Microbiology: Viruses
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- What are typical virus sizes?
- 30-200 nm
- Shapes of viruses (3)
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1. helical capsid
2. icosahedral capsid
3. viral specific proteins - 5 Properties of viruses
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1. small
2. non-cellular
3. replicate within host and take over host machienery
4. released from host cell to infect other cells
5. often damage or kill the host. - The definition of virion is
- the extracellular state of a virus.
- Humans warts is an example of which type of viral shape?
- icosahedral symmetry (20 regular faces)
- The tobacco mosaic virus is an
- RNA virus which is helical.
- How is the flu virus shaped?
- it is enveloped
- Lambda viruses are
- bacteriophages, they are "bacteria eaters"
- The viral genome contains
-
all the hereditary material of a virus, 4-200 genes.
dsDNA, ssDNA, dsRNA, ssRNA - A virus capsid is
- a protein shell that surrounds the genome
- what is the virus capsid used for?
-
-protecting the viral genome
-often needed for attachment to the host cell - A viral envelope is
- the outer most later of the enveloped viruses which is composed of host lipids and viral proteins, it is often used for attatchment.
- what is a packaged protein?
- a protein that is found within the capsid. they are different for different viruses.
- What is reverse transcriptase?
- it is an enzyme that synthesizes DNA from an RNA template
- What is RNA dependent RNA polymerase?
- it is an enzyme that synhtesizes RNA from an RNA template.
- Seven steps in phage attatchement.
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1. attachement
2. penetration
3. expression of viral genes
4. genome replication
5. capsid formation
6. packaging
7. release - Attatchment of a phage is
- the binding of a capsid or envelope protein to a host receptor (usually a specific protein, lipid, or polysachharide).
- What determines the virus host range?
- the specificity for host receptor
- What is Viral penetration?
- the injection of viral nucleic acid and packaged proteins.
- When is a viral gene expressed?
- once it replicates inside of the host via the host's machienery
- What are some typical viral proteins?
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1. capsid proteins
2. proteins that block gene expression
3. proteins that block restriction systems
4. proteins for genome replication
5. proteins for assembly of viral particles - What are various methods of genome replication?
- via host enzymes only, viral enzymes only or host and viral enzymes
- Capsid protein formation occurs via
- self assembly
- Packaging of a virus is?
- the insertion of the nucleic acid into the capsid
- what is a common packaging method?
- the "headfull" method
- How is a virus release from the host cell?
- via lysis or budding
- What are the 3 steps in lysogenic phage?
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1. lysis
2. lysogeny
3. prophage induction - what is the most frequent method of reproduction?
- lysis
- What is lysogeny?
- prophage integration. a virus integrates itself into the host genome
- A lysogen is?
- a cell with an integrated virus
- How is a prophage replicated?
- when the host replicates
- what is prophage induction?
- excision of the prophage followed by lytic replication.
- what causes prophage induction?
- UV light and other DNA damaging agents
- How is a virus uptaken by an animal cell?
- first attatchemtn and penetration occur, then the cell uptakes the virus via endocytosis
- Do viruses need to adapt for eukaryotic cells?
- yes, they need to follow eukaryotic rules like eukaryotic RNA processing compartmentation
- Virus/ Host interactions.
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1. lysis
2. persistent infection
3. latent infection
4. transformation - Lysis is
- the destruction of the host cell.
- Persistent infection is
- viruses budding from host over a long period of time
- Laten infection are
- infections that reoccur periodically
- Transformation is
- the increased growth rate of host cells