Chapter 9 1. Differentiate a virus from a bacterium, with regard to

2. List and briefly describe the key characteristics of a typical virus.

bacteria virus

size range Larger Smaller 20-1000 nmToo 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

● 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.

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

4. List the criteria used in viral classification, with an example for eachFamily: HerpesviridaeGenus: 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 animals2) Embyonic eggs3) Cell cultures

7. Briefly describe two methods for viral identificationWestern Blotting RFLP- restrictive fragment length polymorphism

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

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

9. Briefly describe “phage conversion” and its effect on lysogenized host bacteria

The second result of lysogeny is phage conversion; thatis, the host cell may exhibit new properties. For example, thebacterium Corynebacterium diphtheriae, which causes diphtheria,is a pathogen whose disease-producing properties are relatedto the synthesis of a toxin. The organism can produce toxin onlywhen it carries a lysogenic phage, because the prophage carriesthe gene coding for the toxin. As another example, only streptococcicarrying a lysogenic phage are capable of causing toxicshock syndrome. The toxin produced by Clostridium botulinum,which causes botulism, is encoded by a prophage gene, as is theShiga toxin produced by pathogenic strains of E. coli.

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

11. Compare and contrast the events in bacteriophage and animal virus multiplication

(penetration) (entry)

12. Differentiate the multiplication of enveloped and non-enveloped viruses13. Differentiate the multiplication of (animal) DNA viruses and retroviruses

14. Define oncogenic viruses, with two examplesViruses capable of inducing tumors in animals are called oncogenic viruses, or oncoviruses-papilloma viruses cause cervical cancer-HBV Hepatitis B virus causes liver cancer

influenza

TBHIV

Shingles

15. Differentiate acute, latent and persistent viral infections, with one example of each

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.

17. Define “viroid”, and give one example of an infection caused by a viroid.

Some plant diseases are caused by viroids, short pieces ofnaked RNA, only 300 to 400 nucleotides long, with no proteincoat. The nucleotides are often internally paired, so the moleculehas a closed, folded, three-dimensional structure that presumablyhelps protect it from attack by cellular enzymes. TheRNA does not code for any proteins. Thus far, viroids have beenconclusively identified as pathogens only of plants. Annually,infections by viroids, such as potato spindle tuber viroid, resultin losses of millions of dollars from crop damage (Figure 13.23).