The enzyme that adds bases to growing DNA strands is called DNA polymerase.

Here's the breakdown:

* DNA replication: The process of copying a DNA molecule.

* DNA polymerase: The enzyme responsible for adding nucleotides (bases) to a growing DNA strand.

* Two new strands: During replication, the original DNA molecule is unwound, and each strand serves as a template for the creation of a new, complementary strand.

So, to answer your question directly: Two new strands of DNA molecules grow as bases are added by the enzyme DNA polymerase.