Final answer:
The formation of mature viruses occurs during the assembly stage of the viral replication cycle, which is a critical phase where viral components are brought together to form complete virions before being released to infect new cells.
Step-by-step explanation:
The formation of mature viruses occurs during the assembly stage.
After a virus has entered a host cell, it goes through several stages of the replication cycle. These stages include attachment, penetration (or entry), uncoating, replication, assembly, and release. During the assembly stage, viral components are brought together to form complete virus particles, called virions. This is a crucial step in the viral life cycle, because without proper assembly, the virus cannot create infectious particles capable of infecting new cells.
Following assembly, the maturation phase sometimes occurs concurrently, where new virions are created and subsequently released from the host cell to infect additional cells. The release is the last stage, where new virions are expelled from the cell through lysis or budding. Both productive viral infections, which result in new virions, and nonproductive infections, where no new virions are produced, include the assembly stage in their cycles. In sum, mature viruses are formed during the assembly stage before being released to continue the infection cycle.