1. VIRUSES

2. WHAT IS A VIRUS?
A virus is a non-living particle that depends on a host to reproduce
Why are viruses considered non-living?
They do not exhibit all of the characteristics of living things

3. CHARACTERISTICS OF LIFE
Living things have genetic material
Living things evolve
Living things reproduce
Living things respond to their environment
Living things are made up of cells
Living things use energy
Living things grow & develop
Living things maintain homeostasis
Living things display cellular organization

5. EXAMPLES OF VIRUSES Measles Gastroenteritis Mumps Polio Chicken Pox
Viral Meningitis
Common Cold
Rabies
Influenza
Smallpox
HIV/AIDS
Hepatitis
Herpes
Warts
Shingle

6. ORIGIN OF VIRUSES So where did viruses come from ???
Evidence suggests that viruses came from parts of cells
Genetic material of viruses is similar to genes
How do they exist outside of the cell?

7. VIRUS SIZE

8. STRUCTURE OF A VIRUS Viruses consist of two main parts:
Outer shell structure made up of a protein called a Capsid
Inner genetic material (DNA or RNA) made of Nucleic Acid

9. A virus that infects bacteria
BACTERIOPHAGE
A virus that infects bacteria

10. VIRAL INFECTION
In order to replicate, a virus must attach to a host cell
Attaches to specific receptors on host cell membrane
Viruses can be specific to certain species
Genetic material is injected into host cell, allowing the virus to replicate
Lytic or Lysogenic Cycle

11. LYTIC CYCLE Viral DNA is injected into host cell
Injected viral DNA instructs the host cell to make more viral DNA and viral structures
Structure assemble into viruses, cause the cell to burst (lyse), releasing new cells
Cells are now virus making machines!!!

12. LYTIC CYCLE

13. LYTIC CYCLE Short cycle
Active infections – symptoms appear in 1-4 days
Examples:
Common Cold
Influenza
Sinus Infections

14. LYSOGENIC CYCLE Viral DNA is injected into host cell.
Injected viral DNA integrates itself into chromosomes of host cell
The infected cell will then go through cell division (mitosis), producing new cells with integrated viral DNA
Infected cells may remain dormant, but eventually activate and enter the lytic cycle

15. LYSOGENIC CYCLE Latent (passive) infections
May remain dormant for years
Examples:
Herpes
HIV

17. RETROVIRUSES Capsid shell
Core of virus: RNA and reverse transcriptase enzyme
Reverse transcriptase uses the injected viral RNA to make viral DNA
Example:
HIV

18. VACCINES
Pathogen – Disease causing agent (virus, bacteria, protest, fungi)
Vaccine – Biological developments that allow the immune system to develop a “memory” of certain pathogens
Preventative Measure
Prevent you from getting a particular virus

19. VACCINES
Vaccines use altered versions of pathogens to trigger an immune response, without causing symptoms
Body produces antibodies, allowing you to fight off a virus when exposed

20. COMMON VIRAL VACCINES Measles Chicken Pox Influenza Polio Hepatitis
Smallpox
Rabies
HPV