SOKOINE UNIVERSITY OF AGRICULTURE
COLLEGE OF VETERINARY MEDICINE AND BIOMEDICAL SCIENCES
DEPARTMENT OF MICROBIOLOGY, PARASITOLOGY AND BIOTECHNOLOGY
BLS 108: VIROLOGY CAT 1
TIME ALLOWED: 1 HOUR DATE: 03-08-2020
Instructions:
1. This paper has FOUR printed pages with three sections (A, B and C)
2. Answer ALL NINE questions
3. ALL answers to ALL questions MUST be written in the respective spaces provided in each question
4. Read instructions carefully before beginning each section and each question
SECTION A (30 marks)
1. Select the best answer among the alternative statements given for each question and circle it (20 marks)
i. Which of the following is the correct set of acellular microorganisms?
A) viruses, protists, viroids and archea B) virusoids, prions, viruses and protists
C) viruses, prions, viroids and virusoids D) prions, bacteria, viruses and archea
ii. Viruses are referred to as obligate intracellular parasites because
A) viral DNA inserts itself into host DNA B) they use host energy to live
C) they replicate only in living susceptible cells D) they are non-living
iii. Viruses are made of
A) Protein coat, DNA B) Protein coat, RNA
C) Protein coat, DNA or RNA D) Protein coat, DNA and RNA
iv. One characteristic shared by a virus and a living cell is that both —
A) store genetic information in nucleic acids B) have a crystalline structure
C) gain energy directly from the sun D) use glucose for respiration
v. The host range of a virus is determined by
A) the enzymes carried by the virus B) whether its nucleic acid is DNA or RNA
C) the proteins in the host’s cytoplasm D) the enzymes produced by the virus
E) the proteins on the capsid and the proteins on host cell membranes
vi. Which of the following statements about viruses is false?
A) They come in many different shapes and sizes
B) They contain genetic material, protein and a few organelles
C) Each type of virus can only infect specific hosts
D) Different viruses infect hosts from all of the 5 kingdoms of life
vii. Viruses have some of the properties of living organisms. Which of the following is a characteristic of all organisms, but not of viruses?
A) plasma membrane B) ability to control metabolism
C) genetic information stored as nucleic acid D) structure includes proteins
E) ability to reproduce at fantastic rate
viii. Which of the following is a true statement about viruses?
A) A single virus particle contains both DNA and RNA
B) Viruses are classified below the cellular level of biological organization
C) Even small virus particles are visible with light microscopes
D) A and B only are true. E) A, B, and C are true
ix. A chemical component that is found in all viruses is:
A) Protein B) Lipid C) DNA D) RNA D) Glycoproteins
x. Viroids are unusual in that they:
A) have no capsid protein or envelops B) contain DNA
C) are barely visible with the light microscope D) can cause disease in animals
E) are retroviral
2. Indicate whether the following statements are true or false by writing TRUE for correct statement and FALSE for incorrect statement in the space provided (10 marks)
i. Most viruses replicate by means of binary fission except HIV………….
ii. It is said that, “a virus is a piece of bad news wrapped up in a carbohydrate coat containing either DNA or RNA but not both” …………………
iii. Koch’s postulates for viruses were modified by Robert Koch 1890 due to proof of filterability………
iv. The history of viruses begins by Adolf Mayer to prove the failure of some disease agents to follow Koch’s postulates in 1876………………
v. Viruses are found everywhere in the universe affecting all cellular organisms except bacteria………
vi. The host range of viruses is determined by specific host attachment sites and cellular factors………
vii. As opposed to bacteria, viruses contain protein synthesis machinery necessary for their survival from one organism to another……………….
viii. The main living characteristic of a virus is the ability of a virus to reproduce and carry out next generation at a fantastic rate, but only in living host cells………….
ix. All viruses possess envelope acquired from the host cell membrane when leaving the cell after replication……………
x. Viruses can be used by scientist to transfer genes between organisms……………………
SECTION B (51 marks)
3. Write a word or phrase that best fits in the blank spaces below (11 marks)
i. A standard an icosahedron virion is formed by……………triangles, …………faces, …………edges and ………vertices (4 marks).
ii. …………. was the year for the first recorded cases of AIDS, mostly in homosexual populations and ……………… the year for the discovery of HIV, the causative agent of AIDS (2 marks)
iii. A type of microscope used to visualize the structure of viruses………………… (1 marks).
iv. …………………………..is a viral disease discovered in the December 2019 in Wuhan, China and it is affecting people all over the word and is caused by a virus named…………………………………………………………..( 4 marks)
4. Give the correct biological term for each of the following descriptions. Write only the term next to the question number (10 Marks)
i. Obligate intracellular parasites containing DNA or RNA but not both…………………………………………………………………………………
ii. The internal part of a virus particle, which consists of the nucleic acid (either DNA or RNA never both) and closely associated proteins………………………………….
iii. The outer shell of the virus which encloses the genetic material (composed of capsomers) is called………………………………………………………………………………
iv. The structure composed of the capsid containing the nucleic acid or core……………………………………………………………………………………
v. The complete infective virus particles (i.e. capsid enclosing the nucleic acid) which are INERT CARRIERS of the genome (do not grow) are called……………………………
5. Select the answer among the alternatives given in list B that best matches with the statement in list A, then write the letter of the correct response in spaces provided in list A. (10 marks)
| LIST A | LIST B |
| i. Baltimore classification of viruses……………………….
ii. Named based on how they were originally thought to be contracted…………………………………………………..
iii. Papova-, hepadna-, circo-, herpes-, pox-, and adeno- viruses………………………………………………………
iv. Tobacco mosaic virus, Ebora virus, influenza, measles and rabies virus are examples of viruses with ……………….. capsid symmetry
v. Viruses originated from cellular (RNA and DNA) genetic material that has acquired the capacity to exist and function independently……………………………………………………………. |
A. Seven groups
B. Dengue virus C. Regressive theory D. RNA viruses E. Icosahedral F. Six groups G. DNA viruses H. Poxvirus I. Progressive theory J. Helical |
6. Differentiate the following terms as they are used in virology. Write your answer in one sentence only (20 marks)
a. A virion from a prion (4 marks) ……………………………………………………………………………………………………………………………………………b. A virus from a provirus (4 marks) ……………………………………………………………………………………………………………………………………
c. A virus from a living cell (4 marks)…………………………………………………………………………………………………………………………………………………
d. A viroid from a virusoid (4 marks) ……………………………………………………………………………………………………………………
e. A positive (+) strand RNA from a negative (-) strand RNA viral genome (4 marks)
……………………………………………………………………………………………………………………………………………………………………………………………………………
SECTION C (19 marks)
7. What are the THREE main structural forms of a viral capsid symmetry (6 marks)
a) ………………………………………………………………………………………………..
b) ………………………………………………………………………………………………..
c) ………………………………………………………………………………………………..
8. List all the SEVEN types of viral genomes (7 marks)
a)……………………………………. b)………………………………………………………..
c) …………………………………….. d)……………………………………………………….. e)……………………………………. f) ……………………………………………………….
g) ………………………………………………………………………………………………..
9. Mention THREE main hypotheses that try to explain the origins of viruses (6 marks)
a)…………………………………………………………………………………………………
b)…………………………………………………………………………………………………
c)…………………………………………………………………………………………………
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