The enzyme that builds new DNA strands from existing ones during replication is DNA polymerase.

Here's a breakdown:

* DNA polymerase reads the existing DNA strand (the template strand) and uses it to add complementary nucleotides to the new strand.

* It moves along the template strand, adding nucleotides one by one, following the base pairing rules (A with T, and G with C).

* There are different types of DNA polymerase involved in replication, each with a specific function. For example, DNA polymerase III is the main polymerase responsible for replicating most of the DNA.

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