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