Chap 13 Flashcards
Can viruses reproduce outside of a living host?
No, viruses are obligate cellular parasites, meaning they cannot reproduce outside of a living host
Can viruses be cultured outside of hosts?
no
Viruses can’t be seen with what kind of microscope?
light microscope
The first human disease associated with a filterable agent was
Yellow fever
Viruses are mostly made of nucleic acids, either
DNA or RNA
Capsid
protein coat of viruses
capsomere
building block of a virus’s capsid
Some viruses have a lipid bilayer envelope, which they get from
host cells upon release
Do viruses have ribosomes?
No
Do viruses have ATP generating mechanisms?
no
contagium vivum fluidum
Fluid with viruses. Couldn’t imagine sub-microscopic organisms
What kind of microscope do you need to see a virus?
Electron microscope
Viruses are inert outside of a host cell, meaning
Their nucleic acids are inactive outside of a living host
virus
submicroscopic, parasitic, filterable agent. Made of nucleic acid surrounding a protein coat.
host range
spectrum of species, strains or cell types that a pathogen can infect
bacteria vs viruses: have a plasma membrane
virus: no
typical bacteria: yes
bacteria vs viruses: binary fission
typical bacteria: yes
virus: no
bacteria vs viruses: intracellular parasite
typical bacteria: no
virus: yes
bacteria vs viruses: pass through bacteriological filters
typical bacteria: no
virus: yes
bacteria vs viruses: possess both DNA and RNA
typical bacteria: yes
virus: no
bacteria vs viruses: ATP generating metabolism
typical bacteria: yes
virus: no
bacteria vs viruses: ribosomes
typical bacteria: yes
viruses: no
bacteria vs viruses: sensitive to antibiotics
typical bacteria: yes
viruses: no
bacteria vs viruses: sensitive to interferon
typical bacteria: no
viruses: yes
Most viruses infect only specific types of ______ in one host
cells
Host range of virus is determined by
specific host attachment sites and cellular factors
Bacteriophages
viruses that infect bacteria
virus size range
Viruses range from 20 to 1000 nm in length
How could the small size of viruses has helped researchers detect viruses before the invention of the electron microscope?
since viruses are smaller than bacteria, they could pass through filters designed to trap bacteria, demonstrating the existence of an infectious agent too small to be seen under a light microscope, thus revealing the presence of viruses.
Virion
complete, fully developed infectious viral particle
Virion is made of
composed of nucleic acid and surrounded by a protein coat outside a host cell
how are viruses classified?
by their nucleic acid and by differences in the structures of their coats.
How can nucleic acid in viruses vary?
acid-D N A or R N A can be single- or double-stranded; linear or circular
Envelope (only found in some viruses) is made of
lipid, protein, and carbohydrate coating on some viruses
Spikes
projections from outer surface. made of carbohydrate protein complex.
what is the purpose of spikes?
help virus attach to host cell
The ability of certain viruses to clump red blood cells is associated with
spikes
How do viruses cause hemagglutination?
Such viruses bind to red blood cells and form bridges between them.
nonenveloped viruses
Viruses whose capsids aren’t covered by an envelope
The capsid of a nonenveloped virus protects the nucleic acid from
nuclease enzymes in biological fluids and promotes the virus’s attachment to susceptible host cell.
Viruses may be classified into several different morphological types on the basis of
Their capsid architecture
The structure of these capsids has been revealed by electron microscopy and a technique called
X-ray crystallography.
Helical viruses resemble
long rods that may be rigid or flexible
hollow, cylindrical capsid
Polyhedral viruses
many sided
within helical viruses, the viral nucleic acid is found within
a hollow, cylindrical capsid that has a helical structure
Examples of diseases caused by helical viruses
viruses that cause rabies and Ebola are helical viruses.
The capsid of most polyhedral viruses is in the shape of an
icosahedron, a regular polyhedron with 20triangular faces and 12 corners
The capsomeres of each face of an icosahedron form an
equilateral triangle
adenovirus and poliovirus
icosahedral polyhedral viruses
Enveloped viruses
the capsid of some viruses is covered by an envelope.
Enveloped viruses shape
roughly spherical
When helical or polyhedral viruses are enclosed by envelopes, they are called
enveloped helical or enveloped polyhedral viruses
An example of an enveloped helical virus is the
influenza virus
An example of an enveloped polyhedral (icosahedral) virus is
the human herpes virus
Virus with complicated structure, such as
a bacteriophage
Some bacteriophages have capsids to which
additional structures are attached.
poxviruses
complex viruses
don’t contain clearly identifiable capsids but do have
several coats around the nucleic acid
bacteriophages are what kind of virus?
complex
Genus names end in
-virus
Family names end in
-viridae
Order names end in
-ales
Viral species
a group of viruses sharing the same genetic information and ecological niche (host)
Descriptive common names are used for
species
Subspecies are designated by a
number
How does a virus species differ from a bacterial species?
Bacteria are single cells that can survive on their own, inside or outside the body. Viruses cause infections by entering and multiplying inside the host’s healthy cells
Viruses must be grown in
living cells
Bacteriophages are grown in
bacteria
What forms plaques?
Bacteriophages
Plaques
clearings on a lawn of bacteria on the surface of the agar
Plaque forming units
Each plaque corresponds to a single virus
Specific epithets for viruses aren’t used t/f?
true, Viral species is designated by descriptive common names.
Why does most understanding of viruses come from bacteriophages?
because bacteriophages grow in bacterial cultures
plaque method
Detects infectious viruses in concentrates in 3-5 days by culturing cells where plaques form
method used for detecting infectious viruses in concentrates by culturing cells, where plaques develop after 3-5 days to indicate the presence of viruses.
How does the plaque method work?
- A bacteriophage sample is mixed with host bacteria and melted agar.
- The agar containing the bacteriophages and host bacteria is then poured into a Petri plate containing a hardened layer of agar growth medium
- The virus-bacteria mixture solidifies into a thin top layer that contains a layer of bacteria approximately one cell thick. Each virus infects a bacterium, multiplies, and releases several hundred new viruses. These newly produced viruses infect other bacteria in the immediate vicinity, and more new viruses are produced.
- all the bacteria in the area surrounding the original virus are destroyed. This produces a number of clearings, or plaques,
What is a plaque-forming unit?
visible clearing in bacterial culture caused by lysis of bacterial cells by bacteriophages
how do you culture animal viruses in a lab?
using living animals, embryonated eggs, or cell cultures.
Most experiments to study the immune system’s response to viral infections must also be performed in
virally infected live animals.
diagnostic procedure for identifying and isolating a virus from a clinical specimen
Animal inoculation; After the animal is inoculated with the specimen, the animal is observed for signs of disease or is killed so that infected tissues can be examined for the virus.
The lack of natural animal models for AIDS has slowed our understanding because
slowed our understanding of its disease process and prevented experimentation with drugs that inhibit growth of the virus in vivo
How are viruses cultured in embryonated eggs?
Virus injected into the egg
Viral growth is signaled by changes or death of the embryo
have replaced embryonated eggs as the preferred type of growth medium for many viruses.
cell cultures
Cell culture lines are started by
treating a slice of animal tissue with enzymes that separate the individual cells.
Normal cells tend to adhere to the glass or plastic container and reproduce to form a monolayer, but viruses infecting such a monolayer sometimes cause
the cells of the monolayer to deteriorate as they multiply.
cytopathic effect
cell deterioration; A visible effect on a host cell, caused by a virus, that may result in host cell damage or death.
Virally infected cells are detected via their
deterioration, known as the cytopathic effect (C P E)
CPE can be detected and counted in much the same way as plaques caused by bacteriophages on a lawn of bacteria and reported as
PFU/ml
Viruses may be grown in _________ or ___________ cell lines
primary or continuous cell lines
Primary cell lines
Human tissue cells that grow for only a few generations in vitro.
widely used for culturing viruses that require a human host.
diploid cell lines
developed from human embryos can be maintained for about 100 generations
diploid cell lines
diploid cell lines
eukaryotic cells grown in vitro
used to culture rabies virus for a rabies vaccine called human diploid culture vaccine
Cell lines developed from embryonic human cells
continuous cell line
Animal cells that can be maintained through an indefinite number of generations in vitro
Which cell lines are used when viruses are routinely grown in a laboratory?
continuous cell lines
transformed (cancerous) cells that can be maintained through an indefinite number of generations, and they’re sometimes called immortal cell lines
continuous cell lines
steps for growing transformed cells
- Tissue is treated with enzymes to separate the cells
- Cells are suspended in a culture medium
- Normal or primary cells grow in a monolayer across the glass or plastic container. Transformed cells or continuous cell cultures do not grow in a monolayer
How are viruses identified?
- Cytopathic effects
- Serological tests
- Nucleic acids
Western blotting serological test
reaction of the virus with antibodies
RFLPs
molecular method that helps identify and characterize viruses. restriction fragment length polymorphisms
identification methods based on nucleic acids?
RFLPs
PCR
PCR polymerase chain reaction
allows specific identification of the infective agents and the detection of multiple/co-infecting viruses.
Western blotting
A technique that uses antibodies to detect the presence of specific proteins separated by electrophoresis.
For a virus to multiply it must
- invade a host cell
- take over the host’s metabolic machinery
The multiplication of viruses can be demonstrated with a
one-step growth curve
The data are obtained by
infecting every cell in a culture and then testing the culture medium and cells for virions and viral proteins and nucleic acids.
Eclipse period of one step growth curve
The time during viral multiplication when complete, infective virions are not present.
No new infective virions are found in a culture until after
biosynthesis and maturation have taken place.
What happens to most infected cells as a result of infection?
cells die as result of infection, consequently, new virions won’t be produced.
Phage causes lysis and death of the host cell
Lytic cycle
Lytic cycle
mechanism of phage mutation that results in host cell lysis
Lytic cycle ends with
the lysis and death of the host cell
host remains alive
lysogenic cycle
lysogenic cycle
Stages in viral development that result in the incorporation of viral DNA into host DNA
Bacteriophages can multiply by two mechanisms
the lytic cycle or the lysogenic cycle
The virions of _______ bacteriophages are large, complex, and nonenveloped, with a characteristic head-and-tail structure
T-even
Lytic cycle phases
1.attachment,
2. penetration,
3.biosynthesis,
4. maturation,
5. release.
Attachment
Phage attaches to host cell
Penetration
Phage penetrates host cell and injects its DNA
Biosynthesis:
Phage DNA directs synthesis of viral components by the host cell.
Maturation
Viral components are assembled into virions
Release
host cell lyses and new virions are released
Phage conversion
Genetic change in the host cell resulting from infection by a bacteriophage. the host cell exhibits new properties
Specialized transduction
process of transferring a piece of cell DNA adjacaent to a prophage to another cell
specialized transduction is initiated during
the lysogenic cycle of temperate bacteriophages
virulent bacteriophages reproduction
carry out lytic cycle
temperate bacteriophages replication
carry out two types of life cycle: lytic and lysogenic
In temperate bacteriophages, after penetration, the phage DNA forms a
circle
The circle of DNA can then
replicate and be transcribed to produce phage components in the lytic cycle, OR can proceed to the lysogenic stage.
During the biosynthesis stage of the lytic cycle in temperate bacteriophages,
the phage DNA directs the host cell to make viral components
after penetration, in the lysogenic cycle, the phage DNA integrates within bacterial chromosome by
recombination
The inserted phage DNA is called a
Prophage
Most of the phage proteins are repressed by
two repressor proteins that are products of phage genes
After combining the DNA, what happens when the bacteria reproduces?
the prophage is also copied
induction
The prophage is excised from the host chromosome.
What causes induction?
can occur spontaneously through recombination, or some other genetic event, UV light, or chemicals
after induction, the phage may enter the
lytic cycle
phage attaches by the tail fibers to the host cell
attachment
phage lysozyme opens the cell wall; tail sheath contracts to force the tail core and D N A into the cell
Penetration
production of phage D N A and protein
biosynthesis
assembly of phage particles
Maturation
phage lysozyme breaks the cell wall
Release
Lysogeny
A state in which phage DNA is incorporated into the host cell without lysis. phage remains latent
In contrast to T-even bacteriophages, some viruses don’t cause lysis and death of the host cell when they multiply.
lysogenic/temperate phages
Steps of lysogenic cycle of bacteriophage I in E. Coli
- Phage attaches to host cell and injects DNA
- Phage DNA makes a circle
- can enter lytic cycle, where circle multiplies and gets transcribed OR
3.bcircle recombines with bacterial DNA and gets replicated every time bacteria divides. Prophage DNA remains latent - phage DNA can be ejected and start lytic cycel
lysogenic cells are immune to reinfection by
the same phage. However, the host cell isn’t immune to infection by other phage type
host cell may exhibit new properties caused by
phage conversion
generalized transduction
Bacterial genes can be picked up in a phage coat and transferred to another bacterium
possible results of lysogeny
- Specialized transduction
- immunity to reinfection by same phage
- Phage conversion
specialized transduction
process of transferring a piece of cell DNA adjacent to a prophage to another cell. packages bacterial DNA along with its own DNA. When viral dna leaves, it carries some of the genes from one bacterium to another.
Specific bacterial genes transferred to another bacterium via a phage. The becaterial genes next to the phage
Changes genetic properties of the bacteria
specialized transduction
Two types of transduction
generalized and specialized
Generalized transduction is initiated during
the lytic cycle of virulent bacteriophage
The donor DNA for generalized transduction can be
any fragment of the bacterial chromosome
Transduction
DNA from one cell is transferred to another cell via a replicating virus
Specialized transduction is initiated during the
lysogenic cycle of a temperate bacteriophage.
Donor DNA for specialized transduction is
a very specific part of the bacterial chromosome adjacent to the prophage
Transducing phages
made of phage and bacterial DNA, when injected the bacterial DNA also spreads to host.
The multiplication of animal viruses follows the basic pattern of bacteriophage multiplication but has several __________,
differences
Animal viruses differ from phages in their mechanism of
entering the host cell
Regarding animal viruses, once the virus is inside, the synthesis and assembly of the new viral components are somewhat _________
different because of diffences in prokaryotic and eukaryotic cells
______ ________may have certain types of enzymes not found in phages
Animal viruses
Finally, the mechanisms of maturation and release, and the effects on the host cell, differ in
animal viruses and phages
Multiplication of Animal Viruses attachment
viruses attach to the cell membrane
Multiplication of Animal Viruses entry by
receptor-mediated endocytosis or fusion
do animal viruses require uncoating?
yes, enzymatic removal of capsid proteins happens
Biosynthesis of animal viruses happens in
nucleus (DNA viruses) or cytoplasm (RNA viruses)
Infection by animal viruses is latent, meaning
slow viral infections; cancer
How are animal viruses released?
Enveloped viruses bud out; nonenveloped viruses rupture plasma membrane.
Animal viruses require uncoating, meaning
viral or host enzymes break down protein coat
Biosynthesis of animal viruses
production of nucleic acid and proteins
Maturation of animal viruses
nucleic acid and capsid proteins assemble
Animal viruses release by:
budding (enveloped viruses) or rupture
naked viruses
Animal viruses without an envelope. Bind to surface of host cell and inject dna similar to bacteriophages.
Some enveloped animal viruses infect the host cell by binding to receptors on the host cell
The viral envelope merges with the host cell membrane and the capsid enters the cell . After entry, the capsid opens and releases the viral genetic material into cytoplasm.
Upon attachment, some enveloped viruses infect the host cell via inducing
phaogytocis.
When the virus has entered the cell, the outer and inner part of the envelope
merge together and the capsid is released into the cytoplasm
The type of nucleic acid in an animal virus determines how the viral nucleic acid and proteins are synthesized.
true
When the single stranded DNA genome of a parvovirus enters a host cell and invades its nucleus a complementary strand is
produced
the complementary strand is replicated
normally
mRNA is transcribed and transported into
Cytoplasm
viral capsomere proteins are produced in
cytoplasm
capsomere protein enter the
nucleus of the host , and the virions containing the original single stranded RNA are assembled
Virus dsDNA synthesis
two strands, same process and single strand DNA virus
synthesis of viruses with single strand RNA genome +RNA
- can act directly as mRNA AKA as sense strand
Sense strand
read by host ribosomes to make viral proteins
Virus with +RNA carries a unique polymerase
polymerase makes a complimentary negative strand. also called an antisense strand.
There is no known animal equivalent of the rna dependent
polymerase
the negative strand RNA can act as a template for
positive strand RNA
positive strand single strand RNA viruses are assembled in the cytoplasm of the
host cell after the viral capsomere proteins have been produced.
viruses with single strand negative sense RNA -RNA are in a special situation
their RNA will not act as messenger RNA until its transcribedd into the sense strand. carries its own rna polymerase to make positive strand.
When -RNA is packages into virions it must contain
RNA POLYMERASE and -RNA
dsRNA
sense strand acts as mRNA for protein production. two strands get packaged along with a polymerase.
retrovirus
special kind of +RNA virus.
When a retrovirus infects a cell, its +RNA strand is transcribed into a
-DNA strand
wat does retrovirus use to make -DNA
viral reverse transcriptase
-DNA IS transcribed into
double stranded DNA, WHICH SERVES AS A TEMPLATE FOR THE VIRAL RNA genome
positive strand RNA serves as
template for viral protein syntheis. Reverse transcriptase is packaged in virion
Which viruses generally leave their host cells?
naked; by accumulating until cell lyses. Causes inflammation and infection in tissues
Enveloped viruses leave by
merging with one of the cell’s membranes, the nuclear membrane , the endoplasmic reticulum membrane, or the cytoplasmic membrane
during synthesis, some viral glycoproteins are embedded in cellular membrane
act as recognition sites for viral capsid.
How do enveloped viruses leave the host?
bud off thanks to glycoproteins. cell membrane forma a bud which pinches off and make an envelope
Advantage of enveloped viruses
does not need cell to lyse, so the cell can stay alive longer and make more copies
D N A viruses replicate their D N A in
the nucleus of the host using viral enzymes
DNA VIRUSES SYNTHESIZE CAPSID IN THE CYTOPLASM USING
HOST CELL ENZYMES
Adenoviridae
DDN, respiratory infection humans, tumors animals
Double-stranded D N A, nonenveloped
Respiratory infections in humans
Tumors in animals
Poxviridae
DDE skin lesions
Double-stranded D N A, enveloped
Cause skin lesions
Vaccinia and smallpox viruses (Orthopoxvirus)
Poxviridae
Herpesviridae
DDE
Double-stranded D N A, enveloped
H H V-1 and H H V-2-Simplexvirus
Cause cold sores
H H V-3-Varicellovirus
causes chickenpox
H H V-4-Lymphocryptovirus
causes mononucleosis
H H V-5-Cytomegalovirus
H H V-6 and H H V-7-Roseolovirus
are types of
herpesviridae
H H V-8-Rhadinovirus
causes Kaposi’s sarcoma
Papovaviridae
DDN
Double-stranded D N A, nonenveloped
Papillomavirus leads to
warts
Hepadnaviridae
DDE
Double-stranded D N A, enveloped
Hepatitis B virus
Use reverse transcriptase to make D N A from R N A
Virus multiplies in the host cell’s cytoplasm using
R N A-dependent R N A polymerase
ss R N A; + (sense) strand
Viral R N A serves as m R N A for protein synthesis
ss R N A; − (antisense) strand
Viral R N A is transcribed to a + strand to serve as m R N A for protein synthesis
ds R N A
double stranded RNA
Picornaviridae
SRN+
Single-stranded R N A, + strand, nonenveloped
Enterovirus
Poliovirus and coxsackievirus
Rhinovirus
hepatitis A virus
Types of picornaviridae
Rhinovirus
common cold
Togaviridae
SRE+
Single-stranded R N A, + strand, enveloped
Alphavirus
(Togaviridae)
Transmitted by arthropods; includes chikungunya
Rubivirus (togaviridae)
Rubella
Rhabdoviridae
SR-, numerous animal diseases
Single-stranded R N A,
, -Strand, one RNA strand
numerous animal diseases
Lyssavirus
rabies (Rhabdoviridae)
Reoviridae
DRN
Double-stranded R N A, nonenveloped
Reovirus (Reoviridae)
(respiratory enteric orphan)
Rotavirus leads to (Reoviridae)
(mild respiratory infections and gastroenteritis)
Use reverse transcriptase to produce D N A from the viral genome
ssRNA
Single stranded RNA , produce DNA
Viral D N A integrates into the host chromosome as a
provirus
Retroviridae examples
Lentivirus (H I V)
Oncoviruses
Several types of cancer are caused by
viruses
Cancer may develop a long time after
viral infection
Cancers caused by viruses are not
contagious
Sarcoma
cancer of connective tissues
Adenocarcinoma
cancers of glandular epithelial tissue
oncogenes
transform normal cells into cancerous cells
Oncogenic viruses
become integrated into the host cell’s D N A and induce tumors
A transformed cell harbors a ______ on the surface
Tumor-specific transplantation antigen
A transformed cell harbors a ______ in the nucleus
T antigen
Adenoviridae
Herpesviridae
-Epstein-Barr virus
Poxviridae
Papovaviridae
-Human papillomavirus
Hepadnaviridae
-Hepatitis B virus
DNA oncogenic viruses
How is retroviridae oncogenic?
viral R N A is transcribed to D N A (using reverse transcriptase), which can integrate into host D N A
H T L V-1 and H T L V-2 cause
adult T cell leukemia and lymphoma
Latent virus remains in asymptomatic host cell for
long periods
A latent virus may reactivate due to
changes in immunity
Examples of things that happen thanks to latent viral infections
Cold sores,
shingles
persistent viral infection
occurs gradually over a long period; is generally fatal
Example of a persistent viral infection
Subacute sclerosing panencephalitis (measles virus)
viruses continuously released
persistent infection
13-13, 13-14 Is shingles a persistent or latent infection?
latent
Plant viruses enter through
wounds or via insects
Plant cells are generally protected from disease by an
inpermeable cell wall
Viroids:
short pieces of naked RNA
Cause potato spindle tuber disease
viroids
virusoids
viroids enclosed in a protein coat
Virusoids only cause disease when
plant cell is coinfected with a virus
Caulimoviridae characteristics
DDN
Double-stranded DNA, nonenveloped
Caulimoviridae viral genus or unclassified members
Cauliflower mosaic virus
Prions
Proteinaceous infectious particles
Prions Inherited and transmissible by
ingestion, transplant, and surgical instruments
Spongiform encephalopathies
neurological diseases caused by large vacuoles in the brain
Examples of Spongiform encephalopathies
“Mad cow disease”
Creutzfeldt-Jakob disease (C J D)
Gerstmann-Sträussler-Scheinker syndrome
Fatal familial insomnia
Sheep scrapie
PrPC
normal cellular prion protein, on the cell surface
PrPSc
scrapie protein; accumulates in brain cells,
accumulates in bran cells forming plaques
How do prions cause illness
They make other cellular proteins misfold into infectious forms
All mammalian cells contain a gene that codes for the primary sequence of aminoacids for the prion protein
PrP
Normally, Prp FOLDS INTO A functional form with a-helices called
cellular PrP
What is the normal function of the prion protein?
not well understood, but important in synaptic development and function
may be involved in stabilizing structure of synapses and establishing memory
PrP
Is also capable of folding into a from with beta pleated sheets
PrP
Do not reproduce like bacteria or viruses
Prions; they make normal prions into infectious prions, by folding into beta pleated sheets.
Number of infectious prions is increased by
conversion instead of reproduction
The number of infectious prions has increased by
conversion instead of reproduction
Multimers
infectious conformation . Very stable and resistant to protease.
probably lead to damage in prion infected tissues
multimers
Creutzfeld Jakob disease
1/1000000 people, appears in mid life20-70 age, avg age of onset 50 , affectscerebrum
Can transform cells and cause cancer
Papillomavirus
Double stranded DNA serves as
TEMPLATE FOR THE VIRAL RNA genome
Hepadnaviridae uses reverse transcriptase to make
(Hepatitis B virus )
D N A from R N A
