1. Virus: Latin for “poison”
Viruses
Virus: Latin for “poison”

2. Viruses can infect all living things
These are all caused by viruses
Cold
Flu
Herpes
Some Cancers
HIV
Mumps
Chickenpox

3. Are all viruses bad? No!!! The tulip mosaic virus Produces highly
prized variegated tulips

4. History
1872 – Mayer and Koch found that a filterable agent caused disease in tobacco plants.
- The disease passed through filters that would trap bacteria
- What they found could not be grown in a laboratory
- Invisible even with the aid of a
microscope

5. More History…..
1935 The first virus was isolated from diseased tobacco plants
The Tobacco Mosaic
Virus

6. Are they living or not?
Living
They REPRODUCE at a fantastic rate, but only in living host cells.
They can mutate.
Non-Living
They are ACELLULAR, that is, they contain no cytoplasm or cellular organelles.
They carry out no metabolism on their own and must replicate using the host cell's metabolic machinery.
They possess DNA or RNA but never both.
They are NOT CONSIDERED LIVING by many scientists.

7. Structure? Inside: DNA or RNA Outside: protein coat
Spherical
rodlike
cubical
polyhedron
May have an outside membrane
Up close and personal with the flu virus

8. Size? too small to be seen with a light microscope
must use an electron microscope
much smaller than bacteria
Ex. Parvovirus 10nm
Poxvirus 250 nm

9. Examples
HIV
Polio
tobacco mosaic
bacteriophage

10. Viral activities?
Viruses do not carry out respiration or other metabolic activities
Viruses can only reproduce when inside a host cell (parasitic)

11. Virus cycles Virus Motto: Get In – Take Over – Get Out
lytic cycle- virus takes over all metabolic activities of host, makes copies of itself & destroys host cell

12. 5 Steps in the Lytic Cycle
Attachment to host
Entry of DNA into host
Replication
Assembly of new viruses
LYSIS: cell breaks open and releases new viruses into the organism or environment

13. Lytic cycle?

14. Virus Cycles
lysogenic cycle- viral DNA becomes integrated with host DNA; provirus
Virus Motto: Get In – (New Step of Hiding inside host) - Take Over – Get Out

15. 8 Steps in the Lysogenic Cycle
Attachment
Entry
Integration into the host cell’s DNA (prophage or provirus)
Replication of cells (including virus DNA)
Trigger to enter the Lytic Cycle
Replication of Virus
Assembly
Lysis

16. Lysogenic cycle?

17. Summary of Both

18. RNA Viruses (Retroviruses) ex. HIV
virus with RNA that can invade a cell with DNA
RNA undergoes reverse transcription to produce double-stranded DNA & become a provirus inside the host's nucleus
Normally: Viral DNA  RNA  Protein
 Retroviruses go the other way

19. RNA Viruses and Retroviruses
These viruses have a HIGH MUTATION RATE
There is no good PROOFREADING mechanism like there is when going from DNA to RNA
These means there are many different STRAINS of RNA viruses and Retroviruses
Makes VACCINES very difficult to develop

21. Review Questions
A virus is composed of two parts, what are they?
List some types of viruses that you know. At least 3
Can viruses reproduce on their own?
What are the two cycles of reproduction for a virus?
Why is the lytic cycle so harmful to a cell?

22. What are the characteristics of living things?
According to the characteristics, are viruses considered to be living? Why or why not.
Can a virus be cured with antibiotics?
What is used to protect against contraction of a virus?
Do viruses evolve? How do you know?