1. Viruses
Virus: A biological particle composed of nucleic acid and protein
pathogen: anything that causes sickness or disease

2. Viral Structure Figure 19-9 Virus Structures Tobacco Mosaic
T4 Bacteriophage
Influenza Virus
RNA
Capsid
proteins
Head/Capsid
Tail sheath
DNA
RNA
Tail fiber
RNA
Capsid
Surface
proteins
Membrane
envelope

3. Are viruses alive? No Yes Not made of cells or organelles
Can’t reproduce on own (without a cell)
Don’t metabolize energy
Don’t perform cellular processes
Reproduce
Have nucleic acid
Adapt to surroundings
Have organization

4. All Have:
1) Capsid: coat of protein that surrounds nucleic acid
2) Nucleic Acid: RNA or DNA
Some Have:
Tail Fibers: Used for attachment (not legs)
Shapes vary
Virus
Parts

5. The Lytic Cycle 1st Step: Attachment Virus attaches to a cell receptor
No attachment = No infection

6. The Lytic Cycle 2nd Step: Entry Virus enzyme weakens cell membrane
Genetic material (DNA or RNA) enters host cell

7. The Lytic Cycle 3rd Step: Replication
Virus DNA/RNA makes virus proteins by transcription/ translation

8. The Lytic Cycle 4th Step: Assembly
New virus proteins are assembled into new viruses

9. The Lytic Cycle 5th Step: Release Virus enzyme causes host to burst
Viruses are released to find new host…Cycle repeats

10. The Lysogenic Cycle 1) Attachment: Virus attaches to host cell
Host cell DNA
Pro-phage
2) Entry: Virus nucleic acid enter the cell, but combines with host cell DNA.

11. The host cell divides by mitosis, making a copy of the prophage each time.
Two infected cells.

12. Two cells divide by mitosis to make 4 infected cells.
Pro-phage
Pro-phage

13. Four infected cells divide by mitosis to make 8…and so on….

14. Virus DNA eventually becomes active and starts to create viruses following the stages of the lytic cycle.
All infected cells burst, releasing many more viruses to restart the cycle.

15. Lytic and Lysogenic Infections

16. Disease caused by specific viruses
Common Diseases Caused by Viruses
Disease caused by specific viruses
Section 19-3
Type of Virus
Nucleic Acid
Disease
Oncogenic viruses
Retrovirus
Adenoviruses
Herpes viruses
Pox viruses
DNA
RNA
Cancer
Cancer, HIV
Respiratory infections
Chickenpox
Smallpox

17. Vaccines Injection of a weakened or dead pathogen
Causes an immune response
Allows your body to make antibodies and memory cells against the disease