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Chapter 27
Prokaryotes
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Overview: They’re (Almost) Everywhere!
• Most prokaryotes are microscopic, but what they
lack in size they make up for in numbers
• There are more in a handful of fertile soil than the
number of people who ever lived
• Prokaryotes thrive almost everywhere, including
places too acidic, too salty, too cold, or too hot for
most other organisms
• They have an astonishing genetic diversity
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 27.1: Structural, functional, and genetic
adaptations contribute to prokaryotic success
• Most prokaryotes are unicellular, although some
species form colonies
• Prokaryotic cells have a variety of shapes
• The three most common of which are spheres
(cocci), rods (bacilli), and spirals
Video: Tubeworms
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LE 27-2
1 µm
Spherical
(cocci)
2 µm
Rod-shaped
(bacilli)
5 µm
Spiral
Cell-Surface Structures
• An important feature of nearly all prokaryotic cells
is their cell wall, which maintains cell shape,
provides physical protection, and prevents the cell
from bursting in a hypotonic environment
• Using the Gram stain, scientists classify many
bacterial species into groups based on cell wall
composition, Gram-positive and Gram-negative
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LE 27-3
Lipopolysaccharide
Cell
wall
Pepridoglycan
layer
Cell
wall
Outer
membrane
Pepridoglycan
layer
Plasma membrane
Plasma membrane
Protein
Protein
Grampositive
bacteria
Gramnegative
bacteria
20 µm
Gram-positive
Gram-negative
• The cell wall of many prokaryotes is covered by a
capsule, a sticky layer of polysaccharide or protein
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LE 27-4
200 nm
Capsule
• Some prokaryotes have fimbriae and pili, which
allow them to stick to their substrate or other
individuals in a colony
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LE 27-5
Fimbriae
200 nm
Motility
• Most motile bacteria propel themselves by flagella
that are structurally and functionally different from
eukaryotic flagella
• In a heterogeneous environment, many bacteria
exhibit taxis, the ability to move toward or away
from certain stimuli
Video: Prokaryotic Flagella (Salmonella typhimurium)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 27-6
Flagellum
Filament
50 nm
Cell wall
Hook
Basal apparatus
Plasma
membrane
Internal and Genomic Organization
• Prokaryotic cells usually lack complex
compartmentalization
• Some prokaryotes do have specialized
membranes that perform metabolic functions
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LE 27-7
1 µm
0.2 µm
Respiratory
membrane
Thylakoid
membranes
Aerobic prokaryote
Photosynthetic prokaryote
• The typical prokaryotic genome is a ring of DNA
that is not surrounded by a membrane and that is
located in a nucleoid region
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LE 27-8
Chromosome
1 µm
• Some species of bacteria also have smaller rings
of DNA called plasmids
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Reproduction and Adaptation
• Prokaryotes reproduce quickly by binary fission
and can divide every 1–3 hours
• Many prokaryotes form endospores, which can
remain viable in harsh conditions for centuries
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LE 27-9
Endospore
0.3 µm
• Rapid reproduction and horizontal gene transfer
facilitate the evolution of prokaryotes in changing
environments
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Concept 27.2: A great diversity of nutritional and
metabolic adaptations have evolved in prokaryotes
• All four models of nutrition are found among
prokaryotes:
– Photoautotrophy
– Chemoautotrophy
– Photoheterotrophy
– Chemoheterotrophy
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Metabolic Relationships to Oxygen
• Prokaryotic metabolism varies with respect to
oxygen:
– Obligate aerobes require oxygen
– Facultative anaerobes can survive with or
without oxygen
– Obligate anaerobes are poisoned by oxygen
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Nitrogen Metabolism
• Prokaryotes can metabolize nitrogen in a variety
of ways
• In nitrogen fixation, some prokaryotes convert
atmospheric nitrogen to ammonia
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Metabolic Cooperation
• Cooperation between prokaryotes allows them to
use environmental resources they could not use
as individual cells
• In the cyanobacterium Anabaena, photosynthetic
cells and nitrogen-fixing cells exchange metabolic
products
Video: Cyanobacteria (Oscillatoria)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 27-10
Photosynthetic
cells
Heterocyte
20 µm
• In some prokaryotic species, metabolic
cooperation occurs in surface-coating colonies
called biofilms
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 27.3: Molecular systematics is
illuminating prokaryotic phylogeny
• Until the late 20th century, systematists based
prokaryotic taxonomy on phenotypic criteria
• Applying molecular systematics to the
investigation of prokaryotic phylogeny has
produced dramatic results
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Lessons from Molecular Systematics
• Molecular systematics is leading to a phylogenetic
classification of prokaryotes
• It allows systematists to identify major new clades
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• A tentative phylogeny of some of the major taxa of
prokaryotes based on molecular systematics
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Proteobacteria
Universal ancestor
Domain
Archaea
Eukaryotes
Nanoarchaeotes
Crenarcaeotes
Domain Bacteria
Euryarchaeotes
Korarchaeotes
Gram-positive
bacteria
Cyanobacteria
Spirochetes
Chlamydias
Epsilon
Delta
Gamma
Beta
Alpha
LE 27-12
Domain
Eukarya
Bacteria
• Diverse nutritional types are scattered among the
major groups of bacteria
• The two largest groups are the proteobacteria and
the Gram-positive bacteria
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LE 27-13
PROTEOBACTERIA
CHLAMYDIAS
2.5 µm
2.5 µm
Subgroup: Alpha Proteobacteria
Chlamydia (arrows)
Rhizobium (arrows)
SPIROCHETES
1 µm
5 µm
Subgroup: Beta Proteobacteria
Leptospira
Nitrosomonas
GRAM-POSITIVE BACTERIA
Mycoplasmas covering
a human fibroblast cell
Streptomyces
Chromatium
5 µm
10 µm
Bdellovibrio
bacteriophorus
Chrondromyces
crocatus
2 µm
Subgroup: Epsilon Proteobacteria
Heliocobacter pylori
50 µm
CYANOBACTERIA
Subgroup: Delta Proteobacteria
Oscillatoria
1 µm
0.5 µm
5 µm
Subgroup: Gamma Proteobacteria
Archaea
• Archaea share certain traits with bacteria and
other traits with eukaryotes
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Some archaea live in extreme environments
• Extreme thermophiles thrive in very hot
environments
• Extreme halophiles live in high saline
environments
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Methanogens live in swamps and marshes and
produce methane as a waste product
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Concept 27.4: Prokaryotes play crucial roles in the
biosphere
• Prokaryotes are so important to the biosphere that
if they were to disappear, the prospects for any
other life surviving would be dim
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Chemical Recycling
• Prokaryotes play a major role in the continual
recycling of chemical elements between the living
and nonliving components of ecosystems
• Chemoheterotrophic prokaryotes function as
decomposers, breaking down corpses, dead
vegetation, and waste products
• Nitrogen-fixing prokaryotes add usable nitrogen to
the environment
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Symbiotic Relationships
• Many prokaryotes live with other organisms in
symbiotic relationships
• In mutualism, both symbiotic organisms benefit
• In commensalism, one organism benefits while
neither harming nor helping the other in any
significant way
• In parasitism, one organism, called a parasite,
benefits at the expense of the host
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 27.5: Prokaryotes have both harmful and
beneficial impacts on humans
• Some prokaryotes are human pathogens, but
others have positive interactions with humans
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Pathogenic Prokaryotes
• Prokaryotes cause about half of all human
diseases
• Lyme disease is an example
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Pathogenic prokaryotes typically cause disease by
releasing exotoxins or endotoxins
• Exotoxins cause disease even if the prokaryotes
that produce them are not present
• Endotoxins are released only when bacteria die
and their cell walls break down
• Many pathogenic bacteria are potential weapons
of bioterrorism
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Prokaryotes in Research and Technology
• Experiments using prokaryotes have led to
important advances in DNA technology
• Prokaryotes are the principal agents in
bioremediation, the use of organisms to remove
pollutants from the environment
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Some other uses of prokaryotes:
– Recovery of metals from ores
– Synthesis of vitamins
– Production of antibiotics, hormones, and other
products
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings