Origin of replication

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The double helical nature of DNA makes it very stable, and for replication to take place the hydrogen bonds between complementary base pairs must be broken to expose the base pairs to allow nucleotides to bind.

This unwinding and 'unzipping' (breaking of hydrogen bonds) always begins in specific sites within chromosomes.These sites are known as the 'Origin of Replication', as it is where DNA replication starts. This is often abbreviated to 'Ori c'.[1]

In bacterial chromosome there tends to be only one origin of replication, and it tends to be opposite the terminal point of replication.[1]

Linear DNA such as the human chromosomes tend to have more than one Ori C site as they replicate differently to circular bacterial DNA (which replicates bi-directionally), and tend to be larger and so would take longer to replicate if they only had one Ori C.[1][2]


  1. 1.0 1.1 1.2 Oric abbreviation
  2. Molecular Biology of the Cell, Alberts et al.,Fifth edition., 2012., 281-283.

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