Introduction to Virology Flashcards
Why are viruses obligate intracellular parasites?
They possess none of the metabolic or synthetic “machinery” needed for replication. This is also why they are not regarded as “living”.
What is the size range of viruses? How are they best visualized?
20-300nM, just beyond the limits of LM. Use electron microscopy.
What is a “polythetic” classification?
“Having many, but not all properties in common”.
From where does the viral envelope originate?
Will an enveloped virus enter via endocytosis or fusion?
From the host cell as the progeny virions bud off.
Fusion.
What is a capsid?
From where is it encoded and translated?
A capsid is a protein shell that packages viral DNA/RNA for transmission.
It is read from viral DNA/RNA but synthesized using host cell ribsomes and amino acids.
Describe the six baltimore classes of viral genomes.
I. Double-stranded DNA, can directly transcribe +mRNA.
II. +ssDNA, can directly transcribe +mRNA.
III. Double-stranded RNA, can directly transcribe +mRNA.
IV. +ssRNA, forms -ssRNA template.
V. -ssRNA, can directly transcribe +mRNA.
VI. +ssRNA, forms DNA template. (retroviruses)
What types of capsid classes are seen in RNA viruses? DNA viruses?
RNA viruses appear to be either icosahedral or helical.
Some DNA viruses are also “complex” (poxviruses).
Distinguish between a virion and a virus.
A virion is a viral particle; a virus is infectious.
All viruses are virions, not all virions are viruses.
What two assays can quantify viral infectivity or number?
Plaque assays (inoculate a cell culture with viruses, look for “holes”)
Focus assays (as above, but look for cell proliferation)
What will be packaged in a virion?
Genetic material (RNA/DNA), proteins that facilitate disassembly/uncoating, as well as fusion/attachment proteins.
I suspect proteases and some polymerases too.
What are the six steps of a typical viral lifecycle?
- Attachment
- Penetration
- Uncoating
- Synthesis/replication
- Assembly
- Exit/maturation
How to viruses recognize and attach to specific cells?
Adherence to surface proteins/receptors.
eg CD4 for HIV, CD21 for EBV, Sialic acid for Influenza
What nucleic acid reactions must be carried out by viral enzymes?
Production of RNA from RNA, or DNA from RNA (reverse transcriptase). Basically, anything that uses RNA as a template.
How do viruses cause cytopathic effect?
Distinguish between a productive and latent infection.
By lysis upon exit, blocking of host translation, inducing apoptosis or causing membrane fusion.
Productive infections generate many viruses and are accompanied by CPE. Latent do not, at least initially.
How are most viruses transmitted?
Inhalation of infected droplets, fecal-oral route, and direct/indirect contact.
