Final answer:
In the lytic cycle of a bacteriophage, step 5 is the release of new viruses after the host cell lysis. In contrast, in the lysogenic cycle, step 5 involves the integration of phage DNA into the host genome or the excision and initiation of the lytic cycle under stress.
Step-by-step explanation:
Step 5 in both the lytic and lysogenic cycles of a bacteriophage involves the release or the potential exit from the lysogenic state to enter the lytic cycle. In the lytic cycle, step 5 is characterized by the release of newly formed phages into the environment after lysis of the host bacterial cell. This is due to the synthesis of enzymes like holin or lysozyme that break down the bacterial cell wall, resulting in cell death and dispersal of progeny viruses. On the other hand, in the lysogenic cycle, step 5 can refer to the integration and dormancy of the phage DNA within the bacterial genome forming a prophage. However, under certain environmental stressors such as starvation or exposure to toxic chemicals, the prophage may excise itself from the bacterial genome and initiate the lytic cycle. Therefore, while step 5 in the lytic cycle always culminates in cell lysis and virus propagation, in the lysogenic cycle the corresponding step is the maintenance of the integrated prophage state with the possibility of transitioning to the lytic cycle under stressful conditions.