Viral replication is a complex process that involves six main steps: 1) adsorption/attachment where the virus binds to receptors on the host cell, 2) penetration of the virus into the cell, 3) uncoating to release the viral genome, 4) biosynthesis of new viral components, 5) assembly of new virus particles, and 6) release of progeny viruses from the host cell through lysis, degeneration, or budding. Each step involves specific mechanisms depending on whether the virus is enveloped or non-enveloped, DNA or RNA based.

1. Replication of virus
Clinical microbiologist -Manoj Mehta

2. VIRAL REPLICATION
Viruses do not undergo binary fission but undergo a complex way of cell division.
The replication of viruses can be divided into six steps.
Adsorption/attachment
Penetration:
Uncoating:
Biosynthesis
Assembly:
Release:

4. ADSORPTION/ATTACHMENT
o This process is also called as binding or adsorption.
o This is a specific process wherein the structures present on the surface of the virus
bind to the receptors on the surface of the host cell.
o The presence of appropriate receptors on the cell surface is a prerequisite for virus
attachment and subsequent infection
VIRAL REPLICATION

5. PENETRATION
There are possible mechanisms which the viruses use to enter a host cell.
These are:
1.Translocation is the process by which the whole non enveloped virus enters the
host cell by moving across the cell membrane.
2.Endocytosis is the engulfment of the virus by the invagination of a section of
plasma membrane
-common mode of penetration of non enveloped viruses.
3.Fusion is the endocytosis of enveloped viruses in which the envelopes of the
viruses fuse with the membrane of the endosome.
VIRAL REPLICATION

6. UNCOATING:
 Capsid is lysed (due to host lysozymes) and the nucleic acid is released
 After entry into the host cell, interaction of the virion with host components and
enzymes leads to a breakdown of the virion and exposure of the genome so that it
can express.
VIRAL REPLICATION

7. BIOSYNTHESIS
Biosynthesis of various viral components: i) nucleic acid, ii) capsid protein, iii)
enzymes iv) other regulatory proteins
Site of Nucleic acid replication
• In DNA viruses, the DNA replication occurs in the nucleus; except in poxviruses
(cytoplasm).
• In RNA viruses: The RNA replication occurs in cytoplasm; except in retroviruses
and orthomyxoviruses (nucleus).
VIRAL REPLICATION

8. ASSEMBLY
Assembly: Viral nucleic acid and proteins are packaged together to form progeny
viruses (nucleocapsids).
• Virion assembly may take place in the host cell in the cytoplasm or the cell
nucleus.
• DNA viruses are assembled in the nucleus except hepadnaviruses and poxviruses
(in cytoplasm)
• RNA viruses are assembled in the cytoplasm
VIRAL REPLICATION

9. RELEASE
There are three mechanisms by which mature virions can escape from the host cell
and start their cycle once again in new host cells. These are:
Cell Lysis
This occurs with most of the non enveloped viruses when the cell lysis occurs after
the completion of the replication of the viruses.
Cell Degeneration
Many viruses such as parvoviruses accumulate within the nucleus of the host and
are released only after the death of the cell which follows the degeneration of the
cell.
Budding
This is the mechanism by which most of the enveloped viruses exit from the host
cell without damaging the cell . This process takes a long time and does not kill the
host cell
VIRAL REPLICATION

10. Thank You