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19 Cards in this Set
- Front
- Back
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In many viruses, how is a lipid membrane usually acquired?
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It is acquired as the viral nucleocapsid exits the host cell. A part of the membrane wraps itself around the nucleocapsid.
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List several viruses that utilize this membrane scavenging approach for forming their virions.
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Influenza virus
Encephalitis virus Smallpox virus Rabies virus herpes virus HIV virus |
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In most cases, the membrane surrounding the nucleocapsid is barbed with an array of virus encoded proteins. True/False
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True. Usually the N -termini of these proteins protrude outward into the fluid outside the viral particle. The C-termini often contact the nucleocapsid inside the membrane.
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Are lipid bilayers easily dissolved by detergents?
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Yes. They are easily inactivated by soaps and detergents. The proteinaceouss virions are much more resistant to soaps.
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Why can most gastro-intestinal viruses(including polio) successfully make it through the GI tract?
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Their virions can resist the strong detergents present in liver bile that is always introduced into the small intestine.
lipid contained virions do not have this ability. |
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What is a rather unique way some viruses enter into host cells?
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Host cells are constantly internalizing their own membrane proteins and recycling them back to the surface. Many viruses are carried on these host cell proteins to gain entrance into the cell.
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Do all viruses complete their replication cycle in the cytoplasm of the cell?
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No. Some do, others move into the nucleus to replicate.
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Most DNA viruses enter the nucleus. True/False
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True. They will parasitize the host cells DNA replication apparatus. Smallpox is an exception. This DNA virus encodes its own DNA replication machinery and remains in the cytoplasm.
Most RNA viruses replicate in the cytoplasm. |
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Once the nucleocapsid of a double stranded DNA virus(dsDNA) enters into the cell, where does it go?
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It proceeds to the nucleus where it will mimic the genome of the host cell.
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How is the viral genome replicated with a dsDNA strand?
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It is replicated by using the host cell DNA polymerase, and the viral genome is transcribed by the host cell RNA polymerase.
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What happens eventually to the resulting transcripts carrying information encoding the viral proteins?
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They are transported to the cytoplasm and seen as a template by the host cell ribosomes.
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How will some of these newly synthesized viral proteins be used?
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They will form the protein capsid around the newly replicated viral DNA molecules. They will be released from the cell, and target other host cells to trigger new infections.
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The enzymes of DNA replication are usually not expressed in quiescent cells. True/False
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True. These cells are categorized as cells in G(0). Most of the cells that are infected will be in G(0) and are unwelcoming hosts.
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List two dsDNA viruses that have genomes greater than 60 genes.
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Herpes
Epstein-Barr virus. However, these viruses can encode their own DNA polymerase and secure their ability to replicate in quiescent cells. |
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Aside from some viruses encoding their own DNA polymerase, how might other viruses get around this problem?
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Some viruses produce a protein that induces the resting host cell to enter the active cell cycle. At this point, the replication enzymes are available for exploitation and continued reproduction of the virus.
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Considering that some viruses may induce cells into the active cell cycle, can this cause a cellular transformation?
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Possibly. This process converts the host cell growth from a normal pattern to a pattern more in line with a cancer cell. In fact, the gene that encodes this growth promoting protein can function as an oncogene that acts to transform the infected cell into a cancer cell.
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Over 90% of human cervical carcinomas are associated with infection by human papilloma virus. True/False
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True. The viral genome must perpetuate itself so when the original cell divides into many cells, each new cell has the virus and the viral growth promoting protein.
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There is a strong association between the EBV and Burkitt's lymphoma. True/False
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True. Burkitt's lymphoma is seen in central Africa as a childhood tumor. These tumors are inadvertent by-products of the need to replicate viral DNA.
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Concerning Burkitt's lymphoma from the EBV, why does the actual outgrowth of tumors occur?
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This happens when virus infected cells are not fully eliminated by the completion of the viral lytic cycle.
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