1. Ch. 17 Warm-up Why do many scientists classify viruses as non-living?
Draw the basic structure of a virus. Label and define capsid, viral envelope and nucleic acid.

2. Ch. 17 Warm-up
Draw the lytic/lysogenic cycle.
What stage of the lytic-lysogenic cycle is a virus virulent? Temperate?
What determines a host range?

3. Viruses
Chapter 17

4. Bacteria vs. Viruses Bacteria Virus Prokaryotic cell
Most are free-living (some parasitic)
Relatively large size
Antibiotics used to kill bacteria
Not a living cell (genes packaged in protein shell)
Intracellular parasite
1/1000 size of bacteria
Vaccines used to prevent viral infection
Antiviral treatment

5. Viruses Very small (<ribosomes) Components = nucleic acid + capsid
Genetic material: DNA or RNA (double or single-stranded)
Capsid: protein shell
Some viruses also have viral envelopes that surround capsid

6. Viruses Limited host range Reproduce quickly within host cells
Entry = attach to host cell membrane receptors through capsid proteins or glycoproteins on viral envelope (animal)
Eg. human cold virus (rhinovirus)  upper respiratory tract (mouth & nose)
Reproduce quickly within host cells
Can mutate easily
RNA viruses: no error-checking mechanisms

8. Simplified viral replicative cycle

9. Viral Reproduction Lytic Cycle:
Use host machinery to replicate, assemble, and release copies of virus
Virulent phages: Cells die through lysis or apoptosis
Lysogenic (Latent) Cycle:
DNA incorporated into host DNA and replicated along with it
Bacteriophage DNA = prophage
Animal virus DNA = provirus
UV radiation, chemicals: lysogenic  lytic cycle
Temperate Phage: uses both methods of replication

10. Bacteriophage
Virus that infects bacterial cells

11. Lytic Cycle of T4 Phage

12. Lytic Cycle vs. Lysogenic Cycle

13. Bacterial defenses against phages:
Natural selection: bacterial surface proteins mutate and prevent phage entry
Restriction enzymes: destroy foreign DNA
CRISPR-Cas9 system: enzymes that identify and cut invading phage DNA
The CRISPR system = bacterial immune system

14. Animal viruses have a membranous envelope
Host membrane forms around exiting virus
Difficult for host immune system to detect virus

15. Retrovirus
RNA virus that uses reverse transcriptase (RNA template  DNA)
Newly made viral DNA inserted into chromosome of host (provirus)
Host transcribes provirus to make new virus parts
Example: HIV (Human Immunodeficiency Virus)

16. HIV = Retrovirus

17. HIV: Origin: Chimpanzee virus Infects white blood cells (helper T)
HIV+: provirus (DNA inserted), latent
AIDS: <200 WBC count, opportunistic infections

18. Other Human Viruses Herpes virus Smallpox
Herpes Simplex Virus 1 (HSV-1)
Herpes Simplex Virus 2 (HSV-2)
Eradicated in 1979 due to worldwide vaccination campaigns

19. RNA viruses = High mutation rates

20. Emerging Viruses Zika Virus Ebola Virus H1N1 Influenza A Virus
Viruses that suddenly become apparent
Caused by existing viruses (combo of viruses)
Human diseases can originate from animals
Zika Virus
H1N1 Influenza A Virus
Ebola Virus
West Nile Virus

21. Current Outbreaks Epidemic: widespread outbreak
Pandemic: global outbreak
Chikungunya Virus
Zika Virus
Measles Virus

22. Drugs for Prevention/Treatment
Vaccine: weakened virus or part of pathogen that triggers immune system response to prevent infection
Ex. HPV, MMR, HepA, Flu shot
Antiviral Drugs: block viral replication after infection
Ex. Tamiflu (influenza), AZT (HIV)

23. Plant Viruses
Similar structure and mode of replication as animal viruses
Horizontal transmission: infected by outside source
Vertical transmission: inherited from parent
No cures for most viral plant diseases
Eg. tobacco mosaic virus (TMV)

24. Prions
Misfolded, infectious proteins that cause misfolding of normal proteins
Eg. scrapie (sheep), mad cow disease (BSE), Creutzfeldt-Jakob disease (humans), kuru (humans – New Guinea)

25. Diseases caused by prions
Prions act slowly – incubation period of at least 10 years before symptoms develop
Prions are virtually indestructible (cannot be denatured by heating)
No known cure for prion diseases
Kuru in New Guinea

26. Prion Neurodegenerative Diseases
Alzheimer’s Disease
Parkinson’s Disease

27. Amoeba Sisters: Viruses: Virus replication and the mysterious common cold