Virus Quiz Flashcards
Viruses
Minuscule, acellular, infectious agents with DNA or RNA; obligate intracellular parasites that cannot reproduce independently.
Obligate intracellular parasites
Viruses that must recruit a host cell’s metabolic pathways to replicate.
Virion
An individual viral particle in the extracellular state, composed of a capsid (protein coat) surrounding nucleic acid, sometimes with an envelope.
Capsid
Protein coat of a virus, made of capsomeres (protein subunits).
Envelope
Phospholipid membrane surrounding some viruses, derived from the host cell membrane during budding.
Host range
The spectrum of host cells a virus can infect, determined by receptor compatibility.
Viral shapes
Three main types: helical (e.g., tobacco mosaic virus), icosahedral/polyhedral (e.g., adenovirus), and complex (e.g., bacteriophage T4).
Bacteriophage
A virus that infects bacteria; complex in shape with a polyhedral capsid, sheath, and tail fibers (e.g., T4 phage).
Lytic replication
Viral replication cycle ending in host cell lysis. Steps: attachment, entry, synthesis, assembly, release.
Lysogenic replication
Viral replication where the genome integrates into the host DNA (prophage) and replicates passively until induction (e.g., phage lambda).
Prophage
Inactive bacteriophage DNA integrated into a bacterial host genome.
Lysogen
A bacterial cell carrying a prophage.
Lysogenic conversion
When a prophage introduces new genes (e.g., toxins) that alter the host bacterium’s phenotype (e.g., Vibrio cholera toxin).
Viral genome types
DNA or RNA (never both); can be dsDNA, ssDNA, dsRNA, or ssRNA; linear/circular; segmented/non-segmented.
Naked vs. enveloped viruses
Naked viruses lack a phospholipid envelope, less susceptible to viruses; enveloped viruses acquire one from the host during budding. Both may have spikes for attachment.
Spikes
Glycoprotein structures on viral surfaces (e.g., influenza, HIV) that mediate host cell attachment.
Reverse transcriptase
Enzyme in retroviruses that synthesizes DNA from an RNA template.
Persistent infection
Slow release of virions over time without immediate cell death (common in enveloped viruses).
Burst size
Number of virions released per lysed bacterial cell (e.g., T4 phage releases ~100 virions).
Burst time
Duration from phage attachment to host cell lysis.
Temperate phage
A bacteriophage capable of both lytic and lysogenic cycles (e.g., phage lambda).
Viral classification
Genus names end in-virus; family names end in-viridae(e.g.,Herpesviridae,Simplexvirus).
Stages of bacteria phase growth
Inoculation, Elispe, burst, burst size
