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General Virology
SG/PP 1
39
Veterinary Medicine
Professional
01/19/2016

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Cards

Term
What are the 2 major components of a virus?
Definition
1) genome (either DNA or RNA)
2) lipoprotein coat (surrounding the genome)
Term
True or False: Viruses replicate inside livings cells using machinery they brought in with them.
Definition
-FALSE; viruses ONLY replicate inside living cells, using the cellular synthetic machinery to replicate
Term
Why are viruses completely dependent on cellular synthetic machinery for replication?
Definition
-they have no ribosomes, mitochondria, or other normal cellular organelles
-they cannot capture and store energy
-they cannot replicate in cell-free media
Term
What is the purpose of the protective coat that surrounds the genome?
Definition
-it allows the virus to survive in th environment
-it allows the viruse to infect cells
Term
How does the protective coat around the genome allow the virus to infect cells?
Definition
-viral glycoproteins attach to cell receptors allowing the virus to enter cells
Term
Definition: Transfected
Definition
-when a naked viral genome is artificially, forcefully introduced into a cell
Term
All the information needed for virus replication is contained within the genome. Does this make the genome infectious? Why or why not?
Definition
-NO, it is very labile and cannot enter cells
Term
What happens if the naked viral genome is artificially transfected into a cell?
Definition
-virus replication will occur allowing the cell to produce thousands of infectious virus particles
Term
Definition: Virion
Definition
-a mature virus particle
Term
Definition: Genome
Definition
-consists of a nucleic acid (either DNA or RNA)
Term
Definition: Capsid
Definition
-the protein coat that surrounds the genome
Term
What is the capsid composed of?
Definition
-capsomeres
Term
What comprises a capsomere?
Definition
-popypeptides that are held together by non-covalent bonds
Term
What are the functions (5)of the viral capsid?
Definition
1) to protect the viral genome: allows for survival of parvovirus for years in soil
2) to provide structural symmetry to the virus particls: endows stability
3) to allow viruses to enter cells by recognizing and attaching to host cell receptors
4) may aid in virus replication: may contain enzymes necessary for virus replication
5) although not a function per se, the capsid proteins are very immunogenic!!!
Term
Definition: Nucleocapsid
Definition
-constitutes the capsid plus the nucleic acid genome
Term
Definition: Envelope
Definition
-outer coat that surrounds the nucleocapsid of some viruses
Term
What is the difference between an enveloped virus and a naked viruses?
Definition
-an enveloped virus' nucleocapsid is surrounded an envelope
-naked viruses structures consist of only a nucleocapsid
Term
How is the viral envelope derived?
Definition
-from the cellular membrane (plasma or nuclear membrane)
Term
Definition: Budding
Definition
-the process by which the virus acquires the envelop as it leaves the infected cell
-prior to budding, viral glycoproteins (peplomers) are inserted into the lipid bilayer cellular membrane
-thus the virus becomes surrounded by this peplomer-modified cellular membrane
Term
The aftermath of budding: the lipid bilayer (______) is of (cellular/viral) origin and the peplomers are of (cellular/viral) origin.
Definition
-envelope
-cellular origin
-viral origin
Term
What are the functions (4) of the viral envelope?
Definition
1) to provide structural symmetry in some instances
2) to allow the virus to enter cells: peplomers attach to host cell receptors (some viral peplomers will cause the viral envelope to fuse with the cell membrane)
3) may contain enzymes essential for virus replication
4) although not a function per se, the glycoproteins peplomers are very immunogenic
Term
What are the 4 important criteria used to classify viruses?
Definition
1. size of the virion
2. symmetry of the nucleocapsi
3. presence or absence of an envelope
4. type of nucleic acid
Term
Virus size is usually expressed in ______ and NOT ______.
Definition
-nanometer (10^-9)
-micron
Term
Definition: Resolving power of the eye
Definition
-the unaided eye cannot distinguish objects smaller than 0.25mm/250um/250,000nm
Term
What is the resolving power of the light micrscope?
Definition
-approx 1000X greater than the eye
Term
What is the resolving power fo the electron microscope (EM)?
Definition
-approx 1000X greater than that of the light microscope
Term
What is the practical limit of the EM?
Definition
-2.5nm
Term
The size of viruses that infect animals and humans range from ___nm-___nm.
Definition
20 nm to 350 nm
Term
What are the three divisions of symmetry of the nucleocapsid?
Definition
-curbic/icosahedral
-helical
-complex symemtry
Term
Describe a general virus with cubic/icosahedral symmetry.
Definition
-20-sided structure
-5:3:2 rotational symmetry
-triangles are made up of symmetrical clusers of capsomeres
Term
What is a penton? What is a hexon?
Definition
-pentons are capsomeres situated at the 12 vertices, eac hhas 5 neighboring capsomeres
-hexons are surrounded by 6 neighboring capsomeres
Term
Definition: Helical Nucleopsid
Definition
-nucleic acid is arranged in a helical conformation with capsomeres closely associated with the helix
-these capsomeres protect the viral genome
Term
True or False: All animal viruses with helical nucleocapsid are enveloped
Definition
TRUE
Term
What is the only example of an animal viruse that has a complex symmetry?
Definition
-pox virus
Term
The nucleic acid of viruses may be either ___ or ___ & _____- or _____-stranded & _____ or _____ & _____ or _____.
Definition
-DNA or RNA
-single- or double-stranded
-linear or circular
-segmented or non-segmented
Term
What does it mean if a genome has positive polarity?
Definition
-it can be translated idrectly into proteins by cellular ribosomes
Term
What does it mean if a genome has negative polarity?
Definition
-it must first be transcribed into a complementary positive strand before it can be translated into proteins
Term
What polymerase enzyme is necessary for the transcription of the gnenome from negative to positive polarity? Where does it come from?
Definition
-RNA dependant RNA polymerase
-not present in normal cells so brought into the cell or manufactured by the virus
Term
What are some of the additional criteria to classify viruses?
Definition
-mode of virus replication
-diameter of nucleocapsid in helical viruses
-number of capsomere in the icosahedral viruses
-molecular weight of nucleic acids
-epidemiological criteria: enteric viruses, respiratory viruses, ARBO viruses
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