2.3.9 Viral Particle Replication

Steps in Viral Particle Replication:

1. Attachment:

• The virus attaches to the host cell using specific attachment proteins on its surface.
• These proteins bind to complementary receptors on the surface of the host cell.

2. Entry of Genetic Material:

• The virus injects its nucleic acid (either DNA or RNA) into the host cell.
• The viral genetic material enters the host cell's cytoplasm, leaving the capsid outside in some cases.

3. Replication of Viral Components:

• The host cell's machinery (e.g., enzymes, ribosomes) is hijacked to:
• Replicate the viral nucleic acids.
• Synthesise viral proteins, including the capsid proteins and enzymes required for assembly.

4. Assembly:

• The newly synthesised nucleic acids and proteins are assembled into new virus particles within the host cell.

5. Release:

• The host cell bursts (lysis) or releases viruses via exocytosis, releasing the new viral particles to infect other cells.

Key Points about Viral Replication:

• Viruses lack cellular structures such as ribosomes and enzymes, so they depend entirely on the host cell's metabolic machinery for replication.
• The process can destroy the host cell, leading to tissue damage and disease.

Types of Viruses:

1. DNA Viruses:

• Use the host cell's DNA polymerase to replicate their DNA.
• Example: Herpes simplex virus.

2. RNA Viruses:

• Some replicate directly using RNA-dependent RNA polymerase.
• Example: Influenza virus.

3. Retroviruses:

• Contain RNA and use the enzyme reverse transcriptase to synthesise DNA from RNA.
• Example: HIV (Human Immunodeficiency Virus).