Viral replication occurs in six sequential phases: (1) attachment to host cell receptors, (2) penetration via endocytosis or membrane fusion, (3) uncoating of the viral capsid and release of genetic material, (4) biosynthesis of viral mRNA, proteins, and new genomes using host cell machinery, (5) assembly of new virus particles, and (6) release through cell lysis or budding. The host cell provides energy and materials for the virus to replicate its proteins and nucleic acids.

1. VIRAL REPLICATION

2.  Viruses multiply in living cells, and the host
cells provide energy and helps in the synthesis
of viral proteins and nucleic acids.
 The viral replication can be divided into six
sequential phases:-

4. 1. Adsorption or attachment
 Attachment is a specific binding between viral
capsid proteins and specific receptors on the
host cell surface.

5. 2. Penetration
 Penetration is after attachment. Virions enter
the host cell through endocytosis or membrane
fusion.
 This is often called viral entry.

6. 3. Uncoating
 Uncoating is a process in which the viral
capsid is removed.
 The end-result is the release of viral genomic
nucleic acid.

7. 4. Biosynthesis
The following components are manufactured by
the virus through the host’s existing organells:-
 Virus mRNA is translated on cell ribosomes.
 The proteins which make up the virus particle
are manufactured and assembled.
 New virus genome are synthesized.

8. 5. Assembly
 In this stage, newly synthesized genome
(nucleic acid) and proteins are assembled to
form new virus particles.

9. 6. Release
 Viruses can be released from the host cell by
lysis, a process that kills the cell by bursting its
membrane and cell wall if present.
 The new viruses may invade or attack other
cells.

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