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Viruses

Biology: Cambridge International A Level, topic 1.1.7

Viruses

Viruses are acellular and non-living. Virus particles include genetic material, a capsid and attachment proteins.

Structure

Structure

  • Viruses are made up of nucleic acids. Viruses can be either DNA or RNA viruses, depending on the nucleic acids they are made up from.
  • The nucleic acids form the core of the virus are surrounded by a protein called a capsid.
  • Viruses are smaller than bacteria.
  • Some viruses are surrounded by a phospholipid envelope exterior to the protein capsid.
Living cells

Living cells

  • Viruses are NOT considered living because:
  • They have no nucleus, plasma membrane, cytoplasm or ribosomes.
  • They are not made of cells.
  • They cannot reproduce independently.
Function

Function

  • To replicate, viruses have to invade and hijack the reproductive mechanism of a living cell. These cells are then termed host cells.
  • Viruses have attachment glycoproteins that bind to complementary receptors on host cells.
  • They then inject DNA or RNA into the host cell.
  • The host cell divides as normal and the virus is replicated.

Test yourself on Viruses

  • Which of the following statements are true of viruses?

  • How do viruses replicate?

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