Lecture 10 Flashcards
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)
What is true about viruses?
- viruses can cause asymptomatic infection
- viruses have a latency period
- viruses can cause chronic infections
- there are both DNA and RNA viruses
Continued: what is true about viruses?
- following attachment, viral titers decreases
- viral titers begin to increase as progeny virions are assembled
- influenza viruses are unique and contains neuraminidase
- synthesis of viral enzymes are required for nucleic acid replication
How is a virus defined?
infectious particles that take over the operation of a cell for the purpose of multiplying
How does a virus replicate?
- gain access (attachment and entry)
- convince cell to make new copies of the virus–the DNA is transcribed into RNA (replication)
- the RNA is translated to produce the new virus (biosynthesis)
- the new virus is assembled inside the host cell (assembly)
- virus emerges from the host cell (release)
What similar characteristics do viruses have?
They are specific in the types of cells they infect.
What does specificity depend on?
On the types of receptors found on the cell. Every cell in the body has a pattern of protein receptors on the surface. The virus uses these proteins to target a specific cell for infection.
Describe the DNA of a virus.
It is simple. It only contains the information needed to make new virus.
When a new virus is translated during replication, where is the new virus?
It is still within the host cell
When a virus is released from a host cell, what happens to the cell? (DNA virus)
The cell dies as they emerge. Sometimes the virus contains parts of the host cell that become the envelope of the virus.
What does an envelope provide to a virus?
it provides some protection from the immune system of the host organism
What do the new virus do after leaving the host cell?
They search out other cells to infect and replicate in.
What is the target of anti-viral drugs?
They target specific points in the virus life cycle to prevent the virus from replicating.
