1. VIRUSES Biology 11

2. What is a virus? A particle which is very small. A particle which is very small. It shows no signs of life outside of a cell. It shows no signs of life outside of a cell. If it can get inside a cell, it takes over the can take over the cell’s metabolism. If it can get inside a cell, it takes over the can take over the cell’s metabolism. It uses a cell’s own organelles to replicate itself. It uses a cell’s own organelles to replicate itself. It can cause viral disease. It can cause viral disease.

3. Where are viruses? Everywhere…..in the air or in water depending on the virus. Everywhere…..in the air or in water depending on the virus. Some can “hide” inside living cells for weeks, months, even years. Some can “hide” inside living cells for weeks, months, even years.

4. What is a virus made of? A protein coat A protein coat Nucleic acid – either DNA or RNA Nucleic acid – either DNA or RNA Some viruses are very simple in structure and others, like bacteriophage, are more complex. Some viruses are very simple in structure and others, like bacteriophage, are more complex.

5. Virus Shapes FLU VIRUS HPV VIRUS BACTERIOPHAGE FLU VIRUS HPV VIRUS BACTERIOPHAGE

6. What diseases do viruses cause? Human Immunodeficiency virus (HIV) causes AIDS. Human Immunodeficiency virus (HIV) causes AIDS. Epstein-Barr virus causes infectious mononucleosis (“mono”) Epstein-Barr virus causes infectious mononucleosis (“mono”) Varicella zoster virus causes chicken pox Varicella zoster virus causes chicken pox There are many more which not only infect humans but plants, animals and bacteria. There are many more which not only infect humans but plants, animals and bacteria.

7. Defence against viruses The best defence is a healthy immune system. The best defence is a healthy immune system. Some vaccines have been developed for stable viruses: those that don’t mutate much over time. Some vaccines have been developed for stable viruses: those that don’t mutate much over time. Antibiotics are USELESS against viruses. Antibiotics are USELESS against viruses.

8. Viruses and Cancer Some viruses are cancer causing including Human Papilloma Virus which causes cervical cancer in woman. Some viruses are cancer causing including Human Papilloma Virus which causes cervical cancer in woman. There may be other viruses associated with cancers as well. There may be other viruses associated with cancers as well.

9. Virus Replication This is NOT reproduction. This is NOT reproduction. Replication starts with one virus particle injecting its nucleic acid into a cell. After only a few hours, the cell has made up to 300 virus particles which are released when the cell breaks open. Replication starts with one virus particle injecting its nucleic acid into a cell. After only a few hours, the cell has made up to 300 virus particles which are released when the cell breaks open. This is called the LYTIC cycle. This is called the LYTIC cycle.

10. Virus Replication Sometimes viruses do not replicate right away inside a cell. Sometimes viruses do not replicate right away inside a cell. These viruses insert themselves into the cell’s own DNA and “hide” until a time when they do undergo the lytic cycle. These viruses insert themselves into the cell’s own DNA and “hide” until a time when they do undergo the lytic cycle. This longer wait time is the LYSOGENIC CYCLE. This longer wait time is the LYSOGENIC CYCLE.

12. Virus Discovery In 1898, Loefler and Frosch discovered that foot and mouth disease in livestock In 1898, Loefler and Frosch discovered that foot and mouth disease in livestock (cattle, sheep) is caused by particles smaller than bacteria. (cattle, sheep) is caused by particles smaller than bacteria. In 1934, virus particles were first seen by an electron microscope. In 1934, virus particles were first seen by an electron microscope.

13. Steps in Viral Replication ATTACHMENT - virus recognizes a host cell and enters it or injects its nucleic acid inside. ATTACHMENT - virus recognizes a host cell and enters it or injects its nucleic acid inside. SYNTHESIS – the viral nucleic acid directs the cell to make virus parts SYNTHESIS – the viral nucleic acid directs the cell to make virus parts ASSEMBLY – the viral particles are assembled in the host cell ASSEMBLY – the viral particles are assembled in the host cell RELEASE – new virus particles are releases and host cell dies RELEASE – new virus particles are releases and host cell dies

14. How Viruses Get Around Most viruses are spread by direct contact such as body fluids. (HIV, HPV) Most viruses are spread by direct contact such as body fluids. (HIV, HPV) They can remain in the air and on surfaces for a long time. (common cold, flu) They can remain in the air and on surfaces for a long time. (common cold, flu) Some are carried by VECTORS like mosquitoes who can spread the virus by biting a series of different animals or people. (West Nile) Some are carried by VECTORS like mosquitoes who can spread the virus by biting a series of different animals or people. (West Nile)