Final answer:
The viral DNA is introduced into a host cell during the penetration stage, following the virus's attachment to the host cell, facilitating viral replication and biosynthesis.
Step-by-step explanation:
The stage at which the viral DNA is introduced into a cell is known as penetration or entry. During this phase, following the initial attachment of the virus to the host cell, the virus penetrates the cell membrane through various mechanisms such as endocytosis or direct fusion of the viral envelope with the cell membrane. Once inside, the virus's capsid is degraded, and the viral DNA or RNA is released into the host cell's cytoplasm. This leads to the synthesis of viral components and the replication of the viral genetic material.
For example, HIV, an enveloped retrovirus, attaches to a cell surface receptor on an immune cell and then fuses with the cell membrane, introducing its RNA into the cell. The HIV RNA is then converted into DNA and incorporated into the host genome. This series of events constitutes the penetration stage, after which the process of biosynthesis of new viral components can begin.