Life cycle of Viruses

The General virus replication cycle

Picture
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The main steps for the replication of a virus


  1.  Attachment
  2. Penetration
  3. Uncoating
  4. Replications and expression
  5. Maturation
  6. Release



*The steps are carried out in chronological order as listed

1) Attachment

Attachment happens when the attachment sites on the virus caspid specifically binds to the receptor on the host cell. The attachment sites on the virus are typically proteins. However the receptor on the host cells may be either protein, glycoprotein or glycolipid.

An example would be-
The HIV virus which infects only the human T cells.
Its surface protein is the gp120.
this surface protein only interacts with the CD4 and the receptors on the T cell's surface.

2) Penetration

Penetration is the next step after the attachment of the virus. the viruses anter the host cells through the receptor via endocytosis or memberane fusion. this step may also be called viral entry. The penetration of viruses in plant and animals differ greatly. This is mainly due to the cell wall the plant cells has (it is made of cellulose). Many new kinda of penetration methods have been adapted by viruses to infect plants.

3) Uncoating

Uncoating involves the sepreation of the nucleic acid of the virus from its protein coat. There are 2 possible ways for this to take place.
  • The host lysozymes degrades the capsid protein, or
  • The action of the viral enzyme

4) Replication

Replication involves the synthesis of the vurial mRNA (except for the (+) sense RNA viruses). The assemble of the viral proteins and viral genome replication is involved in this stage.

5) Maturation

Maturation involves the assemble of the viral capsid and prepares the virus for its release.

6) Release

There are 2 typical ways virus releases itself from the cell after replication.
  1. Enveloped virus          : the release of virion is via budding; lipid envelope around the capsid
  2. Non-enveloped virus : the release of virion is via membrane rupture