SOKOINE UNIVERSITY OF AGRICULTURE
COLLEGE OF VETERINARY MEDICINE AND BIOMEDICAL SCIENCES
DEPARTMENT OF MICROBIOLOGY, PARASITOLOGY AND BIOTECHNOLOGY
BLS 108: VIROLOGY PROBATION THEORY
Instructions:
1. Answer ALL questions
2. All questions carry EQUAL weight
3. Diagrams SHOULD be drawn neatly
4. Read each question CAREFULLY before you start attempting
QUESTION ONE
a) List 3 criteria used to define a virus (3 marks)
b) Describe any three reasons why it is important to study viruses (6 marks)
c) Explain why viruses are able to be so much smaller than bacteria? (3 marks)
d) Briefly describe how the prions cause disease? (5 marks)
e) Describe any four criteria used to classify viruses? (8 marks)
QUESTION TWO
a) With the aid of a well labeled diagram (s), describe the structures of naked and enveloped viruses (12 marks)
b) What are the main functions of the following viral components? (3 marks each)
(i) Capsid
(ii) Nucleic acids
(iii) Non-structural proteins
c) State why bacteriophages are more complex than typical icosahedron or helical viruses (4 marks)
QUESTION THREE
a) Why are viruses generally very specific as to the types of hosts, tissues, and cells they are able to infect? (3 marks)
b) Animal viruses adsorb to receptors on the cytoplasmic membrane of host cells. Why would our cells possess receptors that viruses could adsorb too? (4 marks)
c) Explain why are viruses considered obligate intracellular pathogens? (4 marks)
d) Describe how enveloped viruses manage to get into the host cell for replication (8 marks)
e) State why viruses can’t replicate on environmental surfaces or in synthetic laboratory medium (4 marks)
f) Which classes of viruses are more prone to introducing mutations during genome replication? (2 marks)
QUESTION FOUR
a) Why is HIV described as a retrovirus? (3 marks)
b) Name 3 types of cells HIV primarily infects and briefly explain why (5 marks)
c) HIV possesses a genome of RNA. How then is HIV able to insert into the DNA of host cells and form a provirus? (6 marks)
d) Why is it hard to cure viral infection? (6 marks)
e) How do Antiretroviral drugs help an HIV patient? (5 marks)
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