Question: where does the synthesis of new dna from existing dna occurs?
Answer: origins of replication

In a cell, DNA replication begins at specific locations, or origins of replication, in the genome.  Unwinding of DNA at the origin and synthesis of new strands, accommodated by an enzyme known as ligase, results in replication forks growing bi-directionally from the origin. A number of proteins are associated with the replication fork to help in the initiation and continuation of DNA synthesis. Most prominently, DNA polymerase synthesizes the new strands by adding nucleotides that complement each (template) strand. DNA replication occurs during the S-stage of interphase.