1. Eukaryotes and Viruses
Chapters 12 and 13

2. Viral Characteristics and Structure
Why Viruses aren’t Alive

3. General Characteristics of Viruses
Name derives from the Latin for “poison”
Obligatory intracellular parasites
Referred to as filterable
Contain a single type of nucleic material
The nucleic material is covered in a protein coat.
Use the synthesis machinery of the host to multiply.

4. Why are they not Alive? No independent metabolism or reproduction
No single phylogenetic origin
No cellular structure
No ribosomes
Though they DO evolve and reproduce.

5. Host Range
Viruses have a specific subset of cell types they will infect, referred to as Host Range.
Most viruses can only infect a single species
Some viruses can cross species barriers
Numerous factors influence host range
Viruses that infect bacteria are referred to as bacteriophage or simply phage.

6. Staphylococcus Bacteria
Viral Particle Size
Staphylococcus Bacteria
1 μm in diameter
Poxviridae
Lentiviruses
Picornaviridae
Bacteriophage

7. Viral Structure
A Virion is a complete, infectious viral particle and is composed of…
Nucleic Acid
Capsid and Envelope

8. Nucleic Acid
Only a single type of nucleic acid (RNA or DNA) is present in any species of virus.
Unlike cellular life, viral nucleic acid can be either single or double-stranded (again only a single type per species)
Size of the genetic structure can range from a few thousand base pairs to a quarter of a million

9. Capsid and Envelope
Capsids are regular repeating protein structures composed of capsomeres.
Some viral species also have a host-derived envelope surrounding the capsid
Some viral species have protein/ carbohydrate “spikes” rising from the surface that can be used for identification

10. Viral Morphology

11. Viral Taxonomy
How do you do a taxonomy of something that isn’t alive?

12. Viral Taxonomy
Without a shared phylogeny there is no use for the higher taxons (Domain, Kingdom, Phylum, and Class)
Typically viral species are referred to by Order, Family, Genus and a descriptive common name (in place of a species epithet)
Based on
Nucleic Acid type
Strategy of replication
Morphology
Host range

13. Viral Replication
No, not 1 becomes 2, more like 1 becomes 1000.

14. Growing Bacteriophage

15. Growing Animal Viruses

16. Viral Identification Polyphasic Identification Morphology
Detection of Antibodies
Western Blotting of known viral proteins
Nucleic Methodologies
PCR
RFLP
RNA PCR

17. Lytic Bacteriophage Cycle
Attachment
Release
Penetration
Biosynthesis
Maturation

18. Lysogenic Bacteriophage Cycle
Lytic Cycle

19. Animal Unenveloped DNA Viral Replication

20. DNA vs. RNA Viral Replication
There are various types of RNA viruses.
Replication of the Genetic Material can be simple or a multistep process.
+RNA, direct translation and replication by viral protein
-RNA, indirect translation and replication by viral protein
dsRNA, direct translation and relication by viral protein
Retroviruses, conversion of RNA to DNA, integration and then production by host.

21. Comparison Bacteriophage Animal Attachment to Cell Wall proteins.
Viral DNA is injected into cell
No removal of capsid required
Biosynthesis in cytoplasm
Lysogeny
Host cell lysed for release
Attachment to plasma membrane proteins and glycoproteins.
Capsid enters cells
Capsid removed by enzymes
Biosynthesis in nucleus or cytoplasm
Latency
Enveloped viruses bud and nonenveloped rupture.

22. Viruses and Cancer
One of many factors

23. Oncogenic Viruses
Some viruses and known to help trigger cancers, called oncogenic viruses.
These viruses affect oncogenes, natural parts of our genetic structure that can cause cancer.
The process of becoming cancerous is termed transformation.
Oncogenic Viruses integrate into the host genetic material.

24. Known Oncogenic Viruses
Type of Virus
Viral Species
Associated Cancer
DNA
Human Papillomavirus
Cervical Cancer
Epstein-Barr Virus
Burkitt’s Lymphoma
Hepatitis B Virus
Liver Cancer
Kaposi Sarcoma-Associated Hepervirus
Kaposi Sarcoma
Merkel Cell Polyomavirus
Merkel Cell Carcinoma
RNA
Human T-Lymphotropic Virus 1
Leukemia
Hepatitis C Virus

25. Latency, Persistence and the Prions

26. Acute, Latent, and Persistent Viral Infections
Acute Infections are those that cause immediate proliferation.
Latent infections can occur by itself or after an acute infection, where the viral load remains undetected for a long period of time before reemerging quickly.
Persistent Infections are ones where the viral load build over a long period of time.

27. Graph of Acute, Latent and Persistent Viral Infections

28. Prions Prions are infectious protein particles
Prions are altered forms of a normal protein in the host that can catalyze the alteration of other “normal” protein particles to the “prion” state
They cause neurological degradation and death with no known treatment.
Since each prion protein is infectious, they are extremely resistant to control measures.

29. Prion Reaction
PrPC + PrPSc  2 PrPSc