How Bacteriophage Replicates

The word phage means 'eater'. A bacteriophage or simply phage consist of nucleic acid, capsid, end plate, tail and tail pin. The interior core is the nuclic acid. The phage has DNA which is also known as genome. The outer coat of protein surrounding nucleic acid is called capsid or head. The head is hexagonal and consist of protein subunit the capsomers, the number of capsomers determines the nature of virus. Bacteriophage is obligate intracellular parasite which shows two types of relationship with its host: Master-slave relationship, lytic cycle and Host-guest relationship, i.e,. Lysogenic cycle.

• Lytic Cycle

It is a master-slave relationship. In this type of relationship virus inserts its genome into bacterial cell which than takes control over the genetic material of bacteria. After taking control over the genetic material it starts replicating its DNA. With in few minutes it produces large number of its copies, which than starts destroying bacterial cell. The phage which causes lysis of the host cell is known as lytic or virulent phage.

• Lysogenic 

The lysogenic cycle is host guest relationship, which is a peaceful relationship. Certain DNA containing bacterial viruses referred to as temperate bacteriophage can infect a cell without producing progeny viruses or demaging the host. This association is called lysogeny i.e, the host guest relationship. It occurs by the following mechanism. After penetration the viral genome instead of taking control over bacterial genetic material gets incorporated into bacterial DNA. The integrated DNA is now called phage or prophage. The viral DNA replicates whenever the bacterial chromosome doubles, so all progeny inherit one copy of the in the chromosome and thus carry the potential for producing lysogenic or temperate bacteriophage. This cycle of phage is called lysogenic cycle. Sometimes the phage becomes reactivate and reproduces like lytic phage.