became permanent.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Endosymbiotic Theory
19-37
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Evolution of the Nucleus

Two hypotheses propose how the nucleus
came to be.
–
An invading cell with a membrane took over the
coordination of cell activities by hijacking the cell’s
DNA.

–
19-38
Thus became the nucleus
Prokaryotic cells developed a nuclear membrane
from membranes in the cell.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Endosymbiosis and the Evolution
of Eucarya
19-39
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Development of
Multicellular Organisms

19-40
Unicellular organisms aggregated to form collections
of cells with no specialization, then evolved to
complex arrangements in which specific cells have
specific jobs.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Geologic Timeline and Evolution
of Life

A geologic timeline shows a chronological history of
organisms.
–
–

Based on the fossil record
Expressed in units called eons that can be divided into eras
Life appears about 3.8 bya during the Archean Eon.
–
–
–
These were prokaryotic
Eukaryotic organisms appeared 1.8 bya.
Multicellular organisms appeared 1-0.6 bya.

19-41

This event was followed by a number of adaptive radiations
(evolutionary explosions) that led to the appearance of plants
on land, the appearance of aquatic then terrestrial animals.
Also followed by some massive extinctions
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Evolutionary Time Line
19-42
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Movement of Life to Land


For 90% of Earth’s history, life has been
confined to water.
The movement of life to land required several
adaptations.
–
–
–
–
19-43
The ability to breathe air; lungs
A way to prevent dehydration; scales and skin
A skeleton for support; cartilage to bones
The ability to reproduce without water; direct
fertilization and the amniotic egg
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Movement of Life to Land


Reptiles moved to land and diversified.
Some developed characteristics and were the
ancestors of vertebrates.
–
–
–
–

19-44
Warm-bloodedness
Feathers
Hair
Internal development of young
Since these characteristics were adaptive, selected
for, reptilian species decreased in number and
primitive birds and mammals evolved.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.