How do viruses propagate?

Viruses propagate by hijacking host cells to replicate their genetic material and produce more viral particles.

Here's a more detailed breakdown of the process:

1. Attachment: The virus attaches to the surface of a host cell. This attachment is highly specific, often relying on interactions between viral surface proteins and receptors on the host cell.

2. Entry: The virus enters the host cell. This can occur through various mechanisms, including:

   • Direct penetration of the cell membrane.
   • Receptor-mediated endocytosis (the cell engulfs the virus).
   • Fusion of the viral envelope with the host cell membrane (for enveloped viruses).

3. Uncoating: Once inside, the virus releases its genetic material (DNA or RNA) from its protective protein coat (capsid). This process is called uncoating.

4. Replication: The viral genome takes control of the host cell's machinery to replicate itself.

   • DNA viruses typically enter the nucleus and use the host's DNA polymerase to make copies of their DNA.
   • RNA viruses may replicate in the cytoplasm using their own RNA-dependent RNA polymerase (an enzyme not found in host cells, but encoded by the virus). Some RNA viruses, like retroviruses, first convert their RNA into DNA using reverse transcriptase before integrating into the host's genome.

5. Protein Synthesis: The viral genome also directs the host cell to produce viral proteins. These proteins include capsid proteins, enzymes needed for replication, and proteins that help the virus escape the host cell.

6. Assembly: Newly synthesized viral genomes and proteins assemble into new viral particles (virions).

7. Release: The new virions are released from the host cell to infect other cells. Release can occur through:

   • Lysis (the host cell bursts open, killing the cell and releasing a large number of virions).
   • Budding (the virions acquire an envelope from the host cell membrane as they exit, often without immediately killing the cell).

Step	Description
Attachment	Virus binds to specific receptors on the host cell surface.
Entry	Virus enters the host cell through penetration, endocytosis, or membrane fusion.
Uncoating	Viral genome is released from the capsid.
Replication	Viral genome hijacks the host cell's machinery to replicate itself.
Protein Synthesis	Viral genome directs the host cell to produce viral proteins.
Assembly	Viral genomes and proteins assemble into new virions.
Release	New virions are released from the host cell through lysis or budding to infect other cells.

In summary, viral propagation is a complex process involving attachment, entry, uncoating, replication, protein synthesis, assembly, and release, all relying on the hijacking of a host cell's resources and machinery.