AAB Molecular Diagnostics Practice Test

The synthesis of the lagging strand during DNA replication occurs in short fragments known as Okazaki fragments. This process takes place in the opposite direction to the overall replication fork movement, which is 5' to 3'. Since DNA polymerase can only add nucleotides in the 5' to 3' direction, the lagging strand must be synthesized discontinuously in the form of these short fragments.

These fragments start with an RNA primer that provides a free 3' hydroxyl (-OH) group for the DNA polymerase to add DNA nucleotides. As replication progresses, new primers are laid down further along the template strand, allowing additional Okazaki fragments to be synthesized. Eventually, these fragments are joined together by the enzyme DNA ligase to form a continuous strand.

This method of synthesis is essential for DNA replication, as it allows the lagging strand to be constructed despite its orientation being inherently opposite to the direction of the replication fork's movement.