Download AP Biology Chapter 19 Virus Guided Notes

LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
Chapter 19
Viruses
Lectures by
Erin Barley
Kathleen Fitzpatrick
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Overview: A Borrowed Life
• Viruses called __________________can infect
and set in motion a genetic takeover of bacteria,
such as Escherichia coli
• Viruses lead “a kind of _______________”
between life-forms and chemicals
• The origins of _______________ biology lie in
early studies of viruses that infect bacteria
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Concept 19.1: A virus consists of a nucleic
acid surrounded by a protein coat
• Viruses were detected ______________ long
before they were actually seen
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The Discovery of Viruses: Scientific Inquiry
• ___________________ disease stunts growth of
tobacco plants and gives their leaves a mosaic
coloration
• In the late 1800s, researchers hypothesized that a
particle ______________ than bacteria caused
the disease
• In 1935, Wendell Stanley confirmed this
hypothesis by crystallizing the infectious particle,
now known as _______________________(TMV)
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Figure 19.2
RESULTS
3 Rubbed filtered
1 Extracted sap 2 Passed sap
through a
sap on healthy
from tobacco
porcelain filter
tobacco plants
plant with
known to trap
tobacco mosaic
bacteria
disease
4 Healthy plants
became infected
Structure of Viruses
• Viruses __________ cells
• A ____________ is a very small infectious particle
consisting of nucleic acid enclosed in a protein
coat and, in some cases, a membranous envelope
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Viral Genomes
• Viral genomes may consist of either
– Double- or single-stranded ________, or
– Double- or single-stranded ________
• Depending on its type of nucleic acid, a virus is
called a _________ virus or an __________ virus
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Capsids and Envelopes
• A __________ is the protein shell that encloses
the viral genome
• Capsids are built from protein subunits called
__________________
• A capsid can have various structures
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Figure 19.3
Capsomere
RNA
DNA
Membranous
RNA
envelope
Capsid
Head
DNA
Tail
sheath
Capsomere
of capsid
Tail
fiber
Glycoprotein
18  250 nm
20 nm
(a) Tobacco
mosaic virus
Glycoproteins
70–90 nm (diameter) 80–200 nm (diameter)
50 nm
(b) Adenoviruses
80  225 nm
50 nm
50 nm
(c) Influenza viruses (d) Bacteriophage T4
• Some viruses have _____________________ that
help them infect hosts
• These _________________surround the capsids
of ______________ viruses and many other
viruses found in animals
• Viral envelopes, which are derived from the host
cell’s membrane, contain a combination of _____
and ____________________
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• ______________ , also called __________, are
viruses that infect bacteria
• They have the most ___________________ found
among viruses
• Phages have an ___________________ that
encloses their DNA
• A _______________ piece attaches the phage to
the host and injects the phage DNA inside
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Concept 19.2: Viruses replicate only in
host cells
• Viruses are ________________________ , which
means they can replicate only within a host cell
• Each virus has a ________________ , a limited
number of host cells that it can infect
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General Features of Viral Replicative
Cycles
• Once a viral genome has entered a cell, the cell
begins to manufacture ________________
• The virus makes use of host ________________
___________________________, and other
molecules
• Viral nucleic acid molecules and capsomeres
spontaneously ________________ into new
viruses
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Figure 19.4
1 Entry and
uncoating
DNA
VIRUS
3 Transcription
and manufacture of
capsid proteins
Capsid
2 Replication
HOST
CELL
Viral DNA
mRNA
Viral
DNA
Capsid
proteins
4 Self-assembly of
new virus particles
and their exit from
the cell
Replicative Cycles of Phages
• __________ are the best understood of all viruses
• Phages have two reproductive mechanisms: the
_______ cycle and the _________________cycle
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The Lytic Cycle
• The _______________ is a phage replicative
cycle that culminates in the death of the host cell
• The lytic cycle produces new phages and ______
(breaks open) the host’s cell wall, releasing the
progeny viruses
• A phage that reproduces only by the lytic cycle is
called a _____________________
• Bacteria have defenses against phages, including
______________________ that recognize and cut
up certain phage DNA
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Figure 19.5-5
1 Attachment
2 Entry of phage
DNA and
degradation
of host DNA
5 Release
Phage assembly
4 Assembly
Head
Tail
Tail
fibers
3 Synthesis of
viral genomes
and proteins
The Lysogenic Cycle
• The ____________________ replicates the phage
genome without destroying the host
• The viral DNA molecule is _______________ into
the ____________________________
• This integrated viral DNA is known as a ________
• Every time the host divides, it ________________
_________ and passes the copies to daughter
cells
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• An ____________________can trigger the virus
genome to exit the bacterial chromosome and
switch to the lytic mode
• Phages that use both the lytic and lysogenic
cycles are called _______________________
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Figure 19.6
Phage
DNA
Daughter cell
with prophage
The phage
injects its DNA.
Cell divisions
produce a
population of
bacteria infected
with the prophage.
Phage DNA
circularizes.
Phage
Bacterial
chromosome
Occasionally, a prophage
exits the bacterial chromosome,
initiating a lytic cycle.
Lytic cycle
The cell lyses, releasing phages.
Lysogenic cycle
Certain factors
determine whether
lytic cycle
is induced
New phage DNA and proteins
are synthesized and assembled
into phages.
or
lysogenic cycle
is entered
Prophage
The bacterium reproduces,
copying the prophage and
transmitting it to daughter
cells.
Phage DNA integrates into
the bacterial chromosome,
becoming a prophage.
Figure 19.6a
Phage
DNA
The phage
injects its DNA.
Phage DNA
circularizes.
Phage
Bacterial
chromosome
Lytic cycle
The cell lyses, releasing phages.
Certain factors
determine whether
lytic cycle or lysogenic cycle
is entered
is induced
New phage DNA and proteins
are synthesized and assembled
into phages.
Figure 19.6b
Daughter cell
with prophage
Cell divisions
produce a
population of
bacteria infected
with the prophage.
Phage DNA
circularizes.
Occasionally, a prophage
exits the bacterial chromosome,
initiating a lytic cycle.
Lysogenic cycle
Certain factors
determine whether
lytic cycle or lysogenic cycle
Prophage
is entered
is induced
The bacterium reproduces,
copying the prophage and
transmitting it to daughter
cells.
Phage DNA integrates into
the bacterial chromosome,
becoming a prophage.
Replicative Cycles of Animal Viruses
• There are two key variables used to classify
viruses that infect animals
– ___________?
– _______________________________________?
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Table 19.1a
Table 19.1b
Viral Envelopes
• Many viruses that infect animals have a
_________________________
• _________________________ on the envelope
bind to specific receptor molecules on the surface
of a host cell
• Some viral envelopes are formed from the host
cell’s plasma membrane as the _______________
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• Other viral membranes form from the ________
______________________ and are then replaced
by an envelope made from Golgi apparatus
membrane
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Figure 19.7
Capsid
Capsid and viral genome
enter the cell
RNA
Envelope (with
glycoproteins)
HOST CELL
Template
Viral genome
(RNA)
mRNA
ER
Capsid
proteins
Copy of
genome
(RNA)
Glycoproteins
New virus
RNA as Viral Genetic Material
• The broadest variety of RNA genomes is found in
viruses that infect _____________
• _______________ use __________________ to
copy their RNA genome into DNA
• _______________________________ is the
retrovirus that causes __________ (acquired
immunodeficiency syndrome)
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Figure 19.8
Glycoprotein
Viral envelope
HIV
Capsid
Reverse
transcriptase HIV
RNA (two
identical
strands)
Membrane
of white
blood cell
HOST
CELL
Reverse
transcriptase
Viral RNA
RNA-DNA
hybrid
0.25 m
DNA
HIV entering a cell
NUCLEUS
Provirus
Chromosomal
DNA
RNA genome
for the
next viral
generation
mRNA
New virus
New HIV leaving a cell
• The viral DNA that is integrated into the host
genome is called a ________________
• Unlike a prophage, a provirus remains a
_________________________of the host cell
• The ______________________ transcribes the
proviral DNA into ___________________
• The RNA molecules function both as mRNA for
synthesis of __________________ and as
_______________________ released from the
cell
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Evolution of Viruses
• Viruses ____________our definition of living
organisms
• Since viruses can replicate only within cells, they
probably evolved as ______________________
• Candidates for the source of viral genomes are
______________ , circular DNA in bacteria and
yeasts, and ________________ , small mobile
DNA segments
• Plasmids, transposons, and viruses are all _____
_______________________________
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• ______________, a double-stranded DNA virus,
the largest virus yet discovered, is the size of a
small bacterium
• There is controversy about whether this virus
evolved before or after cells
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Concept 19.3: Viruses, viroids, and prions
are formidable pathogens in animals and
plants
• Diseases caused by viral infections affect humans,
agricultural crops, and livestock worldwide
• Smaller, less complex entities called __________
and ___________ also cause disease in plants
and animals, respectively
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Viral Diseases in Animals
• Viruses may damage or kill cells by causing the
release of ___________________ from
lysosomes
• Some viruses cause infected cells to produce
__________ that lead to disease symptoms
• Others have molecular components such as
______________________ that are toxic
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• _______________ are harmless derivatives of
pathogenic microbes that stimulate the immune
system to mount defenses against the harmful
pathogen
• Vaccines can prevent certain _________ illnesses
• Viral infections cannot be treated by __________
• ___________________ can help to treat, though
not cure, viral infections
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Emerging Viruses
• ____________________ are those that suddenly
become apparent
• Recently, a general outbreak (___________) of a
flu-like illness appeared in Mexico and the United
States, caused by an influenza virus named _____
• ____________________ are caused by new
strains of influenza virus to which people have little
immunity
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• These strains can cause _____________, global
epidemics
• The 2009 flu pandemic was likely passed to
humans from ______; for this reason it was
originally called the “______________”
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• Viral diseases in a small isolated population can
emerge and become ___________
• New viral diseases can emerge when viruses
spread from ____________________
• Viral strains that _____________ can exchange
genetic information with other viruses to which
humans have no immunity
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Figure 19.9
1 m
(a) 2009 pandemic H1N1 (b) 2009 pandemic
screening
influenza A virus
(c) 1918 flu pandemic
Viral Diseases in Plants
• More than 2,000 types of viral diseases of ______
are known and cause spots on leaves and fruits,
stunted growth, and damaged flowers or roots
• Most plant viruses have an ___________ genome
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Figure 19.10
• Plant viruses spread disease in two major modes
– ____________________, entering through
damaged cell walls
– ____________________, inheriting the virus from
a parent
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Viroids and Prions: The Simplest Infectious
Agents
• __________ are small circular RNA molecules
that infect plants and disrupt their growth
• __________are slow-acting, virtually indestructible
infectious proteins that cause brain diseases in
mammals
• Prions propagate by _____________________
into the prion version
• Scrapie in sheep, mad cow disease, and
Creutzfeldt-Jakob disease in humans are all
caused by prions
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Figure 19.11
Prion
Normal
protein
Original
prion
New
prion
Aggregates
of prions