Supercoiling refers to the additional twisting of a DNA strand and is an expression of the strain on that strand

  • DNA can be overwound (positive supercoiling) or underwound (negative supercoiling) – most DNA is negatively supercoiled

Supercoiling functions to reduce the space required for DNA packaging, allowing for more efficient storage of DNA

  • DNA will form positive supercoils when unwound by helicase and requires an enzyme (DNA gyrase) to reduce the strain
  • In eukaryotic cells, nucleosomes help to supercoil DNA 

Supercoiling in a Prokaryotic Cell