Viral Replication

Basics of Viral Structure

• Viruses are composed of proteins and a single type of nucleic acid.
• Lack organelles for self-replication.
• Require host cells for ATP and organelles to replicate.

Entry into Host Cells

• Three Methods of Entry:
  1. Bacteriophages: Inject genetic material directly.
  2. Non-enveloped viruses: Trick cell receptors to gain entry.
  3. Enveloped viruses: Fuse with the host cell membrane or use receptor trick.

Viral Replication Strategies

• Once inside, viruses take over host cell machinery.

Lytic Cycle (Impatient Virus)

• Virus uses host's ATP, ribosomes, nucleic acids, and amino acids.
• Copies its genetic material (RNA/DNA) and proteins to form a protein coat.
• Self-assembly of virus particles.
• Cell lysis occurs, releasing viruses to infect nearby cells.
• Goal: Rapid army creation; suited for environments with many hosts.

Lysogenic Cycle (Hitch a Ride Virus)

• Virus integrates into host genome, becoming a "provirus" or "prophage."

• Virus remains dormant or latent, not expressed or transcribed.

• Host continues replication, inadvertently replicating the virus.

• Dormancy is repressed by repressor genes.

  Activation from Dormancy:

  • Rare (<1%): External factors (e.g., UV light) can weaken repressor genes.
  • Host genome attempts repair, excises viral DNA unintentionally.
  • Virus becomes active: begins lytic cycle, lysing cell to infect others.

Summary

• Lytic Cycle: Rapid replication and dispersal through cell lysis.
• Lysogenic Cycle: Integration and dormancy within host genome, later potential activation.