In DNA replication, in which direction do DNA polymerases synthesize new DNA strands?

In DNA replication, in which direction do DNA polymerases synthesize new DNA strands?

• A. 3' to 5'
• B. In both directions
• C. 5' to 3'
• D. They do not have a fixed direction

Answer: (C)

DNA polymerases add nucleotides to a free 3' end, building the new strand by forming bonds at the 3' hydroxyl group. This makes DNA synthesis proceed in the 5' to 3' direction. The template is read 3' to 5', so bases pair properly and the complementary strand grows in the opposite orientation. On the leading strand, this is continuous toward the replication fork; on the lagging strand, synthesis occurs as short fragments away from the fork, but each fragment is still extended 5' to 3'. The directionality isn’t 3' to 5', nor bidirectional for a single strand’s growth, nor variable—it's consistently 5' to 3'.

DNA polymerases add nucleotides to a free 3' end, building the new strand by forming bonds at the 3' hydroxyl group. This makes DNA synthesis proceed in the 5' to 3' direction. The template is read 3' to 5', so bases pair properly and the complementary strand grows in the opposite orientation. On the leading strand, this is continuous toward the replication fork; on the lagging strand, synthesis occurs as short fragments away from the fork, but each fragment is still extended 5' to 3'. The directionality isn’t 3' to 5', nor bidirectional for a single strand’s growth, nor variable—it's consistently 5' to 3'.