1. SB3d. Compare and contrast viruses with living organisms.
Chapter 20: Viruses
SB3d. Compare and contrast viruses with living organisms.

2. Is a virus alive?
Viruses are not considered living because they are missing key characteristics of living organisms.
Need a host cell to reproduce
Does not maintain homeostasis
Does not carry out metabolic activities
Does not have organelles or cytoplasm

3. Temperate- have to incubate
2 Categories of Viruses
Virulent- fast acting
Ex. Stomach flu
-Go through the lytic cycle
Temperate- have to incubate
Ex. Chickenpox
-Go through the lysogenic cycle before entering the lytic cycle

4. Viral Structure Nucleic Acid Capsid or Protein coat
Either DNA or RNA (not both)
Capsid or Protein coat
DNA or RNA is contained in a capsid which is composed of protein
Some viruses have an envelope
a lipid membrane that surrounds the entire virus particle
Many serious viruses have an envelope
Some viruses have tail fibers
These fibers act as syringes to inject viral DNA into its bacterial host
These viruses are often called bacteriophages.

5. Viral Structure cont. Examples: Influenza is an enveloped virus

6. Shapes of Viruses Icosahedral
is a geometric shape with twenty triangular flat sides.
Ex. Polio virus, a type of picornavirus

7. Virus Shapes cont. Helical Shaped like a cork screw
Ex. Tobacco Mosaic Virus (TMV)

8. Virus classification Based on three categories Enveloped or not
DNA or RNA
Helical or Icosahedral

9. Viral Reproduction Differs based on genetic material
All viral reproduction takes place inside the hosts cell (obligate intracellular parasite)
DNA viruses use their DNA to make RNA which directs the production of new viruses
Some DNA viruses combine their DNA with the hosts DNA to direct new virus synthesis
Example of DNA virus:
Herpes, the disease that causes chickenpox

10. Viral Reproduction cont.
RNA viruses use their RNA to direct the host cells ribosomes to make proteins that make new viruses
EX. Rabies, a type of rhabdovirus
Retroviruses are RNA viruses
They replicate by using an enzyme called reverse transcriptase
Reverse transcriptase uses the viral RNA to make a DNA template to make a new virus (mutates rapidly)

11. Retroviruses Type of RNA virus Retroviruses are RNA viruses
They replicate by using an enzyme called reverse transcriptase
Reverse transcriptase uses the viral RNA as a template to make viral DNA
The viral DNA is integrated into the host DNA to make new viruses
Ex. HIV

12. Bacteriophages Viruses that infect bacteria
They have been a significant tool in studying viral reproduction

13. The Lytic Cycle

14. Lysogenic Cycle

15. Treatment of viral disease
Viruses are difficult to treat because they are not living organisms
Viruses are unaffected by antibiotics
They lack all of the physical features that antibiotics act on
Vaccines and antiretroviral drugs are the only treatments
Antiretroviral drugs do not kill the virus, they interfere with its reproduction
Ex. AZT is used for HIV

16. Viroids Not viruses Composed only of one loop of RNA
Cause disease in plants
Ex. Orange blight, potato blight, etc.

17. Prions Prions are not viruses
Prions are simply malformed proteins that clump on to neurons and disrupt their function
Ex. Mad Cow disease (BSE)
Ex. Creutzfeld-Jacob disease (CJ disease)
All prion diseases cause neural degeneration