1. Virus Basics

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 or organelles
Can’t reproduce on own
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)
Shape & size varies
Virus
Parts

5. Virus Video

6. 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

7. 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

8. 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

9. 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

10. The Lytic Cycle 4th Step: Assembly
New virus proteins are assembled in the cytoplasm

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

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

13. Review
True or False: All viruses have a capsid, nucleic acid, and tail fibers.
List 3 reasons why viruses may be living? Nonliving?
What is the virus capsid made from?
What type of organism do phages infect?
In order list the stages of the lytic cycle.
In which stage…
does the host cell explode?
are virus proteins built to make new viruses?
does a virus connect with the host cell’s receptors?