1. Viruses What is the structure and function of viruses?
How Germs Spread

2. What is a virus? Tiny, nonliving particles
Need a host cell to reproduce
Named based on disease or tissue – NO Latin names
Ex. bacteriophage, rabies virus, adenovirus

3. Viral Structure Core - nucleic acid DNA/RNA Protein coat - capsid
Some larger viruses have an outer viral envelope

4. Capsid
Nucleic
acid
Envelope

5. Viral Shapes Importance - recognize specific host cell
Cell-type specific or species specific
Ex: polio virus – human nerve cells
Ebola virus

6. Common virus shapes Polyhedral Cylindrical Spherical
Polyhedral w/a tail

7. Attachment and Entry

8. Lytic Cycle Attachment Entry Replication Assembly Lysis and Release
Ex. flu or Influenza

9. Bacteriophage Bacterial DNA Nucleic acid Bacterial host cell 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.

10. Lytic Cycle Animation

11. Lysogenic Cycle Attachment & Entry Provirus forms Cell Division
Provirus leaves host DNA – why?
Lytic cycle

12. Lysogenic Cycle Animation

13. Lytic and Lysogenic cycles

14. B. Provirus Formation A. Attachment and Entry C. Cell Division
LYSOGENIC CYCLE
LYTIC CYCLE
The provirus leaves
the chromosome.
Viral nucleic acid and
proteins are made.
The cell breaks
open releasing
viruses.
A lysogenic virus
injects its nucleic
acid into a bacterium.
Bacterial host
chromosome
A. Attachment and Entry
B. Provirus Formation
Provirus
The viral nucleic acid is called
a provirus when it becomes
part of the host’s chromosome.
C. Cell Division
Although
the provirus
is inactive,
it replicates
along with
the host cell’s
chromosome.

15. HIV virus  AIDS Lysogenic cycle Retrovirus – RNADNA
HIV bud off w/out killing white blood cells

16. Other Viral Diseases Common Colds & Influenza Smallpox
Human papillomavirus  warts
Herpes simplex  Cold sores fever blisters

17. Defenses & Treatments Phagocytes white blood cells Antibodies
Vaccine –before exposure
Antibiotics do NOT work
Treat symptoms
Wash hands – remember the video clip