1. Other biological particles
Viruses
Other biological particles

2. I. Virus A. Non-cellular infectious agent
B. Characteristics of all viruses
1) protein coat wrapped around DNA or RNA
2) cannot reproduce by itself
(not a living thing)
3) rapid replication= rapid evolution
new phenotypes/protein coats

3. II. Classification of Viruses
A. Based on
1. type of protein coat (capsid)
2. nucleic acid type
3. Envelope presence
Size ranges:
18nm – 350nm

4. III. Protein Coat = Capsid
A. simple virus -
1. hollow protein shell
2. protruding molecules that bind to host cell
B. complex virus –
1. head, neck, tail
2. bacteriophage
C. Enveloped Virus –
capsid surrounded
by layer of membrane

5. IV. Nucleic Acids A. Double/single stranded DNA
B. Double/single stranded RNA
C. Largest segment containing 4 genes

6. V. RNA Virus = Retrovirus
A. RNA can be …
1) used as a template to make viral mRNA
2) copied into DNA by reverse transcriptase
a. normal transcription converts DNA -> RNA
b. reverse transcriptase
converts viral RNA -> DNA
B. RNA polymerase and reverse transcriptase
have no proofreading so..
retroviruses mutate faster than DNA virus

7. HIV retrovirus in action

8. VI. Enveloped Viruses A. wrapped in a layer of host cell membrane
B. Intermembrane viral glycoproteins protruding out of membrane bind to host cell
C. Protovirus DNA integrates into host DNA
D. New viruses can leave host cell without lysis.

11. VII. HIV = enveloped retrovirus
A. HIV virus binds to cellular receptors on
white blood cells called T-cells.
B. T-cells = immune cells so Immune Deficiency
C. Protovirus integrates into T-cell DNA
D. We can not get to the protovirus so
very difficult to treat
E. protovirus can remain inactive in T-cells for years = HIV positive but not AIDS

12. VIII. Viral Multiplication (component assembly model)
A) Attachment – virus chemically recognizes host and locks on
B) Penetration- entire virus or virus DNA/RNA enters host cell
C) Replication & protein synthesis of Viral genes makes viral proteins and DNA/RNA
D)Assembly – new viruses put together
E) Release – new viruses leave host cell

13. IX. Lytic pathway
Steps proceed rapidly and end in lysing of cell

14. X. Lysogenic Pathway A. Viral DNA integrated into host DNA
B. Viral DNA copied each time host cell divides
C. Latent period = no symptoms but more and more host cells are becoming infected
D. Stimulus causes switch to lytic cycle and symptoms appear (Type I Herpes simplex)
cold sores
E. Can give new properties to host cells
ex. Increased pathogenicity in bacteria

16. XI. Transduction
Bacterial genes transferred from one bacteria to another via virus particles

17. XII. Viral mutation A. Viral proteins mutate rapidly due to
1. replication & transcription errors
2. rapid reproduction rates
3. obtaining genes from other viruses that occupy the same host cell – bird flu? swine flu?
B. New shots needed to help immune system recognize the changed virus

18. XIII. Infectious Prions
A. prions =proteins in nervous tissue
B. Infectious prions are misfolded
C. Misfolded prions deposit in brain
D. Misfolded prions can cause normal prions to misfold
E. Infectious Prions not destroyed by cooking!

19. Mad Cow! Mad cow disease = BSE (bovine spongiform encephalopathy)
Beef infected with BSE can cause vCDJ in humans
Don’t eat cow brains or spinal tissues!