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C hair of Medical Biology, M icrobiology, V irology, and I mmunology

C hair of Medical Biology, M icrobiology, V irology, and I mmunology. MORPHOLOGY AND PHYSIOLOGY OF VIRUSES. Lecturer As. Prof. Olena V.Pokryshko. 3000 BC. Virus:. a noncellular small obligate intracellular parasites (genetic element)

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C hair of Medical Biology, M icrobiology, V irology, and I mmunology

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  1. Chair of Medical Biology, Microbiology, Virology, and Immunology MORPHOLOGY AND PHYSIOLOGY OF VIRUSES Lecturer As. Prof. Olena V.Pokryshko

  2. 3000BC

  3. Virus: • a noncellular small obligate intracellular parasites (genetic element) • contains either a RNA or DNA genome surrounded by a protective, virus-coded protein coat • has no its own biosynthetic machinery for energy generation and protein synthesis • For propagation virus depends on specialized host cells • infects a cell for its own replication, it has an extracellular state.

  4. Virus: • A virus particle containing nucleic acid surrounded by protein and other macromolecular components is called virion. • Viruses have a heavy dependence on host-cell structural and metabolic components. • Viruses can confer important new properties on their host cell. • Viruses may be non productive, latent, oncogenic, chronic or lytic.

  5. The main purpose of a virus is to deliver its genome into the host cell to allow its expression (transcription and translation) by the host cell.

  6. Methods of Analysis • Filtration Through Membranes of Graded Porosity • Sedimentation in the Ultracentrifuge • Direct Observation in the Electron Microscope The resolution is 5nm (1nm = 10-9 m) • Ionizing Radiation • X-ray crystallography

  7. Size of Viruses A small virus has a diameter of about 20nm. Parvovirus A large virus has a diameter of up to 400nm. Poxviruses

  8. Shape of Viruses • Spherical • Rod-shaped • Brick-shaped • Tadpole-shaped • Bullet-shaped • Filament

  9. Shapes of Viruses:Spherical

  10. Shapes of Viruses :Rod-shaped

  11. Shapes of Viruses :Brick-shaped .

  12. Tadpole-shaped

  13. Shapes of Viruses :Bullet-shaped

  14. Shapes of Viruses :Filament

  15. Some viruses infected human body

  16. Viruses

  17. Viral Structure • All viruses have two parts • a nucleic acid core • a protein coat called a capsid.

  18. Viral Structure • envelope • Viruses without an envelope are known as naked viruses

  19. Packaging or condensation of nucleic acid Protection of nucleic acid Transport nucleic acid from cell to cell Provides specificity for attachment Capsid functions

  20. Functions of envelope • Antigenicity some viruses possess neuraminidase • Infectivity • Resistance

  21. Virus Specific Enzymes • Some viruses have enzymes for • Penetration of the host cell • ex. Haemagglutinin, Neuraminidase, bacteriophages have Lysozyme for penetration of bacterial cell walls • Replication of viral nucleic acid • ex. Retroviruses carry Reverse transcriptase

  22. Chemical composition of viruses • Nucleic acids (1-40 %) • Proteins (70-90 %) • Lipids (15-35 %) • Glycolipids • Glycoproteins

  23. Viral proteins(70-90 %): • structural (capside, envelope, matrix, core, associated with nucleic acid) • non-structural • Structuralproteins are in virion in its extracellular state. • Functions: • protection of nucleic acid, • interaction with the membrane of susceptible cell • provide viral penetration into the cell, • have RNA- and DNA-polymerase activity etc. • Non-structural proteins are absent in virion in its extracellular state, but they are formed during viral reproduction • Functions: • provide regulation of viral genome expression, • are viral precursorproteins and can inhibit cell biosynthesis.

  24. Lipids(15-35 %) are in enveloped viruses in their envelope • Functions: • Stabilization of viral shell, • Protection of inner virion shells and nucleic acid, • Deproteinization of virions Carbohydrates molecules are in glycoproteins and glycolipids (3,5-9 %). They protect these molecules from cell proteases action

  25. How Viruses are classified • Main criteria presently used are: • Acid type. •   Size and morphology, including type of symmetry, number of capsomeres, and presence of membranes. •  Presence of specific enzymes, particularly RNA and DNA polymerases, and neuraminidase •  Susceptibility to physical and chemical agents, especially ether. •  Immunologic properties. •  Natural methods of transmission. •  Host, tissue, and cell tropisms. •  Pathology; inclusion body formation. •  Symptomatology.

  26. Viral Classification 1. By the type of nucleic acid • RNA or DNA; • single-stranded or double-stranded; • strategy of replication

  27. Viral Classification 2.By what type of outer covering they have • capsid - naked (simple) • envelope - complex

  28. Naked viruses( Non Enveloped ) • Adeno-associated Virus (AAV)AdenovirusCoxsackievirus - ACoxsackievirus - BEchovirusHepatitis A Virus (HAV)Hepatitis E Virus (HEV)Norwalk Virus

  29. California Encephalitis Virus Coronavirus Eastern Equine Encephalitis Virus (EEEV) Epstein-Barr Virus (EBV) Hepatitis B Virus (HBV) Hepatitis C Virus (HCV) Hepatitis Delta Virus (HDV) Rotavirus Rubella Virus Saint Louis Encephalitis Virus Smallpox Virus (Variola) Vaccinia Virus Herpes Simplex Virus 1 (HHV1) Herpes Simplex Virus 2 (HHV2) Cytomegalovirus (CMV) Human Immunodeficiency Virus (HIV) Human T-lymphotrophic Virus (HTLV) Influenza Virus (Flu Virus) Varicella-Zoster Virus (HHV3) Venezuelan Equine Encephal. Vir. (VEEV) Western Equine Encephalitis Virus (WEEV) Yellow Fever Virus Enveloped viruses

  30. Viral Classification 3. By the shape (symmetry) of the virus Determined by its capsid • Icosahedral (cubic) • Helical • Complex

  31. Helical Capsid In the replication of viruses with helical symmetry, identical protein subunits (protomers) self-assemble into a helical array surrounding the nucleic acid, which follows a similar spiral path. Such nucleocapsids form rigid, highly elongated rods or flexible filaments Tobacco mosaic diseases virus

  32. Helical Symmetry California Encephalitis VirusCoronavirusHantavirusInfluenza Virus (Flu Virus)Measles Virus ( Rubeola)Mumps VirusParainfluenza VirusRabies VirusRespiratory Syncytial Virus(RSV)

  33. Icosahedral Capsid • A polyhedron with 20 equilateral faces and 12 vertices • capsomers • ring or knob-shaped units made of 5 or 6 protomers • pentamers (pentons)– 5 subunit capsomers • hexamers (hexons)– 6 subunit capsomers

  34. Adeno-associated Virus (AAV)AdenovirusB19Coxsackievirus - ACoxsackievirus - BCytomegalovirus (CMV)Eastern Equine Encephalitis Virus (EEEV)EchovirusEpstein-Barr Virus (EBV)Hepatitis A Virus (HAV)Hepatitis B Virus (HBV)Hepatitis C Virus (HCV)Hepatitis Delta Virus (HDV)Hepatitis E Virus (HEV) Herpes Simplex Virus 1 (HHV1)Herpes Simplex Virus 2 (HHV2)Human Immunodeficiency Virus (HIV)Human T-lymphotrophic Virus (HTLV)Norwalk VirusPapilloma Virus (HPV)Polio virusRhinovirusRubella VirusSaint Louis Encephalitis VirusVaricella-Zoster Virus (HHV3)Western Equine Encephalitis Virus (WEEV)Yellow Fever Virus Icosahedral

  35. Capsid symmetry Matrix Lipid Glycoprotein Icosahedral Helical Naked capsid Enveloped

  36. Complex Symmetry Vaccinia virus T4 phage 200x400x250 nm, enveloped virus DNA With double membrane envelope. Binal symetry: head icosahedron, tail helical. Tail fibers and sheath used for binding and pins for injecting genome • many viruses do not fit into helical or icosahedralsymmetry • Examples: poxviruses and large bacteriophages

  37. Viral Classification 4. by who they infect Host Cell Specificity • Very specific--Three levels

  38. Viral Classification • DNA viruses • joins with host’s DNA • (goes) to RNA • RNA viruses • (goes) straight to protein with use of host’s ribosomes (in the cytoplasm) • Retroviruses • use enzymereverse transcriptase converts viral RNA to DNA and new DNA can become part of host DNA or go to RNA 5. By how they infect

  39. Classification of Viruses • By symptomatology - oldest • By routes of transmission • Plant, animal or bacterial

  40. Classification by Symptomatology • Dermatotropic - lesions of skin and mucous membranes • cold sores, shingles, warts • Pneumotropic • flue, parainfluenza, respiratory syncytial viral pneumonia, • Neurotropic - CNS • encephalitis • Viscerotropic - organs • hepatitis, infectious parotitis • Generalized

  41. Classification According to Routes of Transmission • Respiratory transmission • Influenza A virus • Faecal-oral transmission • Enterovirus • Blood-borne transmission • Hepatitis B virus • Sexual Transmission • HIV • Animal or insect vectors • Rabies virus, Western equine encephalitis, yellow fever, West Nile fever, dengue fever

  42. Life cycle of a virus • Process of virus replication • Lysogenic Cycle • Lytic cycle

  43. Viral Replication1. Attachment Virus comes in contact with receptor sites on surface of host cell (specific host cell) Virus attaches to cell

  44. Attachment of viruses • Chemical attraction • Have glycoprotein spikes or other attachment molecules that mediate attachment

  45. Viral Replication2.Penetration • Enveloped viruses join with cell membrane

  46. Viral Replication2.Penetration Penetration of animal viruses occur by direct penetration (a), fusion (b) between the viral envelope and the the host cell membrane or endocytosis (c) - clathrin-coated pits

  47. Viral Replication2. Inject DNA • Inject DNA • Naked virus injects nucleic acid into host

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