Which enzyme copies the template strand to produce a DNA molecule in prokaryotes?

• A. DNA Polymerase III
• B. DNA Polymerase I
• C. Ligase
• D. Primase

Answer: (A)

Copying the template strand to build a new DNA molecule in prokaryotes is done by a DNA polymerase that adds nucleotides to the 3' end in a 5' to 3' direction, using the parent strand as a guide. In bacteria, this primary replicative enzyme is DNA polymerase III, which works with a sliding clamp to achieve high processivity and rapidly synthesize most of the DNA on both the leading and lagging strands. It also has proofreading activity to minimize errors. Primase makes the RNA primers that start synthesis; DNA polymerase I trims those primers and fills in with DNA, and ligase seals the nicks to finish the fragments. So the enzyme that copies the template to form the new DNA molecule is DNA polymerase III.