1. Viruses
Essential Questions: What is the structure of a virus and how do viruses cause infection?

2. The Sneeze: How Germs are Spread

3. What is a virus?
Tiny, non living particle that can cause disease

5. What is a virus?
Viruses are NOT considered to be living organisms because they do NOT meet ALL the characteristics of life

6. Naming Viruses
Often named for the disease they cause or the tissue they infect (NO LATIN NAMES!!!)
Examples: rabies virus and polio virus

7. Bacteriophage Virus that infects bacteria
Bacteriophages can infect E. coli bacteria making it harmful to humans.

8. Viral Structure Basic structure includes: Nucleic Acid Core
Protein Coat (Capsid)
Viral Envelope (found in some viruses) which covers the capsid

9. Viral Structure

10. Nucleic Acid Core Contains genetic material which is either DNA or RNA
The DNA or RNA is only instructions for making more copies of the virus –nothing else!!

11. Viral Shapes are determined by the capsid.
Polyhedral
Cylindrical
Spherical
Polyhedral Head w/Tail
Ex) Polio Virus
Ex) Tobacco Mosaic Virus
Ex) Influenza Virus (Flu)
Ex) Bacteriophage

12. Importance of Shape
Allows virus to recognize, attach, and invade a specific host cell.
Some are species specific.
Ex: Bacteriophage only infects bacteria
Some are also cell-type specific.
Ex: HIV virus only infects human immune cells

13. Attachment and Entry

14. Viral Infection
Once inside the host cell, two different processes may occur:
Some replicate immediately, killing the host cell (Lytic Cycle)
Others replicate in a way that does not kill the host cell immediately (Lysogenic Cycle)

15. Turn to a Partner
Explain the diagram below. Use the words attachment and entry, lytic and lysogenic cycles.

16. Lytic Cycle
In a lytic infection, a virus enters a cell, makes copies of itself, and causes the cell to burst.
Individuals get sick relatively quickly after infection
EX: Influenza (flu) & common cold

17. Lytic Cycle Animation

18. Lytic Cycle Attachment Entry/ Host DNA disintegrates
Viral Parts are Replicated
Assembly
Lysis and Release

19. Lytic Cycle Attachment: Virus recognizes and attaches to host cell
Entry: Viral DNA is injected into cell/ Host DNA is disintegrated
Replication: Viral genes and capsids are copied
Assembly: viral genes are put together inside protein coats
Lysis and Release: cell bursts and releases viral particles

20. Lytic Cycle Bacteriophage Bacterial DNA Nucleic acid Bacterial
host cell
Bacteriophage
Bacterial DNA B. A. C. D. E.
Lytic Cycle

21. Lytic Cycle Bacteriophage Bacterial DNA Nucleic acid Bacterial
host cell
Bacteriophage
Bacterial DNA
B. Entry
The bacteriophage
injects its nucleic acid
into the bacterial cell.
A. Attachment
C. Replication
D. Assembly
E. Lysis and Release
The host’s metabolic
machinery makes viral
nucleic acid and proteins.
New virus particles
are assembled.
The host cell breaks open and
releases new virus particles.
Lytic Cycle

22. Lysogenic Infection
Unlike lytic viruses, lysogenic viruses do not lyse (burst and kill) the host cell right away.
Instead a lysogenic virus remains inactive for a period of time.

23. Lysogenic Cycle Animation

24. Lysogenic Cycle Attachment & Entry Provirus formation DNA Replication
Cell Division
Lytic Cycle

25. Lysogenic Cycle Attachment & Entry
Provirus formation: Viral DNA is embedded into host DNA
DNA Replication: Viral DNA is copied along with host DNA
Cell Division: Cell divides with host DNA
Lytic Cycle: At any time, the Viral DNA leaves the host DNA and enters the lytic cycle

26. Lytic and Lysogenic Cycles

27. Turn to a Partner

28. Viral Diseases

29. HIV/AIDS HIV is a Retrovirus: Virus that contains RNA instead of DNA
Does not kill the host immediately. (Lytic or Lysogenic??)
HIV turns into AIDS when the virus goes into the Lytic Cycle

30. Polio virus infects and kills cells of the nervous system, producing paralysis.
Human papillomavirus infects cells in the outermost layer of the skin, producing an abnormal growth known as a wart.

31. Other Viral Diseases Common Colds & Influenza
Smallpox  high fever, head and body aches, sometimes vomiting, severe rash
Herpes simplex  Cold sores, fever blisters

32. Treatment/Prevention
Unlike bacterial diseases, viral diseases cannot be treated with antibiotics. WHY??
The best way to protect against most viral diseases is to prevent them with vaccines.
Once the viral disease has been contracted, only symptoms of the infection can be treated.
ANTIBIOTICS DO NOT WORK AGAINST VIRUSES!!!

33. Viruses

34. Comparison BACTERIA VIRUS Living, Prokaryotic Cells Reproduction:
Binary Fission (asexual)
Conjugation (sexual)
Treatments:
Anitbiotics
Causes:
Strep Throat
Tuberculosis
Lyme Disease
Bacterial meningitis
Tetanus
Non-living
Reproduction: MUST infect Host Cell
Lytic Cycle
Lysogenic Cycle
Treatments:
Symptoms ONLY!
Vaccines
Causes:
Common cold
Influenza (Flu)
AIDS
Warts
Hepatitis A, B, C
Polio
Chicken pox