Virus Overview Flashcards
phase of virus replication that lasts ~10-12 hours and corresponds to the period during which the input virus becomes uncoated, but is not yet detectable
eclipse phase
plateau phase of virus replication that starts ~12 hours post infection and ends when new virus particles are assembled and released
synthetic phase
phase of viral replication in which no extracellular virus is detected
latent phase
what a virus is called when it exists extracellulary
virion
naked or enveloped viruses are better at withstanding environmental stress and drying?
naked
HSV and Adenovirus (type 2) are:
- enveloped or naked?
- icosahedral or helical?
these viruses are enveloped and icosahedral
Put the steps of virus replication in order:
- Egress from cell
- Genome replication
- Uncoating of genome
- Attachment to host cell
- Penetration/virion internalization
- Assembly
- Gene expression
- Attachment to host cell
- Penetration/virion internalization
- Uncoating of genome
- Gene expression
- Genome replication
- Assembly
- Egress from cell
Which of the following statements concerning the early events of viral replication is TRUE?
A. viruses usually infect endothelial cells indiscriminately and spread laterally to neighboring cells
B. viruses have an attachment protein (VAP) that most often binds to lipids or sugars as their receptors
C. for enveloped viruses, the VAP is usually a protein
D. after binding, a virus may either enter the cell or detatch and selectively bind another receptor on a nearby cell
E. usually, naked virus binding leads to internalization into endosomes
E.
Viruses bind specific cell receptors on specific cell types - their attachment is not random or indiscriminate, and once initiated, they must enter the cell. This is why A and D are incorrect.
The VAP is a viral-encoded glycoprotein embedded in the membrane of enveloped viruses, and a protein or structure on the capsid of non-enveloped viruses. The VAP usually attaches to cell surface proteins of target endothelial cells. This is why B and C are incorrect.
Which of the following statements about viral cell entry is FALSE?
A. viral envelopes contain host cell proteins in addition to viral proteins
B. naked viruses are only able to enter a target host cell at low pH conditions
C. enveloped viruses initiate uptake via a glycoprotein embedded in its membrane
D. inhibiting the interaction of a virus with its receptor would prevent initiation of all steps of its life cycle
E. naked viruses initiate pore formation in the host cell to gain entry
B. Some naked viruses enter a host cell under neutral pH conditions while others require a low pH for entry.
how do enveloped viruses gain entry to a host cell?
they have a hydrophobic fusion peptide within their glycoproteins that is exposed when appropriate conditions for entry are achieved.
this virus attacks CD4 t cells, monocytes, or macrophages
HIV
this virus’s VAP (glycoprotein HA) binds to sialic acid and is then taken up into endosomes, where the low pH leads to membrane fusion and viral uncoating
influenza
All DNA viruses except which one replicate in the cell nucleus and use host cell DNA dependent RNA polymerase to synthesize their new viral transcripts?
A. Papillomavirus
B. Parvovirus
C. Poxvirus
D. Adenovirus
E. Polyomavirus
C. Poxviruses replicate in the cytoplasm and encode both their own DDRP and DDDP.
What is the first step for (+) sense RNA replication of the viral genome?
A. Translation
B. Reverse transcription
C. Transformation
D. Transcription
E. Expression
A
All (+) sense RNA viruses except which one are directly translated, and therefore do not need to bring polymerase into the infected cell?
A. Norovirus
B. Retrovirus
C. HEV
D. Rotavirus
E. Poliovirus
B.
All RNA viruses with which exception replicate in the cytoplasm of infected cells?
A. HBV
B. Coronavirus
C. HCV
D. Flavivirus
E. HDV
E.
HDV, along with orthomyxoviruses (ie influenza) are the sole exceptions to this general rule - they replicate in the cell nucleus.
What type of polymerase is packaged into virions that contain a (-) sense RNA genome?
A. RDRP
B. DDDP
C. DDRP
D. RDDP
A.
(-) sense RNA viruses must bring RDRP (RNA-dependent RNA polymerase) into the host cell with them. It is packaged in their genome and transcribed in the cytoplasm to make the (+) strand RNA needed for translation.
What type of polymerase is packaged into retrovirus genomes so that they can replicate within their host’s cytoplasm?
A. RDRP
B. DDDP
C. DDRP
D. RDDP
D. This is also known as Reverse Transcriptase.
once retroviral DNA is integrated into the genome of a host cell, it is called a what?
provirus
*it now uses the host cellular machinery to replicate and its gene sequences are fully part of the host genome. thus, while retrovirus replication occurs in the cytoplasm with its own RDDP (reverse transcriptase), replication of the proviral genome happens in the cell nucleus using host DDRP (Pol II).
Which of the following statements is FALSE?
A. All viruses use host cell ribosomes for translation of viral proteins
B. All viruses use host translation machinery for protein synthesis (tRNAs, initiation factors, etc)
C. All viruses modify cellular machinery to favor viral protein synthesis over cell protein synthesis
D. most DNA and icosahedral viruses have capsids that self-assemble, into which their genome is later inserted
E. All helical and some icosahedral RNA viruses have capsids that self assemble around their genomes
C. Some viruses do this, but not all.
many enveloped viruses such as HIV bud from the plasma membrane from their host cell when they egress. which is an example given in the notes of one virus that buds from the ER membrane?
HCV
Most (enveloped or non-enveloped) viruses bleb from the plasma membrane of the cell when they egress, while most (enveloped or non-enveloped) viruses lyse the host cell when they egress
enveloped viruses bleb; non-enveloped viruses lyse
when does a proprotein, assembled into an immature virion, become infectious?
when a protease is incorporated into the virion that can cleave the proprotein, activating it. this usually happens after the virion has left the viral cell.
Which of the following statements about viral acquisition and pathogenesis is FALSE?
A. Smallpox, polio, and HIV exclusively infect humans.
B. If influenza is transmitted via an animal reservoir, it is considered a zoonotic infection.
C. Severity of illness generally correlates with the virus titer.
D. The host immune response to viruses is mediated by CD4 T cells activating macrophages.
E. Factors influencing acquisition of a vius include seasonality, age and immune status.
D. The host immune response to viruses is generally activation of CD8 T cells.
Which of the following viruses does NOT cause tumor transformation of host cells?
A. HAV
B. EBV
C. HTLV
D. HCV
E. HPV
A.
Hepatitis A is not a tumorigenic virus.
All of the following are effective methods for detecting virus infection EXCEPT:
A. tissue, swab or blood exudates
B. light microscopy and cell culture
C. PCR for nucleic acids
D. ELISA and Western blot for IgM/IgG differentiation
E. Cytopathic effects on host cells
B.
Viruses are invisible under light microscopy and often do not replicate in cell culture.
Which of the following statements about pathogen recognition receptors (PRRs) is TRUE?
A. They are located only on antigen presenting cells
B. PRRs are encoded in the genome and are highly conserved, remaning unchanged in response to pathogen interactions
C. RIG1 are important receptors for binding viral DNA and triggering an immune response
D. RIG1 receptors form large inflammasomes that generate pro-inflammatory cytokines like IL-1B
E. In response to viral binding of TLRs, non-immune cells (ie fibroblasts) produce TNF alpha to induce inflammation
B.
A is incorrect: PRRs are located on most human cell types, including non-immune cells.
C is incorrect: RIG1 and their related receptors bind to cytoplasmic RNA helicases to activate signaling pathways and turn on type 1 IFN genes.
D is incorrect: it is the NOD-like receptors that form inflammasomes.
E is incorrect: TNF alpha is produced by immune cells and results in fever, inflammation and apoptosis. Non-immune cells do produce IFN-beta upon activation of their TLRs, however, which interferes with viral replication.
Which of these is NOT a function of type 1 IFN?
A. Recruit and activate NK cells and CD8 T cells
B. Block inflammasome formation, inhibiting the pro-inflammatory response & setting up the “antiviral state”
C. Stimulate production of effector and memory CD8 T cells
D. Upregulate co-stimulatory molecues CD40 and CD28 on APCs
E. Upregulate MHC class II on APCs
C. This is what type 2 IFN does, as part of the adaptive immune response. Type 1 IFN is associated with innate immune response.
Which of the following statements is FALSE?
A. CD4 T helper cells are critical for response to intracellular pathogens, as they recognize and respond to viral peptides presented on MHC class II
B. CD8+ T cells kill target cells via Fas pathway and perforin
C. Most viral infections are cleared by CD8+ T cells.
D. Vaccines work by stimulating the production of memory CD8 T cells as well as memory B cells
E. IgM is the best predictor of acute illness
E
Which of the following is NOT a way in which a virus evades immune detection?
A. Restricted gene expression (latency)
B. Antigenic variation
C. Reduce cell surface expression of MHC
D. Production of its own cytokines to block immune response
E. Infect anatomic sites that are poorly accessible to the immune system
D. This is certainly a viral defense, but not one that helps it evade or hide within the host. Other viral defenses include blocking type 1 IFN (which inhibits viral replication), making decoy molecules that reduce activation of immune system, and stimulating the release of cytokines that favor their spread (ie, poxviruses).
