The enzymes that move along each of the DNA strands during replication adding nucleotides to exposed bases are called DNA polymerases.

Here's a breakdown of their role:

* DNA polymerases are a family of enzymes that play a crucial role in DNA replication. They act like "molecular copy machines," adding nucleotides to the newly synthesized DNA strand, one by one.

* They can only add nucleotides to a pre-existing 3'-OH group (the hydroxyl group at the 3' carbon of the sugar molecule in the DNA backbone). This is why DNA replication proceeds in a 5' to 3' direction.

* There are different types of DNA polymerases involved in replication, each with specific functions. For example, DNA polymerase III is the main enzyme responsible for building the new DNA strand in bacteria, while in eukaryotes, multiple DNA polymerases work together.

Let me know if you'd like more details about DNA replication or the different types of DNA polymerases!