Lytic cycle

The lytic cycle (ˈlɪtɪk ) is one of the two cycles of viral reproduction (referring to bacterial viruses or bacteriophages), the other being the lysogenic cycle. The lytic cycle results in the destruction of the infected cell and its membrane. Bacteriophages that only use the lytic cycle are called virulent phages (in contrast to temperate phages). In the lytic cycle, the viral DNA exists as a separate free floating molecule within the bacterial cell, and replicates separately from the host bacterial DNA, whereas in the lysogenic cycle, the viral DNA is located within the host DNA. This is the key difference between the lytic and lysogenic (bacterio)phage cycles. However, in both cases the virus/phage replicates using the host DNA machinery. The lytic cycle, which is also commonly referred to as the "reproductive cycle" of the bacteriophage, is a six-stage cycle. The six stages are: attachment, penetration, transcription, biosynthesis, maturation, and lysis. Attachment – the phage attaches itself to the surface of the host cell in order to inject its DNA into the cell Penetration – the phage injects its DNA into the host cell by penetrating through the cell membrane Transcription – the host cell's DNA is degraded and the cell's metabolism is directed to initiate phage biosynthesis Biosynthesis – the phage DNA replicates inside the cell, synthesizing new phage DNA and proteins Maturation – the replicated material assembles into fully formed viral phages (each made up of a head, a tail and tail fibers) To infect a host cell, the virus must first inject its own nucleic acid into the cell through the plasma membrane and (if present) the cell wall. The virus does so by either attaching to a receptor on the cell's surface or by simple mechanical force. The binding is due to electrostatic interactions and is influenced by pH and the presence of ions. The virus then releases its genetic material (either single- or double-stranded RNA or DNA) into the cell. In some viruses this genetic material is circular and mimics a bacterial plasmid.