Lecture 10 Flashcards
(36 cards)
How is viral infection characterized?
By an incubation period
What happens during an incubation period?
The virus replicates within the host before disease symptoms and signs become evident
In synthetic events, what happens in the early stages?
Synthesis of viral enzymes required for nucleic acid replication
In synthetic events, what happens in the late stages?
- Production of viral genome
- Polypeptides
- Processing of polypeptides and formation of infective virus
What are some examples of production of viral genome?
- viruses with double stranded DNA synthesize mRNA just as the host cell does, using a DNA dependent RNA polymerase
- RNA viruses must make their mRNA from RNA (if they are not mRNA), which involves a different mechanism
What are synthetic events?
- replication
- transcription
- translation
There are a wide variety of virus types? Which type has the most viruses, DNA or RNA?
RNA has more
What is retrovirus (HIV) ?
- RNA
- Icosahedral
- Enveloped virus
What is herpes virus?
- DNA
- Icosahedral
- Enveloped virus
What is the difference between retrovirus and herpes virus?
- retrovirus = RNA
* herpes virus = DNA
What is orthomyxovirus (Influenza)?
- RNA
- Helical
- Enveloped virus
What does the assembly of enveloped viruses require?
Requires the association of nucleocapsid with cell membranes modified by viral glycoproteins
In assembly, what are some examples of subunits?
- nucleic acid
- structural proteins
- enzymes
What does each subunit need to do?
They have to fit into compact arrangement to generate infectious virion.
What happens during release to non-enveloped viruses?
They are released by cell lysis
What happens during release to enveloped viruses?
They are released gradually by budding from plasma membrane or exocytosis.
How do influenza virus act during release?
They are unique and have enzyme on their surface called neuraminidase (involved in release of progeny virions from host cells).
What kind of damage can happen from viral infections?
Direct effects of viral replication on host cells via:
- cytolytic damage
- enhanced apoptosis
- or damage due to host response to the infection
(side note: virus can make indirect damage)
What are the events that happen during virus replication (viral growth curve)?
During a single infectious cycle:
- following attachment, viral titer declines precipitously
- eclipse: virus undergoes disassembly, transcription, translation, and genome replication
- viral titer begins to increase as progeny virions, which are fully infectious, are assembled
What are the 5 possible outcomes of viral infection? What is an example?
- asymptomatic infection (resolution)
- acute infection (influenza)
- latency (herpes virus)
- chronic infection (leading to immortalization, transformation of host cells to neoplasia, or cancer)
- reactivation (episodic–HPV)
Describe what happens in acute infections to a virus.
Virus undergoes multiple rounds of replication. It results in the death of the host cell. The number of virus particles produced in a single cell varies from a few for some viruses to thousands for others.
Describe what happens in latent infection to a virus.
It does NOT result in the production of progeny virus.
Latent infections reflect the persistence of:
- viral DNA either as an extra chromosomal element (herpes viruses)
- as an integrated sequence within the host genome (retrovirus)
What happens in reactivation to a virus?
At times (of poor control of infection due to compromised cell mediation immunity), reactivation of latent infection occurs.
What happens in chronic infection to a virus?
- virus particles continue to be shed after the period of acute illness
- continues without death of the host cell or overt cellular injury
- associated with host immune responses that are insufficient to clear the infection
- may progress to cancer (example: chronic hepatitis becomes liver cancer)
