Download PROKARYOTES The Importance of Prokaryotes KEY POINTS

9/13/11
The Importance of Prokaryotes
KEY POINTS
1.  Decomposers: recycle organic and
inorganic molecules in environment; makes
them available to other organisms.
2.  Essential components of symbioses.
3.  Encompasses the origins of metabolism and
metabolic diversity.
4.  Origin of photosynthesis and formation of
atmospheric Oxygen
PROKARYOTES
Domains Bacteria & Archaea
ANTIQUITY
ic
zo
oMes
zoic
Cenozoic
General characteristics
Humans
leo
Pa
Colonization
of land
Animals
Bil
lio
2
ns
of
Archaean
m
Proterozoic
Small
No organelles
Cell wall
Numerous
-5µ
4
1
1. 
2. 
3. 
4. 
0.5
Origin of solar
system and
Earth
Prokaryotes
go
sa
ar 3
ye
Multicellular
eukaryotes
Single-celled
eukaryotes
Atmospheric
oxygen
1
9/13/11
General characteristics
General characteristics
6.  Important decomposers and recyclers
7.  Symbionts
a.  Parasites
b.  Commensalists
c.  Mutualists
5.  Metabolic diversity established nutritional
modes of eukaryotes.
TAXONOMY is problematic
•  Relationships obscured by billions of
years of evolution
•  Also obscured by unique bacterial
means of recombination (more later).
•  Grouped primarily by DNA sequence
data.
•  Immense genetic/genomic diversity.
i.  Endosymbiotic theory for origin of Eukaryotes
ii.  Cellulose consumption by animals
iii.  Essential nutrients
iv.  Other cool examples
Current taxonomy is
stabilizing
•  Note that Prokaryote
is paraphyletic. Why?
•  Two Domains:
•  Archaea: extremophiles
(mostly), ancient,
probable progenitors of
eukaryotes.
•  Bacteria: most
commonly-encountered
prokaryotes.
2
9/13/11
Cell Surface
• 
• 
Archaea: plasma
membrane of
ether-lipids
(unique in life).
Bacteria: a sugar
polymer peptidoglycan
Motility
•  ~half the species can move.
1.  Flagella
2.  Spiral filaments: spirochetes
corkscrew
3.  Gliding
•  Capable of taxis
Cell Surface
•  Fimbriae & pili
Genome
•  Small genomes:
~1/1000th DNA
content of
eukaryotes.
•  No nucleus.
•  ‘nucleoid region.
•  Circular
chromosome
•  Plasmids
3
9/13/11
Genome: Recombination via
transformation
•  DNA taken up from
the environment
Genome: Recombination via
transduction
•  Transfer of DNA via
phage viruses.
Genome: Recombination via
conjugation
•  Direct transfer of
DNA between cells.
•  Both plasmids and
portions of bacterial
chromosome.
Reproduction & Growth
•  Meiosis & Mitosis NOT
PRESENT.
•  Asexual binary
fission.
4
9/13/11
Metabolism
Metabolic Diversity: Metabolism
Source of Carbon
Metabolic Diversity
•  Nutrition:
•  Requires a source of carbon
•  Requires a source of energy
•  AUTOTROPHS: Need only carbon
dioxide (CO2) as carbon source
•  HETEROTROPHS: Need at least one
organic nutrient as carbon source (e.g.
glucose; petroleum)
•  Both of these present in domain
Eucarya as well.
Metabolic Diversity: Metabolism
Source of Energy
Metabolism
Metabolic Diversity: Combined
•  PHOTOTROPHS: Need only sunlight as
energy source
•  CHEMOTROPHS: Derive energy from
oxidation of organic molecules.
Carbon
Source:
•  Both of these present in domain
Eucarya as well.
Energy Source:
Sun
Environment
CO2
Photoautotroph
Chemoautotroph
Organic
molecules
Photoheterotroph
Chemoheterotroph
Which of these are present in multicellular Eucarya?
5
9/13/11
Metabolism
Photoautotrophs
Chemoautotrophs
•  Oxidize inorganics
(H2S, NH3) for energy.
•  Need only CO2 as
carbon source.
•  Unique to Bacteria and
Archaea.
•  E.g. Methanococcus
jannaschii lives on
hydrothermal vents at
2600m below sea level.
•  Reduces H2 + CO2 to
CH4 + 2H2O.
•  Use sun for energy,
CO2 for carbon.
•  Photosynthetic
bacteria (e.g.
cyanobacteria).
•  Present in many
plants and singlecelled Eucarya
Metabolism
Photoheterotrophs
•  Get enery from light
but must obtain
carbon in organic
form (NOT CO2).
•  Unique to Bacteria
and Archaea.
•  E.g. Halobacterium
salinarium.
Metabolism
Chemoheterotrophs
Metabolism
•  Consume organic
molecules for both
energy and carbon.
•  Common among
prokaryotes:
–  saprobes
(decomposers)
–  parasites (rely on
living hosts)
•  Also widespread in
Protista, Animalia,
Plantae.
6
9/13/11
Metabolism
Nitrogen metabolism
•  Nitrogen fixation:
•  N2 to ammonia (NH3) to
ammonium (NH4+).
•  Essential for multicellular
life!
Taxonomy of Prokaryotes
•  Archaea or Archaebacteria
–  Methanogens
–  Halophiles
–  Thermophiles
•  Bacteria or Eubacteria
– 
– 
– 
– 
– 
Protobacteria
Chlamyidias
Spirochetes
Cyanobacteria
Gram-positive bacteria
Oxygen Relationships
•  Aerobic vs. Anaerobic
•  Obligate aerobes
•  Cellular respiration:
•  Facultative anaerobes
•  Fermentation:
•  Obligate anaerobes
•  Anaerobic respiration:
Archaea or Archaebacteria
•  Live in extreme
environments
(extremophiles): sulfur
hot springs, deep sea
vents, high salt
environments.
•  Lack peptidoglycan,
unique plasma
membrane of liquids
•  Likely sister group of
Eukaryotes
7
9/13/11
Prokaryotes: Summary
•  You should now have a good sense of
prokaryote biology and diversity.
•  Including roles in metabolism,
symbioses, global energy cycles.
•  Important distinguishing characteristics
of cell wall, motility, genome, replication.
•  General aspects of their systematics.
8