Viruses (Cambridge (CIE) AS Biology): Revision Note

Key features of viruses

• Viruses are non-cellular particles that infect living cells

  • Note that viruses are not cells, and they are not considered to be living organisms, so are referred to as 'particles'

• They are much smaller than prokaryotic cells, with a diameter of 20-300 nm

• Structurally they have

  • A nucleic acid core made of either DNA or RNA

  • A protein coat called a capsid

• Some viruses have an outer layer called an envelope; this forms from the membrane phospholipids of the host cell in which they were produced

• Viruses can only reproduce by infecting living cells and using their protein-building machinery to produce new viral particles

  • Viruses use attachment proteins on their surface to bind to and infect their host cells