Introduction to Virology – 1

  • Virus is an obligate intracellular parasite containing genetic material surrounded by proteins
  • Not living organisms, cannot produce energy or synthesize proteins independently, host cell machinery is needed
  • Viruses that infect bacteria are called bacteriophages




Difference between Naked Virus and Enveloped Virus



Enveloped Naked
Environmental stability Are destroyed by acids, detergents and drying (easily die) Stable to temperaure, acids, proteases, disinfectants and drying


Release from cell Budding Lysis


Spread to host Spreads in large droplets, secretions, transplanted organs, blood transfusions


Spread easily by direct contact, dust, small air droplets
Stability outside cells Must stay wet


Can dry out and retain infectivity


Effective immune respone May need antibody and cell mediated immunity for protection Antibodies are sufficient


Difference between bacteria and viruses



Obligate intracellular parasites Free living, can be parasitic


No ribosomes Has ribosomes


DNA or RNA, not both DNA and RNA


Need electronic microscopes Seen in light microscopes


10-100 genes 100-1000 genes


Tangled phylogeny


Natural phylogeny


Baltimore Classification of Viruses

2018-05-28 19 44 56


Replication of viruses

Image result for replication of viruses



All RNA viruses replicate in the cytoplasm except Orthomyxoviruses and Retroviruses that have replicative stages in nuclei

All DNA viruses replicate in the cytoplasm except Poxviruses that can replicate in the cytoplasm.


Image result for effect of animal viruses on cells


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