1. VIRUSES
Chapter 24
Video

2. VIRAL STRUCTURE AND REPLICATION
Section 24.1

3. Discovering Viruses: Late 1800’s –
Something very small is causing diseases!
1935 –
It is not made of cells (living things).
TMV
Polio
HIV

4. What is a virus?
A nonliving particle composed of a nucleic acid and a protein coat.
Study of viruses = virology

5. Why do we study them? Cause disease in living organisms
Useful tools for genetic research

6. Are viruses living? NOPE! The Characteristic of life: growth
homeostasis
metabolism
organization
cells
reproduction
Viral characteristics: NO
YES
within host cell
NOPE!

7. Common Diseases Caused by Viruses
AIDS
Influenza
Chickenpox
Rabies
Polio
Mumps
Colds

8. Viral Structure All viruses have: Nucleic acid: (DNA or RNA)
Capsid: protein coat
Some viruses have:
Glycoprotein projections: signals
Envelope: Bilipid membrane surrounding the capsid.
Can fit “lock-and-key” with receptors on host cell.

9. HIV

10. Grouping viruses based upon…
SHAPE AND STRUCTURE:
Envelope present or not?
DNA or RNA?
Single stranded or double stranded?
How does it affect a human?
Rabies
Hepatitus
Herpes

11. Viral Size & Shape Size: Shape: 20 to 250 nm
Cannot be seen by a light microscope
Shape:
Determined by the genome (DNA) or capsid

12. Some shapes:
H1N1 or influenza
Video

13. Obligate Intracellular Parasites (huh?)
Viral Replication:
Obligate Intracellular Parasites (huh?)

14. Viral Replication in Eukaryotes
DNA viruses:
DNA  mRNA  proteins
Provirus: inserted viral DNA into host cell
RNA viruses:
mRNA  protein
Retroviruses:
RNA  DNA  mRNA  protein
Reverse transcriptase: enzyme
Example: HIV

15. Viral Replication in Prokaryotes
Bacteriophage: virus that infects bacteria
Helped scientists discover how viruses replicated
Two replication cycles
Lytic cycle: virulent
Lysogenic cycle: temperate

16. LYTIC
CYCLE
Animation

17. LYSOGENIC
CYCLE
Animation

18. Origin of Viruses Early viruses evolved from early cells
Viruses mutate quickly and frequently
Thus they evolve quickly
New strains formed this way

19. Viral Disease
Section 24.2
Flu Video

20. Vectors
An intermediate host that transfers pathogens from one organism to another
Examples:
Humans
Animals
mosquitoes
Fleas
ticks

21. Chicken Pox & Shingles Virus: varicella-zoster herpesvirus
Symptoms: rash & fever
Replication: Multiplies in lungs and uses blood network to reach skin
Transmission: direct contact with skin rash

22. Viral Hepatitis Virus: Hepatitis A, B, C, D, E Symptoms: Transmission:
Fever, nausea, jaundice, liver failure
Transmission:
Sexual contact (B,C,D)
Fecal matter in food & water (A,E)

23. AIDS Virus: HIV Transmission: through bodily tissues and fluids
retrovirus
Transmission: through bodily tissues and fluids
Symptoms: weakened immune system
Treatment: Drugs target reverse transcriptase OR
stop new capsids from forming
(protease inhibitors).

25. Viruses and Cancer
Cancer: when cells divide at an uncontrolled rate and form a tumor
Oncogenes: viral genes that cause cancer
Examples:
HPV  cervical cancer
Hepatitis B  liver cancer
Epstein-barr  lymphoma

26. Emerging Viruses
New viruses are being discovered every year as humans alter ecosystems
Examples:
HIV
Ebola
SARS
West Nile

27. Preventions and Treatments
Vaccinations: to prevent disease
Solution containing harmless version of virus
Causes an immune response in the body
Vector Control:
Wildlife population control
Drug Therapy:
Interfere with viral nucleic acid

28. 2 types of Vaccines: Inactivated (killed)- virus particles
Attenuated (live)- weakened form of the virus
Provide greater protection from disease
Has lead to the eradication of some diseases
ex) smallpox
Common vaccines: measles, mumps, rubella, polio, hepatitis A & B, chickenpox

29. How to protect yourself and others…
1. Wash your hands!
2. Don’t share tools (cups, toothbrushes)
3. Use protection when transmitting bodily fluids
4. Don’t become someone’s “Blood brother”
5. Avoid being bitten by any animal
6. Cover your mouth when sneezing

30. Non-virus Disease Causers:
Viroids – a short singular strand of RNA
smallest known particle to cause disease
infects mostly plants
Prions - protein particles
without a genome
mad cow disease

31. Practice Graphing Problem