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 A different way to study Taxonomy…
Biology: Life on Earth, 9e
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Chapter 19
The Diversity of
Prokaryotes and Viruses
Lecture Outlines by Gregory Ahearn,
University of North Florida
Copyright © 2011 Pearson Education Inc.
Chapter 19 At a Glance
 19.1 Which Organisms Are Members of the
Domains Archaea and Bacteria?
 19.2 How Do Prokaryotes Survive and
Reproduce?
 19.3 How Do Prokaryotes Affect Humans and
Other Eukaryotes?
 19.4 What Are Viruses, Viroids, and Prions?
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19.1 Which Organisms Are Members of the
Domains Archaea and Bacteria?
– Earth’s first organisms were prokaryotes, singlecelled microbes that lacked organelles
– Prokaryotes are still abundant, forming two of
life’s three domains
–Bacteria
–Archaea
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19.1 Which Organisms Are Members of the
Domains Archaea and Bacteria?
 Bacteria and Archaea are fundamentally
different
– They have some similarities
–They are both prokaryotic
–They are both single-celled organisms
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19.1 Which Organisms Are Members of the
Domains Archaea and Bacteria?
 Differences between Bacteria and Archaea
– Structural and biochemical features
–Bacteria have peptidoglycan in their cell walls;
Archaea don’t
–There are also differences in the plasma
membrane composition, ribosomes, and RNA
polymerases between the two domains
–Differences in transcription and translation
also exist between the two
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 Archaea
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4.1 What Is the Cell Theory?
 Three principles comprise the cell theory
– Every living organism is made of one or more
cells
– The smallest organisms are single cells, and
cells are the functional units of multicellular
organisms
– All cells arise from preexisting cells
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4.2 What Are the Basic Attributes of Cells?
 There are two basic types of cells:
–Prokaryotic cells (“before the nucleus”) form
the bodies of bacteria and archaea, the
simplest forms of life
–Eukaryotic cells (“true nucleus”) form the
bodies of animals, plants, fungi, and protists
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The Sizes of Microorganisms
1 m
Staphylococcus
cyanobacterium
Escherichia
coli
Eukaryotic cells
(10–100 m)
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Prokaryotic cells
(0.2–10 m)
Viruses
(0.05–0.2 m)
Fig. 19-10
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4.3 What Are the Major Features of Eukaryotic
Cells?
 Eukaryotic cells are usually larger than
prokaryotic cells
– The cytoplasm of eukaryotic cells includes a
variety of organelles, such as the nucleus and
mitochondria
– The cytoskeleton gives shape and organization
to the cytoplasm of eukaryotic cells
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4.4 What Are the Major Features of Prokaryotic
Cells?
 Prokaryotic cells are small and possess
specialized surface features
 Prokaryotic cells have fewer specialized
structures within their cytoplasm
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4.4 What Are the Major Features of Prokaryotic
Cells?
 Most prokaryotic cells (bacteria) are less than
5 µm long, with a simple internal structure
compared to eukaryotic cells
– They usually have a stiff cell wall
– Prokaryotic cells can take several shapes:
–Rod-shaped
–Spiral-shaped
–Spherical
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Prokaryotic Cells Are Simpler Than Eukaryotic
Cells
chromosome
(nucleoid region)
cell wall
plasma membrane
ribosomes
capsule
chromosome
(nucleoid region)
(d) Internal structure
pili
(c) Cocci
ribosomes
food granule
(b) Spirilla
prokaryotic
flagellum
plasmid (DNA)
cytoplasm
capsule or
slime layer
cell wall
plasma membrane
photosynthetic
membranes
(a) Generalized prokaryotic cell (bacillus)
(e) Photosynthetic prokaryote
Fig. 4-19
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4.4 What Are the Major Features of Prokaryotic
Cells?
 Prokaryotic cells
– Some bacteria and archaea are propelled by
flagella
– Infectious bacteria may have polysaccharide
adhesive capsules and slime layers on their
surfaces
– Pili are protein projections in some bacteria that
further enhance adhesion
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4.4 What Are the Major Features of Prokaryotic
Cells?
 Prokaryotic cells (continued)
– In the central region of the cell is an area called
the nucleoid, which is separate from the
cytoplasm
–Within the nucleoid is a single, circular
chromosome of DNA
–Small rings of DNA (plasmids) are located in
the cytoplasm
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4.4 What Are the Major Features of Prokaryotic
Cells?
 Prokaryotic cells (continued)
– Prokaryotic cells have no nuclear membrane or
membrane-bound organelles present
– Some have internal membranes used to capture
light
– The cytoplasm may contain food granules and
ribosomes, the latter with a similar function as
that of ribosomes in eukaryotic cells
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19.1 Which Organisms Are Members of the
Domains Archaea and Bacteria?
 Classification of prokaryotes within each domain
is difficult
– Prokaryotes are very small and structurally
simple
– Prokaryotes do not have a huge array of
anatomical differences that can be used to
distinguish between groups
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19.1 Which Organisms Are Members of the
Domains Archaea and Bacteria?
 Classification of prokaryotes within each domain
is difficult (continued)
– Features used in prokaryotic classification are:
–Shape
–Means of locomotion
–Pigments
–Nutrient requirements
–Colony appearance
–Gram staining characteristics
–Nucleotide sequences
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19.1 Which Organisms Are Members of the
Domains Archaea and Bacteria?
 Prokaryotes differ in shape and structure
– Both bacteria and archaea are very small,
ranging from 0.2 to 10 micrometers in diameter
– Prokaryotes have three common shapes
–Spherical
–Rod-like
–Corkscrew-shaped
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Three Common Prokaryote Shapes
Fig. 19-1
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19.2 How Do Prokaryotes Survive and Reproduce?
 Some prokaryotes are motile
– Flagella are the primary means of locomotion in
prokaryotes
– Flagella are found singly, in pairs, as a tuft at one end
of the cell, or scattered over the entire cell surface
– In bacteria, a “wheel-and-axle” arrangement anchors
the flagellum within the cell wall and plasma
membrane, enabling the flagellum to rotate rapidly
– The archaeal flagella are thinner than those of
bacteria and are made of different proteins
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The Prokaryote Flagellum
Fig. 19-2
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19.2 How Do Prokaryotes Survive and Reproduce?
 Many bacteria form films on surfaces
– Some bacteria secrete sticky layers of
polysaccharide or protein slime
– Aggregates (communities) of slime-secreting
bacteria are called biofilms; dental plaque is a
biofilm
– Bacteria embedded in biofilms are protected
from disinfectants and antibiotics
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The Cause of Tooth Decay
Fig. 19-3
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19.2 How Do Prokaryotes Survive and Reproduce?
 Protective endospores allow some bacteria to
withstand adverse conditions
– Endospores are thickly wrapped particles of
genetic material and a few enzymes
– Endospores form inside some bacteria under
inhospitable environmental conditions
–When the endospores form, the bacterium
breaks open, releasing the endospores
–When a hospitable environment is found,
metabolism resumes and the endospore
develops into a fully functioning bacterium
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19.2 How Do Prokaryotes Survive and Reproduce?
 Protective endospores allow some bacteria to
withstand adverse conditions (continued)
– Endospores are resistant even to extremely
harsh conditions, including boiling for an hour
–Endospores found sealed within a rock for 250
million years produced live bacteria when
incubated in a test tube
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Spores Protect Some Bacteria
Fig. 19-4
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19.2 How Do Prokaryotes Survive and Reproduce?
 Prokaryotes are specialized for specific habitats
– Each species is specialized for certain
environmental conditions and usually cannot
survive outside a narrow range around those
conditions
– Prokaryotes occupy a wide range of habitats
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19.2 How Do Prokaryotes Survive and Reproduce?
 Prokaryote habitats
– High-pressure underground environments
– Cold environments (the Antarctic sea ice)
– High-salt environments (the Dead Sea)
– Acidic or alkaline environments (vinegar,
ammonia)
– Moderate environments (the human body)
– Hot environments (deep-sea vents, hot springs)
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Some Prokaryotes Thrive in Extreme Conditions
Fig. 19-5
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19.2 How Do Prokaryotes Survive and Reproduce?
 Prokaryotes exhibit diverse metabolisms
– Anaerobic metabolism
–Some bacteria, such as the tetanus bacterium,
are anaerobes and live without oxygen (and
are poisoned by it)
– Some bacteria can switch between aerobic and
anaerobic respiration
–For example, Escherichia coli in our large
intestines
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19.2 How Do Prokaryotes Survive and Reproduce?
 Prokaryotes exhibit diverse metabolisms
(continued)
– Prokaryotes can extract their energy from
familiar organic compounds
–Sugars, carbohydrates, fats, and proteins
– Prokaryotes can also extract energy from
compounds poisonous to humans
–Petroleum, methane, benzene, toluene
– Prokaryotes can even extract energy from
inorganic molecules such as hydrogen, sulfur,
ammonia, iron, and nitrite
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19.2 How Do Prokaryotes Survive and Reproduce?
 Prokaryotes exhibit diverse metabolisms
(continued)
– Some bacteria get energy from sunlight
–Cyanobacteria perform photosynthesis
–Sulfur bacteria use H2S instead of water in
photosynthesis
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Cyanobacteria
Fig. 19-6
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19.2 How Do Prokaryotes Survive and Reproduce?
 Prokaryotes reproduce by binary fission, which
is simpler than mitotic division
– Asexual cell division produces identical copies
– Binary fission can occur every 20 minutes
 A rapid reproductive rate allows for rapid
evolution
– Mutations in DNA replication are rapidly spread
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Reproduction in Prokaryotes
Fig. 19-7
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19.2 How Do Prokaryotes Survive and Reproduce?
 Prokaryotes may exchange genetic material
without reproducing
– Conjugation allows for DNA transfer between
donor and recipient
– Sex pili connect donor to recipient cell, drawing
the recipient to the donor and forming a
cytoplasmic bridge
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19.2 How Do Prokaryotes Survive and Reproduce?
 Prokaryotes may exchange genetic material without
reproducing (continued)
– Conjugation can occur between different species
– Small circular DNA molecules (plasmids) that are
separate from the bacterial chromosome, carry genes
from donor to recipient
– The plasmids may contain alleles conferring
resistance to antibiotics or alleles also found on the
main chromosome
– Conjugation produces new genetic combinations that
may allow the resulting bacteria to survive under a
greater variety of conditions
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Author Animation: Bacterial Conjugation
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Conjugation: Prokaryotic ‘Mating’
Fig. 19-8
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19.3 How Do Prokaryotes Affect Humans and
Other Eukaryotes?
 Prokaryotes play important roles in animal
nutrition
– Leaf-eating animals (e.g., rabbits, cattle) depend
on digestive tract bacteria to break down
cellulose in the cell walls of plants and thus
release the nutrients in the cells
–The animals lack the ability to digest cellulose
– Many human foods are produced by bacterial
action (e.g., cheese and yogurt)
– Bacteria in our intestines produce vitamins (e.g.,
vitamins K and B12)
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19.3 How Do Prokaryotes Affect Humans and
Other Eukaryotes?
 Prokaryotes capture the nitrogen needed by plants
– Plants cannot metabolize the nitrogen available as a gas
in the air
– Nitrogen-fixing bacteria that may be present in the soil,
or in specialized nodules in some plant roots, convert
atmospheric N2(gas) to NH4+(ammonium) that plants can
use directly
– Plants require nitrogen to grow and are thus
dependent on these bacteria for survival
– Since humans could not live without plants, they also
cannot live without bacteria
– Nitrogen fixation is found in alfalfa, soybeans, lupines,
and clover
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Nitrogen-Fixing Bacteria in Root Nodules
Fig. 19-9
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19.3 How Do Prokaryotes Affect Humans and
Other Eukaryotes?
 Prokaryotes are nature’s recyclers
– Many prokaryotes obtain energy by breaking down
complex organic molecules into the basic building blocks
of biomolecules
– These prokaryotes obtain their energy from waste
products and the dead bodies of plants and animals
– Decomposition of dead organisms frees nutrients for
reuse by new life
– The recycling of nutrients by prokaryotes and other
decomposers provides the basis for continued life on
Earth
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19.3 How Do Prokaryotes Affect Humans and
Other Eukaryotes?
 Prokaryotes can clean up pollution
– Nearly all human-made substances are
biodegradable by some bacterial species
– Oil-eating bacteria were used in clean up the
Exxon Valdez oil-spill disaster
– The practice of manipulating conditions to
stimulate breakdown of pollutants by living
organisms is known as bioremediation
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19.3 How Do Prokaryotes Affect Humans and
Other Eukaryotes?
 Some bacteria pose a threat to human health
– Disease-producing bacteria are termed
pathogenic
– Pathogenic archaea have not been discovered to
date
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19.3 How Do Prokaryotes Affect Humans and
Other Eukaryotes?
 Some bacteria pose a threat to human health
(continued)
– Some anaerobic bacteria produce dangerous poisons
– Clostridium tetani causes tetanus
– It enters the body through a puncture wound
– If it is lodged deeply enough in the body to avoid
oxygen, it grows, producing a paralyzing poison
– Bacterial diseases cause bubonic plague, Lyme disease,
and tuberculosis
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19.3 How Do Prokaryotes Affect Humans and
Other Eukaryotes?
 Humans have battled bacterial diseases
throughout history
– Bubonic plague (Black Death)
–It spread by rat fleas
–It killed 100 million people in the 1300s
(roughly a third of the population in some
areas)
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19.3 How Do Prokaryotes Affect Humans and
Other Eukaryotes?
 Humans have battled bacterial diseases
throughout history (continued)
– Lyme disease (emerged in 1975)
–It is caused by spiral-shaped Borrelia
burgdorferi
–It is carried by deer ticks, which bite humans
–Flu-like symptoms can lead to arthritis and
heart and nervous system problems
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19.3 How Do Prokaryotes Affect Humans and
Other Eukaryotes?
 Humans have battled bacterial diseases throughout
history (continued)
– Other historical bacterial diseases disappear and then
reoccur
– Tuberculosis (once thought to be vanquished from the
United States) is making a comeback
– Gonorrhea and syphilis (sexually transmitted
diseases) have reached epidemic proportions around
the globe
– Cholera (water-transmitted in contaminated drinking
water) is under control in developed countries but
remains a major killer in poorer parts of the world
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19.3 How Do Prokaryotes Affect Humans and
Other Eukaryotes?
 Common bacterial species can be harmful
– Streptococcus bacteria
– Cause tooth decay, pneumonia, and necrotizing
fasciitis (“flesh-eating” bacterial infection)
– Escherichia coli
– This bacterium is a common inhabitant of the human
digestive system
– The O157:H7 E. coli strain is pathogenic
– It can be transmitted through undercooked
hamburger from infected cattle
– It causes intestinal bleeding and can be fatal
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19.4 What Are Viruses, Viroids, and Prions?
 A virus consists of a molecule of DNA or RNA
surrounded by a protein coat
– Characteristics of a virus
–They have no cell membranes, no cytoplasm,
no ribosomes
–They can reproduce only inside a host cell
–They are very small (0.05–0.2 micrometers)
–They come in a variety of shapes
– The simplicity of viruses seems to place them
outside the realm of living things
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The Sizes of Microorganisms
1 m
Staphylococcus
cyanobacterium
Escherichia
coli
Eukaryotic cells
(10–100 m)
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Prokaryotic cells
(0.2–10 m)
Viruses
(0.05–0.2 m)
Fig. 19-10
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Viruses Come in a Variety of Shapes
Fig. 19-11
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19.4 What Are Viruses, Viroids, and Prions?
 A virus consists of a molecule of DNA or RNA
surrounded by a protein coat (continued)
– Two major components constitute a virus
–The hereditary material is single- or doublestranded DNA or RNA, which may be linear or
circular
–The protein coat may be surrounded by an
envelope formed from the plasma membrane
of the host cell
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Viral Structure and Replication
glycoproteins
envelope
(lipid bilayer)
protein
coat
spikes
core
proteins
genetic material
(viral RNA)
coated with protein
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reverse
transcriptase
Fig. 19-12
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19.4 What Are Viruses, Viroids, and Prions?
 Viruses are parasites
– They cannot grow or reproduce on their own and
thus parasitize living cells
– They have a specialized protein coat that
enables entry into a host cell
– Viral genetic material “hijacks” the host cell to
produce new viral components
– The viral components assemble rapidly into new
viruses and burst from the host cell
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19.4 What Are Viruses, Viroids, and Prions?
 Each viral type is specialized to attack specific
host cells
– Bacteria are infected by bacteriophage viruses
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Some Viruses Infect Bacteria
Fig. 19-13
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19.4 What Are Viruses, Viroids, and Prions?
 Bacteriophages can treat bacterial diseases
– The rise in bacterial antibiotic resistance makes
standard drugs less effective
– Bacteriophages specifically target host bacteria
– Bacteriophages are harmless to human body
cells
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19.4 What Are Viruses, Viroids, and Prions?
 In multicellular organisms, viruses specialize in
attacking particular cell types
– Cold viruses attack membranes of the
respiratory tract
– Rabies viruses attack nerve cells
– Herpes viruses live in the body and periodically
erupt as infectious sores
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19.4 What Are Viruses, Viroids, and Prions?
 In multicellular organisms, viruses specialize in
attacking particular cell types (continued)
– HIV virus attacks a specific white blood cell type,
causing AIDS
– Viruses have been linked to some types of
cancer, such as T-cell leukemia, liver cancer,
and cervical cancer
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Author Animation: Retrovirus Replication
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Author Animation: Herpes Virus Replication
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 How does the flu virus spread and infect us?
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19.4 What Are Viruses, Viroids, and Prions?
 Viral infections are difficult to treat
– Antibiotics against bacteria are infective against
viruses
– Antiviral drugs may also kill host cells
– Viruses “hide” within cells and are hard to detect
– Many antiviral drugs destroy or block the function
of enzymes that targeted viruses require for
replication
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19.4 What Are Viruses, Viroids, and Prions?
 Viral infections are difficult to treat (continued)
– Viruses have high mutation rates because they
lack the mechanisms to correct errors that occur
during replication of their genomes
–Mutations can confer resistance to an antiviral
drug
–Resistant viruses spread and multiply,
rendering a drug ineffective
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19.4 What Are Viruses, Viroids, and Prions?
 Some infectious agents are even simpler than
viruses
– Viroids are infectious particles with only short
RNA strands (no protein coat)
– These particles can enter a host cell nucleus and
direct new viroid synthesis
– A number of crop diseases are caused by
viroids, including cucumber pale fruit disease,
avocado sunblotch, and potato spindle tuber
disease
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19.4 What Are Viruses, Viroids, and Prions?
 Some infectious agents are even simpler than
viruses (continued)
– Prions are even more puzzling than viroids
– A fatal degenerative disease called kuru was
discovered in a New Guinea tribe (the Fore) in
1950
– Kuru causes a loss of coordination, dementia,
and death
– Kuru in the Fore tribe was transmitted by ritual
cannibalism of the dead
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19.4 What Are Viruses, Viroids, and Prions?
 Some infectious agents are even simpler than
viruses (continued)
– It was noted that kuru resembled certain other
diseases
–Creutzfeldt-Jakob (disease CJD) in humans
–Scrapie in sheep
–Bovine spongiform encephalopathy (BSE, or
“mad cow disease”) in cattle
– These diseases create holes in brain tissue
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19.4 What Are Viruses, Viroids, and Prions?
 Some infectious agents are even simpler than
viruses (continued)
– In 1982, Stanley Prusiner demonstrated that
scrapie (and by extension, other similar
diseases) was caused by an infectious protein
particle devoid of any genetic material
– Prion-caused diseases may be heritable
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Prions: Puzzling Proteins
Fig. 19-14
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19.4 What Are Viruses, Viroids, and Prions?
 Proposed model for replication of prions
1. Prion protein is a normal part of nerve cells
2. Misfolded versions of the normal protein are the
infectious particles
3. The misfolded proteins induce normal copies to
misfold, too
4. A high concentration of prions in nerve tissue
causes cell damage and degeneration
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19.4 What Are Viruses, Viroids, and Prions?
 Prions can be inherited
– Certain small mutations in the gene that codes
for “normal” prion protein increase the likelihood
that the protein will fold into its abnormal form
– If one of these mutations is genetically passed
on to offspring, the tendency to develop a prion
disease may be inherited
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19.4 What Are Viruses, Viroids, and Prions?
 No one is certain how these infectious particles
originated
– One theory is that they are evolutionary remnants of life’s
early history
– This is suggested by the huge variety of mechanisms
for self-replication among these particles, as has been
proposed for the pre-DNA world
– They could be degenerate descendants of parasitic cells
– Ancient parasites may have become dependent on
hosts’ biochemical machinery
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 Are viruses alive? Are they “life”?
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 Does Agent Smith understand viruses?
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