Some viruses can carry out either a lysogenic or a lytic cycle. The lysogenic cycle of phage lambda begins when a phage binds to the surface of a host bacterium. The phage injects its DNA into the host cell, leaving the empty protein coat outside. In the lysogenic cycle, the viral DNA is incorporated into the host cell DNA, where it is called a prophage. Every time the host bacterium reproduces, it replicates the phage DNA along with its own DNA and passes the copies on to daughter cells. Occasionally, the phage DNA exits the bacterial chromosome and initiates a lytic cycle. The viral DNA takes over the metabolic machinery of the host cell to make phage DNA and proteins. The host cell lyses, releasing phages, which can infect other cells. This diagram summarizes the lysogenic and lytic cycles of phage lambda. In contrast to the lytic cycle, the lysogenic cycle replicates the viral genetic material without destroying the host.