1. Viruses

2. What is a Virus?
Virus: A biological particle composed of nucleic acid and protein
Intracellular Parasites: organism that must “live” inside a host

3. Are viruses alive? No Yes Not made of cells Can’t reproduce on own
Don’t metabolize energy
Don’t perform cellular processes
Reproduce with help of host
Contain nucleic acid
Adapt to surroundings
Have organization

4. Virus Parts
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

5. Viral Replication
Bacteriophages (viruses that attack bacteria) are often studied
Replication is similar with many animal viruses
Two “life” cycles: Lytic & Lysogenic
Dozens of phage viruses attacking an E. coli bacteria cell
The bacteria cell is destroyed and new viruses escape

6. The Lytic Cycle 1st Step: Attachment Virus lands on cell membrane
Virus attaches to a cell receptor
Virus acts as key; receptor acts as lock

7. The Lytic Cycle 2nd Step: Entry Virus enzyme weakens cell membrane
DNA/RNA enters the host cell
Another way viruses may enter a cell… through phagocytosis

8. The Lytic Cycle 3rd Step: Replication
Virus DNA/RNA uses ribosomes to make virus proteins
Virus proteins created by transcription/ translation
transcription
translation
Viral DNA
Viral RNA
Viral Proteins

9. The Lytic Cycle 4th Step: Assembly
Virus proteins are assembled into new viruses

10. The Lytic Cycle 5th Step: Release
Virus enzyme causes cell membrane to lyse (burst)
Viruses are released
Cycle repeats

11. All stages on one slide Attachment Entry Replication & Assembly
Release

12. The Lysogenic Cycle
1st step: Attachment
Same
2nd Step: Entry
Same

13. The Lysogenic Cycle 3rd step: Replication Provirus Created
Virus DNA combines with cell DNA
Infected cell divides by mitosis and copies the provirus
Each new cell will contain the provirus
Virus DNA
Pro-virus
cell DNA
Pro-virus
Pro-virus

14. The Lysogenic Cycle 5th Step: Release 4th Step: Assembly:
many cells burst releasing many more viruses
4th Step: Assembly:
new viruses are assembled in many cells

15. The viral DNA become active and starts making new viral proteins
The infected cells burst…releasing the new viruses

16. The Retrovirus

17. Retroviruses Type of RNA virus
Contain enzyme called “reverse transcriptase”
Steps
1) Virus RNA enters host cell
2) Reverse transcription changes the virus RNA into DNA
3) Virus DNA combines with cell DNA (provirus created)
4) Cell divides and copies the virus
5) Eventually, the viral DNA becomes active

19. What is AIDS? Acquired Immunodeficiency Syndrome AIDS results when:
1) Amount of T-cells drop (200 T-cells per 1mm³ blood)
2) Multiple symptoms/infections appear
Rash, fever, headache, sore throat, swollen lymph nodes
Therefore, the HIV virus causes the disease AIDS by killing your T-cells
New Exposures to HIV (2006)
Gender of those living with HIV (2003)