STUDY OF VIRUSES.pptx

The presentation describes the general properties, morphology, structure, lytic and lysogenic life cycles, cultivation of viruses (Animal, chick embryo, cell culture), cell cultures etc.

1. Study of Viruses Mr. A.T. Sharma Assistant Professor Department of Pharmaceutics Nanded Pharmacy College, Nanded

2. Viruses: Introduction Infectious agents seen by electron microscope 10 – 100 times smaller than bacteria Obligate intra-cellular parasites Can’t grow in artificial media Living or nonliving….??

3. General Properties Too small (20-300nm), electron microscope Either DNA or RNA, never both Obligate intracellular parasites, can grow in a host cell only Nucleus enclosed in a protein coat Can not generate energy or synthesize proteins Unaffected by antibiotics Multiply by complex process, no binary fission

4. Size and Shape

5. Structure Nucleic acid: DNA/RNA Capsid and Envelope: Capsomers, Envelope, Spikes

6. Morphology of Viruses Helical viruses (Symmetry) Polyhedral (Icosahedral) viruses Enveloped viruses Complex viruses

7. Helical viruses Long rods, rigid/ flexible NA in hollow, cylindrical, helical capsid e.g. Rabies virus, Tobacco mosaic virus

8. Icosahedral viruses Many sided/ polyhedral Polyhedral capsid with 20 triangular faces 12 corners Capsomers form equilateral triangles NA packed in central core as a pool of parallel loops E.g. Adeno virus, Polio virus

9. Enveloped viruses Spherical/ Pleomorphic Enveloped e.g. Influenza virus Herpes simplex virus

10. Complex viruses Complex structure T-even phages of E. coli Tadpole shape Hexagonal head, cylindrical tail Head- NA in capsid Tail- Hollow core, contractile sheath, base plate Prongs, tail fibres

11. Life Cycles of Bacteriophages Lytic/ Virulent cycle Temperate/ Avirulent/ Lysogenic cycle Lytic Cycle Attachment/ Adsorption Penetration Biosynthesis of phage components Maturation Release of progeny phage particles

12. Lytic Cycle

13. Attachment/ Adsorption Random collision and attachment Complementary chemical groups on receptors Flagella, pili, cell wall Host specificity Transfection

14. Penetration Injection of viral DNA Cell wall break by lysozyme Contractile sheath contracts Shell/ ghost Multiple hole – Lysis from without

15. Penetration

16. Biosynthesis of Phage Components Transcription of genome – early mRNA – early proteins DNA replication – late mRNA – proteins of capsid – head, tail, tail fibres Maturation DNA condensed, packaged into head Tail structures added, assembling Release of Progeny Phage Particles Sudden explosion/ bursting Lysozyme – Cell lysis Progeny phage released 20-60 minutes, 200 or more progeny

17. Lysogenic Cycle No bacterial cell lysis Viral DNA gets integrated with bacterial chromosome – prophage Prophage replicates synchronously – lysogeny – lysogenic bacterium Lysogenic conversion/ phage conversion Superinfection immunity Prophage remains latent in progeny Rare spontaneous event/UV light/ Chemicals – excision – lytic cycle……Spontaneous induction of prophage

18. Lysogenic Life Cycle

19. Cultivation of Viruses Laboratory animals Embryonated eggs Tissue culture Laboratory Animals Reed and colleagues (1990) – human volunteers Landsteiner and Popper (1909) – monkeys – polio virus Theiler – white mice (1903) – still used Rabbits, guinea pigs , ferrets Death, disease or lesions

20. Embryonated Eggs Goodpasture (1931) – Burnet Several sites Fertile chicken eggs incubated for 5 to 10 days Seal with paraffin wax Incubation Pocks on chorioallantoic membrane Haemagglutination in amniotic and allantoic fluid Allantoic cavity – influenza, paramyxo viruses Ammniotic sac – influenza virus Yolk sac – viruses, chlamydiae, rickettsiae Yellow fever, Rabies vaccine

21. Chick Embryo

22. Advantages: Simple to handle Economic, easily available Clean, sterile No feeding, caging No immune mechanism Several sites Disadvantages : No growth Bacterial contamination Contamination with mycoplasma, fowl viruses

23. Tissue Culture Steinhardt and colleagues (1913) Maitland (1928) Enders, Weller and Robbins (1949) Types: Organ culture – Organ/ tissue Explant culture – Minced tissue Cell culture

24. Cell Culture Tissue dissociated into cells Cells washed, counted, suspended in medium Monolayer sheet Primary cell cultures – e.g. Rhesus monkey kidney cell culture Diploid cell strains – e.g. Human embryonic lung cell strain (WI-38) Continuous cell lines – e.g. Human carcinoma of cervix cell line ( HeLa )

25. Cytopathic Effect

26. (Disclaimer: The images and diagrams in this presentation have been downloaded from the google source. I am grateful to all the publishers & the google.) Any Doubt..???