Virology MCQs: Viral Genetics, Prions, Viroids and Bacteriophages

MCQs in virology-2 post contains ten (10) multiple-choice questions from various areas of virology. Most of the questions are can be addressed if you have a basic concept about genomic structure and replication of various clinically important viruses (or Baltimore classification of virus). Some of the questions are about prions, and others are about bacteriophages.

## Viral genomes and replication

11. Viruses that contain two complete copies of positive-strand RNA and the enzyme reverse transcriptase are:
    a. Toga viruses
    b. Rhabdoviruses
    c. Retroviruses
    d. Reoviruses
    e. Enteroviruses
12. The time from adsorption of a bacteriophage to release of newly synthesized bacteriophage is generally
    a. 1-5 minutes
    b. 20-40 minutes
    c. 1-4 hours
    d. 6-24 hours
    e. 1-2 days
13. Bacteriophages that can enter into stable, long-term relationships with their hosts are called:
    a. Lytic phages
    b. Defective phages
    c. virulent phages
    d. lazy phages
    e. Temperate phages

14. The positive strand of certain viruses does not act as a message but becomes converted into DNA and integrated into the host cellular DNA. These viruses area.
    a. Rhinoviruses
    b. Enteroviruses
    c. Retroviruses
    d. Reoviruses
    e. Picornaviruses

Oncogenic viruses, prions, and viroids

15. Infants infected with cytomegaloviruses (CMV) in utero may suffer from:
    a. mental retardation
    b. enlarged spleen
    c. liver damage
    d. any of these
    e. none of these
16. Viroids are unusual in that they:
    a. have no capsid protein or envelope
    b. contain RNA
    c. are barely visible with the light microscope
    d. can cause disease in plants
    e. are retroviral
17. Creutzfeldt-Jakob disease (CJD) , kuru, scrapie, and Mad Cow disease are caused by:
    a. Viroids
    b. Retroviruses
    c. DNA viruses
    d. Prions
    e. RNA viruses
18. The human virus that has been associated with Burkitt lymphoma (a malignant tumor of the jaw) is:
    a. Cytomegalovirus
    b. Human papilloma virus (HPV)
    c. Retroviruses
    d. Epstein- Barr virus
    e. Enterovirus

Viral proteins and inactivation

19. Viral surface proteins have various roles to play for their survival and in pathogenesis. Which of the following statement is most accurate about them?
    
    a. Misfolded viral surface proteins cause prions disease.
    b. They act as proteases that degrade cellular proteins leading to cell death.
    c. They are the polymerases that synthesize viral messenger RNA.
    d. Neutralizing antibodies are formed against viral surface proteins.
    e. They play role in the regulation of viral transcription.
20. Enveloped viruses are more easily inactivated by lipid solvents and detergents than viruses that do not have an envelope. Which one of the following viruses is the most sensitive to inactivation by lipid solvents and detergents?
    a. Coxsackie virus
    b. Hepatitis A virus
    c. Herpes simplex virus
    d. Poliovirus
    e. Rotavirus

Answer key

11. c. Retroviruses
12. b. 20-40 minutes
13. e. Temperate phages
14. c. Retroviruses
15. d. Any of these
16. a. Have no capsid protein or envelope
17. d. Prions
18. d. Epstein-Barr virus
19. d. Neutralizing antibodies are formed against viral surface proteins
20. c. Herpes simplex virus

Why these are the answers

11. Retroviruses. Retroviruses are unique in being diploid: each virion carries two complete copies of positive-strand RNA, along with the enzyme reverse transcriptase, which copies that RNA into DNA after the virus enters the cell. The other viruses listed carry a single genome copy and no reverse transcriptase. The pairing of two RNA copies plus reverse transcriptase is the retrovirus signature.
12. 20 to 40 minutes. The time from adsorption to release of new phage, the latent period plus burst, is short for bacteriophages. A typical phage such as T4 completes its cycle in roughly 25 minutes, far faster than animal viruses, which need hours. This is measured with a one-step growth curve, which also gives the burst size (the number of new phages released per infected cell). The options measured in hours or days describe animal virus cycles, not phages.
13. Temperate phages. Temperate phages can do more than immediately kill the host: they can integrate their genome into the host chromosome (as a prophage) and persist quietly for many generations, a state called lysogeny. This is the stable, long-term relationship the question describes. Lytic (virulent) phages, by contrast, replicate and burst the cell immediately. The other options are not standard phage categories.
14. Retroviruses. This describes reverse transcription and integration: the positive-strand RNA genome is not translated directly but is first copied into DNA, which then integrates into the host chromosome as a provirus. That is the defining retroviral strategy. The other viruses listed are picornaviruses (rhinoviruses, enteroviruses) or reoviruses, which replicate their RNA without a DNA intermediate and do not integrate.
15. Any of these. Congenital cytomegalovirus infection, acquired in the womb, is a leading infectious cause of birth defects. It can cause mental retardation (from central nervous system damage), an enlarged spleen and liver with jaundice (hepatosplenomegaly and liver damage), along with hearing loss and other problems. Because CMV can produce all of these, the inclusive answer is correct.
16. Have no capsid protein or envelope. Viroids are the unusual part of this set: they are naked, small, circular RNA molecules with no capsid and no envelope, unlike true viruses, which always have at least a protein capsid. They cause disease in plants. Containing RNA and causing plant disease are true of viroids but are not what makes them unusual; the absence of any protein coat is the striking feature that sets them apart from viruses.
17. Prions. Creutzfeldt-Jakob disease, kuru, scrapie, and bovine spongiform encephalopathy (mad cow disease) are transmissible spongiform encephalopathies, and they are caused by prions, infectious misfolded proteins that contain no nucleic acid at all. This is what makes prions so unusual: they transmit disease without any DNA or RNA, by inducing normal host protein to misfold. None of the nucleic-acid agents listed (viroids, retroviruses, DNA or RNA viruses) cause these diseases.
18. Epstein-Barr virus. EBV is associated with Burkitt lymphoma, a B-cell lymphoma that classically involves the jaw in its endemic African form. EBV is also linked to nasopharyngeal carcinoma and infectious mononucleosis. The other viruses listed cause different conditions: CMV causes congenital and opportunistic disease, and HPV is linked to cervical cancer, but the jaw lymphoma association is EBV's.
19. Neutralizing antibodies are formed against viral surface proteins. Surface proteins sit on the outside of the virus, where the immune system can reach them, so they are the main targets of neutralizing antibodies, and this is why they matter so much for vaccines. The distractors misassign functions: prion disease comes from misfolded host protein, not viral surface protein; the enzymes that degrade cell proteins or synthesize viral mRNA are internal, not surface, proteins; and transcription regulation is not the role of surface proteins.
20. Herpes simplex virus. Enveloped viruses depend on their lipid membrane to infect, and lipid solvents and detergents dissolve that envelope, inactivating the virus. Of the viruses listed, herpes simplex is the only enveloped one, so it is the most sensitive. Coxsackievirus, hepatitis A, poliovirus, and rotavirus are all naked (non-enveloped) viruses, which makes them far more resistant to these agents, and, in the case of the enteric ones, able to survive the harsh conditions of the gut.