Transcript Chap 15 – Three Domain System

Chapter 15
Tracing Evolutionary History
PowerPoint Lectures for
Campbell Biology: Concepts & Connections, Seventh Edition
Reece, Taylor, Simon, and Dickey
© 2012 Pearson Education, Inc.
Lecture by Edward J. Zalisko
MAJOR EVENTS IN THE
HISTORY OF LIFE
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Life’s Calendar
Figure 15.4
Archaean
eon
Proterozoic
eon
Phanerozoic
eon
Colonization
of land
Animals
Multicellular eukaryotes
Single-celled eukaryotes
Origin
of Earth
4.6
Atmospheric oxygen
Prokaryotes
4
3
2
Billions of years ago
1
Present
15.4 The origins of single-celled and multicelled
organisms and the colonization of land were
key events in life’s history
 Prokaryotes lived alone on Earth for 1.5 billion
years, from 3.5 to 2 billion years ago.
– During this time, prokaryotes transformed the
atmosphere.
– Prokaryotic photosynthesis produced oxygen that
enriched the water and atmosphere of Earth.
– Anaerobic and aerobic cellular respiration allowed
prokaryotes to flourish.
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15.4 The origins of single-celled and multicelled
organisms and the colonization of land were
key events in life’s history
 The oldest fossils of eukaryotes are about 2.1
billion years old.
 The common ancestor of all multicellular
eukaryotes lived about 1.5 billion years ago.
 The oldest fossils of multicellular eukaryotes are
about 1.2 billion years old.
 The first multicellular plants and fungi began to
colonize land about 500 million years ago.
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15.4 The origins of single-celled and multicelled
organisms and the colonization of land were
key events in life’s history
 Humans diverged from other primates about 6 to 7
million years ago.
 Our species, Homo sapiens, originated about
195,000 years ago.
 If the Earth’s history were compressed into an
hour, humans appeared less than 0.2 seconds
ago!
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Larger Cells and Organisms Need More Oxygen
More O2 allows for CR and
aerobic metabolism =
greater ATP yield!!
Molecular Homologies Provide Greatest Evidence
for Life’s Common Ancestor
 All living organisms share many biochemical and
developmental pathways:
 DNA --> RNA --> Protein
 Same genetic code
 Transcription/translation/replication processes same
 Glycolysis and cellular respiration similar
 Many genes are amazingly similar
– About 99% of the genes of humans and mice are
homologous.
– About 50% of human genes are homologous with those of
yeast.
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Three Domain System
 Molecular homologies have unveiled a new organization to
life’s history.
 Comparison of rRNA gene sequences by Carl Woese
 Remember, rRNA gene sequences allow for
comparison of long-distance relationships
 Biologists currently recognize a three-domain system
consisting of
– two domains of prokaryotes: Bacteria and Archaea, and
– one domain of eukaryotes called Eukarya including
– fungi, protists, plants, animals
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Figure 15.19A
1 Most recent common ancestor of all living things
2 Gene transfer between mitochondrial ancestor
and ancestor of eukaryotes
3 Gene transfer between chloroplast ancestor
and ancestor of green plants
Bacteria
3
2
1
Eukarya
Archaea
4
3
2
Billions of years ago
1
0
Figure 1.4 The Tree of Life
Implications of Updated Tree of Life
 Bacteria and Archaea diverged very early in the evolutionary
history of life
 Archaea are more closely related to eukaryotes than to
bacteria.
 Eukarya diverged from line of Archaea
 Several endosymbiotic events lead to evolution of eukaryotes
 Mitochrondria acquired from aerobic bacteria
 Chloroplast from photosynthetic bacteria
 Mitochondria acquired first; 1st eukaryotes heterotrophic
 Multicellularity in eukaryotes arose multiple times (convergent
evolution)
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Endosymbiosis theory
 Mitochondria & chloroplasts were once
free living bacteria

engulfed by ancestral eukaryote
 Endosymbiont

cell that lives within another cell (host)
 as a partnership
 evolutionary advantage
for both
 one supplies energy
 the other supplies raw materials
& protection
Honors Biology
Lynn Margulis
U of M, Amherst
Endosymbiosis theory
Evolution of eukaryotes
Honors Biology