Epidemiology and Pathogenesis of Viral Disease & Viral Lifecycle - Genome Replication and Protein Expression Flashcards
The Baltimore classification, classifies viruses based on the processes used for synthesising…
-Protein
-DNA
-Envelope
-mRNA
-Capsids
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- mRNA
All viruses, regardless of the content of their genomes, are entirely dependent on the host cell for the synthesis of proteins from an mRNA template. Therefore all viruses need to produce mRNA from a genomic template – the Baltimore system classifies viruses on how they achieve this.
Retroviruses encode for which of the following enzymes:
(Please select all answers that are correct)
-DNA polymerase
-RNA-dependent DNA polymerase (reverse transcriptase)
-Protease
-RNA-dependent RNA polymerase
-Integrase
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- RNA- dependent DNA polymerase
- Protease
- Integrase
Retroviruses have a positive sense RNA genome that is copied into dsDNA by Reverse Transcriptase, before it is integrated into the host genome through the action of the viral Integrase enzyme. Retroviruses also encode a protease enzyme which is essential for rearrangement and maturation of the virus nucleocapsid after the virus exits the cell.
RNA viruses (other than retroviruses) encode for which of these polymerases?
-DNA polymerase
-RNA-dependent DNA polymerase
-DNA-dependent RNA polymerase
-RNA-dependent RNA polymerase
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RNA dependent RNA polymerase
Viruses with an RNA genome must make copies, and also produce mRNA for the synthesis of proteins. This is achieved through the action of an RNA-dependent RNA polymerase encoded by the virus. Eukaryotic cells do not encode for an RNA-dependent RNA polymerase.
Which of the following are true?
-Negative sense RNA is the non-coding strand
-All RNA viruses replicate in the cytoplasm
-Positive sense RNA is equivalent to mRNA
-Negative sense RNA viruses have a virion-associated RNA-dependent RNA-polymerase
-Eukaryotic cells encode for RNA-dependent RNA polymerase
Qiuz
- True
- False
- True
-True
-False
Negative sense RNA viruses must carry a virion associated RNA polymerase to allow positive sense RNA synthesis (mRNA) on entry into the cell because eukaryotic cells do not encode such an enzyme. Although most RNA viruses replicate in the cytoplasm some, like Influenza viruses, replicate in the nucleus. Equally, most DNA viruses replicate in the nucleus.
What are some examples of horizantal transmission?
Direct contact (secretions, blood etc) =HIV
Respiratory (aersol)= influenza, SARS Cov2
Contaminated inanimate objects= SARS, EBV
Fecal/orcal = Poliovirus
Insect vector (mosquitoes, ticks, etc.) = Dengue
Zoonoses = Ebola, Hantavirus
What are some examples of vertical transmission?
Mother to fetus: transplacental (congenital) and perinatally
eg Rubella, HIV
What is the order of the cycle of infection?
- Entry
- Primary site of replication
- Spread within the host
- Secondary site(s) of replication
- Shedding
- Transmission
Influenza only has one primary site, while chicken pox has two
entry is usually mucous membranes or skin, primary site of replication is usually respiratory tract
What is the difference between acute, chronic, and latent infections
know how to label each on a graph
Acute: days-weeks (eg flu)
Chronic: years, low level of infection, continous replication (eg Hep B)
Latent: years, periodically replicates but never fully eradicated (Herpes)
Describe the cytopathic effect (CPE) on host cells caused by infection. What CPE does Herpes have?
- syncita (multinucleated fused cells)
- Inclusion bodies (aggregates of virus/ viral proteins, virus production center)
- Herpes: causes plaques in tissue culture
Cytopathic effect: The changes in cell morphology due to infecting virus
Why does host protein translation shut off happen? What does this look like in Poliovirus and Influenza?
- virus is manipulating cell to make it more efficient for viral replication
- Polio: poliovirus protein 2A cleaves CBC, which is needed for 5’ capping
- Influenza: virus steals mRNA cap from host
CBC= cap binding complex
How does viral infection influence apoptosis?
- some viruses cause apoptosis, ie force cell to express receptor for phagocytes
- other viruses BLOCK apoptosis to allow for replication before cell dies
What does HPV do that makes it a transforming virus?
A transforming virus= changes growth/phenotype &indefiinite reproduction
The E6 and E7 genes of HPV (cancer causing kind) destroy p53 and pRB (tumor supressor genes)
- results in uncontrolled S phase, which lets tumor replicate more effciently but also causes cancer
Transformation is an effect of virus infection on cells that result in uncontrollable proliferation. These viruses include HPV, Retroviruses, Herpesviruses, Hepatitis B and C
How does the innate immune system respond to viral infection?
TLRs can recognize DNA on the endosome, which leads to production of IFNs (eg IFN-y)
IFN-y has huge role in activatinig adaptive response
How does viral infection contribute to cytokine storms?
Cytokine storm is a response to viral infection, not caused by it.
Harmfuul positive feedback loop, more cytokines=more damage=more cytokines
cytokine storm results in inflammation,
What are immune modulation strategies used by viruses?
- secreted modulators (cytokine mimics; binders) eg Pox/Herpes
- modulators on infected cell surface (mimics/antagonists of immune signalling) eg Herpes
- Stealth/latency (express few proteins) eg Herpes
- Antigenic hypervariability e.g. Influenza/HIV
- Block adaptive immune response
- Inhibit complement
- Interfere with pattern recognition receptors (PRRs)
- Block Interferon and/or inflammatory cytokines
