The enzyme that places nucleotides on the DNA strand during DNA replication is DNA polymerase. DNA polymerase adds nucleotides one by one to the growing DNA strand by matching them to the complementary bases on the template strand, extending the new strand in the 5' to 3' direction. It requires a free 3' hydroxyl (3'-OH) group to add nucleotides, which is initially provided by an RNA primer laid down by RNA primase
. In summary:
- DNA polymerase synthesizes the new DNA strand by adding nucleotides complementary to the template strand.
- It can only add nucleotides to the 3' end of the growing strand, thus elongating the strand in the 5' to 3' direction.
- DNA polymerase cannot start synthesis from scratch; it extends from an RNA primer created by RNA primase.
- Other enzymes like helicase unwind the DNA, and ligase joins fragments on the lagging strand, but the actual placement of nucleotides is done by DNA polymerase
