1. Unit 6 – Organismal Biology Part 1: Bacteria and Viruses

2. Are these viruses alive?
What does it mean to be “living”?

3. A “borrowed” life Cannot reproduce
Cannot carry out metabolic activity outside of a host
Exist as “entities” between life-forms and chemical.

4. Virus Structure
Nucleic acid arranged as single linear or circular molecules.
Double-stranded DNA
Single-stranded NA
Double-stranded RNA
Single-stranded RNA
Not your typical DNA structure option…virus genome can vary and we categorize the virus as an RNA or DNA virus based on that genomic structure.
Relatively little amount of genetic information, with as few as 4 genes and ranging up to a few hundred to a thousand genes.

5. Virus Structure Capsid – protein coat that covers the viral genome.
Varies in shape
Built from capsomere protein subunits
Not your typical DNA structure option…virus genome can vary and we categorize the virus as an RNA or DNA virus based on that genomic structure.
Relatively little amount of genetic information, with as few as 4 genes and ranging up to a few hundred to a thousand genes.

6. Virus Structure Envelope Accessory structure (not found in all)
Membrane w/proteins that surrounds envelop
Derived from host cell
Derived from the phospholipids and membrane proteins of the host cells along with some proteins of viral origin

7. Virus Reproduction Limited by the host range
Prokaryotic cells (bacteria)
Eukaryotic cells (plants, animals)
Lock-and-key recognition mechanism (specificity)
Host range is a product of evolution of the recognition systems by the viruses
Example: West nile virus can only infect mosquitos, birds, horses, and humans. In eukaryotic cells, virus infection can be limited by tissue.

8. General Features Virus binds to host cell and viral genome is inserted
Mechanism varies:
Inject DNA
Endocytosis (taken in)
Fusion of viral envelop with host membrane

9. General Features
Once genome is inside, viral proteins take over control
Host provides raw materials and energy to make more viruses
New viruses exit the cell, damaging or killing it
This all varies…based on which type of host the virus infect!

10. 2 3 1
1. Virus enters cell and is uncoated + releases viral DNA and capsid proteins 4

11. Reproductive Cycles of Bacteriophages
Phages infect only bacteria
Two alternative mechanisms:
Lytic Cycle  Ends in host death
Lysogenic Cycle  Replication without host death

12. Lytic Cycle
If phage only reproduces this way, it is considered virulent phages. 1 2 5
Warm-up for Monday: Outline the steps of the lytic cycle from the perspective of the virus. 4 3

13. Lysogenic Cycle
Phages that use both lytic and lysogenic are considered temperate phages. 1 6 2 7 3 5 4

14. Classes of Animal Viruses
Double-stranded DNA
Envelope?
Examples/disease
Papovavirus
Herpesvirus
Poxvirus No
Yes
HPV (human papillomavirus)
Herpes, shingles, chickenpox
Smallpox, cowpox
Envelopes are host-specific and used to enter the host. Receptors on exterior.

15. Classes of Animal Viruses
Single-stranded DNA
Envelope?
Examples/disease
Parvovirus No
B19 virus

16. Classes of Animal Viruses
Double-stranded RNA
Envelope?
Examples/disease
Reovirus No
Rotavirus (diarrhea; infants)

17. Classes of Animal Viruses
Single-stranded RNA
Envelope?
Examples/disease
Picornavirus
Coronavirus
Flavivirus No
Yes
Rhinovirus (common cold); poliovirus; hepatitis A
SARS (Sever Acute Respiratory Syndrome
Yellow fever; West Nile; hepatitis C

18. Classes of Animal Viruses
Single-stranded RNA – Template for mRNA
Envelope?
Examples/disease
Filovirus
Orthomyxovirus
Rhabdovirus
Yes
Ebola
Influenza
Rabies

19. Classes of Animal Viruses
Single-stranded RNA –Template for DNA (*backwards)
Envelope?
Examples/disease
Retrovirus
Yes
HIV (human immunodeficiency virus), AIDS

20. Retroviruses Highly complex reproductive cycle
Have an enzyme (reverse transcriptase)  transcribes RNA template into DNA (opposite direction!)
HIV causes AIDS (acquired immunodeficiency syndrome)

21. HIV Reproductive Cycle

22. Viral Disease in Animals
Some cause host to produce toxins
Some have toxic molecular components (envelop proteins)
Difficult to treat once infection occurs
Minimal success with antiviral drugs
Usually treat with multidrug approach – “cocktails”
Antiviral drugs typically target the nucleic acid of viruses and interfere with nucleic acid synthesis.

23. Vaccines Tool for preventing infection Main types
Harmless variant or derivative of a pathogen
Stimulates immune system response
Main types
Killed  Previously virulent micro-organisms
Attenuated  Live micro-orgs w/virus that has been cultivated to disable virulent properties
The system is then ready to fight if it encounters the virus in the future, as it “remembers” that virus.

24. Emerging Viruses Appear suddenly, new to medical science
Examples: HIV (1980’s); Ebola
Contributing factors:
Mutation of existing viruses
Spread from small, isolated population (globalization, travel, technology)
Spread of existing animal viruses to humans
Example: Spanish Flu pandemic (birds  humans)

25. Viroids and Prions Simple infectious agents
Viroids  Circular RNA molecules that infect plants
Abnormal growth patterns
Prions  Infection proteins that infect animals
Degenerative brain diseases (scrapie in sheep, mad cow, Creutzfeld-Jakob in humans)
Transmitted in food

26. Viroids and Prions Prions  Infection proteins that infect animals
Degenerative brain diseases
Scrapie (sheep)
Mad cow
Creutzfeld-Jakob (humans)
Kuru (humans)
Transmitted in food
Example: Beef to human; cannibalisms (New Guinea)
Worrisome  long incubation periods, difficult to identify sources of infection years later. Virtually indestructible, no known cure