Chapter 10 - Viruses & Virology
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chickadee4th on April 24, 2009
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85 terms
Terms | Definitions |
|---|---|
 virus (as a genetic element) | a genetic element that cannot replicate independently of the host cell |
| virus (components) | a genetic element containing either RNA or DNA surrounded by a protein capsid |
| the virus particle or virion | an extracellular form that allows viruses to exist outside the host for long periods & aids transmission from one host cell to another |
| infection | the process by which viruses enter a cell and replicate |
| virology | the study of viruses |
| the virion or virus particle | the infectious virus particle; the nucleic acid genome surrounded by a protein coat, and sometimes other layers of material |
| bacteriophage or "phage" | a virus that infects prokaryotic cells |
| capsid | the protein shell that surrounds the genome of a virus particle |
| capsomer | subunit of a capsid, composed of several chemically distinct proteins; the smallest morphological unit seen with an electron microscope |
| self-assembly | the overall process of virion assembly |
| nucleocapsid | the complex of nucleic acid and protein packaging within the virion |
| helical symmetry | the type of symmetry associated with rod-shaped viruses, such as TMV |
| icosahedral symmetry | the type of symmetry associated with spherical viruses; the most efficient arrangement of subunits in a closed shell |
| icosahedron | 3-D figure with 20 triangular faces and 12 vertices; roughly spherical in shape |
| "enveloped" virus | have a membrane surrounding the nucleocapsid |
| viral envelope | composed of a lipid bilayer with proteins (usually glycoproteins) embedded in it |
| virus-specific protein | embedded in the lipid bilayer of the viral envelope, encoded by viral genes; critical for attachment & release of the virion to the host |
| bacteriophage T4 | an icosahedral bacterial virus of E. coli |
| lysozyme | an enzyme that viruses can use to make a small hole in the bacterial cell wall, allowing the viral nucleic acid to enter |
| reverse transcriptase | an RNA-dependent DNA polymerase that transcribes viral RNA into a DNA intermediate; a backward information transfer from RNA to DNA |
| neuraminadases | enzymes that cleave glycosidic bonds in glycoproteins and glycolipids of animal cell connective tissue, liberating the virions |
| monolayer | the thin layer of cells adhering to the bottom of a culture flask or Petri dish, which is overlaid with culture medium and incubated for culturing |
| permanent cell lines | cell cultures prepared by incubation in enriched media which grow indefinitely; especially convenient for virus research |
| primary cell cultures | cell cultures that do not grow indefinitely, but remain alive for a number of days; useful but can be expensive and time-consuming |
| titer | a measure of virus quantity; the number of infectious units per volume of fluid |
| plaque | a zone of lysis (clearance) or cell inhibition, causes by virus infection of a lawn of sensitive cells; essentially "windows" in the lawn of confluent cell growth |
| plaque-forming unit | one unit of plaque; each one represents one virus infectious unit present in the original sample |
| efficiency of plating | an important concept in quantitative virology; allows one to estimate how concentrated a viral suspension needs to be (its titer) to yield a certain number of plaques |
| viral eclipse | the first few minutes of viral infection, during which infectious particles cannot be detected in the culture medium |
| one-step growth curve | characteristic of virus replication, since the release of virions is basically simultaneous |
| virus-permissive | a cell that allows the complete replication cycle of a virus to take place |
| virus-restriction | a phenomenon of the general host mechanism, preventing the invasion of foreign nucleic acid |
| restriction enzymes | host restriction endonucleases that cleave viral DNA, preventing replication; specific for double-stranded DNA |
| glucosylation | one chemical modification pattern of viral DNA; used by the T-even bactriophages to prevent nuclease attack |
| methylation | one chemical modification pattern of viral DNA; used by T3 and T7 to counteract host restriction enzymes |
| positive-strand RNA virus | a virus with a single-stranded genome, which has the same complementarity as the viral mRNA |
| negative-strand RNA virus | a virus with a single-stranded genome, which has the opposite sense to the viral mRNA |
| Baltimore Classification Scheme | a classification scheme for viruses including 7 classes, based on the relationship of the viral genome to its mRNA, or genome type & reproductive strategy |
| class I virus | double-stranded DNA genome |
| class II virus | single-stranded DNA genome |
| class III virus | double-stranded RNA genome |
| class IV virus | single-stranded RNA genome of plus sense |
| class V virus | single-stranded RNA genome of minus sense |
| class VI virus | single-stranded RNA genome that replicates with DNA intermediate |
| class VII virus | double-stranded DNA genome that replicates with RNA intermediate |
| retrovirus | a virus whose RNA genome has a DNA intermediate as part of its replication cycle |
| reverse transcription | the process of copying information found in RNA into DNA, by the enzyme reverse transcriptase |
| viral proteins | synthesized after viral mRNA is made |
| early protein | a protein synthesized soon after the virus infection, before viral genome replication; primarily enzymes for DNA replication & transcription |
| late protein | a protein synthesized later in virus infection, after viral genome replication; the head and tail proteins |
| lysogeny | a state following virus infection in which the viral genome is replicated as a provirus, along with the host genome |
| temperate virus | a virus whose genome is able to replicate along with its host's genome, without causing cell death, in a state of lysogeny |
| virulent virus | a temperate virus that lyses or kills the host cell after infection |
| provirus or prophage | the genome of a temperate virus, when it is replicating in step with or integrated into the host chromosome |
| lysogen | a bacterium containing a provirus |
| "T" | refers to a tailed phage |
| circular permutation | built from one or more sets of elements in cyclic order |
| terminal repeats | a short non-coding DNA sequence found at each end of the viral genome; contains elements necessary viral DNA replication & packaging |
| concatemer | a long DNA molecule, formed by the end-to-end recombination of several genomic units |
| 5-hydroxymethylcytosine | the modified T4 DNA base |
| middle proteins | primarily enzymes for DNA replication & transcription |
| phage-specific proteins | encoded by early genes; covalently modify the host RNA polymerase a-subunits |
| phage-encoded proteins | bind to the RNA polymerase |
| deoxycytidine triphosphate | the typical DNA precursor |
| late genes | encode structural proteins for the virion, including those for the head & tail |
| lytic pathway | a series of steps after virus infection, that leads to virus replication and the destruction (lysis) of the host cell |
| lambda | one of the two best-characterized temperate phages |
| P1 | one of the two best-characterized temperate phages |
| rolling circle replication | the asymmetric synthesis of the lambda genome; one of the parental strands is used only once, while the other is re-used as a template strand |
| cos sites | sites at which the double-stranded concatemer is cut into genome-sized lengths, giving cohesive ends |
| the lambda repressor (cI protein) | one of the two key repressor proteins; represses the synthesis of all other lambda-encoded proteins, establishing lysogeny |
| Cro repressor | one of the two key repressor proteins; repressed the expresseion of cII and cIII proteins |
| FtsH protein | a host cell protease that degrades cII |
| cII protein | induces synthesis of the cI protein; sufficient amount allows cI and integrase promoters to activate |
| cIII protein | induces synthesis of the cI protein; protects cII against protease attack; stabilizes lysogeny |
| latent infection | there is a delay between virus infection and lytic events |
| eukaryotic transformation | a process by which a normal cells becomes a cancer cell |
| gag | a retrivirus gene that encodes structural proteins |
| pol | a retrivirus gene that encodes reverse transcriptase & integrase |
| env | a retrovirus gene that encodes envelope proteins |
| provirus (prophage) | a stable genetic element; the genome of a temperate virus when it is replicating in step with or integrated into the host chromosome |
| helper virus | a virus that provides some necessary components for a defective virus |
| defective virus | a virus that relies on the helper virus to provide some of its components |
| AAV | adeno-associated virus; a human satellite virus that depends on the adenovirus as helper |
| viroid | infecious RNA molecules which lack a protein coat; a small, circular, single-stranded RNA that causes certain plant diseases |
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