VM 232 CAT June 2014

SOKOINE UNIVERSITY OF AGRICULTURE

FACULTY OF VETERINARY MEDICINE
DEPARTMENT OF VETERINARY MICROBIOLOGY AND PARASITOLOGY

VM 232: VIROLOGY CAT
TIME ALLOWED: TWO HOURS DATE: 09/06/2014
Instructions:
1. This paper has FOUR printed pages with three sections
2. Answer ALL questions
3. ALL answers to ALL questions MUST be written in the respective spaces provided in each question except for question 6 and 7 use the back of the paper
4. Read instructions carefully before beginning each section and 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 reproduce and then exit the cell.
C) they are non-living D) they use the host’s energy to live.
E) they use the host cell’s nucleotides and enzymes to reproduce.

iii. Viruses are made of
A) Protein coat, DNA B) Protein coat, DNA or RNA
C) Protein coat, DNA and Ribosomes D) Cell membrane, DNA, 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 before it infects the cell 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

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. Most viruses infect a specific kind of cell. Which of the following are infected by the human immunodeficiency virus (HIV)?
A) Helper T cells B) Liver cells
B) GABA-receptor cells D) Red blood cells

x. Certain virus has an enzyme called “RNA-dependent RNA polymerase” packed inside its capsid (along with the virus’ genome). This virus…
A) Is a retrovirus B) Makes a DNA copy of its RNA genome and inserts the cDNA into the host cell genome C) Has a DNA genome D) Transcribes mRNA from its RNA genome E) Relies on the host cell to transcribe its genes into mRNA

2. Indicate whether the following statements are true or false by writing T for correct statement and F 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 (50 marks)
3. Write a word or phrase that best fits in the blank spaces below (10 marks)
i. An icosahedron virion is formed by…………..triangles …………faces, ———–edges and ————vertices (4 marks).
ii. ………….was the year for 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 recent discovered amoeba’s giant virus (2013) with a huge genome compared to other known viruses is called………………………………… (2 marks).
iv. …………………..is a viral disease transmitted by Aedes mosquitoes that has affected some people in Dar es Salaam (2 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)…………………………….
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)

6. Differentiate the following terms as they are used in virology (20 marks)
a. A virus from a provirus (4 marks)
b. A virion from a prion (4 marks)
c. A viroid from a virusoid (4)
d. A susceptible cell from a permissive cell (4 marks)
e. A positive (+) single strand RNA from a negative (-) single strand RNA of viral genomes (4 marks)