Question

List the 5 steps of the lytic Viral Replication Cycle of a Bacteriophage and briefly describe each of those steps. More correct, relevant detail is better.

Answer 1

Lytic cycle is a five step process involving- Attachment, Penetration, Biosynthesis, Maturation and Release.

•After a chance contact between phage particles and bacteria, attachment or adsorption occurs.The phages use tail fibres for attachment to the complementary receptor sites on the bacterial cell wall.

•Attachment is followed by the process of penetration,during which the tail sheath of the phage contracts,and the tail core is driven in through the bacterial cell wall.When the tip of the core reaches the plasma membrane,the DNA from the bacterioohage head passes through the tail core through the plasma membrane and enters the bacterial cell.The capsid remains outside the bacterial cell and is referred to as ghost.Thus,the phage particle functions like a hypodermic syringe and injects its DNA into the bacterial cell.

•Once the phage DNA reaches the cytoplasm of the host cell,many copies of phage DNA, enzymes and capsid proteins are synthesized,using the cellular machinery of the host cell.

•Next in the sequence of events is the process of maturation.In this process, bacteriophage DNA and capsids are assembled into complete virions.

•The final stage of viral multiplication is the lysis phase of the host cell and the release of virions from the host cell.The plasma membrane of the host cell gets dissolved or lysed due to the viral enzyme,called lysozyme,an enzyme synthesized within the cell and bacterial cell wall breaks releasing the newly produced phage particles/virions.