1. Chapter 9
1. Differentiate a virus from a bacterium, with regard to
bacteria virus
size range Larger Smaller 20-1000 nm
Too small to be seen w naked eye
structural features Capsid, capsomere, envelope, spikes,
DNA/RNA
host-dependence Needs a living host; inert outside a host
mode of reproduction Binary fission Biosynthesis
2. List and briefly describe the key characteristics
of a typical virus.
● Contain a single type of nucleic acid, either DNA or RNA.
● Contain a protein coat (sometimes itself enclosed by an
envelope of lipids, proteins, and carbohydrates) that
surrounds the nucleic acid.
● Multiply inside living cells by using the synthesizing
machinery of the cell.
● Cause the synthesis of specialized structures that can
transfer the viral nucleic acid to other cells.

2. 3. Give an example each of viral family, genus, and strain

3. 4. List the criteria used in viral classification, with an example for each
Family: Herpesviridae
Genus: Simplexvirus, human herpesvirus 2
5. Name the unit used for measuring viral growth
(PFU) plaque-forming units
6. Briefly describe two methods routinely used for culturing viruses in the laboratory
1) In living animals
2) Embyonic eggs
3) Cell cultures
7. Briefly describe two methods for viral identification
Western Blotting
RFLP- restrictive fragment length polymorphism

4. 8. List all the stages of the lytic
(Fig.11) and the lysogenic (Fig. 12)
cycles of bacteriophage
multiplication, and describe the
key event in each stage

5. 8. List all the stages of the lytic
(Fig.11) and the lysogenic (Fig. 12)
cycles of bacteriophage
multiplication, and describe the
key event in each stage

6. 9. Briefly describe “phage conversion” and its effect on lysogenized host bacteria
The second result of lysogeny is phage conversion; that
is, the host cell may exhibit new properties. For example, the
bacterium Corynebacterium diphtheriae, which causes diphtheria,
is a pathogen whose disease-producing properties are related
to the synthesis of a toxin. The organism can produce toxin only
when it carries a lysogenic phage, because the prophage carries
the gene coding for the toxin. As another example, only streptococci
carrying a lysogenic phage are capable of causing toxic
shock syndrome. The toxin produced by Clostridium botulinum,
which causes botulism, is encoded by a prophage gene, as is the
Shiga toxin produced by pathogenic strains of E. coli.

7. 10. List all the stages in the multiplication of animal viruses, and describe the key event in each
stage

8. 11. Compare and contrast the events in bacteriophage and animal virus multiplication
(penetration) (entry)

9. 12. Differentiate the multiplication of enveloped and non-enveloped viruses
13. Differentiate the multiplication of (animal) DNA viruses and retroviruses
14. Define oncogenic viruses, with two examples
Viruses capable of inducing tumors in animals are called oncogenic viruses, or
oncoviruses
-papilloma viruses cause cervical cancer
-HBV Hepatitis B virus causes liver cancer

10. 15. Differentiate acute, latent and persistent viral infections, with one example of each
influenza
Shingles
TB
HIV

11. 16. Define “prion”, list its key characteristics, and give one
example each of prion diseases in
Animals: Mad cow disease (BSE)
and
Humans: Creutzfeldt-Jakob disease (CJD)
Stanley Prusiner proposed that infectious proteins caused a
neurological disease in sheep called scrapie. The infectivity of
scrapie-infected brain tissue is reduced by treatment with
proteases but not by treatment with radiation, suggesting that
the infectious agent is pure protein. Prusiner coined the name
prion for proteinaceous infectious particle.

12. 17. Define “viroid”, and give one example of an infection caused by a viroid.
Some plant diseases are caused by viroids, short pieces of
naked RNA, only 300 to 400 nucleotides long, with no protein
coat. The nucleotides are often internally paired, so the molecule
has a closed, folded, three-dimensional structure that presumably
helps protect it from attack by cellular enzymes. The
RNA does not code for any proteins. Thus far, viroids have been
conclusively identified as pathogens only of plants. Annually,
infections by viroids, such as potato spindle tuber viroid, result
in losses of millions of dollars from crop damage (Figure 13.23).