Practice Test: Viruses, Viroids, and Prions
Section A: Multiple Choice Questions
1. What is the primary environmental need for virus replication?
a. Oxygen
b. Nutrients
c. Host cell
d. Sunlight
2. Which of the following is NOT a common genome arrangement for viruses?
a. Single-stranded RNA
b. Double-stranded RNA
c. Single-stranded DNA
d. Triple-stranded DNA
3. Tail fibers or spikes/glycoproteins in viruses primarily aid in:
a. Nucleic acid replication
b. Host cell lysis
c. Attachment to host cells
d. Maturation of virions
4. What are the three basic shapes of viral particles?
a. Spherical, cubic, tubular
b. Helical, icosahedral, complex
c. Linear, circular, spherical
d. Cuboidal, tetrahedral, spiral
5. Which cycle involves the integration of viral DNA into the host genome?
a. Lytic cycle
b. Lysogenic cycle
c. Temperate cycle
d. Viral replication cycle
Section B: True or False
6. Transduction involves the transfer of bacterial DNA via viruses.
- True
- False
7. Viroids encode proteins necessary for their replication.
- True
- False
8. Prions cause diseases by infecting host cells and replicating inside them.
- True
- False
Section C: Matching
Match the term with its description.
9. Plaque assay
- A. Process by which viral DNA integrates into the host genome
10. Lysogenic cycle
- B. Technique used to quantitate viruses in laboratory settings
11. Direct counts
- C. Method for cultivating viruses using host cells
12. Temperate phage
- D. Cycle involving attachment, penetration, biosynthesis, maturation, and release
Section D: Short Answer
13. Describe the main function of tail fibers or spikes/glycoproteins in the viral life cycle.
14. Explain the difference between lytic and lysogenic phages.
Section E: Essay
15. Compare and contrast generalized and specialized transduction, including the mechanisms by which bacterial DNA is transferred horizontally in each case.
16. Describe the replication cycle of animal viruses, highlighting major differences between animal viruses and bacteriophages.
Section F: Application
17. Provide an example of a viroid-induced disease in plants and explain how viroids cause this disease.
18. Discuss the implications of prion diseases in terms of public health and animal agriculture.
Section G: Critical Thinking
19. Evaluate the significance of viral cultivation techniques in understanding viral replication and pathogenesis.
20. Predict potential challenges in developing antiviral therapies targeting specific stages of the viral replication cycle.
Feel free to modify or expand upon these questions to better suit your needs.
Here's the answer key for the practice test:
Answer Key
Section A: Multiple Choice Questions
1. c. Host cell
2. d. Triple-stranded DNA
3. c. Attachment to host cells
4. b. Helical, icosahedral, complex
5. b. Lysogenic cycle
Section B: True or False
6. True
7. False
8. False
Section C: Matching
9. B. Technique used to quantitate viruses in laboratory settings - Plaque assay
10. A. Process by which viral DNA integrates into the host genome - Lysogenic cycle
11. D. Cycle involving attachment, penetration, biosynthesis, maturation, and release - Direct counts
12. C. Method for cultivating viruses using host cells - Temperate phage
Section D: Short Answer
13. Tail fibers or spikes/glycoproteins in viruses primarily aid in attaching to host cells during the viral life cycle.
14. Lytic phages undergo a rapid replication cycle resulting in the lysis of the host cell, while temperate phages can integrate their DNA into the host genome and undergo a lysogenic cycle.
Section E: Essay
15. Generalized transduction involves the random transfer of bacterial DNA by a phage during lytic infection, while specialized transduction involves the specific transfer of bacterial genes located near the prophage attachment site. In generalized transduction, bacterial DNA is mistakenly packaged into the phage capsid during assembly, while in specialized transduction, specific bacterial genes adjacent to the prophage are transferred when the prophage is excised from the host genome.
16. The replication cycle of animal viruses typically involves attachment to host cell receptors, entry via fusion or endocytosis, release of the viral genome into the host cell, replication and transcription of viral genes, assembly of new virions, and release of mature virions from the host cell. Major differences between animal viruses and bacteriophages include the nature of attachment (receptor specificity), means of entry (fusion or endocytosis), and mechanisms of release (budding from host cell membrane).
Section F: Application
17. Example of a viroid-induced disease in plants: Potato spindle tuber disease caused by the Potato spindle tuber viroid (PSTVd). Viroids cause disease by interfering with host cell processes, disrupting normal growth and development. In the case of PSTVd, symptoms include spindle-shaped tubers, stunted growth, and reduced yields.
18. Prion diseases, such as Creutzfeldt-Jakob disease in humans and bovine spongiform encephalopathy in cattle, pose significant public health and agricultural concerns. Prions are highly resistant to traditional sterilization methods and can spread through contaminated meat products, leading to the potential for zoonotic transmission. Control measures include surveillance, strict food safety protocols, and research into prion detection and treatment methods.
Section G: Critical Thinking
19. Viral cultivation techniques are essential for studying viral replication, pathogenesis, and developing vaccines and antiviral therapies. These techniques allow researchers to isolate and characterize viruses, understand their host range and tropism, and investigate factors influencing viral growth and transmission. Furthermore, viral cultivation plays a crucial role in vaccine production, as live attenuated or inactivated viruses are often used as vaccine candidates.
20. Developing antiviral therapies targeting specific stages of the viral replication cycle faces several challenges, including viral resistance, host cell toxicity, and off-target effects. Viruses can rapidly mutate, leading to the emergence of resistant strains that are less susceptible to antiviral drugs. Additionally, many antiviral drugs have narrow spectra of activity and may exhibit adverse effects on host cells. Furthermore, targeting specific stages of the replication cycle may not be effective against all viruses, as some viruses utilize alternative pathways or mechanisms for replication. Therefore, a comprehensive understanding of viral biology and host-pathogen interactions is necessary for the development of effective antiviral therapies.