Viral Replication

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As the virus do not have any cellular structure, the process of reproduction in virus is termed as viral replication. Viral replication only takes place within the host and normally initiated by nucleic acid core and it is the inactive component of the virus. In case of bacteriophage the phenomenal of viral replication can be studied quite clearly. There are six major stages for this replication, those are:

1) Invasion or absorption.
2) Penetration.
3) Eclipse or biochemical state.
4) Maturation.
5) Assembly.
6) Lysis or release.

Now we shall go for the description of each stage.

1) Invasion or absorption: – in this phase of viral replication the virus particle invades the host’s cell, settles down on the bacteria cell wall surface with the help of tail and penetrates the host’s cell surface with the infection hook. Between the virus and bacterial cell surface receptor a chemical bond is formed from which makes the virus host specific. In case of plant and animal virus, the media of transport is water, food or air. A mechanical wound created by any insect or other organism, who which the absorption occurs.

2) Penetration: – penetration is the second phase of viral replication. This is the place when the bacterial cell wall is digested by an enzyme lysozyme produced from the tail fibre by hydrolysis of the peptidoglycan and a hole is created. The tail sheath contracts and the inner enter the cytoplasm of the bacterial cell. The DNA descends through this cylindrical core and enters the bacterial cell. Outside the bacterial cell the part of the bacteriophage remaining is non-infective and is called extracellular virion, on the other hand the entering the bacterial cell is infected and is called intracellular virion.

3) Eclipse: – this phase of viral replication is marked with the entry of the nucleic acid core into the bacterial cell, which is followed by the lysis of the bacterial DNA. In this case the bacterial metabolism becomes totally paralysed and the viral DNA takes complete metabolic control over bacterial cell. This phase is long in lysogenic cycle and short in lytic cycle.

4) Maturation: -- In this phase the components of the virus particle are synthesized, the bacterial DNA divides and transformed to form the viral DNA and the protein is transformed to viral capsid. The bacterial DNA is utilized to synthesize viral capsid protein alternatively.

5) Assembly: -- In this phase of viral replication the components assemble with each other in a gradual stepwise manner. The steps are as follow:

i) Condensation of viral DNA.
ii) Formation of head by aggregation of monomers.
iii) Assembly of tail and its head attachment.
iv) Formation of the tail sheath.
v) The base plate attachment.
vi) Fixation of the tail fibres and the infection pegs.

6) Lysis or Release: -- This is the last phase of viral replication, in which the phage particles get completely assembled and the bacterial cell wall ruptures with the enzyme lysozyme. Total time taken for this replication is 20 to 50 minutes. The average bacterial cell can produce 200 to 250 phage particles.