Question

In which direction, 5’-3’ or 3’-5’, are the new strands of DNA formed during replication?

Answer 1

New DNA strands are always formed in the 5’–3’ direction. This occurs because DNA polymerase can only add new nucleotides to the free 3’-OH group of an existing strand. As a result, the “leading strand” is synthesised continuously toward the replication fork, while the “lagging strand” is synthesised in short segments (Okazaki fragments) away from the fork, but both are built in the 5’–3’ direction.