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45 Cards in this Set
- Front
- Back
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Are positive nucleic acid strands transcribed or translated?
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Positive nucleic acid strands are translated directly into protein.
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Are negative nucleic acid strands transcribed or translated?
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Negative nucleic acid strands, such as the negative DNA strand of a DNA virus or a negative RNA strand in a RNA virus, must be transcribed into positive stranded RNA before being translated into protein.
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Which orientation of RNA strand, positive or negative, can be directly translated into protein?
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Only positive stranded RNA can be directly translated protein. Negative nucleic acid strands, both DNA and RNA, must first be TRANSCRIBED into positive stranded RNA before being translated.
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Which is the only nucleic acid type (DNA vs. RNA) and orientation (positive vs. negative) that can be directly translated into protein?
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Positive stranded RNA molecules are the only ones that can be translated into protein. Negative stranded DNA molecules and negative stranded RNA molecules must first be TRANSCRIBED into positive stranded RNA molecules before translation.
Negative stranded nucleic molecules stand as templates for replication while the positive stranded RNA makes the proteins. Positive stranded DNA molecules are ignored altogether. |
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Describe the transcription, translation, and replication of negative stranded RNA viruses.
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After absorption and penetration, positive stranded RNA viruses must be transcribed. Their transcription into positive stranded RNA is catalyzed by RNA-dependant RNA polymerase, which they carry in their capsids.
Once transcription is completed, translation can proceed. |
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What does RNA-dependent RNA polymerase do?
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RNA-dependant RNA polymerase catalyzes the replication of RNA from an RNA template.
As such, it is required by both positive stranded and negative stranded RNA viruses. Positive stranded RNA viruses, which are directly translated, must make the enzyme right away so that a negative stranded "template" can be synthesized and replication can proceed. Negative stranded RNA viruses, which must be transcribed, already possess the enzyme in their capsids and use it to make a positive stranded copy that can be translated into protein. |
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Describe the transcription, translation, and replication of positive stranded RNA viruses.
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Positive stranded RNA viruses can be directly translated into protein. However, what's the point? The point is replication and to do that they need RNA polymerase, which they do not possess intrinsically in their capsids. So the first thing they do is make RNA polymerase, which then allows them to make and negative stranded template. This template can be replicated.
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What's the first thing positive stranded RNA viruses do after absorption and penetration into their host and why?
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Amongst the first proteins translated from the positive stranded RNA molecule is RNA polymerase. The viruses need this enzyme to make copies of themselves. Once RNA polymerase is made a negative stranded RNA molecule is synthesized and used as a template for further replication.
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Name the 4 steps viruses must complete in order to reproduce.
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1) Adsorption/penetration
2) Uncoating 3) Synthesis and assembly of viral products (as well as inhibition of the hot cell's own DNA, RNA, and protein synthesis) 4) Release of virions form the host cell (either by lysis or by budding) |
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What is a virion?
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A virion is the infectious form of a virus consisting of a nucleic acid core, a protein coat, and, in some species, an external envelope.
In other words, a virion is a "put-together" version of the virus rather than the sum of the disassembled units that may be undergoing transcription and translation. |
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How might virions escape from their host cell naked (i.e. without a lipid bilayer membrane)?
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The cell might lyse, thereby releasing the virions naked, or they might exit via exocytosis.
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What is budding?
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Budding is the process by which some virions exit the host cell, bursting through the membranous layers as they go and thereby acquiring an envelope of their own.
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What are the 4 outcomes possible for a cell after it has been infected with a virus?
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1) Death
2) Transformation -infection can activate or introduce oncogenes resulting in uncontrolled and uninhibited growth 3) Latent infection -the virus survives in a sleeping state, surviving but not producing clinically overt infection. Various factors can result in viral reinfection. 4) Chronic slow infection -Some viruses will cause disease only after many years, often decades, of indolent infection |
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Do viruses possess ribosomes?
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NO!
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Do viruses possess organelles?
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NO!
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Do viruses have a lipid bilayer?
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Sometimes. Some viruses’ capsid is further enclosed by an external lipid bilayer that may contain glycoproteins.
Viruses acquire this lipid bilayer membrane by budding through the host cell nuclear or cytoplasmic membrane and tearing off a piece of the membrane as they’re passing through. A virus that has acquired a lipid bilayer membrane is said to be enveloped. A virus that has no lipid bilayer membrane is said to be non-enveloped or “naked.” |
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• Can viruses posses both DNA and RNA?
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o No! All viruses have either DNA or RNA, but never both.
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• What are the two types of RNA viruses?
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o RNA viruses are either positive (+) stranded or negative (-) stranded
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• Describe the difference between positive and negative stranded RNA.
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o Positive stranded RNA has the same orientation as mRNA and thus may be directly translated into proteins. Negative stranded RNA has the opposite orientation of mRNA and positive stranded RNA. It must therefore be TRANSCRIBED into positive stranded RNA before being translated. The enzyme RNA-dependent RNA polymerase, present in the capsid of negative stranded RNA viruses, is necessary for this initial transcription to occur.
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• Name the enzyme present in the capsid of negative stranded RNA that is necessary for transcription to occur.
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RNA-dependent RNA polymerase
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• Do DNA viruses have one or two strands of DNA?
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o Almost all DNA viruses, with the exception of parvoviruses, have two strands of DNA, a positive (+) and a negative (-) strand
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• Which strand of DNA in a DNA virus is ignored and not read?
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o The negative (-) strand
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• What are the two types of capsids?
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o Icosahedral and helical
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• What is a capsomer?
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o A capsomer is a globular protein subunit that is arranged into icosahedrons or helices to form capsids
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• How many sides does an icosahedral capsid have?
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o 20 sides, each an equilateral triangle
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• What are the protein subunits that make up a capsid called?
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Capsomers
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What shape are DNA virus capsids?
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Almost all DNA viruses, with the exception of poxviridae, have icosahedral capsids.
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• What shape are RNA virus capsids?
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o Almost RNA viruses have helical capsids. There are five exceptions...
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• A virus is discovered with an icosahedral capsid. What type of nucleic acid does this virus likely possess?
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o DNA
o Almost all DNA viruses, with the exception poxviruses, have icosahedral capsids |
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A virus is discovered with a helical capsid. What type of nucleic acid does this virus likely possess?
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RNA.
Most RNA viruses possess helical capsids. There are five exceptions: reoveridae, picornaviridae, togaviridae, flaviviridae, caliciviridae. |
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How do viruses acquire their lipid bilayer membrane?
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Viruses acquire their lipid bilayer membrane by budding through the host cell nuclear or cytoplasmic membrane and tearing off a piece of the membrane as they’re passing through.
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• What is an enveloped virus?
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o Enveloped viruses are those with a lipid bilayer membrane outside their capsid. Viruses acquire this lipid bilayer membrane by budding through the host cell nuclear or cytoplasmic membrane and tearing off a piece of the membrane as they’re passing through.
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What is a naked virus?
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A naked or nonenveloped virus is one without a lipid bilayer membrane.
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What’s another name for the lipid bilayer membrane acquired by some viruses outside their capsid?
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Envelope
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Are DNA viruses typically double or single stranded?
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Most DNA viruses are double stranded.
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• What is the only family of DNA viruses to have single stranded DNA?
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o Parvoviridae
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• What is the only family of DNA viruses not to possess icosahedral capsids?
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o Poxviridae
o The poxviridae consist of DNA surrounded by complex structural proteins looking much like a box. POX IN A BOX. |
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Name 4 characteristics or parameters used to classify viruses.
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1) Nucleic acid type (DNA vs. RNA)
2) Capsid shape (isohedral vs. helical) 3) Lipid bilayer membrane (enveloped vs. naked) 4) Size |
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Name the 6 families of DNA viruses that cause disease in humans.
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1) Herpesviridae
2) Hepadnaviridae 3) Adenoviridae 4) Parvoviridae 5) Poxviridae 6) Papovaviridae These are sometimes referred to as the HHAPPPy viruses |
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Are RNA viruses single or double stranded?
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Almost all RNA viruses, with the exception of reoviridae, are single-stranded.
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• Which is the only family of RNA viruses that is not single-stranded?
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o Reoviridae
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Which type of virus—DNA or RNA—typically replicates in the host cell cytoplasm?
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RNA viruses typically replicate in the host cell's cytoplasm rather than in the nucleus.
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• Where do RNA viruses replicate?
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o With a few exceptions, RNA viruses replicate in host cell cytoplasm
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• Which type of virus—DNA or RNA—typically replicates in the host cell nucleus?
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o DNA viruses typically replicate in the host cell nucleus
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• Where do DNA viruses typically replicate?
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o With a few exceptions, DNA viruses replicate in the host cell’s nucleus
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