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DNA polymerase

An enzyme involved in the production of a new nucleotide strand to form a new DNA double helix.

DNA helicase

An enzyme which unzips the hydrogen bonds between the two strands of DNA during DNA replication.


The transfer of characteristics from parents to children through their genes.

DNA ligase

An enzyme which is involved in DNA replication by catalysing the formation of phosphodiester bonds.


The male sex cell or gamete. The full name is spermatazoan, abbreviated to sperm cell or sperm.

DNA replication

Sleeping baby

Every cell of this baby contains an exact copy of the DNA from the original fertilised egg.

The ability of the DNA molecule to make exact copies of itself is what makes it ideal as the molecule of inheritance. DNA replication allows all of the cells of your body – all produced from the original cell formed when an ovum and a sperm met – to carry the same genetic information. The importance of enzymes such as DNA helicase, DNA polymerase and DNA ligase for life on earth cannot be overestimated. Look at the diagram below to see how this elegant process happens, and follow it through in the animation which follows.

DNA replication

DNA replication

For some years after the structure of the DNA double helix had been worked out, scientists argued about how DNA replicated itself. There were two main theories:

  • Conservative replication, which assumed that the original DNA double helix remained intact with new strands forming on the outside
  • Semi-conservative replication, which assumed the original strand opens up and each new helix contains one old and one new strand of DNA

The arguments were finally settled by Matthew Meselson and Franklin Stahl in a series of experiments which are best seen in action (click here to view animation).

DNA replication experiment

This classic experiment showed scientists exactly how DNA replicated