Question

During which stage of the viral life cycle would viral capsid proteins be manufactured?

A. Assembly

B. Biosynthesis

C. Release

D. Entry

Answer 1

Answer is B. Biosynthesis phase

Viruses do not undergo binary fission, but undergo a complex way of cell division. Replication of viruses passes through seven sequential steps:

Attachment - Penetration - Uncoating - Biosynthesis - Assembly - Maturation - Release.

1) Attachment:- The viruses have attachment site on their envelopes or capsid proteins that bind to the complementary receptor site present on host cell surface.

2) Penetration/ Entry:- Virus particles penetrate into host cells either by:. a) Phagocytosis - It occurs through receptor mediated endocytosis resulting in uptake of virus particle within the endosome.

b) Membrane fusion - Fusion of envelope protein with plasma membrane of host cell so that only nucleocapsid enters into cytoplasm.

c) Injection of nucleic acid - Bacteriophages only inject their nucleic acid ; while capsid remain attached to cell wall.

3) Uncoating:- ​​​​​​ The viral capsid gets separated and the nucleic acid is released into cytoplasm by action of lysosomal enzymes of host cell. ( This step absent in Bacteriophages)

4) Biosynthesis:- The following viral components are synthesized in this step:-

a) Nucleic acid

b) Capsid protein

c) Enzymes required for various stages of viral replication.

d) Regulatory proteins to shut down the host cell metabolism.

5) Assembly:- Viral nucleic acid and Capsid proteins are packaged together to form progeny viruses. It may take place in the host cell nucleus or cytoplasm.

6) Maturation:- Daughter virions get matured either in the host cell nucleus or cytoplasm or membranes.

7) Release:- Release of daughter virions occur either by:-

a) Lysis of host cell: Shown by non- enveloped viruses and Bacteriophages.

b) Budding through host cell membrane: Shown by Enveloped viruses.