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Molly Hunter
641C Marley
621-9350
[email protected]
Will have office hours Wed. Feb 1,
Fri. Feb 3 (next week)
• Or make an appt. by email or phone
• Lecture style: questions, questions
• Key concepts/outline posted before
lecture , ppt posted after lecture
Prokaryotes
Outline of lecture today
• Why you should care about
the little stuff
• Today - two of the three
domains of life
Just like organization of life (cells,
tissues….populations,
communities), the organization of
groups of organisms is hierarchical
How can we reconstruct the
evolution of living things?
(Chapter 25…)
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• Systematists study evolutionary
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I. Prokaryotes - Bacteria and
Archaea
A. The three domains of life,
phylogeny
B. Morphology
C. Physiology/metabolism
C. Ecology and key adaptations
D. A few prokaryotic groups
II. The evolution of the eukaryotic
cell
relationships
• Look for shared derived
(=different from ancestor) traits
to group organisms
• Evidence used: morphology,
development, and molecular data
(especially DNA sequences)
1
Why can’t we figure it out
perfectly?
• More distant history is obscured
by more changes
• Among oldest lineages of
Bacteria and Archaea in
particular, lots of “lateral gene
transfer.” Makes it difficult to
infer relationships from
phylogeny of single genes.
A. Phylogeny
The Archaea and Bacteria are
both prokaryotic,but differ
more from each other than does the
Archaea from the Eukarya
(=plants, animals, fungi, protists).
A. Phylogeny
• The three domains: Bacteria,
Archaea, and Eukarya.
~3 billion years
~2 billion years
How did we learn the existence
of the Archaea?
• Difference between
prokaryotes and
eukaryotes long been
known.
• Bacteria and Archaea are
superficially similar
• But they are genetically
different:
u
I. Prokaryotes - Bacteria
and Archaea
• The prokaryotes are the most
numerous organisms on Earth
•With tremendous diversity in
metabolism, habitats
The first Archaean genome
was sequenced in 1996 most genes were very
different from bacterial
genes - birth of the “three
domain” concept
B. Morphology of prokaryotes
What are they
missing?
Nuclei
Membrane-enclosed
organelles
Cytoskeletons (actin
and microtubules)
What have they got
that’s different from
protists and animals?
Cell wall
2
B. Morphology of the
prokaryotes
Prokaryotic cells are
usually much
smaller than
eukaryotic cells
Closer to the size of a
mitochondrion or
chloroplast
Is that a coincidence?
B. Morphology of the
prokaryotes - Movement
Simple
flagella
Eukaryote
Cell
Prokaryote
Cell
Gas vesicles to
adjust
buoyancy
cyanobacteria
Or gliding
mechanisms
spirochaete
C. Ecology of the prokaryotes
B. Morphology of the
prokaryotes - Cell walls
• Prokaryotic cell walls differ from
those of eukaryotes.
• Cell walls of Bacteria contain
peptidoglycan (a polymer of amino
sugars). Cell walls of Archaea
contain proteins.
• How do prokaryotes reproduce?
• Asexually by fission
Bacterial
cell wall
C. Physiology/metabolism of
the prokaryotes
• How do prokaryotes reproduce?
• Asexually by fission
• Exchange genetic information
(e.g. by conjugation). In
conjugation,
DNA travels
from
donor to
recipient
via a
cytoplasmic
bridge
C. Physiology/metabolism of
prokaryotes
• Prokaryotes - fairly narrow range
of shapes and sizes, not very
exciting movement: What have
prokaryotes been doing for more
than 3 billion years?
• Learning chemical tricks
3
C. Physiology/metabolism of
prokaryotes
• All ancestral prokaryotes were
anaerobic, and some still are:
• Anaerobic: metabolism in the
absence of oxygen
• Aerobic: metabolism that requires
oxygen
• Some can shift back and forth
C. Physiology/metabolism of
prokaryotes
• What do plants do for energy and
carbon?
• They use light for energy and C02
for carbon. Some prokaryotes do
as well - e.g. Cyanobacteria. These
are autotrophs
• Why were
Cyanobacteria so
important in the
history of life
on Earth?
C. Physiology/metabolism of
the prokaryotes
• Some chemolithotrophs
live near deep sea
hydrothermal vents at up
to 2,500 m deep where
there is no light.
• Prokaryotes (mostly
Archaea)
that use hydrogen
sulfide from deep sea
volcanic vents for energy
provide food for
an entire bizarre
community.
C. Physiology/metabolism of
prokaryotes
• All living organisms need a source
of energy and a source of carbon in
order to survive and grow
• What is the source of our energy
and carbon?
• We ingest molecules for both
energy and carbon, so we’re
heterotrophs
• Most Bacteria and Archaea are
heterotrophs as well
C. Physiology/metabolism of
Prokaryotes
• Others have completely unique
solutions, not found in eukaryotes
• Some use simple nitrogen or sulfur
compounds for energy, but CO2 for
carbon (needing neither light nor
organic compounds for food!).
• Called chemolithotrophs
• Have enabled life in extremely
inhospitable places!
C. Physiology/metabolism of
the prokaryotes
Lastly, some
use light for energy,
but need food for
carbon:
photoheterotrophs
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C. Physiology/metabolism of
the prokaryotes
• Other chemical tricks
• Fix nitrogen from
atmosphere
• Digest cellulose
• Produce amazing
toxins
like polyketides
(many antibiotics,
e.g. tetracycline,
anti-tumor drugs)
• Polyketide in
Paederus beetle
Paederus
C. Physiology/metabolism of
the prokaryotes
• Paederus has long
been known because
if crushed against
skin causes rashes
• Produces pederin, a
polyketide
• Pederin also has
anti-tumor activity
• Guess where
Paederus gets its
pederin?
Paederus beetle
D. Ecology of the prokaryotes
- extreme habitats
D. Ecology of the prokaryotes
• Some Archaea are
heat-loving and acidloving.
• Some live in hot
sulfur springs and die
of “cold” at 131°F
(55°C)
• Some anaerobic Archaea produce
methane from CO2 as a key part of
their energy metabolism.
• They account for the methane in the
atmosphere.
Archaea
in
sulfurous
volcanic
vent
D. Ecology of the prokaryotes
D. Ecology of the prokaryotes
Some of these methane producers live in
the guts of herbivorous animals
More about those prokaryotes in
mammalian guts - the human
gut flora
How many cells relative to other
cells in our body?
About how many species of
bacteria?
How much of your weight is
bacteria?
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D. Ecology of the prokaryotes
Role of gut flora?
Long thought to be commensal - i.e.
beneficial to the bacteria, neutral for us
Recent research tells a very different
story
E.g. bacteria are important for digesting
carbohydrates, and variation in
efficiencies between individuals may
explain variation in tendencies towards
obesity
Also influence immune system (and
autoimmune diseases) in development
E. Important prokaryotic
groups - just a few
• There are far more known
Bacteria than Archaea.
The Bacteria
The Proteobacteria
Mitochondria evolved
from Proteobacteria
by endosymbiosis.
D. Ecology of the
prokaryotes
• Some prokaryotes play key roles in
global nitrogen cycles. E.g., nitrogen
fixers, nitrifiers, and denitrifiers.
Fig. 37.8 in
your text
Nitrogen fixation –
out of the air
Nitrification – from
one solid form to
another better for
plants
Denitrification –
back to the air
The Bacteria
The Proteobacteria
• By far the biggest
group of Bacteria
• Includes Rhizobium,
the nitrogen fixing
bacterium found in
legume root nodules.
• Also Salmonella,
cholera, and E. coli.
The Bacteria:
Cyanobacteria
• Cyanobacteria are
photosynthetic
•They created the
oxygen atmosphere
•Chloroplasts evolved
from cyanobacteria by
endosymbiosis
•Makes you
think differently
about “pond scum,” no?
6
The Bacteria: Spirochaetes
• Spirochaetes are
corkscrew shaped
•Move by axial
filaments
•Some are parasites
of humans, e.g.
agent causing
syphilis, Lyme
disease
The Bacteria: Chlamydias
Chlamydia are among
the tiniest living
things.
Almost all parasites,
e.g. a sexually
transmitted disease of
humans
Have complex life
cycle with two stages:
a resting stage gets
taken into
host cell, the other
grows and divides
E. Important prokaryotic groups :
Summary of the Archaea
II. The origin of the
eukaryotic cell
• Archeans differ from Bacteria:
Cell wall: proteins not
peptidoglycans
• Step 1? (no one knows the
sequence) Increase in size
• A central problem with being big is
that surface area doesn’t increase as
fast as volume, yet surfaces are
needed for gas exchange and
feeding
• What’s the solution?
•Very different genetically
•Archeans often live in extreme
habitats: tolerate high
temperature, salt, low pH,
absence of oxygen.
II. The origin of the
eukaryotic cell
What’s the solution?
Lose the cell wall,
allow infolding
of the plasma
membrane to
increase area
The origin of the eukaryotic cell
Step 2? Infolded
plasma membrane
attached to the
chromosome may
have led to a nuclear
envelope.
Step 3? A primitive
cytoskeleton of actin and
microtubules evolved.
This allowed cell to
change shape and
move things around
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II. The origin of the
eukaryotic cell
• The first eukaryotes were
anaerobic.
• But as oxygen increased, the
oxidizing atmosphere was
poisonous to anaerobes.
• Step 4? Engulfing an aerobic
proteobacterium resulted in
mitochondria.
• (Step 5? For some) Some
organisms engulfed
cyanobacteria and become
photosynthetic
(chloroplasts).
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