1. VIRUSES

2. INTRODUCTION Viruses – Latin for ‘poison’ Viruses – Latin for ‘poison’ Viruses are NOT classified as living (they lack cytoplasm, organelles and a cell membrane) Viruses are NOT classified as living (they lack cytoplasm, organelles and a cell membrane) Viruses cannot carry any metabolic functions and cannot reproduce on its own Viruses cannot carry any metabolic functions and cannot reproduce on its own Viruses require a living HOST cell to reproduce Viruses require a living HOST cell to reproduce

3. PARTS OF THE VIRUS An inner genetic material (nucleic acid - DNA or RNA) An inner genetic material (nucleic acid - DNA or RNA) Capsid – outer protein coat (provides shape and accounts for 95% of the virus) Capsid – outer protein coat (provides shape and accounts for 95% of the virus)

4. Some viruses have spikes or a mechanism to attach to host cells Some viruses have spikes or a mechanism to attach to host cells

5. Scientists classify viruses based on their unique characteristics, including: size and shape of the capsid shape and structure of the virus type(s) of diseases the virus causes type of genetic material (RNA or DNA) method of reproduction

6. Virus Shape and Structure: There are different shapes for viruses: 1) Helical (Spiral) 1) Helical (Spiral) 2) Enveloped 2) Enveloped 3) Phage (many sides with a tail) 3) Phage (many sides with a tail)

7. LOOKING IN… Viruses were first looked at under electron microscopes Viruses were first looked at under electron microscopes Size Range: 20 nm to 400 nm Size Range: 20 nm to 400 nm 1 nm = 1 billionth of a metre (10 -9 m) 1 nm = 1 billionth of a metre (10 -9 m) 1 mm = 1 millionth of a metre (10 -6 m) 1 mm = 1 millionth of a metre (10 -6 m) PICTURE THIS…You can fit almost 5000 influenza viruses on the head of a pin

8. VIRUS TYPES There are many virus types including: Retroviruses Retroviruses Reoviruses Reoviruses Adenoviruses Adenoviruses Rhabdoviruses Rhabdoviruses Orthomyxoviruses, etc. Orthomyxoviruses, etc. Each has a different inner nucleic acid, coat and structure Each has a different inner nucleic acid, coat and structure

10. BACTERIOPHAGE Special category of virus Word means ‘bacteria- eater’ – they infect and destroy bacterial cells Have a unique shape with a head and tail region

11. THE HOST Host – the cell on which another organism lives Host – the cell on which another organism lives Host Range – the limited # of host species, tissues or cells a virus can infect Host Range – the limited # of host species, tissues or cells a virus can infect Ex. Rabies virus – infects rodents, dogs, humans (it has a broad host range) Ex. Rabies virus – infects rodents, dogs, humans (it has a broad host range) Ex. Human Cold Virus – only infects cells of the upper respiratory tract Ex. Human Cold Virus – only infects cells of the upper respiratory tract Ex. HIV - only infects certain types of white blood cells (both have a narrow range) Ex. HIV - only infects certain types of white blood cells (both have a narrow range)

12. Methods of Reproduction Incubation period = the time it takes between when the virus infects a cell and when symptoms appear (when the virus ruptures the cell). There are two types of reproduction/replication:  The LYTIC cycle  The LYSOGENIC cycle

13. Lytic cycle:  ATTACHMENT & ENTRY  ATTACHMENT & ENTRY - The virus invades a host cell and injects its genetic material into the host cell. material into the host cell.  REPLICATION  REPLICATION - The host cell replicates the parts of the virus (synthesis of proteins and nucleic acids). proteins and nucleic acids).  ASSEMBLY:  ASSEMBLY: - New viruses are assembled in the host cell. - New viruses are assembled in the host cell.  RELEASE:  RELEASE: - The new viruses are released from the infected host cell to - The new viruses are released from the infected host cell to invade new cells invade new cells - The host cell is LYSED (bursts open) and dies. - The host cell is LYSED (bursts open) and dies. Note: 25-45 min. production of 100s of viruses

14. LYTIC CYCLE

15. LySOGENic cycle:  ATTACHMENT & ENTRY  ATTACHMENT & ENTRY - The virus invades a host cell and injects its genetic material into the host cell. material into the host cell.  PROVIRUS FORMATION  PROVIRUS FORMATION - The viral DNA is inserted into the host cell’s DNA and is referred to as a provirus.  DORMANCY:  DORMANCY: - The viral DNA remains dormant (inactive) for a period of time - The viral DNA remains dormant (inactive) for a period of time while replication of the host cell occurs without any harm to it. while replication of the host cell occurs without any harm to it. - The viral DNA is activated and extracted from the host cell by a - The viral DNA is activated and extracted from the host cell by a “trigger” or “stimulus”. “trigger” or “stimulus”. - This trigger stimulates the lytic cycle to begin and the infection - This trigger stimulates the lytic cycle to begin and the infection and death of the host cell. and death of the host cell.

16.  REPLICATION  REPLICATION - The host cell replicates the parts of the virus (synthesis of proteins and nucleic acids). proteins and nucleic acids).  ASSEMBLY:  ASSEMBLY: - New viruses are assembled in the host cell. - New viruses are assembled in the host cell.  RELEASE:  RELEASE: - The new viruses are released from the infected host cell to - The new viruses are released from the infected host cell to invade new cells invade new cells - The host cell is LYSED (bursts open) and dies. - The host cell is LYSED (bursts open) and dies.

17. LYTIC/LYSOGENIC CYCLE

18. HUMANS AND VIRUSES Many common human diseases are caused by viruses Many common human diseases are caused by viruses Viruses attack cells as it reproduces Viruses attack cells as it reproduces The destruction of the cells causes the symptoms of disease The destruction of the cells causes the symptoms of disease

19. VIRUSES AND CANCER Some viruses can cause cancer by adding specific genes to an infected cell transforming it into a cancer cell Some viruses can cause cancer by adding specific genes to an infected cell transforming it into a cancer cellVirus Cancer Type Human papillomavirus Cervical, skin, etc. Hepatitis B/C Liver cancer, lymphomas Epstein-Barr virus Burkitt’s lymphoma, Hodgkin’s lymphoma

20. ANTIBIOTICS and VACCINES  Antibiotics - substances inhibiting the growth of some microorganisms - They destroy bacteria NOT viruses  Vaccines - Liquid preparations of dead or weakened viral/bacterial cells that stimulate the body’s immune system to fight and produce antibodies

21. INFLUENZA VIRUS Physical/chemical differences result in flu types A,B,C Physical/chemical differences result in flu types A,B,C Strains described by protein coat, isolation year and location Strains described by protein coat, isolation year and location Destroys cells in upper respiratory tract so there is no sweeping of foreign particles Destroys cells in upper respiratory tract so there is no sweeping of foreign particles Symptoms – sore throat, congested lungs Symptoms – sore throat, congested lungs

22. Human Immunodeficiency Virus (HIV) Virus that causes AIDS (Aquired Immunodeficiency Syndrome) Virus that causes AIDS (Aquired Immunodeficiency Syndrome) Retrovirus is transmitted through variety of bodily fluids: blood, semen, vaginal fluid, breast milk Retrovirus is transmitted through variety of bodily fluids: blood, semen, vaginal fluid, breast milk HIV attacks the immune system HIV attacks the immune system Since 1981, almost 25 million people have died from AIDS Since 1981, almost 25 million people have died from AIDS

23. Other Viral Diseases Varicella zoster virus: chickenpox (children) and shingles (adults) Variola major virus: smallpox Poliovirus - Polio SARS coronovirus: Severe Acute Respiratory Syndrome (SARS)