Evolution

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Evolution Mon, Wed Fri 1100 1150
pm Spring Semester 2006
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Evolution 1 2006 Spring
Photosynthesis
The carbon source -gt as important to autotrophs
as to heterotrophs The electron source -gt
H2S -gt H2O 2 H2S CO2 -gt light -gt CH2O H2O
2 S 6 CO2 6 H2O -gt light -gt C6H12O6 6 O2
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Evolution 2 2006 Spring
Photosynthesis
A revolution -gt that changed the face of the
Earth The electron source -gt H2S -gt H2O 2 H2S
CO2 -gt light -gt CH2O H2O 2 S 6 CO2 6 H2O
-gt light -gt C6H12O6 6 O2
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Evolution 3 2006 Spring
Oxygen
liberation of molecular oxygen -gt a formerly
reducing atmosphere -gt changed into an oxidizing
one gt Need of anti-oxidixing metabolic
compounds enzymes to neutralize H2O2 and O2
radicals
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Evolution 1 2004 Spring
Oxygen
Fossil evidence Oxygenating cyanobacteria Sout
h African Bulawayan limestone -gt 3 bio years
old Australia Warrawoona -gt 3.5 bio years
old http//earth.usc.edu/geol150/evolutio
n/precambrianfossils.html
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Evolution 4 2006 Spring
Oxygen
Until 2 bio years ago -gt Oxygen concentration in
the atmosphere remained at 1 -gt then it
gradually increased to the present
concentration of ___ gt Increased success of
photosynthetic forms!
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Evolution 5 2006 Spring
Oxygen
Another important effect -gt development of the
ozone layer in the stratosphere gt Protects
organisms by absorbing lethal UV
radiation . made it possible to colonize
shallow aquatic and terrestrial habitats
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Evolution 6 2006 Spring
Aerobic Metabolism
Oxygen is now available -gt evolution of
respiratory pathways -gt a lot more efficient
than fermentation!
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Evolution 7 2006 Spring
Aerobic Metabolism
Respiration Glycolysis Krebs cycle Electron
transport chain chemiosmosis gt Complete
aerobic oxidation of Glucose yields ___ ATP
molecules
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Evolution 8 2006 Spring
Aerobic Metabolism
Efficiency
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Evolution 9 2006 Spring
Metabolism
Progression of metabolic pathways Anaerobic
systems (fermentation) -gt photosynthesis -gt
aerobic respiration
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Evolution 10 2006 Spring
Early fossilized cells
Cell-like fossils appear around 3.5 bio years
ago -gt in unmetamorphosed rock formations
(cherts) -gt associated with layered organic
deposits gt stromatolites
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Evolution 11 2006 Spring
Early fossilized cells
Modern forms of stromatolites -gt mats of
microorganisms -gt live in inhospital habitats
- salinities 10 times that of sea water
- temperatures higher than 65ºC -gt
protection from predators
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Evolution 12 2006 Spring
Early fossilized cells
-gt shallow water environments were inhabited by
prokaryotic microorganisms 3.5 bio years
ago -gt stromatolite communities were finely
lamented and multi-component -gt members of the
community were - filamentous -
photo-responsive - possibly phototactically
mobile (gliding) - both autotrophic and
heterotrophic
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Evolution 13 2006 Spring
Prokaryotes and Eukaryotes
Significant change in cellular complexity Prokar
yotes Eukaryotes
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Evolution 14 2006 Spring
Prokaryotes and Eukaryotes
Significant change in cellular complexity
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Evolution 15 2006 Spring
Prokaryotes and Eukaryotes

• Prokaryotes
• Eubacteria
• -gt cyanobacteria and other forms of bacteria
• -gt peptidoglycan or murein cell walls
• Archaebacteria
• -gt different material for cell walls
• -gt live in hot sulfur springs and high
  salinity habitats

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Evolution 16 2006 Spring
Prokaryotes and Eukaryotes

• Eukaryotes
• Single-celled algae and protozoans
• Multi-cellular plants, animals and fungi

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Evolution 17 2006 Spring
Prokaryotes and Eukaryotes
Prokaryotes Eukaryotes - no nuclear envelope -
nuclear envelope - cell size 1 - 10 ?m - cell
size 10 100 ?m - binary fission - mitotic
cell division - lack ER, Golgi, - have those
organelles cytoskeleton
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Evolution 18 2006 Spring
Prokaryotes and Eukaryotes
Prokaryotes Eukaryotes - no split genes -
split genes -gt exons (expressed
sequences) -gt introns ( intervening
sequences) is there an advantage? found in
many eukaryotes
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Evolution 19 2006 Spring
Prokaryotes and Eukaryotes
How did introns enter eukaryotic DNA? Why are
introns maintained? gt Alternative mRNA
splicing
Exons
DNA
RNAtranscript
RNA splicing
or
mRNA
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Evolution 20 2006 Spring
Prokaryotes and Eukaryotes
How did introns enter eukaryotic DNA? Why are
introns maintained? gt Could be mobile DNA
splice into or out of target sites
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Evolution 21 2006 Spring
Prokaryotes and Eukaryotes
Phylogenetic relationships -gt archaebacteria
occupy an intermediate position between
eubacteria and eukaryotes -gt the three groups
may have a common root -gt various
theories which one is the oldest group
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Evolution 22 2006 Spring
E
Eukaryotic organelles
The origin of mitochondria and chloroplasts gt
Eukaryotic cells evolved by incorporating
prokaryotic organisms -gt endocytosis
loss of the rigid prokaryote cell wall -gt
more flexible cytoskeleton
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Evolution 23 2006 Spring
E
Eukaryotic organelles

• some eukaryotes became active predators
• -gt increase in size
• -gt more mobile
• -gt innovation of prey capture
• -gt digestion
• Prey
• gt aerobe bacteria-like organisms
• gt cyanobacteria capable of photosynthesis

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Evolution 24 2006 Spring
Eukaryotic organelles

• Ingested prey may have provided
• a mutually advantageous symbiotic relationship
• Still occur nowadays
• Paramecium
• algae
• Corals
• Zooxanthellae

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Evolution 25 2006 Spring
Eukaryotic organelles
Ancestors of mitochondria were probably ingested
first Improved metabolism gt selective
advantage gt better predatory abilities Later
some improved eukaryotes ingested the ancestral
chloroplast (ancestors of algae and plants)