Replication of Viruses

REPLICATION OF VIRUSES

Viruses rely completely on living host cells for their replication. The small genome size

put them at disadvantage. Also, they lack organelles and other machineries required for

protein synthesis. Although some viruses enter the host cell with few virus-encoded

enzymes, others do not possess any protein of their own and therefore depend completely

on those produced by the host cell. Virus replication is facilitated by the host cell which

provides the required energy and synthetic machinery and sometimes essential enzymes

for replication and also by the viral nucleic acid which carries the genetic information

required for the synthesis of viral components.

The replicative cycle of a virus can be divided into a number of stages:

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1. Attachment to surface receptors on a susceptible host cell

2. Entry into the cell

3. Uncoating of the viral nucleic acid

4. Transcription of the viral nucleic acid and translation of mRNA for synthesis of virusencoded

proteins

5. Replication of the viral nucleic acid into progeny/daughter nucleic acid

6. Assembly of newly formed virus particles

7. Release of the daughter virions from the host cell

The duration of the replicative cycle ranges from 6 to 40 hours. Infection of a susceptible

host c ell is usually followed by an eclipse phase.

Eclipse phase: this is the initial stage of virus replication whereby the infecting virus

loses its physical identity and most or all of its infectivity. At this time, no virus is

detectable in the infected host. The eclipse phase is followed by the productive stage as

new virus particles are formed and released from the cell.

for details please see the next post.