Which enzyme is initially used to allow DNA polymerase III to replicate the 3' strand?

Primase plays a crucial role in DNA replication by synthesizing a short RNA primer that provides a free 3' hydroxyl (OH) group for DNA polymerase III to build upon. DNA polymerases cannot initiate synthesis on a single-stranded DNA template; they can only add nucleotides to an existing strand. The RNA primer created by primase is essential because it allows DNA polymerase III to start adding DNA nucleotides complementary to the template strand, resulting in new DNA synthesis.

The other enzymes listed serve different purposes in the replication process. Helicase unwinds the double-stranded DNA, creating the replication fork but does not initiate the synthesis. Ligase is involved in joining Okazaki fragments on the lagging strand after replication is complete, and endonuclease functions in removing RNA primers and repairing DNA. Thus, primase is specifically needed at the start of the replication process to provide the necessary starting point for DNA polymerase III.