Viral Replication: Lytic Cycle

A T-even bacteriophage, such as T4, infects E. coli to replicate.

The phage first attaches to specific receptors on the E. coli cell wall using its tail fibers, ensuring host specificity.

Lysozyme released from the phage’s baseplate weakens the bacterial cell wall, creating an entry point.

The phage then contracts its tail sheath, injecting its DNA into the bacterial cytoplasm while leaving the empty capsid outside.

Inside the host cell, bacterial transcription and translation are shut down, the host DNA is degraded, and cellular resources, such as RNA and DNA polymerases, are redirected toward viral protein synthesis and genome replication.

Newly synthesized viral components self-assemble into complete phages.

Once enough virions have formed, they release holin proteins to create pores in the host membrane, and together with lysozyme degrade the bacterial cell wall.

Within 25–30 minutes, the bacterial cell lyses, releasing new virions to infect other E. coli, thereby repeating the lytic cycle.