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86 Cards in this Set
- Front
- Back
Who first proposed the term "virus"?
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Louis Pasteur
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Who showed that that a disease in tobacco was caused by a virus in the 1890s
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Ivanovski and Beijerinck
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Who discovered an animal virus that causes foot –and-mouth disease in cattle
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Loeffler and Frosch
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Viruses can infect _____ _____ __ ____
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every type of cell
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Why aren't viruses considered to be living things?
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Cannot exist independently from the host cell
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why are viruses considered more than lifeless molecules?
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Because they can direct life processes
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what are viruses called?
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infectious particles, either active or inactive
Also called obligate intracellular parasites |
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what is the general way a virus multiplies
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they invade a specific host cell and instruct its genetic and metabolic machinery to make and release new viruses
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what is needed to see most viruses?
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electron microscope
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what is the smallest infectious agent known?
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viruses
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How are viruses viewed?
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Special stains and an electron microscope
Negative staining outlines the shape Positive staining shows internal details Shadowcasting technique |
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what is the general molecular structure of viruses?
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composed of regular, repeating subunits that give rise to their crystalline appearance
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what are the two parts of a virus?
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external coating
core |
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what does the external coating consist of?
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capsid
envelope in 13 of the 20 families of animal viruses OR |
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what does the core consist of
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DNA (Single or Double)
RNA (Single or Double) |
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If there is no envelope, it is called a ______ ________
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naked virus
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what is the capsid and the nucleic acid together called?
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nucleocapsid
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define "virion"
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Fully formed virus that is able to establish an infection in a host cell- virion
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The viral capsid is the ______ _____ ______
It is constructed from _______ _______ called ________ Made up of _______ ______ |
Protective Outer shell
identical subunits, capsomers protein molecules |
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what are the two different types of capsomers?
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1. Helical
2. Icosahederal |
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describe helical capsids
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Rod-shaped capsomers
Assemble in to helical nucleocapsid |
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describe icosahederal capsids
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Three-dimensional, 20-sided figure with 12 evenly spaced corners
Although they all display this symmetry, there are wide variations |
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what is an enveloped virus?
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Enveloped viruses take a bit of the host cell membrane in the form of an envelope
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what happens in the host cell membrane that the enveloped virus has taken?
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In the envelope, some or all of the regular membrane proteins are replaced with viral proteins
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what happens with the viral proteins in the membrane?
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Some proteins form a binding layer between the envelope and the capsid
Glycoproteins remain exposed as spikes (peplomers)- essential for attachment |
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what are the functions of the viral capsid/envelope
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Protects nucleic acids
Help introduce the viral DNA or RNA into a suitable host cell Stimulate the immune system to produce antibodies that can protect the host cells against future infections |
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define "genome"
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Genome- the sum total of the genetic information carried by an organism
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how do the number of viral genes compare with cells genes
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Number of viral genes compared with a cell- quite small
They only have the genes necessary to invade host cells and redirect their activity |
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What are some exceptions to the commonly small amount of genes?
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Parvoviruses contain single-stranded DNA
Reoviruses contain double-stranded RNA |
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Describe DNA viruses
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ssDNA
dsDNA linear circular |
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describe RNA viruses
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Mostly single-stranded
Segmented- individual genes exist on separate pieces of RNA |
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single stranded RNA is divided into two groups: describe each
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Positive-sense RNA: genomes that are ready for immediate translation into proteins
Negative-sense RNA: genomes have to be converted into the proper form to be made into proteins |
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DNA viruses can be either _____ or ________
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enveloped or nonenveloped
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Enveloped DNA viruses can be
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only double stranded
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nonenveloped DNA can be
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either double or single stranded
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describe a retrovirus
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an RNA enveloped genome that is single-stranded and encodes reverse transcriptase, which reverse transcripts RNA to DNA
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what are some Other Substances in the Virus Particle
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Can contain enzymes for specific operations within the host cell
Polymerases to synthesize DNA and RNA Replicases to copy RNA (RNA dependent RNA polymerase) Integrase (Allows for integration of viral genome into host genome) |
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what are the main criteria for how viruses are classified and named?
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Structure
Chemical composition Similarities in genetic makeup |
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the International Committe on the Taxonomy of Viruses in 2000 designated how many:
orders? Families? Genera? |
3
63 - "-viridae" 263 - "virus" |
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What are the multiplication cycles in animal viruses?
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Adsorption
Penetration Uncoating Synthesis Assembly Release |
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describe the adsorption stage
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Virus encounters susceptible host cells
Adsorbs specifically to receptor sites on the cell membrane Because of the exact fit required, viruses have a limited host range |
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Describe the penetration stage
(different ways of penetration) |
Flexible cell membrane of the host is penetrated by the whole virus or its nucleic acid
Endocytosis: entire virus engulfed by the cell and enclosed in a vacuole or vesicle The viral envelope can also directly fuse with the host cell membrane |
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Describe the uncoating stage
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Enzymes in the vacuole dissolve the envelope and capsid
The virus is now uncoated |
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Describe the general synthesis stage
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Free viral nucleic acid exerts control over the host’s synthetic and metabolic machinery
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Describe the synthesis stage with DNA viruses
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DNA viruses- enter host cell’s nucleus where they are replicated and assembled
DNA enters the nucleus and is transcribed into RNA The RNA becomes a message for synthesizing viral proteins (translation) New DNA is synthesized using host nucleotides |
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*
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*
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Describe the synthesis stage with RNA viruses
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RNA viruses- replicated and assembled in the cytoplasm
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Describe the Assembly stage
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Mature virus particles are constructed from the growing pool of parts
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Describe the Release stage
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Nonenveloped and complex viruses are released when the cell lyses or ruptures
Enveloped viruses are liberated by budding or exocytosis Anywhere from 3,000 to 100,000 virions may be released, depending on the virus |
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Entire length of cycle- anywhere from
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8 to 36 hours
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define cytopathic effects
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virus-induced damage to the cell that alters its microscopic appearance
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what are inclusion bodies?
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Inclusion bodies- compacted masses of viruses or damaged cell organelles
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THe specific cytopathic effects of a virus is important for the _______ of _______ _______.
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diagnosis of viral infections
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what is an oncogenic virus?
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viruses that enter their host cell and permanently alter its genetic material, leading to cancer
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what are oncoviruses?
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Oncoviruses- mammalian viruses capable of initiating tumors
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what is a virus that infects bacteria called?
What do most of them contain? What effect do they have on the bacteria they infect? |
bacteriophage
most contain dsDNA Often make the bacteria they infect more pathogenic for humans |
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Describe the physical appearance of T-even Phages
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Icosahedral capsid head containing DNA
Central tube surrounded by a sheath Collar Base plate Tail pins Fibers |
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+
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+
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Describe the stages of T-even Phages
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Adsorb to host bacteria
The nucleic acid penetrates the host after being injected through a rigid tube inserted through the bacterial membrane and wall Entry of the nucleic acid causes the cessation of host cell DNA replication and protein synthesis The host cell machinery is then used for viral replication and synthesis of viral proteins As the host cell produces new parts, they spontaneously assemble |
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T-even Phages cycle
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*
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*
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what are temperate phages?
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Temperate phages- special DNA phages that undergo adsorption and penetration but are not replicated or released immediately
Instead the viral DNA enters an inactive prophage stage Lysogeny: the cell’s progeny will also have the temperate phage DNA |
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Define lysogenic conversion
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Lysogenic conversion: when a bacterium acquires a new trait from its temperate phage
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what is the difference between bacteriophages and animal viruses during the adsorption stage?
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bacteriophages have precise attacment of special tail fibers to the cell wall
animal viruses attach via their capsid or envelope to cell surface receptors |
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what is the difference between bacteriophages and animal viruses during the penetration stage?
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bacteriophages inject their nucleic acid through the cel wall - no uncoating of nucleic acid
animal viruses are fully engulfed and uncoated, or the virus surface fuses with the cell membrane to release nucleic acid. |
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what is the difference between bacteriophages and animal viruses during the Assembly stage?
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both are the same except that bacteriophages assembly occurs only in the cytoplasm, while in animal viruses, assembly occurs in both cytoplasm and nucleus
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what is the difference between bacteriophages and animal viruses during the release stage?
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bacteriophages cause the cell to lyse when viral enzymes weaken it,
animal viruses cause some cells to lyse, enveloped viruses bud off host cell membrane |
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Bacteriophages cause cell destruction _________
Animal viruses cause cell destruction ___________ |
immediately upon release
immediately upon release or later (delayed) |
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what are the primary purposes of viral cultivation?
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To isolate and identify viruses in clinical specimens
To prepare viruses for vaccines To do detailed research on viral structure, multiplication cycles, genetics, and effects on host cells |
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what is it called when animals are exposed to a virus by injection in order to cultivate the virus?
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live animal inoculation
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what is a nearly perfect condition for viral propagation
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using bird embryos within their eggs.
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Cell/Tissue culture techniques involve:
How do the cultured cells grow? |
Animal cell cultures grown in sterile chambers with special media.
In the form of a monolayer |
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viruses are the most common cause of :
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acute infections that do not result in hospitalization
Most do not cause death but those that do can have very high mortality rates Others can lead to long-term debility |
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the Deposition of protein fibrils (prions) in the brain tissue is caused by:
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Spongiform encephalopathies
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Spongiform encephalopathies cause _______ ________ diseases with ______ _____ __ _______
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chronic, persistant
long periods of latency |
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what are satellite viruses?
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Defective forms of viruses
Dependent on other viruses for replication |
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what are viroids?
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Parasitize plants
Very small Composed only of naked strands of RNA |
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How do antiviral drugs work?
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By blocking virus replication by targeting one of the steps in the viral life cycle
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what drug has shown potential for treating and preventing viral infections?
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interferon
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