Fig. 11: DNA Replication by Complementary Base Pairing: Adding DNA Nucleotides to the RNA Primer

DNA polymerase III
replaces the primase and is able to add DNA nucleotides to the RNA primer. As the free deoxyribonucleoside triphosphates line up by complementary base pairing with the nucleotides on each parent strand of the unwound DNA in the replication fork, the phosphate on the 5' carbon of the newest building block lining up then forms a phosphodiester bond with the 3' carbon of the last nucleotide in the growing strand. During the process, two phosphates are lost . Because the parent strands are antiparallel and DNA can only be replicated in a 5' to 3' direction, the the two new strands must be synthesized in opposite directions.

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