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Distinguishing characteristics of viruses • Obligate intracellular parasites • Extreme genetic simplicity • Contain DNA

Distinguishing characteristics of viruses • Obligate intracellular parasites • Extreme genetic simplicity • Contain DNA or RNA • Replication involves disassembly and reassembly • Replicate by "one-step growth”. Steps in replication • Attachment • Penetration • Uncoating

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Distinguishing characteristics of viruses • Obligate intracellular parasites • Extreme genetic simplicity • Contain DNA

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  1. Distinguishing characteristics of viruses • Obligate intracellular parasites • Extreme genetic simplicity • Contain DNA or RNA • Replication involves disassembly and reassembly • Replicate by "one-step growth”

  2. Steps in replication • Attachment • Penetration • Uncoating • (Transcription, Translation) • Genome replication • Assembly • Release

  3. Reasons to study viruses • Cause infectious diseases • Some viruses cause cancer • Provide accessible experimental systems • Virus-based vectors

  4. Viruses differ from otherinfectious organisms in their... STRUCTURE,BIOLOGYand REPRODUCTION.

  5. The SYMMETRY OF THE VIRUS PARTICLEcan be... ICOSAHEDRAL,

  6. HELICAL or

  7. Viruses have genetic materialwhich can be either... RNA       or       DNA.

  8. Viral genome strategies •dsDNA (herpes, papova, adeno, pox) •ssDNA (parvo) •dsRNA (reo, rota) •ssRNA (+) (picorna, toga, flavi, corona) •ssRNA (-) (rhabdo, paramyxo, orthomyxo, bunya, filo) •ssRNA (+/-) (arena, bunya) •ssRNA (+RTase) (retro, lenti)

  9. Nucleic acid Strandedness Topology Sense Examples • DNA Single-stranded Linear + & - Parvoviruses • DNA Double-stranded Linear + & - Adenoviruses • Herpesviruses • Poxviruses • DNA Double-stranded Circular + & - Papovaviruses • RNA Single-stranded Linear + Picornaviruses • Togaviruses • RNA Single-stranded Circular - Hepatitis delta virus • Viroids • RNA Single-stranded Linear - Rhabdoviruses • Paramyxoviruses • RNA Single-stranded Linear and - Orthomyxoviruses • segmented Bunyaviruses • RNA Single-stranded Linear and Ambi- Arenaviruses • segmented sense • RNA Double-stranded Linear and + & - Reoviruses • segmented Rotaviruses

  10. This genetic material is... packed into protein capsules calledCAPSIDS.

  11. Because viruses lacknormal cellular material, for example... cell membranes,... cytoplasm and the... machinery forsynthesizing macromolecules,they cannot live on their ownbut need a living organismto survive and replicate. They are therefore calledOBLIGATORYINTRACELLULARPARASITES.

  12. they have a special moleculecalled a RECEPTORto attach tothe cellular surface.

  13. After attachment the virusmay enter the cell by aprocess called ENDOCYTOSISand then be released intothe cytoplasm.

  14. NORMAL CELLS

  15. ABNORMAL CELLSThe cells become round and enlargeand may eventually die whenthe new viral particles are released

  16. The many viruses that infect man, ... can be classified according tothe NUCLEIC ACID present- either DNA or RNA.

  17. The size of viruses can range from... very small, for examplethe POLIOVIRUS at 30 nanometerto quite large for examplethe POXVIRUS at 400 nanometer.

  18. Viruses enter the body of the hostin a variety of ways, for example...

  19. The commonest forms oftransmission are via... INHALED DROPLETSin sneezing of choughingfor example the COMMON COLDor INFLUENZA VIRUSES.

  20. or by... drinking water oreating raw food, for example,HEPATITIS A and POLIOVIRUS.

  21. The commonest forms oftransmission are also via... sexual intercourse for exampleHIV and HEPATITIS B and...

  22. also... vertical transmission -from mother to baby for exampleHIV, HEPATITIS B and RUBELLA...

  23. also... bites of vector arthropods such asmosquitoes for example YELLOW FEVER,RIFT VALLEY FEVER and DENGUE.

  24. After contracting a viral infectionthe following may happen to the host: ... the virus may becomeLATENT in its host and...

  25. REACTIVATE at a later stage to giverise to symptoms, for example...

  26. the herpes simplex virus gives rise to FEVER BLISTERS and...

  27. the chickenpox virus resultsin SHINGLES.

  28. Infection may lead to the deathof the host e.g. HIV infected individuals mostly die after8-10 years

  29. HEPATITIS B virus infection leads to chronic hepatitis in 5-10% of infected patients and a small percentage of these may eventually develop primary liver cancer.

  30. Most viral infections... do not lead to such seriouscomplications and the host...

  31. get well after a period of sicknessto be immune for the rest of their lives.Examples are MEASLES INFECTION,RUBELLA or German measles,MUMPS and many others...

  32. Virus-host cell interactions • Productive Lethal to the cell - typical lytic virus Not lethal to the cell - transformation - persistence • Non-productive Lethal to the cell - apoptosis Not lethal to the cell - transformation - latency

  33. Effects on host cell metabolism •DNA metabolism •RNA metabolism •Protein metabolism Cellular and organismal defenses •Avoidance, public health measures •Immune system •Anti-viral drugs •Interferon system

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