Viruses Living or Not

1. VirusesLiving 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 • A virus can not replicate on their own– they need to infect a HOST and use the hosts organelles and enzymes to do this!

7. Viruses - 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)

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

9. LYSOGENIC CYCLE See clip on desktop!!!

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

11. 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!

12. Virus Structure Envelope Nucleic acid Capsid

13. 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

14. Host Range • HIV, for example, only will enter cells that have a surface protein molecule called CD4. These molecules are found only on white blood cells. Thus, HIV will only infect white blood cells and not lung cells or other cell types. • Sometimes, a virus can mutate and change its host range. This appears to be happening with the avian flu virus (influenza A/H5N1) currently circulating. At first, the flu virus could infect only birds, but changes in the virus genome have allowed it to infect humans. So now, its host range has expanded. The change in host range of a virus can be one factor in the emergence of a new disease.

15. 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

16. 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.

17. 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

18. HSV1 vs HSV2

21. Human Papilloma Virus – 14yo boy

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

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

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

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

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

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

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

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

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

34. 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)

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