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Virology is the study of viruses – submicroscopic, parasitic particles of genetic material contained in a protein coat and virus-like agents. It focuses on the following aspects of viruses: their structure, classification and evolution, their ways to infect and exploit host cells for reproduction, their interaction with host organism physiology and immunity, the diseases they cause, the techniques to isolate and culture them, and their use in research and therapy. Virology is considered to be a subfield of microbiology or of medicine.

Publié dans : Santé & Médecine
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  1. 1. VIROLOGY
  2. 2. Dr. Farzin Asghari Sana
  3. 3. Discovery of viruses  In 1884 C. Chamber land, in Pasteur's lab, discovered that if you passed a liquid containing bacteria through an unglazed PORCELAIN tube, the bacteria were COMPLETELY RETAINED and the solution that passed through (the FILTRATE) was sterile. In1892 D. IWANOWSKI applied this test to a filtrate of plants suffering from TOBACCO MOSAIC DISEASE with shocking results; the filtrate was FULLY CAPABLE of producing the ORIGINAL DISEASE in new hosts. Filtration of a mixture of bacteria and viruses. If a mixture of viruses and bacteria are filtered through a bacterial-proof filter (red), the viruses will pass through into the filtrate in the flask. Filtered beer is produced by a similar process. Dr. Farzin Asghari Sana
  4. 4. What are Viruses? Definition- Viruses are noncellular particles made up of genetic material and protein that can invade living cells. Discovery of Viruses Martinus Willem Beijerinck (1897) coined the Latin name “virus” meaning poison Dr. Farzin Asghari Sana
  5. 5. Tobacco Mosaic Virus Wendell Stanley (1935) discovered viruses were made of nucleic acid and protein Dr. Farzin Asghari Sana
  6. 6. Dr. Farzin Asghari Sana
  7. 7. Dr. Farzin Asghari Sana
  8. 8. Are Viruses Living or Non-living? Biologists consider viruses to be non-living because: -Are not cells -Do not grow or respond to their surroundings -Cannot make food, take in food, or produce wastes -Viruses do not respond to stimuli. They can only multiply if in another living cell Dr. Farzin Asghari Sana
  9. 9. General characteristics of viruses Viruses are smaller than bacteria, they range in size between 20-300 nanometer (nm) Viruses contain only one type of nucleic acid, either DNA or RNA, but never both. Viruses consist of nucleic acid surrounded by a protein coat. Some viruses have additional lipoprotein envelope. Viruses lack cellular organelles, such as mitochondria and ribosomes. Dr. Farzin Asghari Sana
  10. 10. General characteristics of viruses Viruses are obligate cellular parasites. They replicate only inside living cells. Viruses replicate through replication of their nucleic acid and synthesis of the viral protein. Viruses do not multiply in chemically defined media. Viruses do not undergo binary fission. Dr. Farzin Asghari Sana
  11. 11. Dr. Farzin Asghari Sana
  12. 12. Dr. Farzin Asghari Sana
  13. 13. Viroids ss RNA genome and the smallest known pathogens. Affects plants Prions Infectious particles that are entirely protein. No nucleic acid Highly heat resistant Animal disease that affects nervous tissue Affects nervous tissue and results in Bovine spongiform encephalitis (BSE) “mad cow disease”, Scrapie in sheep kuru & Creutzfeldt-Jakob Disease (CJD) in humans Dr. Farzin Asghari Sana
  14. 14. The capsid is composed of small structural units called capsomeres. The capsid protects nucleic acid from inactivation by the outer physical conditions. Dr. Farzin Asghari Sana
  15. 15. Some viruses have additional lipoprotein envelope , composed of virally coded protein and host lipid. The viral envelope is covered with glycoprotein spikes Dr. Farzin Asghari Sana
  16. 16. Dr. Farzin Asghari Sana
  17. 17. Symmetry of viruses Viruses are divided into three groups, based on the morphology of the nucleocapsid and the arrangement of capsomeres. Cubic symmetry: The virus particle is icosahedral in shape (almost spherical particle ) and the nucleic acid contained inside the capsid. The icosahedrons particle is composed of 20 equilateral triangles , 12 vertices and has 2,3,5 rotational symmetry Helical symmetry : The virus particle is elongated or pleomorphic (not spherical), and the nucleic acid is spiral. Caposomeres are arranged round the nucleic acid complex symmetry: The virus particle does not confirm either cubic or helical symmetry. Dr. Farzin Asghari Sana
  18. 18. Dr. Farzin Asghari Sana
  19. 19. Virion structures. Nonenveloped (naked) viruses consist of a genome surrounded by a protein shell, or capsid. Shown here is an icosahedral capsid, the most common type in nonenveloped viruses. Enveloped viruses have a membrane that surrounds the nucleocapsid, which can have an icosahedral, icosadeltahedral, or helical shape. The helical nucleocapsid, found only in most enveloped (−) RNA viruses, is formed by association of viral proteins, including RNA polymerase, with the genome. Dr. Farzin Asghari Sana
  20. 20. Dr. Farzin Asghari Sana
  21. 21. Assembly of the icosahedral capsid of a picornavirus. Individual proteins associate into subunits, which associate into protomers, capsomeres, and an empty procapsid. Dr. Farzin Asghari Sana
  22. 22. Dr. Farzin Asghari Sana
  23. 23. Dr. Farzin Asghari Sana
  24. 24. Dr. Farzin Asghari Sana
  25. 25. Dr. Farzin Asghari Sana
  26. 26. Baltimore classification Viruses were divided into six groups based on the their nucleic acid and m-RNA production. 1- ds-DNA viruses. 2- ss-DNA viruses. 3- ds- RNA viruses. 4- ss-RNA viruses with positive strands( positive polarity). 5- ss-RNA viruses with negative strands(negative polarity). 6- ss-RNA viruses associated with the enzyme reverse transcriptase. • (+) sense: Positive-sense viral RNA is identical to viral mRNA and thus can be immediately translated into protein by the host cell. • (-) sense: Negative-sense viral RNA is complementary to mRNA and thus must be converted to positive-sense RNA by an RNA polymerase before translation. Dr. Farzin Asghari Sana
  27. 27. Dr. Farzin Asghari Sana
  28. 28. Dr. Farzin Asghari Sana
  29. 29. Classification of major viral families based on genome structure and virion morphology. A, DNA viruses. L, linear genome; C, circular genome. B, RNA viruses. S, segmented genome. Dr. Farzin Asghari Sana
  30. 30. Morphology and relative size of viruses. Herpesvirus, adenovirus, poxvirus, retroviruses, and rhabdoviruses have characteristic shapes, whereas other viruses are distinguished by size, presence of an envelope, or an icosa(delta)hedral capsid. Dr. Farzin Asghari Sana
  31. 31. Dr. Farzin Asghari Sana
  32. 32. Some viruses have enzymes inside the virion. All ss- RNA viruses with negative polarity have the enzyme transcriptase ( RNA dependent RNA polymerase) inside virions. Retroviruses and hepatitis B virus contain the enzyme reverse transcriptase. Dr. Farzin Asghari Sana
  33. 33. VIROLOGY