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
