Viral Particle Replication (AQA A Level Biology): Revision Note

Division of viral particles

• Viruses are acellular infectious particles

• Being non-living, viruses do not undergo cell division

• Viruses are relatively simple in structure with:

  • A nucleic acid core (their genomes are either DNA or RNA, and can be single or double-stranded)

  • A protein coat known as a ‘capsid’

  • Some viruses have an outer layer known as an ‘envelope’ formed usually from the membrane-phospholipids of a cell they were made in

Viral replication

• Viruses are non-living and parasitic - they can only replicate inside host cells

  Replication process:

  1. Attachment proteins bind to complementary receptors on host cell surface

  2. Viral DNA or RNA is injected into the host cell

  3. Host cell uses its own enzymes and ribosomes to synthesise viral proteins and nucleic acids

  4. New viral particles are assembled

  5. Viruses are released by

     • cell lysis (bursting)

     • budding (takes host membrane – forms viral envelope)

• Virus release damages or destroys host cells, causing disease

  • Unit 2: Cell structure provides details of how HIV replication occurs by this process