Lecture #2 -- Medical Virology Continued Flashcards
What enzymes are required in DNA virus macromolecular synthesis?
DNA-dependent RNA polymerase (Host) DNA polymerase (Host)
Describe the process of DS DNA virus replication.
DNA-dependent DNA polymerase copy the + and - strands, creating more DS DNA. DNA-dependent RNA polymerase copies the - DNA strand into mRNA to generate viral proteins.
Describe the process of SS DNA virus replication.
Genome is replicated by DNA dependent DNA polymerase. Make a ds intermediate, then copy the - DNA strand into + SS DNA genomes.
DNA-dependent RNA polymerase copies the - strand into + viral mRNA. The + viral mRNA is translated into viral proteins.
Every RNA virus has a gene that encodes _______.
RNA polymerase
Where does RNA virus replication occur?
Cytoplasm
What enzyme allows RNA–>RNA?
RNA-dependent RNA polymerase
What enzyme allows DNA –> RNA?
Reverse Transcriptase
What enzyme allows DNA –> RNA?
DNA dependent RNA polymerase
How does +ssRNA virus replication work?
RNA-dependent RNA polymerase enzymes copy the + genome into -ssRNA. RDRP then copies the - strands into +ssRNA genomes.
+mRNA can be translated into viral proteins.
How does -ssRNA virus replication work?
RDRP copies the -ssRNA to make +ssRNA. RDRP copies the +ssRNA into the -ssRNA genome.
The +ssRNA is used to make viral proteins.
How does dsRNA virus replication work?
RDRP copies both strands of the RNA to make ds genome. RDRP copies the - strand into +ssRNA to be translated into viral proteins.
Describe the process of retrovirus replication?
+mRNA–>DNA/RNA–>dsDNA–>Incorporate into Genome–>use host cell machinery to generate genome and proteins.
What step in retrovirus replication uses Reverse Transcriptase?
+mRNA–>DNA-RNA hybrid
Aside from generating a DNA strand from RNA, what else can rev. transcriptase do?
Function as a DDDP, copying - strands to produce a dsDNA intermediate.
What enzyme is required to incorporate viral DNA into a host genome?
Integrase
What is the difference between proteins transcribed early and late in viral replication?
Early – Nonstructural proteins required for the replication of viral genome + prevention of host cell suicide.
Late – Structural Proteins
What are mono- and poly cistronic RNA?
Monocistronic – One gene per RNA translates into a single protein
Polycistronic – Transcripts of several genes translated into a large polypeptide that is later cut into functional units by proteases.
Which mRNA will viruses preferentially translate – Viral or Cellular?
Viral
Where does assembly of DNA viruses occur?
Nucleus (except pox)
Where does assembly of RNA viruses occur?
Cytoplasm
What has to happen before enveloped viruses acquire their envelope?
Association of the nucleocaspid with biral glycoprotein regions of the host cell
Matrix proteins for - strand RNA viruses line the membrane to promote adhesion
How are non-enveloped viruses released?
Cell Lysis
How are Enveloped viruses released?
Budding
How are enveloped viruses that acquire their envelop inside the cytoplasm released?
Exocytosis
Describe the process of budding.
Viral proteins and glycoproteins are incorporated into host membranes.
The host cell membrane with incorporated viral proteins pinches off.
What three locations can budding occur at?
Cytoplasmic membrane, nuclear membrane, or Golgi Apparatus.
Describe the process of replication for herpes simplex virus. (enveloped)
Virus binds and fuses –> DNA into nucleus –> transcription/translation (early immediate, early, and late) –> Caspid proteins migrate to nuc, form icosahedral –> bud through the ER/Golgi –> exocytosis
How does (+RNA) picornavirus replication work?
Injected genome, one large protein generated from +RNA, cleavage into proteins required for replication, makes a - strand for replication, caspid, cell lysis
How is -RNA virus (ex. rhabdo) different than +?
Carries a polymerase responsible for producing 5 mRNAs and a full length RNA template.
What are the four types of viral infection?
failed/abortive infection, productive viral infection, latent viral infection, and destructive/lytic infection
Result of a failed/abortive infection?
No progeny produced, no disease
Result of a productive viral infection?
Doesn’t necessarily kill cells - enveloped viruses
Final result of destructive/lytic viral infection?
Killed host cell
What virus type uses latent viral infection?
Retrovirus
What is viremia?
Spread of the virus from local to distant sites via the blood
Why are cell to cell transmission viruses hard to vaccinate?
Rarely exposed to Abs
Name some possible cellular effects of viral infection.
Cell killing, transformation, fusion, cell rounding
How can one diagnose a viral disease with labwork?
Descriptions of CPEs on cells, electron microscopic detection, isolation/growth of the virus, detection of viral components, serology
When looking for viral characteristic CPEs on cells, what should you look for?
Changes of morphology Cell Lysis Vacuolation Syncytia Inclusion Bodies
How are viruses grown?
Tissue culture, Embryonic Eggs, Experimental Animals
What do you see in cell culture when cells are virally infected?
Plaques
How does a hemagglutination assay work?
Detects presence of viruses that agglutinate RBCs, such as influenza
