Honors Biology Final Practice Exam

Joining individual nucleotides to form a new DNA strand is the job of DNA polymerase. During DNA replication, this enzyme reads the template strand and links incoming nucleotides together by forming phosphodiester bonds, building the new strand in the 5' to 3' direction. It needs a primer to start and relies on correct base pairing to ensure the sequence matches the template.

Other enzymes have different roles: helicase unwinds the double helix, primase lays down the short RNA primer to provide a starting point for synthesis, and ligase seals gaps between fragments on the lagging strand. But the actual addition of nucleotides to extend the DNA strand is carried out by DNA polymerase.