Molecular Genetics Practice Exam

On the lagging strand, DNA is made in short, separate pieces because the polymerase can only synthesize in the 5' to 3' direction as the fork opens. Each piece starts with an RNA primer laid down by primase, and DNA polymerase extends from that primer until it runs into the previous fragment. These short DNA pieces are called Okazaki fragments. After synthesis, the RNA primers are removed and replaced with DNA, and DNA ligase joins the fragments to form a continuous strand. Therefore, Okazaki fragments are the short DNA fragments formed on the lagging strand.