Micro Chapter 13
A latent viral infection is one in which the virus remains in the host cell for long periods without producing an infection. Examples are cold sores and shingles.
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A lysogenic phage can transfer bacterial genes from one cell to another through transduction. Any genes can be transferred in generalized transduction, and specific genes can be transferred in specialized transduction.
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A provirus can remain latent, can produce viruses, or can transform the host cell.
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A viral species is a group of viruses sharing the same genetic information and ecological niche.
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After maturation, viruses are released. One method of release (and envelope formation) is
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After several viral multiplication cycles, the bacteria in the area surrounding the original virus are destroyed; the area of lysis is called a plaque.
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Among the RNA viruses, only retroviruses seem to be oncogenic.
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Animal viruses are uncoated by viral or host cell enzymes.
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Animal viruses attach to the plasma membrane of the host cell.
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Because of lysogeny, lysogenic cells become immune to reinfection with the same phage and may undergo phage conversion.
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Cell cultures are cells growing in culture media in the laboratory.
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Classification of viruses is based on type of nucleic acid, strategy for replication, and morphology.
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Complex viruses have complex structures. For example, many bacteriophages have a polyhedral capsid with a helical tail attached.
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Continuous cell lines can be maintained in vitro indefinitely.
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Cultivation of some animal viruses requires whole animals.
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DNA viruses include members of the families Adenoviridae, Poxviridae, Herpesviridae, Papovaviridae, and Hepadnaviridae.
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During release, phage lysozyme breaks down the bacterial cell wall, and the new phages are released.
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During the attachment phase of the lytic cycle, sites on the phage's tail fibers attach to complementary receptor sites on the bacterial cell.
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During the eclipse period, separate phage DNA and protein can be found. During maturation, phage DNA and capsids are assembled into complete viruses.
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During the lysogenic cycle, prophage genes are regulated by a repressor coded for by the prophage. The prophage is replicated each time the cell divides.
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During the lytic cycle, a phage causes the lysis and death of a host cell.
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Each plaque originates with a single viral particle; the concentration of viruses is given as plaque-forming units.
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Entry occurs by receptor-mediated endocytosis or fusion.
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Enveloped viruses are covered by an envelope and are roughly spherical but highly pleomorphic. There are also enveloped helical viruses (for example, influenza virus) and enveloped polyhedral viruses (for example, Simplexvirus).
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Exposure to certain mutagens can lead to excision of the prophage and initiation of the lytic cycle.
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For a virus to multiply, it must invade a host cell and direct the host's metabolic machinery to produce viral enzymes and components.
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HTLV-1 and HTLV-2 have been associated with human leukemia and lymphoma.
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Helical viruses (for example, Ebola virus) resemble long rods, and their capsids are hollow cylinders surrounding the nucleic acid.
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In biosynthesis, transcription of phage DNA produces mRNA coding for proteins necessary for phage multiplication. Phage DNA is replicated, and capsid proteins are produced.
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In penetration, phage lysozyme opens a portion of the bacterial cell wall, the tail sheath contracts to force the tail core through the cell wall, and phage DNA enters the bacterial cell. The capsid remains outside.
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Multiplication of RNA viruses occurs in the cytoplasm of the host cell. RNA-dependent
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Oncogenic viruses are found among the Adenoviridae, Herpesviridae, Poxviridae, Papovaviridae, and Hepadnaviridae.
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Persistent viral infections are caused by conventional viruses; viruses accumulate over a long period.
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Persistent viral infections are disease processes that occur over a long period and are generally fatal.
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Picornaviridae + strand RNA acts as mRNA and directs the synthesis of RNA-dependent RNA polymerase.
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Plant viruses must enter plant hosts through wounds or with invasive parasites, such as insects.
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Polyhedral viruses (for example, adenovirus) are many-sided. Usually the capsid is an icosahedron.
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Primary cell lines and embryonic diploid cell lines grow for a short time in vitro.
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Prion diseases are the result of an altered protein; the cause can be a mutation in the
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Prion diseases, such as CJD and mad cow disease, all involve the degeneration of brain tissue.
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Prions are infectious proteins first discovered in the 1980s.
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RNA polymerase synthesizes a doublestranded RNA.
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Reoviridae are digested in host cell cytoplasm to release mRNA for viral biosynthesis.
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Retroviridae reverse transcriptase (RNA-dependent DNA polymerase) transcribes DNA from RNA.
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Rhabdoviridae − strand RNA is a template for viral RNA-dependent RNA polymerase, which transcribes mRNA.
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Serological tests are used most often to identify viruses.
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Several DNA viruses and retroviruses are oncogenic.
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Simian AIDS and feline AIDS provide models for studying human AIDS.
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Some animal viruses can be cultivated in embryonated eggs.
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Some envelopes are covered with carbohydrate-protein complexes called spikes.
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Some plant viruses also multiply in insect (vector) cells.
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Some viruses can either cause lysis or have their DNA incorporated as a prophage into the DNA of the host cell. The latter situation is called lysogeny.
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The DNA of most DNA viruses is released into the nucleus of the host cell. Transcription of viral DNA and translation produce viral DNA and, later, capsid proteins. Capsid proteins are synthesized in the cytoplasm of the host cell.
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The DNA synthesized from the viral RNA becomes incorporated as a provirus into the host cell's DNA.
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The capsid of some viruses is enclosed by an envelope consisting of lipids, proteins, and carbohydrates.
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The earliest relationship between cancer and viruses was demonstrated in the early 1900s, when chicken leukemia and chicken sarcoma were transferred to healthy animals by cell-free filtrates.
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The easiest viruses to grow are bacteriophages.
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The genetic material of oncogenic viruses becomes integrated into the host cell's DNA.
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The plaque method mixes bacteriophages with host bacteria and nutrient agar.
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The proportion of nucleic acid in relation to protein in viruses ranges from about 1% to about 50%.
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The virus's ability to produce tumors is related to the production of reverse transcriptase.
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Togaviridae + strand RNA acts as a template for RNA-dependent RNA polymerase, and
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Transformed cells lose contact inhibition, contain virus-specific antigens (TSTA and T antigen), exhibit chromosome abnormalities, and can produce tumors when injected into susceptible animals.
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Viral growth can cause cytopathic effects in the cell culture.
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Virus family names end in -viridae; genus names end in -virus.
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Viruses capable of producing tumors are called oncogenic viruses.
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Viruses do not contain enzymes for energy production or protein synthesis.
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Viruses may be identified by RFLPs and PCR.
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Viruses must be grown in living cells.
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When activated, oncogenes transform normal cells into cancerous cells.
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budding. Nonenveloped viruses are released through ruptures in the host cell membrane.
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mRNA is transcribed from a new − RNA strand.
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normal gene for PrPC or contact with an altered protein (PrPSc).
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Viruses range from _________ nm in length.
20 to 1000
The protein coat surrounding the nucleic acid of a virus is called the __________.
capsid
Which of the following is NOT utilized to culture viruses?
culture media
Viral size is ascertained by __________ microscopy.
electron
A viral species is a group of viruses that
has the same genetic information and ecological niche.
Viruses are ______________. They multiply by using the host cell's synthesizing machinery to cause the synthesis of specialized elements that can transfer the viral nucleic acid to other cells.
obligatory intracellular parasites
Host range is determined by ____________________
the specific attachment site on the host cell's surface and the availability of host cellular factors.
What is a viruses' host range?
the spectrum of host cells in which a virus can multiply.
We sometimes are able to generate antibodies (immune system proteins) that bind to and cover up some of the proteins on the outermost portion of a virus while it is in the bloodstream. This renders the virus unable to reproduce. Which step of viral replication are antibodies directly preventing?
Attachment
Which of the following statements concerning viruses is true? a) Viruses contain both DNA and RNA, and they undergo binary fusion. b) Viruses are usually about the same size as bacteria. c) Viruses possess enzymes for protein synthesis and ATP generation. d) The "host range" for a virus is determined by the presence or absence of particular components on the surface of a host cell that are required for the virus to attach.
D
Enveloped viruses have a layer of lipids surrounding their capsid. This envelope is made mostly of host cell membrane. In which step does the virus acquire this envelope?
Release
What occurs during viral uncoating?
The capsid breaks apart, releasing the viral genome.
____________are infectious pieces of RNA that cause some plant diseases, such as potato spindle tuber disease.
Viroids
How do all viruses differ from bacteria?
Viruses are not composed of cells.
What is a virion?
a complete, fully developed viral particle composed of nucleic acid surrounded by a coat.
What are viruses composed of?
a single type of nucleic acid (DNA or RNA) and a protein coat; sometimes enclosed by an envelope composed of lipids, proteins, and carbohydrates.