DNA replication


DNA stands for Deoxyribonucleic acid and contains the genes that are necessary to code for proteins in our bodies. DNA is composed of sugars, phosphates and complimentary base pairs, these three things together make up a nucleotide and join together to form a double helix. There are four different bases involved in this complimentary pairing. They are; Adenine, Thymine, Cytosine and Guanine. They pair up consistently following a specific pattern- Adenine always pairs with Thymine and Cytosine always pairs with Guanine.

When DNA replicates it copies itself with very few errors. These errors, which do occur occasionally, are called Mutations and are quite rare.


DNA performs semi conservative replication. When it replicates a new DNA double helix is formed, consisting of half the original DNA molecule and half an entirely new molecule. Therefore half the original DNA is conserved, giving the process of replication its name.

A DNA double helix

DNA unzips and unwinds

Free Nucleotides attach themselves to exposed base pairs

DNA polymerase joins up the molecule

End result is 2 DNA molecules- each with half the original DNA and half the new DNA


  • Orange Strand = Original DNA backbone
  • Purple Strand = New DNA backbone
  • Green = Guanine
  • Blue = Cytosine
  • Orange = Adenine
  • Pink = Thymine

Produced by Shabnam Rashid, Claire Wilson and Matthew Naylor