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100 Cards in this Set
- Front
- Back
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What are viruses?
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Viruses are infectious particles (rather than organisms) and is either active or inactive (rather than aliver or dead)
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Why are viruses called obligate intracellular parasite?
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They are obligate intracellular parasite that cannot multiply unless it invades a specific host cell and instructs its genetic and metabolic machinery to make and release quantities of new viruses.
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What is a viral capsid?
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The viral capsid is constructed from a number of identical protein subunits called capsomers.
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What are the different types of viral capsid?
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Helical capsids and Icosahedron
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What is helical capsid?
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Rod-shaped capsomeres that bind together to form a series of hollow discs resembling a bracelet.
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What happen during the formation of nucleocapsid with the helical capsid?
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The hollow discs link together and form a continuous helix into which the nucleic acid strand is coiled.
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What are the different types of helical viruses?
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Naked helical viruses; enveloped helical viruses
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What is naked helical virus? Give example.
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Naked helical virus - very rigid and tightly wound into a cylder shaped package.
Example: virus that infect plants |
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What are enveloped helical viruses? Give example.
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Enveloped helical viruses - more flexible and tend to be arranged as a looser helix within the envelope
Example: influenza, measles and rabies |
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What is icosahedron?
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tree-dimensional, 20-sided figure with 12 evenly spaced corners
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What happen during the assembly of nucleic acid of icosahedron virus?
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During the assembly of the virus, the nucleic acid is packed into the center of this icosahedron, forming a nucleocapsid.
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What are the other factor the alters the appearance of icosahedron virus?
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Whether or not they have an outer envelope.
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How is viral enveloped derived from its host different?
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Enveloped derived from its host is different because some or all of the regular membrane proteins are replaced with special viral proteins during the virus assembly process.
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What still remain on the outside of the viral envelope?
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Some proteins form a binding layer between the envelope and capsid of the virus, and glycoproteins
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What are glycoproteins?
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Proteins bound to a carbohydrates
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What are examples of complex viruses?
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Poxviruses and Bacteriophages
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What are poxviruses?
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Poxviruses - including agent of smallpox, are very large DA viruses that lack a typical capsid and are covered by a dense layer of lipoproteins and course fibrils on their outer surface.
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What are bacteriophages?
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Bacteriophages - have polyhedral capsid head as well as a helical tail and fibers for attachment to the host cell.
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What is genome?
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Sum totaol of genetic information carried by an organisms
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How is nucleic acid expressed in virus?
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Viruses contain either RNA or DNA but never both.
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What do large genome allow the cells to do?
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Allows cells to carry out the complex metabolic necessary for independent life.
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What kind of genes do viruses possess?
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Viruses possess only genes needed to invade host cells and direct their activity to make new viruses.
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How do dsDNA arranged?
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Can be arranged linearly or circles.
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What is an example of virus that contain ssDNA?
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Parvoviruses
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What are Reoviruses?
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They contain dsRNA and causes respiratory and intestinal tract infections
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How do proteins are made by viruses?
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By translating the nucleic acid code on a single strand of RNA into an amino acid sequence.
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What are + strand RNA
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single-stranded genomes that are ready for immediate translation into proteins
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What are - strand RNA?
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RNA genomes that have to be converted into the proper form for translation.
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What is an example of segmented RNA genomes
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Influenza virus
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What are retrovirus?
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converts its nucleic acid from RNA to DNA inside its host cell
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Why are viruses considered to be genetic parasites?
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Because they cannot multiply until their nucleic acid has reached the internal habitat of a host cell.
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Why do virus has to carry genes for synthesizing the viral capsid and genetic material?
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To regulate the actions of the hosts, and for packaging the mature virus
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What are polymerases?
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Polymerases - synthesizes DNA and RNA and replicases that copy of RNA
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What does reverse transcriptase of AIDS virus do?
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Synthesizes DNA from RNA
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What are Arenaviruses, as an example of viruses carrying away substances from their host cell?
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Pack along host ribosomes
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What do retroviruses carry away from its host cell?
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Retroviruses "borrow" the host's tRNA molecules
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What are spikes or peplomers?
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Protruding molecules essential for the attachemnt of viruses to the next host cell.
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What are the multiplication cycle of an enveloped animal virus?
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Adsorption, Penetration, Uncoating, Synthesis: Replication and Protein Production; Assembly and Release
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What is Adsorption?
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The virus attaches to its host cell by specific binding of its spikes to cell receptors.
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What receptors do the viruses normally attached into?
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glycoproteins
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How do naked viruses adhere to the cell membrane receptors?
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They use molecules on their capsids.
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Give an example of different host range.
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Hepatitis B - infects only liver cells of humans
Poliovirus - infects primarily intestinal and nerve cells of primates (humans, apes, and monkeys) Rabies virus - infects nerve cells of most mammals |
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When do we consider a cell resistant to the adsorption and invasion of a virus? Give example
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Cells that lack the compatible virus receptors
Human livers cells are not infected by canine hepatitis virus. Dog liver cells cannot host the human hepatitis A virus. |
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What are tropisms?
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Virus having special affinity for an object or a substance.
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Give examples of virus that exibits tropisms.
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Hepatitis B virus targes the liver. Mumps virus targets the salivary gland.
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What is penetration?
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For a virus to infect a cell, it must penetrate the cell membrane of the host cell and deliver the viral nucleic acid into the host cell's interior.
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What is fusion?
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The viral envelope fuses directly with the host cell membrane, so it can occur only in enveloped viruses.
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What happens after the attachment of enveloped virus to the host cell receptors?
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The lipids within the adjacent membranes become rearranged so that the nucleocapsid can be translocated into the cytoplasm for the synthesis.
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What is endocytosis?
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Version of penetration, the virus can be either enveloped or naked, and it is engulf entirely into a vesicle after its initial attachment.
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What happens to the endocytocized virus once inside the cell?
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It is uncoated. Its nuclei acid or nucleocapsid is released by the actions of enzymes in the cytoplasm that dissolve the vesicle wall.
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What happens during synthesis?
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Under the control of viral genes, the cell synthesizes the basic components of new viruses, RNA molecules,capsomers and spikes.
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How do DNA and RNA virus exerts control over host metabolism and synthetic machinery?
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DNA viruses (except poxviruses) enter the host's cell's nucleus and replicated and assembled there. RNA viruses are replicated in the cytoplasm, with some exceptions.
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What do RNA virus do in order to alter genetic expression of the hosts, and synthesixe the building block for new viruses?
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First, RNA of the virus becomes a message for synthesizing viral proteins (translation). + strand RNA = ready for translation, - strand RNA must be converted to + strand first before it can get translated. Some viruses come equipped with the necessary enzymes for synthesis of viral components, other utilizes those of the host. During th final phase, the host replication and synthesis machinery produces new RNA, proteins for the capsids, spikes, and viral enzymes.
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What is assembly?
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Viral spike proteins are inserted into the cell membrane for the viral envelope; nucleocapsid is formed from RNA and capsomers.
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What happen to the capsid during assembly?
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The capsid is first laid down as an empty shell that will serve as a receptacle for the nucleic acid strand.
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What is an important event that leads to the release of enveloped viruses?
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Insertion of viral spikes into the host's cell membrane so they can pick up as the virus buds off with its envelope.
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What is Release in the multiplication cycle of enveloped virus?
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Enveloped viruses bud off of the membrane, carrying away an envelope with the spikes. This complete virus or virion is ready to infect another cell.
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How do nonenveloped and complex viruses get released?
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Noneveloped and complex viruses that reach maturation in the cell nucleus or cytoplasm are released through cell lysis or rupturing.
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How do enveloped viruses get released?
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Enveloped viruses are liberated by budding or exocytosis from the membrane of the cytoplasm,nucleus, endoplasmic reticulum or vesicles.
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What happen to the nucleocapsid of enveloped virus during the process of release?
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Nucleocapsid binds to the membrane, which curves completely around it and form a small pouch. Pinching off the pouch releases the virus with its envelope.
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What are the lethal accumulated damage of viral infections?
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permanent shutdown of metabolism, genetic expression, destruction of cell membranes and organelles, toxicity of virus components and release of lysosomes
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What is the multiplication cycle for poliovirus?
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Poliovirus takes about 8 hours
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What is the multiplication cycle for Parvovirus?
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Parvovirus takes about 16 to 18 hours
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What is the multiplication cycle fro herpesvirus?
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Herpesviruses require 72 hours ore more
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What is a virion?
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A fully formed, extracellular virus particle that is virulent, and able to establish infection in a host.
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What are the control factors for the release of virion cells?
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Size of the virus and health of the host cell
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How many virions are released in Poxviruses? Polioviruses?
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Poxviruses - 3,000 to 4,000 virions from a single cell
Polioviruses - 100,000 virions |
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What are cytopathic effects (CPEs)?
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Virus induced damage to the cell that alters its microscopic appearance.
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What happens to the cell that undergoes CPEs?
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Cells can become disoriented, undergo gross changes in shape or size, or develop intracellular changes.
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What are inclusion bodies?
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Compacted masses of viruses or damaged cell organelles, in the nucleus or cytoplasm.
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Why is examination of cells and tissues for CPEs important?
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Diagnosis for viral infections
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What is an example of common CPE?
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Fursion of mutliple host cells into single large cells containing multiple nuclei
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What is a synctia?
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Result of some viruses' ability to fuse membrane.
Ex. Respiratory synctial virus |
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What is persisten infections?
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It can last from a few weeks to years and even for the life of the hosts.
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What is an example of persistent infection?
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Measles virus -
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What is a latent stage?
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Inactive over long periods
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What are examples of latent infections?
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Herpes simplex viruses - cold sores, genital herpes
Herpes zoster virus - chicken pox, shingles |
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What are oncogenic virus?
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Viruses that enter the host cell and permanently alter its genetic material leading to cancer.
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What is transformation?
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Effects of oncogenic virus on cell.
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What happen to transformed cells?
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Their nucleic acid becomes integrated into the host DNA. Transformed cells have increased rate of growth, aterations in chromosomes, changes in the cell's surface molecules, and the capacity to divide for an indefinite period.
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What are oncoviruses?
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Mammalian viruses capable of initiating tumors
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What are examples of oncoviruses?
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Papillomavirus - associated with cervical cancer
Herpesvirus - Epstein-Barr virus causes Burkitt's lymphoma Hepatitis B virus - liver cancer |
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How do the phage enter the host cell?
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The nucleic acid is injected through a rigid tube a phage inserts through the bacterial membrane and wall.
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What happen after the entry of nucleic acid in bacteriophage?
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Entry of nucleic acid stop host cell DNA replication and protein synthesis, and it soon prepares the cell machinery for viral replication and synthesis for viral proteins.
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What are the stages for Lysogency?
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Temperate phage, Prophage state, Lysogency and Induction
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What is a temperate phage?
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Special DNA phages, undergo adsorption and penetration into the bacterial host cell but are not replicated or released immediately.
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What is a prophage state?
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Inactive viral DNA enter and is inserted into the bacterial chromosome. This viral DNA will be retained by the by the bacterial cell and copied during its normal cell division so that the cell's progency will also have the phage DNA.
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What is lysogency?
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Condition of which host chromosome carries bacteriophage DNA. Because viral particles are not produced, the bacterial cells carrying temperate phages do not lyse and appear normal.
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What is induction?
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Prophage in a lysogenic cell will be activated and progess directly into viral replication and the lytic cycle.
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What is lysogenic conversion?
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When a bacterium acquires genes from its temperate phage
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What are prions?
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Proteinaceous infectious particle
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What is transmissible spongiform encephalopathies (TSEs)
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Diseases associated with prions, and are spread from host to host by direct contact, contaminated food, or other means. Refers to the effects of the agent on nervouos tissue, which develops a spongelike appearance due to loss of nerve and glial cells. Build up of tiny protein fibrils in the brain tissue.
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What are the prions diseases in mammals?
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Scrapie in sheep, Bovine spongiform encephalopathy (mad cow disease) in cattel, wasting disease in elk, deer and mink.
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What are the symptoms of prion disease on mammals?
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The animals loss coordination, have difficulty moving, and eventually progress to collapse and death.
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What are prion associated disease in humans?
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Creutzfeldt-Jakob syndrome (CJS), Kuru, fatal familial insomnia
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What are the symptoms of prion associated diseases in humans?
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The brain progessively deteriorates and the patient loses motor coordination, along with sendory and cognitive abilities
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What are satellite viruses?
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Viruslike agents in human disease, which are defective and actually depend on other viruses for replication?
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What are examples of satellite viruses?
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Adeno-associated virus (AAV) - replicate only in cells infected with adenovirus
Delta agent, a naked strand of RNA - expressed only in the presence of hepatitis B virus and can worsen severity of the liver damage. |
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What are viroids?
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Viruslike agents in plants
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How do viroids differ from ordinary viruses?
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By being very small (about 1/10 the size of average virus) and being composed only naked strands of RNA, lacking a capsid or any other type of coating.
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