Microimm 2500: Virology Exam
Questions With Verified Solutions
Section 1: Virus Structure and Classification (Q1 - Q20)
Q1. Which of these viruses will release their genome into the host cell cytoplasm at the most
basic pH?
- A) Rotavirus
- B) Measles Virus
- C) Ebola Virus
- D) Dengue Virus
> Answer: A) Rotavirus. Rotaviruses are non-enveloped viruses of the Reoviridae family. Their
entry requires exposure to a basic pH, which triggers a conformational change in the endosome
to release their genomic material.
Q2. Which virus family below does NOT require polymerase activity prior to translation by the
host cell ribosomal machinery?
- A) Reoviridae (dsRNA)
- B) Polyomaviridae (dsDNA)
- C) Parvoviridae (ssDNA)
- D) Picornaviridae (+ssRNA)
> Answer: D) Picornaviridae. The positive-sense single-stranded RNA genome of a picornavirus
(e.g., poliovirus) can function directly as mRNA and is immediately translated by the host cell's
ribosomes upon entry.
Q3. Picornaviridae 'canyons' can interact with what?
- A) A nuclear receptor
- B) PVR (Poliovirus Receptor)
- C) An envelope
- D) The viral genome
> Answer: B) PVR (Poliovirus Receptor). Picornaviruses have characteristic "canyons" which
are depressions on their surface that serve as the binding site for cellular receptors like PVR
(CD155) to initiate viral entry.
,Q4. What does an endogenous retrovirus such as Human Endogenous Retrovirus (HERV)
represent?
- A) Infectious pieces of viral genomes that cause pathogenesis in humans
- B) HIV-1 group N viruses
- C) A type of HIV-2
- D) Remnants of ancient infections that integrated into the human germline
> Answer: D) Remnants of ancient infections that integrated into the human germline. HERVs
are non-infectious fossil viral sequences that make up about 8% of the human genome,
representing ancient infections that occurred millions of years ago.
Q5. What is the primary route of transmission for HIV?
- A) Fecal-oral
- B) Aerosol
- C) Direct contact with infected blood or bodily fluids
- D) Vector-borne (e.g., mosquito)
> Answer: C) Direct contact with infected blood or bodily fluids. HIV is transmitted primarily
through unprotected sexual contact, sharing needles, from mother to child during birth or
breastfeeding, or through transfusion of contaminated blood products.
Q6. What technique has allowed scientists to determine the origin of HIV-1?
- A) Plaque formation assay
- B) Electron microscopy
- C) Immunostaining
- D) Sequencing (molecular clock analysis)
> Answer: D) Sequencing (molecular clock analysis). Molecular clock sequencing allowed
researchers to trace HIV-1 back to a simian immunodeficiency virus (SIVcpz) from chimpanzees
in Central Africa and estimate the zoonotic transmission occurred around the early 20th century.
Q7. Which virus is a dsDNA virus from the Poxviridae family, which encodes its own
DNA-dependent RNA polymerase for transcription in the host cytoplasm?
- A) JC Virus
- B) Variola virus (smallpox)
- C) HIV
- D) Influenza virus
> Answer: B) Variola virus (smallpox). Poxviruses are large dsDNA viruses with a complex
structure, unique for replicating entirely in the host's cytoplasm thanks to a viral-encoded RNA
polymerase.
Q8. What best describes the unique genome of the Hepatitis B virus (HBV)?
- A) Double-stranded RNA (dsRNA)
,- B) Single-stranded DNA (ssDNA)
- C) Gapped double-stranded DNA
- D) Positive-sense single-stranded RNA (+ssRNA)
> Answer: C) Gapped double-stranded DNA. HBV is a hepadnavirus with a partially
double-stranded DNA genome. After infection, it is converted into a complete, covalently closed
circular DNA (cccDNA) in the nucleus.
Q9. What is an example of a virus from the Polyomaviridae family that can cause degenerative
brain diseases in immunocompromised patients?
- A) JC Virus
- B) Adenovirus
- C) Rhinovirus
- D) Rotavirus
> Answer: A) JC Virus. The JC virus is a small dsDNA polyomavirus. It is usually harmless but
can reactivate in immunocompromised individuals (e.g., with HIV or on immunosuppressant
drugs), causing progressive multifocal leukoencephalopathy (PML).
Q10. Which of the following is a measure of infectivity for a virus?
- A) Plaque assay
- B) Hemagglutination assay
- C) Western blot
- D) PCR
> Answer: A) Plaque assay. The plaque assay quantifies the number of infectious viral particles
(plaque-forming units or PFU) by measuring their ability to form clear zones of cell lysis in a cell
monolayer.
Q11. Which Baltimore classification group describes viruses with a single-stranded RNA
genome that is identical in sequence to mRNA and can be directly translated by host ribosomes
upon entry?
- A) Group III (dsRNA)
- B) Group IV (+ssRNA)
- C) Group V (-ssRNA)
- D) Group VI (ssRNA-RT)
> Answer: B) Group IV (+ssRNA). This is the defining feature of the Baltimore classification,
which categorizes viruses based on their genome type and replication strategy. Positive-sense
RNA viruses can immediately use their genome as mRNA.
Q12. Why is Influenza A virus able to cause yearly seasonal epidemics and occasional
pandemics?
- A) It has a very stable, unchanging genome.
, - B) It mutates slowly and is highly immunogenic.
- C) It undergoes antigenic drift and, less frequently, antigenic shift.
- D) It is not affected by the host's immune system.
> Answer: C) It undergoes antigenic drift and, less frequently, antigenic shift. Antigenic drift
refers to minor, gradual changes in surface proteins (hemagglutinin and neuraminidase), while
antigenic shift is a more sudden, major change caused by genome segment reassortment,
which can create a novel pandemic strain.
Q13. A scientist is trying to study a newly discovered virus. They observe that the virus's
genome functions directly as mRNA. The virus's genetic material can be classified as:
- A) dsRNA
- B) +ssRNA
- C) -ssRNA
- D) ssDNA
> Answer: B) +ssRNA. Direct translation by host ribosomes is the hallmark of a positive-sense
single-stranded RNA virus.
Q14. Which of the following correctly describes a retrovirus, which uses reverse transcriptase?
- A) dsDNA -> mRNA -> viral protein
- B) +ssRNA -> -ssRNA -> dsRNA
- C) +ssRNA -> dsDNA -> mRNA -> viral protein
- D) dsRNA -> +ssRNA -> viral protein
> Answer: C) +ssRNA -> dsDNA -> mRNA -> viral protein. This is the unique replication cycle of
retroviruses, where their RNA genome is reverse-transcribed into DNA, which then integrates
into the host genome and is transcribed back into RNA.
Q15. What is the genetic material of the Human Papillomavirus (HPV)?
- A) +ssRNA
- B) dsRNA
- C) dsDNA
- D) ssDNA
> Answer: C) dsDNA. HPV is a non-enveloped virus with a circular double-stranded DNA
genome.
Q16. A researcher is studying a virus that has a genome composed of two identical strands of
RNA, which is a rare configuration among viruses. This virus belongs to the family?
- A) Retroviridae
- B) Reoviridae
- C) Arenaviridae
- D) Flaviviridae
Questions With Verified Solutions
Section 1: Virus Structure and Classification (Q1 - Q20)
Q1. Which of these viruses will release their genome into the host cell cytoplasm at the most
basic pH?
- A) Rotavirus
- B) Measles Virus
- C) Ebola Virus
- D) Dengue Virus
> Answer: A) Rotavirus. Rotaviruses are non-enveloped viruses of the Reoviridae family. Their
entry requires exposure to a basic pH, which triggers a conformational change in the endosome
to release their genomic material.
Q2. Which virus family below does NOT require polymerase activity prior to translation by the
host cell ribosomal machinery?
- A) Reoviridae (dsRNA)
- B) Polyomaviridae (dsDNA)
- C) Parvoviridae (ssDNA)
- D) Picornaviridae (+ssRNA)
> Answer: D) Picornaviridae. The positive-sense single-stranded RNA genome of a picornavirus
(e.g., poliovirus) can function directly as mRNA and is immediately translated by the host cell's
ribosomes upon entry.
Q3. Picornaviridae 'canyons' can interact with what?
- A) A nuclear receptor
- B) PVR (Poliovirus Receptor)
- C) An envelope
- D) The viral genome
> Answer: B) PVR (Poliovirus Receptor). Picornaviruses have characteristic "canyons" which
are depressions on their surface that serve as the binding site for cellular receptors like PVR
(CD155) to initiate viral entry.
,Q4. What does an endogenous retrovirus such as Human Endogenous Retrovirus (HERV)
represent?
- A) Infectious pieces of viral genomes that cause pathogenesis in humans
- B) HIV-1 group N viruses
- C) A type of HIV-2
- D) Remnants of ancient infections that integrated into the human germline
> Answer: D) Remnants of ancient infections that integrated into the human germline. HERVs
are non-infectious fossil viral sequences that make up about 8% of the human genome,
representing ancient infections that occurred millions of years ago.
Q5. What is the primary route of transmission for HIV?
- A) Fecal-oral
- B) Aerosol
- C) Direct contact with infected blood or bodily fluids
- D) Vector-borne (e.g., mosquito)
> Answer: C) Direct contact with infected blood or bodily fluids. HIV is transmitted primarily
through unprotected sexual contact, sharing needles, from mother to child during birth or
breastfeeding, or through transfusion of contaminated blood products.
Q6. What technique has allowed scientists to determine the origin of HIV-1?
- A) Plaque formation assay
- B) Electron microscopy
- C) Immunostaining
- D) Sequencing (molecular clock analysis)
> Answer: D) Sequencing (molecular clock analysis). Molecular clock sequencing allowed
researchers to trace HIV-1 back to a simian immunodeficiency virus (SIVcpz) from chimpanzees
in Central Africa and estimate the zoonotic transmission occurred around the early 20th century.
Q7. Which virus is a dsDNA virus from the Poxviridae family, which encodes its own
DNA-dependent RNA polymerase for transcription in the host cytoplasm?
- A) JC Virus
- B) Variola virus (smallpox)
- C) HIV
- D) Influenza virus
> Answer: B) Variola virus (smallpox). Poxviruses are large dsDNA viruses with a complex
structure, unique for replicating entirely in the host's cytoplasm thanks to a viral-encoded RNA
polymerase.
Q8. What best describes the unique genome of the Hepatitis B virus (HBV)?
- A) Double-stranded RNA (dsRNA)
,- B) Single-stranded DNA (ssDNA)
- C) Gapped double-stranded DNA
- D) Positive-sense single-stranded RNA (+ssRNA)
> Answer: C) Gapped double-stranded DNA. HBV is a hepadnavirus with a partially
double-stranded DNA genome. After infection, it is converted into a complete, covalently closed
circular DNA (cccDNA) in the nucleus.
Q9. What is an example of a virus from the Polyomaviridae family that can cause degenerative
brain diseases in immunocompromised patients?
- A) JC Virus
- B) Adenovirus
- C) Rhinovirus
- D) Rotavirus
> Answer: A) JC Virus. The JC virus is a small dsDNA polyomavirus. It is usually harmless but
can reactivate in immunocompromised individuals (e.g., with HIV or on immunosuppressant
drugs), causing progressive multifocal leukoencephalopathy (PML).
Q10. Which of the following is a measure of infectivity for a virus?
- A) Plaque assay
- B) Hemagglutination assay
- C) Western blot
- D) PCR
> Answer: A) Plaque assay. The plaque assay quantifies the number of infectious viral particles
(plaque-forming units or PFU) by measuring their ability to form clear zones of cell lysis in a cell
monolayer.
Q11. Which Baltimore classification group describes viruses with a single-stranded RNA
genome that is identical in sequence to mRNA and can be directly translated by host ribosomes
upon entry?
- A) Group III (dsRNA)
- B) Group IV (+ssRNA)
- C) Group V (-ssRNA)
- D) Group VI (ssRNA-RT)
> Answer: B) Group IV (+ssRNA). This is the defining feature of the Baltimore classification,
which categorizes viruses based on their genome type and replication strategy. Positive-sense
RNA viruses can immediately use their genome as mRNA.
Q12. Why is Influenza A virus able to cause yearly seasonal epidemics and occasional
pandemics?
- A) It has a very stable, unchanging genome.
, - B) It mutates slowly and is highly immunogenic.
- C) It undergoes antigenic drift and, less frequently, antigenic shift.
- D) It is not affected by the host's immune system.
> Answer: C) It undergoes antigenic drift and, less frequently, antigenic shift. Antigenic drift
refers to minor, gradual changes in surface proteins (hemagglutinin and neuraminidase), while
antigenic shift is a more sudden, major change caused by genome segment reassortment,
which can create a novel pandemic strain.
Q13. A scientist is trying to study a newly discovered virus. They observe that the virus's
genome functions directly as mRNA. The virus's genetic material can be classified as:
- A) dsRNA
- B) +ssRNA
- C) -ssRNA
- D) ssDNA
> Answer: B) +ssRNA. Direct translation by host ribosomes is the hallmark of a positive-sense
single-stranded RNA virus.
Q14. Which of the following correctly describes a retrovirus, which uses reverse transcriptase?
- A) dsDNA -> mRNA -> viral protein
- B) +ssRNA -> -ssRNA -> dsRNA
- C) +ssRNA -> dsDNA -> mRNA -> viral protein
- D) dsRNA -> +ssRNA -> viral protein
> Answer: C) +ssRNA -> dsDNA -> mRNA -> viral protein. This is the unique replication cycle of
retroviruses, where their RNA genome is reverse-transcribed into DNA, which then integrates
into the host genome and is transcribed back into RNA.
Q15. What is the genetic material of the Human Papillomavirus (HPV)?
- A) +ssRNA
- B) dsRNA
- C) dsDNA
- D) ssDNA
> Answer: C) dsDNA. HPV is a non-enveloped virus with a circular double-stranded DNA
genome.
Q16. A researcher is studying a virus that has a genome composed of two identical strands of
RNA, which is a rare configuration among viruses. This virus belongs to the family?
- A) Retroviridae
- B) Reoviridae
- C) Arenaviridae
- D) Flaviviridae
