Coupon Accepted Successfully!


Replication of viruses

Attachment-Mediated by binding of virion surface structures (ligands) to receptors on the cell surface therefore the attachment is specific





Epstein-Barr virus

CD 21/ complement receptor 2 (CR2)

Measles virus

CD 2

Rabies virus

Acetylcholine receptors


P antigen


B. Penetration

  1. After binding, the virus particle is taken up inside the cell
  2. In some viruses (sp. non-enveloped) there is receptor-mediated endocytosis, with uptake of ingested virus particles within endosomes
  3. In others, fusion of viral envelope with the plasma membrane. This requires the interaction of viral fusion protein with a second cellular receptor (eg, chemokine receptors for HIV)
C. Uncoating
  1. Occurs concomitantly or shortly after penetration
  2. It is the physical separation of the viral nucleic acid from the outer
  3. structural components of the virion such that it can function.
  4. Infectivity of the parental virus is lost at the uncoating stage
  5. Expression of viral genome and synthesis of viral components
  6. Specific mRNAs are transcribed from the viral nucleic acid
  7. Some viruses (negative sense RNA viruses) carry their own RNA polymerases to synthesize mRNA (conventionally designated positive sense). Viruses then use the cell components to translate the mRNA
  8. Initially early or non-structural proteins are synthesized these are enzymes which initiate the synthesis of viral components and induce the shut down of host protein and nucleic acid synthesis
  9. This is followed by replication of viral nucleic acid
  10. Finally there is synthesis of late or structural proteins which constitute daughter virion capsids 
D. Morphogenesis

Newly synthesized viral genomes and capsid polypeptides assemble together to form progeny viruses

E. Release

  1. Non-enveloped viruses lyse the infected cells and are released eg, poliovirus
  2. Enveloped viruses are released by the process of budding through the special areas of the host cell membrane, where virus encoded glycoproteins have been inserted.
    Enveloped viruses are not infectious until they have acquired their envelopes.
    1. Productive infection: results after infection of the permissive cells and leads to the production of infectious virus particles
    2. Abortive infection: results in failure of production of infectious progeny. It may either be due to infection of nonpermissive cell, which does not allow the expression of all the viral genes or because of the defective virus, lacking in some functional viral gene.
    3. Latent infection: it is characterized by persistence of viral genome in the infected cell. The infected cell survives, as there is expression of no or very few viral genes.
    4. Eclipse phase: between the stage of penetration to the release of daughter virion the infective virion is disrupted and its measurable infectivity is lost. This phase is called as eclipse phase.

Test Your Skills Now!
Take a Quiz now
Reviewer Name