Prokaryotes
(the fancy way to say Bacteria)
Chapter 27
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Outline
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Prevalence of Prokaryotes
Prokaryotic Diversity
Prokaryotic Complexity
Prokaryotic Variation
Prokaryotic Metabolism
Human Bacterial Diseases
Benefits of Prokaryotes
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Prevalence of Prokaryotes
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In almost every place or environment
microbiologists (scientists who study small
organisms) look, prokaryotes have been found.
– Hot springs, hypersaline environments, highly
toxic gaseous environment, within clean
rooms of hospitals
In the 1980’s a new method of classification
was used
Divided prokaryotes into 2 groups:
– Archaebacteria (Archae) and bacteria
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Prevalence of Prokaryotes
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Prokaryotes are the oldest, structurally
simplest, and most abundant forms of life on
earth.
– abundant for over 2 billion years before
the appearance of eukaryotes
– Prokaryotic synthesis (from cyanobacteria)
is thought to have been the source for
much of the earth’s oxygen in atmosphere
– 5,000 different kinds currently recognized
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Structure of a Prokaryotic Cell
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Structure of a Prokaryotic Cell
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Most prokaryotic cells are small and lack
interior organization.
The plasma membrane is enclosed within a
rigid cell wall
DNA not contained within a membranebounded nucleus.
Prokaryotes exteriorly may have a flagellum
and other outgrowths called pili.
Pili aid in attachment to other cells
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Prevalence of Prokaryotes
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Prokaryotic form
– bacillus (bacilli) straight and rod-shaped
– coccus (cocci) spherical shaped
– spirillum (spirilla) long and helical shaped
Some bacillus and coccus bacteria form
colonies
Spirilla generally do not form colonies and
are often free swimming
Some bacterial colonies form spore
producing structures.
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Prevalence of Prokaryotes
Prokaryotic form
Coccus
– Diplococcus
 pairs
– Streptococcus
 chains
– Tetrad
 quads
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Prevalence of Prokaryotes
Coccus
Sarcina
Staphalo
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Prevalence of Prokaryotes
Bacillus
Single
Strepto
coccobacillus (no pics)
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Prevalence of Prokaryotes
Spiral Types
Vibrio
Comma shaped
Sprillium
Thick rigid spiral
Spirochete
Thin flexible
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Prevalence of Prokaryotes
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Prokaryotes versus Eukaryotes
– unicellularity
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cell size
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No internal compartments (mitochondria or chloroplasts)
only organelle is the ribosome
flagella
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binary fission (asexual)
internal compartmentalization
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“naked” (no protein) circular DNA located in nucleoid
cell division and recombination
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1 μm or less in diameter
May vary by 5 orders of magnitude
chromosomes
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some may form filamentous matrices
Single protein flagella of flagellin
Spin like propellers instead of whiplike
metabolic diversity
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Several kinds of anaerobic and aerobic photosynthesis
Chemoautotrophs
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Prokaryotic Diversity
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Original key classification characteristics
– photosynthetic or nonphotosynthetic
– motile or nonmotile
– unicellular or colony-forming or
filamentous
– spore formation by division or transverse
binary fission
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Prokaryotic Diversity
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Now prokaryotic classification completed
with genetic and molecular approaches
– Analysis of amino acids sequence of key
proteins
– Nucleic acid analysis by establishing %
guanine (G) and cytosine (C)
– nucleic acid hybridization
– ribosomal RNA sequencing
– whole genome sequencing
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Kinds of Prokaryotes
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Very early, prokaryotes split into two lines
– Archaea and bacteria are as different in
structure and metabolism from each other
as either is from eukarya.
 Archae (archebacteria) not actually as
old as Bacteria
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Prokaryotic Diversity
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Comparing archaebacteria and bacteria
– plasma membranes
 composed of different lipids
– cell wall
 archaebacteria lack peptidoglycan
– gene translation machinery
 Bacteria ribosomal proteins and RNA
polymerases different from eukaryotes
 archaebacteria similar to eukaryotes
– gene architecture
 bacteria genome not interrupted by introns
 some archaebacteria posses introns
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Prokaryotic Complexity
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Prokaryotic cell surface – identifying features
– cell wall maintains shape and protects the cell
from swelling and rupturing
 usually consist of peptidoglycan
 Gram-positive - thicker peptidoglycan
 (purple color after stain)
 Gram-negative - thinner peptidoglycan
 (red color after stain)
– flagella – slender protein - locomotion
– pili - hairlike structures – attachment (7.5 – 10 nm)
– endospores - resistant to environment
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Gram Stain
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Flagellar Motor
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The Cell Interior
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Internal membranes
– invaginated plasma membrane for respiration and/or
photosynthesis
Nucleoid region
– lack nucleus - genes encoded with single doublestranded DNA
*Prokaryotes often posses plasmids: independently
replicating circle of DNA that contain only a few genes
(not usually essential for survival)
Ribosomes
– Prokaryotic ribosomes are smaller than eukaryotic
ribosomes, and differ in protein and RNA content.
– Some antibiotics (tetracycline and chloramphenicol) bind
to prokaryotic ribosomes to block protein synthesis
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The Cell Interior
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Internal membranes
– (a) aerobic bacterium exhibits extensive respiratory
membranes within cytoplasm
– (b) cyanobacterium has thylakoid-like membranes that
provide sites for photosynthesis
Do you think that it
is likely that
photosynthetic and
respiratory
membranes evolved
more than once?
How could your
idea be tested
experimentally?
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Processes to Create Prokaryotic Variation
mutation
– spontaneous errors in DNA replication
 prokaryotic ability to mutate rapidly often has
adverse effect on humans
– Radiation, UV light, and various chemicals
(mutagens) cause DNA replication errors
– Normal mutation rate 1 per million bases
– E. coli has 5000 genes
– This means that 1 out of every 200 bacteria will
have a mutation
– 1 spoonful of soil has 1 billion bacteria, so there
should be 5 million mutant individuals per
spoonful!
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Processes to create Prokaryotic Variation
mutation
– with sufficient nutrients, a typical bacterium
population could double in 20 minutes.
– this allows for mutations to spread rapidly
– individual bacterium not killed by an antibiotic can
then reproduce rapidly and after 30 generations (10
hours) there would be over 1 billion clones of this
resistive bacteria
– Some hospitals now have strains of Staphyloccus
aureus that are penicillin resistant
– Why then could antibiotic soaps be a problem?
– Why should you take all 10 days of your
medication?
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Processes to create Prokaryotic Variation
mutation –figure 27.7
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Processes to create Prokaryotic Variation
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genetic recombination
– occurs by gene transfer from one cell to
another by viruses or conjugation
 conjugation: temporary union of 2
unicellular organisms, during which
genetic material is transferred from one
cell to another.
– this is another method that can lead to
resistant bacteria
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Prokaryotic Metabolism
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Autotrophs
– obtain carbon from inorganic CO2
 photoautotrophs – use sunlight to build organic
molecules from CO2
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chlorophyll a as pigment and H20 as electron donor
bacteriochlorophyll as pigment and H2S as electron donor
chemoautotrophs - inorganic chemicals
 obtain energy by oxidizing inorganic
substances
 Nitrifiers – oxidize ammonia or nitrite
 On ocean floors H2S is oxidized as it escapes
from thermal vents
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Prokaryotic Metabolism
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Heterotrophs
– obtain carbon from organic molecules
 photoheterotrophs – sunlight + organic C
 purple non-sulfur bacteria
 organic molecules such as
carbohydrates or alcohols source for C
 chemoheterotrophs (most prokaryotes)
 carbon and energy from organic
molecules
 most decomposers and pathogens
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Prokaryotic Metabolism
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How heterotrophs infect host organisms
– proteins secreted by type III system
 may be used to transfer other virulence
proteins into nearby eukaryotic cells
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Human Bacterial Diseases
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Tuberculosis
– afflicts respiratory system and easily
transmitted from person to person through
the air
Dental caries
– tooth decay caused by bacteria present in
plaque
 high sugar diets increase tooth decay
 lactic acid bacteria ferment sugars and
reduce pH, thus degenerating tooth
enamel
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Human Bacterial Diseases
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Sexually transmitted diseases
– Gonorrhea (Neisseria gonorrhoeae)
– Syphilis (Treponema pallidum)
– Chlamydia (Chlamydia trachomatis)
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Benefits of Prokaryotes
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Environment
– chemical cycling
– decomposition
– nitrogen fixation
 reduces N2 to NH3
Symbiotic properties
– nitrogen-fixation
– digestive tract of animals
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Benefits of Prokaryotes
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Genetic engineering
– nonpolluting insect control
– bioremediation
 pollutant removal
– biofactories
 commercial production of antibiotics
Bioweapons
– anthrax
– smallpox
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Bioremediation
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