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01 Deja Review -Micro Basic Virology
Terms in this set (33)
How are viruses different from other cellular organisms?
Viruses are not capable of self-replication. They can neither produce their own proteins nor generate energy necessary to replicate.
What type of nucleic acid do viruses have?
Either DNA or RNA but not both
How is the shape of the virus described?
In terms of the symmetry of the capsid
What is a viral capsid?
Protein coat surrounding the genomic material that is formed by repeating subunits of capsomers
What is the function of viral capsids?
Viral capsids promote viral assembly, protect the genetic material, and facilitate viral attachment to cells.
What are the possible forms of symmetries in viral capsids?
Icosahedral and helical
What is nucleocapsid?
Genome-capsid complex, which is the packaged form of the viral genome
What is a virion?
The complete virus particle that includes the nucleocapsid plus an envelope for enveloped viruses or just the nucleocapsid for nonenveloped viruses
What structure protects the virus and also facilitates viral attachment to cells?
Viral lipoprotein envelope
Which viruses do not have a lipoprotein envelope?
DNA viruses: parvovirus, adenovirus, polyomaviruses, and papillomaviruses RNA
viruses: picornavirus, calicivirus, and reovirus
What are some advantages of having a lipoprotein envelope?
It allows the virus to replicate without lysing the cell and facilitates avoidance of the immune system.
What are some disadvantages of having a lipoprotein envelope?
Enveloped viruses are generally more sensitive to acid, heat, and detergents. All fecal-oral viruses are nonenveloped.
Where do viruses obtain their lipoprotein envelope?
Viruses obtain their envelopes typically from the cell membrane except the herpes-virus which obtains its envelope from the nuclear membrane.
What protein facilitates attachment of the capsid to the envelope?
What protein spikes out of the lipoprotein envelope and facilitates attachment to cell surface receptors?
What happens during the eclipse period regarding detectable virus levels?
Viruses become undetectable in the serum and intracellularly as they attach, penetrate, and uncoat the viral genome.
What is the latent period?
Time period starting from adsorption of the virus and ending with detectable extracellular virus. Note that the latent period is always longer than the eclipse period because by definition the eclipse period ends with detectable intracellular virus.
What are the general steps in viral replication?
Attachment and uncoating, early mRNA/ protein synthesis, genome replication, late mRNA/protein synthesis, assembly and release
Name the important host cell receptor for Human immunodeficiency virus (HIV)
Name the important host cell receptor for Epstein-Barr virus (EBV)
Name the important host cell receptor for Rabies
Acetylcholine (Ach) receptor
Where do DNA viruses replicate their genome?
In cell nucleus except poxviruses which replicate in the cytoplasm (they are too big to fit in the nucleus)
Where do RNA viruses replicate their genome?
In cytoplasm, except for retroviruses and orthomyxoviruses
What is the difference between early mRNA/ protein synthesis and late mRNA/protein synthesis?
While they can occur simultaneously, early mRNA/protein synthesis functions to help replicate the genome and late mRNA/pro- tein synthesis forms the structure for assembly and release.
Where do DNA viruses synthesize mRNA?
In cell nucleus with host cell DNA-dependent RNA polymerase, except poxviruses, which synthesize mRNA in the cytoplasm using a viral DNA-dependent RNA polymerase
How do single-stranded positive-sense RNA viruses synthesize mRNA?
From the genome, directly as mRNA
How do retroviruses synthesize mRNA?
They utilize a viral reverse transcriptase to form DNA and then a host cell DNA-dependent RNA polymerase to make mRNA.
How do double- and single-stranded negative-sense RNA viruses synthesize RNA?
Viral RNA-dependent RNA polymerase
since no corresponding host enzyme exists
Which DNA virus uses a reverse transcriptase to replicate its genome?
Hepatitis B virus, a DNA virus, makes an intermediate RNA genome that then uses reverse transcriptase to covert into DNA.
Why are certain viral genome types infectious while others are not?
Viral genomes such as single-stranded positive-sense RNA viruses and DNA vir uses (except poxviruses, which replicate in the cytoplasm, and hepatitis B virus, which has a partially single-stranded genome) are infectious because their genome can synthesize all required viral proteins directly with host enzymes.
What is the importance of viral proteases?
Certain viruses make only one mRNA which gets translated into a single polypeptide. Viral proteases cleave the single polypeptide into multiple polypeptides, allowing multiple proteins to be encoded by a single
gene. Proteases are important targets in anti-viral therapy.
What is the role of the matrix protein in budding of enveloped viruses?
Matrix protein facilitates interaction of the nucleocapsid with the specific site on the membrane.
Are there persistent productive infections in nonenveloped viruses?
No, nonenveloped viruses must either become latent or cause cell lysis. Only enveloped viruses cause persistent, productive infections via budding.
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