<P> The pairing of complementary bases in DNA (through hydrogen bonding) means that the information contained within each strand is useless . phosphoodiester (intra-strand) bonds are stronger than hydrogen (inter-strand) bonds . This allows the strands to be separated from one another . The nucleotides on a single strand can therefore be used to reconstruct nucleotides on a newly synthesized partner strand . </P> <P> DNA polymerases are a family of enzymes that carry out all forms of DNA replication . DNA polymerases in general cannot initiate synthesis of new strands, but can only extend an existing DNA or RNA strand paired with a template strand . To begin synthesis, a short fragment of RNA, called a primer, must be created and paired with the template DNA strand . </P> <P> DNA polymerase adds a new strand of DNA by extending the 3' end of an existing nucleotide chain, adding new nucleotides matched to the template strand one at a time via the creation of phosphodiester bonds . The energy for this process of DNA polymerization comes from hydrolysis of the high - energy phosphate (phosphoanhydride) bonds between the three phosphates attached to each unincorporated base . Free bases with their attached phosphate groups are called nucleotides; in particular, bases with three attached phosphate groups are called nucleoside triphosphates . When a nucleotide is being added to a growing DNA strand, the formation of a phosphodiester bond between the proximal phosphate of the nucleotide to the growing chain is accompanied by hydrolysis of a high - energy phosphate bond with release of the two distal phosphates as a pyrophosphate . Enzymatic hydrolysis of the resulting pyrophosphate into inorganic phosphate consumes a second high - energy phosphate bond and renders the reaction effectively irreversible . </P> <P> In general, DNA polymerases are highly accurate, with an intrinsic error rate of less than one mistake for every 10 nucleotides added . In addition, some DNA polymerases also have proofreading ability; they can remove nucleotides from the end of a growing strand in order to correct mismatched bases . Finally, post-replication mismatch repair mechanisms monitor the DNA for errors, being capable of distinguishing mismatches in the newly synthesized DNA strand from the original strand sequence . Together, these three discrimination steps enable replication fidelity of less than one mistake for every 10 nucleotides added . </P>

Where does the energy for replication come from