<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> <P> The rate of DNA replication in a living cell was first measured as the rate of phage T4 DNA elongation in phage - infected E. coli . During the period of exponential DNA increase at 37 ° C, the rate was 749 nucleotides per second . The mutation rate per base pair per replication during phage T4 DNA synthesis is 1.7 per 10 . </P> <P> DNA replication, like all biological polymerization processes, proceeds in three enzymatically catalyzed and coordinated steps: initiation, elongation and termination . </P> <P> For a cell to divide, it must first replicate its DNA . This process is initiated at particular points in the DNA, known as "origins", which are targeted by initiator proteins . In E. coli this protein is DnaA; in yeast, this is the origin recognition complex . Sequences used by initiator proteins tend to be "AT - rich" (rich in adenine and thymine bases), because A-T base pairs have two hydrogen bonds (rather than the three formed in a C-G pair) and thus are easier to strand separate . Once the origin has been located, these initiators recruit other proteins and form the pre-replication complex, which unzips the double - stranded DNA . </P>

For dna replication a primer of what is needed at the origin of nucleotide addition