Replication — biological assembly of new DNA

                 The process of formation of new DNA molecules is catalysed by the enzyme DNA polymerase. The new nucleotide   units are fe into the reaction process in the form of nucleotide triphosphates. The breakdown of the triphosphate to the monophosphate   liberates an inorganic pyrophosphate. The pyrophosphate is then hydrolysed. This exothermic reaction provides the energy for the addition    of the next nucleic acid residue.

               During replication, the hydrogen bonds and instantaneous dipole-induced dipole forces between the base pairs in   the    double helix are broken. The original strands act the templates for the synthesis of two new strands. Each new strand contains  a   sequence    of bases complementary to the bases of the original strand.

              Since the nucleotides in DNA differ only in the bases they carry, the sequence of the   monomers   in   a   DNA  strand   can   be recorded simply as the base sequence. Each nucleotide can be thought of as a single letter in an alphabet that consist of only  four  letters — A, T, G and C.

              The DNA in almost every cell in our bodies should be an identical copy of the DNA in the   original   fertilised   egg. The   only exceptions are certain white blood cells and sex cells. Replication is a complex process and crucially   errors   (mutations)   are   rare — a remarkable average of only one incorrect base per cell division. Such mutations can be lethal. For example, if they were to  occur   in   a gene involved in deciding whether a cell should divide or not, they might  cause    incontrolled    cell   division    and     thence   cancer. Fortunately, as genes make up only a small percantage of DNA, most mutations are harmless.