1. Viruses

2. 1 nanometer (nm) = one billionth of a meter
What is a Virus?
1 nanometer (nm) = one billionth of a meter
100 nm
eukaryotics cells 10, ,000 nm
viroids nm
viruses nm
prokaryotics cells ,000 nm
prion 2-10 nm
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
No attachment = No infection

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

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 to find new host
Cycle repeats

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

13. The Lysogenic Cycle 1st step: Attachment = Same as lytic cycle
2nd Step: Entry = Same as lytic cycle

14. 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

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

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

17. HIV/AIDS

18. 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/lysogenic cycles.
In which stage…
does the host cell explode?
are virus proteins built to make new viruses?
is a provirus created?
does a virus connect with the host cell’s receptors?
Which two objects make up a provirus?
Which virus “life” cycle is considered the most harmful? Why?