The Lytic Cycle
The lytic cycle involves the infection of the host by the virus, followed by lysis, which is the bursting and death of the host cell. It also involves the release of new infectious phages. The lytic cycle is composed of the following stages:
1. Adsorption - The virus attaches itself to the host cell. Adsorption of specific receptors on the bacterial surface takes place, which can involve lipopolysaccharides, proteins or even flagella.
2. Injection of genetic material - The phages use a syringe-like motion for injection of genetic material. After finding the right receptor, the base plate is brought closer to the cell surface. Tail fibers help accomplish this, and after attachment the tail fibers shrink, releasing genetic material into the host membrane.
3. Eclipse phase - During the eclipse phase, the genetic material of the phage takes over the cell machinery of the host, and specified phage m-RNA's, as well as proteins, are produced. The production of the host's genetic material is halted, and the host cell becomes a "factory" for viral material. Phage DNA is also produced, follwed by the production of late m-RNA's and late proteins. The purpose of the late proteins is the lysis of the bacterial cell.
4. Virion production - Helper proteins assemble new virions, which infect other host cells upon release. First, the base plates are assembled, followed by the tails. The head capsids are separately assembled and join the tails. Genetic DNA is placed within the head capsids. While all this is happening, the cell is drawing raw material from its environment. Also, the genes of the phage allow only viral components to be built. The host's DNA becomes completely inactive or is destroyed.
5. Lysis Phase - In this final phase, a specific enzyme breaks down the cell wall peptodiglycan, resulting in the host cell bursting and new phages being released to search for new host cells, so the cycle can continue.