Viral Life Cycle: Five Steps from Entry to Release

Obligate Intracellular Parasites

Viruses require living host cells to replicate. Five essential steps:

1. Attachment & Entry: Viral surface proteins bind host receptors → fusion (enveloped) or endocytosis (non-enveloped).
2. Uncoating: Capsid removal → viral genome released into cytoplasm or nucleus.
3. Replication: Genome copying + viral protein synthesis (hijacks host machinery: ribosomes, polymerases, nucleotides).
4. Assembly: Genomes + structural proteins → new virions (nucleocapsid formation).
5. Release: Budding (enveloped, acquire host membrane) or lysis (non-enveloped, cell death).

Key Concepts

• No independent metabolism.
• Host specificity determined by receptor compatibility.
• High mutation rates (especially RNA viruses) → immune escape, antiviral resistance.
• Latency possible (herpesviruses, retroviruses).

Therapeutic Targets

Entry inhibitors, polymerase/protease inhibitors, assembly blockers, release inhibitors (neuraminidase inhibitors for influenza).