BLS 113 UE 2021

SOKOINE UNIVERSITY OF AGRICULTURE

COLLEGE OF VETERINARY MEDICINE AND BIOMEDICAL SCIENCES
DEPARTMENT OF MICROBIOLOGY, PARASITOLOGY AND BIOTECHNOLOGY

BLS 113: VIROLOGY UE THEORY
Instructions:
1. Answer ALL questions
2. Diagrams SHOULD be drawn neatly
3. Read each question CAREFULLY before you start attempting

QUESTION 1 (25 marks)
a) There are two schools of thought on whether viruses are living or non-living. Many scientists think viruses are alive while there are also many scientists who think viruses are not alive. Why are there different opinions? (2 marks) What would you do to convince someone who disagreed with your ideas about whether viruses were alive or not? (4 marks)
b) Briefly discuss the main four applications of bacteriophages in biotechnology (8 marks)
c) What are the similarities and differences between the lytic and lysogenic cycles in bacteriophages? (5 marks)
d) What determines whether a lambda phage (λ) takes a lytic or lysogenic cycle? (4 marks)
e) What name is given to the process of switching the replication cycles of bacteriophages? (2 marks)

QUESTION 2 (15 marks)
a) The genome inside a virion is always a nucleic acid. If you could get the genome into a cell, would it start the replication cycle? Consider this question for each of the known viral genome types and provide a reason to your answer (4 marks)
b) Do DNA viral genomes always encode their own DNA polymerase? In any case If not, where does the polymerase come from? (3 marks)
c) Most DNA viruses replicate within the nucleus of a host cell, using host enzymes to replicate their DNA. In contrast, poxviruses replicate in the cytoplasm of host cells. What problem does this create for poxvirus replication? (2 marks) How could the virus overcome this problem? (3 marks)
d) Discuss why viruses can only replicate inside living cells (3 marks)

QUESTION 3 (25 marks)
Severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) is a virus that, starting in the end of 2019, has caused the largest global pandemic in recent history. Coronavirus disease 2019 (COVID-19), a disease caused by this virus was reported for the first time in Wuhan, China and has affected millions of people worldwide. Complete SARS-Cov-2 genome sequences from hundreds of infected individuals have shown that, the virus has undergone numerous mutations leading to different disease manifestations. The latest third wave of disease reported to start in India caused by SARS-Cov-2 Delta variant has shown to cause severe disease and mortalities in affected individuals compared to the former two waves. Vaccines to control the disease are in different stages and some are in use with promising results.
Based on the information provided above and your knowledge on SARS-Cov-2/COVID-19, answer the following questions.
a) By using a well labelled structure of SARS-Cov-2, identify any three structural components of the virus (3 marks)
b) Classify SARS-Cov-2 based on Baltimore system (2 marks)
c) Write one sentence describing the role of spike protein in the virus replication process (2 marks)
d) Which receptor is used by the virus during attachment to the host cells? (1 marks)
e) Name the mode of internalization used by this virus (2 marks)
f) Where do you think in the SARS-Cov-2 replication cycle, antivirals can be employed to prevent replication of the virus? (4 marks)
g) How could sequencing many SARS-Cov-2 genomes be used to track how the virus has changed over time due to mutations? (4 marks)
h) What might be the effect of mutations in the gene that encodes the spike protein to the types of cells the virus infects? (4 marks)
i) What impacts might mutations have on the control of the virus? (3 marks)

QUESTION 4 (20 marks)
a) How does retroviruses differ from other viruses? (3 marks)
b) How is a retrovirus able to recognize and attach to a host cell? (2 marks)
c) How does a retrovirus get into a host cell? (2 marks)
d) Describe how retroviruses manage to integrate their genome into a double stranded DNA host genome (4 marks)
e) Why would an individual, once infected with HIV have it for life despite chemotherapy? (3 marks)
f) Explain why babies born to HIV positive mothers will always test HIV positive using an HIV antibody test, but the same babies will test negative to molecular tools or cell culture techniques (4 marks). Does it mean the babies have HIV? (2 marks)

QUESTION 5 (15 marks)

Carefully study the figure above and use it to answer the following questions
a) Classify the virus in the figure above based on the outer covering (2 marks)
b) State what is happening at each step labelled I, II, III and IV (4 marks)
c) Name enzymes responsible for making the following during virus replication in the figure above. State if is a host or viral enzyme (3 marks)
i. the copies of the viral DNA
ii. the viral mRNA
ii. the viral proteins
d) If this is among the smallest virus, where do you think the replication of the genome will take place (2 marks)
e) Describe briefly how this virus leave the host cell and the possible effects to the cell? (4 marks)

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