Microbiology 31

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Question

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Answer

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fundamental difference between viruses and other infectious agents

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viruses are obligate intracellular parasite that carry out replication entirely with host cell machinery.

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structure that surrounds viral nucleic acid

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capsid

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nucleic acid + capsid

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nucleocapsid

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2 basic structural patterns for viruses

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icosahedral and helical

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some viruses have this, which surrounds the nucleocapsid

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envelope

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contents of viral envelope (in addition to nucleocapsid) include

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virus specific proteins, lipids, and carbohydrates, sometimes a matrix protein

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adsorption

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attachment of virus to host cell surface

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clathrin coated pits

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aggregation sites for some viruses such as influenza on the plasma membrane,

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these viruses cannot fuse with cellular membranes

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nonenveloped viruses

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uncoating

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once the virus is adsorpted and releases its payload into the host cell, the capsid is removed to make the viral genome asessable to the cellular transcription/translation machinery

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how do ss + RNA viruses such as picornaviruses (polio) and flaviviruses (west nile) produce proteins, reproduce their RNA

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to produce protein, the + RNA genome simply acts as mRNA and is translated by cellular ribosomes into proteins. To replicate viral RNA, a virus encoded RNA dependant RNA polymerase produces a negative complimentary RNA molecule, in turn this acts as a template to make complimentary + RNA molecules for progeny

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how do ss- RNA viruses such as influenza virus produce proteins, reproduce their RNA

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negative sense RNA cannot act as mRNA. It must be converted to a complimentary positive sense RNA to produce proteins. Since our cells have no machinery for RNA dependent RNA polymerase, the virion must contain this. Once the + sense mRNA is created proteins can be replicated using ribosomes, and - sense RNA can be regenerated for progeny using the RNA dependent RNA polymerase

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segmented genomes

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some viruses have genomes that exist as multiple strands of RNA, often there are individual genes or groups of genes on these strands

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how do ds RNA viruses produce proteins, reproduce their RNA

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like ss -RNA viruses, they must come preloaded with a RNA dependent RNA polymerase. This polymerase takes the neg sense RNA strand and produces a single pos sense RNA strand from which the negative sense strand can be replicated, or ribosomes can use as mRNA to make viral proteins

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describe the unique replication strategy of retroviruses

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retroviruses like HIV are ss + sense RNA viruses however, they come preloaded with a RNA dependent DNA polymerase (reverse transcriptase) which created DNA from the original RNA molecule, this DNA is then incorporated into the host genome where it stays forever, and is transcribed using DNA dependent RNA polymerase

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early vs late transcripts

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in DNA viruses the first (early) transcripts contain regulatory proteins and proteins required for viral DNA replication, while late transcripts are structial proteins of virion

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exons vs introns

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exons contain the gene sequences, introns are junk sequences….just like in our DNA

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how does the release of nonenveloped viruses differ from enveloped

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nonenveloped released when cell lyses, enveloped released by budding

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acute vs latent vs chronic viral infections

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acute is the virus undergoes multiple replication rounds and there is death of host cell. Latent is seen in DNA/retroviruses, and chronic is seen is Hep C where viral particles are still shed following period of acute illness

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immunoglobulin that contributes to defense at mucosal membranes such as respiratory and GI tract

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IgA

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iatrogenic inoculation

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transmission of virus caused by diagonistic or thereputic procedures

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horizontal/vertical sprea

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horizontal spread is between members of susceptable population and vertical is between mother and fetus when virus is carried in germ cell line,placenta, or maternal birth canal

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HSV rabies virus and VZV all spread how

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through nerves using mechanisms involved in fast axonal transport

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most important adaptive defense mechanism against viral infections is

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cell mediated immunity

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interellular defense mechanisms against viruses include

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apoptosis and autophagy (which results in sequestration of virus particles)

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early and late cytotoxic defenses against viruses

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early is from NK cells while later its CTLs and virus specific antibody responses

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viruses are delt with by T lymphocytes that express MHC1 or MHC2

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MHC1

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interferons

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synthesized by host cells in response to viruses that induces the expression of proteins that INHIBIT the protein synthesis machinery to limit viruses ability to replicate

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alpha interferon is produced by

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leukocytes

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beta interferon is produced by

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fibroblasts and epithelial cells

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gamma interferon is produced by

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T cells activated by speciic anigens