Multiplication of Virus - Lytic Cycle

Description:

The multiplication process of virulent phage is called lytic cycle because the host bacterium is lysed at the end.

Steps for the process of lytic cycle are as follows −

Adsorption

• Attachment of the virus particle to the host bacterial cell.
• Attachment occurs at the specific receptor sites present at the wall of the host cell.
• T- even phages attach to the host with the help of tail fibres.

Penetration

• Injection of the nucleic acid into the host cell.
• The wall of the host is hydrolyzed by the lysozymes present at the tip of the tail.
• A hole is formed at the wall of the host cell and the nucleic acid is passed through the hole into the host cell.
• The tail sheath contracts and the central tube is pushed through the hole in the wall.
• The process is active and uses ATP.
• The protein coat remains attached outside the host cell wall and are called ghost.

The eclipse phase

• Further infection by same type of phage is prevented by the production of specific enzymes called repressors.
• Suppression of all host cellular activities.
• Synthesis of new enzymes by the viral nucleic acid called early proteins.
• Viral coat proteins are synthesized called as late proteins.

Maturation

• Assembly of various components into mature or complete virions.
• Heads and tails are first assembled separately and then they attach to form new phage particles.
• The time between the injection of viral nucleic acid and appearance of a new phage progeny is called eclipse period.
• The total time taken from the injection of nucleic acid to the rupture of host cell wall is called latent period.

Lysis and release of new virions

• Cell wall burst at the end of the latent period and virions are released. This phenomenon is called lysis.

• The number of virions produced per host cell is specific and is termed as the burst size.