intro to virology 6 Flashcards
(23 cards)
Match the virus with the virus family
ss DNA = Paroviridae
ds DNA = Papovaviridae, Adenoviridae, herpesviridae, poxviridae, hepadnaviridae
ds RNA = Reoviridae
- ssRNA = Orthomyxoviridae, paramyxoviridae, Rhabdoviridae, Bunyaviridae, arenaviridae, filoviridae
+ ss RNA = Togaviridae, flaviviridae, Coronaviridae, Retroviridae, Picornaviridae, Hepeviridae
Describe properties of RNA viruses
- RNA is labile and transient
- Most RNA viruses replicate in cytoplasm
- CELLS CANNOT replicate RNA (RNA viruses must encode an RNA-dependent RNA polymerase)
- RNA viruses except (+) RNA genome, must carry polymerase
- RNA viruses are prone to mutation
Describe the types of capsids
Helical
Icosahedral
complex
Define Naked capsid
- Are environmentally stable to temp, acid, proteases, detergents, drying
- released from cell by lysis
- spread easily
- survive the adverse conditions of the gut
- resistant to detergents and poor sewage treatment
Define Envelope viruses
- Environmentally labile, disrupted by acid, detergents, drying, heat
- Modifies cell membrane during replication
- are released by budding and cell lysis
- must stay wet
- CANNOT survive gastrointestinal tract
- spreads in large droplets, secretions, organ transplants, and blood transfusions
- DOES NOT NEED to kill the cell to spread
Describe the virus life cycles
Attachement –> entry –> mRNA production –> protein and genome synthesis –> virion assembly –> egress
Define plaque assay
DETECTS = Infectious virus ADV = positivity shows active viral infection LIMITS = restricted to viruses that replicate in tissue culture and produce cytopathic effect
Election Microscopy
DETECTS = Virion Particles ADV = Especially helpful in the identification of emerging viruses LIMITS = Relatively expensive and technically challenging
Antigen Detection = ELISHA
DETECTS = Viral proteins and glycoproteins ADV = Sensitive and quick LIMITS = requires specific antibodys
PCR
DETECTS = DNA genomes ADV = highly sensitive LIMITS = DNA sequence information must be available
RT-PCR
DETECTS = RNA genomes ADV = highly sensitive LIMITS = RNA sequence must be available
Western Blot
DETECTS = Anti-viral antibodies ADV = sensitive and quick LIMITS = time must be allowed for the initiation of the immune response. Care must be taken to differentiate present from past infections
How does ds DNA undergo Gene transcription
dsDNA uses cellular RNA pol to form mRNA
How does ssDNA undergo gene transcription
ssDNA uses cellular DNA repair enzymes to form dsDNA and then utilizes cellular RNA pol to form mRNA
How does retrovirus used +ssRNA to undergo gene transcription
+ssRNA (retrovirus) use viral reverse transcriptase to form dsDNA. Once dsDNA is formed then they use cellular RNA pol to form mRNA
How does +ssRNA undergo gene transcription
+ssRNA do not need any enzymes to form mRNA. They are already in the correct configuration.
How does -ssRNA undergo gene transcription
-ssRNA use viral RdRp (RNA-dependent-RNA polymerase) to form mRNA
How does dsRNA undergo gene transcription
dsRNA utilize viral RdRp to form mRNA (similar to -ssRNA)
Describe solutions to if cellular DNA replication machinery is not available at all time
- Make cellular DNA replication machinery available. (Papovaviruses stimualte cell growth and DNA synthesis)
- Encode viral proteins to synthesis genome (Poxviruses encode their own polymerase and enzymes to provide deoxyribonucleotides for DNA synthesis, replication machinery and transcption machinery in cytoplasm
Describe solutions to if cellular RNA replication machinery is not available.
- Encode a RdRp in your genome (+ssRNA)
- Encode a RdRp in your genome and carry the enzyme in your virion (-ssRNA)
-ssRNA = Always Bring Polymerase Or Fail Replication = Arenaviridae, Bunyaviridae, Paramyxoviridae, Orthomyxoviridae, Filoviridae, Rhabdoviridae
Describe general pathway to viral assembly and Egress
1) Individual viral proteins form into capsid subunits
2) subunits combine to form complete capsid
3) viral genome and other essential virion components are selectively packaged into capsids
4) Envelope is acquired (only for enveloped viruses)
5) virus exits cells
6) virions mature (only for certain viruses)
Describe budding (only in envelope viruses)
similar to exocytosis:
1) RNA synthesized by virus accumulates and will form part of an envelope
2) modified region of host plasma membrane extends out from cell surface
3) modified region is pinched off from host cell, enclosing viral matrix protein and RNA within capsid; modified membrane and matrix form viral envelope
describe Lysis
lysis of the cell is similar to poking holes in the cell. Kills the cell as virus leaves.
