Viruses are strands of genetic material surrounded by a protein coating that multiply by making copies of themselves inside host cells. They do not have cell structures like a nucleus or organelles. Viruses come in various shapes and sizes and can only be seen with an electron microscope. They infect animals, plants, fungi and bacteria by entering host cells and either immediately destroying the cell to release new virus particles or becoming dormant for years before being reactivated to spread infection further. While antiviral drugs can help treat viral infections, prevention through vaccinations, sanitation and isolation is most effective since treatment is difficult. Our bodies also produce interferons to protect uninfected cells when a virus is detected. Vaccines work by introducing a weakened form

1. Viruses
Chapter 8, Section 4

2. What are viruses?
• Strand of heredity material surrounded by a
protein coating.
• Multiplies by making copies of itself with the
help of a host cell
• Do not have a nucleus, other organelles or a cell
membrane
• Variety of shapes, small
• Discovered after the electron microscope was
invented

3. Active viruses
• What are the steps that an active virus takes to
destroy a cell and multiply?
• P. 232 chart at the bottom

4. Latent Viruses
• Inactive
• After it enters the cell, its hereditary material
becomes part of the cell’s hereditary material.
• It does not immediately make new viruses or
destroy the cell.
• Can be latent for many years
• Anything can activate it
• Cold sore—a latent virus has become active and
starts destroying cells, then becomes latent again

5. How do they affect organisms?
• Animals, plants, fungi, protists, bacteria
• Most viruses can infect only specific kinds of
cells---they are limited to one host species or to
one type of tissue within a species
• A few viruses affect a broad range of hosts
(rabies)
• Cannot move by itself, but can reach the host in
several ways: (p. 233 last paragraph)

6. Treatment and Prevention
• Antiviral drugs can help fight, but not widely
used because of side effects
• Prevention is best…treatment is very difficult
▫ Vaccinations
▫ Improve sanitary conditions
▫ Separating patients with diseases
▫ Controlling animals that spread disease

7. Natural Immunity
• We make interferons
▫ Proteins that protect cells from viruses
▫ Produced rapidly by infected cells and move to
noninfected cells in the hosts.
▫ This causes the non infected cells to produce
protective substances

8. Vaccines
• Used to prevent disease
• Made from weakened virus particles that cause
your body to produce interferons to fight the
infections.
• Measles, mumps, smallpox, chicken pox, polio,
rabies
• Edward Jenner made first one 1796

9. Research with Viruses
• Gene therapy: (p. 235)
• HIV/AIDS
▫ Attacks the immune system (protects body from
disease)
▫ The virus leads to AIDS which allows body to be
attacked.
▫ No cure
▫ Research will hopefully help