1. Viruses
Chapter 19

2. What do you know about viruses?

3. Viral Characteristics
Non-living
Non-cellular
Cannot grow or reproduce on its own
No metabolism
Cause disease
AIDS, colds, flu, measles, mono
Cause cancer
Cervical, leukemia
T4 bacteriophages infecting an E. coli bacteria

4. 19.1
A virus consists of a nucleic acid surrounded by a protein coat

5. Viral Structure Genetic material Capsid Envelope Mode of entry
DNA or RNA
Capsid
Protein coat surrounding nucleic acid
Envelope
Some; comes from host cell membrane
Mode of entry
Spikes, receptors, etc.

6. 19.2
Viruses replicate only in host cells

7. Lytic Cycle Transduction
Viral replication that rapidly kills the host cell causing it to lyse or burst
Involves 5 steps
Virus attaches to host cell membrane
Virus injects its DNA into host cell
Virus DNA inactivates host cell's DNA & uses host's raw materials & ribosomes to make viral DNA, capsids, tails, etc.
New viral parts are assembled into new viruses
Viral enzymes made by host lyse and release new viruses
Transduction
DNA from one bacteria (host) is transferred to another by a virus after a lytic cycle

8. Lytic Animation

9. Lysogenic Cycle
Viral replication that allows replication of the genome without killing the host
Involves 3 steps
Bacteriophage infects bacteria cell and injects its DNA
DNA becomes incorporated into bacterial chromosome
Prophage
Bacteria reproduces, making more copies of viral DNA
Lytic cycle can be triggered

10. Lysogenic Animation

11. Transduction Animation

12. Viruses & Genetic Variation
Mutations
Replicate rapidly, many errors
Leads to evolution (sometimes quickly, like the flu)
Recombination
Viruses pick up genes from each other
Can allow them to infect new hosts

13. Retroviruses Contain RNA
Reverse transcriptase enzyme uses the RNA to make DNA
Normal flow of information is DNA  RNA  Protein
Especially prone to errors in replication
Use the host cell's ribosomes & raw materials to make viral proteins
Cause some cancers & AIDS

14. Retrovirus Animation

15. HIV Infection