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Virus ppt

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Virus ppt

  1. 1. Rajendra Kr. Dangol BSc biotech,sem II Maitidevi,Ktm
  2. 2. Contents Definition of viruses Discovery of viruses Concept of viruses Characteristics of viruses Structure of viruses Symmetry of viruses Classification of viruses
  3. 3. What are viruses ? ● A virus is a non-cellular particle made up of genetic material and protein that can invade living cells.
  4. 4. Discovery of virusesn 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 he solution that passed through (the FILTRATE) was sterile. n1892 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.
  5. 5.  When repeated, filtrations produced the same results and nothing could be seen in the filtrates using the most powerful microscopes, nor could anything be cultivated from the filtrates, Iwanowski and associates concluded that they had discovered a new pathogenic life-form which they called by the unimaginative, but functional, name of "FILTERABLE VIRUS".
  6. 6. The concept of virus Edward Jenner (1798), introduced the term virus in microbiology. Virus in Greek means poison. Edward Jenner noticed that milk maids who infected with cowpox develop immunity against smallpox. He inoculated a boy with the vesicle fluid taken from the hand of infected maid. The boy developed sustained immunity against smallpox.
  7. 7. Edward Jenner assumed that the vesicle fluid that has been taken from the hand of the milk maid contained a poison ( virus ), that was responsible for immunity.
  8. 8. 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.
  9. 9. 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.
  10. 10. General structure of viruses Viruses composed of nucleic acid either DNA or RNA, surrounded by a protein coat called the capsid. The capsid is composed of small structural units called capsomeres. The capsid protects nucleic acid from inactivation by the outer physical conditions. CAPSOMERES
  11. 11. General structure of viruses Some viruses have additional lipoprotein envelope , composed of virally coded protein and host lipid. The viral envelope is covered with glycoprotein spikes 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.
  12. 12. 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.
  13. 13. Helical symmetry : The virus particle is elongated or pleomorphic (not spherical), and the nucleic acid is spiral. Caposomeres are arranged round the nucleic acid
  14. 14. complex symmetry: The virus particle does not confirm either cubic or helical symmetry.
  15. 15. 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.
  16. 16. References Caspar DLD: Design principles in virus particle construction. In Horsfall FL, Tamm I (eds): Viral and Rickettsial Infections in Man. 4th Ed. JB Lippincott, Philadelphia, 1975 . Mattern CFT: Symmetry in virus architecture. In Nayak DP (ed): Molecular Biology of Animal Viruses. Marcel Dekker, New York, 1977 . Morse SS (ed): The Evolutionary Biology of Viruses. Raven Press, New York, 1994 . Palmer EL, Martin ML: An Atlas of Mammalian Viruses. CRC Press, Boca Raton, 1988 . Nermut MV, Stevens AC (eds): Animal Virus Structure. Elsevier, Amsterdam, 1989 . THANK YOU

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