1. Attachment: The virus first attaches to specific receptors on the surface of the host cell. These receptors are like keys that fit into locks on the cell's surface, allowing the virus to bind.
2. Entry: After attachment, the virus enters the cell. This can happen in several ways:
* Fusion: The viral envelope fuses with the cell membrane, releasing the viral contents into the cell.
* Endocytosis: The cell engulfs the virus in a vesicle, which then releases the viral genome inside the cell.
3. Replication: Once inside, the virus uses the host cell's machinery to replicate its own genetic material. Depending on the type of virus:
* DNA viruses: They use the host cell's enzymes to replicate their DNA, which is then transcribed into mRNA.
* RNA viruses: They can either use their own enzymes to replicate their RNA or integrate their RNA into the host cell's genome.
4. Assembly: New viral proteins and genetic material are assembled into new virus particles.
5. Release: The newly formed viruses are released from the cell, either by budding (where they acquire a new envelope) or by lysis (where they burst out of the cell).
Insertion (for some viruses):
While viruses don't directly "insert" their genetic material into the host cell's genome in most cases, some viruses have a unique ability. Retroviruses, such as HIV, have an enzyme called reverse transcriptase, which allows them to convert their RNA genome into DNA. This DNA can then integrate into the host cell's genome using another enzyme called integrase. This integration is permanent and allows the virus to remain dormant in the cell. When the cell replicates, it also copies the viral DNA, spreading the virus to new cells.
In summary:
Viral genetic material is delivered to animal cells through a combination of attachment, entry, replication, assembly, and release, not by direct insertion. However, some viruses, like retroviruses, have the ability to integrate their genetic material into the host cell's genome, leading to persistent infection.
