Transcript history of cells ppt

Biology, Seventh Edition
Solomon • Berg • Martin
The Origin of the first
cells
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 20 The Origin and Evolutionary History of Life
• Conditions on early Earth
• Age of Earth is ~4.6 billion years
• Atmosphere had little free O2
–Included CO2, H2O, CO, H2, N2
–Maybe also NH3, H2S, CH4
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 20 The Origin and Evolutionary History of Life
• Requirements for chemical
evolution to produce life
• Absence of oxygen
• Energy
• Chemical building blocks
• Sufficient time
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 20 The Origin and Evolutionary History of Life
• Prebiotic soup hypothesis
• Molecules formed near the
Earth’s surface
• Sugars, nucleotides, amino acids
formed spontaneously
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 20 The Origin and Evolutionary History of Life
Miller-Urey
experiment
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 20 The Origin and Evolutionary History of Life
• Origin of cells
• Spontaneous assembly of small
organic molecules into
macromolecules
• Deep sea vent w/ iron sulfide for
energy
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 20 The Origin and Evolutionary History of Life
• Microspheres
• Formed from water and
polypeptides
• Electric gradient on surface
• Selective permeability
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 20 The Origin and Evolutionary History of Life
Microspheres – a type of protobiont
(early lipid membrane)
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 20 The Origin and Evolutionary History of Life
• RNA for early genetic
inheritance.
• Self-replicating RNA molecules
• Function as both enzyme and
substrate for replication
–Ribozyme is enzymatic RNA
• First step in evolution of the
DNA / RNA / protein system
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 20 The Origin and Evolutionary History of Life
• Directed evolution
• Large pool of RNA molecules
with different sequences
• Selected for ability to catalyze a
reaction
• Amplify / mutate / repeat
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Biology, Seventh Edition
CHAPTER 20 The Origin and Evolutionary History of Life
Directed evolution
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 20 The Origin and Evolutionary History of Life
• In the RNA world, ribozymes
catalyzed protein synthesis
• DNA formed from double
strands of RNA
• DNA more stable than RNA
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The prokaryotes
The first cells
Image Credits Gary Gaugler Bacillus anthracis
Image Credits: Thermophilic archaebacteria
Biology, Seventh Edition
CHAPTER 20 The Origin and Evolutionary History of Life
• The first cells
• Heterotrophs that feed on organic
molecules
• Anaerobic fermentation process
to obtain energy
Copyright © 2005 Brooks/Cole — Thomson Learning
Origins
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Evidence for prokaryotic cells is found as
early as 3.9 billion years ago
The prokaryotes had the Earth to themselves
for another 2.4 billion years
Prokaryotes show an extraordinary diversity
of biochemistry
Structurally prokaryotes are quite small and
simple (1-10µm in diameter).
© 2010 Paul Billiet ODWS
Where?
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“(a) warm little pond, with all sorts of ammonia and
phosphoric salts, lights, heat, electricity, etc.
present, so that a protein compound was chemically
formed ready to undergo still more complex
changes” Charles Darwin (1871)
organic compounds would accumulate in the Earth's
oceans until they "reached the consistency of hot,
dilute soup." JBS Haldane (1929)
Deep sea hydrothermal vents
Volcanoes
Outer space.
© 2010 Paul Billiet ODWS
Biology, Seventh Edition
CHAPTER 20 The Origin and Evolutionary History of Life
Endosymbiont theory- evolution of
eukaryotes
• Eukaryotes arose from
prokaryotes: a large anaerobic
cell teams up with an aerobic
cell
–Mitochondria and chloroplasts
derived from prokaryotes
–Ingested but not digested
–Reproduced along with host cell
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 20 The Origin and Evolutionary History of Life
The evidence for endosymbiosis
• Certain eukaryotic organelles have their own DNA
• Single naked loop of DNA, like the prokaryotes
• The amount of hereditary information is a lot less
than free-living prokaryotes
• These organelles have their own ribosomes
• Smaller (70S) than those in the cytoplasm (80S)
• The ribosomes of mitochondria and chloroplasts are
the same size as those in prokaryotes
• The protein synthesis of these organelles is semiindependent of that taking place in the cytoplasm
• It is inhibited by the same antibiotic that affects
prokaryotes (chloramphenicol).
© 2010 Paul Billiet ODWS
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 20 The Origin and Evolutionary History of Life
Endosymbiont
theory
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 20 The Origin and Evolutionary History of Life
The structural evidence
• These organelles are
found in membrane
envelopes
• As though they were
captured in a vacuole
or vesicle by a larger
cell
• These organelles are
about the same size as
a prokaryotic cell.
Image Credit: Mitochondrion
© 2010 Paul Billiet ODWS
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 20 The Origin and Evolutionary History of Life
Mitochondria
• These represent an
aerobic prokaryote
that took up residence
in a larger cell
• These are found in all
the eukaryotic
kingdoms
(plants, animals, fungi
and protoctista).
Image Credit: Mitochondrion
© 2010 Paul Billiet ODWS
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 20 The Origin and Evolutionary History of Life
Chloroplasts
These represent a
cyanobacterium type of
prokaryote that was
trapped in ancestral plants
and some protoctista
Image Credit: Cyanobacterium heterocyst
© 2010 Paul Billiet ODWS
Copyright © 2005 Brooks/Cole — Thomson Learning