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Viruses: Living or Not

Viruses: Living or Not. ???????. Viruses . Virus – Latin for “poison” Russian Biologist Dmitri Ivanovski (1892) – Tobacco Mosaic Disease…not determined to be a virus until 1930…known as the first virus to be discovered!~.

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Viruses: Living or Not

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  1. Viruses:Living or Not ???????

  2. Viruses • Virus – Latin for “poison” • Russian Biologist Dmitri Ivanovski (1892) – Tobacco Mosaic Disease…not determined to be a virus until 1930…known as the first virus to be discovered!~

  3. Characteristics of VirusesScientist that studies viruses is called a virologist! • Among the smallest biological particles (not cells) that are capable of causing harm in living organisms. • Virus particles are called virions • 5000 influenza viruses can fit inside the head of a pin!

  4. Studying the “T4-Bacteriophage • Also known as: “eaters of bacteria” have a head and tail region – (serve as the principle experimental object in studying viruses) Why study it?

  5. VIRUSES & CELLS

  6. Not Considered Living • A virus is not a bacteria, fungus, protist, plant or animal. • They do not carry out cellular functions. • They do not grow or undergo division

  7. Not Considered Living • Viruses cannot replicate on their own– they need to infect a HOST and use the hosts organelles and enzymes to do this! • Obligate intracellular parasites

  8. Viral Disease Viral infections generally behave in 2 ways: 1. Viruses reproduce and cause disease immediately (lytic or active) 2. Viruses integrate into the host cell (lysogenic or dormant)

  9. Viral Replication – Lytic Cycle Infection See clip on desktop!!

  10. LYSOGENIC CYCLE See clip on desktop!!!

  11. Quick Review…. • http://www.phschool.com/webcodes10/index.cfm?fuseaction=home.gotoWebCode&wcprefix=cbp&wcsuffix=6192

  12. What Organisms and Host Cells Do Viruses Infect? • Infection by viruses • viruses infect bacteria, plants, animals and other living organisms in order to reproduce • a given virus usually infects a limited number of species. • within a host organism, usually only a limited number of cell types are susceptible to infection by a given virus • Host range • array of host cells that a particular virus can infect • determined by a “lock-and-key” fit between the virus and a receptor on the surface of a host cell • Ex: one type of herpes virus causes cold sore, a different one causes genital sores!

  13. Virus Structure Envelope Nucleic acid Capsid

  14. How are Viruses Classified? • Genetic Material • DNA or • RNA (retrovirus/mutates frequently) • But not both • Capsid (Protein) Structure = 95% of virus • Helical (rod shaped) • Polyhedral (spherical) • Complex • Presence or absence of a membranous envelope surrounding the capsid **No envelope = naked virus Helical Marburg virus Polyhedral SV40 virus Complex bacteriophage

  15. Host Range • HIV, for example, only will enter cells that have a surface protein molecule called CD4. • CD4 are only found on white blood cells. • Sometimes, a virus can mutate and change its host range. • Avian flu virus (influenza A/H5N1) – at first only birds, then humans • Swine flu (influenza A/H1N1) – pigs to humans. • The change in host range of a virus can be one factor in the emergence of a new disease.

  16. What Diseases are Caused by Viruses? • Infectious diseases RNA viruses (retroviruses) DNA viruses AIDS Respiratory Disease Influenza (flu) Smallpox Common cold Chickenpox Polio Mononucleosis Measles Cold Sores • Tumor Viruses – cause Cancer ex: HPV • Oncoviruses

  17. How Can Viral Diseases Be Prevented and Treated? • Good hygiene • Avoid contact with contaminated food, water, fecal material or body fluids. • Wash hands frequently. • Vaccines • Stimulate natural defenses with in the body. • Contain a component of or a weakened or killed virus particles. • Are developed for many once common illnesses such as smallpox, polio, mumps, chicken pox. • Not available for all viruses. • Anti-viral drugs (but not antibiotics) • Available for only a few viruses. • Inhibit some virus development and/or relieve symptoms.

  18. How Do New Viruses Emerge? • Through mutation and evolution of genetic code…changes to the protein coat therefore changing the “lock and key” fit! And no longer recognizable to a host’s immune system! • Human population expanding into previously uninhabited areas (increased contact between humans and animals) • Through the detection of previously unrecognized viruses

  19. HSV1 vs HSV2

  20. Human Papilloma Virus – 14yo boy

  21. Polio Virus Six countries (Afghanistan, Egypt, India, Niger, Nigeria, and Pakistan) still have polio circulating

  22. VIRUS MINI QUIZ • THE PRIMARY FUNCTION OF ALL VIRUSES IS TO REPLICATE!!

  23. MINI QUIZ… 2. WHAT IS THE TYPICAL/COMMON VIRUS THAT STUDENTS STUDY WHEN LEARNING ABOUT VIRUSES? T4 Bacteriophage

  24. MINI QUIZ… 3. IN ORDER FOR A VIRUS TO REPLICATE IT NEEDS TO BE IN A HOST CELL

  25. MINI QUIZ… 4. VIRAL REPRODUCTION THAT KILLS THE HOST CELL IS CALLED THE Lytic CYCLE!

  26. MINI QUIZ… 5. WHEN VIRAL DNA IS EMBEDDED INTO A HOST CELL’S DNA IT FORMS A PROPHAGE

  27. MINI QUIZ… 6. ANOTHER NAME FOR INFLUENZA IS FLU VIRUS

  28. MINI QUIZ… 7. 3 WAYS VIRUSES CAN BE TREATED/PREVENTED ARE…. • Hygiene • Vaccines • AntiVirals

  29. MINI QUIZ… 8. SCIENTISTS THAT STUDY VIRUSES ARE CALLED VIROLOGISTS

  30. MINI QUIZ… • 3 WAYS THAT VIRUSES CAN BE TRANSMITTED ARE…. -- droplets in the air (e.g. cold, flu, tuberculosis) -- via food or water (e.g. Salmonella, food poisoning) -- via mosquitoes, ticks (e.g. malaria, West Nile virus, Lyme disease) -- physical contact (e.g. pinkeye, herpes, chickenpox, sexually transmitted diseases)

  31. MINI QUIZ… 10. A VIRUS THAT HAS ONLY A CAPSID SURROUNDING IT’S GENETIC INFORMATION AND NO ENVELOPE IS CALLED A NAKED VIRUS.

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