Viruses Do Not Divide Like Cells
Cells can increase their number by dividing. Viruses increase only after their genetic material makes a host cell build viral parts, which is why the sequence starts with entry into a suitable cell.
Viral Replication Uses Cell Machinery
Bacteria can divide from one cell into two cells. Viruses do not reproduce that way. A virus reproduces by delivering its genome into a host cell and redirecting that cell's machinery to make new viral components.
Picture the host cell as a workshop that already has workers, tools, and materials. The virus arrives with instructions. Once those instructions enter, the workshop can be redirected to make capsids, copy the viral genome, assemble new virions, and release them.
Attachment to a matching host-cell receptor is an important starting point before infection proceeds. The host and infection concept is summarized in .